Easy way to measure solar output (Amps)?

[rexlion]

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.

[NinerBikes]

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]

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]

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]

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]

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]

A clamp on meter may not give you a reading but an in-line meter should.

[Almot]

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]

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]

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]

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.

[rexlion]

BFL13 wrote:

You first want to see what the panel is doing. For that take the Isc by disconnecting the panel from the controller's array side. Now put the meter across the two panel wires (ignore pos and neg, doesn't matter)

My solar setup is portable and I have a plug between the panel and controller. If I'm understanding this correctly, I can unplug the panel and place my meter across the plug prongs for a reading? This is new to me; I thought I had to place the meter in line. If I can use the meter to complete the circuit, taking the readings I want will be simple. It's getting dark here now, so I'll try that tomorrow. Thanks very much.

The suggestions about an inline dedicated meter would be very good. Unfortunately I elected to keep the system portable and outdoors, so any meter would have to be weatherproof.

[BFL13]

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

That 1a might be ok or not--

You first want to see what the panel is doing. For that take the Isc by disconnecting the panel from the controller's array side. Now put the meter across the two panel wires (ignore pos and neg, doesn't matter) You will get some amps depending on how well the panel is aimed at the sun, etc. If it is a 4a Isc rated panel, you might get that much or a bit more or a lot less, depending on aiming and the amount of sunlight. Say you get 3a. (panel aimed right but sun low, eg)

Now you want to know how much of that 3a is getting to the battery. Connect controller to battery and array to controller in that order, but with meter in line with battery controller. Say it says 1a.

(You can't do this with lots of white clouds rushing by the sun changing the amps every minute. You need a time of sun in the clear so you have time to do all this.)

Now you can find out where did the 2a go missing? -- Batteries might be full so only take 1a, or wiring losses including connections.

With batteries low enough to accept the amps, the panel aimed at the sun will have the nearly the same Isc amps reading as you see at the battery

[EsoxLucius]

The Blue Sky 2512iX or 3024iL and IPN-ProRemote will readout amps in and amps out of the controller, as well as voltage, SOC, battery temperature, and AH from full.

[TurnThePage]

Agreed! My TM2020 can tell me all about amperage, voltage, percent charged, etc. Way more than I typically want to know.