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half-moon-bar-lodge avatar image
half-moon-bar-lodge asked

Wiring diagram for Quattro split phase with autotransformer?

We have an off-grid system with two 48/10000 Quattro inverter/chargers configured for split phase, with a battery bank and solar chargers. We also have a generator feeding the Quattros on AC input 1 when the batteries are low and the sun is not shining. We have a few 110 appliances that consume significant load, causing the legs to become unbalanced.

I'd like to add a 100 amp Victron autotransformer between the Quattros and the breaker panel so that we can balance the legs, especially when the generator is running.

The autotransformer manual has a wiring diagram for balancing two inverters in split phase, but it's not very specific -- it's more conceptual than "connect this to that". The manual also says "split phase output balancing may require some more attention", but never goes into more detail on how to do it. Does anyone have a more specific wiring diagram for balancing two Quattros with the 100 amp autotransformer?

Also, the Quattros open the ground relay when the generator is running. I've wired that up to the autotransformer so that it will drive the autotransformer ground relay. However when the Quattro is powered by the generator the ground relay is opened, which I don't think I want to happen -- the autotransformer ground relay should always be closed, as far as I can tell. Does anyone have any tips for forcing the autotransfomer ground relay to always stay closed?

MultiPlus Quattro Inverter ChargerAutotransformersplit phase
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solardude avatar image
solardude answered ·

I will assume your generator has a neutral to ground bond, since most 120/240 generators do.

Your Quattros will still control the opening/closing of the ground relay, but will now physically happen inside the AT. The Quattro will no longer physically use its internal ground relay if configured properly.

First, you need to wire the ground relay output from the Quattro to the ground relay input on the AT. (Only needed from one Quattro) Then, you need to flip the dipswitch SW1 up (on) to enable external switching. (This part unfortunately is not covered in the manual). Also make sure ground relay is enabled in the Quattro settings. The AT ground relay will now automatically open/close when necessary.

I can’t see a situation where you would want the ground relay always closed. If your gen is running, you want the relay open. If gen is not running, relay should be closed. This is the default operation, and is Done that way to avoid more than 1 N-G bond at the same time.

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half-moon-bar-lodge avatar image half-moon-bar-lodge commented ·

Thank you solardude! I really appreciate you taking the time to answer. I've got it wired up as you said -- one of the Quattros is controlling the ground relay on the autotransformer. It took a while to figure out to flip the dip switch... thank goodness for the community! :-)

Here's what I'm trying to figure out: when I'm running off batteries, the autotransformer balances the two legs. However when I'm running off generator (and hence the ground relay in the autotransformer is open), the legs are not balanced. Any ideas?

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