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How to detect excess power?!


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I'm planning to buy a new car: Hybrid plug-in.  My solar panels produce enough power during summer time to charge the car's battery after noon. 

All the chargers i found rely on the red connection: If it detects power going to the red it will re-direct it to the car.  

As i do not have a red connection (island) ... how could that problem be solved? Red = Car?  

Theoretically i could use the SOC: IF at 100% then car charger ON.  The problem with this would be that the SOC falls as soon as the load changes.  Means, after a few minutes the SOC will be down to 98...95 indicating to stop charging the car, go back to charging the batteries. We call this a jo-jo effect.

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  • 4 weeks later...

I've thought about this a bit. I have a system that can't use AC current sensors to detect exported power (it never exports), so that rules out all the off-the-shelf EVSEs like a Zappi.

My vague plan, nowhere near implementation, is to basically back off EV charging whenever there is battery discharge. But also periodically try more EV charging. If that results in battery discharge, again back off EV charging. If not, try even more. Sort of like a maximum power point tracker, but running once a minute or so.

But it needs some refinement, so that the house battery is likely to fill over the course of the day. So rather than the fixed threshold being zero discharge, it should be a  certain minimum battery charge current, depending on the time of day, and maybe influenced by the weather forecast. And of course when the house battery is full, the threshold should be zero.

Also a manual override or possibly a variable setting that allows for "need car soon" or "will need 70% car SOC by end of the day". Making that setting intuitive for the family and reasonably functional will be a challenge. 

Edited by Coulomb
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