Solar panel output

Do you have a dog that barks all night, maybe? Left a battery hatch unlocked? I've heard of people changing polarity but not electronics unless they had help.

It is possible to reverse the battery itself by going to total discharge and then some so it recharges with pos and neg now reversed.

No idea how you could have done that, but that would explain the readings where it is not the meter wires reversed.

A Forum member was playing with that as a way to desulfate his batteries, with some success, although it was a complicated procedure and didn't work on every one of his sulfated batts, but did on some of them.

OK, a faulty dvm was my first thought, I checked it 3 times, pulled the battery and returned to vendor and he checked it, it was charged at -9V, he couldn't believe it either. I have been away for a week and will get back to checking the solar panel this week. I will keep it posted here.

BFL13 wrote:
I was ignoring the OP's minus voltages. I assume he just got his meter's wires backwards so it showed minus. (I usually don't fuss which wire is which with mine unless it is a test where it matters) I have no clue what the OP's actual situation is from the description given, but the open FET seemed like a possible. Who knows?

I too would be puzzled by -19 volts from a controller, or a 12V battery reading -9.5V. I agree that the digital meters probes were backwards and the battery is dead.

I was ignoring the OP's minus voltages. I assume he just got his meter's wires backwards so it showed minus. (I usually don't fuss which wire is which with mine unless it is a test where it matters) I have no clue what the OP's actual situation is from the description given, but the open FET seemed like a possible. Who knows?

Almot wrote:
"do not connect the array to the battery when the array is connected to the controller at the same time"

BFL, why would anybody connect the array to the battery? I thought this is what controller is for :)

That's for when ya want to stir up the electrolyte a little. :)

I did that once, battery was stinkin and smoking before I knew it.

"do not connect the array to the battery when the array is connected to the controller at the same time"

BFL, why would anybody connect the array to the battery? I thought this is what controller is for :)

high voltage i understand

he said 19 negative, reverse polarity charging
and battery at -9.5v

The chassis battery voltage was reversed and read -9.5 volts, not a good thing, it was ruined! I was into finding out how this happened after disconnecting lots of stuff and finding a couple of blown fuses, I found that out of my solar panel controller it was putting out -19 volts,

he didn't mention controller mfg & model, or amount of solar

i don't know if an mppt controller could fail and produce reverse voltage, but i don't believe a PWM CC could do so

Not clear what the OP's situation was that might be similar, but last year I accidentally fried my solar controller, where it stayed on line ok, but just did not control the voltage anymore.

So here is a WAG on what might have happened to the OP.

It turned out that mine must have had an "open FET (power transistor)"
where if the FET is shorted, the controller will not charge a battery at all, but one with an open FET will overcharge a battery.

Just how I fried it is unclear :( ,but I think I managed to break one of the rules which was "do not connect the array to the battery when the array is connected to the controller at the same time. This will damage the controller when the battery voltage reaches the Charge Termination set- point."

(I sometimes go battery- direct from array to do an overcharge on purpose. I spotted the trouble soon when the Trimetric showed things were not behaving right, so no damage done to the batteries etc.)

OK, so the OP has some fuses gone and whatever, so perhaps in the middle of all that, he fried the controller with an "open FET" situation, allowing the voltage to reach 19v, and that fried the batteries.

MrWizard wrote:
how long have you had the solar panel and controller when was the last time any wiring was 'disturbed'

panels or controllers don't suddenly reverse polarity
wiring has been changed somewhere

batteries hooked up backwards?

x2. Are you sure you are measuring the voltage correctly?

If you just parked it a month ago and didn't do anything to it it's not likely the battery wiring was changed. Also I can't image a normal solar panel system (several hundred watts) being able to reverse and partially recharge a battery in that direction, simply not enough power there. I know somebody that tried that on a dead battery for fun, took weeks with a standard battery charger to get any reverse measureable charge.