I tried measuring the circuit between my solar panel and the controller today, but couldn't get a reading. I was wondering, should a digital multimeter (I have a Fluke 115) be able to read small amounts of current like 2 or 3 amps? My panel should put out a max of 4A in bright sun, but I would like to see what the actual output is in a variety of conditions (bright haze, cloudy, etc).Has anyone done this or have ideas on an easy way to do it? Will a clamp meter (TRMS) do the job?I know the system is functioning, because I can measure the voltage inside the trailer (in a 12V socket) and it goes to 14.14V when the panel is hooked up.

I take the amps between the controller and battery, not from the array side of the controller. For under 10a, you can just put your multimeter pos and neg as part of either the pos or neg controller to battery wire and read the amps. You will want alligator clips on the meter leads because you only have two hands! Some multimeters instructions don't want you to leave it on amps more than a few seconds, so with them you can't leave it hooked up as a gauge you can keep watching. For that you can go on ebay and see a zillion cheap little ammeters you can get that work ok too.

The Fluke 115 should be able to measure dc current. The probes have to go from the A(amp) input to Com and the internal fuse must be intact. It's good for 10 amp and 20 amps for 30 seconds.Most inexpensive clamp on current probes only measure AC current. You'll need a more expensive DC clamp on current probe.But your Fluke should do it.

Ok, I tried taking the positive cable off the battery and measuring across there. The meter will very briefly say an amp or two, then the numbers dance wildly for perhaps two seconds, and it settles down to about .1A. Doesn't matter if the panel is in full sun or in shade, same thing happens. I'm not sure how to interpret that. I do have it set for dc, not ac.The controller 'sees' the battery condition and charges accordingly. I wonder if my Morningstar Sunguard SG-4 sees the meter in the circuit and thinks it's supposed to go into float mode?

Hi,The battery terminals need to stay connected and you need to open the circuit (you can accomplish this by removing one battery terminal if you wish). Then your meter goes where you opened up the circuit (i.e.; if you removed one battery cable, then the meter will connect between that battery terminal and the cable that you removed from it).Don't forget to set your meter to DC Amps and, most likely, you will have to move the red test lead to a different jack on the meter....to something that says something like "Amps"If you don't get something when doing the above, maybe the fuse inside your multi-meter is open. Should be easy enough to replace.Steve

I did all of the above. I am getting "something" but it's not right.

Easy way to measure solar output (Amps)? | Good Sam Community

20 Replies

NinerBikes
Explorer
Feb 26, 2014
rexlion wrote:
I tried measuring the circuit between my solar panel and the controller today, but couldn't get a reading. I was wondering, should a digital multimeter (I have a Fluke 115) be able to read small amounts of current like 2 or 3 amps? My panel should put out a max of 4A in bright sun, but I would like to see what the actual output is in a variety of conditions (bright haze, cloudy, etc).

Has anyone done this or have ideas on an easy way to do it? Will a clamp meter (TRMS) do the job?

I know the system is functioning, because I can measure the voltage inside the trailer (in a 12V socket) and it goes to 14.14V when the panel is hooked up.

Watt amp meter for solar panel.
Almot
Explorer III
Feb 25, 2014
Read maybe this on battery charging - from the diagram and below.

Battery CAN and SHOULD go to 14-something volts by the end of charging process, which can occur by late morning, or mid-day, or later (or never, if your battery is too low and solar harvest is too poor because of weather or because the panel is small).

Yes, 7-pin pigtail might be convenient for low-current controllers, though I don't like it for the following reasons:

1) Voltage drop. With my 30A array the drop would not only be very high, but probably would burn those thin pigtail wires, I think they are only designed for 10A per lead.

2) This plug is exposed to elements and brass contacts on my plug are more green than yellow now. Less contact = higher losses.

3) God only knows what is connected to what contact on that 7-pin plug. There are few different wiring diagrams for this plug, depending on the manufacturer.
BFL13
Explorer II
Feb 25, 2014
My old "shunt" type controller had steady readings until batteries got near full then the controller started controlling its output by the amps and voltage going up and down like crazy. Normal.

My "series" PWM controller is a little different where the voltage stays fairly steady but amps go up and down sometimes, haven't watched it enough to be clear how that goes for how it "controls"

Nothing wrong with using the 7-pin cord to get from controller to battery except there might be a voltage drop, but with only a 4a panel the amps won't be high enough to make much of a drop anyway

Smk, a member here, suggested using the 7-pin a while back and I did use that method for a while and it worked. I got full amps to the battery. I made up a special adapter using one of those connectors like on the truck. Our trailer even has a "battery" fuse on the 7-pin #4 pin wire so you get that too.

