[Murphy]

Hi folks,
Seems that this is the place to go for information so I thought I'd join and post my question.


My home is powered by a large grid-tied solar system that makes over 1200KW per month. I want to install a battery backup "off-grid" sub-system. I live in the countryside and we lose power out here every time the wind blows for a week at a time. I'm also a bit of a prepper so I want a system that will work if the grid goes down for a longer time frame.



I found a 2014 Chevy Volt battery (Gen 1) that is local to me. Car had 30k miles on it, seller wants $1500 for the battery. Its in the original shell.

I'm using an Outback Radian 8048 inverter (48volt nominal). Puts out 8000W continuous split phase 120/240. (our home draws an average of about 1000 watts but can spike to 4000 when the well pump runs)



I'm considering purchasing the chevy volt battery because it is cheap. But what I then end up with is 7 individual packs at 48 volts each and will need 7 BMS boards for those 7 packs.

The Chevy volt battery is also not re-configurable so easily as the tabs are welded and difficult to work with.

I also don't know which BMS system would be recommended for a 2kw 48v pack.. I would need 7 of them.



On the other hand, if I hold out for a Nissan Leaf type battery, I spend two to three times as much money but I get a much larger battery with screw terminals that are easily configured to do whatever I want. The Leaf cells would also allow me to go with a 13 or 14 series configuration to kick the voltage up to around 64 volts. The higher voltage means less current through the inverter which means less heat as well. I would also be able to use a single BMS system because the packs would be wired parallel first, then series.



The Chevy Volt batteries are of a higher quality and because the Chevy has an engine, GM didn't push the batteries to their outside limits. The Chevy battery also had better thermal management as they are liquid cooled.



The Nissan Leaf batteries are much larger, easier to work with, but since their vehicle doesn't have a backup engine, those batteries are worked hard and they are air cooled.



Finding a BMS for the Nissan battery is easy.. Any of the high quality Orion BMS units, or other similar large high quality systems, would work fine. But I'm not into buying 7 different BMS units at $800 each for a Chevy battery. So the option is to go with a cheaper Chinese unit and I have no idea where to start with that.


Ears wide open, I'd like to hear your opinions.

 

[Yabert]

Welcome. You are right about nissan VS chevy Volt cells except on one thing.
For 12 cells in serie (45V nominal) you only need one 300$ Zeva BMS16 for chevy Volt or Nissan cells.
It's what I've done in my smart, but I've also do this for solar system.
In my Smart I linked* the cells tabs between parallele cells**, but for a 48V solar battery, I linked the cells by the BMS connector (orange on pic). So, two cells link togeter can be consider as one cell.
13 small wires and two large conductors at each end of the battery. This work well if you are sure than no more than 1A will ever flow in those small wires who is generally the case with high quality LG chem cells of the Volt battery.


*Weld with a TIG, but it's too complex and not need for a simple solar battery.
** same exact voltage before connecting them.

 

[Murphy]

Welcome. You are right about nissan VS chevy Volt cells except on one thing.
For 12 cells in serie (45V nominal) you only need one 300$ Zeva BMS16 for chevy Volt or Nissan cells.
It's what I've done in my smart, but I've also do this for solar system.
In my Smart I linked* the cells tabs between parallele cells**, but for a 48V solar battery, I linked the cells by the BMS connector (orange on pic). So, two cells link togeter can be consider as one cell.
13 small wires and two large conductors at each end of the battery. This work well if you are sure than no more than 1A will ever flow in those small wires who is generally the case with high quality LG chem cells of the Volt battery.


*Weld with a TIG, but it's too complex and not need for a simple solar battery.
** same exact voltage before connecting them.

I'm not getting this. How are you using a 16 cell bms to balance 24 cells? on two different packs?

 

[Immo1282]

If you connect two cells in parallel - a BMS will just treat it as one, larger cell instead of two distinct cells. It's pretty much accepted to be fine to do this for cells of the same origin and past cycles etc.

 

[Murphy]

If you connect two cells in parallel - a BMS will just treat it as one, larger cell instead of two distinct cells. It's pretty much accepted to be fine to do this for cells of the same origin and past cycles etc.

