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The Victron Autotransformer, explained
An autotransformer balances the two legs of a 120/240V split-phase supply and can step 120V up to 240V (or 240V down to 120V) — the piece that makes North American shore power and split-phase inverter setups play nicely together.
| Product | Ratings | What it does | From |
|---|---|---|---|
| Victron Autotransformer | 32A · 50A · 100A | 120/240V split-phase balancing + 120↔240V conversion | $451.35 USD |
Pairs with a 120V MultiPlus / Quattro when you need a 240V output, or with 240V shore power when your loads are mostly 120V.
Three jobs an autotransformer does
If one of these sounds like your situation, this is the device.
Balance an unbalanced split-phase load
On 120/240V split-phase, if one leg carries far more load than the other, the legs get unbalanced. The autotransformer shares the neutral current and evens the two legs out — protecting equipment and keeping voltages where they should be.
Make 240V from a 120V inverter
Many North American Victron inverter/chargers output 120V. Add an autotransformer and you can derive a 240V split-phase output to run a 240V appliance like a well pump or dryer from a 120V MultiPlus or Quattro.
Run mostly-120V loads off 240V shore power
Plugged into 240V shore power but most of your panel is 120V? The autotransformer steps it down and balances the legs so your 120V circuits are properly fed.
Why buy from Blue Marine
True Blue Victron distributor
Warranty and setup support handled by us, not a ticket queue.
ABYC-certified advisors
We'll confirm whether your build actually needs an autotransformer — and which amp rating.
Free US shipping over $49
Fast shipping from Seattle and 60-day returns on non-lithium items.
Real people, real boats
Call (800) 628-6306 Mon–Sat.
Not sure if you need one?
Tell us your inverter/charger, your shore service (120V or 240V), and your big loads — we'll confirm whether an autotransformer belongs in your build and which rating to choose.
Autotransformer FAQ
What does an autotransformer actually do?
Two main jobs: it balances the current between the two legs of a 120/240V split-phase supply so neither leg is overloaded, and it converts between 120V and 240V. That makes it the bridge between North American split-phase shore power and a Victron inverter/charger system.
Do I need one with my MultiPlus or Quattro?
Only in specific cases — mainly when you need a 240V output from a 120V inverter, or you're feeding mostly-120V loads from 240V shore power and want the legs balanced. Plenty of straightforward 120V systems don't need one. We're happy to confirm for your build.
Which amp rating — 32A, 50A or 100A?
Size it to the current it has to balance or pass for your loads and shore connection. As a starting point, match it to your service (e.g. a 50A shore setup), with headroom for the loads moving between legs. Tell us your numbers and we'll point you to the right one.
Is this the same as an isolation transformer?
No. An autotransformer balances and converts voltage but doesn't galvanically isolate your boat from shore ground. If corrosion protection is your goal, see isolation transformers and galvanic isolators.