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G has a "swell" time kayaking

G has a "swell" time kayaking
G has a "swell" time on Lake Michigan in an inflatable canoe

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Dawn on the Gulf of Mexico
Dawn on the Gulf of Mexico

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Warren Dunes Sunset
Warren Dunes Sunset
Showing posts with label Digital Voltmeter. Show all posts
Showing posts with label Digital Voltmeter. Show all posts

Saturday, September 30, 2017

AGM Batteries, Separator Operation, Charging and Voltmeter

Replacement Battery Separator



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December 2019:
I installed a replacement battery separator and it works differently from the old one. See Note 5 in the Battery Separator section, below.

September 26, 2019:
After I installed the digital voltmeter I was able to more closely monitor the coach battery voltage as well as the operation of the separator. Earlier this year I purchased a replacement separator as a "spare".  The old separator seems to work inconsistently or intermittently. For example with the engine running and a 14V chassis battery voltage the separator will connect the chassis and coach batteries. But sometimes it does not!  Go figure. I've decided to install the spare and I'll provide an update after I do.

October 6:  I added information on "clicking" battery separators. This has been reported by owners.
To go to the section on the battery separator, click here: Click here to go to the post section about the battery separator.

June 26, 2019 added the SOC table for the AGM batteries in my 210P. Note, I replaced those batteries and the table for your batteries may differ.

July 3, 2019 clarified separator main and aux connections.
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Read the notes at the end before proceeding! This post is not a recommendation that owners perform their own electrical service. Working with electricity can be dangerous and can result in personal injury, or death or damage to your Roadtrek. 
Sorry if I created a scare, but one does have to be careful if tinkering with electrical systems. Mistakes can be very costly, or can result in personal injury.




My 2013 Roadtrek 210P has:
  • 2 x 6 volt AGM coach batteries, about 220Ah
  • Tripplite 750W Charger/inverter
  • Battery Separator (bidirectional)
  • LED 12V display (four round indicators)
  • Digital 12V display (added by me)
  • Onan generator (2800 watt)
  • 50 watt solar panel, for charging the coach batteries (added by me)
2013 Roadtrek 210P display/switch panel
This is the display/switch panel on my 210P. In the photo the Onan generator is running and supplying 120VAC power. The Battery Disconnect is ON and this is indicated by the Battery On blue indicator. As a consequence the batteries are charging:

Charging the coach batteries
It is possible to charge the coach batteries:
  • While on 120V "shore power"  and using the Tripplite
  • While running the vehicle engine (see the Battery Separator section for limitations)
  • By running the Onan generator and using the Tripplite.
  • On solar
The limitations of the battery LED indicator
The LED indicator of the Roadtrek is a voltmeter which is somewhat limited. It indicates these battery conditions while the soft BATT button is pressed:
  • L - Low
  • F- Fair
  • G- Good
  • C- Charging
Note that the "C" indicator may be on even when the battery is discharging. This may occur shortly after disconnecting the coach from AC or stopping the vehicle engine. The reason is because the coach battery voltage is higher than normal 100% charge. This is what is called a battery "surface charge" and after a few minutes with a small DC load such as the slowly running roof fan, this charge will be dissipated and the true condition of the battery will be indicated. 

In the photo the Battery Disconnect switch BATT is ON as indicated by the illuminated "Battery ON" light. Pressing the Battery button displays the battery situation. The highest (rightmost) illuminated indicator displays the condition, which in the photo is a C for Charging:


Using a Voltmeter to Monitor the Battery Voltage
Monitoring the coach battery voltage is helpful for determining battery capacity. We may want to know how much energy is available in our coach batteries. A voltmeter is useful for doing this.

My Roadtrek didn't have a voltmeter, and the power/switch/display area isn't set up for one. However, there is a 12V "cigarette lighter" style receptacle in the rear overhead compartment, above the DVD player. Unplugging my powered antenna allows me to plug in a voltmeter to check the battery voltage:

12V receptacle

Here's a typical digital plug-in voltmeter. These can be purchased for as little as $7:

Plug-in Digital Voltmeter
What does that voltmeter display mean?
Here's a typical chart for AGM batteries. If we are aware of the voltage at the batteries, we have a rough idea of the "capacity" remaining. For example, if your voltmeter displays 12.50 volts, then you have used about 20% of the capacity or available energy in your batteries. However, I must note that it is not recommended to fully discharge batteries to 0%. That will ruin them.

You will have to decide how low you want to run your batteries. For longest life under moderate temperatures (77F is ideal) some recommend not dropping below 50%, or  about 12.05V.  Dropping to 20% (80% discharge) reduces battery life, but provides energy for a longer time. That's discharging to about 11.66V. Going lower will severely reduce battery life. Fully discharging AGM batteries can damage and ruin them. What does repeatedly discharge below 20% mean? It means severely reducing battery capacity, to the point the batteries cannot provide energy when disconnected from the Tripplite charger (when charging the battery).

