Off Grid battery backup system charging question.

[90cummins]

I have an off grid battery backup system with two battery banks one is 370ah and the other is 225ah..
I have acquired another set of batteries 3 years old that were left discharged (J185H-AC 225ah) and I'm working on reviving them to add capacity
My current battery banks have an amp/hr rating of 370ah and the other has a rating of 225ah. Both battery banks are parallel except when servicing.
My question is this;
When setting up the charging rate which is programmable do I use the combined ah rating of 595ah or the highest of the group which in this case is 370ah?
When I charge the banks separately I use the individual battery ah rating.
90cummins

 

[oosik]

Way back in the dark recesses a red flag went up when I read your post. What I remember goes something like this - if you are charging two batteries of the same rating at the same time, you will be OK. If the two batteries have different amp hour ratings - its best to charge them separately. If the batteries are hooked together the charger will see the "larger" of the two and charge until the larger is finished. Thereby possibly overcharging the smaller battery.

Don't hold me to this - but its what I seem to remember. Perhaps, as an example - I use both AAA & AA LI rechargeable batteries. My charger very specifically states to charge one size only at a time.

Now there are LI rechargers that allow recharge of two sizes at the same time. However, if you look closely at the way the batteries fit in the charger - you will see that each size is on a seperate charging circuit.

 

[scdeerslayer]

Way back in the dark recesses a red flag went up when I read your post. What I remember goes something like this - if you are charging two batteries of the same rating at the same time, you will be OK. If the two batteries have different amp hour ratings - its best to charge them separately. If the batteries are hooked together the charger will see the "larger" of the two and charge until the larger is finished. Thereby possibly overcharging the smaller battery.

I THINK that's if wired in series, but if wired in parallel it sees it as one big battery. Wired in parallel the stronger battery will charge the weaker battery anyway. I don't know much about all this multiple battery stuff though. I use a charger that has three different charging circuits to charge the three batteries in my boat to make things simpler.

 

[dmccarty]

In the boating world where people run the boats power system off of batteries, it is a big no no to run different sized batteries, i.e., AHs, or different aged batteries in the same battery bank. Furthermore, the batteries need to be the same, AGM, flooded batteries, or some of the other types. Don't mix them together in the same bank. Different battery types have different charging requirements. Best case with incorrect charging means decreased lifetime of the battery. Worse case could be an explosion.

Different battery makers might also specify different charging rates as well as how many batteries can be connected in parallel.

Later,
Dan

 

[1stDeuce]

Please explain what you mean by "both banks are parallel except when servicing".

If they're both connected, and all in parallel, then the charger doesn't see it as two banks, but rather as one bank of 595ah (370+225). If you disconnect one bank, then the charger only sees the connected one.

Either way, you select the charge rate based on total ah of batteries that you will be charging, whether it's one battery, or twenty, or in your case one bank or both...

If you're running the batteries all in parallel, with multiple sizes and ages, you are not really going to get optimal charging on all of them, but running an equalize more often will help... It's still not ideal, but it will provide you with more capacity, at the expense of life of some of the batteries due to incomplete charging, and others due to over charging...

If you have separated them into banks based on size, or age, that's fine, but you can't then connect those banks in parallel and overcome the above... You'll still have the same problems as if you connected them all together in one huge bank...

 

[Tractor Seabee]

Like Deerslayer I am reaching into the brain locker for old data that used to be routine stuff. I worked some with backup battery systems called UPS (Uninterruptible Power Supply). First, proper terminology: A battery is a group of individual cells connected in series to meet the output voltage required;
Each cell is rated at 2 volts for calculation of battery output; therefore, a 12 volt battery has 6 cells rated at 12 volts; arrangements for battery banks can use a mixture of series and parallel connections to get required output voltage and AH capacity depending on cell/battery selections. Each cell has rated capacity depending on plate size. The math I will leave to the engineers.

Op has not really identified all these parameters to understand his system. Individual 2 volt cells connected in series (voltage) or parallel (AH capacity) or a mixture of 6 or 12 volt batteries connected in series/parallel to produce the output needed. Conversion to AC for standard power backup/supply requires a converter and maybe a transformer to match voltages. A mixture of cells as noted past can provide a false indication of QH available versus that calculated due to uneven charging of a mixture of different manufacturers or cell/battery that I know I would not do what he is doing unless all the parameters described are met. then no brainier.

End of battery 101 minus 90. Keep the series and parallel definitions in mind always when cogitating this conundrum.

