Measuring amps from solar

Submitted: Tuesday, Apr 16, 2013 at 16:19
ThreadID: 101734 Views:2057 Replies:10 FollowUps:9
This Thread has been Archived
I couldn't find an answer to my question, but I'm sure it's been asked.
I'm wanting to measure Amps to understand why my battery isn't holding charge.
The panel is 80 watt, and is outputting around 20Volts, Voc.
When I connect my multi meter in the circuit, I can't get a reading. I use the 10Amp jack and connect in series.

I connect between the +ve lead from the panel and the +ve terminal on the controller. I get zero Amps. I've confirmed that the MM works OK by connecting it in series with a mains battery charger and I read the charge current.

I'm wondering if the battery voltage impacts the reading. Cancels it out?? But shouldn't the electronics in the controller manage that?

I also note that when the panel is charging, the voltage accross the battery terminals is only about 12.5 volts. I understand that normally you need about 14 volts to charge a battery. Is solar different?

I've swapped the controller from another installation, but no change.

Can some of you solar experts enlighten me please.

Back Expand Un-Read 0 Moderator

Reply By: Notso - Tuesday, Apr 16, 2013 at 16:42

Tuesday, Apr 16, 2013 at 16:42
It sounds a lot like you have zero output from the controller. Is there a fuse in the line somewhere. Does the voltage rise over time whilst charging from solar?

Solar is not different, it still needs the 14 odd volts to fully charge a battery..
AnswerID: 509140

Follow Up By: Notso - Tuesday, Apr 16, 2013 at 16:45

Tuesday, Apr 16, 2013 at 16:45
With the multi meter you should put it in series in the output line between the controller and the battery.
FollowupID: 786847

Reply By: Ross M - Tuesday, Apr 16, 2013 at 17:06

Tuesday, Apr 16, 2013 at 17:06

If you changed to another controller and it is wired correctly then it would seem the controller is receiving nothing from the panel.
Does the panel actually output voltage and current? 20v oc is good but it might have a high resistive contact and will pass no amps. Multimeters are sensitive little things.

Is there a fuse in the panel junction box? loose wire in the screwed connectors? Break in the cable somewhere.? Have you checked the cable for continuity on both the pos and neg wires? are all cable to the battery sound and continuous so they can deliver current to the battery?
Is there battery voltage at the regulator when the panel is not connected? This will be a check of the reg to battery cables.

A battery at 12.5 v will only rise slowly in voltage as it receives charge and absorbs it.
If it suddenly went from 12.5v to 14+v then the regulator would think it is charged and stop delivering. This doesn't happen and it is the slightly less voltage the controller "sees" and allows current pulses to be delivered until the regulator sees the battery is up to 14+, then it should float charge.
AnswerID: 509143

Reply By: Johng - Tuesday, Apr 16, 2013 at 17:34

Tuesday, Apr 16, 2013 at 17:34
Thanks for the replies.
The panel, regulator and battery are all within arms reach of each other. All cables are intact. The input to the regulator shows 18-20 volts until I connect the battery, and then the input drops to about battery voltage. Like Ross said.

I think I also measured between regulator and battery and still got no reading, but I'll check.

I did read something about the battery voltage feeding back and nullifying the reading. Hence my question about this aspect.

I'll do some more tests tomorrow and seek your further wisdom.
AnswerID: 509145

Reply By: The Bantam - Tuesday, Apr 16, 2013 at 17:57

Tuesday, Apr 16, 2013 at 17:57
We need to step back to some basics.

remember modern multi-meters will read voltage when the circuit is very poor.

you have 4 places to measure a voltage.
at the panel, at the input to the regulator, at the output to the regulator and at the battery...they should all differ at least slightly.

you need to measure all 4 and see if there are any major voltage going missing.

I have a gut feeling that you may have a poor connection between the panel and the controller

Have you checked the terminations inside the terminal box on the panel.

If there are diodes inside the terminal box have you checked should see about 0.6 volts across the diodes with the system running.

In full sun
When you connect the regulator to the battery it is expected to see the input to the regulator drop....but if it drops all the way to the resting terminal voltage of the battery and the neither the terminal voltage of the battery nor the input to the regulator rise...over time I'd suspect you have no current flowing.

step by step one thing at a time.

