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sco avatar image
sco asked

Victron MPPT 100/20 fuse keeps blowing

Hi,

I got the MPPT SmartSolar 100/20 controller a few weeks ago and have so far tested it with solar panels and lead-acid batteries, both in 12V and 24V configurations, and everything's worked fine.

Now however I just got a LiFePO4 battery, 8 cells connected in series for 24V but when trying to connect the battery to the controller (no panels or anything else connected) I get a strong spark and then the controller's (25A) fuse blows. Batteries seem to work as they should, showing voltage of 26.16V. I haven't tried connecting any loads yet.

What could be the issue here? And what should I do to troubleshoot?

MPPT Controllersfuses
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3 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Check the polarity of the battery connections with a multimeter before connecting them to the MPPT.

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sco answered ·

Obviously I have checked that, it's quite hard to do wrong...

Edit: Apparently it is. Apparently when I initially checked the cell's balance I never registered that the black cell terminals are positive and silver negative. I just assumed that black was negative. Everything is working as it should now!

Luckily the Victron seems well designed so I only got a sooted terminal and a couple of blown fuses.

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ commented ·

Edit Thanks for reporting back. It helps others know that you really do need to assume nothing, and double check everything when things aren't working properly.

Reverse polarity at the MPPT terminals before connection is the obvious thing.

After testing, if that did not show to be the fault then there could be fault with the unit, and the MPPT should be returned to the supplier for them to test on another battery and if reproduced there, the unit replaced.

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rickp answered ·

I am always reminded to check everything, except the things I’m sure of. Those I check twice! I can’t count the times I’ve had to laugh at myself for missing something really obvious. I’m glad you found the issue!

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