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Discussion Starter · #1 ·
Hey guys/gals we just finished our first conversion ( mostly) but I'm having a really tough time finding a BMS I like. Mostly because it probably doesn't exist yet or I am just looking in the wrong places. Heres my complicated wants..
1. flexibility, we will be building cars with different and/or upgradable packs Need a BMS to accommodate growth.
2. Connectivity via Bluetooth or WiFi
3. GPS, we would love to monitor the cells and be able to use map features/MPH etc. (I feel that since the cell condition will be the number one thing to monitor, having a screen, Tesla like, that integrates some functions like this would be beneficial..if it doesn't exist I am willing to work with the community and manufacturers to make this happen.)
4. obviously active balancing
5. DC/DC I know this is likely far fetched at this point but having a DC/DC converter for 12v built in would limit yet more wiring and another module needed.

This is all fairly new to me so I appreciate your advice, knowledge.

BTW, our current build is 295v 72cell. With the BMS's I have found we will most likely have to run 4 packs 18cells @ 74v and 4 bms
 

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Hey guys/gals we just finished our first conversion ( mostly) but I'm having a really tough time finding a BMS I like. Mostly because it probably doesn't exist yet or I am just looking in the wrong places. Heres my complicated wants..
1. flexibility, we will be building cars with different and/or upgradable packs Need a BMS to accommodate growth.
2. Connectivity via Bluetooth or WiFi
3. GPS, we would love to monitor the cells and be able to use map features/MPH etc. (I feel that since the cell condition will be the number one thing to monitor, having a screen, Tesla like, that integrates some functions like this would be beneficial..if it doesn't exist I am willing to work with the community and manufacturers to make this happen.)
4. obviously active balancing
5. DC/DC I know this is likely far fetched at this point but having a DC/DC converter for 12v built in would limit yet more wiring and another module needed.

This is all fairly new to me so I appreciate your advice, knowledge.

BTW, our current build is 295v 72cell. With the BMS's I have found we will most likely have to run 4 packs 18cells @ 74v and 4 bms
I don't know of any BMS that has an integrated DC/DC converter, and it wouldn't make much sense for that to exist. You just have to buy another unit.

If I'm reading your post right, you have 72 cells in series, which is within spec for the Orion 2 BMS. BMSes only care about the number of series connections, not parallel connections. Orion sells up to 180 cell BMSes. If you want to run 4 packs in parallel, then you do need a BMS for each pack. Orion has a way to parallel the BMSes so that you only have one main BMS and then 3 satellite BMSes.

Orion has a module that you can buy that syncs over Wi-Fi to monitor cells and SoC.
 

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Discussion Starter · #3 ·
I don't know of any BMS that has an integrated DC/DC converter, and it wouldn't make much sense for that to exist. You just have to buy another unit.

If I'm reading your post right, you have 72 cells in series, which is within spec for the Orion 2 BMS. BMSes only care about the number of series connections, not parallel connections. Orion sells up to 180 cell BMSes. If you want to run 4 packs in parallel, then you do need a BMS for each pack. Orion has a way to parallel the BMSes so that you only have one main BMS and then 3 satellite BMSes.

Orion has a module that you can buy that syncs over Wi-Fi to monitor cells and SoC.
Thank you for the reply. Ive been looking at Orion. They look like good units. My plan was to run series/parallel. I might be way off but 72v x4 parallel for charging, bms, dc/dc and then series over to the controller. Am Out of line to think this would work?
 

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I might be way off but 72v x4 parallel for charging, bms, dc/dc and then series over to the controller.
I might be a little lost here, but are you suggesting a way of re-wiring the pack on the fly to switch between 4x 18s modules of 72v (74v?) to a configuration of 72s and 295v? It would be a strange approach if you are trying to simplify the wiring.

As for lumping a bunch of other stuff into the BMS, I am not sure how that would make things simpler for you. The BMSes only real job is to monitor the cell level voltages, balance them if they are drifting, and raise alerts over CAN bus to shut down any process that threatens to over or under-discharge a cell. The BMS pulls tiny amounts of power from the pack, so if it included a DC-DC converter, for example, you would have to wire it separately anyway.

Since DIY EV cars are so diverse, there will probably never be just one integrated system like you are describing - there are just too many variable for something like that to make sense. If you want to integrate a bunch of information into a single display, including GPS navigation, you would probably have to look into getting a tablet that communicates with the BMS over CAN. You can get CAN-USB interface units, but programming something like that, and making your own GUI for the tablet is going to be a big project.
 

