Opinions on Chevy Volt Battery part time BMS ?

[patdufo1]

You can't re-configure the cells. They come out of the pack in 12s and 6s modules and have welded terminals that can't be unwelded. You can combine two of the 6s modules into a 12s, but its damn near impossible to do much of anything else.

Its my understanding that the Chevy Volt battery has two things going for it over the leaf.. 1) its a higher quality battery.. but this doesn't matter much for solar storage.. 2) they are usually in better condition on the used market because the Chevy Volt has an engine and GM set the vehicle up so that the battery isn't stressed. There are multiple reports of Chevy Volts going 200,000+ miles without any real battery degradation. No first hand experience on that though.

The biggest drawback is that the Chevy battery cells can't be reconfigured.. its a major stumbling block.

There is a video of a guy cutting out each individual pouchs for ebikes then recombining them,I personally use 28 of the 44v nominal packs and have several 22v nominal packs for future project,no BMS at this point but working on it and looking for sugestions?PS I know this an old post

[HollySprings]

I am late to the party on this, but I have several follow-up comments/questions. My scenario is a Leaf vs. the Chevy, but I am also using the SMA SI 6048-US. My test configuraton is a minimalistic 14s2p, so that's 7 "modules" (the smallest individual component that are set up as 2s2p) connected in series. I plan to expand significantly once I can get past the SMA technical issue (they lack documentation on multiple fronts.) Salts, did you REC BMS working with the SMA SI? Did you get the SMA CAN BUS document?

I've gone a different route on the BMS for multiple reasons. I don't think the $10 products have CAN BUS support and doubt that would work with the SMA SI. But until I see SMA's implementation, it may not matter. My battery configuration right now is set to FLA just so I can get 120V out. I really don't want to spend the time on reverse engineering this interface. I don't have any loads currently on the SI, so the only activity (other than testing) is the SI inverter at about 25w. The SI will not boot if you have LiIon ExtBMS configured and the SI isn't receiving properly constructed packets. I too have asked for the "Connecting Batteries with External Battery Management System to Sunny Island 4548-US/ 6048-US" document, but have not heard back from SMA yet.

I'm early in process of implementing the OpenEnergyMonitor system (OEMS) and will use the DIYBMSv4 along with the emonPi and emonCMS. I'm not a EE so getting the BOM and CPL files right for JLCPCB to layout and populate the board w/ SMT parts has taken me a while, considering my learning curve in involved My plan is to 'standarize' on this (OEMS) platform and hope to use it as the main integration platform when I get everything running... then use it for a CHAdeMO charger and my V2G project, which I hope to build on emonPi/OEMS.

For me, I like the idea of a BMS lead on every cell. It's probably overkill., but with 14sXp where X gets bigger... I'll stick to overkill.

[tom rickard]

I purchased mine through their Australian dealer, not directly.

[Salts]

Haha, maybe on the internet. I know of dozens of systems using Sunny Island and REC with LiFePO4 cells. Surely there must be thousands worldwide!

I guess most people just email REC, get what they need - and it just works. No need to go on the net.

I'd love it if you drop a post on this thread from time to time. At some stage i plan on adding a EV battery into my off-grid setup.

Hey Tom,
When you purchased your Rec-BMS (They are in Slovenia), what was the VAT you had to pay? My total came to a bit over $700 Euro and I'm trying to figure out if they're going to tack on the extra 22% or how that works.

Thanks,

[tom rickard]

Haha, maybe on the internet. I know of dozens of systems using Sunny Island and REC with LiFePO4 cells. Surely there must be thousands worldwide!

I guess most people just email REC, get what they need - and it just works. No need to go on the net.

I'd love it if you drop a post on this thread from time to time. At some stage i plan on adding a EV battery into my off-grid setup.

[Salts]

Hi, sorry for the delay. If you have a "no fault" open circuit in the parallel bridging wire the system will not detect it. As soon as the disconnected cell has a voltage drift the REC will pick up the discrepancy, as all cell voltages are measured from a common point (zero volts on the pack)

As for the Sunny Island comms, you used to be able to buy a wifi kit for them, but the later ones have built in wifi.

I only look at the data from the REC, it tells me all i need to know. You can get a bluetooth module for the REC if you want to monitor it remotely.

As i mentioned earlier, i would encourage you to contact REC directly, they probably have first hand knowledge of using their unit on a Volt battery. If not they will be keen to get you sorted.

Thanks Tom!
I contacted Rec last week, went through an few emails with them, and have worked out what I need to order. Getting the SI compatible BMS unit, shunt, battery contactor, software, cables, etc. I'm also getting 7 extra BMS connectors so I'm going to switch from pack to pack occasionally just to make sure they all stay balanced.

Eventually, I'll probably end up keeping the Rec SI BMS on the Sunny Island because it can communicate with it, then I'll get a (slightly) lesser quality BMS like the ZEVA Master w/slaves. As I add more Chevy volt modules, I can just purchase the extra slave unit for $100. I'll wire the ZEVA so it's in series with the main battery contactor.. If both BMS's don't agree, the contactor doesn't open.

