Multimeter + Charge PV Terminals = POP!?

[Alex9]

I have 4x 145w panels in series @ about 8amps and 75 volts going into a 60amp mppt outback charge controller. So it's Floating the batteries and the lcd reads 1amp IN 8amps out or something, so I wanted to test how many amps are going in cause it was cloudy and I think it's fun... When I put the test leads on the pv terminals in the CC they went POP! The multimeter seems fine besides mildly melted test leads and the CC didn't seem to miss a beat. Why did it do that? The multimeter is set to the 10amp terminal and is on the 10amp setting too.

[RussN9ZP]

I have 4x 145w panels in series @ about 8amps and 75 volts going into a 60amp mppt outback charge controller. So it's Floating the batteries and the lcd reads 1amp IN 8amps out or something, so I wanted to test how many amps are going in cause it was cloudy and I think it's fun... When I put the test leads on the pv terminals in the CC they went POP! The multimeter seems fine besides mildly melted test leads and the CC didn't seem to miss a beat. Why did it do that? The multimeter is set to the 10amp terminal and is on the 10amp setting too.

Because the test leads go inline with one of power wires not to the +/- terminals. Most multi meters only go up to 10 amps before the fuse pops. You created a direct short with your meter.

[Alex9]

Because the test leads go inline with one of power wires not to the +/- terminals. Most multi meters only go up to 10 amps before the fuse pops. You created a direct short with your meter.

So I'm supposed to put the + lead on the pv+ and the - lead where?

[inetdog]

So I'm supposed to put the + lead on the pv+ and the - lead where?

You disconnect the panel + lead from the + pv terminal at the CC. Then you connect the + meter lead to the + panel lead and the - meter lead to the + pv terminal on the CC.
NOTE: Do not disconnect the panel lead while the sun is shining on the panels! Cover them or open a rated DC disconnect switch first.

Or you get a clamp-on DC ammeter and avoid the whole hassle of re-connecting wires.
Or you wire in a permanent shunt (precise low voltage resistor) and measure the voltage across it.

Most old-timers feel that a "normal" multimeter on Amps is dangerous to have anywhere near your panels or batteries.

One reason is that if a high DC voltage and a high current source like a battery bank is involved, the internal fuse in the meter may well not be able to stop the resulting arc, causing much more of the meter, etc. to melt or explode. This is especially true of the small multimeters with the teeny fuses.

[Alex9]

You disconnect the panel + lead from the + pv terminal at the CC. Then you connect the + meter lead to the + panel lead and the - meter lead to the + pv terminal on the CC.
NOTE: Do not disconnect the panel lead while the sun is shining on the panels! Cover them or open a rated DC disconnect switch first.

Or you get a clamp-on DC ammeter and avoid the whole hassle of re-connecting wires.
Or you wire in a permanent shunt (precise low voltage resistor) and measure the voltage across it.

Most old-timers feel that a "normal" multimeter on Amps is dangerous to have anywhere near your panels or batteries.

One reason is that if a high DC voltage and a high current source like a battery bank is involved, the internal fuse in the meter may well not be able to stop the resulting arc, causing much more of the meter, etc. to melt or explode. This is especially true of the small multimeters with the teeny fuses.

Wow. Can I flip off the breaker between the pv and cc and put the +lead on the +pv end of it and the -lead on the -side? Why do you have to cover the pv or do it in the dark?

[inetdog]

Wow. Can I flip off the breaker between the pv and cc and put the +lead on the +pv end of it and the -lead on the -side? Why do you have to cover the pv or do it in the dark?

Nope. You want the current to flow through the meter to the CC. Not directly from one terminal of the panel to another bypassing the CC. So another way to do it would be to open the DC disconnect, then jumper the two - wires at the disconnect and run the meter leads between the two + terminals of the disconnect. (That is a though experiment only. I do not intend you to actually do that.)

What you propose will measure the short-circuit current of the panels, not the amount of current flowing into the CC for that particular battery state of charge, etc.

How many panels in series and how much current?
I tend to be (overly?) conservative in instructions which might be read by anybody out of the context of the thread.