If I have six or seven of the 48v packs, that still works out to over $900.. and I'd still need a bms for the 7th pack.


Is there a cheaper alternative? The way this is looking, I might have to pass on the volt pack and find cells I can parallel and then series.

 

[Duncan]

You can simply parallel the volt modules AND the cells inside them

The connector on the top of each module has wires to each cell (actually there are already some in parallel)

You just connect the modules using the nice bolt on connections and use the connectors to parallel up the cells

From memory a 48 volt module is actually 12S x 3P (internally connected)

So four of them would end up 12S x 12P - and would need one 12S BMS

 

[Yabert]

Exactly as Duncan describe. 12S + XXP
In the case of a 16 kWh Volt pack that mean 8 pack of 45V and so 12S 24P (24 cells in paralel or differently, 8 groupe of 3 cells in parallel). 45V 360Ah instead of 360V 45Ah
At the end, only one 12S BMS

 

[swoozle]

If you are willing to play with CAN, you can use the stock Volt BMS slaves to monitor and balance your pack even if configured as 45V in parallel. TomDB's SimpBMS might even do it.
The one caveat is that each slave must be fully populated with modules to work correctly. If you are using the whole pack then you have no problem.

 

[Ocean]

I purchased several Chevy Volt complete packs (16kwH, like what you are considering) - mainly for use in my Bradley EV project, and also a couple for a Chevy S10 Conversion.

I ended up with extra 12s units (2kWh) and 6s units (1kWh) and I am using them both in my Off Grid solar energy systems - the 12s units in parallel (3 of them for 6kWh's in a 48v system) and the 6s units also in parallel in a different system (24v system)

I do not have any BMS. I have noticed that they actually keep within 0.01 or 0.02 voltage pretty darn good.

However, if any of them needed adjustment, I would simply use a power resister to drain down a little voltage, or use a small power supply to lift it up, on individual cells.

I have not really needed to do that so far, and I am running off grid with deep cycles almost every day.

I agree it's a sacrifice that you have to run a lower voltage and therefore higher amperage.

Also, in order to realize the full potential of your Chevy Volt batteries as a 12s unit, you must be able to program your inverted to have a LBCO of 36 - 38 volts (3v x 12s = 36 volts which is a safe / conservative LV for the Chevy Volt modules). Most inverters only go down to 42v. You might check yours, or you may end up with great batteries but you can use only half their potential.

On the other hand, if you look on Ebay for Tesla batteries, you may come across some 7S Tesla modules, which were designed by Tesla for Mercedes for their B-Class Hybrid. Those modules are awesome, because they have a high voltage of 29.4 and a low voltage of 21. I use them in my 24v system and they are a perfect drop in. I bulk to 29.2 and float at 28.8. They perform excellent. They are 3kWh each. If you put two in series they would be a perfect fit for any standard 48v system. Or, of course, 2p x 2s for 12kWh's. A bit more expensive than the Volt's, but still pretty good.

Both the Chevy's and the Tesla's are awesome. In fact I find the Chevy's to be a little more even with themselves as far as cell balance.... but I haven't balanced them (the Tesla's) yet because they are still within .02 or .03 of each other and I never really push them to their limits.

If you are willing to manually keep and eye and balance your batteries once in a while, they will serve you amazing. Virtually no sag starting motors - and I run a 1.5hp deep well pump that pulls almost 3kw continuous.

I actually had a situation with one of the 12s Volt modules where one cell was very low - about 2.5 volts. I let it sit that way for a couple years. Finally I decided to just try and balance it. I put a 4v DC supply on it, and watched the voltage slowly go up. Eventually I balanced that cell with the others. I then tested the unit with a couple cycles to see if the cell would maintain balance with the rest. It did. I finally integrated it into my 48v system and so far so good. Been a few months now... crossing my fingers maybe I will go check one of these days soon... But I think something must have fallen across the cell - maybe a stick or twig or something - and slowly drained it down - every other cell in the pack is good. They hold a balance really well IMO... and dang only 30k on that car! I would grab it up if I could use it! Again, will your inverter go that low? Down to 36 or 38v LBCO?

