asked
I want to feed my MPPT150/100 with a dc power supply (115VAC to 60VDC 20Amps) so during rainy low solar output weather I can charge my batteries. Open circuit is 70VDC on the power supply.
Hi, yes this should work. But it is not an official supported solution though.
Keep an eye on your power supply to not overload it. Adjust proper amp limit on your MPPT in case, to avoid overloading. I would also disconnect the solar panels when connecting a power supply.
Regards,
Markus
Hi @Markus; can you advise on why the MPPT FAQ states "no" with regard to
"Can I use the MPPT Solar Charger as DC-DC charger?" ?
The answer to that question adds an example of a 24V battery as the DC source. This would seem to be quite correct for a battery source; it would be a very bad idea to power the MPPT from a battery with respect to the lack of any short-circuit protection should the MPPT shunt the PV input per error conditions 38 and 39, as discussed in this thread.
If that's the only concern, it seems that question should be expanded to something like "Yes, but only where the DC power source is current-limited to less than the MPPT rating. For example, it is not suitable to charge a 12 Volt battery from a 24V battery bank."
I think the reason the FAQ says "no" is just because they don't want to see people fry their hardware and/or deal with support or warranty related to this.
I have powered several SmartSolar MPPTs with my lab power supply, but that has short circuit protection and should be good even if the error conditions 38/39 occurs.
Most important task is to avoid the two error conditions entirely. That is why I only had one SmartSolar (with dc lab power) connected alongside my Multiplus when charging 16.4V - making sure there was no other charging source that could exceed the SmartSolar.
Wasn't there an update just recently that would allow two SmartSolar MPPT to synchronize the charging? Would this help if say you had one SmartSolar for PV and one for a CC/CV power supply connected at the same time?
Hi,
If you get an overvoltage error, and the PV input short protection is triggered, you will damage the MPPT charger.
Hi, @Espen thank you.
I don't exactly get what you mean. Can you further describe this please?
You mean overvoltage on the PV input?
Regards
Old post. But I am thinking of using a laptop power supply at 19.5v and 4.6amps for occasionally charging a 100ah LiFePO4 batt through a 75/15 MPPT. (the batt will be primarily solar charged)
Can I fuse the DC side of the power supply before the PV connection and be safe?
@bluejeans
It's voltage that does the damage. Your charger will get nowhere near the 75V limit of the MPPT.
Not sure this will work, quite apart from the non-standard feed to the MPPT and possible warranty issues. The MPPT needs to see an input that is 5V over battery voltage before it kicks in. With a battery at 14V, say, there's little headroom.