Note that you might have poor batteries and be unaware. The 750W Tripplite inverter/charger can provide up to 45A (amperes) of charging current when on shore power. That's about 540 Watts. The Tripplite can not only charge batteries, but also power 12V DC appliances including lights, fan, propane furnace and so on when the Roadtrek is connected to shore power, even with poor batteries.

Having a voltmeter helps to determine just how long your batteries can support your RV when you are disconnected from AC power. For example, suppose you are running your fan, there are interior lights on, the occasional water pump, and your 3-way refrigerator is on propane (some 12V is used). After three hours the voltmeter indicates 12.5V. That means it took 3 hours to use about 20% of your battery capacity. Another 3 hours will use an additional 20% or more. That implies you'll have enough battery power to make it through the night (lights off, pump off and fan on).

This table is typical. Your AGM batteries may vary somewhat.
Typical AGM Battery Table
I replaced my AGM batteries and this is the SOC table provided by the manufacturer.  Your batteries may differ:


What does "reducing battery life" really mean?
AGM and gel lead-acid batteries are chemical devices. They generate electricity using lead plates or mats and an acid liquid. As we repeatedly discharge these batteries, certain deposits form inside them that reduces the capacity. Capacity is the ability to deliver full current for a certain amount of time before the voltage decreases below a useable level. As batteries age, that ability diminishes. For example, a new, fully charged battery can provide a specific amount of current for a specific length of time. Think of this as ability to run your fan, lights, DC for a propane refrigerator and a laptop. With new batteries, you might be able to do that all night. As the batteries age, the length of time decreases and you will find the batteries can no longer do so. And the lights will go out before dawn, whereas before they could be left on all night.

Alternative Voltmeter
I decided to add a digital voltmeter/ammeter. The advantage is I can monitor the amount of current being used and the digital meter provides me with a better idea of the "state of charge" and how much electrical energy might be available. The higher the current, the faster I will drain the batteries. The meter includes a Watt hour counter ("energy"), so I can roughly monitor how much energy is used overnight, should I choose to do so. The meter includes both high and low voltage alarms. This is detailed in another post:


The following data is according to the Tripplite 932768 manual for  750 Watt "PowerVerter DC-to-AC Inverter/Chargers", the Tripplite data sheet and a Roadtrek Manual

Charging the AGM batteries
The batteries can be charged from 120VAC. This is either via shore power or by running my Onan generator. One thing to keep in mind is to turn ON the battery disconnect switch before plugging the RV into AC power or starting the Onan generator. That is per Roadtrek recommendations for my RV.

How long can it take? If the batteries are depleted, it can take 12 hours or longer to fully charge the batteries.

Are there circumstances under which I can't charge the batteries? If  the battery voltage decreases to below 10.0V (+/- 3%, or somewhere between 9.7 and 10.3 volts) a low voltage cutoff will occur. The Tripplite inverter/charger will not charge the batteries if the battery terminal voltages fall that low.   If your vehicle engine is running, the battery may be charged via the standard alternator, if the battery separator allows (see the Battery Separator comments below). A underhood battery separator isolates the chassis battery from the coach batteries when the engine is not running.  However, batteries below 10.5 volts should be checked. They could be damaged.

How can I determine the state of charge? The Tripplite charger/inverter includes a display. However, it cannot be viewed without removing a cover.  Here is a photo with the cover removed. The Tripplite has two rows of LED indicators. One blinks green when on 120VAC and the Inverter switch is "OFF". Otherwise if on 120VAC and the Inverter switch is "ON" then it will be steady green. The switch is located on the Roadtrek display/switch panel near the side entry door. (see the first photo in this post, above).

The other Tripplite indicator goes from off to red to yellow to green depending upon the state of charge of the coach batteries. If charged more than 91% and on AC, one will be blinking green (on AC and inverter off) and the other will be steady green (91% or better charge).

The Tripplite is located in an interior compartment to the left and in front of the powered sofa when you are facing the rear of the RT. The Trippite has a fan and at times you will hear it running. However, there are exposed connectors/wiring so you do need to be careful. If you have any concerns, get a pro to do this.  DO NOT TOUCH ANYTHING.  After you have a pro demonstrate this to you, you can decide if you want to do it yourself in the future.

To reveal the Tripplite, lift up on the top wooden cover at the front and then slide it forward.

Tripplite and DC Electrical Compartment
The next photo is a close-up of the indicators on the Tripplite. The arrow points to a flashing green LED. That means the Tripplite is on AC with inverter OFF. The other indicator which is below the blue cable is the charging indicator. In the photo the bottom LED is green which according to the Tripplite manual indicates "battery capacity charging/discharging 91% - Full"

Here's the table from the Tripplite manual. There are a number of switches for configuring the Tripplite. These LEDs function with Switch in "AUTO/REMOTE" or “Charge  Only” Position. That is how my Roadtrek was delivered.

