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Arbitrage…Grid inverter with battery charging timer?

Clipper81

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Aug 22, 2021
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Hi, I am an electric car guy and I have a whole lot of 160 Ah prismatic LIFeP04 cells that have been removed from vehicles, with about 130 to 150 Ah capacity left in them. I am in San Diego and my peak rate is about $.64, and my super-off-peak rate is $.10. So I want to do arbitrage. No interest in selling back to the grid.

I pretty consistently use a maximum of 20 kWh Per day, a third of which is car charging from midnight to six. When I don’t charge my car, I use about 12-14 kWh per day. During the recent week long heatwave, I was using about 30 kWh per day. My highest hourly usage is about 1.7kWh. Highest ever (in the last year) was 3.3.

I am planning to make a 16 kWh pack (2p19s) or perhaps a 20-24 kWh pack. (3p)

I have more or less settled on an Outback Radian GS4048 inverter, but if there’s a better one for my purposes, I’m all ears. Basically I just want to charge from midnight to six, and then use my battery pack until it runs out, at which time it will switch back to using the grid for loads. By my calculations, I will only be using peak or off-peak power maybe a couple of hours on a couple of days per year… I can live with that.

The “mini grid“ function of the Outback inverter does exactly this, except for the fact that it starts charging immediately when the batteries run out. I want my house loads to stay on the grid until midnight or after, but I don’t want it to charge batteries until midnight. Unfortunately, the Outback charger has no timer function.

The only workaround I’ve thought of is to turn off the inverter’s internal charger, and charge with a separate charger on an external timer. I have a couple of 3kW chargers laying around because of my car activities, so that’s no problem.

Does anyone have a better solution? Or know of an inverter that has a charge timer function?

Thanks in advance!
 

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Sounds like a good plan all around. For a 16kwh pack, you'll need one 3kw charger, and two will cover you up to 32kwh.

It sounds like you still want to use the grid 1) during the super low rate and 2) when the batteries are depleted.

I believe you can do as you suggest: Put the Radian inverter into Grid Zero mode, which will only use the grid when the batteries are depleted, and then put the external chargers on the batteries to top them off every night. Set the external chargers to only operated during your desired hours, and you should be all set.
 
Can't help you, but I have to ask, is that the car they used in Goldmember? :p
Yes, it’s called Corbin Sparrow. They modified one to use in Goldmember, put a tail on it. They also used one in an episode of the Big Bang Theory.
 

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