You can have the converter charging on shore power or generator and still be charging with solar. It depends on their respective charging voltages how their amps will get mixed or not at the battery, same as with any two chargers. They will add their amps best if their voltages are nearly the same.
Almot
Explorer III
Feb 25, 2014
rexlion wrote:
I still don't understand why I get such strange readings
Readings are strange because the circuit is "strange". It is also possible that your meter is a lemon, or needs a fresh 9V battery.

I sense some misconceptions here.

You don't - normally - plug controller into trailer's pigtail. Controller should be connected to black and red wires that are sticking from under the front of your rig, same wires as you connect the battery to.

Converter doesn't come into play when you are not on shore power.

TV is charging the trailer battery directly - because again, converter is Off when there is no 120VAC input.
rexlion wrote:
I have found that the voltage in the TT interior (it has a cigarette-lighter style receptacle that I can easily check) runs as high as 14.3V during the midday charging, so that led me to believe that the converter is not reducing what the solar controller puts out.

In the absence of loads during solar charging the voltage in DC circuit is a bit higher than 12V unless your battery is very-very low. Normal voltage during charging starts near 13V, then it goes up to pre-set value of 14-something (called Bulk setpoint), and then drops to pre-set value of 13-something (called Float). This is called a 3-stage charging. If there is a temperature compensation feature in your controller (not likely in a cheap controller) and it is cold where it is mounted, the voltages will be higher, at any stage. OTH, in presence of loads the voltage can be lower, at any stage.

Maybe somebody here could suggest gentleman a good, easy 101 on battery charging?
rexlion
Explorer
Feb 25, 2014
I still don't understand why I get such strange readings when I detach one cable from the battery and place the multimeter in line, one probe on cable and other probe on battery terminal. The digital display shows wildly changing numbers, starting at maybe 2+A and quickly descending until it reads almost nothing.

Since My controller plugs into the trailer's pigtail, I'm wondering if the TT converter comes into play in this? Maybe someone can tell me, when I drive down the road with the pigtail plugged into the TV is my TV charging the battery directly? Or only indirectly, through some governance of the converter? If the latter, maybe I would be much better served by rigging up something going directly from the solar controller to the battery terminals. Maybe the on-board converter is greatly reducing the amount of current reaching the battery from solar via pigtail.

I have found that the voltage in the TT interior (it has a cigarette-lighter style receptacle that I can easily check) runs as high as 14.3V during the midday charging, so that led me to believe that the converter is not reducing what the solar controller puts out.
wa8yxm
Explorer III
Feb 24, 2014
A clamp on meter may not give you a reading but an in-line meter should.
Almot
Explorer III
Feb 24, 2014
If this is without controller, then you didn't even have to measure :)... I bet this is - more or less - what it says on the back of the panel, ex. Isc = 4-something Amps, Voc = 22V. Direct measurement without controller confirms that panel isn't dead though.

What is more interesting, is how your batteries work with this panel. What voltage they start from, do they ever get to Bulk 14-something volt, and do they ever get to Float. Measuring amps in line while battery is charging, is a useful info as well, but this has to be "in line", i.e. in series, with controller output connected to battery.
rexlion
Explorer
Feb 24, 2014
I was able to get good measurements today. The panel was giving me 3.1A around 10 am, and 4.3A (22V) in early afternoon (full sun). In late shade it registered 17V but no current. I will have to wait for some clouds to get other readings that I've been wanting. Thanks to all.
Almot
Explorer III
Feb 24, 2014
BFL13 wrote:
The panel might be doing 8 amps but the almost full batteries might only take 2 amps.

When that is happening, you can get a freebie! Run a 6 amp load like a laptop on inverter, and you still get the 2 amps to the battery plus run the 6a laptop from solar

Yes. This is what I'm normally doing. Charging laptop, cordless tools, vacuum etc when batteries are full. Though I don't have to, with my solar capable a bit more than Rex's 4A. Running loads when batteries are full, is good for batteries, because they cycle less and live longer. Love my charger with display.
BFL13
Explorer II
Feb 22, 2014
Yes, you have the two wires from the panel and short them with the meter, one meter lead on panel pos and the other meter lead on panel neg. Aim the panel at the sun when the sun is fairly high and you should get an amps reading (called Isc) near the panel's rated Isc.

It could be less than that for various reasons- low light, etc.

Now you can also switch the meter to DC voltage (probably have to use the 200 because Voc can be over 20v) and read that too. Your panel might be rated for 22v Voc but you might only see 20.5v---this is normal! When the panel warms up in the sun it loses some voltage, but amps stay ok. (coefficients per temperature are opposite direction for V and I )

But that does not tell you what amps you are getting at the battery. The panel might be doing 8 amps but the almost full batteries might only take 2 amps.

When that is happening, you can get a freebie! Run a 6 amp load like a laptop on inverter, and you still get the 2 amps to the battery plus run the 6a laptop from solar to use up the 8a.

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Easy way to measure solar output (Amps)?

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