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johnm1 asked

On/Off/Charger Only switch on MultiPlus-II

MultiPlus-II 12/3000/120-50 2 x 120V switch setting in a camper/rv ...

If the "On/Off/Charger Only switch" is set to "ON", which is inverting and charging, and we're not plugged into "shore" power (no incoming AC power), will the Multiplus try to charge the batteries using the batteries? Or, is it smart enough to know that there is no incoming AC power so it won't try to charge the batteries?

Multiplus-II
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nickdb avatar image
nickdb answered ·

Uhm.. Without a charge source (power/PV) it can't charge anything.

When there is no AC, the multi switches to inverter mode so the switch position is mostly irrelevant.

In any case, a battery can't charge itself, that would be some interesting wormhole physics.

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johnm1 answered ·

Thanks Nick ...

If I understand correctly, if the Multi is in the ON position (charging and inverting), unplugged from shore power and my IP22 charger is plugged in to the camper and turned ON, the IP22 will be charging the batteries using the batteries through the Multi.

That's why I'm asking about the Multi. Can it do the same thing?

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derrick thomas avatar image derrick thomas commented ·
If the ip22 is connected to the mp2 output then yes it will "attempt" to charge when no shore power is available and inverting. If you connect the ip22 to ac output 2 then it will disconnect when there is no ac input to the mp2. If you have a gx device you could use it to drive an external relay to enable or disable the ip22 according to the ac input availability.
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johnm1 avatar image johnm1 derrick thomas commented ·

Hmmm ... that's a great idea! I hadn't though that part through as I'm only plugging in the IP22 when needed (which hasn't happened yet since it's a new system for us).

However, back to the original question ... the multi can't/won't try to charge the batteries while inverting with no shore power? I know it may sound like a stupid question but I'm trying to learn to avoid mistakes while off-grid camping.

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derrick thomas avatar image derrick thomas johnm1 commented ·
The multi itself cannot/will not charge while no shore power is available. The toroidal transformer is used for both inverting and charging, and it can only do one job at a time. If there is no ac power coming into the multi, there is nowhere for the transformer to get power from to charge the batteries. The ip22 however is a separate component so if it is plugged in while the multi is inverting, it will attempt to charge, basically creating a loop with a net loss. Laws of thermodynamics and all that.
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