Approximate Battery Charge Level while charging and discharging (bottom indicator in the photo below):
  • Green = 91% to Full Capacity (see the Tip below)
  • Green and Yellow = 81%-90%
  • Yellow = 61%-80%
  • Yellow and Red = 41%-60%
  • Red = 21% to 40%
  • All three LEDs off = 1% to 20%
  • Flashing Red = 0% (Inverter shutdown)
Tip: How can we determine the Battery Charge Level above 91%?  At about 91% the AC power of the Tripplite is about 10 amperes. At about 100% charge it will decrease to 2 to 4 amperes, assuming the inverter function is OFF. Monitoring the AC current consumption of the Tripplite can aid us in determining the battery charge level above 91%. I have a Progressive Industries EMS on my 210P and I can monitor the AC current consumption. If you have a similar arrangement, so can you. However, you do have to avoid running anything else in the coach to get a reliable reading from the AC draw of the coach.

Tripplite Fault Conditions (bottom indicator in the photo below):
  • All three flashing slowly (1/2 second on, 1/2 second off) = Excessive discharge (inverter shutdown)
  • All three flashing quickly (1/4 second on, 1/4 second off) = Overcharge (Charger shutdown)
The arrow in the photo points to the 120v power "Line green LED":
  • Steady Green = Roadtrek inverter switch "ON" and the coach is on AC power (shore power or Onan generator)
  • Flashing Green = Roadtrek inverter switch "OFF"
  • Yellow = Roadtrek inverter switch "ON" and Coach battery providing power to 120V receptacles via the inverter.
  • Red = Roadtrek inverter switch "ON" and power demanded of the inverter exceeds 100% load capacity

Tripplite LED Indicators
Tripplite Operation and Inverter Selector
The Tripplite has a 3-way slide switch for selecting the "Operating Mode". See the photo below:

Left Position - Auto/Remote
Center Position - DC OFF
Right Position - Charge Only

The "Auto Remote" position ensures that the connected equipment receives constant, uninterrupted AC power. It also permits the Inverter/Charger to be remotely monitored and controlled (in my 210P the Roadtrek inverter switch turns on and off the "inverter" operation if the Tripp-Lite slide switch is in this position).

The "DC OFF" position de-energizes the unit and connects AC OUT to AC IN. In my 210P this slide switch position disables the Roadtrek inverter selector.

The "CHARGE ONLY" setting allows the Tripplite to charge the batteries faster by turning off the inverter, which halts battery discharging.

Operation Switch in DC OFF position

Battery Separator.

Battery Separator - Bidirectional
The battery separator is under the vehicle hood. It controls the connection of the vehicle battery and the coach batteries. In my 210P the battery separator is a "bidirectional" 200A module with a relay for 12V systems. You may have a "unidirectional" model and if so, your battery separator operates differently than the following; for a unidirectional separator see the description in the next section.

The [bidirectional] separator monitors the engine ("Main") and coach ("Aux") batteries. The manual states "If either battery bank is above the connect threshold [13.2V], the relay [closes and] connects the two banks together. If either battery is below the disconnect threshold [12.8V] the unit will open the relay." However, once connected both batteries are at the same voltage. Opening the relay disconnects the engine and coach batteries, preventing the draining of both.  "The connect threshold is set to a nominal voltage of 13.2V, which would only be reached when the charging system is operating. The disconnect voltage is set to a nominal 12.8V, which is near the full charge resting voltage of the batteries. " 

I've monitored the separator and it seems to be intermittent. At times, if the coach battery voltage is less than 12.8V the engine battery will not charge the coach batteries because the separator disconnects if either battery bank is below that voltage. When this occurs, the battery must be charged via 120VAC (shore power or Onan generator). Or via solar. In other words, the battery separator in my Roadtrek doesn't seem to consistently connect my vehicle alternator to the coach battery if the engine battery is 14V and the coach battery is less than 12.8V. That's a coach battery that is 90% charged. See note 7.

According to the separator manufacturer:  The connect threshold is set to a nominal voltage of 13.2V, which would only be reached when the charging system is operating. This will cause the relay to close and the charging system can charge both banks of batteries. The disconnect voltage is set to a nominal 12.8V, which is near the full charge resting voltage of the batteries. This will cause the relay to be opened shortly after the engine is stopped, attempting to preserve 100% of the starting battery capacity for engine cranking."

Note 1: In my Roadtrek the terminal labelled "Aux" is connected to the coach batteries. The terminal labelled "Main" is connected to the chassis battery:

Note 2: The vehicle alternator (Main)  will connect to the coach batteries (Aux) if either the vehicle or coach batteries are above the "connect" threshold of about 13.2V, which is 100% charge. After connecting the batteries will remain connected unless one of the batteries falls below 12.8V. This was confirmed with a new battery separator. See Note 5.

