Checking solar panel output

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Checking solar panel output

September 05, 2015, 08:18:49 am

How do I check the solar panel output? Do I disconnect both wires coming from the panel to the battery compartment? Then hook my voltmeter to the wires? Voltmeter set at what?
The solar panel came with the coach and isn't all that big, maybe 12" wide x 30"- 36" long and the wires terminate in the battery compartment under the steps. There doesn't appear to be any regulator as the wire ends just hook directly to the same terminals as the batteries.

Re: Checking solar panel output

Reply #1 – September 05, 2015, 08:22:53 am

I used a fluke amp clamp, that clamps over the wire and measures the amperage traveling thru it.

You can also buy a DC amp shunt off ebay from china for a few dollars and wire the shunt inline with the solar wiring to check amp output in the sun.

just testing the open circuit voltage of the panel leads while not attached to anything will give you a good idea if it is properly hooked up and sending voltage, but wont give you any insight into how much actual power it is putting into your batteries.

Re: Checking solar panel output

Reply #2 – September 05, 2015, 08:24:50 am

to test with your multimeter, disconnect one wire, does not matter which. attach the multimeter to one battery terminal with the wire still connected and the other lead to the disconnected wire. set it to DC range, 30-200 volts, depending on the meter if it is auto ranging or manual.

Re: Checking solar panel output

Reply #3 – September 05, 2015, 08:39:49 am

Thanks Matt. I'll give it a shot if the sun comes out today. Right now it is overcast, but it is only 7:35 in the AM here.
I've never been too confident around electricity since my farmer uncle (wearing his rubber boots) told me & a cousin that we boys could straddle the electric fence as it was off. "See?" At 12 years of age we were the perfect height for that experience to have an impact on us!!

Guess that explains the look on my avatar picture

Re: Checking solar panel output

Reply #4 – September 05, 2015, 03:00:06 pm

Just measuring the voltage from wire to wire, not connected to anything but the voltmeter, will tell you that it works and the open circuit, no load voltage. Have the meter set for doc volts. You will probably measure around 15-18 volts.

To get an idea of power, connect it to a 12v incandescent light bulb. Measure the volts, which will drop below 12v. Then disconnect one wire and measure the Amps going through the meter connected in series. The 10A range should do, although you can switch the leads and use a lower range if needed. Multiply the volts times the amps to calculate power in watts.

Re: Checking solar panel output

Reply #5 – September 05, 2015, 03:12:31 pm

The size of the panel would indicate to me that it is a trickle charge for your start battery. If you are unplugged and in the sun, measure the voltage of the start battery. It it's connected to the panel you will see in excess of 12.6 V. If not it will be <12.6.

Re: Checking solar panel output

Reply #6 – September 05, 2015, 05:23:00 pm

32-36? watts if it's the ones I used to install new then. Siemans panel.

Foretravels would run down the house batteries quickly back then.

Re: Checking solar panel output

Reply #7 – September 06, 2015, 12:07:37 pm

Well, went out and tried to check the solar panel output. Tried the wires in the battery compartment that I thought were the ones. Big mistake--there I go thinking again--always seems to get me in trouble.
No voltage reading at all so I went around to the driver's side & opened the refrigerator louvered panel. Checked up top and saw where the blue wire and white wire went down into the refrigerator top vent. SO-O-O, back down the ladder to the back or the ref. Found the two wires coming down from above. SURPRISE--taped off, not connected to anything!! Unwrapped the tape, checked the voltage--16V, both at the wire ends and up above where the wires disappeared. Voltage did vary when sun was behind clouds. Checked amps--1.25 up to 1.56
Solar panel is 1.5" thick x 13" wide x 42.5 long and has 30 "cells"
Do I leave this disconnected or what? Don't see any kind of control/regulator at all. Or do I just take it off the roof and plug the holes?
There was a new convertor/charger installed when we bought the coach that is in the dump valve compartment. When we are plugged in to 115 V AC the batteries are maintained at 14.3 volts by this convertor/charger.