For now, I don't think I'm going to parallel the BMS wires but opt to change from one pack to the next occasionally. Operating time on my unit is going to be very very low.. its just for the three or four times a year when we lose grid power for a week or so.. I'm not even going to be hooking up the AC2 contacts.

I'm busy building the battery box right now.. NEMA 4 Hoffman panel 3ft x 4ft.. Installing Unistrut for adjustable shelves and looking for a good deal on some heavy duty casters. The battery box and Sunny Islands are all going to be one unit that can roll around should I decided to re-organize the basement.. It'll just be four wires from the AC1 terminal I have to change out.

Thank you so much for your help.. I can't believe I found someone with Sunny Island experience, and Rec BMS experience to boot! Its like finding a Unicorn.

[tom rickard]

Hi, sorry for the delay. If you have a "no fault" open circuit in the parallel bridging wire the system will not detect it. As soon as the disconnected cell has a voltage drift the REC will pick up the discrepancy, as all cell voltages are measured from a common point (zero volts on the pack)

As for the Sunny Island comms, you used to be able to buy a wifi kit for them, but the later ones have built in wifi.

I only look at the data from the REC, it tells me all i need to know. You can get a bluetooth module for the REC if you want to monitor it remotely.

As i mentioned earlier, i would encourage you to contact REC directly, they probably have first hand knowledge of using their unit on a Volt battery. If not they will be keen to get you sorted.

[Salts]

I never thought of that.
Could I run the parallel cell tap wire from cell to cell in a daisy chain or do you think I need to make sure all the wires are the same physical length going back to the BMS?

Any individual cell failure (short circuit) will blow the fuselink wire and trigger the BMS disconnect.

If multiple cells are paralleled onto the same conductor and each is fused, how would the BMS know if one of them is disconnected? How would the BMS know if 8 cells paralleled on the same conductor is now only 7?

One more question for you Tom, You seem to be "the expert" on the Sunny Islands.. In fact, SMA should start paying you because you're more helpful than they are! LOL

When I want to see how my current SMA SunnyBoy grid tied inverter is doing, I enter an IP address into my browser and just log into the interface for the inverter. The inverter is connected to my home's Ethernet network. The interface shows me everything I could ever want to know about the inverter's settings and performance.

How is this accomplished with the Sunny Island 6048 ? There doesn't seem to be any Ethernet interface for home networks. Did I miss something?

Thanks!

[tom rickard]

The current flow between parallel sets of batteries is going to be very low. I'd use the thinnest gauge fuselink wire you can get, eg 10amp.

All this is doing is accounting for the slightly different rates of charge of different cells, it isn't conducting the full charge current.

[tom rickard]

If you connect the parallel sets with fuselink wire, you will not have any need for fuses. There are no extra connections to the batteries by doing this.

Any individual cell failure (short circuit) will blow the fuselink wire and trigger the BMS disconnect.

All paralleled cells will be monitored/balanced as if they were one cell. You will obviously be paralleling 2 sets in any case..

The failure modes for a battery are open or short circuit, low or high voltage, low or high temperature, physical damage.

I can't see how any of these failure modes aren't best protected by linking the cells in parallel groups.

[Salts]

2/O cable is rated for 145A, unless you are buying high temp insulation. And the distance you plan to run seems excessive with marginal wire.

If you have double checked your specs and are happy, proceed.

Hi Mike, thank you for the prudence in double checking things like this.

I'm using Carolprene 2/0 90C Welding Cable (600V) Made in the USA

https://www.awcwire.com/mfg/general-cable/product/general-cable-carolprene-welding-cable

Specs say its good for 223 amps continuous duty. I don't have enough stuff assembled to check my distances yet, but I'm guessing from the 2" wide x 1/4" thick bus bar inside the battery box to the Sunny Island inverter(s) should be around 6 feet.. It might be as much as 8 feet, but I doubt it.

I have two DC circuit breakers Eaton Heinemann GJ1 175ADC w/2sec delay. Considering the addition of a fuse to back them up. If nothing else, they make for a good disconnect switch.

Thank you for watching out.

[Mike90250]

... I have two 175amp DC circuit breakers I plan to use with 2/0 battery cable........
......Total battery cable length should be less than 10 feet to each Sunny Island.......

2/O cable is rated for 145A, unless you are buying high temp insulation. And the distance you plan to run seems excessive with marginal wire.

If you have double checked your specs and are happy, proceed.

[Salts]

So let me see if I have this straight. You're suggesting I use the Rec-BMS on one string and hook up the rest with the cheap Chinese BMS's just to use as monitoring packs? Or should those cheap BMS's also perform balancing? I've heard people say that the BMS is one of the leading causes of pack failures.. I "assumed" they were talking about the cheap BMS's and not the units that cost several hundreds of dollars.. Am I wrong? I'm open to all input.

