MPPT or PWM solar controller

Jul 15, 2009
72
24
Bridgend south wales
Funster No
7,503
MH
PVC
Exp
12
im having trouble keeping my 2 leisure batteries topped up using my 100w solar panel it’s since we changed van and the new van has a compressor fridge.
Seen somewhere about the MPPT solar controller will keep the leisure batteries topped up in overcast weather better than the PWM controller,any thoughts would be appreciated
Thanks in advance for all your comments and advice
 
Jan 8, 2013
3,302
2,686
Dronfield - Derbyshire
Funster No
24,202
MH
Burstner Nexxo T660
Exp
7 Years
It seems compresser fridges are vey power hungry. It unlikely that an 100w solar panel will keep pace, even with the best controller in the world. What other demands do you have on the batteries? How big are your batteries?
 
Jan 11, 2018
350
124
Funster No
51,943
In my humble opinion, yes it will but the difference might not be enough to keep everything going.
I've not googled the difference but I seem to remember the difference is about 10% overall yield expressed as amp hours.
It is true that MPPT is more efficient in less optimum conditions.
 

hilldweller

LIFE MEMBER
Dec 5, 2008
31,890
31,873
Macclesfield
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5,089
MH
Swift Sundance 620FB
Exp
From Aug 2007
We have 200W panel and one battery, that works -- you need more solar.
 
OP
paulj
Jul 15, 2009
72
24
Bridgend south wales
Funster No
7,503
MH
PVC
Exp
12
Stealaway thanks for the reply our other power uses are tv 4hrs a day lights 5 hours per day and toilet and water pump.
So maybe have to get some more solar power on the roof then,I have 2 100amp leisure batteris
 
Aug 19, 2013
1,255
551
Wells, Somerset
Funster No
27,611
MH
Auto-Trail Tribute
Exp
since 2004
Previously I had a compressor fridge and 2 x 100watt solar panels, and 2 x 105 amp batteries. The first pair of batteries went in less than 2 years, but then I kept the fridge on more or less 24/7. That setup just about kept pace with the fridge. I now have an adsorption fridge, it's nothing like as heavy on the battery, but I did like the former fridges. Be careful if you buy a cheaper regulator that claims to be an MPPT, they seem to use it as a generic name, sometimes claiming it to be both pcm and mppt. I've had both types, presently have MPPT, no idea if they are worth the extra, but it seems to work well.
 
Last edited:
Mar 23, 2012
3,134
6,169
leicester
Funster No
20,245
MH
c class
Exp
1
I'm looking at fitting solar but may well go for a bigger panel and cheaper PWM regulator it looks like you may get more output than a smaller panel and MPPT one
 
Mar 23, 2012
3,134
6,169
leicester
Funster No
20,245
MH
c class
Exp
1
I would sooner spend my money on more/bigger panels than on any expensive controller that might give you 10% more charge.
Just what I'm thinking and although I haven't measured yet I think we will have plenty of room no TV/Satellite etc. Just wondering if I,m brave enough to fit myself worried about drilling the roof/sealing etc
 
Jan 8, 2013
3,302
2,686
Dronfield - Derbyshire
Funster No
24,202
MH
Burstner Nexxo T660
Exp
7 Years
Mine are only glued down with a Sikaflex. I would measure the gaps you have to fit them into. I just managed to fit 2x 125w panels. I did have to fit one right to front so fitted an aluminium shield at the front to stop the wind getting underneath it. They have been up there for over 3 years and 30,000 miles now. I bought mine second hand of Ebay for £60.00 each.
 
Nov 22, 2007
4,056
4,678
East Yorkshire
Funster No
900
MH
Rapido "A" Class, Mecedes
Exp
18+yrs plus 25+Towing
Just remember to ensure your controller can cope with the No of panels, I made the mistake of of fitting more panels to the R-V and BLEW the 20amp rated controller!.
 
Mar 30, 2016
354
565
Funster No
42,208
im having trouble keeping my 2 leisure batteries topped up using my 100w solar panel it’s since we changed van and the new van has a compressor fridge.
Seen somewhere about the MPPT solar controller will keep the leisure batteries topped up in overcast weather better than the PWM controller,any thoughts would be appreciated
Thanks in advance for all your comments and advice
Can I ask how many days off grid are you managing before you hit problems or can it not even cope with an overnighter, just trying to understand what kind of problem you are having
 
Mar 20, 2013
892
560
Kingdom of Fife
Funster No
25,172
MH
coacbuilt
Exp
newbie
You definitely need more solar, what ever controller you use. Yes MPPT controllers are meant to give more amps but it has been suggested that at low power levels such as found on boats and vans the benefits may not justify the cost.
 