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Discussion Starter · #7 ·
I might be a little lost here, but are you suggesting a way of re-wiring the pack on the fly to switch between 4x 18s modules of 72v (74v?) to a configuration of 72s and 295v? It would be a strange approach if you are trying to simplify the wiring.
Yes, its closer to 74v. How I see it in my head is bus bar with 4packs paralleled for charging and for (4)BMS.. I was trying to keep within the confines of some of the China made systems with GPS/Bluetooth and a simple gauge app for the phone/tablet. Then out to the controller/ V/Amp monitor in series.
 

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Just to clarify

best practice is for all the paralleling to be done first, aka "groups" of cells at the 1S level

so that the pack is just one "string" of those groups connected in series.

In effect the groups function each as a larger single cell, the individual units becoming "invisible" electrically until isolated from each other.

This is only needed if your choice of cell model / line is unavailable in the Ah capacity you need for the pack as a whole.

Better if you need a 180Ah pack, you find 180+Ah cells to build it with, but of course other factors may prevent that.

_
Building modular sub packs and then connecting those in series is fine (if you have a strong reason to do so) but many BMS can't handle that design.

But building multiple packs to then be paralleled is really sub-optimal, certainly once you get past two or three strings. Can be done if you have a truly compelling reason,

a single BMS can control the whole pack, so long as the individual groups at 1S are connected between the sub packs,

but current flow in use and while charging will inevitably be unbalanced, thus whole-pack lifespan shortened.
 

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Yes, its closer to 74v. How I see it in my head is bus bar with 4packs paralleled for charging and for (4)BMS.. I was trying to keep within the confines of some of the China made systems with GPS/Bluetooth and a simple gauge app for the phone/tablet. Then out to the controller/ V/Amp monitor in series.
So if you have 4 modules with all the positive terminals ganged together (and all the negatives as well) then in order to connect them in series you have to break all those connections or else you are going to short the whole pack when you go and try and put them in series. So to do this would need 3(6x?) contactors to break the parallel arrangement, and 3 more to switch them into series. Make sure you fuse them all up too, or a single failure would be a problem. A BMS does not really care what the overall pack voltage is, it just looks at cells - often in groups of 12, so the only advantage here would be that you could charge with a 72 volt charger?

Am I right to assume that you are thinking of using prismatic LFP cells, or perhaps lead acids? Based on the fact that you are leaning towards getting a warp 9, I assume you are building a "classic" style EV like was all the rage about 20 years ago?
 

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Discussion Starter · #10 ·
Am I right to assume that you are thinking of using prismatic LFP cells, or perhaps lead acids? Based on the fact that you are leaning towards getting a warp 9, I assume you are building a "classic" style EV like was all the rage about 20 years ago?
We already have the car running, Just no BMS. We purchased all our current equipment used to keep our first build on the cheap. 2006 Mini Cooper. But we plan on converting classics using AC going forward. Currently we have Nissan Leaf cells.
 

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Sorry for the snarky reply, I was amused at the thought of there someday being vintage EV enthusiasts who restore old lead-acid geo metros :) There are of course still plenty of good things to be said for reusing a DC motor.

As for BMS options, I believe there are a few others out there. I used a thunderstruck Dilithium on my project. It is modular, with support of up to 24 cells per module. So you would need 3 (one BMSC and 2 BMSS) to handle 72 cells, but it can be expanded with up to 384 cells in a single system.
I suspect the Orion would also let you combine several BMSes together if you wanted to add more cells later. It has been a while since I researched BMSes, but I seem to recall there was at least one other option i looked at, by the makers of the Zilla line of controllers, maybe?

There are CAN enabled displays out there, but they are really just a BMS interface, so they would not be suitable to run other programs like you are envisioning. I got an Engage, which just shows me a handful of stats on the dash. If I really want to dig into all the statistics, a laptop can pull up a text-line interface for both BMS and Charger. Anyway, I have been really happy with that system, but I think most of the options out there are pretty solid.

 

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Discussion Starter · #13 ·
Sorry for the snarky reply, I was amused at the thought of there someday being vintage EV enthusiasts who restore old lead-acid geo metros :) There are of course still plenty of good things to be said for reusing a DC motor.

No worries.. Having a YouTube Channel and Facebook forum I have become immune to most BS, If I took offense I would have responded appropriately.

Thank you for the info We are running a Zilla charger since we plan on making a few of these and the customer will be the end all to the total Power we wanted a charger that is adjustable on the fly. I know they have a data port to talk to the BMS, something to consider. Really, I am looking for the ease of use for the end user. If someone brings me a BMW 2002 and wants a full restore with EV conversion, I want to make it fairly integrated with display and east to manage readouts. We already deal with China for our other business so I might look into having one of these companies make something... WE are just getting our feet wet and hope to learn and advance some of our current options.
 
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