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Old 03-19-2019, 09:54 AM   #1
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Battery charging abuse by the numbers

Battery charging abuse by the numbers

I am a newbie Class A owner but have a lot of experience with batteries, enough to call myself a battery geek (career in electronics).
I have a typical battery set, 4 GC2 6v batteries with a total 450 AH rating @ 12V. The Magmun Inverter charger is capable of delivering 2000 watts which is 148 amps at 13.5vdc.
The controller has the ability to do three stage charging, Bulk absorption and float.

After a day of discharging when I start the generator the battery set gets hit with 100 amps and holds well above 70 amps for quite some time depending on its state of discharge. Magmun was set to 80%.

But here are the battery manufacture charging numbers. For a 450AH set the max charge rate shall not exceed c/10 or 45 amps. That means the charger must be set to a 30% charge and if the house is using some 12v power I could add some more. This bulk charge is to last 1 hour.

Then the absorption time is to be 2-4 hours before switching to float.

More numbers; Bulk charging voltage is 14.8, Absorption is 14.8 and Float is 13.4

So in 5 hours I can get about a 50% recharge. This tells me I need to know how much total power was used and monitor the charging times. Not doing so will either over or under charge the battery. Running the generator for a couple hours will not be enough. Letting 100 amps charge rate will destroy the battery over time by heating it up, boiling off the fluid and potentially blow it up.

I bought the Victron BMV-702 Battery Monitor to better manage the battery bank because this is not fully automated, I must decide when and how long to run the generator. I also know the Magmun amp meter measure total amps provided the house not just battery charging amps.

There is also another battery that can take some charge, the Chassis battery can steel some power up to 15 amps when the voltages differ enough.

Are you a battery geek like me or do you not watch this very closely? Or if your plugged in all the time then much of this never matters.
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Old 03-19-2019, 10:15 AM   #2
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Quote:
Originally Posted by gpounder View Post
Battery charging abuse by the numbers

I am a newbie Class A owner but have a lot of experience with batteries, enough to call myself a battery geek (career in electronics).
I have a typical battery set, 4 GC2 6v batteries with a total 450 AH rating @ 12V. The Magmun Inverter charger is capable of delivering 2000 watts which is 148 amps at 13.5vdc.
The controller has the ability to do three stage charging, Bulk absorption and float.

After a day of discharging when I start the generator the battery set gets hit with 100 amps and holds well above 70 amps for quite some time depending on its state of discharge. Magmun was set to 80%.

But here are the battery manufacture charging numbers. For a 450AH set the max charge rate shall not exceed c/10 or 45 amps. That means the charger must be set to a 30% charge and if the house is using some 12v power I could add some more. This bulk charge is to last 1 hour.

Then the absorption time is to be 2-4 hours before switching to float.

More numbers; Bulk charging voltage is 14.46, Absorption is 15.3 and Float is 13.4

So in 5 hours I can get about a 50% recharge. This tells me I need to know how much total power was used and monitor the charging times. Not doing so will either over or under charge the battery. Running the generator for a couple hours will not be enough. Letting 100 amps charge rate will destroy the battery over time by heating it up, boiling off the fluid and potentially blow it up.

I bought the Victron BMV-702 Battery Monitor to better manage the battery bank because this is not fully automated, I must decide when and how long to run the generator. I also know the Magmun amp meter measure total amps provided the house not just battery charging amps.

There is also another battery that can take some charge, the Chassis battery can steel some power up to 15 amps when the voltages differ enough.

Are you a battery geek like me or do you not watch this very closely? Or if your plugged in all the time then much of this never matters.
Welcome to the world of batteries where everything has consequences. First I think your charge parameters are not correct. Bulk\adsorption should be the same voltage usually around 14.4 - 14.6 volts. What you are calling your adsorption voltage I believe is actually the setting for equalization which is not part of the standard charge cycle. In a perfect world your charge rate should be 10 - 13% however charging at 100 amps is not going to cause your batteries to explode or be overcharged. The charger will go into adsorb phase long before any of that happens. Like most things there's a trade off. Charging at a higher current will shorten the charge time at the cost of reduced battery cycle life but I doubt it will be a dramatic reduction. Draining them below 50% DOD or not charging them fully will probably have a much more significant effect. Lead acid batteries do not like to be partially charged.
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Old 03-19-2019, 10:24 AM   #3
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Yes to monitoring the In/Out of battery AMP's! And yes, I'd review your current values too. When the time comes for new batteries, one of the things I like about the Lifeline AGM's - is you can really pump some AMP's into them. The ability to do so, does reduce the total run time of your generator.

Welcome to the Class A side of things... Go have some fun,
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Old 03-19-2019, 10:28 AM   #4
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Interesting read
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Old 03-19-2019, 10:31 AM   #5
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Definitely some valid points. We have 6, 6V at +/- 725Ah so a 100A charge rate isn’t too much above the C/10. Our read out is in 25A and .5V increments, so not exactly a precision instrument. The house batteries are 4 years old and seem to be holding up well. I’ve never dug into the settings of the charger, although it would probably be wise to do so. The current plan is to add solar and switch to lithium in 2 years which will eliminate a great deal of concern over proper battery charging protocol.

