Back of solar controller very hot!

[Warby12]

Hi, I have what I am pretty sure is a PWM controller rated for 260 watts which delivers max 10 amps (measured with Victron battery monitor) in full sunshine. I don't know the solar panel output but there are four.

Thing is the back of the controller (aluminium heatsink) becomes extremely hot, I can only keep my fingers on it for a second when the sun is shining fully. Seems like a lot of wasted power!

Question is, is this normal and is the controller possibly too small for the panels?

[smac999]

you need to figure out big your panels are.... 4 panels is probbaly over 260 watts unless they are pretty small. you also need to know the voltage ratings of the panels and if they are wired in parallel or not. as the PWM will have voltage limits

[daletournier]

Look at the back of the panels, it will have the wattage on them, add them up. As long as they are as stated above in parallel then divide by 12( I'm assuming your using 12v) this will give you the theoretical current output, reg should be sized to handle that, although 70% of the output is more realistic. ie 3x 60w (180w) panels theoretically pump out 15amp.

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[Warby12]

Thanks a lot. Ok I am not helping by being totally inaccurate, sorry There are actually ten panels ( I know that's a big difference) but six of them are tiny ones of quite aged appearance.

There are no markings on any of them, all faded away. Four standard sized panels wired in parralel and six very small panels in series which are then added into the junction with the others.

So I have no info on their output. How then can I then work out what size controller I need? Is it normal for my current controller's heatsink to be too hot to touch?

Thanks if you can help

[noelex 77]

Solar controllers do get warm, but what you are describing is too hot.

Unless the controller is mounted in a hot area with no ventilation, it is likely the controller is defective. I would replace it.

There is a small chance the controller is just overloaded with too many watts from the solar panels. Most controllers in this situation will limit the current to self protect themselves. So even if hooked up to a large solar array the controller will not get as hot as you describe, but there are a small number of controllers without this feature, so it is a possibly.

If i understand correcly your controller rated for a maximum of 260w and a maximum current of 10A. This suggests that the controller is only rated for 260w with a 24v battery system. If you have a 12v house system it is likely the controller is only rated at 130W.

You can get an approximate idea of the wattage of solar panels by simply measuring the surface area. If they are older rigid panels, the efficiency is likely to be around 13-14%.

So watts = area of solar panels (in meters squared) x 1000 x 0.14

The other option is to measure the current with your battery monitor or multimeter, but this does not tell you if the controller is defective or limiting the output.

[noelex 77]

Originally Posted by Warby12

There are no markings on any of them, all faded away. Four standard sized panels wired in parralel and six very small panels in series which are then added into the junction with the others.

Most small panels are still the same voltage as larger models so you cannot normally mix series and parallel conection in the way you describe.

The number of individual cells in the panel will give you some idea of the voltage. "12v" panels have 36 cells.

[john61ct]

I don't think PWM is designed to handle unmatched panels.

I'd be willing to bet investing in the right MPPT controller, panels configured serial/parallel by someone knowledgeable, will boost your end output.

In that situation sometimes just getting rid of the smaller mismatched panels will increase total output, without doing anything else.

Controller getting that hot is not good, maybe fire danger.

[Salty Mike]

Get yourself one of these so you can check the output of each individual panel. I got mine from Amazon. Is it the most accurate out there? Probably not, but at it's price if it falls into the drink it isn't a great loss.

Mine is Model UNI-T UT210E it is about 6 months old and working fine but I'm sure there is a newer cheaper model out by now.

[S/V Alchemy]

^^^ We have a winner. You are operating in a bit of a knowledge vacuum without knowing each panel's output. You may also have a series/parallel wiring issue of which you are unaware, or shorting out connectors (Mc-3 and MC-4, usually, unless it's just a splice job), etc., etc.

The best way to start might be to disconnect all but one panel over a lunch hour and see what each contributes. If the PMW doesn't get hot until a certain panel is reconnected, you have a suspect for "broken" or "too much".

[Warby12]

Thanks everyone

Here are some photos of the motley bunch which may help:

[dlymn]

all panels get hot just like the roof of your house gets hot in the sun. transforming light to electricity won't cool your panels. as panels get hotter, they become quite a lot less efficient in generating electricity. If you read the current, it will be less on hot days,but that is normal.

[newhaul]

Looks life,e you have 4 50 watt rigid panels with 6 20 or 25 watt flex panels mounted on the edge. So I would have to say you are well above the capability of the controller. 4x50 = 200 watts. And 6x20 = 120 watts or 6x25 =150 for a total of 320 or 350 watts or 25 amp. Definitely to small of a controller. And likely it isn't a pwm but an even older shunt type. First thing is to get actual power output figured out and then size an appropriate controller.
Personally with this array I would split it and run the bigger panels thru one 30 amp controller and run the smaller panels thru another controller.

[Warby12]

Thanks everyone

Really appreciate your help. I have disconnected the lot as the controller was dangerously hot. Then I will disconnect the little panels and run the big ones through the controller and check for heat. In the mean time I am ordering a 30amp Victron Light PWM controller. This is all my budget can fit at the moment and I will look at different set-ups, panel controller combinations.

Also with the individual panels separated I can use my multi metre (10amp limit) to check the out put).

Thanks for shedding light on this for me

[john61ct]

Most controllers can take input amps over their spec, it just means higher average output, peaks get wasted.

But going over the VOLTS rating can fry the controller, so make sure you verify that against the "open volts" listed for the panels.

You should have matched panels together per PWM controller, so now you have two you may be fine, long as their output matches, parallel them to your bank.

[sailorchic34]

Looking at the photos, the small panels are 4 cell panels. A single solar cell is roughly 0.55V. and amperage is based on area of cells, so each small panel looks to my eyes as 2 volts at possible 6 amps. It looks like you have 12.25V for the small panels and the larger panels standard 12V panel which output 17 volts.

I don't think the small panels will do much for you as their voltage output in series is roughly 12V +/- while the somewhat larger panels can and will produce up to 17 V.

I would dump the small panels or hook them to a separate PWM controller (or the one you have after you get another) and run it to the start battery. The issue is at 12.25V output, the voltage in the small cells is too low to really charge the battery.

You need at least 14.4V's for battery charging. (15V for 6v GC6 in sets of 2). Solar cells are temperature variable, so a higher cell temperature drops the output voltage. This is why 12V panels actually output 17 volts at 20C (68F) every 25 degree F rise in cell temperature, over 68 degrees, drops output voltage by roughly 1 volt. (varies depending on cell type.)