Re: Checking solar panel output

Reply #8 – September 06, 2015, 01:20:25 pm

Quote from: nitehawk – September 06, 2015, 12:07:37 pm

Well, went out and tried to check the solar panel output. Tried the wires in the battery compartment that I thought were the ones. Big mistake--there I go thinking again--always seems to get me in trouble.
No voltage reading at all so I went around to the driver's side & opened the refrigerator louvered panel. Checked up top and saw where the blue wire and white wire went down into the refrigerator top vent. SO-O-O, back down the ladder to the back or the ref. Found the two wires coming down from above. SURPRISE--taped off, not connected to anything!! Unwrapped the tape, checked the voltage--16V, both at the wire ends and up above where the wires disappeared. Voltage did vary when sun was behind clouds. Checked amps--1.25 up to 1.56

I tied them into the refer wires back then. Does not need a controller. 3 amp trickle charger to the house batteries.

Solar panel is 1.5" thick x 13" wide x 42.5 long and has 30 "cells"
Do I leave this disconnected or what? Don't see any kind of control/regulator at all. Or do I just take it off the roof and plug the holes?
There was a new convertor/charger installed when we bought the coach that is in the dump valve compartment. When we are plugged in to 115 V AC the batteries are maintained at 14.3 volts by this convertor/charger.

Re: Checking solar panel output

Reply #9 – September 06, 2015, 01:25:10 pm

Quote from: Caflashbob – September 06, 2015, 01:20:25 pm

Pretty sure that coach came from my store in ca.

Solar electric specialists sold me siemans panels.

Tired of dead display coaches. I do not think anyone else was putting on solar but me in 1988

Does yours have a bracket to allow it to swivel?

If not came from SES

Re: Checking solar panel output

Reply #10 – September 06, 2015, 01:46:10 pm

Loosen the roof panel until you can see the backside. Use a cell phone to take a photo of the spec sticker on the back. Go to ebay and buy a controller that is a bit larger than the output of the solar panel as listed on the sticker. Mount the controller after reading online sites for how to do it and how not to do it. Don't listen to a neighbor as 99% have no clue along with a good percentage of "professional" installers.

Here is a MPPT controller off ebay. Solar Panel Regulator LCD 10 20 30 40A 12V 24V MPPT Charge Controller 3... MPPT controllers are more efficient than PWM controllers. How can you lose for less than $30?

Pierce

Re: Checking solar panel output

Reply #11 – September 06, 2015, 02:30:58 pm

I would want to run that panel to the start battery. It is not enough amps to make a hill of beans with the house batteries. Since the charger does not charge the start battery when plugged in, the solar panel will. Do what Pierce says, though and run thru a cheap controller. Does not have to be anything other than PWM unless you plan on adding much more amps for the house batteries and use solar for those. There is almost no amp draw on the start battery except for the cigarette lighter plug.

Re: Checking solar panel output

Reply #12 – September 06, 2015, 02:48:05 pm

With no load on the solar wires, except the volt meter, if the voltage reads about 21 volts, you should have a solar controller. If panel no-load voltage is about 16 volts the panel may be self-regulating style and works without a regulator.
No-load 21 volt panels will read about 17-volts under load. Regulators also stop panels from draining batteries at night. Solar panels will generate voltage and charge batteries when under sun, and will turn into a load and drain battery when there is no sun.
Panels may also be designed for higher voltage ranges and there are many different solar panel specifications. So you must find more info on what you have. I assume you will benefit from the panel and would not recommend removing it.
When panel is covered with a blanket, there should be no voltage reading on the output wires.

Re: Checking solar panel output

Reply #13 – September 06, 2015, 04:21:33 pm

I agree with Barry, except that most (not all) solar panels are diode protected to prevent draining batteries at night.
Check the amps at night, if zero and VOC is 17 volts or less, you will not benefit from a controller.
I would connect this panel to the start batteries, because I found the drain on my start batteries was sufficient to cause NO start after about a month (engine/tranny computers, security, dash radio and clock).