Note 3 :  The separator includes a momentary "auxiliary start function".  The start terminal must see at least 3V* to activate. The auxiliary [coach] battery must read at least 10V*." "This is the input for engine start signal override. When power is applied to this input, the relay will close if the Aux. Battery [coach] is no less than 0.85 Volts below the Main battery [chassis]."  In my Roadtrek this is not used.

Note 4:  According to the separator manufacturer, "* = Typical voltage settings have a +/- 2% tolerance".

Note 5:  Update December 2019. I replaced the battery separator and the operation of the new one is different than the old one.  If either the coach or engine battery is above the "connect" voltage threshold of about 13.2 volts  then the separator connects both coach and engine batteries.  I've monitored this for several weeks and the operation is consistent. If the engine is running the engine battery voltage is about 14.0 volts and the separator connects the engine battery to the chassis battery. If the engine is not running and I connect the Roadtrek to shore power, the Tripplite charge voltage rises to above 13.4 V and the chassis batteries and Tripplite are connected to the engine battery. This is not the way the old separator operated and I can only assume that the old separator had a flaw or failure.

Separator Options
The separator includes some options, including a "start signal" but that is not wired on my Roadtrek. The "start signal input" is the input for engine start signal override. When power is applied to this input, the relay will close if the Aux. [coach] Battery is no less than 0.85 Volts below the Main [chassis] battery.


Where is the Separator located?
The battery separator is the device in the center of this photo with the two red rubber boots. In my Roadtrek the terminal on the right is labelled "Aux" and is connected to the coach batteries. The terminal on the left is labelled "Main" and is connected to the chassis battery:



Alternate Battery Separator - "Unidirectional" Type
The battery separator is under the vehicle hood, see the photo above. It controls the connection between the vehicle battery and the coach batteries. In my 210P the battery separator is a "bidirectional" 200A module with a relay for 12V systems.  The following is the description of a "unidirectional" model. These two models operate differently. You need to determine which you have in your RV.

The unidirectional separator is a 200A battery separator modules with an integrated relay for 12V systems. The separator monitors the engine and coach batteries. If the Main battery is above the connect threshold, the relay connects the two battery banks together. If the Main battery is below the disconnect threshold the separator will open the relay. You will have to determine which battery bank, Chassis or Coach is connected to the "Main" terminal.

The connect threshold is set to a nominal voltage of 13.2V, which would only be reached when the vehicle charging system is operating. This will cause the relay to close and the engine charging system can charge both the engine and coach batteries. The disconnect voltage is set to a nominal 12.8V, which is near the full charge resting voltage of the batteries. This will cause the relay to be opened shortly after the engine is stopped, attempting to preserve 100% of the starting battery capacity for engine cranking.

Battery Separator - Bidirectional - "Clicking"
The battery separator is under the vehicle hood, see the photo above.  From time to time, you might hear a "clicking" sound if your hood is open. That could be the relay of the separator opening or closing.

For a bidirectional separator the relay will close as noted above if the vehicle battery/alternator is above 13.2V and the coach batteries are above 12.8V. Or vice-versa. If either of these falls below 12.8V the relay will open. When the relay closes it connects the vehicle battery/alternator to the coach batteries and when it opens it disconnects or separates these batteries.

The bidirectional will connect the vehicle and coach battery systems if the coach rises about 13.2V and the vehicle is above 12.8V.

At rest, my vehicle battery is about 12.6V. Fully charged my coach batteries are about 13.2 volts after dissipating the "surface charge".

If one has a solar charging system for the coach batteries, it would be possible for intermittent connection of the two systems if the solar system rises above 13.2V and the engine battery is above 12.8V.  Depending upon load and sunlight conditions, if the coach battery falls below 12.8V or about 90%, then the separator relay will open, disconnecting the vehicle and coach batteries. If the sun comes out, or solar improves and the coach battery terminal voltage increases to above 13.2V (which will happen while charging) then the separator relay will close, connecting the two battery systems.  As the coach battery discharges, the terminal voltage will decrease. When sunlight increases, then the separator will again close the relay, "click" and the two battery systems will be connected.

Of course, a faulty separator may also close the relay at unexpected moments.

Solar.

Solar:
In 2014 I  added a 50-watt solar panel and a desulfating solar controller.  Using a 50-watt solar panel provides a maximum 4.17 amperes of charging current at 12V during peak sunlight conditions. That's more than sufficient for maintaining or topping off the batteries.



