Solar Multimeter Testing

[travellerw]

Originally Posted by Canibul

So, if that's the case, whenever I touch my two probes to live wires I should get sparks at the meter probes as I just shorted the circuit?

No the reason it works if its just the meter and the panel, is the meter then becomes the entire circuit.

If there was a battery involved, then the meter would be parallel and the current would flow "around" the meter. Unless you put the meter in series with the battery.

Ahhh clear as mud!

[RolfP]

Wow great discussion, thanks everyone. I'm now wondering if it isn't the meter. Here is a clarification of what I did:

I disconnected the panel and took it off the boat and put it on the dock and pointed it at the sun. Connected the red to positive, the black to negative, and got the about-20 volt reading. Disconnected the meter, switched the red wire to the other pole on the meter (see pictures), plugged the black lead to negative and red to positive and set the meter at 10 Amps. (see pictures). Nothing. tried 500mAmpj, then 50, then 5, no movement of the meter.

So now I am worried that just because I replaced the fuse. I know I blew a fuse because I can test the meter using the "beep" function that is part of the battery testing portion of the meter. However, could it still could be a bad meter, no longer able to test amps, but rather just volts, as someone said earlier? It will NOT beep if the fuse is blown, and WILL when I replace it.

I also wondered if it was the panel so I tried the whole thing on another panel, completely disconnecting, etc.... Same results.

I took the back off the meter. Set the meter to "buzz" if there is a "circuit". Touched the red to the fuse on one end, then the other end, both ends got a buzz. hmmm, still wondering though. switched in a new fuse, touched both ends of the old fuse, got the buzz.

Is there something I can do to test the meter for its ability to read amps? Some other common connection on a boat - hmmm, a light!! So the pic below is the test I did of a light, trying to complete a circuit. No reading on the meter, does that mean my meter is blown? I took out the "bulb" and replaced it with the meter connectors, no reading, but the light goes on. I switched polarity, on the meter connectors, still nothing. Checked smaller amp values as well, both polarities.

I am very grateful for the help, BTW, I am so definitely "challenged" by electricity - I told my neighbor here that my goal is still to "learn electricity", but I failed all but the first three tests in Charlie Wing's book. Got lost on the parallel/series questions, but I still have to figure things out on my boat.






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[RolfP]

Oh, and there is no more sun here, just raihn and clouds, so I'll have to wait until tomorrow to test a light bulb.


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[jeepbluetj]

On many meters the fuse is only in the amperage circuit. Therefore voltage and continuity (the beep) would work while amps would not.

If the panel is putting out voltage, shy of a horrible high resistance connection somewhere, it'll be able to put out current. If the panel has a Isc higher than 10A, it'll pop the fuse every time you try to measure it.

OTOH, you don't need to. Hook up the panel to your controller and see what your controller does.

[travellerw]

Originally Posted by RolfP

Oh, and there is no more sun here, just raihn and clouds, so I'll have to wait until tomorrow to test a light bulb.


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Since a light bulb is a load, you will need to put the meter in series with it. Here is a graphic of how to hook it up. Pay attention to where the leads are plugged in as well.

[Paul Elliott]

Originally Posted by Canibul

So, if that's the case, whenever I touch my two probes to live wires I should get sparks at the meter probes as I just shorted the circuit?

If your meter is operating as an AMMETER, then yes, you will get sparks if you put the probes across a battery or solar panel. With a battery, there will be a big spark, or perhaps no visible spark at all if the fuse blows fast enough. In that case the spark will be inside the fuse! As has been mentioned, make sure your meter can handle the shirt-circuit current of the panel before you try to measure it this way. An Ammeter looks like a dead short to the circuit under test.

If your meter is operating as a VOLTMETER, then there should be no sparks. A modern DVM (Digital Volt Meter) looks like an extremely big resistor (11 Meg Ohms is common), and so there will be virtually no current flowing when you probe your battery terminals. The analog meter that Rolf is using probably looks like 200,000 Ohms to the circuit when it is in Voltmeter mode. This is still large enough to not cause any sparks.

[RolfP]

okay, so I also tried putting the "bulb" (led) in the circuit with the multimeter set up just as it is in the picture. The "bulb" did not light when connected to the MM in either direction (red/black on either side). I'lll have to get my neighbor over with his multi meter, or go to ACE when it stops raining and buy one of those clamp meters, as travellerw said, I will thank myself later. The pliers did make the bulb light, so there just IS NO CIRCUIT through the MM, right?

It sounds like the meter could be bad - even with the the beep and fuse still good - thanks jeepbluetj.

Can someone confirm that my test of the meter above is showing that I have a bad meter, or what/how else can i test the meter, without another meter (see these are the puzzles I LIKE hahahaha)




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[Paul Elliott]

Rolf, there are usually two fuses in a multimeter: a small one for the low-current ranges, and a bigger one for the high-current range. Make sure the big one is OK. That's my best guess at the moment.

