MPPT pickle- reconnection needed

lazza Solar Expert Posts: 336 ✭✭✭
HI Forum

Well i'm in a right pickle with an installation.

It has 8 x 245Wp Trunsun panels (36Voc, 30Vmp). It is a system upgrade, which was originally put with a 24V PWM Xantrex C60 charge controller, obviously not ideal for this kind of installation.

So we put in a hybrid inverter with a built-in MPPT which supposedly takes up to 145Voc. As 4 of these panels in series gives 144Voc, i presumed this wiring was ok, so they are wired up in two parallel strings of 4 (4x1, 4x1). However, having just spoken with the technical service department of the supplier, they said that as the MPPT voltage range is 60-115Vdc, that this wiring could blow the MPPT as 4x30Vmp from the panels gives 120Vdc. Their solution is to wire it in series of 3.

- So, firstly, is this correct? Could this blow the MPPT even though it is within the range for Voc??

. If so, as there are only 8 panels, could I keep 4 in series and then put 2 parallel series of 2 (4x1 and 2x2). These combined would give the equivalent voltage of 108Voc and 90Vmp?? (would make the ones in parallel work at too high a voltage??)

Arrghh what a disaster, any assistance much appreciated



  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: MPPT pickle- reconnection needed

    Or yet another example of why all-in-one units aren't such a good idea.

    I doubt it would "blow the MPPT" but obviously if the thing stops working at 115 (ridiculously low) there's no point in running an array with a Vmp of 120. Also keep in mind that should you get cold temperatures the array Voltages will be even higher.

    You can't parallel strings of two different Voltages.

    So with eight panels you're stuck: two strings of three giving 108 Voc / 90 Vmp and two panels left over unless you can find and fit a ninth identical panel.

    Or buy a decent MPPT charge controller and don't use the built-in one which frankly is badly designed. But that's another $500 or so.