Changing solar controller - MPPT vs PWM (1 Viewer)

Aug 27, 2014
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My van came with a panel (I think it's only about 100W) already fitted, but I'd found it was giving a couple of problems with not enough output.

Firstly, since buying a compressor coolbox, I'd found that even in the midst of summer it wasn't quite giving enough power to keep up - after 3-4 days the leisure batteries (2 x 100A/H) were running down.

Secondly, where the van is parked on my drive it is in shade for pretty much all of the day - in winter, the solar panel wasn't giving enough output to keep the van batteries fully topped up.

Having a PWM type controller, and having read in a few different places that the MPPT type are better, as I do struggle a bit for payload I thought I'd try changing the controller before adding any more panels - the old controller would have to be changed anyway. Fitted a MPPT one yesterday, I can see the difference already - on the old controller it would be reading maybe 0.1 or 0.2 amps this morning (cloudy, van in shady position), on the new one it's reading 0.8 amps.

Hopefully, problem solved!

https://www.bimblesolar.com/beginnersguide#mpptpwm
 

DBK

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Did you size the controller to allow a second panel to be fitted later? I think you will have a lot more "stamina" with 200W. :)
 
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My van came with a panel (I think it's only about 100W) already fitted, but I'd found it was giving a couple of problems with not enough output.

Firstly, since buying a compressor coolbox, I'd found that even in the midst of summer it wasn't quite giving enough power to keep up - after 3-4 days the leisure batteries (2 x 100A/H) were running down.

Secondly, where the van is parked on my drive it is in shade for pretty much all of the day - in winter, the solar panel wasn't giving enough output to keep the van batteries fully topped up.

Having a PWM type controller, and having read in a few different places that the MPPT type are better, as I do struggle a bit for payload I thought I'd try changing the controller before adding any more panels - the old controller would have to be changed anyway. Fitted a MPPT one yesterday, I can see the difference already - on the old controller it would be reading maybe 0.1 or 0.2 amps this morning (cloudy, van in shady position), on the new one it's reading 0.8 amps.

Hopefully, problem solved!

https://www.bimblesolar.com/beginnersguide#mpptpwm
The link you give for a
"PWM vs MPPT Charge Controller Test" they don't even tell you how large the solar panel are. :rolleyes:
 

two

Aug 4, 2011
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Very interesting. That's a bigger difference than I'd expect. Hope you're not trying to kid yourself that it's money well spent.
I agree with DBK. If you want more power, you need more collectors. I wouldn't expect MPPT to have such a significant improvement on PWM overall but it'll be interesting to see.
The best way to compare would be to run two identical systems side-by-side over a period of time, but I'm not sure if anyone's done that. Maybe the Centre for Alternative Energy (Powys) has done something.

EDIT:
Just noted the link. So there has been a test but I'm a little doubtful about the conclusions. I'd trust the CAT - I think they'd be a bit more scientific and have no vested interest.

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Feltwell
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Yes, I bought a MPPT type that is large enough to cope with an extra panel. I would have had to replace the old one anyway if buying an extra panel, it was only rated high enough for one.

So this is a first step really - just replace the controller and see if it gives the slight boost I need, if not I'll have to add an extra panel as well.

We're not big users of electricity - lights are all LED now, the TV hardly gets used at all, no hairdryers or coffee makers or any other power hungry gadgets. The only exception is the compressor coolbox - it's a luxury, but with 2 adults + 3 kids in the van the fridge is always full, just nice to have somewhere extra to keep soft drinks cold in summer.

I may get away with just the controller - we don't tend to stay on site for more than a couple of days without going out somewhere in the van. Only time will tell!
 

DBK

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Yes, I bought a MPPT type that is large enough to cope with an extra panel. I would have had to replace the old one anyway if buying an extra panel, it was only rated high enough for one.

So this is a first step really - just replace the controller and see if it gives the slight boost I need, if not I'll have to add an extra panel as well.

We're not big users of electricity - lights are all LED now, the TV hardly gets used at all, no hairdryers or coffee makers or any other power hungry gadgets. The only exception is the compressor coolbox - it's a luxury, but with 2 adults + 3 kids in the van the fridge is always full, just nice to have somewhere extra to keep soft drinks cold in summer.

I may get away with just the controller - we don't tend to stay on site for more than a couple of days without going out somewhere in the van. Only time will tell!
We use a compressor coolbox to supplement our small fridge too. We could have had a bigger fridge but we wanted an oven so had to compromise. It fits between the front seats when we stop. As you can see below it tends to be used for bulky salad stuff but if you look closer there are booze hints! As an aside, this image was stored in the "cloud" in Google photos and I just had to search for "refrigerator" and this is what came back. Very impressive.

DSC_0194.JPG
 
OP
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Feltwell
Aug 27, 2014
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Looks like you've got the same one we have. I took the basket out - not sure what it does except reduce the available space! I have noticed the little section at the back definitely isn't as cold as the main section.

We too have it between the seats, but permanently in our case - stops me going from the cab into the back of the van, but it was always a squeeze, (fixed overcab bed + tall and none-too-svelte driver...) I tended to get out and come back in the hab door anyway.

It does use more power than I thought it would - we had a cheapie thermoelectric coolbox before, I thought the new one would be a lot better, never measured it but I'm not convinced that it is. Works much better though at keeping everything cold.
 

funflair

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Very interesting. That's a bigger difference than I'd expect. Hope you're not trying to kid yourself that it's money well spent.
I agree with DBK. If you want more power, you need more collectors. I wouldn't expect MPPT to have such a significant improvement on PWM overall but it'll be interesting to see.
The best way to compare would be to run two identical systems side-by-side over a period of time, but I'm not sure if anyone's done that. Maybe the Centre for Alternative Energy (Powys) has done something.

