Test of cheap MPPT controller

[Timleech]

Gibbo said:-

Yes. You'll need a couple of voltmeters, a couple of ammeters and some good sunshine.

 

Run the batteries down a bit then switch everything off.

 

Measure the voltage at the batteries and the voltage coming from the solar panels. Let the solar panels charge up the batteries until the voltage at the solar panels is higher than that at the batteries (this may happen immediately) but the battery voltage is still lower than the regulation voltage of the solar controller. If this simply doesn't happen then it's not an MPPT.

 

Now measure the current going into the batteries and the current coming from the panels. If the battery current is higher than the solar panel current then it's an MPPT.

 

What you're looking for is a higher current at the batteries than is coming from the solar panels. Coinciding with this will be a higher voltage at the solar panels than at the batteries. Both have to be happening at the same time.

 

You have to be slightly careful in condemning one as not being MPPT (which is a trap that angry Ebay feebacker may have fallen into) because some controllers can take several minutes messing around before they actually find the correct tracking point which results in the above scenario of higher battery current than solar panel current.

 

Did that make sense?

 

 

Finally got around to this today, with a Wellsee controller and a 40W semi-flexible panel.

Battery is an old starter battery, it was left fully charged a couple of months ago, voltage before the test was 12.48.

 

 

Volts measured with two DMM, one only reads to 0.1V but the two were checked as being consistent with one another.

Current read with two old uncalibrated AVOmeters, these were swapped after a while in case the current discrepancy was a metering issue but results were the same.

After an hour, typical readings were (obviously with wild current fluctuation according to sunshine level)

 

Battery 13.13V

Current to battery 1.1A

 

Panel input to controller 13.4V

Current to controller 1.2A

 

Whatever the actual level, the current from the panel was about 0.1A higher than that into the battery, while the voltage at the panel was in the region of 0.3V higher than that at the battery.

 

It looks as though by Gibbo's criteria the controller is not working as claimed.

Any comments or other worthwhile tests?

Should I have started with a flatter battery?

 

When the panel is disconnected, the controller draws about 20mA. Is this to be expected?

The ultimate purpose of the panel and controller is to top up and maintain batteries on a boat which is likely to be left for a while from time to time with the batteries less than fully charged, including during winter months, but any contribution gained while the boat is in use will be welcomed. It'll actually be two panels on 24V, the controller is claimed to cover both 12 and 24V applications.

 

Even though it seems to have 'failed' the test, is this controller nevertheless still likely to be suitable for the job? If not, can anyone recommend another controller for the job which won't break the bank?

 

Tim

Edited June 20, 2011 by Timleech

[Nickhlx]

I am no expert on MPPT controllers, but I wonder if there is not enough "headroom" for it to be able to work in "MPPT mode" and select the maximum power point in the curve it is wanting to ?

 

This might be because of a number of things but a couple that come to mind are the solar array is not working in the "voltage window" the MPPT box needs to work properly, which could be either incorrect spec. of panels hooked up onto its input, or perhaps not enough sun, although the sun seems to be strong enough ( I assume that the panel was approx at right angles to the sun and no part shaded / broken, NOT as in the photo ?)

 

Nick

[Gibbo]

The sun appears to be behind your solar panel?

[Timleech]

I am no expert on MPPT controllers, but I wonder if there is not enough "headroom" for it to be able to work in "MPPT mode" and select the maximum power point in the curve it is wanting to ?

 

This might be because of a number of things but a couple that come to mind are the solar array is not working in the "voltage window" the MPPT box needs to work properly, which could be either incorrect spec. of panels hooked up onto its input, or perhaps not enough sun, although the sun seems to be strong enough ( I assume that the panel was approx at right angles to the sun and no part shaded / broken, NOT as in the photo ?)

 

Nick

 

The shadow is me with the camera

The panels were supplied by the same people as the controller, for use with one another (proves nothing, though!)

 

Edit - the voltage and current differences stay pretty much as they are whether full sun or cloud.

