I’m looking at an autotransformer and would like clarity regarding its maximum current for purposes of sizing wire.
Regardless of model, I see they both have the same size transformer - it maxes at 32A.
The manual says:
The transformer itself is equal in both models and has a 32A capacity (peak) and 28A nominal. This is the maximal current that can be used to transfer energy from leg to leg or from 120Vac to 240Vac.
If I am connecting the autotransformer to a multiplus II that outputs 120v with a goal of creating split phase 120/240vac, what is the max the autotransformer can handle?
Am I correct ion thinking it can manage at most 120v / 32 amps into the autotransformer giving me at most 240v / 16amps on the other side of the autotransformer? And since that’s on two legs, the wire on the split phase size only needs to be able to take 16 amps, right?
Or am I reading that wrong and it could take closer to 64 amps going in and have two legs of split phase out with 120v / 32amps max each?
The 28A continuous/32A max limitation is for Neutral current though the coil.
In a purely step-up configuration (120V → 120/240V split phase), the Neutral is used as both an input and an output for the device.
Let’s say you have only a 240V load that pulls 10A. The input Neutral current will be 20A.
Because Watts = Watts (minus some small losses). So you are effectively limited to 14A @ 240V which is 3360W continuous, 3840W max.
It is more tricky if you have a mix of 120 and 240V loads spread across L1 and L2.
In this case, you can have extra 120V loads on L1 (bottom terminal on diagram below) because there is a direct path through without going through the coil.
Got it. I saw the mention of neutral but didn’t interpret it correctly.
Close enough overall to come up with 14 continuous/16 max, but didn’t process the neutral enough to realize I could use the higher max passthrough if I put the loads on the L1 and take advantage of the passthrough - I got the 100A one so I can go a bit higher there.
I own both the 32A and 100A, and never has there been a more misunderstood device.
The issue is that it is extremely versatile. The Step-Up configuration is very different than a Step-Down configuration. I currently use mine for inverter and generator balancing, which is different as well. I originally used a 32A one as a Step-Up, so I know it’s peculiarities.
The 100A one is great for balancing applications, as the AT just passes through 240V to any 240V loads. Not sure the 100A matters as much for a step-up application (other than allowing more L1 current).
