I have a design for a no-frills BMS I’d like to bring to market and would love to hear what you think about it.
We have inexpensive “dumb” and “smart” BMS’. But that low cost often means lower reliability and can lead to us being the beta-testers for new models with the manufacturer saying they’ll fix things in the next batch.
We have very capable, fully configurable “smart” BMS’. But that flexibility can sometimes mean dealing with confusing software/app installation, firmware upgrades, cabling issues, incorrect settings, and inadequate or confusing documentation.
I think there is room in the market for another type of BMS. A no-frills, high-reliability* device that does one job and does it very well. No settings, no telemetry, and no apps or software. It just works.
In my opinion a big reason why we want our BMS’ to be smart is because we don’t trust them. Sure, we’re DIY’ers and like seeing all the details but would we care about cell voltages and balancing if we knew the BMS did its job? We don’t care about the voltages of the cells in our other devices.
Why can’t we have this for esk8 too? Why can’t we just install a pack with a fully integrated BMS and trust it to do its job? Why do we accept having to treat our packs like something could go wrong at any moment?
You might feel that the BMS needs to be outside of the pack and easily replaceable because they can be unreliable. Why do we accept having to do this?
We build packs that make it a tough to replace a cell because we trust decent cells to have a long life. Why not have that kind of trust in our BMS’?
We should never have to worry about needing to remove the BMS. We should never have to deal with flimsy connectors, crimping connector pins onto wires, or having a pile of balancing wires outside the pack (this is insanity IMO). We should never need to upgrade the BMS’ firmware or deal with buggy apps. Heck, we should never even need to read an instruction manual!
I want to create a high-reliability BMS that “disappears”, that can be embedded into the pack. The only wires leaving the pack are the main charging and discharging leads. No settings, nothing for the user to deal with, just some balancing status LEDs to watch if desired.
An integrated BMS is standard practice for so many products and I think we should have a good option to do that in esk8 too. It’s not the perfect option for everyone but in my opinion it could be a great choice for many. Here’s why…
- No balancing wires outside of the pack.
- No dealing with apps, programs, firmware upgrades, or programming cables.
- Reduced user confusion, no incorrect settings.
- No assembling of connectors and crimping of wires to terminals.
- Easier, more sensible layout of balancing wires within the pack.
- Easy swapping of packs, no delicate balancing connectors to deal with.
- Shorter development time, comes to market faster.
- More time spent on creating good hardware rather than telemetry and apps.
Features
- This is a “dumb” BMS, no Bluetooth, no comm ports, no display.
- No firmware upgrades (no compatibility issues, no version number confusion).
- Two charge-only models: 9S-15S and 12S-20S
- 24S possible but only if the sales volume is there…100pc minimum.
- True continuous 20A protected charge rating with 20A protected discharge rating (for powering buck converters for accessories).
- 50mA balancing, begins at 3.8V and only during charging.
- 4.25V over-voltage/2.8V under-voltage protection, triggers after one second.
- No LFP (LiFePO4) chemistry support for this first version….sorry.
- Two levels of time-based over-current protection. Charge and discharge overcurrent is stopped after about 200mS, short circuits are stopped in about 1mS.
- 50°C charge/70°C discharge over-temperature protection.
- 0°C charge/-20°C discharge under-temperature protection.
- LEDs to check balancing status of each p-group.
- On-board 12V and/or 5V buck converter can be included but adds to the cost, size, heat, and development time.
- Design goal is 35mm x 105mm x 5mm maximum for the 12S-20S version. The 9S-15S version will be smaller.
- Connector types are unknown as of now. Strain-relief-protected solder pad balancing wire connections are being considered to create a very low-profile BMS. No connectors. This can be made reliable, it does not have to be a short-circuit danger.
- The balancing status LEDs can be viewed through the shrink wrap.
- A diagnostics port can be added to allow easy checking of all the cell voltages.
I do not present this BMS design as the perfect solution for everyone. Like all of the BMS’ we can choose from there are compromises. My BMS makes different compromises though and is a simple unit that does one thing only and does it very well.
You’re wondering what it will cost…I don’t know. It will not be cheap, we cannot expect it to compete with higher sales volume China BMS’. It might not even be considered affordable by many as a very reliable design has a much higher parts cost and months of testing will be done (which is hugely expensive since other revenue-creating projects cannot be worked on). But this thing will be close to bulletproof.
So, is it worth bringing to market?
Your thoughts and feedback are invaluable and would be very much appreciated. Thank you for your patience in reading this long post!
I do have a “smart” BMS design in the works too. But that could easily take another year to develop, if not longer.
*Since 1992 only two of the hundreds of devices I have designed and built have failed. One was dropped from a height of about 70ft but still worked when I replaced the battery connector. The other was partial loss of function due to, I believe, static (ESD) damage. Since then all connections and ports on my devices are ESD-protected. There have been no reported failures for over eleven years now, for any of the devices I have built.