 

[vauron]

Thanks, swoozle, you've given me new hope!


I have a complete Gen1 that I have yet to take apart. I want to use the whole thing to power my electrified Delorean. As the motors are in-wheel, the entire space taken up by the original PRV V6 engine is available for the battery. After relocating the front third of the battery to the car's frunk (which will no longer have the gas tank inside the front wishbone), by pure luck the T-shaped remainder fits perfectly in the lower half of the engine bay, leaving enough space above the battery to use the Delorean as a pickup or whatever.


It is easy enough to connect the wiring and cooling of the front third in the frunk back to the rest of the battery in the rear. So the battery as a whole should therefore have no idea what hit it, either electrically or cooling-wise.


So if I understand you I should be able to use the Gen1's original BMS without modification, right?


That would be a fabulous labor-saver.


Here's the skateboard half of the Delorean in my driveway.

And here it is in my garage.

The Volt battery is between the body (background) and the skateboard (foreground). Let me know if these two images don't show up.


So can I do this, easily?

 

[Joshie225]

I'm doing the same thing as Ocean, running without active BMS and manual balancing. I monitor the cells with a Tenergy 5-in-1 Battery Meter

If I had a 48V system I would be using Gen 2 Leaf modules.

I have a 24V nominal system and am running 7S as 6S drops the voltage out of my inverter/charger's operating range. While the Volt pack you've found is a great value the welded construction and 12S arrangement may be a deal breaker if your inverter won't accept the 12S voltage range. I chose Ford C-Max Energi cells so that I could rearrange them into 7S connection which is not so easy with Leaf modules which are of course 2 cells each and 8S again takes me out of my inverter's happy place. There are 84 cells in the 7.6kW C-Max Energi pack. I put 14 cells from the pack in a 24V eGo scooter and the remaining 70 cells (6.3kW) in the home backup power system.

 

[Murphy]

I purchased several Chevy Volt complete packs (16kwH, like what you are considering) - mainly for use in my Bradley EV project, and also a couple for a Chevy S10 Conversion.

I ended up with extra 12s units (2kWh) and 6s units (1kWh) and I am using them both in my Off Grid solar energy systems - the 12s units in parallel (3 of them for 6kWh's in a 48v system) and the 6s units also in parallel in a different system (24v system)

I do not have any BMS. I have noticed that they actually keep within 0.01 or 0.02 voltage pretty darn good.

However, if any of them needed adjustment, I would simply use a power resister to drain down a little voltage, or use a small power supply to lift it up, on individual cells.

I have not really needed to do that so far, and I am running off grid with deep cycles almost every day.

I agree it's a sacrifice that you have to run a lower voltage and therefore higher amperage.

Also, in order to realize the full potential of your Chevy Volt batteries as a 12s unit, you must be able to program your inverted to have a LBCO of 36 - 38 volts (3v x 12s = 36 volts which is a safe / conservative LV for the Chevy Volt modules). Most inverters only go down to 42v. You might check yours, or you may end up with great batteries but you can use only half their potential.

On the other hand, if you look on Ebay for Tesla batteries, you may come across some 7S Tesla modules, which were designed by Tesla for Mercedes for their B-Class Hybrid. Those modules are awesome, because they have a high voltage of 29.4 and a low voltage of 21. I use them in my 24v system and they are a perfect drop in. I bulk to 29.2 and float at 28.8. They perform excellent. They are 3kWh each. If you put two in series they would be a perfect fit for any standard 48v system. Or, of course, 2p x 2s for 12kWh's. A bit more expensive than the Volt's, but still pretty good.

Both the Chevy's and the Tesla's are awesome. In fact I find the Chevy's to be a little more even with themselves as far as cell balance.... but I haven't balanced them (the Tesla's) yet because they are still within .02 or .03 of each other and I never really push them to their limits.

If you are willing to manually keep and eye and balance your batteries once in a while, they will serve you amazing. Virtually no sag starting motors - and I run a 1.5hp deep well pump that pulls almost 3kw continuous.

