Using an EV battery pack as back-up home power

General Discussion about electric vehicles.
Post Reply
FL bomber   100 W

100 W
Posts: 173
Joined: Feb 12 2016 12:57pm

Using an EV battery pack as back-up home power

Post by FL bomber » Aug 29 2019 3:18pm

[moderator edit: this post has been split-off from another thread, because it was "off topic"]

we have a cat-4 hurricane barreling down on us in Florida. I own a 2013 Chevy Volt. I was wondering if any of you guys know how to or if it's possible to use it for backup power.
Thanks

User avatar
spinningmagnets   100 GW

100 GW
Posts: 11878
Joined: Dec 21 2007 10:27pm
Location: Ft Riley, NE Kansas

Using an EV battery pack as back-up home power

Post by spinningmagnets » Aug 31 2019 9:34am

I have specifically chosen 13S 52V battery packs as my default ebike voltage. I currently have three. There are many "48V" nominal inverters that will accept an input voltage as high as 60V, and a fully-charged 14S pack is usually 58,8V if charging to the common 4.2V per cell. Although these cells will take 4.2V per cell, I continue to be shocked at how so many ebike batteries and chargers that still use 4.2V as the default.

First: your pack may last up to twice as long at 4.1V per cell, and 4.0V is even better for cycle-life. (there is no benefit to charging to 3.9V per cell). There is less than a 10% drop in range when doing this. How often do you actually run your pack completely dry?

Second: When your charger and BMS are balancing at 4.2V per cell, how accurate is that? If you bought the absolute most affordable components and devices, accuracy is a relative term. Charging to 4.1V gives you some headroom and a safety margin.

The OP's question goes to other EV voltages. The Zero motorcycle uses 28S, which is roughly 102V nominal, and about 115V fully charged.

The defunct Alta Motors company used 355V.

Tesla uses a nominal 355V/375V depending on model.

Chevy Volt uses 96S, and at their fully-charged 4.05V per cell, that is roughly 388V

The Nissan Leaf is roughly 360V, from various sources.

So, apparently...there is a market for an inverter that can take an input up to 400V DC, and convert it to 120V AC.

User avatar
spinningmagnets   100 GW

100 GW
Posts: 11878
Joined: Dec 21 2007 10:27pm
Location: Ft Riley, NE Kansas

Re: Using an EV battery pack as back-up home power

Post by spinningmagnets » Aug 31 2019 9:50am

The main issue with using a large EV battery pack as temporary home back-up power is the liability around "back feeding" the grid, if your homes electrical system is still connected to the city grid.

If you have solar panels and a large home battery, most people have a "grid connected" system, instead of free-standing (I am a fan of free standing). The main feature of a grid-connected system is a switch that meets all the performance and safety requirements. This means when the power from the city goes down during a storm, the switch automatically cuts off your home from the city-grid, and powers your home only from your home back-up battery pack. It will have to be "re-set" when the city power comes back online...

The safety fear is that...if a power line is down on the ground during a storm, and a utility worker is trying to fix it, they will have tested it for current, and with a zero reading, they will proceed with the repair. Then suddenly, you power-up your home by flipping some UN-authorized switch, which not only powers up your home, it sends power down the outdoor lines that are in the process of being repaired, and may electrocute someone who is standing near a power cable that is laying on the wet ground.

There is a large simple switch in a fusebox that connects the city power grid to your home. Rather than fiddle with that, I prefer to run an extension cord from an inverter that is connected to my ebike batteries. In an emergency, I will not be running my air conditioning. I only need to power my refrigerator, a few low-watt lights, and my TV plus laptop computer.

john61ct   100 GW

100 GW
Posts: 7293
Joined: Dec 18 2018 2:06pm

Re: Using an EV battery pack as back-up home power

Post by john61ct » Aug 31 2019 1:18pm


spinningmagnets wrote:there is a market for an inverter that can take an input up to 400V DC, and convert it to 120V AC.
Vicor makes top-notch isolated DC-DC buck converters, sometimes come through eBay for peanuts.


Post Reply