Opinions on Chevy Volt Battery part time BMS ?

[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.

[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.

[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]

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]

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]

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]

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]

I purchased mine through their Australian dealer, not directly.

[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.