# Chevy Volt batteries as source of DIY Storage



## Moltenmetal (Mar 20, 2014)

Been reading and reading this battery forum and am still in a bit of shock about how cheap per useful Wh storage these Volt batteries are. The downsides seem limited to the cell chemistry ( not as safe or forgiving as the LiFePO4 prismatic cells, cells configured in a high voltage configuration unless you want the mess and bother of dissecting them cell from cell, and of course an inscrutable OEM BMS sitting there useless. So my questions are as follows: 

1) is it practical to use the blocks of cells without a BMS given this chemistry?

2) how have people managed with vehicles based around this battery pack as an assembly?

Dunno if the calcs are wrong, but I'm looking at this as being 1/2 the cost of a prismatic cell pack without BMS, based on cell prices I'm seeing advertised. Pretty tempting!


----------



## Sunking (Aug 10, 2009)

My two-cents worth.

Generally speaking EV users want every drop of power they can get. To do that you have to charge each cell to 100% to achieve that goal. Regardless of which lithium chemistry you use will require a BMS to do that.

On the other hand LiFePo4 aka LFP is the most forgiving to over charging, and the safest of the Lithium family. The trade-off for is you have to sacrifice specific energy density of roughly 100 wh\Kg in contrast to something like LiCo of 200 to 250 wh/Kg. Having said that if you are willing to give up 100% state of charge, you do not have to use BMS, at least in the sense of what a BMS is used for. If you only charge up to 80 to 90%, overcharging becomes a moot point if you follow some simple initial and preventive maintenance procedure. Initially you want to balance the cells to get off to a good start. Then periodically check cell balance and take corrective action when necessary in the form of cell balancing by either bringing the lower cells up, or draining higher cells down. Whatever floats your boat. 

As for the other lithium chemistry, IMHO they are just too unstable to risk thermal runaway and should use a BMS.

Hope that helps. Good luck.


----------



## onegreenev (May 18, 2012)

Generally speaking, no, not all ev people want every last drop from the pack. They more want to have a pack that will provide the range and life. I'd say go for it without a bms but you will need a way to disconnect from the pack at a specified voltage. A simple BMS may be just fine. Don't over charge and don't over discharge. No different than using your LiFePO4 cells in a vehicle without a BMS. I purchased two used Leaf Packs that are still in decent condition for cheap. I will have plenty of power and range with that pack. I don't plan on using a BMS but I will have a way to disconnect or stop when I reach a specific voltage so I don't over discharge them.


----------



## piotrsko (Dec 9, 2007)

So far 1000 miles no bms, no issues. Still waiting for the explosive core meltdown in the bed of the truck. Your voltage choices in modules is 120, 72, 96. Haven't really seen the need to cool these, but I run the waterjacket anyways. For stationary might not ever use cooling. I stop charging at 4.05 because I don't trust my measuring equipment, the Simpson doesn't work any more. If I ran the bms, I'd lose about 2.2 kWh capacity, maybe more because it might have a low limit that I don't use.

I have hit 700 amps out or about 8c for 4 minutes on big a$$ hill, I hear they can hit 15c reliably, but that's rumored, I can't do that without cooking my controller or motor.

At $0.25 USD a wh, delivered, pretty good deal for me, although some have gotten that down to $0.10. YMMV.


----------



## chaseadam (Mar 20, 2014)

It appears nominal voltage for these is calculated as 3.75v/cell based on the specification numbers Chevolet publishes about the battery. The packs are broken down into various sizes with the most common one being labeled "2kWh" which would be a 12 cell 45V nominal pack.

I use an entire chevy volt battery (16kWh) in addition to 2 more 2kWh modules from another pack in my Lectric Leopard running at 90V. This puts the arrangement as 5p24s3p (5 parallel 90V packs, 24 "cells" in each pack, 3 prismatic pouches in parallel for each "cell"). Each pack is protected from one another using a 200A semiconductor fuse and the terminal lines are run opposite from one another to ensure even cable resistance across all packs. The controller is protected by a 500A semiconductor fuse.

Never hooked up the coolant circuit, but then again, I don't push the batteries hard. I rarely charge over 95V or discharge under 88V. I charge it with a hacked PFC3000 TCCH (Elcon OEM).

Over 2000 miles so far.

I did have some trouble with one of the packs which I over-discharged early on, but after rebalancing, it has stayed balanced. Still, would love to get the BMS on these things working.

Because I am on a time of use demand schedule for power, my cost per kWh is ~$.07 in Raleigh, NC (not including the demand reservation if during peak hours)

Purchased 3 chevy volt batteries for an average of ~$2000 each shipped, but looks like people have figured out how valuable these batteries are now...


----------



## planetscott (Aug 19, 2014)

Do you have any pics of how you wired them. I have 8 48V packs I will be wiring 4 sets of 2 in series for 46V and then connecting the 4 sets in parallel.


----------



## Moltenmetal (Mar 20, 2014)

If I had the project to do again, a Volt or Leaf pack would have been my choice for sure. A little extra work, but for considerable savings. I understand that the miniBMS can be set up for the voltages required for these cells so there is a BMS option if you want it.


----------