 

The panel is new, it does still have it's protective film over the cells but I wouldn't expect that to make a fundamental difference?

 

The sun appears to be behind your solar panel?

 

Not.

 

Must be a trick of the light

 

Tim

Edited June 20, 2011 by Timleech

[Gibbo]

Edit - the voltage and current differences stay pretty much as they are whether full sun or cloud.

 

That would sort of imply that it's not MPPT

 

But....

 

If it is designed for both 12 and 24 volt how does it know? Is there a switch for this?

[Timleech]

That would sort of imply that it's not MPPT

 

But....

 

If it is designed for both 12 and 24 volt how does it know? Is there a switch for this?

 

No switch.

 

I just checked it again, and moved the panel round for peak sun, the currents started oscillating and the panel volts went up to about 20. I'm guessing that it was doing its regulating bit, but the battery volts were only about 13.2 & the current around .5A. It did that for a bit & then went back to a steady higher current & lower panel volts.

 

I'll try putting a substantial load on the battery, see what that brings.

 

Tim

[Evo]

That controller looks exactly the same as the cheap £13 one I've got...except its in a white box. Thats not an MPPT or whatever its called.

 

solar controller

Edited June 20, 2011 by Evo

[Robin2]

No switch.

 

I just checked it again, and moved the panel round for peak sun, the currents started oscillating and the panel volts went up to about 20. I'm guessing that it was doing its regulating bit, but the battery volts were only about 13.2 & the current around .5A. It did that for a bit & then went back to a steady higher current & lower panel volts.

 

I'll try putting a substantial load on the battery, see what that brings.

 

Tim

 

I think it would be a good idea to write down what numerical results are expected. For example I bought a small Maplin 1.5w solar panel for testing. It says it produces maximum power at 17.5v and I joined up a few resistors to put a suitable load on it and it did produce the expected 86mA at 17.5 volts in bright sunlight.

 

I know it would be ridiculous to connect an MPPT controller to a 1.5w panel but if I did I expect it would load that panel up to 17.5v in order to get maximum power and then convert the 86mA at 17.5v into (say) 107mA at 14v to charge the battery.

 

I presume the data for your solar panel gives the voltage and current values at which it produces its rated power.

[Roger Gunkel]

The output voltage from the panel seems low if it is sitting generally at 13.** volts. My two 100w panels seem to output from 17-21v in sunlight, and I just set up my Maplin suitcase 13w panel and that was giving 14.5v into a battery showing 12.3 volts.

 

Any small area of the panel shaded, could have a big effect on the output voltage.

 

Roger

[Proper Job]

That controller looks exactly the same as the cheap £13 one I've got...except its in a white box. Thats not an MPPT or whatever its called.

 

solar controller

The 'PWM' on the front of it gives it away

[Evo]

Mine is doing exactly as you said you require and its doing it brilliantly. I went to the boat yesterday having not been for over a month an all batteries were reading 14.5v and charge controller was flicking in and out. It will do what you want it to do for £13

[WotEver]

The 'PWM' on the front of it gives it away

Indeed, but assuming that OP's is this one it does state that his is indeed MPPT.

 

Tony

[Timleech]

Indeed, but assuming that OP's is this one it does state that his is indeed MPPT.

 

Tony

 

That's the one.

 

I tried it briefly on another battery, similar results, but on reconnecting to the first one it did show a higher output current than input for a minute or so, then back to 'normal'. I'm going to try hooking the two panels together, as well as partially discharging a smaller battery prior to trying that.

It's clouding over now, though

 

 

Tim

[Proper Job]

Indeed, but assuming that OP's is this one it does state that his is indeed MPPT.

 

Tony

That's the same as I've got, but without the 'wellsee' bit on it.

 

It works as a controller (whether MPPT or not)

[Nickhlx]

What is the open circuit voltage of each panel and are they in series or parallel ?

 

Nick

[Timleech]

What is the open circuit voltage of each panel and are they in series or parallel ?

 

Nick

 

Curiouser and curiouser.

 

I've tried the two panels in series.

