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mathias-pull asked

Battery switch and load always on MMPT 75/15

Hi, just bought a 150w panel and a smart solar mmpt 75/15 for my boat but got 2 questions.

Got a battery switch (1,2,1+2) to be able to also charge the starter battery (if need be) at shore with my CTEK M300 charger. Can I connect the MMPT parallel with the charger on the battery switch to get the same functionality off shore and would I be able to turn the switch from “house “ to “starter “ w/o frying the mmpt?

I will connect my 3 usb power ports (with voltage meter) as (the only) loads to the mmpt, do I need to include a switch as well, or can they be “always on”? The manual stated that all loads need to be “turned off” during installation (loads being step 1).

smart solar set-up help
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2 Answers
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mathias-pull answered ·

Bumping thread

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gazza answered ·

Hi. Yea it's ok to connect an MPPT charger and another DC charge source in parallel. The issue to be aware of is the charge cycle on each source, specifically settings for Absorption, Float etc. What often happens is the charge cycle of both devices get out of step, it can take a bit of tinkering to get right in terms of what takes precedent.
Also be aware of potential "total charge" current available, for example, I think the CTEK you mention is 25A and in parallel with the MPPT 75/15 at max then you would have 40A current "potentially" which may (or may not) be too much for battery in question?. However, with one 150w panel you will not max out the MPPT.

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