Ron

 

[Zerk]

Way back in the dark recesses a red flag went up when I read your post. What I remember goes something like this - if you are charging two batteries of the same rating at the same time, you will be OK. If the two batteries have different amp hour ratings - its best to charge them separately. If the batteries are hooked together the charger will see the "larger" of the two and charge until the larger is finished. Thereby possibly overcharging the smaller battery.

Don't hold me to this - but its what I seem to remember. Perhaps, as an example - I use both AAA & AA LI rechargeable batteries. My charger very specifically states to charge one size only at a time.

Now there are LI rechargers that allow recharge of two sizes at the same time. However, if you look closely at the way the batteries fit in the charger - you will see that each size is on a seperate charging circuit.

I don't have a ton if experience in this area, but I think you are right. Your batteries should be same size.

I THINK that's if wired in series, but if wired in parallel it sees it as one big battery. Wired in parallel the stronger battery will charge the weaker battery anyway. I don't know much about all this multiple battery stuff though. I use a charger that has three different charging circuits to charge the three batteries in my boat to make things simpler.

I work with large amount of batteries in series to get up to 125vdc. There are all the same size, and charger does see them as one. I think you are taking chances by putting batteries of different ratings on the same charger, with an automatic cut off. Maybe I am wrong and the bigger battery will take the current until it is charged. I would talk to a battery person, and not guess at this.

Maybe SCR that will stop flow to the small battery when charged, but it would have to be wired seperatly. Which is probably what the charger has built in.

Maybe one does charger the other until both equal out. I would talk to battery supplier.

 

[Zerk]

Like Deerslayer I am reaching into the brain locker for old data that used to be routine stuff. I worked some with backup battery systems called UPS (Uninterruptible Power Supply). First, proper terminology: A battery is a group of individual cells connected in series to meet the output voltage required;
Each cell is rated at 2 volts for calculation of battery output; therefore, a 12 volt battery has 6 cells rated at 12 volts; arrangements for battery banks can use a mixture of series and parallel connections to get required output voltage and AH capacity depending on cell/battery selections. Each cell has rated capacity depending on plate size. The math I will leave to the engineers.

Op has not really identified all these parameters to understand his system. Individual 2 volt cells connected in series (voltage) or parallel (AH capacity) or a mixture of 6 or 12 volt batteries connected in series/parallel to produce the output needed. Conversion to AC for standard power backup/supply requires a converter and maybe a transformer to match voltages. A mixture of cells as noted past can provide a false indication of QH available versus that calculated due to uneven charging of a mixture of different manufacturers or cell/battery that I know I would not do what he is doing unless all the parameters described are met. then no brainier.

End of battery 101 minus 90. Keep the series and parallel definitions in mind always when cogitating this conundrum.

Ron

I suspect all his batteries are the same voltage in parallel. My concern is rating of the battery. Maybe the charger does see it as a whole. But when we add batteries together, to add about 125, they are all the same. But this is simple lead acid batteries, with the same amount of plates and fluid level.


Personally I would be nervous to take a 12 volt atv battery, put in parallel with truck battery, and put it on one charger. I would want to research it in depth.

 

[Zerk]

You could have just googled this yourself and found answer pretty quick. I didn't have to do it. Though if we all did it ourselves, we wouldn't have stuff to talk about.


Moral of the story, don't mix rating on batteries, series or parallel.


Figure 3 shows two 12-volt batteries connected in parallel. The important things to note about a parallel connection are: 1) The battery pack voltage is the same as the voltage of the individual battery. This assumes that the individual battery voltages are the same. In fact, this is an absolute must. Do not mix and match different battery voltages in the same battery pack. In this example the battery pack voltage is 12 volts which is exactly the same as each of the individual 12-volt batteries. 2) The capacity of the battery pack is the sum of the capacities of the individual batteries. Again, make sure that all of the batteries are the same size, that is that they have the same amp-hour capacity.


Most battery chemistries lend themselves to series and parallel connection. It is important to use the same battery type with equal voltage and capacity (Ah) and never to mix different makes and sizes. A weaker cell would cause an imbalance. This is especially critical in a series configuration because a battery is only as strong as the weakest link in the chain

 

[buickanddeere]

I suspect all his batteries are the same voltage in parallel. My concern is rating of the battery. Maybe the charger does see it as a whole. But when we add batteries together, to add about 125, they are all the same. But this is simple lead acid batteries, with the same amount of plates and fluid level.


Personally I would be nervous to take a 12 volt atv battery, put in parallel with truck battery, and put it on one charger. I would want to research it in depth.

Not a problem to do such when charging or while under load. The problem is when the disimilar batteries are connected and on standby. There will be a slightly different voltage on each battery and they will self discharge faster vs if they where isolated from each other .