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Emergency mobile charging via Prius (test)

speedy

Member
Aug 21, 2017
341
330
MA, USA
Ok, I did this as a test and can't envision any situation where I would use it myself, but maybe it could be a service (albeit a slow one...) for stranded EVs.

As a background, during power outages, I use my Prius in conjunction with a 5kW UPS to power my house. I had recently upgraded the UPS from a large cumbersome one to a more compact one. Normally, the battery feed from the Prius is run from the car through my garage to the UPS in the basement, next to the load panel. The UPS is now small enough to sit in the back of the Prius, so I wondered how well it would function in powering my EV charger. Pictures of the test are below:

So basically, with the 5kW UPS putting out 230v, I was able to get about 10 miles per hour of charge when the current was set for 15A. At 15A, the UPS load LEDs were showing about 100% so I didn't go beyond that. 10 miles per hour charge rate is less than a L2 charger, but hey, this charger can come to you!

The duty cycle of the Prius engine when the current was set for 12A was 55% on, 45% off. That's about right since the Prius is capable of putting out about 6kW.


IMG_1152.jpg
IMG_1153.jpg

IMG_1147.jpg
 

speedy

Member
Aug 21, 2017
341
330
MA, USA
Not warm at all. It has active cooling fans running all the time. Normally the UPS is ethernet connected and I can monitor the temperature via a browser, but since it was in the car, it wasn't connected. During home use at a nominal 20% load, it's less than 19C. I didn't feel any warm spots during my 20 minute test but I had dropped it to 12A for most of that time...

Co-incidentally, we're having a fall nor'easter 'bomb' right now and I've been on Prius power for the last 4 hours :cool:
 

int32_t

Tesla Spotter
Nov 21, 2015
624
398
Calgary area, AB, Canada
That’s too cool! Where’d you get the idea to combine a UPS with your Prius in the first place?

I’m not very familiar with the Prius battery. What’s its chemistry and nominal voltage? I assume the voltage handily falls within the spec for the UPS, which made this a no-brainer.
 

ecospider5

Member
Nov 6, 2018
32
51
Duvall
I did this with my prius 10 years ago when the power was out for 10 days. But I just did a 1000w inverter off the 12v system. Since the 12v inverter in the prius is 100amp it worked well. I was starting to source a 400v server ups but my spouse would not let me touch the traction battery.

It was amazingly efficient and only used 2.5 gallons a day to keep the refrigerator and some lights on.

Nice test charging an electric car. Well done.
 

miimura

Well-Known Member
Aug 21, 2013
6,270
5,901
Los Altos, CA
That’s too cool! Where’d you get the idea to combine a UPS with your Prius in the first place?

I’m not very familiar with the Prius battery. What’s its chemistry and nominal voltage? I assume the voltage handily falls within the spec for the UPS, which made this a no-brainer.
This is actually a fairly well known technique. The Prius battery is NiMH and the nominial voltage is about 202VDC. So, a UPS designed for a 192VDC lead acid pack works. That 192V nominal pack will charge up to about 220VDC, within the range of the hybrid pack. The Highlander and Lexus RX hybrids use a 288V nominal pack, so it won't work with the same UPS unit.

This page has a good overview of the various hybrid battery packs.
The Hybrid Car Battery: A Definitive Guide - HybridCars.com
 
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Cape Coddess

Working 2 ROTHS - hold and swing
Aug 18, 2019
226
616
Florida
This is wonderful! Thanks for the photos too. Let us know when you do it with your Tesla. By the way, I was in that bomb yesterday too. The cleanup crew just went through my yard to take down and haul off broken branches and brush everywhere.
 

jdcollins5

Member
Aug 14, 2018
761
491
Wilmington, NC
Ok, I did this as a test and can't envision any situation where I would use it myself, but maybe it could be a service (albeit a slow one...) for stranded EVs.

As a background, during power outages, I use my Prius in conjunction with a 5kW UPS to power my house. I had recently upgraded the UPS from a large cumbersome one to a more compact one. Normally, the battery feed from the Prius is run from the car through my garage to the UPS in the basement, next to the load panel. The UPS is now small enough to sit in the back of the Prius, so I wondered how well it would function in powering my EV charger. Pictures of the test are below:

So basically, with the 5kW UPS putting out 230v, I was able to get about 10 miles per hour of charge when the current was set for 15A. At 15A, the UPS load LEDs were showing about 100% so I didn't go beyond that. 10 miles per hour charge rate is less than a L2 charger, but hey, this charger can come to you!

The duty cycle of the Prius engine when the current was set for 12A was 55% on, 45% off. That's about right since the Prius is capable of putting out about 6kW.


View attachment 466883 View attachment 466884
View attachment 466890


This is really interesting. I had a 2000W inverter that I connected to my Prius HV battery to supply my house during hurricanes. I still have the inverter but sold the Prius. I wish I still had the Prius to test the inverter with my car.
 

speedy

Member
Aug 21, 2017
341
330
MA, USA
Does your UPS simulate the ground? We tried something similar in the past but the UMC refused to charge due to the lack of a ground.
I didn't do anything special. The ground of the UPS is connected to the UPS chassis but not true ground, and the voltage of the UPS is somewhat unevenly referenced to that ground. My UMC didn't complain....
 

speedy

Member
Aug 21, 2017
341
330
MA, USA
Let us know when you do it with your Tesla.

You mean using the Tesla as a battery source? I suspect the Tesla BMS is too sophisticated to allow you to pull power from the traction battery indiscriminately. Other than the Prius, I haven't heard of any other Hybrid or EV vehicle traction battery being tapped. Most people just tap the 12V battery, but that provides limited power. Though, I think some EV manufacturer is touting a car to grid solution, but I can't remember who. I think it makes sense as the Tesla battery could power a house for a few days, but they have their Powerwall business so it wouldn't make sense to cannibalize it, even though it's somewhat different use...
 

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