Positive ground controllers?

machineman
machineman Solar Expert Posts: 129 ✭✭✭
in General Solar Power Topics #1
What's up with these low cost positive ground controllers, What is the purpose of positive ground and can a positive ground controller be hooked up normally; panel + to controller +, and load + to controller +.

https://www.renogy-store.com/10-amp-charge-controller-p/ctrl-pwm10.htm

Thanks..

Off Grid Cabin, 24V 440ah 6V GC battery bank, Xantrex MPPT60-150 CC, Magnum MS4024 inverter-charger, >1200w Solar bank

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Positive ground controllers?
    machineman wrote: »
    What's up with these low cost positive ground controllers, What is the purpose of positive ground and can a positive ground controller be hooked up normally; panel + to controller +, and load + to controller +.

    https://www.renogy-store.com/10-amp-charge-controller-p/ctrl-pwm10.htm

    Thanks..

    Yes, but no.

    Very few systems will be positive ground. Only some panels require it, and for the most part it is only used in the telecom industry. A few controllers can be used either way.

    My advice is to avoid these.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,685 admin
    #3
    Re: Positive ground controllers?

    Positive ground is common for Telecom systems. Basically, if there is a nick in the insulation, the exposed wire will not be positive to the "earth" (dirt, etc.). and will not "plate" out the copper from the wire.

    I am not quite sure why this is "positive ground" charge controller... More or less, as I understand, if there is no additional communications/control input/outputs, it really does not matter too much how the battery is grounded (i.e., RS 233 circuits and such use a common ground for communication reference voltage... If you "reverse" the grounding of the controller, then your ground reference (for example) will not be zero volts, but -12 or -24 volts instead.

    There is one other reason that it could matter for this controller... It has "low control/timer" circuit. Normally, you would put the "switch" in the "Hot" lead with respect to ground... So a negative ground controller would have the "Switch" in the positive lead.

    A positive ground controller should have the switch in the negative lead. That way, then the controller "turns off" the circuit, there are not "hot leads" with respect to ground at the load.

    Similarly, if there is a short circuit detection/protection circuit, you would normally want that to be in the "hot" relative to ground wiring too.

    Is that what they did here? I do not know.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #4
    Re: Positive ground controllers?

    Many/most of the cheap 10A PWM controllers ive seen are common positive. Its just a cheap/lazy MOSFET configuration. If you take it apart youll see that the load positive ,pv positive, and batt positive are joined by a fat copper trace. However for a floating/ungrounded system it matters not the slightest. You just dont want to go grounding the negative or joining the load and batt negatives. That wont be pretty. For small systems like that floated is pretty common, as theres no high voltages anywhere.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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