Notes:
  1. This post is not a recommendation that owners perform their own electrical service. Working with electricity can be dangerous and can result in personal injury, or death or damage to your Roadtrek. 
  2. This information is provided "As Is" and no warranty or claim of accuracy is given. Your Roadtrek and its equipment may be very different than what is portrayed here. 
  3. Refer to the Roadtrek owners manual and the Tripplite Owner's Manual for complete information. 
  4. The Tripplite inverter/charge includes 120V surge protection. In other words, outlets that are powered by the "invert" mode will have surge protection. Any others in the coach will not have any surge protection unless it is added. In my case, I have an electrical management system (EMS) on the shore power line. I don't have such a thing on the generator power output. 
  5. For troubleshooting of the Tripplite, refer to the owners manual. 
  6. This post is based on several other posts in this blog as well as recent social media posts by me. I'm providing this so I won't have to write this up again. 
  7. My coach batteries exhibited difficulty at about 3 years. I suspect the problem was the model battery separator Roadtrek installed in my 210P. The separator won't connect the vehicle alternator to the coach batteries unless the coach batteries are at 100% charge. 
  8. All info on the battery separator is per the manufacturer's data sheet. 


Sunday, August 6, 2017

New Voltmeter-Ammeter-Wattmeter for AGM batteries - Part 2

New Ammeter-Voltmeter-Wattmeter
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September 15, 2017: Added short video clip

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All content in this blog is provided for information purposes only. This blog contains the actions, opinions, and views of the author. The information contained here should not be consider “expert” and not taken as specific advice. The author makes no representations as to the accuracy, completeness, or reliability of the information on this site or that is found by following any link. The information contained here and in the links may become outdated.The author will not be held liable for any errors or omissions in this information. The author will not be held liable for any losses, injuries, or damages from the use or display of this information.

Short video:


New Ammeter-Voltmeter-Wattmeter
See Part 1 for the background information about the AGM batteries in my roadtrek 210P:

http://roadtrek210.blogspot.com/2017/08/new-voltmeter-ammeter-wattmeter-for-agm.html

Why add a digital voltmeter-ammeter?
The decision to add a digital meter was easy. Then I proceeded to decide upon the type of meter. I had seen a FMCA Roadtrek Chapter Cyberrally post about how someone added a digital meter and I wanted to do the same.

Finding a meter wasn't all that difficult. A meter which stored "Ampere Hours" would have been ideal, but I opted for a digital voltmeter-ammeter-wattmeter. The selected meter also included adjustable alarm points for high and low voltage. That would be useful for monitoring low battery voltage, or a point at which I wanted to pay closer attention to battery draw.

I ordered the meter ($15.99 at the time) with DC shunt. I wanted to connect it directly to the battery so I could monitor battery voltage even with the battery disconnect "off". A switch and protective fuse was necessary. The parts list included:
  1. Meter with 100A shunt
  2. Off-On switch
  3. Case for meter and switch (Case dimensions: 5-1/2" x 3-1/8" x 1-1/2")
  4. 25 ft. 4-conductor cable
  5. Automotive fuse holder (I used a fuse from my kit)
  6. Miscellaneous connectors.
  7. Note: for details, see the parts list at end of this post. 
The most difficult part for me was determining where to mount the meter. I had decided that I wanted a surface mount case, so I could remove the meter in the future and leave no trace. Determining how to run the 4/C cable was also a bit of a challenge. I decided to route it behind the fiberglass side panel, into the coach along side the door, then behind the side panel and exiting just below the 120VAC/12VDC power distribution center. This required the temporary removal of the rear passenger seat. Lots of screws.

Passenger seat removed, propane furnace exposed
With the passenger seat removed, it was possible to remove the side panel, and pull the cable behind the panel. I pulled the cable from the battery compartment to the passenger seat area, and re-assembled the interior panel. I left a foot lomg "pigtail" for connecting the meter.

Cable at Passenger Seat
I then mounted the rear of the meter case to the wall. I used 3M Dual Lock™ General Purpose Reclosable Fasteners. Note the female electrical connectors on the cable from the battery compartment:

Base of Meter Case
I assembled the meter in the case. Marked the case and cut the opening with a Dremel tool and cutting wheel. I used connectors so I can remove this if necessary. The "female" end goes on the cable from the battery compartment. The "male" end is in the meter case. This is so there should not be any exposed live parts if I pull the meter, even if the fuse at the shunt is intact.

Meter and Off-On switch in case
This is the front of the meter and switch, assembled in the case:

Front of meter case with Off-On switch

I mounted the meter to the case mounted on the wall:

Meter case mounted to the wall
This is the shunt, which was supplied with the meter. For the meter I purchased the shunt is connected between the negative battery post and the negative conductor. The shunt is rated 100A/75mV. The shunt is actually a precision resistor and the higher the current flowing through it, the higher the voltage drop across it. The voltage drop is 75 millivolts at 100 amperes.
Shunt
The shunt was installed in accordance with the manufacturer's instructions. A right angle screwdriver is helpful for installing the wiring to the shunt (I used a phillips).

CAUTION - Installing the shunt requires removing the negative battery lead. Exercise great care not to short a tool from negative to the nearby positive terminal. DEATH OR INJURY CAN RESULT. Be sure there is no battery load when doing this procedure.

