Off Grid battery backup system charging question.

[ForestGrump]

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

Ok I'm confused. I used to have 3 J185H's so I am familiar with your situation. Your use of the word servicing I don't understand and you never state what type or size of charger you use.

Soooo, each battery bank should be made up with the same battery, same age, type, size etc. Service is usually used in the sense of the battery being in use.

Batteries when hooked in parallel have the same voltage but their amperage are additive. In series the voltages are additive and the amperage is the same, therefore the need for the same battery. Two 6v 360 Ah in series are 12v at 360Ah. Hooked in parallel they are 6v at 720Ah - good enough to start my old VW bug.

The J185's are big batteries - Ah and the charger must also be of sufficient amperage to do the job in a reasonable amount of time.

You now have 3 banks - close to 1000Ah. Charging in parallel is 12v at 1000Ah. Charging in series is 36v at the greatest amperage which is a mess.

A discharged battery on a modern smart charger will try to give as many amps as possible at a specific voltage till the 90 to 95% recharge is reached. Then it will go into the second cycle where a preprogrammed voltage is forced into the battery - for most Trojans this would be 14.8 volts till close to 100% is reached then to float. Too many amps and too many volts you go boom. Solar charge controllers will have a temperature sensor to keep the boom factor and battery temperature to a minimum.

A 150A charger on an 18Ah battery - boom.

A 10A charger on a 500Ah battery bank, go fishing. Speaking of which go to Bass Pro's website and look at their battery chargers. You will see single, double and triple bank chargers at different amperages. Bass fishermen like batteries and battery banks and they want them ready for the next day.

To insure longevity do not mix batteries in a bank. Charge each bank separately. Each battery has a mind of its own and it wants to retire to battery heaven. Keep the batteries desulfonated.

 

[Zerk]

Soooo, each battery bank should be made up with the same battery, same age, type, size etc. Service is usually used in the sense of the battery being in use.
.

You serviced something you did maintenance. In service in use, is the way I use the words.

 

[Zerk]

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 .

I am going to disagree.

One of the problem lies with the chargers auto shut off. If you just turned the charger off, maybe not a problem. But even then you would have to know when to shut it off.

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

 

[ForestGrump]

You serviced something you did maintenance. In service in use, is the way I use the words.

Serviced does not equal service. A service can also be a ceremony. A serviced is not an old ceremony!

 

[Zerk]

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 .

Serviced does not equal service. A service can also be a ceremony. A serviced is not an old ceremony!

A ceremony was a service, just as changing oil is a service.

 

[ForestGrump]

A ceremony was a service, just as changing oil is a service.

But changing oil for me is not a ceremony and a ceremony does not mean past tense - was vs. is and ceremonies are not always a service either. So there....

 

[dmccarty]

ForestGump covered charging but it is important to drive this home.

If you overcharge a battery it can go boom. Even sealed batteries.

I know of one boat where the battery bank exploded. We won't ever know WHY the batteries exploded but it was either a bad battery or more likely, the charging system was not configured correctly and too much current was put into the battery causing them to overheat, produce H gas, which then found a spark and the H went boom. Thankfully, nobody was seriously injured by the explosion, though if the boom had happened a bit earlier, a person would have been seriously injured or killed. As it was, the boat, a brand new 50 foot trawler, started to flood after the explosion, the source of the leak(s) could not be found, and the boat sank on its maiden voyage. The crew was safely rescued.

An advantage of AGM batteries is that they can take a higher charge rate the flooded lead acid batteries. Depending on the manufacturer, the ATMs can take about twice as much energy than flooded lead acids. If a charger was pushing power at an AGM rate to flooded lead acid batteries, I don't think it is going to end well.

Mixing battery types and sizes in a configuration is not a good idea.

Later,
Dan

 

[Zerk]

But changing oil for me is not a ceremony and a ceremony does not mean past tense - was vs. is and ceremonies are not always a service either. So there....

I am not taking advice from Forest Gump. Were you given that nick name?

 

[Zerk]

ForestGump covered charging but it is important to drive this home.

If you overcharge a battery it can go boom. Even sealed batteries.

I know of one boat where the battery bank exploded. We won't ever know WHY the batteries exploded but it was either a bad battery or more likely, the charging system was not configured correctly and too much current was put into the battery causing them to overheat, produce H gas, which then found a spark and the H went boom. Thankfully, nobody was seriously injured by the explosion, though if the boom had happened a bit earlier, a person would have been seriously injured or killed. As it was, the boat, a brand new 50 foot trawler, started to flood after the explosion, the source of the leak(s) could not be found, and the boat sank on its maiden voyage. The crew was safely rescued.

An advantage of AGM batteries is that they can take a higher charge rate the flooded lead acid batteries. Depending on the manufacturer, the ATMs can take about twice as much energy than flooded lead acids. If a charger was pushing power at an AGM rate to flooded lead acid batteries, I don't think it is going to end well.

Mixing battery types and sizes in a configuration is not a good idea.

Later,
Dan

We have exhaust fans that come on when batteries are charging.

 

[ForestGrump]

I am not taking advice from Forest Gump. Were you given that nick name?

Used to volunteer for the OHV program, grumpy old man became Forest Grump.