Measuring Current

quique

When we say:

"you’ll have to open the circuit and put the meter in series with it to measure the current"

Does that mean connect the + and - terminals of the pv module using a male-female conductor...

and then peel the conductor at two different spots...

and place the terminals of the ammeter in those spots?

NorthGuy

Re: Measuring Current

1. Set your meter to measure current.
2. Cover the panel or turn it away from the sun (this step is very important)
3. Connect one lead to + PV terminal
4. Connect secod lead to - PV terminal
5. Making sure your leads are firmly connected and won't disconnect on the next step
6. Uncover the panel
7. Read the meter
8. Cover the panel
9. Disconnect leads

icarus

Re: Measuring Current

Better yet, consider a clamp on ammeter. As BB suggests so often, Sears sells a good one for under $100. (make sure you get the AC/DC version. They make an AC only version that looks just like the dual version.

Tony

quique

Re: Measuring Current

oh for some reason i thought it was different for measuring current

vtmaps

Re: Measuring Current

quique wrote: »

oh for some reason i thought it was different for measuring current

Those instructions that NorthGuy gave you are for measuring Isc. The ammeter acts like a short circuit on the panel.

If you want to measure the Imp the instructions would be a bit different, and you would be wise to take Tony's suggestion and use a DC clamp meter.

--vtMaps

quique

Re: Measuring Current

Yes I understand it's quite dangerous to measure current by intercepting the short-circuit. I wasn't planning on doing it, I was simply understanding what I read in the course I'm taking.

I'm still wondering if that would be the way to do it. I also would personally prefer the clamp meter.

BB.

Re: Measuring Current

You set the meter to (for example) 10 amps maximum (and don't use on a circuit that has a higher current than your meter is rated for) and "break" the circuit where it is easy to get connections, and then simply insert the meter into the break to carry the current.

Isc is simply shorting out the solar panel.

Imp would be with the solar charge controller (MPPT type) charging a battery at full available current (in MPPT mode, with the battery less than ~85% or so State of Charge--Or you have a large load on the system--such as an electric heater or something).

You can estimate Imp by connecting a "12 volt" panel to a 12 volt battery (car battery, etc.) and you should measure pretty close to Imp (of course, the solar panel current is proportional to the amount of sunlight--which can vary pretty easy from 50% to 100% in apparently full sun).

-Bill

quique

Re: Measuring Current

So something like this.

Connect both ends to themselves in the pv module.

Peel the connecting wire at 2 different points, and measure?Attachment not found.

Cariboocoot

Re: Measuring Current

Why do you want to peel the wire? For a single panel you just connect the positive lead of the multimeter to one of the PV wires and the negative to the other. If it's on Volts it will read Voc. If it's on Amps it will read Isc.

For a series string of panels or paralleled panels it's better to use the clamp on as the series presents a higher Voltage (greater potential for arcing) and the parallel will increase the current beyond the DMM's 10 Amp limit.

Testing one panel is easy. Not much danger from either the Voltage or the current.

BB.

Re: Measuring Current

In your drawing, the "gray" wire is redundant, you should just connect the leads directly to the panel (to measure shorted current). And the gray wire should be "open" between the two meter leads (you want the current flowing through the meter).

If you were to use a Current Clamp Meter, then you would just put the clamp over the wire and measure the current (or short the panel first, and then put clamp other the wire for short circuit current).

More or less, solar panel shorted current is exactly equal to the amount of solar energy hitting the panel (within ~5% linearity).

Imp is pretty much zero until there is weak direct sun on the panel (to get near Vmp voltage), then the current is pretty much proportional to any increase in solar radiation (assuming you have a good panel and wiring).

-Bill

Cariboocoot

Re: Measuring Current

Or in short; the meter itself completes the circuit from the panel (+) to the panel (-).

With a clamp-on meter there would be the wire between the two panel leads and it would clamp around that to take the current reading.

Clear now?

quique

Re: Measuring Current

Yes the clamp way has always been clear. I'm just trying to visualize he other one. Ok so it would be just as measuring Volts (but using the amp config on the mmd.

BB.

Re: Measuring Current

quique wrote: »

... Ok so it would be just as measuring Volts (but using the amp config on the mmd.

No--You have to be very careful here (that is why I like to suggest the Clamp Meter--Just about impossible to screw up and hurt yourself or your equipment in normal use).

A volt meter measuring voltage is "safe" (assuming everything is within limits of meter) to connect across any load/energy source. The meter has very high internal resistance and usually only passes a 1/1,000 to 1/1,000,000 of an Ampere.

A leaded current meter (or a DMM set to measure current) is almost a dead short so that when you "cut a circuit" and put the meter in series with the current flow, all of the current flows through the meter (so it can measure the current).

If you put a meter configured for current across a voltage source (lead acid battery) or across a high current source (a solar array with > 10 amps of output current), the meter will draw as much current as the source is capable of (within the limits of the meter leads and internal shunt). Most DMM's when set to 10 (or 20) amp full scale do not even have a fuse on the input leads. And will draw excessive/dangerous current until either the circuit is broken, or the something fails.

Be VERY CAREFUL with a DMM set/configured to measure current. It is an accident waiting to happen. Most of the time, you will just ruin the meter with over current--But worse can happen (it all depends on what you are connecting too).

-Bill

Mike at Energy Commission

Re: Measuring Current

yes indeed those DMM will fry if you close the circuit with a > 10 amp potential, one of my first lessons in solar hobby!