The shunt is connected directly to the negative battery post. The black (Negative) cable is connected to the other side of the shunt; the yellow arrow points to that connection. Three of the leads of the 4-conductor cable is connected to the shunt. The fourth conductor goes to the red (Positive) battery terminal.  I installed an automotive fuse between the positive battery terminal and the lead going to the meter. That is to protect the wire in the event of a short circuit

CAUTION - A properly sized fuse is necessary to protect the wire in the event of equipment failure or short circuit. Fire, damage,  injury or death can result from an unprotected circuit.
Shunt installation and automotive fuse on positive battery terminal
With the installation complete I threw the "Off-On" switch to the "On" position.


I checked the display using a precision digital VOM. I measured the mV at the shunt and calculated the meter reading. The meter agreed.

Meter Setup
The meter has alarm points and some options:
  1. Set backlight off or on. The default is "on".
  2. Set voltage alarm threshold. The meter includes both "high" and "low" voltage alarms. These are set independently. The presence of an alarm flashes the backlight alternating "off" and "on". I set the low voltage alarm at the 50% DoD level for my coach batteries.
  3. Set the measuring range. This meter will work with a 50A/75mV shunt or a 100A/75mV shunt. I set this to match the installed shunt, which is 100A/75mV.
  4. Energy reset. The meter will accumulate and store kilo-watt hours (kWh). This value can be reset to zero.  
Meter Limitations
The meter is a DC meter. This means that the ammeter measurement is polarity sensitive. The meter as connected can only measure discharge current from the battery across the shunt. When charging the meter displays 0.00 amperes. However, by reversing the connections it is possible to measure charging current. I tried this and it works.

It was interesting to watch the Tripplite inverter/charger step through the charging levels. I may add a DPDT switch for this purpose, but it is completely optional. I've monitored the Tripplite by watching the AC current; as the Tripplite throttles back the AC current decreases. However, other 120VAC loads will mask that.  It is also possible to pull the compartment cover over the Tripplite and observe the charge state LEDs:

Green = Full Charge
Detailed Parts list, my cost $36.45 plus tax and any shipping:
  1. MICTUNING DC 6.5-100V 0-100A LCD Digital Display Ammeter Voltmeter Multimeter Volt Watt Power Energy Meter Blue with 100A/75mV Shunt, Part No. MIC-DVG-015.
  2. Serpac black plastic case, model 151i, BK.
  3. Rocker switch, Philmore No. 30-882.
  4. 4-conductor shielded cable, 24 AWG. (Use #22-24 AWG; smaller AWG is easier to pull).
  5. Insulated terminal disconnects, male and female (from toolbox, not included in price total).
  6. Fuse and fuseholder to protect the wire from the meter to the (+) positive battery terminal. Size of the fuse is determined by the size of the wire. 

Saturday, August 5, 2017

New Voltmeter-Ammeter-Wattmeter for AGM batteries - Part 1


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Earlier this year I replaced the AGM batteries in the Roadtrek with new AGMs. I decided against lithium (LiFePO4) batteries for the time being. For one thing, I hadn't decided which real estate I would give up. I wasn't sure I'd put them in the battery compartment as it is outside the rig and uninsulated.

I've posted on social media (G+ and FB) that I wasn't happy with the 4-point L-F-G-C "idiot light" arrangement in the Roadtrek, in particular because I discovered that the "G" or "Good" indicator was illuminated even when the batteries were below 50% depth of discharge (DoD).

What was my issue? It was about battery life and capacity. To get optimal life from AGM batteries most experts recommend not allowing the battery to regularly fall below 50% state of charge (SoC). The "G" or "Good" LED extinguishes below that level. The "F" or "Fair" light on the Roadtrek is below that. A simple plug-in digital meter was an option and one can be purchased for between $5 and $15. Here's one:
12V Plug-in digital Voltmeter
Our rental rig had such a simple meter, and I could plug one into the rear cabinet above the entertainment center in our 210P, which had a cigarette lighter for the 12V amplified antenna. I added a "Y" connector for this purpose. However, I also wanted an ammeter and a wattmeter, but I didn't want to spend the amount necessary for a Trimetric and I wanted something easy to install.

Here's the 12V connector I used to install a "Y" cable. That allowed me to connect a meter in addition to the 12V TV antenna amplifier. But viewing the meter in this location isn't very convenient.

Location of simple plug-in digital meter connector:

12V Connector in rear compartment
Installed and functional digital meter:

New Digital Meter
Battery Life Issues
All of this is really about getting full value and maximum capacity from the batteries. As AGM batteries age, they will lose capacity. Such batteries have specifications based on specific conditions, such as an ideal temperature of 77F. AGM batteries operate on chemical principles, and chemistry is influenced by temperature.