Lenny HB

LIFE MEMBER
Oct 18, 2007
18,563
17,924
On the coast in West Sussex
Funster No
658
MH
Hymer B678 Dynamic Line
Exp
Since 2008 & many years tugging
I also have a Votronic MPPT regulator the higher output was even noticeable against the previous good MPPT regulator.
PWM regulators are OK if you only want it for summer use.
 
Sep 17, 2017
628
889
Birmingham, UK
Funster No
50,575
MH
Van conversion
Exp
2017
If every motorhoming day were perfect, i.e. a endless blue skys in the middle of summer, MPPT wouldn't give you much extra juice. However, because Blighty has clouds and we don't just holiday in July, MPPT can be quite handy.

My brother has two identical panels for his camping setup (he's a tenter.... eugh!). He recently upgraded from a cheap PWM charger to a Victron MPPT, so he did some experimenting with a panel attached to each. On sunny days, there was nothing in it. The PWM sometimes produced more energy, but we think that's just because it was being rougher on the battery or maybe the battery levels weren't the same. On cloudy days, or later in the day when the sun is lower in the sky, the MPPT was the clear winner. It kept on producing ~20% of the peak output whereas the PWM was giving nothing.

The best analogy I've got is that PWM is like an engine with only 6th gear. In ideal conditions, on a perfectly straight and flat road, PWM will give you top speed (maximum power). But if you hit a hill or more than a couple of percent (i.e. the sun is getting low), you're screwed and you stop. MPPT is like having a gearbox, so you can drop down a couple of cogs if you hit a hill (clouds) and still keep going, not as quick, but still keep going (and keep producing energy).
 
Jul 22, 2014
62
53
Cobram, 3644, Victoria, AUSTRALIA
Funster No
32,515
MH
Aust bus cnv, UK C, USA A
Exp
Since 1995
I am not surprised you are struggling with a compressor fridge and only 1 x 100 watt panel. In your situation I would be inclined to:
  • Add much more solar to the roof (eg another 200 watts at least)
  • Change your controller to MPPT for better efficiency in cloudy and partly shaded conditions.
I have added two 100 watt panels to increase our solar to 320 watts on our UK motorhome. Both additional panels are attached to the roof with Sikaflex 512 Caravan to PVC corner and side mounts without any screws into the roof as shown below.

IMG_20190504_125729-600x800.jpg
 
Sep 16, 2010
2,493
2,023
Bungay Suffolk
Funster No
13,734
MH
C Class
Exp
Since 2010
I know nothing about compressor fridges. don't they have a gas option ??
Genuine question.
We have 80watt of solar on the roof and a foldout 100watt panel, which can be angled to the sun to get maximum power. We also have 2 X Varta 105AH leisure batteries.
the first batteries lasted 3 1/2 years, we are always off grid so pretty good.
The 80 watt roof panel goes through the regulator in the Sargent 500 PCU and the 100watt fold out has a MPPT regulator on the panel and plugged straight into the 2 leisure batteries.
You really need your solar wattage to match your leasure battery AH.
Mitch.
 
Jul 22, 2014
62
53
Cobram, 3644, Victoria, AUSTRALIA
Funster No
32,515
MH
Aust bus cnv, UK C, USA A
Exp
Since 1995
We have a Waeco 210 litre compressor fridge/freezer in our motorhome in Australia. These units are dual voltage, ie. 12v & 24v. We run ours on 24v as there are greater efficiency with respect to wiring size and voltage drop. I would estimate I need at least 200 watts of solar to be available for the fridge, particularly in warmer climates.
 
Nov 12, 2015
449
180
Colchester
Funster No
40,159
MH
Dethleffs Esprit I7150 EB
Exp
Since 2016
I am not surprised you are struggling with a compressor fridge and only 1 x 100 watt panel. In your situation I would be inclined to:
  • Add much more solar to the roof (eg another 200 watts at least)
  • Change your controller to MPPT for better efficiency in cloudy and partly shaded conditions.
I have added two 100 watt panels to increase our solar to 320 watts on our UK motorhome. Both additional panels are attached to the roof with Sikaflex 512 Caravan to PVC corner and side mounts without any screws into the roof as shown below.

View attachment 302549
What is your battery set up with these please?
 
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