Pass Through Power - How Much is Too Much?


I have the AC200 MAX and I’d like to use it to allow for ongoing pass through power. I plan on using an average of 250 watts at any given time - which would be less than the charger input of ~450 watts. Will this damage the battery once the battery reaches 100% charge? Is it ok to allow pass through power even when the battery is 100% charged? How long can I leave it plugged in and passing power through in this way? Ultimately, will this damage the LiFePo4 batteries the same way it does AGM batteries?

We live in our rig full time, usually with shore power from an RV park - but sometimes we’re off grid. We’ll usually be plugged into shore power for a week to a month at a time and all of our devices will be plugged into the AC200, preferably 24/7. I’m very concerned I’ll do long term damage to the unit by using it for pass through power for weeks at a time.

Thank you!

First, the Battery Management System (BMS) won’t allow the battery to be “over charged”. Having said that, the battery WILL slowly degrade with what is essentially continually charging and discharging the battery at the same time. A true UPS system (the AC200MAX is not a true UPS system) will actually pass the input power to the output without charging and quickly switch over when it sees the input power drop.

I don’t know if it would be continuously charging and discharging. The final charger input is connected to the battery, and the output inverter is also connected to the battery. As long as the input rate and output rate, the battery should be cycling at all. Since they are all electrically connected, there is no difference between drawing from the battery vs via the connected charger.

Now, the details is in the charging system. If the charging stops until the battery SOC falls to say 95% then starts up again, then yes it would be cycling between 95-100 SOC. However, if the charger is smart and only charges as much as necessary but never stops, then the SOC will stay at 100% and the battery never cycles. My old school Goal Zero AGM based power station does that. When at 100% SOC, it will accept as much charge as it is outputting (as long as output less than max input rate).

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@snowstorm - Thank you! I had an old school Goal Zero Yeti, with the same experience as well :slight_smile:

It sounds like I’ll need to do a bit of testing. Good news is, with 3500 cycles down to 80% discharge, I can do this daily for about 9.5 years. So it sounds like I’ll be good to go either way!

Thank you again!

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