I had noticed that, after 4 years the batteries in the Roadtrek didn't seem to be able of providing the desired voltage for the time I wanted to use them "off the power grid". That indicated a loss of capacity.

The entire point of adding a digital voltmeter-ammeter is to get a better idea of the condition of the coach batteries. Even better than battery voltage is specific gravity, but that can't be readily determined. Below is a table for my current batteries which provides some idea of the life of the batteries when discharged repeatedly to certain levels of DoD (depth of discharge). As can be seen, the 50% DoD provides about 1200 charge-discharge cycles. Decreasing to 80% DoD provides a life of about 700 cycles. Avoiding DoD below 50% provides a good compromise between battery life (cycles) while providing adequate capacity.

The problem we face is that to extend battery life we either use them less (fewer cycles per year means more years of service before reaching end of life). Or, we can reduce the DoD. As noted in the table below, if the DoD is only 20% it is possible for a battery to provide 3600 charge-discharge cycles. Of course, to achieve only 20% DoD requires much less use of the available battery capacity.

Why Measure Battery Volts and Amperes?
How long can we run things in the coach on batteries and avoid discharging the batteries below 50% DoD? The ammeter and voltmeter with the tables for our batteries can be an aid to this.

For example, my batteries can provide 18.33AH for 12 hours. However, that is to 100% discharge, which is what I want to avoid. 50% DoD will allow a draw for only about half that time, or about 18.33AH for 6 hours.  Or, I could reduce the load and extend the time. If I really need to run solely on batteries for 12 hours, my batteries can provide about 9 amperes per hour:

                                           220AH/12H = 18.33A
                                           18.33A x 50% = 9.165A

The times are approximate. If we have an ammeter we can determine what the actual current draw on the batteries are. If we have a voltmeter. we can determine the state of charge of the batteries.

Battery Life and Charge-Discharge Cycles

Depth of Discharge - New AGMs


Using the Voltmeter
The digital voltmeter will provide an indicator of the state of charge (SoC) of the batteries. "OCV" is open circuit voltage, or the state when the batteries are not connected to a load:

Relative State of Charge @ 77F - New AGMs
Note that SoC tables may vary. Here is a "typical" AGM table, which differs from the chart above.

Typical AGM battery SoC table

Battery Life 
Taking care of batteries and extending their life will obviously reduce costs. They are expensive. 220AH of AGM batteries is about $450 to $600. However, the other desireable thing is capacity. I want to be assured that the battery is capable of providing the amperes I need for as long as I need them. A battery with reduced capacity may not be able to do that.

Capacity is the ability of a battery to deliver the amount of power it was designed to do. Over time, battery capacity will decrease. As the battery nears end of life, it's capacity will diminish significantly. The batteries I have are designed to provide 25A @ 460 minutes  (7.7 hours) when new. As the batteries lose capacity, they will provide 25A but for shorter periods of time. And as the battery discharges, the voltage will decrease. A battery with diminished capacity will experience more rapid voltage fall-off. DC power is volts x amperes. As the voltage diminishes, so does the power if the amperes are constant.

While extending battery life does reduce operating costs, I am more interested in having the desired capacity available to me.  My batteries are rated 220AH. That means that they can continuously provide about 18 amperes for 12 hours, if they can provide full capacity (see notes):

220AH/12H = 18.33A.

Real World Capacity
The capacity achieved is based on battery condition, ambient temperature and other factors.

As noted above, the 12 hour rating for my AGM batteries is 18.33A.

In the real worlds AGM battery capacity does gradually decline, and by 700 cycles capacity decrease to 50-60% is usual. That means that the above number will gradually decrease:
  • New AGM battery (80-100% capacity) = 18.33A for 12 hours
  • Battery after 400 cycles (80% capacity) =  14.7A for 12 hours.
  • Battery after 700 cycles 50-60% capacity = 9.2A for 12 hours

Lithium batteries also have a gradual reduction in capacity, but generally a 220AH battery:
  • Lithium battery after 400-500 cycles (80% capacity) = 14.7A for 12 hours. 
Note: The above numbers are based on battery manufacturer published data and this information does vary from manufacturer to manufacturer. It is important to realize that battery data is usually under ideal conditions such as 77F temperature. AGM battery capacity decreases as battery temperature decreases and can perform (charge and discharge) over temperature ranges of (-)4F to 104F. Lithium batteries generally can operate with charging temperature of 32F-113F and discharge temperatures of (-)4F to 140F. Electric vehicle and experimental data indicates that high environment temperature could accelerate the aging of LiFePO4 batteries, while low temperature could reduce output power capability. Data suggests normal life can be achieve if operated in the range 50F to 104F.
However, it is important to check with each manufacturer for their specifications.

