Troubleshooting 0A from array

mepv · May 2014

I'm trying to troubleshoot a small PV installation that came with an off-grid house I bought recently. Two panels totaling 150W, connected in parallel to a ProStar-12 controller, connected to a single battery.

I bought the house in December. The system worked fine all winter. But for the past month or so, whenever I hook up the battery, the controller shows zero amps coming from the panels. Possible sources of faults: (1) bad controller, (2) bad wiring or connections between controller and panels, (3) bad panels, (4) bad angle on the panels leading to near-zero insolation as the sun gets higher and further north in the sky. (Anything else?)

I have a little experience doing small wiring repairs in an AC-wired house, using a multimeter to check ground on wall sockets, and the like. And I have done quite a bit of reading as I think about how to upgrade the (now non-working) PV installation. But very little experience working with PV stuff.

I don't have another controller to plug in, which would be the simplest way to check the controller. So other than visual checks, what do I measure to check the performance of the panels/connections/wiring?

Thanks!
mepv

Cariboocoot · May 2014

Re: Troubleshooting 0A from array

Welcome to the forum.

You need a digital multimeter. It is the primary tool for diagnosing problems. With that you can check if there's any Voltage from the panels and more importantly any current.

First thing you do is disconnect the panels from everything. Then check each one for Voltage. If you don't get a Voc (Voltage open circuit) then the panel is dead.

Second thing you do if you have Voltage is put the meter on DC current and check to see if there is any current (same lead connections as for Voltage). In full sun you should get something close to Isc (current short circuit). With 12 Volt panels of 75 Watts the numbers should be Voc around 22 Volts and Isc around 4 Amps.

If you've got that then you can bypass the controller and see if there is any current going to the battery (through the meter). If that works then the controller is bad.

Another possibility is that the battery has failed. If it has really, really failed the controller may not even activate because the Voltage is too low. 150 Watts isn't much for supporting batteries. Do you have specs on how much battery you have? It should have an Amp hour rating as well as Voltage.

mike95490 · May 2014

Re: Troubleshooting 0A from array

power sequence for most controllers requires BATTERY power be applied first, then connect the PV array after the controller boots up (even the small 10a controllers need to boot up before the PV is connected)

Before you connect the PV to the controller, measure the voltage (open circuit) It should be about 18 to 25 Volts DC. If it's good, you can measure the PV amps (still not connected to the controller) from the panels and for your 300W of panels, I'd expect to see at least 10amps in good sun, 15A if everything is working right. Make sure your meter can manage that. (and be sure to reset your meter back to volts when you are done with the amps measurement.)

BB. · May 2014

Re: Troubleshooting 0A from array

And I would suggest you get an inexpensive DC Current Clamp / DMM (digital multi-meter) like this one from Sears.

It makes it real easy to measure current flow in the various wires in your power system.

However, as the guys above have said... You start with needing to measure voltage at various points in your system. On the battery posts, at the charge controller battery connections, at the solar panel connections, etc...

If the battery is dead (less than ~10 volts), the solar charge controller will probably not even turn on.

And if the battery is dead--It will almost certainly need to be replaced before you can make good use of your system again (dead lead acid batteries generally do not come back to life, reliably).

You can charge the old battery and get it to sort of work--And that may be "good enough" to at least debug the rest of the system. If it is difficult to recharge, I would "jump" the battery from the car (if handy) for 10 minutes.

As always, be very careful with batteries, cables, and sparks. Hooking batteries up backwards can destroy equipment and start fires. Sparks from jumper cables can light hydrogen gas in the battery cells and cause explosions, spraying around acid (electrolyte) and parts of batteries.

-Bill

niel · May 2014

Re: Troubleshooting 0A from array

i'll 2nd what mike said adding that when disconnecting you should disconnect the pvs 1st and then the battery. you may not be doing this correctly and blew out the cc. when you determine the cc to be bad and you replace it get a dc rated switch or circuit breaker on the pv input if not already on it and shut down the pvs with it. after that a switch or breaker for the cc can shut down the power to the battery.

summary---
power up is battery on 1st then pvs.
power down is pvs 1st then battery.

mepv · May 2014

Re: Troubleshooting 0A from array

Thank you, all. Very helpful.