As far as exact voltages for each stage of charging, it is important to follow the recommendations of the manufacturer. Flooded, AGM and Gel all have different specifications and even the same type will differ between manufacturers.

In a nutshell:
Bulk provides a constant current that may approach C/25 while voltage is increased. This brings the battery to 80% capacity.
Absorption provides a constant voltage while current is reduced. This brings the battery to 85-95% capacity.
Float provides a reduced voltage that is held constant while current is reduced. This brings the battery to 100% capacity and maintains that level of charge.
Equalization is a controlled overcharge.

I have noticed many owners who mention “charging” their batteries for 30-60 minutes in the morning and evening with the generator. That would seem to be detrimental to the longevity of a LA battery.

Thanks for starting the discussion.
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Old 03-19-2019, 10:40 AM   #6
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Originally Posted by PbdBlue View Post
Welcome to the world of batteries where everything has consequences. First I think your charge parameters are not correct. Bulk\adsorption should be the same voltage usually around 14.4 - 14.6 volts. What you are calling your adsorption voltage I believe is actually the setting for equalization which is not part of the standard charge cycle. In a perfect world your charge rate should be 10 - 13% however charging at 100 amps is not going to cause your batteries to explode or be overcharged. The charger will go into adsorb phase long before any of that happens. Like most things there's a trade off. Charging at a higher current will shorten the charge time at the cost of reduced battery cycle life but I doubt it will be a dramatic reduction. Draining them below 50% DOD or not charging them fully will probably have a much more significant effect. Lead acid batteries do not like to be partially charged.
One source gave me the numbers I posted, I called the factory and gave me new numbers, bulk and absorption to be the same. I have had batteries blow up when I have not been diligent or watering them and that happened at a much lower charge rate so it does happen.
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Old 03-19-2019, 10:56 AM   #7
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Definitely some valid points. We have 6, 6V at +/- 725Ah so a 100A charge rate isnít too much above the C/10. Our read out is in 25A and .5V increments, so not exactly a precision instrument. The house batteries are 4 years old and seem to be holding up well. Iíve never dug into the settings of the charger, although it would probably be wise to do so. The current plan is to add solar and switch to lithium in 2 years which will eliminate a great deal of concern over proper battery charging protocol.

I have noticed many owners who mention ďchargingĒ their batteries for 30-60 minutes in the morning and evening with the generator. That would seem to be detrimental to the longevity of a LA battery.

Thanks for starting the discussion.
That's a huge system. L16 batteries I am guessing, have those for the house solar off grid system. They would take all day to recharge from a 2K charger.
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Old 03-19-2019, 11:10 AM   #8
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There was a good point made. Discharging below 50% will shorten the life of a battery. Other implications to a real deep discharge. You may not be able to start the generator for one. Low voltage may damage some electric devises.

If you do a deep discharge then at least recharge immediately. Chemical sulfation starts when batteries are deeply discharged. To minimize this keep your battery above 12.4 volts.

When figuring load vs time and charging it is best to figure only 50% of your Amp Hour capacity as available energy.
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Old 03-19-2019, 11:59 AM   #9
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Hello All,

I too am new to the RV lifestyle. I purchased my 2000 Winnebago Ultimate Advantage in Dec 2016. I completely discharged the house batteries the first trip. The second trip I learned my three 12 volt house batteries were leaking all over the battery compartment. It was like the previous owner found the cheapest used batteries to load in there before he sold me the motorhome. Summer of 2017 I went to visit my uncle and plugged into an open neutral power at his house and destroyed my charger inverter. At thanksgiving I saw this video from the RV geeks and purchased this inverter and charger. https://youtu.be/-a8ijzg80OI and had Blue Dog RV install it. ( Big mistake) I am new and so I do a lot of reading on the forums and watch a few youtube videos. I then replace the three leaking 12 volt batteries with 2 costco 6 volt batteries in January of 2018. I learned how to discharge only to 50% and then recharge them. 2018 was fun with this set up and knowledge. For Christmas 2018 I purchased 4 more golf cart batteries and a battery box to hold all six batteries. I now have 630 amp hours.

I choose the 6 6 volt batteries because they are tough. I am not an expert and make mistakes and these batteries I hope will be more forgiving to me when I make mistakes. The new charger I have when initially started pushes 150 amps to the batteries and then the amp load starts to adjust. I do a lot of boondocking and I start the generator to charge the batteries and in my experience it takes about 3 hours to completely charge the battery bank. This has been consistant for me. I think my set up is good now and I am not finding a problem pushing 150 amps to the batteries. I have checked and they are not as hot as I would expect.

I just replaced a my battery solenoid in my RV and now the alternator is charging the house batteries when the engine is running. Another piece of the charging puzzle repaired i hope. Need to still check voltages to make sure B.I.R.D. system is working correctly. Sorry for the lengthy response.

