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capdave asked

Quattro Parallel Deconstruction

My boat has two Quattro 24V/5000 units from 2009. They are installed to invert only, no charging. They are configured in parallel. There are three remote on/off switches around the boat that are each in parallel to both units. Each unit has its own DC source twin circuit breaker. Each unit has a single pole circuit breaker on the AC out Line between the unit and the parallel connection. My boat no longer has the high wattage consumers that would require parallel operation. I would prefer to have each unit operate in standalone mode so that I have two redundant duplicate inverters which will only be operated one unit at a time - never both. I have read the manual and I understand how to remove the RJ45 UTP cable between the two units and use the dip switches to reprogram back to standalone configuration. For the DC source twin circuit breakers I can buy an $18 lockout slide which allows only one unit at a time to have those breakers on. I'm assuming I can leave the remote on/off switches as they are - the inactive unit won't switch on with its DC source circuit breakers off. My question is on the AC out side. I can buy a toggle cover to prevent inadvertent switching of the AC out Line circuit breakers - but is it sufficient to switch off the single pole Line circuit breaker of the inactive unit? Is there any risk from having Neutral still in parallel? Is there some issue in my plan that I'm overlooking? Thanks in advance for your help.

MultiPlus Quattro Inverter Chargerbattery charging
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Kevin Windrem answered ·

Remember there is a huge inrush current when connecting DC to the Quatro. This current can cause a Lithium battery BMS to shut down or damage to the switch to occur. Most recommend a soft start to gradually increase voltage at the inverter DC input terminals. The soft start is a resistor between the battery and the inverter DC input. The resistor is connected before the main DC switch is closed. The inverter's internal capacitors then charge slowly and when the voltage reaches the battery voltage, the main switch can then be closed without a huge inrush current.

It might be better to leave the DC connected to both Quatros and switch the control circuitry between units instead. DC leakage current is very small when the inverter is off.

To be safe, both neutral and hot leads of the AC output connections should be switched between units. This could be handled by a manual switch that insures break before make, or a relay could be used. The relay's coil would connect to one of the Quatro's AC output and it's normally open contacts connected that Quatro's AC output. The normally open contacts would connect to the OTHER Quatro AC output. That way the changeover between Quatros is controlled completely by whichever unit you turn on. Even if both were turned on, only one would power the loads.

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capdave avatar image capdave commented ·
Kevin - thanks for this. On the DC inrush to charge the caps, we have PbA AGMs so they probably can't hit a high enough discharge rate to damage the breaker, the boat's 13 years old and no trouble so far. I have scoped the lithium conversion, and this issue is on the list to deal with.


That said, I can easily leave the DC breakers on for both units, and switch off the inactive unit locally on its front panel. On the output side, I'm hearing you say that leaving the Neutral in parallel is not acceptable even with the Hot wire breaker switched off, and I need a two-pole disconnection. Might be easiest to convert my single pole breakers to two-pole, and then use a lock out slide - basically the same as a break before make selector switch.

Thanks!

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