Battery is new and should be fine. It does hold a charge, and the CC does power up. However there is no breaker between the panels and the CC (a problem I will be fixing), and the battery has been connected and disconnected many times (by me and presumably the previous owner) without first disconnecting the panels. So a fried CC sounds like a possibility; but, I will begin at the beginning and check everything.

One question about amp rating of multimeters: The digital multimeter I have now is rated, I think, for 10A. I have used it from time to time to check ground on three-prong AC outlets on 15A circuits, without ever noting that its amp rating is less than the circuit is capable of delivering. I've used the same meter to check voltage on lead acid batteries that are again capable of delivering currents much larger than 10A. In both cases, I've had no problems that I know of. But when I started thinking about checking the output of the PV panels, I wondered to myself whether I needed a higher-rated multimeter. This has now been confirmed by mike. The question, then, is why are PV panels different in this respect from batteries or outlets? Or have I just been lucky so far?

Thanks again,
mepv

inetdog · May 2014

Re: Troubleshooting 0A from array

mepv wrote: »

The question, then, is why are PV panels different in this respect from batteries or outlets? Or have I just been lucky so far?

1. Unlike batteries or outlets, a PV panel has a strictly limited current output if you short circuit it through the ammeter. Less likely to blow the fuse or the meter.
2. Most digital meters can tolerate a 50% to 100% overload when on the amps range. It does not matter if you overdrive the input to the digital voltmeter circuit, and a short over current is not going to burn out the shunt inside the meter. A constant overcurrent or a pulse of much higher current could damage the meter. If you short the ammeter across a battery that damage may include you.

mike95490 · May 2014

Re: Troubleshooting 0A from array

mepv wrote: »

.....The question, then, is why are PV panels different in this respect from batteries or outlets? Or have I just been lucky so far?

Go buy that lottery ticket NOW

read back in my post where i said

(and be sure to reset your meter back to volts when you are done with the amps measurement.)

(no bold red in my original)

Measuring VOLTS is a very different measurement than AMPS. I can guarantee you did not measure any battery or household outlets with the meter configured for amps, you learn VERY quickly you made a big mistake. Your meter leads vaporize, along with half of the meter.
if you look at your meter, it likely has a different set of jacks for the leads for AMPS. That's the danger - that jack goes to a 0.01ohm shunt, which does not affect the amps when used properly. But if you forget, and use the shunt to measure voltage, you find yourself holding a flaming ball of plasma.

BB. · May 2014

Re: Troubleshooting 0A from array

Another reason I like AC/DC current clamp DMM (digital multi-meter)--Such as this inexpensive one from Sears.

No issues of connecting meter set to amps to a 120 VAC or XX DC battery bank and ruining your day. Plus the typical clamp meter will read around 40-400 amps full scale.

A 10 amp meter on DC off grid power systems is really limited.

-Bill

mepv · May 2014

Re: Troubleshooting 0A from array

Very interesting, and good to know. Indeed, all of my previous measuring was of voltage. Will indeed go buy something with a higher amp rating. Thanks again, again. mepv

mepv · May 2014

Re: Troubleshooting 0A from array

Okay, I'm getting about 20V from each panel, but zero amps. Rereading the replies, though, I realize that I didn't measure the current correctly: I measured it using the clamp around the positive PV leads to the CC, with everything connected; but that wouldn't discriminate between faulty panels and a faulty CC. Problem is that the meter I got goes up to 400A on the clamp, but only 2000 uA on the leads, so there is no way of lead-testing a 5.8A panel. Is there a way of doing it with the clamp? My every instinct says "do not short the positive and negative studs on the PV panel," but maybe that is the right way of doing it... Any more ideas? Thanks again, mepv

Cariboocoot · May 2014

Re: Troubleshooting 0A from array

Short the positive and negative leads on the panel: it won't hurt it.
Panels are current-based and self-limiting. The "Isc" rating is in fact current at short circuit.

mepv · May 2014

Re: Troubleshooting 0A from array

Re-tested it. The panels are putting out plenty of voltage and current. Haven't tried charging the batteries directly, but I was getting good voltage at the CC end of the cables, so I'm guessing the controller is bad. Will confirm before I buy a new one, but thanks everyone for the help. --mepv

Troubleshooting 0A from array

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