Just like disconnecting the battery cable on your stopped engine with the headlights on will make a big spark, the same will happen when you connect and disconnect the PV wiring while the panels are generating. But the voltage will be greater than the 12 volts, and if somebody tries it on the battery side of the CC instead of on the panel side, the short-circuit current could be horribly large. (Scenario: you disconnect and the spark startles you so you jerk back and the + cable you are holding shorts to a - somewhere. Or if you hold the terminal with one hand and the connector lug with the other, then when you remove the connector you are what is completing the circuit. Not bad for 12 volts, but really dangerous on a 300 volt grid-tie panel string.)

[Sunking]

Well to measure the Isc from the panels you do not need to disconnect anything. Set your meter to read amps on the appropriate range, and then connect the test leads directly onto the panel input terminals to short out the panels. Your meter will create a short circuit so you can read Isc.

[Mike90250]

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Never happens !

[Sunking]

[ATTACH=CONFIG]2156[/ATTACH]

Never happens !

Mike I have seen that happen to meter, and the guy holding it at the time. That is high voltage damage I am looking at. A solar panel is a current source, not voltage.

With that said a panel array can do that kind of damage, but it take ignorance to do it like trying to measure Isc on a XKwh Grid tied array operating at 300+ volts. Isc measurments should only be done on single up to 2 or 3 panels at a time and the rated Isc does not exceed the meter shunt capability. Only exception would be a Clamp-On Amp Meter.

You picture reminds me of someone setting up the meter to read current then attached the leads from line to ground on a 120 Vac circuit. In that case it will go BOOM! and burn th ecrap out of you and quite possibly start a fire. On a 10 amp shunt connected to 120 Vac would induce in theory 24,000 amps, although the transformer could not source that much fault current. Bottom line several thousand watts being dissipated in your hand for a second or two. AKA Arc Flash.

Speaking of Arc Flas here is a cool video. They delivered the body in a small paper sack to the wife.

[billvon]

Wow. Can I flip off the breaker between the pv and cc and put the +lead on the +pv end of it and the -lead on the -side?

You can but you will not measure load current - you will measure short circuit current of the panel array. Load current into the controller will always be lower depending on the charge controller, battery state etc. And at higher array voltages you end up with dangers from arcing as you try to break the circuit afterwards.

[Alex9]

You can but you will not measure load current - you will measure short circuit current of the panel array. Load current into the controller will always be lower depending on the charge controller, battery state etc. And at higher array voltages you end up with dangers from arcing as you try to break the circuit afterwards.

This stuff is scary. I'll stick to measuring individual panels for now.

[Sunking]

Alex the real danger to solar, and it is a big danger and why US electrical codes are going to get really tough and strict is you cannot turn off the power. For single panels is no problem., an array, especially a grid tied array the voltages can be up to 600 volts open circuit. You get a hold of that (high voltage) on say a 1000 watt panel array can be fatal even though it only can deliver 1 or 2 amps. Your body resistance would be very close or higher than MPPT resistance at those voltage. That is when it gets real dangerous.

[Alex9]

Alex the real danger to solar, and it is a big danger and why US electrical codes are going to get really tough and strict is you cannot turn off the power. For single panels is no problem., an array, especially a grid tied array the voltages can be up to 600 volts open circuit. You get a hold of that (high voltage) on say a 1000 watt panel array can be fatal even though it only can deliver 1 or 2 amps. Your body resistance would be very close or higher than MPPT resistance at those voltage. That is when it gets real dangerous.

I'm headed to a 1kw system and all DIY. I wouldn't of thought I could get hurt on that size a system. I'm glad I found out before the fact. I'm grateful for this forum!

[Sunking]

I'm headed to a 1kw system and all DIY. I wouldn't of thought I could get hurt on that size a system. I'm glad I found out before the fact. I'm grateful for this forum!

Well alex if a battery system say using 24 volt panels is around 36 volts and 80 amps. Open circuit voltage is no problem at 44 volts. Measuring 80 amps is an equipment problem. I would only use a Clamp On Amp meter.

My references was grid tied system where a 1000 watt panel voltage will be 300 volts or more. That will kill you under the right conditions.

[Mike90250]

Many meters get smoked when someone trys to measure the amps in the battery. 1 battery, not so bad, just blows a fuse or test lead. More than 1 battery, and the arc has enough power to create enough plasma to really cook things.