Batteries percolating..

hillside

I have a simple backup water system powered by two 60W panels (24volts) powering 2 large 4D batteries (not deep cycle-- left over from a previous set-up). They are in new condition and I know they're not ideal for this situation, but they were here and not doing anything useful.
Pump is a 24v Dankoff.
Charge controller is a cheap PWM 30 Amp 12-24V.
We don't use the water system full time, and even when we do, the batteries are percolating, obviously overcharging, and the electrolyte level is already low after barely a month of use.
I can put a small 24v fan on the batteries to soak up the extra charge but that takes constant monitoring.
Do I need a better charge controller? Would that stop the overcharging or are the batteries totally wrong for this app.?
I've searched for a DC timer that could run the fan at peak periods but no luck.
(located in the Caribbean so sunlight is plentiful)

Cariboocoot

Re: Batteries percolating..

Welcome to the forum.

For one thing it is normal for batteries to percolate and use water when being charge. It's more a matter of degree as to how much.

Degree. In this case that is a telling word as your Caribbean location means your equipment is warm if not hot. Normally charge Voltage would be reduce as temperature goes up, which means using a remote temperature sensor on the charge controller. Chances are your cheap PWM controller has no temp compensation whatsoever and the batteries are seeing too much Voltage and/or too much time (non deep cycles would not have the same charging profile the controller is meant for). That would explain any excessive percolating and water loss.

So the question is: can you take a reading of exactly what Voltage the batteries are being charged at and how long it is lasting at that level? Then the question is: can you manually adjust the charge controller for lower Absorb Voltage/time?

hillside

Re: Batteries percolating..

Thanks for the welcome.
I just took a voltage meter reading from the panels at the charge controller and it shows 30.7 volts. Not sure how to measure how long it's lasting at that level, as you wrote. But on cloudless days we get at least 5-6 hours of blasting sunlight on the panels.
I've had a tarp over the panels all day, and just took it off, and the batteries show 32.4 volts.
Not seeing anything in the instructions about manually adjusting the charge controller.

Cariboocoot

Re: Batteries percolating..

On a 24 Volt system 30 to 32 Volts at the battery would be an Equalization level, definitely higher than normal Absorb which should be down around 28 Volts. That difference would certainly add to the percolation and water loss, and is not good for the batteries.

Note that the Voltage measurement should be on the output of the controller, as the input side will read panel Voltage varied by loading as the PWM cycles on/off (normal panel Vmp on a 24 Volt system is around 35).

hillside

Re: Batteries percolating..

30.5V at the controller output with some cloud cover at present. (now it's starting to rain ..
These batteries are new enough to try to get the most out of them even though they're not deep cycle..what's the best solution for the time being, an adjustable charge controller?
Thanks

Cariboocoot

Re: Batteries percolating..

Definitely change the charge controller if that one is trying to raise the batteries to 30 Volts.

120 Watts of PV won't put out much current on a 24 Volt system. If it's all you need, consider a small 10 Amp PWM unit like a Morningstar SunSaver 10 http://www.solar-electric.com/inverters-controllers-accessories/chco/mochco/stpwmchco/ss-10l.html

BB.

Re: Batteries percolating..

Welcome to off grid solar and the "free energy" you are now getting.

There are quite a few controller options... If you have a local supplier, you can contact them and see what they sell (always nice to support a local/knoledgable dealer).

Otherwise, which country/internet site would be a possible option (some countries have very difficult customs people, and it is an option to take a flight to the mainland and put the hardware in your luggage).

http://www.solar-electric.com/inverters-controllers-accessories/chco.html (for many listed below--Our host, you are welcome to buy elsewhere too):
http://www.roguepowertech.com/products/chargecontrollers/mppt/mpt3048.htm

Midnite Solar (MPPT)
Outback (MPPT)
Rogue (MPPT)
Morning Star (MPPT+PWM)

Are all good options. There are others too. Make sure you include all costs (remote battery temperature sensor--recommended; LCD display/computer interfaces; shipping+handling+customs+etc.) to your front door.

If you have the "right panels" and a short run from the array to the battery bank+charge controller, you can get away with a less expensive PWM charge controller.

Otherwise, you may have to look at a good MPPT type charge controller (~2-5x more expensive).

Also, if flooded cell batteries, get a good glass hydrometer to measure specific gravity. And an inexpensive panel voltage meter (accurate to 32.x volts minimum) will get you started.

An inexpensive DC Current Clamp meter (like this $60 one from Sears) is also a good diagnostic tool.

But don't buy any new hardware until you do the research--It is easy to end up with a mish-mash of equipment that is difficult to connect together in a system.

-Bill

westbranch

Re: Batteries percolating..

A cautionary note: Solar Power is ADDICTIVE, once you have some you want more!So, please think down the line and consider if you will be adding to this system sometime in the future. If so, you will want to estimate those loads, by how much, and design appropriately...

hth

hillside

Re: Batteries percolating..

Thanks for the replies. It's good to have expert opinions!
I'm in Puerto Rico so no customs or overseas shipping charges.
This is not my only setup. I've had a small 3000 watt backup power system for a few years now with no problems (since the Aims inverter failed-actually got 3 years out of it).
I won't go off grid completely as there are too many unknowns with the tropics. We get tremendous lightning storms in the summer and I don't know how much wind speed my panels could take before they end up in Brazil. It's just that after the last major hurricane there was no power and no water for 3 months. So with my small solar and honda eu3000, we're covered. That way I stay married.
Will look at a new charge controller, but the one I have now states it is MPPT...supposed to prevent overcharging..

westbranch

Re: Batteries percolating..

From the sound of it you really need a true MPPT CC that is temp compensated. If you went for a ~30Amp model you would have a backup for your larger system if it failed or got struck...

mike95490

Re: Batteries percolating..

@ Westbranch -

New House system: coming - 2 arrays @ 2240W

So I see you have a new avatar, could you start a thread and tell us about it? (sorry about being off topic)