AnswerID: 509148

Follow Up By: Dingojim - Tuesday, Apr 16, 2013 at 18:04

Tuesday, Apr 16, 2013 at 18:04
Hail The Bantam. When you explain it like that even fellas like me can understand it. I would dearly love to know as much as some of you guys have forgotten, which would make me much smarter than I am now. Cheers.
FollowupID: 786862

Follow Up By: Johng - Tuesday, Apr 16, 2013 at 18:07

Tuesday, Apr 16, 2013 at 18:07
Hmm. Thanks. I do have a switch in the positive lead from the panel. Maybe that's faulty, although I have checked continuity.
The fact that I can read VOC at spec, suggests leads, terminals, etc are OK. It's just the ellusive Amps. :)

I installed the switch naively thinking I could address the warning on the panel that says, do not connect panel with load connected, or something similar. But the switch doesn't address that because the load is there whether the switch is there or not. But why is the warning there anyway?

More checks tomorrow.

FollowupID: 786863

Reply By: Sand Man (SA) - Tuesday, Apr 16, 2013 at 18:14

Tuesday, Apr 16, 2013 at 18:14
You also need to determine the health of your battery.
Does it charge and hold that charge from your 240v charger?
If not, you may have a defective battery.
If one or more cells are gone, no current would be drawn from the supply source.

I would check the battery before tinkering with the solar panel/regulator.
Perhaps get it load tested at a battery retailer.


I'm diagonally parked in a parallel Universe!

My Profile  My Blog  My Position  Send Message

AnswerID: 509150

Reply By: phil300 - Tuesday, Apr 16, 2013 at 20:24

Tuesday, Apr 16, 2013 at 20:24
Measuring amps from solar

I would disconnect from the battery and put a on load on the cables eg a 240v light globe with the multimeter in series and measure the amps and the volts.
cheers Phil.
AnswerID: 509157

Follow Up By: V8 Troopie - Tuesday, Apr 16, 2013 at 22:27

Tuesday, Apr 16, 2013 at 22:27
The answers above are mostly too detailed and confusing.

To measure the output from a solar panel do this:

Disconnect both leads of the panel from any controller, battery or any other van wiring.
Take your multimeter, set at a suitable voltage range and measure what's coming out at the two wires, making sure your panel receives sunlight of course.
With a digital multi meter it does not matter which meter lead goes to which wire, the meter just displays a negative reading if its reverse connected.
There should be between 18 & 21 volts for a 12V nominal panel, depending on how many cells the panel has.

Next, and this might worry some people, it is quite OK to short circuit a single solar panel by itself (its not connected to anything else). The max current (Amps) that can flow is what's shown on the label under short circuit current.
Just set the multimeter to the 10A DC range, assuming the panel has less than 10A sc rating. Connect the meter probes to each wire of the panel, this is the same as short circuiting the panel BTW, and measure the short circuit current.
It should be close to the spec on the label but is dependent on the amount of sunlight. If it shows a healthy Amp reading the panel is fine and you can eliminate it from the cause of your problem.
FollowupID: 786888

Reply By: Member - Murray R (VIC) - Tuesday, Apr 16, 2013 at 22:17

Tuesday, Apr 16, 2013 at 22:17
You can disconnect the panel wires from the controller and use your multi meter on amps to short the panel out to test the panel. Buy that I mean the panel positive to one ammeter lead and the panel negative to the other lead. You should get a reading of about 4.5 amps. If no reading you have a faulty panel or bad connection on the panel wiring termination.
Just another test

Another Mexican

Lifetime Member
My Profile  My Blog  My Position  Send Message

AnswerID: 509174

Reply By: Allan B (Member, SunCoast) - Tuesday, Apr 16, 2013 at 22:22

Tuesday, Apr 16, 2013 at 22:22
John, Apart from the comprehensive advice above there is one more possibility for not reading amps.
Your multimeter is rated to read a maximum of 10 Amps. It contains an internal fuse rated a little above this to protect the meter from major damage of excessive current. It is quite easy to blow this fuse and if you do then not only is there no meter reading but also no current will pass through the meter.
Note that this fuse is only in the meter's Current circuit. Even if blown the meter will still read voltage.
The fuse can be blown if 1) If connect to a circuit with higher current than the fuse rating or 2) You inadvertently connect the meter leads across a supply with the meter lead still in the 10A jack.
Try reconfirming that your meter is OK by repeating the test with the battery charger.

