Battery bank problems?

[Gundog]

I am new here I registered to try and find some answers for my father he does not own a computer and lives off the grid in rural Idaho. A little about myself and why my dad looks to me for answers, I have worked in the electric utility industry for 30 years as a lineman and now as a system operator, operating a portion of the electric grid. My father is in his late 70's and has a very small fixed income which is the bigest problem for an easy solution.

He has an older diesel military generator made by Onan I believe it is a 10 KW 3Ø unit. He has some solar panels I can find out how many and how big. His battery bank is made up of 6 volt golf cart type batteries purchased from Costco. He has an inverter system I can find out the make and model. His problem is his battery bank made up of 16 batteries is not holding a charge and he must run his generator every 12 hours. He wants to add some more batteries and I explained to him that adding new batteries to the old ones will equalize the whole system and probably not improve his situation. At one point these batteries lasted him a couple days between rechargeing.

I am wondering if he could add a battery isolator to this system or a couple of them to stop the discharge of a new bank by the old banks?

I know this is backwards of how a system would be designed or fixed if he had a budget to do so but I am trying to help him to get something figured out. This is out of my area of expertise but I am wondering why a battery isolator would not work well and to split up his 16 batteries into 4 banks with an isolator so his batteries don't get drained down by the weak batteries. It would also allow him to just replace one of those banks once split into 4 with a newer bank.

Thanks for any help you can give and if you need to know any more particular info just ask I will have him provide me with that info. My father lives 7 hours away from me so I am not there but he is pretty sharp if I tell him what to check or look for.

Thanks Mike

[inetdog]

I am new here I registered to try and find some answers for my father he does not own a computer and lives off the grid in rural Idaho. A little about myself and why my dad looks to me for answers, I have worked in the electric utility industry for 30 years as a lineman and now as a system operator, operating a portion of the electric grid. My father is in his late 70's and has a very small fixed income which is the bigest problem for an easy solution.

He has an older diesel military generator made by Onan I believe it is a 10 KW 3Ø unit. He has some solar panels I can find out how many and how big. His battery bank is made up of 6 volt golf cart type batteries purchased from Costco. He has an inverter system I can find out the make and model. His problem is his battery bank made up of 16 batteries is not holding a charge and he must run his generator every 12 hours. He wants to add some more batteries and I explained to him that adding new batteries to the old ones will equalize the whole system and probably not improve his situation. At one point these batteries lasted him a couple days between rechargeing.

I am wondering if he could add a battery isolator to this system or a couple of them to stop the discharge of a new bank by the old banks?

I know this is backwards of how a system would be designed or fixed if he had a budget to do so but I am trying to help him to get something figured out. This is out of my area of expertise but I am wondering why a battery isolator would not work well and to split up his 16 batteries into 4 banks with an isolator so his batteries don't get drained down by the weak batteries. It would also allow him to just replace one of those banks once split into 4 with a newer bank.

Thanks for any help you can give and if you need to know any more particular info just ask I will have him provide me with that info. My father lives 7 hours away from me so I am not there but he is pretty sharp if I tell him what to check or look for.

Thanks Mike

A few very quick comments to start:

1. Waiting a couple of days before running the generator to recharge the batteries can be costing him battery life.
2. Doing the finishing charging using a large generator will be very wasteful. Adding solar can help a lot in this respect. A 10kW diesel will not be working economically or getting its best service life when actually producing less than 5kW. A second smaller (1-2kW) generator for battery charging is another alternative.)
3. Depending on what cutoff voltage he is using, he may be discharging the batteries too deeply for best life, especially with the delayed recharging.

Using battery isolators will not do much to improve the situation over just using the bank of new batteries alone and selling off the old ones for their scrap value.
But the first thing you need to have him do is get a temperature compensated hydrometer and measure the specific gravity (SG) of every cell of every battery to see just what he is dealing with. It is possible that his biggest problem can be isolated to 1 or 2 batteries, and proper equalization may help there too. If some of the batteries are better than others, putting together the best set of 8 or 12 may be the best thing in the short run.
What exact brand and model battery charger is he using with the generator?
What is the total voltage of the system and inverter? 12V, 24V or 48V? I am guessing 24, since you mention 4 banks of 4 batteries each.
For off-grid 48V is almost always the best choice. Having 16 six-volt batteries tells me that he is losing performance and life by putting battery strings in parallel. Two strings are workable, four strings is too much.

[Gundog]

Thanks I will find out some more info but yes I forgot to mention he is on 24 volts.

[Naptown]

How old are the batteries?

[Gundog]

The batteries are 2 mos to 3 years old. He has 4 solar panels 175 watt each these he got from a solar place and were fairly expensive. His cutout voltage is 23.5 volts. He was not sure what brand inverter he has he is going to check.

He wants to know if he can replace some of the 6 volt banks with 12 volt banks maintaining the 24 volts of course? I know he can't afford to change all the batteries at once which I think he should do.

Thanks Mike

[inetdog]

The batteries are 2 mos to 3 years old. He has 4 solar panels 175 watt each these he got from a solar place and were fairly expensive. His cutout voltage is 23.5 volts. He was not sure what brand inverter he has he is going to check.

He wants to know if he can replace some of the 6 volt banks with 12 volt banks maintaining the 24 volts of course? I know he can't afford to change all the batteries at once which I think he should do.

Thanks Mike

If he has gone from running the generator every couple of days to running it every 12 hours, he could get that level of performance from a small number of new batteries without using the old ones at all, or just choosing the best from among them. The problem with mixing batteries is that the 3 year old ones will be dragging down the performance of the 2 month old ones to the point of ruining them. Isolators will not help with that, since they are not designed to let the different battery banks share the load. Using a manual switch from one battery bank to the next might be worth trying, but no automatic process will be workable.
To charge the batteries through the isolators is likely to require changing the voltage settings on the charger.

Measure Specific Gravity of each cell (when fully charged if possible) and measure the voltage of each battery when fully charged and when the bank reaches the cutoff voltage. We can give more specific advice from there.

(Can I assume that he has kept the water level in the batteries up by adding distilled water as needed?)

[Naptown]

The three year old batteries are killing the new ones. Probably due to chronic undercharge or over discharge of the old batteries.
I hate to tell you this but he has probably ruined all the batteries.
Check SG as inetdog has said and tell us what you find.

[Gundog]

Thanks I have talked him into buying a good hydrometer he only has a cheap one and I don't think it is accurate. I will see what he comes up with. I have been reading your responces to him. A lot of the info you provided I have told him but I think the echo is sinking in.

Thanks Mike

[inetdog]

Thanks I have talked him into buying a good hydrometer he only has a cheap one and I don't think it is accurate. I will see what he comes up with. I have been reading your responces to him. A lot of the info you provided I have told him but I think the echo is sinking in.

Thanks Mike

Even a cheap one, carefully used, can show up differences between cells and trends over time even it it is not particularly accurate. It does have to be read precisely (ball type is useless) and then temperature correction applied if the batteries are hot from use/charging or are outside at varying temperatures.