Bill
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Old 03-19-2019, 12:00 PM   #10
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I have a good 3 stage charger
I check water levels weekly at first...then monthly

Now I check every 3 months and rarely need to top off


Rest of time......I go camping and enjoy the simplicity
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Old 03-19-2019, 12:02 PM   #11
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Trojan says 10% to 13% of total AH capacity, that will make your 45 amp charging a bit lower the max.

They also say to use the TOTAL AH of the combined batteries. No mention of series or parallel.

Does that mean the total of 4, 225 AH batteries, equaling 900 AH ?

OR is it the 450 AH at 12 volts, that you use the bank at ?
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Old 03-19-2019, 12:26 PM   #12
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There was a good point made. Discharging below 50% will shorten the life of a battery.
It reduces the cycle life but in terms of amp hours delivered, you're still getting what you're paying for going down to 80%DOD. It depends a lot on the application. If you're a full timer and put an 80% cycle on your bank every day, then you might care whether you get 300 or 500 cycles. If you're like most RV owners that might put a few dozen cycles on a bank during the course of a year, then you can care less whether you get 300 or 500 cycles. To try and economize by limiting your discharge to 50% will only result in owner inconvenience, or lost value when you recycle the pack with cycles left over when it reaches calendar life.

Another way to look at it is it's better to burn out than fade away. I would rather replace a pack I thrashed for two years and craps out than baby a pack and limp it along for 5 years or more. You're more likely to get your money's worth on a pack you use up than one that times out.

Just reading the forums here it's a safe bet that most packs aren't dying from cycling or going below 50% DOD, its deficient charging - not enough, too much or left for dead over the winter. You can agonize over the cycle minutia if you want but if you pay even half attention to charging them after use and doing an equalize cycle once in a while, you will get dependable service and your money's worth.

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Old 03-19-2019, 12:28 PM   #13
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Quote:
Originally Posted by gpounder View Post
Battery charging abuse by the numbers

I am a newbie Class A owner but have a lot of experience with batteries, enough to call myself a battery geek (career in electronics).
I have a typical battery set, 4 GC2 6v batteries with a total 450 AH rating @ 12V. The Magmun Inverter charger is capable of delivering 2000 watts which is 148 amps at 13.5vdc.
The controller has the ability to do three stage charging, Bulk absorption and float.

After a day of discharging when I start the generator the battery set gets hit with 100 amps and holds well above 70 amps for quite some time depending on its state of discharge. Magmun was set to 80%.

But here are the battery manufacture charging numbers. For a 450AH set the max charge rate shall not exceed c/10 or 45 amps. That means the charger must be set to a 30% charge and if the house is using some 12v power I could add some more. This bulk charge is to last 1 hour.

Then the absorption time is to be 2-4 hours before switching to float.

More numbers; Bulk charging voltage is 14.8, Absorption is 14.8 and Float is 13.4

So in 5 hours I can get about a 50% recharge. This tells me I need to know how much total power was used and monitor the charging times. Not doing so will either over or under charge the battery. Running the generator for a couple hours will not be enough. Letting 100 amps charge rate will destroy the battery over time by heating it up, boiling off the fluid and potentially blow it up.

I bought the Victron BMV-702 Battery Monitor to better manage the battery bank because this is not fully automated, I must decide when and how long to run the generator. I also know the Magmun amp meter measure total amps provided the house not just battery charging amps.

There is also another battery that can take some charge, the Chassis battery can steel some power up to 15 amps when the voltages differ enough.

Are you a battery geek like me or do you not watch this very closely? Or if your plugged in all the time then much of this never matters.
I think that if you check your Magnum inverters specs you will find it has a 100 amp battery charger. I am assuming that you do not have a separate converter in addition to the Magnum inverter/charger. Yes, I agree that that charger set too high is hard on a flooded battery and will do damage over the long run. If it was AGM no problem.

While your coach is in use you are using some DC amps for lights, fridge control board, inverter control etc, which probably amounts to about 10-15 AH. Most manufacturers of flooded batteries recommend between 10-15% of the C rating for charging. For your battery bank this would be 45-67.5 amps. If you took the middle ground and used 12.5% of C you would have a charge of 56.25 amps. Now add in what the coach is using while living in it and you have a charge rate that should be set to 60-70% in the Magnum remote panel. If in storage and plugged in I would dial the charge rate back to 50%.
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Old 03-19-2019, 12:43 PM   #14
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I am no expert on batteries, or anything else for that matter but that wont stop me from posting

Batteries are charged with voltage, not amps. The alternator charges at 14.8 volts until the battery is at 12.8 volts then shuts off. The only amps involved are what ever the wire size provides in Ohms which are resistance to the voltage.

One Ohm resisting One Volt creates One Amp of current. You dont charge at 100 amps or at any amps, just volts. The battery wires are large and provide minimum resistance to the voltage (in the case of an alternator, 14.4 volts)

Float chargers will charge to full battery voltage, about 12.8 volts then shuts off for a while, say a week or two then starts and brings the battery voltage up to proper voltage again. Modern motorhomes should have virtually a worry free maintenance system.

Of course this is JMHO based on experience and forms like this.
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