My Profile  My Blog  My Position  Send Message

AnswerID: 509175

Follow Up By: Member - Boobook - Wednesday, Apr 17, 2013 at 09:10

Wednesday, Apr 17, 2013 at 09:10
What he said.
FollowupID: 786921

Follow Up By: Johng - Wednesday, Apr 17, 2013 at 12:39

Wednesday, Apr 17, 2013 at 12:39
Allan, I think I have eliminated the possibility of a blown fuse, as I mentioned earlier, I checked the current from a mains battery charger that I had charging another battery, and I could read 5 Amps OK. So I conclude the MM is working OK.
Back out to do some more tests.
FollowupID: 786955

Follow Up By: Allan B (Member, SunCoast) - Wednesday, Apr 17, 2013 at 12:52

Wednesday, Apr 17, 2013 at 12:52
I think you have missed my point.
I know you read 5 Amps on the charger earlier but since then you have applied the meter to a circuit of unknown current. It is possible that this current exceeded the meter fuse rating and has blown the fuse.
I suggest checking it again on Current Range in the charger circuit to verify that the meter is still working or you will be chasing your tail.
It is correct electrical practice to re-verify your instruments if the measurement is not what was expected. Believe me, I and many others have been caught by assuming that all was right with the instruments.

My Profile  My Blog  My Position  Send Message

FollowupID: 786960

Reply By: cruiser 3 - Wednesday, Apr 17, 2013 at 18:40

Wednesday, Apr 17, 2013 at 18:40
Here is another 2 cents worth.
Voltage can usually be read even if a circuit has a very poor connection Ie loose connection or high resistant joint.
But that same poor connection most likely will not be good enough to carry any current.
So just because voltage can be seen it doesnt mean that there is a good circuit.
AnswerID: 509217

Follow Up By: Allan B (Member, SunCoast) - Wednesday, Apr 17, 2013 at 18:45

Wednesday, Apr 17, 2013 at 18:45
True cruiser. That is why when testing it is important to have the circuit or equipment operating or in the same mode as when the condition of interest is present.

My Profile  My Blog  My Position  Send Message

FollowupID: 786986

Reply By: Johng - Thursday, Apr 18, 2013 at 13:35

Thursday, Apr 18, 2013 at 13:35
I think my issue related to the following.

Because I was measuring Voc at spec, even though it was a partly cloudy day, I assumed Amps would also be close to spec. But it seems that's not how it works.

I confirmed yesterday that in clear sunshine, the panel is performing to spec.
I also noted that when the sun dissappeared briefly, the Amps dropped way down, to 1.0 or so, but Voc remained at 21. As soon as the sun came out, back up to 5.5 Amps and Voltage still about 21.

So why was I originally reading zero Amps?

I initially replaced the flat battery with a fully charged battery, and the regulator would have responded to that by cutting back the Amps, and that, in combination with a cloudy period during measurement resulted in the zero reading. In clear sunshine, and a fully charged battery, I now read about 1.5 Amps.

I did experiment with a flat battery, and while the initial Amps was around 3.5, after maybe 20 seconds the reading dropped to about the 1.5 mark again. Don't know why it should behave like that.

I'm wondering if my $24 regulator is too basic, and if I should upgrade to something that operates with more sophistication. Does anyone have experience with a regulator that is too basic?

And thanks for the helpful dialogue.


AnswerID: 509254

Follow Up By: KenInPerth - Thursday, Apr 18, 2013 at 15:48

Thursday, Apr 18, 2013 at 15:48

I will not profess to be well conversed in all the various regulators and other devices on the market and many people out there will have much more experience than me with other systems, but generally if you pay $24 for a regulator it will not be much "chop" - you pretty much get what you pay for.

I have been using and am a fan of the D250Sdual from ctek which as far as I know is an MPPT regulator and lets you have one device (around $250) to control battery charging from both alternator and solar (max 20Amp into the battery which is generally enough for most configurations).

That may give you an option to explore depending on what your requirements are.

If you want to add mains charging into the design that complicates it a little more as I have found (smart) mains chargers do not like being connected to the battery without first disconnecting the ctek and while I have not blown my D250Sdual up I don't know what it's tolerance is to do such a thing - although ctek do have a mains charger designed for this purpose but at a cost. There are ways around this that can be automated or manual.

I am sure others out there will correct anything here that I may be wrong about or not thought of.

FollowupID: 787051

Sponsored Links

Popular Products (9)