Monday, June 15, 2009

A little quiz for you all-

In keeping with my revolting machinery- I've got a problem with my greenhouse battery bank.

The greenhouse is powered entirely by solar panels (with diesel backup we rarely use); and of course when off grid, that means a big battery bank. In our case, it's 16 golf cart batteries, hooked up to give nominal 24VDC .

So; here's the problem. We've got chicks in a brooder again, which means a load for a heat lamp all night long. Stressful on the batteries, but well within normal specs.

But- right now, on a sunny day, the voltage on the electric system computer reads 25.6 V - when the sun is shining on the panels. 25-26 volts while charging is good. Actual "full battery" voltage under charge is going to be over 28V. But; if a cloud passes over, and the panels are receiving only partial input- the system voltage (with loads running) drops quickly to: 22.3 V; a very bad number.

Now, I know exactly what that means, and am going to be working on fixing it next time it rains.

But- do YOU know what it means? I think it would be good for you to know. Someday; you may need this information. Allowing the battery bank to continue in this state for very long can drastically harm all the batteries, and cut their capacity and life very seriously.

So. What is the problem? I think I'm going to let answers accumulate for a day before putting them up- so none of your comments will be public until tomorrow. So you can't peek!


historicstitcher said...

Are the panels dirty? No...they wouldn't be charging so well that way. But since they aren't ever "full" right now, I'll bet the batteries don't have enough liquid in them, and need to be topped off with water.

Shelley said...

Since that last number is negative...your diode is shorted out and the batteries are trying to charge the solar panels?

feonixrift said...

I am rotten with circuitry, but that screams wiring fault to me. Something not entirely getting to, or from, the batteries right, or even worse going across them just a smidge. Rusts, shorts, ... I can see reasons why you'd say "next time it rains" there.

Greenpa said...

hm; sorry; that DID look like a negative 22V; but it wasn't. It was just a dash, which I tend to overuse. So, it's not a negative voltage.

Adam said...

Are one or more of your batteries bad/defective? That's the only way I can figure on a voltage drop like that.


knutty knitter said...

I'm no good at that - possibly need a clean? We have solar hot water but not electric.

It was snow here today - I think we need a mite more insulation. You could see your breath in the kitchen and hall where there isn't any heating. I made the equivalent of London fog cooking pasta for dinner:)

viv in nz

Eric the Red said...

Between your rain comment and the fact that all electrical circuits require a ground, my guess is that you don't have a solid ground - which means that you would have to reposition the ground when the soil is wet.


Eric the Red said...

My initial guess is that you don't have a solid ground connection and that you need a wet soil to reset the grounding cable.