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earlvillestu's avatar
earlvillestu
Explorer
Nov 19, 2013

PWM or MPPT?

I just took delivery of a 120W portable solar panel from SolarBlvd, which I will use to charge a single AGM Group 31 with an AH capacity of 105. We have a popup and are minimal electricity users, so I believe this will meet our needs.

The panel specs are Vmp 18.0, Imp 6.67, Voc 22.7, Ioc not specified. I plan to ditch the cheesy supplied controller and put a 3-stage adjacent to the battery.

My question is, would there be a significant benefit to buying an MPPT controller over a good PWM? I know that if I expand the number of panels in the future, there are benefits to MPPT, but assuming I'm planning to stay with the current setup, is it worth the substantial extra cost?

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  • BFL13's avatar
    BFL13
    Explorer II
    Nov 19, 2013
    A 120w panel usually has an Isc around 7.6a, so you can expect that with PWM when it is pointed at the sun, when the sun is high enough on a clear day.

    The rule is to have a 20% margin over that in controller size for when you get more than rated amps (happens), so that means another 1.5a for 9.1 so a 10a controller should be ok.

    There are dozens of 10 or 20a PWM controllers on ebay for under $20, and some have free shipping. they work just fine as several forum members have reported, including me.

    MPPT with a 12v 120w panel will get you maybe another part of an amp above that 7.6. Don't even bother. :)
  • JiminDenver's avatar
    JiminDenver
    Explorer II
    Nov 19, 2013
    In this instance I don't believe you would see enough benefit for the extra you would spend for a MPPT controller.

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