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Old 05-07-2012, 04:27   #1
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Do fast Discharges Damage Wet Cell Batteries?

Hi
Just curious if fast discharges can cause damage to flooded cell batteries?
I have a 5 x 140Ah house bank (700Ah). They are charged via wind and 540w solar panels.
I would like to use my inverter sometimes to heat the Hot Water Service.
Its a 1200w 220v element, and draws 130amps for about 30 minutes while it heats.
Im not concerned about losing the 75Ah from the bank as I will just run it when I have 90-100% charge state, but I was wondering if drawing high loads over that period of time will shorten my battery life/damage my batteries? Effectively Im effectively draining 10% of the total charge (25% of usable charge) in 30 mins.
Thanks for ideas.
PS, my other option is to put a smaller wattage element or 12V in the HWS to slow the discharge rate if this is a healthier lifestyle for my batteries
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Old 05-07-2012, 04:42   #2
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Re: Do fast Discharges Damage Wet Cell Batteries?

What you describe won't hurt the batteries, but it will consume more than 75Ah. The faster you draw power out of a battery, the more you drain it beyond the useful power you pulled out. In other words, pulling 75Ah out quickly like that will effectively drain 90Ah or so, maybe more. I'm just making up the number, but it's predicted by a guy with the unfortunate name of Peukert who came up with the Peukert Equation.

For large heating loads like that, a better approach may be to run your engine or generator for 30-60 minutes to heat the water and charge your batteries at the same time.
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Old 05-07-2012, 04:48   #3
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Re: Do fast Discharges Damage Wet Cell Batteries?

thanks tt
the HWS is also heated by the engine so if I run the engine for 30 mins it will heat via the engine cooling system. But I dont want to run the engine...ever.
I did read about Peukerts Equasion as well and I don't like his name either..
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Old 05-07-2012, 10:01   #4
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Re: Do fast Discharges Damage Wet Cell Batteries?

You should factor in the efficiency of the inverter which will also increase total consumption. The application inself is not destructive however it does count as a cycle in the limited life of the batteries.

I don't have direct experience but I belive you can get 12 volt heaters for water. I think some solar/wind systems use it to dump excess capacity. Something like that would be nearly 100% efficient and not use up battery life or charging capacity. I'm not sure how you would do it but it seems like the perfect solution, even if you need a small 12 volt pump to circulate the water through an external heater element.
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Old 05-07-2012, 16:03   #5
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Re: Do fast Discharges Damage Wet Cell Batteries?

There are 12/120 volt hot water heaters available as replacement units.
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Old 06-07-2012, 03:11   #6
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Re: Do fast Discharges Damage Wet Cell Batteries?

Yes thanks
Im looking into the 12V elements as well as setting up dump load from the solar, but just wanted to make sure till I have that organised using the inverter with the existing 220V element wont harm the batteries
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Old 07-07-2012, 23:29   #7
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Re: Do fast Discharges Damage Wet Cell Batteries?

A fast discharge does about the same damage as a fast overcharge. High current moving in discharge or charge for long periods causes the same problem....warping of the plates caused by excessive heating.

Lloyd



Quote:
Originally Posted by monte View Post
Yes thanks
Im looking into the 12V elements as well as setting up dump load from the solar, but just wanted to make sure till I have that organised using the inverter with the existing 220V element wont harm the batteries
Monte
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