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solaruser125 asked

Smartsolar 100/50 Goal Zero 25 amp Fast Charger as PV input

I'm trying to use a Goal Zero 25 am Fast charger as the PV input to charged 3 connected 100amp AGM batteries connected in parallel. For some reason, when I use the Goal Zero fast charger, the only thing that shows up on the victron app under Solar is 15.24V (voltage) and 0.0 A (current) and under battery it says 12.70V (voltage) and 0.0A (Current).

Why isn't this setup working?

I tested the same setup but connected a 100 W solar panel to the PV input and the app showed 62 W from solar and 59 W charging the AGMs.

Thanks for any help here.


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Justin Cook answered ·

For an MPPT to initialize and start permitting throughput, it needs to see battery voltage +5v at the PV input, so if your batteries are at 12.70v, the MPPT won't initialize until it sees >17.70v at the PV input. Since your GoalZero battery charger is generally charging at around 14.4v (apparently 15.24 at fast-charge), your setup won't work unless you have <10.24v on your batteries, which is obviously a bit too late.

If you're set on using a charger through your MPPT, get a 24v version. That way you can put around 26.5v to the PV side, your MPPT will initialize and step down the voltage and step up the amperage just like it does when it's connected to actual PVs. (I know this works because I have this setup on my test bench for the express purpose of testing MPPTs).

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solaruser125 avatar image solaruser125 commented ·

Thank you for the explanation. Can you recommend a 24V charger? Thank you again.

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solaruser125 avatar image solaruser125 commented ·

One more question. if what you are saying about the +5v at the PV is correct, then why was it charging when i plugged in a single 100W panel. I know that the battery was at like 12.5 when the MPPT was charging. Thanks.

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Justin Cook avatar image Justin Cook ♦♦ solaruser125 commented ·

@solaruser125, if you're looking for a good portable plug-in 24v charger, I definitely recommend the Victron Smart IP67 charger: https://www.victronenergy.com/chargers/blue-smart-ip67-charger-waterproof

orrrrr the Victron Smart IP65 charger https://www.victronenergy.com/chargers/blue-smart-ip65-charger

I fundamentally like the IP65 better because it's a bit more customizable... the IP67 has pre-wired ring terminals at the battery side whereas the IP65 has interchangeable end connectors with quick-disconnect fittings, which is super convenient particularly if you plan to use it for other things than just hooking into your MPPT. The IP65 is the one I use on my test bench. That being said, the IP67 version has a higher amperage; up to 12A in the 24v version as opposed to 8A in 24v on the IP65. Your call on that.

The reason the MPPT started charging when you hooked up your solar panel is because your PV panel is outputting ~19.5v... VOC should be somewhere between 20.5vDC and 22vDC (typically), which means on average you'll be seeing around 18.5-20vDC depending on the day, the time, and the angle of the panel in relation to the sun; this voltage meets the +5v requirement of the MPPT. Remember that you have high voltage and low amperage coming from your panel; the MPPT turns that into low voltage and high amperage to charge your battery.

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