PWM charge controller

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I had a Steca PR1010 failing and so I tried to repair it.

The problem looks to be a shorted mosfet. What made me think is the power circuit of this controller.

There are 4x 75329P mosfets inside:

1 - short-circuit the solar panel
2 - connect the solar panel to "BUS"
3 - connect battery to "BUS"
4 - connect load to "BUS"

So the question is: what is the purpose of the mosfet 1? What can be the use of shorting the solar panel?

Regards,
Nuno

Comments

  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
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    Re: PWM charge controller

    That is how some of the smaller shunt type controllers work - instead of cutting off the flow from the panel to the battery, they short the panels out enough to shunt all or part of the current before it gets to the batteries.
  • nunojpg
    nunojpg Registered Users Posts: 3
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    Re: PWM charge controller

    Why doesnt it simply disconect and connect the panel with pwm modulation? Is there any disadvantage?
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
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    Re: PWM charge controller
    nunojpg wrote: »
    Why doesn't it simply disconnect and connect the panel with pwm modulation? Is there any disadvantage?

    Simplicity, cheap, easy, and the end result in charging the batteries is the same.
  • nunojpg
    nunojpg Registered Users Posts: 3
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    Re: PWM charge controller

    I dont see how having a mosfet in series is more complex than in parallel.
    I see that a shunt regulator can have optimum (without a voltage converter - MPPT) performance because there is "zero" resistance on the charging path, but this controller have a mosfet in parallel and two mosfets in series to the battery.

    I believe this might be to protect from solar panel reverse polarity connection..
  • BB.
    BB. Super Moderators, Administrators Posts: 33,522 admin
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    Re: PWM charge controller

    It also may reduce the "Inductive Kick" of the wiring. Turning current off with a "fast" transistor and long wiring can create quite a voltage spike. Shunting simply diverts the current from the battery to the bypass MOSFET without needing an extra diode and/or capacitor to absorb the voltage spike. (Just a guess).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
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    Re: PWM charge controller

    There is a good description here of the major differences and pros and cons http://www.solorb.com/elect/solarcirc/shuntreg1/

    Nearly all of the early charge controllers were shunt type. For one reason, at that time solar was very expensive, small wind was cheap.