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hojo2000 asked

Power Assist Victron MultiPlus-II 12/3000/120-50

I have a Class A motor home considered to be a 50 amp service. It has a Victron MultiPlus-II 12/3000/120-50 2x120V inverter/charger. It has the Cerbo, some solar, lithium batteries and various Victron/lynx supporting equipment. I have a question about Power Assist. I read the manual and dig into the forums and get two different descriptions for what Power Assist does.

  1. Power Assist will supply additional power for sudden power draws such as the kick required when an air conditioner starts up. This is a short time boost and the wattage will return to the rated source power. It is primarily designed to prevent blowing a breaker. This is how the guy who installed it described it to me and what the manual seems to describe.
  2. Or, Power Assist will pass through the AC source power and then will add power from the batteries should you exceed the AC source amperage. This would be a long term boost that will last as long as the batteries. For a 30 amp power pedestal source I would have the 30 amps from the pedestal plus another 25 amps (3000 watts at 120 volts) from the inverter. I’ve seen discussions in the forums and a couple of You Tube videos that present this description.

My system seems to be working as a short term boost (#1). The forum discussions talk about “turning on the Power Boost.” I’ve dug through the manuals, the discussions, and the Cerbo menus and haven’t found a description or button for turning on Power Assist. The closest thing I find is, Power Assist is an automatic function that you don’t need to manage. At most you may need to set the AC Current Limit to match your power source amperage.

At 50 Amps I have all the power I need and don’t need Power Assist. At 30 amps I may have need for Power Assist, either the short term (#1) or long term (#2). So, which is it, a short term boost as described above in #1 or a long term boost as described in #2?

So far as setting the AC Current Limit, should I set it at 30 amps when hooked to a 30 Amp pedestal, or should I set it a couple amps lower, say 28 amps, as a cushion to reduce the risk of blowing the pedestal breaker?

powerassist
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2 Answers
snoobler avatar image
snoobler answered ·

As you stated them, PowerAssist works with features from both, but not all. Let me try to simplify it:


For whatever reason (steady or surge load), if AC input limit is exceeded by loads, PowerAssist is activated. It stops charging and acts as a pure inverter that's synched to the incoming AC to add power somewhat analogous to how Solar grid-tied inverters work on a residential install.

The length of PowerAssist is determined by the load and battery capacity. If the load drops back to the level that it can be fed purely by the AC input, PowerAssist terminates, and it reverts to pass-thru only and will charge with any surplus AC input as needed. If load does not drop below AC input limit, it will continue to assist until battery capacity is exhausted and the unit shuts down due to a low battery fault.

When PowerAssist first activates, to avoid tripping the breaker on the input, it grabs MORE than what is needed (controlled by powerassist boost factor setting, default 2.0). It then tapers its output until the input current raises to the limit and then provides steady state operation where the AC input is near maxed out, and the inverter is only assisting with what is needed.

When switching back and forth between sources, it is prudent to change your AC input current limit. If you have VRM, you can do this from the dashboard.

It's always wise to leave a 10-20% margin to avoid nuisance tripping of breakers, particularly when they aren't yours, and you have to go outside to reset them... :)

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Kevin Windrem avatar image
Kevin Windrem answered ·

Snoober describes Power Assist well. It's enabled in the Multi/Quatro configuration either via VictronConnect or the veConfig Windows app.

Note that the 120x2 models have a single inverter so Power Assist will only function on L1. L2 is always just pass-thru. When shore power is absent, the L1 and L2 outputs are fed off the inverter and are in phase.

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