Scenario - van is getting an upgrade to a lithium battery system. Previously had a CTEK charger connected to (AGM) battery that charged it when the van was connected to mains power. Running a SmartSolar MPPT 100/20 and a RPi Venus.
Current charger doesn't do lithium chemistries. I can buy a new one (~$190) but I can buy a 48v 300W PSU for a lot, lot less and wire it with a relay so it takes the place of the panel when there is mains power.
Any thoughts why this isn't a good idea?
I assume you are trying to find a cheaper way to have three stage/controlled charging here.
Since the mppt will try track, it may cause issues since the PSU has constant voltage.
The second one would be if the mppt tries to protect the battery by shorting the PV input you may have a dead PSU.
Will it work, probably yes. Will it be trouble free, no.
It would be better to have the PSU directly connected to the battery itself. But you still wont have 3 stage charging. I guess not totally important for lithium set the bulk voltage. CV CC.
The second one would be if the mppt tries to protect the battery by shorting the PV input you may have a dead PSU
Is this really a thing the SmartSolar does? Not a disconnect? Would sure be an issue on some systems having the panels in full sun driving just their wiring!
I read here in the appendix it is indeed :
7.4.19. Error 38, Error 39 - PV Input shutdown To protect the battery from over-charging the panel input is shorted.
Yep.
Hence it is important to get the install correct.
Panels can be shorted they don't mind.
But the short circuit amps have to be under the short circuit rating for the MPPT.
Some PSUs are short circuit proof... Meaning you might get away with it.
You shouldn't see the #38 39, but it i have seen it does happen more often with lithium.
