Hello, I have a question similar to this one https://community.victronenergy.com/questions/7106/i-want-to-feed-my-mppt150100-with-a-dc-power-suppl.html
However I am not 100% clear on the answer given on some points, and also I wish to have both PV and DC power supply connected at all times.
I am upgrading the very old 12v / solar power in our camper. I’m looking at one of the 50 amp MPPT solar controller with a couple of 12v 100kW panels connected in series for a nominal 24v input (VoC ~40v, Vmp ~36v). The system will expand as battery capacity and budget allow, hence the oversized solar controller.
My question is regarding mains charging of the batteries when on mains. The configuration previously in the van, using a separate mains charger is one option, however without spending lots, I would likely be limited to 5amps for a decent charger.
As we would already have a high quality 50amp charge controller (in the MPPT controller) I was wondering if it would be possible to buy a relatively cheap 48v 10-20amp ac-dc power supply, and input it into the “solar” terminals on the MPPT along with the solar panels at the same time, that way when on mains the solar controller would charge the batteries but block the input from the panels (due to the higher voltage) therefore making sure the maximum amperage of the solar controller is not exceeded even if the sun is shinning.
I assume that the panels inbuilt diodes will prevent reverse current from the power supply damaging the panels, and if i install suitable diodes on the PSU it will be protected when not switched on.
In the above mentioned thread, one answer suggested potential issues with overvoltage error on batteries, potentially causing a short on the PV terminals (depending on firmware). However all the PSU I've looked at have short circuit protection inbuilt, so wouldn't that protect both the PSU and MPPT?
Also the above mentioned thread suggest disconnecting the panels before connecting the PSU. Obviously I would rather avoid this, so i was wondering why this is suggested?
Another thread mentioned a potential issue with PV inputs possibly requiring an isolated floating ground https://community.victronenergy.com/questions/5274/using-mppt-7515-with-charger-12v15.html?childToView=42944#comment-42944 would a switching PSU have a floating ground on the DC side?
Many thanks, in advance.
John
