question

neoneddy avatar image
neoneddy asked

Prefer PV MPPT over Alternator DC Charging for mobile aplication.

My situation is this. I have a large PV array 2600 watts running into two 100|50 MPPT charge controllers, I have 2x 3000|24 Multiplus inverters, BMV702 and a raspberry pie connecting it all together running Venus OS. I also have a 260 amp 24v DC alternator onboard that will charge the battery bank and help power loads.


My question is, how can I force the PV / MMPT chargers to always output if there is a draw on the system. I have set my alternator to charge to 27.8v while my MPPT chargers charge to 28.4 (temp compensated) . Often times I'll run two air conditioners, using close to 3000 watts. If my battery bank is not full and the MPPT chargers are still in bulk mode, it will work pretty well with the chargers continuing to contribute to the loads and the battery bank will fill. However once the bank is near full the MPPTs throttle down and the alternator takes more of the AC load, which puts my strain on my diesel engine costing me fuel and power.


With the tools at my disposal here, how can I have the MPPT chargers contribute even if the battery bank is full. I thought a few years ago the DVCC used to work this way and it would trigger the chargers to assist.


Thanks for any help you can provide.

battery chargingsolaralternator
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

4 Answers
jwfrary avatar image
jwfrary answered ·

Hi,


assuming your using a split charge system of some kind for a starter and domestic, you could disconnect the alternator (leaving it connected to the starter) with a DC contractor using logic in the MPPT or multi to prioritise solar over alternator.


dvcc can't allow for alternator charge sources.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

JohnC avatar image
JohnC answered ·

Hi @neoneddy

Try lowering your diesel charger down to (say) 27V. It will still charge your batts when needed, but won't dominate the mppts when they're in float mode.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

neoneddy avatar image
neoneddy answered ·

I don’t think I should drop the voltage of the alternator because if it’s cloudy or at night, I still need to get a good charge. I need a remote adjustment knob maybe.

I was hoping there was some GX switch or something I can enable to force the charger to stay in absorption ( absorb is as good as bulk in this case)

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

dazey77 avatar image
dazey77 answered ·

And an even more basic solution (that I use in a simpler system). You could put a switch in the dashboard to disable the feed from the split charge/DC-DC. Depends on how much you need your alternator charging, in my case I basically never need alternator charging in summer so the split charge is off until winter.

I am sure it must be possible to do this in an automated way from the Pi, you could trigger a relay cutout the alternator when batteries are full.

If the 702 has a relay output (like the 712) you could also use this to cut the split charging.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Related Resources

Additional resources still need to be added for this topic