Can I run 2 MPPT controllers from the same solar array? One for 12V and one for 24V.

[spudboy]

I've got 6 x 100W panels, which I've wired up as 3 pairs, so I am getting about 40V open circuit.

I combine all 3 pairs into a single input into my MPPT, so the 3 pairs are paralleled.

I have 12V and 24V batteries that need charging. Can I share the solar panel input across to a 2nd MPPT?

So what I'd have is 2 MPPT controllers 'sharing' the 600W input feed, but one feeding 12V and the other feeding 24V batteries.

Would it be the case that:

When both 12V and 24V batteries need charging, the amps are split across the 2 MPPT controllers so they might get half each perhaps
Let's say the 24V batteries become fully charged, so the 24V MPPT controller will not suck in so much power, as it has finished charging, so basically all the amps will go to the 12V system


Is this automatically 'self balancing' and a brilliant way to hook things up, or will I have trouble?

Thanks
David

[DeeJay]

I think it would work as you say.
I have 3 strings of solar panels feeding in to 18x 105 amp batteries via 3x 85 amp controllers. The controllers are attached to different batteries (various distances between Pos & Neg.
The panels cop the maximum sun at different times & it all evens out with charging, so the principle is the same.
Cheers, David

[spudboy]

OK - thanks for that information. That's one positive vote for that theory!

[DeanoH]

Solar panels are funny devices, their output voltage is dependent on the load applied. At one end of the scale with no load (o/c) their voltage is maximum (Voc) with zero current and at the other end of the scale with a s/c on the panel you can measure its maximum current (Isc) at zero output voltage.

What a MPPT regulator does is vary the load on the panel so as to obtain maximum power output. It does this by varying the load so that the panel voltage runs at or around its most efficient or maximum power output voltage (Vmp).

If you have two independent MPPT regs connected to one panel array both regs will be varying their loads in an uncoordinated manner to reach Vmp and they will end up 'chasing their tails'.

IMO you will be better off having two arrays, one for the 12 volt battery and one for 24 volt battery. The solar panel (power) allocation per array will depend on the 12 volt and 24 volt load. Whilst this may not give best utilisation of the maximum possible array power output it is simple and basically foolproof.

eg.With a Voc of 40 volts per panel pair you could have one pair of panels feeding each reg (as long as max reg input voltage is >40 volts) with the third pair of panels able to be switched between each reg input depending on where the power is needed.

Another solution could be to run a single 24 volt array feeding both the vehicle 24 volt battery and a 24 volt house battery with a 24 volt to 12 volt 'converter' feeding a small 12 volt battery (for regulation and backup) to run whatever 12 volt only devices you have. It all depends on what auxiliary load can run on 24 volts instead of 12 volts. ie. most Engel and Waeco fridges run OK on 24 volts.

Deano :)

[Blknight.aus]

it would work with dumb as a post regulation and very closely to how you describe however MPPT regulators will interfere with each other a little for the reasons Deanoh described.

I think it would work but from what I recall from your setup your primary usage is your 12V side and the 24V side just needs to deal with the vehicles accessories.

what I would do is (ignoring convert everything to one voltage preferably 24v) put all your charge amps into the 12V side and have a small 5ish Amp dc-dc setup up charger that only cycles online when the 12v battery voltage is .2V over whatever your batteries nominal full charge no load voltage is along with a manual over ride.