Mis-matched batteries

2 Posts

Feb 5, 2009 08:26 am

Battery Question:

Preliminaries:
1. Location: Eastern VT, Cabin located at 3000' Elevation
2. Consumption: 300W+/Day
3. Question: Best way of connecting unmatched/unequal batteries

I am in the process of helping a friend who has a small weather station on a mountain top in Vermont. Over the years he has acquired varies pieces of solar equipment to run his outpost. The correct answers are known for making a proper system solar system, however our problem lies in the fact that this is strictly a "not for profit" setting and we simple need to use what we have until further improvements can be made accordingly. Thus, we are seeking your input for the next best solution using, "what we have." Again, we know what is correct and understand this, but hope you can give us some good insight on best practices with what we have at this point.

My question deals with mismatched storage batteries: batteries of unequal values. We have one set of 12V Gel Cells and another set of 12V deep cycles. The charging supply is that of solar panels on a single 25A regulator. Presently only one set of batteries (gel cells) are connected and working well. However another set of brand new deep cycles were donated for his project. How would you suggest connecting these two sets of batteries to get the best configuration for charging and power consumption?

Dave

James Cormican

578 Posts

Feb 5, 2009 12:10 pm

Re: Mis-matched batteries

leaving aside the ideal as requested, this is in the direction i might go.

http://store.altenergystore.com/Charge-Controllers/Solar-Charge-Controllers/Pwm-Type-Solar-Charge-Contollers/Morningstar-Charge-Controllers-Pwm/Morningstar-Sunsaver-Duo-Dual-Battery-Charger-25A/p5600/

i would not hook the batteries up together.

depending on inverter size, something like this could work, and again, not ideal.

http://store.altenergystore.com/Enclosures-Electrical-and-Safety/Miscellaneous-Electrical-Parts/Switches/DC-Switches/Blue-Seas-Battery-Switch-Selector/p4750/

although i think blue seas has one without the both selection.

do you mean 300 watt hours per day, or 300w max instantaneous load?

given your parameters, that is just my opinion/ stab at the problem.

james
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Jonathan W

33 Posts

Feb 6, 2009 04:09 pm

Re: Mis-matched batteries

If it runs ok on just the gels I don't see why you can't just add the wet batteries into it and have the charge voltage set at the gel settings. If it works better then it works better. If it doesn't then you can just take them back out.

But if you are only using 300 watts per day then your only drawing about an amp anyway. Most batteries will operate in the 85 percent or better efficiency range at those current draws so you really have something you don't need. You could switch over to the wets and use them for while since the gels will store better but you really have something you don't need.

Thomas Allen Schmidt

679 Posts

Feb 6, 2009 07:16 pm

Re: Mis-matched batteries

There is no "best way" based on what you have unless the older gel cells are in the "final stretch" of their lively hood anyway. If you don't need the additional amphours that the gel cells can provide try selling them. Unless of course they are, on their "last leg."
I suppose if you have a way to spare maybe one PV module every now and then to maintain the new "deep cycle" (I assume that those are flood cell lead acid deep cycle) batteries in "storage" until such time as the gel cells are useless.
A lot depends on the age of the gel cells.
Surely there is something that can be done with them, somewhere by somebody. Are there any high schools nearby that have a need for them? How doe's that saying go? Oh yeah, pay it forward.
Best of luck to you.

Thomas Allen Schmidt

679 Posts

Feb 10, 2009 06:32 am

Re: Mis-matched batteries

"The correct answers are known for making a proper system solar system, however our problem lies in the fact that this is strictly a "not for profit" setting and we simple need to use what we have until further improvements can be made accordingly."

Sacrifices are to be made. In an earlier time this was done quite literally. From the choice of livestock to virgin brides. There was at least, the hope of getting something in return. In a more modern time, automation is what we are paying for. As time goes by we (the human race) rely more and more on machines to carry out life's mundane tasks for us and whats more is we want these machines to be as automated as possible, freeing us to indulge in life's pleasures. Do we know what it is we are sacrificing for this?
http://www.cdc.gov/Features/dsObesity/

Mr. Comeau
While searching the internet for the lowest prices on PV and related electrical, as I often do, I came across the article below and was reminded of your questions. Of course it involves adding equipment, something I think you expressed a concern about, but what you suggested has been done by somebody. Recharging two dissimilar battery types (sealed gel and flooded lead acid) from one (PV) source.
The description starts after the second photograph.
http://www.solarseller.com/photovoltaic_systems_at_our_location_.htm

I am sure if you think about it you will come up with a solution to this. But you may not like the sacrifice to be made. I just don't know.

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Mis-matched batteries

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