HELP please how to measure the AMPs from a panel

Just taken delivery of two new panels, 12v 300w, 16.7amps. Took them out into the sun, put the clamp meter onto the positive cable and only got .3 of an amp. Went to my old panels (which the new ones are meant to replace) and got 3.5 amps measuring the same way. However the new panels still gave over 23 volts. I went through this process twice, am I doing something wrong? Any help would be appreciated.

Did you short the two panel leads to each other? This is necessary for current to flow.

Does the meter measure DC current? AC current only meters seem a little more common.

Hi, thanks for your reply, ok so that may be the problem, just putting a clamp meter on the positive cable (yes it is DC) is not shorting the cables. New to all this stuff, I will try again today, if the sun comes out. I can hook it up to my existing charge controller with some effort but first I will try the shorting method with another multi meter. Cheers

Just realised that the old panel I measured was actually connected to the solar charge controller.. I am a dork!

Hello Dork. The first time I plugged the + and - together on a sunny day to measure current I was quite surprised at how well dc current carries an arc. If you happen to connect a couple, or more, be careful.

Thanks Kronbread, yea I covered the panel first. So the outcome was that I got 4.99amps with 23.6volts on one panel and 4.95amps and 20.7volts on the other panel. As I purchased these with a description of 12V, 300-399W, Short Circuit Current 18.27A, Open Circuit Volage 21.4V, I thought that I had been as usual taken for the ride. So I sent a message to the seller (Ebay of course) and told him the testing showed that the panels he sold me were not what he was advertising. No problem he sent me a return post label. No issues at all. Great, but in the meantime on "EBay" there are a million adds for these panels, aimed at the RV and Caravan market. So I imagine that many people will buy these and just mount them up then find out later that they do not do the job they are supposed to do without knowing why! Needless to say that I had already sized the rest of my system based on the specs of these panels, so I have fairly big wire and another new Solar Charge Controller capable of 40A coming.

So after doing a LOT more research and trying to find panels that would suit my purpose I came across a very interesting article which has now helped me understand a lot more about solar panels and have "some chance" of buying better next time. I am in Australia and the options here do not seem to be that great, you either have to pay a mint for proper brand name stuff or crap from EBay.

Eleven years ago (before I ever thought of buying stuff over the internet) I bought my first 12v 120w solar panel for this project from a local store who specialises in stuff for caravans, RV's etc the dude also sold me the wire I needed and the Solar Charge Controller and the inverter and it is all still working fine. A few years later I added another 120W panel from EBay, it is working but has what looks like tracks across some of the cells so I imagine that this could be shorts happening, but it is still measuring the correct numbers according to it's label. These were charging a 110AH lead acid battery, which died many years ago and I have only just been able to get back to sorting it out.

Now I want to upgrade my system so that maybe I can run it completely off grid only using the grid as a back up battery charger when needed. I have built a 12V LiPo4 400AH battery, with cells from QSO. So now I need more solar panels to actually keep the thing charged, I have a JK BMS, and a max 1200W inverter, I am only powering pond pumps, water and air. I grow fish for our own consumption. (Aquaponicly), they cannot go long without air, no longer than about 20 minutes, I also have a petrol 5kw generator, which is setup to feed directly to the system when needed. Which is several times a year and on one occasion for 3 days!! We live outside the metro area, more or less in the bush, they call it peri-urban, we are urban when they want to charge us for services but in the bush when we want something! But nevertheless we are fortunate enough to live where there are a lot of trees and when we get a storm or strong winds we get power outages.

According to this article https://www.4wdingaustralia.com/4x4/ebay-solar-panel-sizes-how-to-avoid-getting-ripped-off/ both my old existing panels measure up or exceed the levels this guy talks about.

NO OTHER panel I have put through this test comes up at the correct level, never mind exceeding them. I have been trying now for 12 months to re-jig my existing system, I had forgotten most of what I learnt eleven years ago, hence forgetting how to measure the output of the panel, which I started this thread on. I have spent hours watching Will Prowse videos, they are fantastic and have been a great help. Also I have spent hours watching the Off Grid Garage, who has also been amazing but so far I cannot recall much ever being said about what panels to buy or how to evaluate different panels. Most of the info seems to be on solar charge controllers, BMS's, batteries, etc. So this article (providing it is acurate which I have no way of knowing as my knowledge is very limited) seems like a MUST read especially for the novice solar power DIYer. Here is the link again... https://www.4wdingaustralia.com/4x4/ebay-solar-panel-sizes-how-to-avoid-getting-ripped-off/

I hope this can be of some help to other newbies, I have certianly learned a heap doing this project.

Are you using a pwm solar charge controller? Why are you stressing on 12v panels?

No MPPT, with the panels, I am pissed off with buying crap panels, which I only learned about after the fact. At this stage my inverter is only 12v so until that gives up the ghost I am stuck with 12v. Maybe later I will switch to 24v.

What model/brand of solar charge controller are you using? If it is an mppt based controller, instead of pwm, those panels are good to go.

How did you connect the panels? Too late now although in the future I suggest that you purchase higher voltage panels, it can make life much easier. But back to your present panels, if I were in your situation I would connect the panels in series rather than parallel. Higher voltages given to an MPPT controller really minimize the voltage drops in the panel to converter wiring. Avoid using pulsewidth convertres!

I have four 300 watt panels on my boat, each have a MPTP around 32VDC but my MPPT controller can process input voltages nearing 150V. Just a warning if you go series connected, observe safety protocols.

If I connect them in series that would give me 10a @24v, so my mppt controller can handle 20a @24v but it will be charging a 12v battery, how does that work? Does the mppt controller manage the voltage back down to 12v to suit the battery.? I don’t understand.

jackodriver said:

If I connect them in series that would give me 10a @24v, so my mppt controller can handle 20a @24v but it will be charging a 12v battery, how does that work? Does the mppt controller manage the voltage back down to 12v to suit the battery.? I don’t understand.

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Yes it has a buck converter topology to switch the panel power to a lower voltage

Really no one should be using pwm scc three days or low voltage panels

24v is a very low mppt voltage. Are you sure these are genuine mppt controllers . A lot of the Chinese stuff is labelled mppt but it’s nothing of the sort

My boat mppt controller are 100v capable and I run at a 44v Voc series panels.

You can’t extract maximum power if the panels are close to the battery voltage.

Connecting panels in a series increases voltage. Connecting panels in parallel increases amperage.

Hawkers on Ebay, and other fine scarfing establishments, intentionally name their products mppt this, or mppt that, in order to make the sale. Not all charge controllers with mppt in the name are really an mppt controller. What is the brand and model of you solar charge controller?