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bryanmorrow avatar image
bryanmorrow asked

Can I use autotransformer to create single phase 240v from 120v multiplus?

Hello!

I'm very new to solar (and electricity in general), so please excuse my ignorance. :) I've been researching as much as I can, but I still don't understand phasing (among a great many other things).

I have a mini-split A/C unit that I'm adding to my RV. (My RV is gutted, so I'm starting from the ground up.)

The manual for my A/C unit says it requires 240VAC single phase 60Hz.

Here's what I don't understand: if I have a Multiplus 24/3000/70 120VAC, can I use an autotransformer to take 120VAC from my multiplus and turn it into 240VAC single phase for my A/C?

Or, would it be better to get the 240VAC Multiplus and step down for all my 120VAC loads?

I also can't seem to find whether or not using an autotransformer results in a loss of efficiency.

Thanks for your help!

Bryan

Multiplus-IIAutotransformer
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itsjsx avatar image itsjsx commented ·
@bryanmorrow Did this end up working out for you? Thinking about doing the same thing, and I'm looking for answers/others who have tried it.
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bryanmorrow avatar image bryanmorrow itsjsx commented ·
Yes! It actually works remarkably well. I can run my 240v single phase mini split off my Tesla battery module using 120v Multiplus and then stepping it up to 240 with the transformer. I use it to heat and cool the RV. No issues with this setup in the ~3 years I’ve had it working.
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badengineer8977 avatar image
badengineer8977 answered ·

Bryan,

You have the options going both ways. Yes there will be copper losses (windings) in the autotransformer. I'd say use whichever method minimizes losses.. So if your 240V HVAC power requirement is less in comparison to your 120V loads, use the step down method using the autotransformer. If your 120V power requirements are less, use a 240V quattro and step it down using the autotransformer. Losses should remain the same whether using a 120V or 240V quattro unit, losses are V*I, so should scale linearly w/ respect to internal switches (IGBTs) of the inverter. So your only variable are the losses in that transformer, I would try to minimize them.

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bryanmorrow avatar image bryanmorrow commented ·

That's helpful. Since my only 240V load is the HVAC, and will typically be much less, I'll step up to 240. Thank you!

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kai avatar image
kai answered ·

To add to the last response, larger transformers = heavier and typically more expensive.


Also check if your non-AC loads are really only 120V. A number of modern equipment have universal input ranges that works for both 120v and 240v.

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bryanmorrow avatar image bryanmorrow commented ·

Thank you - that's a good point. After looking at my minimal 120V loads, they're all 120V only.

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