question

I suspect that the surge in current draw from the heat pump/air conditioner is causing the generator's output voltage to -momentarily or otherwise- drop below the MultiPlus' acceptance range, causing it to kick over into inverting.

Have you read the "MultiPlus Generator FAQ" and followed the suggestions therein? Specifically the bit about disabling UPS function and enabling Weak AC? It's a little dated, since it's still referencing VEConfigure which is no longer needed, you can access both those settings through VictronConnect (via a wired connection through an MK3 of course) but the suggestions and explanations of the issues still hold true: https://www.victronenergy.com/live/multiplus_faq

Hi @CalledTo Journey,

I have just added a new amendment to the PowerAssist section of the generator FAQ that @Justin Cook linked above.

This is based on some feedback I've got from the field from others that were experiencing similar issues to you, and were then able to solve them.

I would be interested in hearing back from you as well after you have tried;

There is an additional configurable parameter of PowerAssist called "Boost factor"

When the Multi is charging from the generator, and the current required exceeds the AC input current limit (due to a sudden additional load) then the Multi will switch to PowerAssist mode.

At that moment the precise current needed is unknown. The Multi uses the "Assist current boost factor" setting as a multiple of the AC input current limit, and attempts to provide that much additional current.

In some cases this multiple is either too high, or too low. This would most likely present as the generator unable to stay connected, or fluctuations to the frequency and voltage.

The fastest way to diagnose if setting may be interfering with your specific generator and load operation is to disable power assist entirely. If that resolves the issue, then try re-enabling PowerAssist, but this time also reducing the Assist current boost factor down until it works reliably and still getting the benefit of the feature without the interference.

One note: with 120/240 power coming in, the 120x2 Multi and Quattro simply pass the L2 incoming leg to the L2 output. The inverter isn't involved.

In the system described by the OP, this is not a factor as they said the source is 120 volt only. In this scenario, both L1 and L2 outputs are in fact fed by the inverter from the L1 input.

By turning OFF the UPS function and the dynamic current limiter, the Multiplus worked perfectly, taking power from the generator while the heat pump was running. I also tried running the air conditioner, but it doesn't have a soft start, so the Multiplus will only power it by inverting and won't take any power from the generator while doing so. That doesn't make sense to me, but running the heat pump alone will be great unless outside temps are in the high 90s F, in which case we'll need shore power.

Thanks to all who've made suggestions!