Re: Checking solar panel output

Reply #14 – September 06, 2015, 06:16:38 pm

Wyatt, the label on the underside of the panel says something about a diode but really faded so not too legible. If I'm hooked up to shore power should I have the solar panel hooked up at the same time--even during the day? My converter/charger does charge house and engine battery according to the voltage tester and the dash monitor.

Bob, no tilt or swivel on this old baby.
Here is what I could decipher of the faded label on the bottom side. I will put a question mark where I couldn't read the figure.
ARCO SOLAR, INC.
P.O. Box 8?32
C?

??o, CA 93910
Photo Voltaic Module Model M66
Voltage 20 volts DC @ ?deg C open c?t
Current 3.48 Amp @ 47 deg C & short c?t
600V Series Fuse 5 Amp (?)
I attached pics of the labels & the panel just in case you might be able to identify this critter.

And If you can make it out there is some mention of a diode.
By the way Bob, this coach's first owner was in CA and I do believe it sold out of your facility.

Re: Checking solar panel output

Reply #15 – September 06, 2015, 09:43:18 pm

As was mentioned does not need a controller.

Like I said the 89 seemed to have various wiring issues that drew the house battery down with the door switch off quickly brand new.

Engine side was finer.

All these years later I wonder if there were induction draws from battery wiring being parallel for long runs to other wires?

Been a long strange trip to end up 17 years after leaving the Rv biz with a 97 u320 mid door.

Karma. Good kind.

A few of us were the gurus then. Better now with a bunch of knowledgeable owners.

And this forum.

Re: Checking solar panel output

Reply #16 – September 06, 2015, 10:20:14 pm

Quote from: car54 – September 05, 2015, 08:22:53 am

I used a fluke amp clamp, that clamps over the wire and measures the amperage traveling thru it.

You can also buy a DC amp shunt off ebay from china for a few dollars and wire the shunt inline with the solar wiring to check amp output in the sun.

Most multimeters can do up to a certain amount of amps...the meter is put inline of the circuit. some can do up to 20amps.

Re: Checking solar panel output

Reply #17 – September 06, 2015, 11:56:52 pm

Quote from: krush – September 06, 2015, 10:20:14 pm

Most multimeters can do up to a certain amount of amps...the meter is put inline of the circuit. some can do up to 20amps.

Even the cheap meters can measure 20A. Place the switch in the 20A position, move the leads to the 20A holes, and place the meter in series.

It sounds like your panel would best serve you wired directly to the start batteries to prevent self discharge.

Re: Checking solar panel output

Reply #18 – September 07, 2015, 01:23:21 am

As usual, I did my dumbass thing. I found the two wires--one blue (ground on my coach) and one white (positive).
I set my cheap Harbor Freight voltmeter to the DC selector and 20 and also 200 volts. I plugged the red (+) into the port specified and pushed the pointed probe into the white wire. I plugged the black (-) into the port specified and pushed the pointed probe into the blue wire. I then turned the voltmeter on. Reading varied from 14.6 (cloudy and sun behind a big pine in the yard) to 16.0 with sun shining on the solar panel. There are a couple cells that have cracks on the top and all cells seem to have gone a lighter copper color.
I checked the voltage at the wire ends and up under the refrig vent.
I didn't see any way to test the white wire (+) all by itself.

Re: Checking solar panel output

Reply #19 – September 07, 2015, 07:22:29 pm

Quote from: Twig – September 06, 2015, 02:30:58 pm

I would want to run that panel to the start battery. It is not enough amps to make a hill of beans with the house batteries. Since the charger does not charge the start battery when plugged in, the solar panel will. Do what Pierce says, though and run thru a cheap controller. Does not have to be anything other than PWM unless you plan on adding much more amps for the house batteries and use solar for those. There is almost no amp draw on the start battery except for the cigarette lighter plug.

previous owner installed this very small 20 watt panel connected to the 2 8d's house batteries with a 4 amp controller for maintaining while in storage. I installed a trik-l-start to chassis batteries and I'm always satisfied to see this voltage. For maintaining fully charged batteries seems to be ok...

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