By the way, make sure you get a clamp meter for DC (it will do AC too). Most inexpensive ones are for AC only, and will not work for measuring DC current. I've got an expensive DC clampmeter from Fluke, and a relatively inexpensive one from Sears.

[NahanniV]

Originally Posted by RolfP

... I took out the "bulb" and replaced it with the meter connectors, no reading, but the light goes on. I switched polarity, on the meter connectors, still nothing. Checked smaller amp values as well, both polarities....

Attachment 115035

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That would probably have blown the fuse if it was not already bad.

Blown fuses in multimeters happen frequently.

To test the fuse, you must remove it from the meter, then set the meter to Ohms (1K) with the lead in the Volt ohm Miliamp socket.
Test the meter first: Touch the probes together and the meter should read close to zero ohms.
Then test the fuse: hold the probes on both ends of the fuse, if it is good it should read close to zero ohms as well.

Cheers,
JM.

[Stu Jackson]

One thing not so clearly mentioned: that is an inexpensive meter. Most of them have very low current capacity for amp measurement. If it is put in series with a connected panel, as mentioned it will blow the fuse, which makes using this meter for measuring amps in a the panel serving the system useless. Rolf, that is why folks are saying either get a shunt (which is put in series with the circuit) or get a clamp on ammeter, which goes around the wire and measures the current. You simply have the wrong meter to measure system flow because the system exceeds the rating of the meter for that measurement.

Ammeters & Shunts 101 Ammeters & Shunts 101

Good luck.

[Captain Bill]

I am going to assume you were testing the panel because you have a problem with your solar and not just for fun. A couple of years ago I was helping a friend trouble shoot his system and got 20+volts when testing using a multimeter, but zero amps when doing the amp test. The panel was bad. It had a high resistance break in the internal wiring. With the high resistance of the voltmeter it could hold up the voltage, but as soon as it tried to carry any amps, we got nada. High resistance breaks in the wiring are a fairly common failure mode in solar panels. Your meter might be working just fine. Put a small light bulb in series with your meter and a battery and see if it measures current. If it does your panel is probably toast.

[RolfP]

Aha, so I took the next layer off the MM and found another fuse - paper covered, with this on the end: F10H 250V. Is this the high load fuse? It appears to be blown - it doesn't beep with the continuity tester (which still work with all these parts all over). I'll go to the store and look for a clamp on meter AND a new F10H 250V. Tomorrow.

Thanks for all the help.


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[Paul Elliott]

That's probably a 10A fuse. Replacing that should do the trick. Make sure you don't overload it though. The specs on the panel you included in the original post showed a Short-Circuit Current (Isc) of 3.5A so that should be safe to measure.

[RolfP]

Thanks Paul, (and traveler) everything takes another day oh well, and now its dark and late and I'm hungry and leaning stupid but I'm optimistic about tomorrow and a DC clamp-on (which I assume won't generally blow a fuse in itself?) and new 10amp fuse.

NaHanniV - thanks for the confirmation - that is what I did to test that fuse - bad.

Stu - thanks, yes and clamp on meter. This meter though, I saw was $50 in the store yesterday, but seems its old school, I've had mine a long long time without knowing how to use it - thanks for the link - good reading for later after FOOD!

Captain Bill, I'm pretty sure its not the panel I tested two both with same result, but you are right, I am not seeing anything on my Link battery monitor from the panels I have working - I have a genesun 10 hooked up to two 50watt panels in parallel and was expecting to see some blinking lights on the controller but only getting a very fast blink indicating a minimal charge. I'm worried that my wire is too long, or I have a bad wire or ??? What I am hoping to do is get my head around how to use the multi-meter for testing the amps I am getting out of my panel all along the way from bimini-top to controller to battery in case the wires is too long. 10AWG - about 18 feet, maybe 20. Even if I'm losing something, shouldn't I be getting more than minimal?

Anyway, back to it tomorrow, and if not tomorrow, then it will have to wait for the holidays....

[Paul Elliott]

#10 wire shouldn't be a problem. If you have two of your 50W panels at the end of a 20-ft pair of wires (40 ft total), the voltage drop will be under 0.3 Volt. That's a little over 2% drop -- could be better, but not too bad. Your controller should work fine.

A lesson in Voltage drop:
V = I * R (Voltage = Current times Resistance) Units are Volts, Amps, Ohms.

#10 wire has a resistance of about 0.001 Ohm per foot (find this on the internet)
20 ft * 2 = 40 ft.
40 ft * 0.001 = 0.04 Ohms

Your solar panel puts out 3.5A maximum, slightly less at optimum load. Assume 3.5A for this analysis. Two panels give you 7A.

7A * 0.04 Ohms = 0.28 Volts. This is the voltage lost in your #10 wires.

I have ignored connector losses, which shouldn't be a big issue if they are done right.

If you have more than 100W of panels I would seriously consider going up to #8 or larger wires. Of course things aren't as bad if the total wire length is less than 20 ft.