Battery Life based on Depth of Discharge
A well maintained AGM (absorbent glass mat) battery has a life of 6-8 years. Average life has been stated to be 3-5 years. If not maintained, that will diminish to 2-4 years. Note that it really is charge-discharge cycles that are the limit. Battery manufacturers assume a certain number of such cycles in a year. That assumes optimal temperatures of 77F and that the batteries are immediately charged to 100% immediately upon the end of the discharge cycle.

For example, with 50% DoD my batteries are designed to provide 1200 charge-discharge cycles:
  1. If used every day, a battery will experience 365 cycles per year.  Under such use, the batteries have a service life of 3.2 years. 
  2. If a charge-discharge cycle occurs every other day, or about 180 times a year, the same batteries could provide a service life of 6.7 years. 
  3. If a charge-discharge cycle occurs every three days, or about 120 times a year, the same batteries could provide a service life of 10.0 years. 
 For example, with 80% DoD my batteries are designed to provide 700 charge-discharge cycles:
  1. If used every day, a battery will experience 365 cycles per year.   Under such use, the batteries have a service life of 1.9 years.  
  2. If a charge-discharge cycle occurs every other day, or about 180 times a year, the same batteries could provide a service life of 3.9 years. 
  3. If a charge-discharge cycle occurs every three days, or about 120 times a year, the same batteries could provide a service life of 5.8 years. 
How does one "maintain" a maintenance free battery?
  1. Recharge as soon as possible after use - preferably within 24 hours.
  2. Recharge the battery properly.
  3. Use a "smart" charger.
  4. Battery should not be charged if the core temperature reaches 120F (49°C).
  5. Avoid discharging below 50% SoC (state of charge).
  6. When recharging, recharge to at least 80% SoC before beginning another discharge cycle. 
  7. Charge to 100% as often as possible. 
  8. Avoid heat; heat shortens battery life. Each 15°F (8C) rise in temperature reduces the life of the battery in half.
  9. Know the correct state of charge (SoC). Knowing this will help to extend overall cycle life. A battery monitor is worthwhile and use one that is accurate.  
Battery Cost 
There is a cost to overtaxing batteries, as noted above. Best case is a battery with 50% DoD, and that yields 1200 cycles under best conditions. As noted above:

  1. If used every day, or 365 cycles per year or a service life of 3.2 years.  The cost is $140 per year ($450/3.2)
  2. If a charge-discharge cycle occurs every other day, or about 180 times a year, the same batteries could provide a service life of 6.7 years. The cost is $67 per year ($450/6.7).
  3. If a charge-discharge cycle occurs every three days, or about 120 times a year, the same batteries  could provide a service life of 10.0 years. The cost is $45 per year ($450/10).
 For example, with 80% DoD, which provided more AH, but sacrifices battery life:
  1. If used every day, a battery will have 365 cycles per year.  At 80% DoD, my batteries are designed to provide 700 cycles.  Under such use, the batteries have a service life of 1.9 years.  (Cost is $236 per year)
  2. If a charge-discharge cycle occurs every other day, or about 180 times a year, the same batteries with a life of 700 cycles could provide a service life of 3.9 years. (Cost is $115 per year).
  3. If a charge-discharge cycle occurs every three days, or about 120 times a year, the same batteries with a life of 700 cycles could provide a service life of 5.8 years. (Cost is $78 per year).
Notes: 
Ampere-Hours. An amp hour (AH) rating is a rating usually used on deep cycle batteries. It is an ampere rating taken for 20 hours. For a 100 AH rated battery a load may draw 100AH from the battery for 20 hours.For such a battery, that's about 5 amperes an hour. 100AH/20H  = 5A).
  1. The total time of discharge and load applied is not a linear relationship. As the battery load increases the actual capacity decreases. For example, a 100 AH battery with a 100 amp load should provide one hour of runtime. But it won't. The capacity of the battery will be severely reduced.
  2. Each battery manufacturer provides AH data under various loads. For example, here is the table for my batteries, with a final voltage of 1.75V per cell (3 x 1.75 = 5.25V, or a dead battery):
    1. 20 hours = 220 AH
    2. 10 hours = 210 AH
    3. 5 hours = 190 AH
    4. 3 hours = 175AH
    5. 2 hours = 155 AH
    6. 1 hour = 130 AH
Using the AH from the battery table, a rough guide for capacity can be determined. For example, 10 hours = 210AH. To achieve a 50% DoD, 210 x 0.5 = 105AH realized capacity. To achieve a 80% DoD, 210 x 0.8 = 168 AH realized capacity.  However, these figures are approximate and are based upon a new battery and 77F. The approximate condition (state of charge, SoC) can be determined with a voltmeter.

Using the above, the 10 hour ability of the batteries is actually about:

10 hours, 50% DoD = 105AH/10H = 10.5A.
10 hours, 80% DoD = 168AH/10H = 16.8A.

Note that the above information is in accordance with the battery data provided by the manufacturer of my batteries. The actual data will vary by manufacturer.

August 10, 2017 added and expanded "real world" battery life data.