I actually had a situation with one of the 12s Volt modules where one cell was very low - about 2.5 volts. I let it sit that way for a couple years. Finally I decided to just try and balance it. I put a 4v DC supply on it, and watched the voltage slowly go up. Eventually I balanced that cell with the others. I then tested the unit with a couple cycles to see if the cell would maintain balance with the rest. It did. I finally integrated it into my 48v system and so far so good. Been a few months now... crossing my fingers maybe I will go check one of these days soon... But I think something must have fallen across the cell - maybe a stick or twig or something - and slowly drained it down - every other cell in the pack is good. They hold a balance really well IMO... and dang only 30k on that car! I would grab it up if I could use it! Again, will your inverter go that low? Down to 36 or 38v LBCO?

My inverter only goes down to 42 volts but I think I'm going to pass on the Chevy battery and hold out for a Nissan Leaf or something similar. I do not like the idea of running an 8000 watt inverter that cost $4300 at low voltage.. Going to opt for something I can configure into 13s or 14s and a configuration that only needs one BMS.


Thanks for your detailed experience, that helped a lot..

 

[Ocean]

Sounds like a good plan! Again, have a look on ebay at those Mercedes B-Class Tesla Batteries.... 7S units 3kWh each. These are a perfect drop in for 24v systems and 2 of them in series would be a perfect drop in for 48v systems - giving a low of 42v (14s x 3v) so two of them would give you 6kWh and you could double that with two strings in parallel.... good luck!

 

[Off the grid]

I purchased several Chevy Volt complete packs (16kwH, like what you are considering) - mainly for use in my Bradley EV project, and also a couple for a Chevy S10 Conversion.

I ended up with extra 12s units (2kWh) and 6s units (1kWh) and I am using them both in my Off Grid solar energy systems - the 12s units in parallel (3 of them for 6kWh's in a 48v system) and the 6s units also in parallel in a different system (24v system)

I do not have any BMS. I have noticed that they actually keep within 0.01 or 0.02 voltage pretty darn good.

However, if any of them needed adjustment, I would simply use a power resister to drain down a little voltage, or use a small power supply to lift it up, on individual cells.

I have not really needed to do that so far, and I am running off grid with deep cycles almost every day.

I agree it's a sacrifice that you have to run a lower voltage and therefore higher amperage.

Also, in order to realize the full potential of your Chevy Volt batteries as a 12s unit, you must be able to program your inverted to have a LBCO of 36 - 38 volts (3v x 12s = 36 volts which is a safe / conservative LV for the Chevy Volt modules). Most inverters only go down to 42v. You might check yours, or you may end up with great batteries but you can use only half their potential.

On the other hand, if you look on Ebay for Tesla batteries, you may come across some 7S Tesla modules, which were designed by Tesla for Mercedes for their B-Class Hybrid. Those modules are awesome, because they have a high voltage of 29.4 and a low voltage of 21. I use them in my 24v system and they are a perfect drop in. I bulk to 29.2 and float at 28.8. They perform excellent. They are 3kWh each. If you put two in series they would be a perfect fit for any standard 48v system. Or, of course, 2p x 2s for 12kWh's. A bit more expensive than the Volt's, but still pretty good.

Both the Chevy's and the Tesla's are awesome. In fact I find the Chevy's to be a little more even with themselves as far as cell balance.... but I haven't balanced them (the Tesla's) yet because they are still within .02 or .03 of each other and I never really push them to their limits.

If you are willing to manually keep and eye and balance your batteries once in a while, they will serve you amazing. Virtually no sag starting motors - and I run a 1.5hp deep well pump that pulls almost 3kw continuous.

I actually had a situation with one of the 12s Volt modules where one cell was very low - about 2.5 volts. I let it sit that way for a couple years. Finally I decided to just try and balance it. I put a 4v DC supply on it, and watched the voltage slowly go up. Eventually I balanced that cell with the others. I then tested the unit with a couple cycles to see if the cell would maintain balance with the rest. It did. I finally integrated it into my 48v system and so far so good. Been a few months now... crossing my fingers maybe I will go check one of these days soon... But I think something must have fallen across the cell - maybe a stick or twig or something - and slowly drained it down - every other cell in the pack is good. They hold a balance really well IMO... and dang only 30k on that car! I would grab it up if I could use it! Again, will your inverter go that low? Down to 36 or 38v LBCO?

