how much can you over spec a charge controller?

[solaar]

Is it ok to use a 15 Amp charge controller with a 100W panel that only outputs around 5A?

I need to upgrade my controller to charge a lifepo4 battery, but may end up getting another 100W of panel in the future, but in the meantime it's going to be a little over spec.

Thanks

[Raj]

It is ok, in fact that's the correct way to plan your system. Advise ensuring the controller can be setup to properly charge LFP battery bank. If 12 volt, I would recommend setting Absorb at 13.8V, End Amps set to (2% of C per 100AH), Float at 13.5

[Sunking]

You can use a 80 amp controller if you want. The issue is trying to push more current than the controller is rated for.

[PNjunction]

I need to upgrade my controller to charge a lifepo4 battery, but may end up getting another 100W of panel in the future, but in the meantime it's going to be a little over spec.

Note - when you shoehorn a lead-acid controller into duty with LFP, be SURE you can DISABLE (or set to zero) the temperature-compensation, and of course disable any sort of EQ.