So far I have killed two battery packs based on the "I'll just check them periodically" approach. I would not rely on anything that requires plugging and unplugging things to maintain safety.
That's sorta hard on the system. Charging all that capacitance at once that often may lead to some early failures. EV's use precharge systems and minimize unnecessary system capacitance to deal with this; home inverters do not.

The Rec-BMS will have a precharger... They suggest I use it so that's what I think I should do.. Won't hurt anything right? Their operating manual even has the precharger drawn in with the Sunny Boy. Sales technique or legit component requirement?

I'm actually not worried about reliability at all. If it breaks or shuts down on you, you can fix it, and the most you will lose is a freezer or two full of food. I am more worried about an unseen high impedance cell getting 8 volts across it and starting a fire. You generally can't "fix" a lithium ion fire that starts in your house. You can't extinguish such fires and you can't move the battery out of your house once the fire starts.

On another forum, an ebiker charged his battery overnight in his garage. This was a little 500 watt-hour battery. The battery caught on fire and destroyed his garage. He was VERY fortunate they were able to save the house.

I'm a bit confused on how you are suggesting I use the cheap BMS's. Monitor only with ability to open the main battery contactor? Or have them fully functional and balancing the cells?

As for fire considerations, the entire pack will be inside a Hoffman hinged cover box that is constructed of 14ga steel. It is 4ft tall, 3ft wide and 20 inches deep. I know I'm going to have to vent it with a muffin fan. Not entirely sure how I'll set that up but I will take the possibility of a fire into consideration and maybe use some 4 inch stainless flex pipe and run it a few feet to cool any combustion gasses should they happen. I had actually considered installing a fire sprinkler in the cabinet.. If the temperature gets past a set point, the little wax plug melts and douses the entire inside of the cabinet. Same way the sprinklers work in any commercial building. I installed sprinklers in my garage because I do a lot of fabrication work in there and welding sparks go everywhere. Luckily I've never needed them, but it lets me sleep easier at night knowing that a stray spark in a garbage can isn't going to burn my home down.

Thank you again for your suggestions.. this is all good stuff.. I'm learning.

[jflorey2]

Thank you for your input. The REC-BMS I am considering using has this long green plug that all the BMS cell tap wires connect to. After they are all connected to the green plug, the plug is then inserted into the BMS. My idea is to order 7 extra plugs so all that I have to do is turn the system off, unplug a single connector, and plug the next one into the BMS. Restart the system, and I'm done. In other words, I'm not physically switching 13 wires going into screw terminals and having to connect and disconnect each individual wire. Its just a single multi-pin plug that each 12s string will have pre-wired.

So far I have killed two battery packs based on the "I'll just check them periodically" approach. I would not rely on anything that requires plugging and unplugging things to maintain safety.

Yes, the main battery contactor will open and shut down the system, I will shut down the system manually in the proper order so as not to put any stress on the BMS or the Sunny Island.

That's sorta hard on the system. Charging all that capacitance at once that often may lead to some early failures. EV's use precharge systems and minimize unnecessary system capacitance to deal with this; home inverters do not.

This is an off-grid system for my home. We do not run a surgical operating room where having power all the time is a life or death issue. Its just an off-grid emergency system to keep the freezers cold, the sump pump running, and a desktop computer or two going.

I'm actually not worried about reliability at all. If it breaks or shuts down on you, you can fix it, and the most you will lose is a freezer or two full of food. I am more worried about an unseen high impedance cell getting 8 volts across it and starting a fire. You generally can't "fix" a lithium ion fire that starts in your house. You can't extinguish such fires and you can't move the battery out of your house once the fire starts.

On another forum, an ebiker charged his battery overnight in his garage. This was a little 500 watt-hour battery. The battery caught on fire and destroyed his garage. He was VERY fortunate they were able to save the house.

[Ampster]

You can get a 12S li-ion BMS from Alibaba for $10.00 each. (I would post a link but that doesn't work well

That is a good suggestion. I would put emphasis on the reporting ability of a cheap BMS. If you can't set voltage parameters then all it would be useful for is a remote cell voltage reporting device. That make diagnosis simpler.

I'd do one good BMS so the Sunny Island gets good info and the rest cheapo BMSes. You can use the onboard power switch for the BMS, or use a contactor (or remotely triggered breaker) to cut power when a cell goes out of bounds (safer.)

That sounds good. Again, consider a remotely operated breaker rather than a contactor; safer and less power required.

Another good suggestion. The only issue is it would not provide fail safe protection in the event that the power to the BMS contactor circuitry failed. If CAN BUS communication is successful the Inverter might detect the BMS going offline and shut down. As suggested earlier that might be the situation and the remote breaker would work well. It is a much better solution for a stationary pack that will be in the on position all the time compared to an EV that is on and off several times a day.