My inverter only goes down to 42 volts but I think I'm going to pass on the Chevy battery and hold out for a Nissan Leaf or something similar. I do not like the idea of running an 8000 watt inverter that cost $4300 at low voltage.. Going to opt for something I can configure into 13s or 14s and a configuration that only needs one BMS.


Thanks for your detailed experience, that helped a lot..

I have 2 radian inverters and 14 model s modules
The inverter turns off at 36v i have the gen come on at 38v. No problem

 

[jlanman]

I live in Florida and have a situation similar to yours. I looked into using batteries in my converted Ford Ranger for backup when the grid goes down. I backed away due to cost and complexity. I elected to continue to use my gasoline generator. (The energy density of fossil fuels is hard to beat.) Based on your stated usage of1000 watts it wouldn't take much of a generator. I believe you might find one for about the same cost as you're considering paying for batteries. It would also eliminate the risk of depleting the batteries before the grid is restored.

 

[Murphy]

I have 2 radian inverters and 14 model s modules
The inverter turns off at 36v i have the gen come on at 38v. No problem

The specs in my Radian 8048 say it shuts down at 42 volts. How do you come all the way down to 36 volts and is that even wise to do? That's a lot of current and heat to be generated.

 

[Murphy]

I live in Florida and have a situation similar to yours. I looked into using batteries in my converted Ford Ranger for backup when the grid goes down. I backed away due to cost and complexity. I elected to continue to use my gasoline generator. (The energy density of fossil fuels is hard to beat.) Based on your stated usage of1000 watts it wouldn't take much of a generator. I believe you might find one for about the same cost as you're considering paying for batteries. It would also eliminate the risk of depleting the batteries before the grid is restored.

1000 watts is just average, not actual use. While the home generally sucks about 1000 watts, it will jump up when freezers turn on or the water pump runs or the sump pump runs. These are short duration spikes, but they will over-load anything not capable of 4000+ watts.

And I haven't even gotten to talking about the mig welder, plasma cutter or air compressor yet. These loads draw 4000, 5000, and even 6000 watts or more on their own, albeit for somewhat short duration as well.



We do run a generator for normal grid down events which happen three or four times a year here. My 5000 watt Coleman is hooked to a natural gas line. But I hate having to listen to it.



Most of what I'm doing is in case the grid goes down for an extended period. Terrorist attack, etc.



I bought the Chevy Volt battery today for $1350 Its in the back of my truck. This doesn't invalidate my desire to purchase more batteries, but it will get me going somewhat. Now I need to figure out if there is a way to turn the 12s modules into 14s modules. I have copper and can fabricate just about anything. I'm wondering if I can rob the 6s modules of a couple plates each and tack them to the end of the 12s modules.

 

[Ocean]

1000 watts is just average, not actual use. While the home generally sucks about 1000 watts, it will jump up when freezers turn on or the water pump runs or the sump pump runs. These are short duration spikes, but they will over-load anything not capable of 4000+ watts.

And I haven't even gotten to talking about the mig welder, plasma cutter or air compressor yet. These loads draw 4000, 5000, and even 6000 watts or more on their own, albeit for somewhat short duration as well.



We do run a generator for normal grid down events which happen three or four times a year here. My 5000 watt Coleman is hooked to a natural gas line. But I hate having to listen to it.



Most of what I'm doing is in case the grid goes down for an extended period. Terrorist attack, etc.



I bought the Chevy Volt battery today for $1350 Its in the back of my truck. This doesn't invalidate my desire to purchase more batteries, but it will get me going somewhat. Now I need to figure out if there is a way to turn the 12s modules into 14s modules. I have copper and can fabricate just about anything. I'm wondering if I can rob the 6s modules of a couple plates each and tack them to the end of the 12s modules.

That VOLT battery for $1350 was a great deal.

I don't know anything about the Radian inverters. But, if Off_The-Grid says his Radian inverters shut down at 36v, then most likely yours can too. Specs often tell you the range as Manufacturer Default. However if you look closely, the actual range may be higher. Go into you Low Battery Cut Off (LBCO) setting and see how low you can adjust it.