First on the original 12V battery. I did put a load on it for a while, hence the lower volts.

 

 

In full sun:-

 

Panel volts at controller 13.2

Panel amps 2.0

Battery amps 2.0

Battery volts 12.85

 

Edit to correct the above voltages slightly

 

Then with two batteries in series (one a 35Ah which I had run down with a 14A load for half an hour)

 

Panel volts 25.9

Panel amps 2.0

Battery amps 2.0

Battery volts 25.4

 

Then with the smaller, partially discharged, battery on its own, still with two panels in series:-

 

13.1

2.0

2.0

12.6

 

I'll check the open circuit voltages later.

 

Tim

Edited June 20, 2011 by Timleech

[Nickhlx]

Curious indeed !

 

Forgive me If I am asking the obvious, but I don't know your level of abilities and wonder if we are all considering the terms series and parallel in the same way, and there is no possibility of the panel being ambiguous as to which side should be facing the sun ? Some of the results that are being listed suggest something is wrong

 

Series for me, means, e.g. with the panels that the positive of one connects to the negative of the other and the remaining two wires are the supply to the MPPT controller. This should be

double the voltage of each when not connected to anything, and about 18 volts when the panel is in sunlight. Series connecting them will make that about 36 volts.

 

A "12V" panel should read about 18 volts open circuit in sunlight, and separately, should read about 8 amps short circuit current flowing if you put an ammeter across it.

 

Nick

 

 

 

 

[Evo]

Argh sorry about that, was talking crap..completely different thing.

So are you saying you dont believe what it says on the box ? Why the testing ?

[Timleech]

What is the open circuit voltage of each panel and are they in series or parallel ?

 

Nick

 

Reted OCV 21.7V per panel.

Actual OCV today about 40.7 for the two together.

 

Tim

[Proper Job]

Argh sorry about that, was talking crap..completely different thing.

So are you saying you dont believe what it says on the box ? Why the testing ?

Someone a while back questioned the fact that cheap MPPT controllers cannot possibly work as MPPT controllers because they are cheap

 

(I'm pretty sure that just about summed it up?)

[Timleech]

Curious indeed !

 

Forgive me If I am asking the obvious, but I don't know your level of abilities and wonder if we are all considering the terms series and parallel in the same way, and there is no possibility of the panel being ambiguous as to which side should be facing the sun ? Some of the results that are being listed suggest something is wrong

 

Series for me, means, e.g. with the panels that the positive of one connects to the negative of the other and the remaining two wires are the supply to the MPPT controller. This should be

double the voltage of each when not connected to anything, and about 18 volts when the panel is in sunlight. Series connecting them will make that about 36 volts.

 

A "12V" panel should read about 18 volts open circuit in sunlight, and separately, should read about 8 amps short circuit current flowing if you put an ammeter across it.

 

Nick

 

Absolutely no doubt about which way round, the reverse is plain aluminium.

As I have said, the clear protective film is still in place on the panels, no doubt that will reduce the output a bit but I wouldn't expect it to matter for this experiment.

 

I do know a little bit about series & parallel

 

Tim (Bsc(Eng) Elec Eng Power systems, albeit 40 years ago & mostly forgotten!)

 

Argh sorry about that, was talking crap..completely different thing.

So are you saying you dont believe what it says on the box ? Why the testing ?

 

The seller had one ebay feedback (among many sales)saying they had tested one & it wasn't MPPT.

I needed a controller anyway so decided to take a chance & experiment for myself.

 

Tim

[Nickhlx]

Absolutely no doubt about which way round, the reverse is plain aluminium.

As I have said, the clear protective film is still in place on the panels, no doubt that will reduce the output a bit but I wouldn't expect it to matter for this experiment.

 

I do know a little bit about series & parallel

 

Tim (Bsc(Eng) Elec Eng Power systems, albeit 40 years ago & mostly forgotten!)

 

 

 

The seller had one ebay feedback (among many sales)saying they had tested one & it wasn't MPPT.

I needed a controller anyway so decided to take a chance & experiment for myself.

