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Adjusting Charge Rate Based on total household power draw on the fly. Possible?

My power bill is at least 50% based on max power usage, not total energy usage. The utility keeps a running 15 minute average and whatever the worst 15 minutes for the month was, I get billed roughly $12/kw. So if I peak at 20kw, then that part of the bill is roughly $240. I would like to be able to monitor my current wattage and tell the Tesla to only charge when I am otherwise pulling less power. For example, I might want the Tesla to not charge at all unless I am using less than 15kw and then only to charge to a max of 18kw total. So if my non-Tesla usage was 15kw, the tesla would be set to 12 amps or roughly 3kw bringing the total to 18kw. If my non-Tesla power were down to 10kw or less, it would be allowed to charge at 8kw (~32 amps). Has anyone done something like this? The car doesn't have to react instantly because it is a running 15 minute average. For example, say I am at 18kw with the Tesla pulling 8 of those, then the building AC clicks on and adds 5kw, that would take me to 23kw, but if the Tesla lowers its power draw gradually over say 20 seconds, it would not be an issue. Anyone done this or know how to?
 

Ogre

Active Member
Sep 6, 2021
3,273
21,241
Oregon
My power bill is at least 50% based on max power usage, not total energy usage. The utility keeps a running 15 minute average and whatever the worst 15 minutes for the month was, I get billed roughly $12/kw. So if I peak at 20kw, then that part of the bill is roughly $240. I would like to be able to monitor my current wattage and tell the Tesla to only charge when I am otherwise pulling less power. For example, I might want the Tesla to not charge at all unless I am using less than 15kw and then only to charge to a max of 18kw total. So if my non-Tesla usage was 15kw, the tesla would be set to 12 amps or roughly 3kw bringing the total to 18kw. If my non-Tesla power were down to 10kw or less, it would be allowed to charge at 8kw (~32 amps). Has anyone done something like this? The car doesn't have to react instantly because it is a running 15 minute average. For example, say I am at 18kw with the Tesla pulling 8 of those, then the building AC clicks on and adds 5kw, that would take me to 23kw, but if the Tesla lowers its power draw gradually over say 20 seconds, it would not be an issue. Anyone done this or know how to?
You can change the amperage your car uses on the console. For example, if you drive 100 miles/ day, you can get by with 15 amps @220v.

This isn’t dynamic, but you can dial it in. You’d probably be surprised at how low you can get away with. Particularly if you don’t mind occassionally dipping below your high water mark.
 
Thanks for the reply, but I need this to be automated. The power usage goes up and down by the minute. I need a way to monitor the power usage and then automatically increase/decrease the tesla amps on the fly. I have a home automation system (ISY) that can control the Tesla, however, it appears that it keeps the Tesla "awake". I had it connected while on vacation and my Tesla was losing 5%/day sitting in the garage. I could use this to control the charging rate, but I have no interest in using a program that consumes 5kwh/day to do so. So looking for a better way.
 

Ogre

Active Member
Sep 6, 2021
3,273
21,241
Oregon
I got mired in the details and forgot to answer your original question.

I’m sure there is a way to hack this using a whole house energy monitor, but there is no simple solution to the problem.

That’s why I suggested lowering the peak. Another simple possibility which would work without any big hacks is to block out a window of time where your AC is off and schedule your car to charge during that window. I know… also not the answer to your question. But there is no simple answer to what you want.
 
Following. My electric provider has an option for a rate plan with demand charges and I'd need something along these lines to be able to make use of it effectively. Seems like something that a service like OptiWatt should support (although at first glance it doesn't appear that they do). Could probably hack something custom up in HomeAssistant if you are technically inclined. You'd obviously need a source for the whole house energy consumption to act on.
 
Just turning it down to low charge rate doesn't really solve the problem. Even if I charged at 1kw, it would end up raising my max from 20 to 21 since no doubt at some point I would otherwise hit the 20kw mark as I seem to do every month and this would just add 1 more. And 1kw charging speed would not put a lot of charge in the battery.

I had considered just putting a relay on the power supply to the Tesla outlet. I could fairly easily monitor one of the AC units and turn off the Tesla relay whenever the AC unit is running. But I am unsure if this is good for the battery, to just shut off the power cold turkey. I would rather turn off the charging using the Tesla computer. But maybe the cold turkey shut down does no harm, I don't know.
 
I think I may have solved this. I have a universal devices ISY. It has the ability to add the Tesla to it and view/control pretty much everything. I had installed it, but abandoned because it wasn't letting the car go to sleep and was killing my battery. I found out that you can turn that off so it only wakes the car up when you want it to rather than just constantly keeping it awake. This should solve the problem. I need to add monitoring of my wattage, or probably what I will do is just monitor my AC units using one of the IO devices that work with ISY and have ISY set the car to charge accordingly. I'll update once I have this working (or not).
 
I found a complete off the shelf solution. Emporia Energy makes a system that will track your total kw as well as up to 16 individual circuits. They also make an EV level 2 wall charger that integrates. You can have it adjust your car charging based on current watt consumption. The package costs $664 and includes the EV charging station, the energy monitor with 16 individual circuit monitors.. They have other stuff including batteries storage, PV monitors, and outlet adapters if you want to integrate all this stuff to control your electric usage better.
 
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I have it working. I am using the Emporia energy monitor to real-time track my wattage. This integrates with my UD ISY which also integrates with my Tesla. The ISY turns charging on when I drop below a certain wattage and then turns it off when I go above a certain wattage. I put 4kw of hysteresis in there along with some time delays to prevent excessive on/off issues. If I didn't already have the ISY, I think I would have just bought the Emporia charger which they claim will directly talk to each other. But I have no need to spend the extra $400 plus I would have also needed to get wifi to the charger location.
 

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