can i use a pwm and a mppt together?

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jimbob01
jimbob01 Solar Expert Posts: 63 ✭✭
Hi guys... im installing my new solar set up on my boat finally...
i have 3 pairs of 235w panels split in to 2 mppt mstar 45s
2 pairs in to one mppt
1 pair into the other
i have 2 banks of slightly different batteries with a change over switch
i have a few 80w panels left from my previous set up which are lower ocv
i also have the xantrex c 60 pwm left over from my previous set up
can i connect the 80w panels via the pwm and connect them in to the batteries alongside mppts?
thanks for your time . jim

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: can i use a pwm and a mppt together?

    Yes you can.
    How well it will work depends on the particular controllers involved especially how close you can get the Voltage set points to agree. The TriStars and the C60 should work together fairly well. There will be a 'difference of opinion' over actual battery Voltage and charge stage, but if you understand that the smaller panels and PWM controller are there to add current during the Bulk stage and allow the MPPT controllers to handle the more precise Voltage needs of Absorb and float it should all work.

    Remote temperature sensors will cause a bigger difference in the Voltage each controller 'sees' but are really a good idea for the Voltage stable Absorb and Float stages. In Bulk it doesn't matter much.

    Incidentally even among 'identical' controllers there are discrepancies, and the only way to get it to work '100%' is using MidNite Classics with the "follow me" function where there's one 'master' controller and the others take their cue from it.

    But over all multiple controllers, even of different types, do work.
  • WillBkool
    WillBkool Solar Expert Posts: 35 ✭✭
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    Re: can i use a pwm and a mppt together?

    I'm am going to have to do something similiar until I can save up for a large enough MPPT controller. So the thing is to set the 2 controller's voltages the same, or as close as possible, correct?
    1220 Watts, 4 Evergreen 120 watt, 1 Eoplly 190 watt; 1 Sungold 200 watt; 2 175 Watt; M-Star 15A MPPT; C40 PWM; 6 105 AH AGM Configured to 315@24V
    Cotek 1500 watt/24v
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: can i use a pwm and a mppt together?
    WillBkool wrote: »
    I'm am going to have to do something similiar until I can save up for a large enough MPPT controller. So the thing is to set the 2 controller's voltages the same, or as close as possible, correct?

    Yes, in theory.
    In practice you may have to adjust the Voltages to get the right charging performance; the target being to actually have the correct Absorb Voltage at the battery when the Absorb stage begins.
    So you may have to crank up the setting on one or the other or turn one down a bit so that both go to Absorb at close to the same time and Voltage. That's the most important set point.
  • jimbob01
    jimbob01 Solar Expert Posts: 63 ✭✭
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    Re: can i use a pwm and a mppt together?

    thanks cariboocoot.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
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    Re: can i use a pwm and a mppt together?

    I've used 3 different controllers from 3 different companies, 3 different designs together, all with little or no problems. The important thing is that at least one of the pair have fine adjustments for voltage settings etc, then take some time to match those settings as closely as you can. Do this and you'll be surprised at how well they play together. :D