I have run two side by side and I would agree with the 25% to 30% claims,



Martin
 
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Lenny HB

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Even MPPT Regulators vary quite a bit. We had a good one but I wanted one that gave a proper absorption charge for my Gell batteries so I changed it for a Voltronic one. The last one was good the Votronic is even better.

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funflair

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Even MPPT Regulators vary quite a bit. We had a good one but I wanted one that gave a proper absorption charge for my Gell batteries so I changed it for a Voltronic one. The last one was good the Votronic is even better.
Voltronic not to be confused with Votronic(y)

Martin
 

two

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It's generally accepted that MPPT are more efficient than PWM, but when I see quotes which include the words "up to" I become suspicious. If the choice was a "no brainer" I wouldn't expect so many PWM controllers to be still on the market.
In the scheme of things, I think it's cheaper to add 30% more panel than go the MPPT route but then you may be limited by roof space or payload.
I don't have any solar on the current van as I have not yet found a need for it. But, if I did, I confess that I'd prefer a good MPPT controller.
 

two

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Bit off-topic, but continuing on the use of a coolbox, I'd try to store it in a cool place.
Under the van is probably best. Surrounded by glass in the cab does not seem to be the best of places to put one (I assume they're used in Summer most of the time).
 

canopus

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If you do upgrade your solar panels, and charge controllers, don't forget to consider the CSA of the cable from the solar panels to your controller/battery bank. Motorhome manufactures tend to install the minimum sized cable they can get away with.

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MPPT doesn't produce much more peak power than PWM. The difference is when light is less than optimal, PWM produces nothing and MPPT will keep trickling power in.
 
Jul 13, 2008
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I don't see that the panel size matters when the quote a %gain/loss.

Martin
I was always lead to believe a MPPT controller isn't worth it unless you have at least 200 watts solar. So looking at the difference I presume the "test" is at least 200W if not more.
 

Lenny HB

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MPPT doesn't produce much more peak power than PWM. The difference is when light is less than optimal, PWM produces nothing and MPPT will keep trickling power in.
True but that's when you need every bit of power you can get.
I was always lead to believe a MPPT controller isn't worth it unless you have at least 200 watts solar. So looking at the difference I presume the "test" is at least 200W if not more.
It's a percentage gain at low light levels size of panel irrelevant.
 
OP
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On the unscientific "1 day so far" test result here in less than optimal light, it's definitely trickling in more power than the old controller. I'll see in a few weeks if it's enough so I can stop needing to plug the van into EHU every few weeks.

As for the "height of summer", alas we're staying in the UK this year - if we get a break in the drizzle I'll let you know ;)

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Jun 30, 2011
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We use a compressor coolbox to supplement our small fridge too. We could have had a bigger fridge but we wanted an oven so had to compromise. It fits between the front seats when we stop. As you can see below it tends to be used for bulky salad stuff but if you look closer there are booze hints! As an aside, this image was stored in the "cloud" in Google photos and I just had to search for "refrigerator" and this is what came back. Very impressive.

View attachment 284274


John in our Murvi we had the bigger fridge and the oven was above at head height.
 

funflair

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MPPT doesn't produce much more peak power than PWM. The difference is when light is less than optimal, PWM produces nothing and MPPT will keep trickling power in.
When I was running MPPT and PWM side by side I got at least 25% more from the MPPT in all conditions, my MPPT is Votronic and the PWM an old morningstar.

Martin
 

funflair

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I was always lead to believe a MPPT controller isn't worth it unless you have at least 200 watts solar. So looking at the difference I presume the "test" is at least 200W if not more.
I guess that is just cost based rather than performance.

Martin
 

funflair

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It's generally accepted that MPPT are more efficient than PWM, but when I see quotes which include the words "up to" I become suspicious. If the choice was a "no brainer" I wouldn't expect so many PWM controllers to be still on the market.
In the scheme of things, I think it's cheaper to add 30% more panel than go the MPPT route but then you may be limited by roof space or payload.
I don't have any solar on the current van as I have not yet found a need for it. But, if I did, I confess that I'd prefer a good MPPT controller.
Our van came with 1x80 watt panel and PWM controller I then added 3x80 watts and MPPT controller, over a few years of watching in all conditions the PWM never made 1/3 of the MPPT set up indeed it was about 25%or 30% behind, so just out of interest I changed the PWM for MPPT and it now reliably shows 1/3 of it's big brothers output.

Yes for the money I spent on the smaller Votronic MPPT controller I would have got more power putting another panel up but that wasn't the point of the exercise.

Possibly not very scientific but good enough for me to say MPPT all the way.


Martin
 
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changing the controller will give you a 10 per cent increase but adding a second panel will give you a hun red percent increase and the outlay will be similar or less assuming your existing controller is big enough and you have the roof space
 
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True but that's when you need every bit of power you can get.

It's a percentage gain at low light levels size of panel irrelevant.
Ok, so one 18V panel might convert a very small amount of volts to amps, where two panels wired in series making 36V is going to give you a lot larger gain in amps?
 

Lenny HB

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Ok, so one 18V panel might convert a very small amount of volts to amps, where two panels wired in series making 36V is going to give you a lot larger gain in amps?
Wired in series they are slightly more efficient but if one panel gets some shade you loose all your output. If wired in parallel if one panel gets shaded you still get full output from the other panel.
Parallel is the only sensible option for a Motorhome

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