MPPT or PWM solar controller

Discussion in 'Motorhome Chat' started by paulj, May 9, 2019.

  1. paulj

    paulj Funster

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    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
     
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  2. Stealaway

    Stealaway Funster

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    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?
     
  3. Jake Royd

    Jake Royd Funster

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    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.
     
  4. hilldweller

    hilldweller Funster Life Member

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    We have 200W panel and one battery, that works -- you need more solar.
     
  5. paulj

    paulj Funster

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    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
     
  6. Dorwyn

    Dorwyn Funster

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    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: May 9, 2019
  7. The Wino

    The Wino Funster

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    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
     
  8. Stealaway

    Stealaway Funster

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    I would sooner spend my money on more/bigger panels than on any expensive controller that might give you 10% more charge.
     
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  9. The Wino

    The Wino Funster

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    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
     
  10. funflair

    funflair Funster Life Member

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    I fitted Votronic MPPT solar regulator and on test against PWM I get the extra 30% claimed by the manufacturers, extra solar panels are great but I would go the whole hog and fit the better regulator as well.

    Martin
     
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  11. Stealaway

    Stealaway Funster

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    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.
     
  12. PeteH

    PeteH Funster

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    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!.
     
  13. Reliant

    Reliant Funster

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    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
     
  14. maxi77

    maxi77 Funster

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    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.
     
  15. Lenny HB

    Lenny HB Funster Life Member

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    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.
     
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  16. Guigsy

    Guigsy Funster

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    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).
     
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  17. OZeRV

    OZeRV Funster

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    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
     
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  18. jenny and mitch

    jenny and mitch Funster

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    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.
     
  19. Lenny HB

    Lenny HB Funster Life Member

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    Nope, same principle as a domestic fridge except the motor driving the compressor is 12v.
     
  20. OZeRV

    OZeRV Funster

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    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.
     
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