 

Tim

 

 

I had to ask, as some of the feedback wasn't what I was expecting... and some people probably get it wrong...

 

Like you I wouldn't have thought the film would make much difference, but would remove to ensure it is not having any effect.

 

I wonder if the panel(s) have high internal resistance and are unable to provide any significant current (power) - if there is a faulty cell and all the current is trying to "funnel" through a small percentage of a cells area, this could be causing the problem - again, unlikely in 2 separate panels, unless they are sold as "faulty" and this is the problem with them..

 

Nick

[Timleech]

I had to ask, as some of the feedback wasn't what I was expecting... and some people probably get it wrong...

 

Like you I wouldn't have thought the film would make much difference, but would remove to ensure it is not having any effect.

 

I wonder if the panel(s) have high internal resistance and are unable to provide any significant current (power) - if there is a faulty cell and all the current is trying to "funnel" through a small percentage of a cells area, this could be causing the problem - again, unlikely in 2 separate panels, unless they are sold as "faulty" and this is the problem with them..

 

Nick

 

I know less than bu**er all about solar panels First time I've had anything to do with them.

I suppose one faulty cell might limit the power when in series. No they weren't sold as faulty or seconds etc.

They're supposed to be 40W panels, so 2A at 12V is about 2/3 of that. That's in strong sun, something does seem to be limiting output to 2A or a touch above.

The controller seems to cut off at around 13.5V (on 12V), seems a bit low to me?

The controller is designed for the 'load' to go to the controller rather than the battery, but there's a 20A limit on that so not useful for general boaty loads. I wonder whether that's relevant here?

 

Would it be worth trying connecting the panels direct to the battery & measuring the result?

 

Tim

[Nickhlx]

I know less than bu**er all about solar panels First time I've had anything to do with them.

I suppose one faulty cell might limit the power when in series. No they weren't sold as faulty or seconds etc.

They're supposed to be 40W panels, so 2A at 12V is about 2/3 of that. That's in strong sun, something does seem to be limiting output to 2A or a touch above.

The controller seems to cut off at around 13.5V (on 12V), seems a bit low to me?

The controller is designed for the 'load' to go to the controller rather than the battery, but there's a 20A limit on that so not useful for general boaty loads. I wonder whether that's relevant here?

 

Would it be worth trying connecting the panels direct to the battery & measuring the result?

 

Tim

 

 

I would definitely try connecting them to the batteries, initially singly and then in parallel - not in series though as that would be deliberately wasteful - this should give around 2 amps in good sunlight, as it won't be operating at its MPP which I would expect to be around 18 volts on a 21 volt panel, and 2 or 3 amps for even a long time won't hurt the batteries ( assuming around 110 Ah).

 

Better controllers do cut off (fold back) when sensing a near fully charged battery to avoid overcharging them, so a cheaper one may not.

 

I would have thought that if your box is working as it should, with one "40 watt" panel, you should be seeing around 18 volts from the panels at around 2 amps, and around 13.5 to 14.5 volts on the battery at around 2.5 amps ( i.e. MORE current at less volts) - the controller should waste little.

 

The way panels are constructed is that all the cells could be in series within, or there may be two strings of half the number of cells each. Cells produce around 0.5 to 0.55 volts each, so 21 volts would be 40 odd cells, and ALL in series - shading even half of one cell, e.g. with a wet leaf, will seriously limit output to maybe 25% to 50% of its potential, and could (will?) damage that cell through overheating with all the current trying to get through a small portion of it.

 

 

I don't know if you have access to a bench PSU, but if you could get one and power the MPPT controller from it instead of the solar panel, set the current limit to say 3 or 4 amps and slowly crank the volts up, comparing ( plotting ?) the volts and current from the power supply (i.e. power) with the volts and current on the battery, the result should reveal whether the controller is working. It might take a few seconds / minutes with the output from the PSU at say a constant 18 volts, for the current being fed to the battery to reach a maximum.

 

Nick

Edited June 20, 2011 by Nickhlx

[Justme]

Take the film off.