36v for a 12s Lithium battery is fine because thats 3v per cell. If you look into the chemistry specs you will find the Low value to be about 2.5v per cell and the high value to be about 4.2 volts per cell. Although there is a quick decline once you get down to about 3v, so having a 3v per cell low is pretty safe.

Of course you are running slightly more amps because you are running in a lower voltage range. But, consider that the Lithiums have virtually no voltage sag under heavy load (unlike Lead Acid which has major sag). For example, I have a mere 2kWh 6s Volt Unit running my 24v system, and I can start my 1hp table saw or my mid-size air compressor and watch the volts go down... maybe 0.4 volts. Hardly any sag and it's only barely a 100amp hour battery.

So they will hold their voltage very well under load. This means less intense surges through your inverter, and perhaps the overall average amperage won't be much different comparing for example an 8kWh Lithium pack running 50v @full vs a 8kWh LA pack running 58.4v @full because under heavy load those LA's will sag major where the Lithium's will not.

Anyways, before you go hacking those beautiful VOLT modules apart (which is probably impossible to do neatly - you will see what I mean once you look closely how they are assembled), look closely at your Radian settings to see if you can bring down the LBCO down to 36 volts. Even at 42 volts LBCO you still have great capacity from a large pack of Lithiums.

Also, be aware that those VOLT packs are under compression. And I mean major compression. If you un-bolt the end-caps, the packs will expand dramatically. You must be prepared for it. the tops of the packs are banded together. If you remove the band, the plastic top will be the only thing holding the module together, and it will eventually break. If you want to re-configure the packs physically, you will need Metric Threaded Rod (M6 I believe).

I have done this operation of physically re-configuring the packs and it is a super pain in the ass. But it is indeed doable. Huge (LONG) clamps really help - like wood working clamps. Also threaded rod and strong steel plates like 1/8 x 3/4 x 7 or 8" with a hole on each end. Turnbuckles.

I truly recommend leaving them as they are - just line them up so you can connect them electrically. Parallel each 12s unit. Run a jumper for the two separate 6s units to make another 12S unit and add it to the parallel setup.

OR, sell me the 6s units!!! haha. But then you would be un-bolting the packs and again I don't recommend it unless you really need to. Major expansion.

I hope you find a setting on your Radian to bring down the LBCO that's really the best solution in my humble opinion.

Awesome Find! Have Fun with those beauties!

 

[swoozle]

That VOLT battery for $1350 was a great deal.

...
Also, be aware that those VOLT packs are under compression. And I mean major compression. If you un-bolt the end-caps, the packs will expand dramatically. You must be prepared for it. the tops of the packs are banded together. If you remove the band, the plastic top will be the only thing holding the module together, and it will eventually break. If you want to re-configure the packs physically, you will need Metric Threaded Rod (M6 I believe).

...

The only compression they are under by the through-bolts is to compress the seals present at each liquid coolant channel running along the sides of the cell modules. Unbolting those to separate the modules and rebolting them is really not a big deal. Rebolting can be done without clamps by using sufficiently long threaded rod and then trimming to length after tightening the nuts down (been there, done that).
The bands at the top really don't do much. They can almost be slid off by hand. I've been running without those with no problem.

Breaking down the modules to the cell level is a whole other story, yes.

 

[Ocean]

The only compression they are under by the through-bolts is to compress the seals present at each liquid coolant channel running along the sides of the cell modules. Unbolting those to separate the modules and rebolting them is really not a big deal. Rebolting can be done without clamps by using sufficiently long threaded rod and then trimming to length after tightening the nuts down (been there, done that).
The bands at the top really don't do much. They can almost be slid off by hand. I've been running without those with no problem.

Breaking down the modules to the cell level is a whole other story, yes.

Ok... maybe so. I've seen a single 2kWh 12s unit with no banding break at the top, where plastic holds it together. The pouch cells starting to separate at the end. I compressed it back and yes, no problem. But I didn't like seeing it press it self apart. Keeping them compressed like they are designed seems right to me.