Smallest BMS in the world?

[morphix]

Check out this, been doing some repairs/experiments in my little electronics workshop, and I discovered what is quite possibly the smallest BMS ever! It's in the red square and is only a couple of mm across, it manages the charging for a tiny 3.7v battery for a DECT gadget device!

At the top of the picture is a BMS circuit from a LiFePo4 e-bike battery.

And to the right, is a neat gadget from China I'm playing with, a 40v voltage down regulator or stepper.. unusually it has an LED display so you can see the precise voltage output as you turn the pot to adjust the DC voltage input and it's got a little terminal block for your voltage output, I'm using it to power a Raspi (microcomputer) and some indicator lights I've designed. It also has a handy USB port that puts out the usual 5v, ideal for charging your phone or powering something mobile on the move! I'll do a video when I have time for those interested.

 

[KirstinS]

The bms inside a smart phone may be smaller still ?

I'm really interested in the signals , please do update as you go - unless it's a top secret patent pending!

 

[Deleted member 4366]

What about those under the end-cap of individual protected 18650 cells?

 

[KirstinS]

Also, id be grateful for a pointer to where you purchased your stepper gizmo

 

[morphix]

Here's another tiny BMS...

 

[morphix]

Also, id be grateful for a pointer to where you purchased your stepper gizmo

It came from a Chinese seller on eBay only £3.18 including postage all the way from China! Here's the item number: 400810822403

 

[morphix]

The bms inside a smart phone may be smaller still ?

I'm really interested in the signals , please do update as you go - unless it's a top secret patent pending!

Oh you mean the DECT stuff? It's just a little gadget from China off eBay, basically it replaces the need for a telephone. It pairs with any GAP/DECT base unit and acts like a telephone handset, allowing you to receive and make calls. It's a clever little device and I've never seen anything like it on the market before, has a lot of potential niche market usages (elderly, disabled people, mothers, office/home-workers etc)

The range (about 30-40 feet) and signal quality is acceptable, sound quality is very good but quite as crisp as a proper DECT phone handset due to the inferior quality earpiece and mic no doubt.

However the gadget has a design flaw (like many Chinese-designed things) and that is the battery runs out unusually quickly and even randomly (even after a full charge with hardly any use). It should last days or a week between charges, and does when new.

I purchased a new LiFePo4 3.7v cell for it which are available cheaply on eBay from China, thinking the cells might be degrading due to long shelf-life (I bought two of these gadgets) but replacing the battery cell hasn't helped the problem (much).

The charger is only 5v 350mA, so I'm wondering if it's giving the unit enough current to charge properly and perhaps a different charger might be needed? Also I noticed the charging port is rather shoddy, it's not an actual proper socket (hard to explain) and so the connection might be very good, as charging seems to go off-intermittently sometimes. It uses one of those incredibly thin barrel-style charger connectors.

Also the gadget has a retractable ear-piece (very poor quality and too short to use from a belt), so I decided to fix these shortcomings by:

1) Replacing the charging inlet with a proper socket and trying a higher current output charger,

2) Removing the retractable ear-piece and fitting a standard 3.5mm earpiece socket to the top so any headset can be used - I might even fit one of those 4-way sockets which would allow the hands-free type headset that comes from mobile phones with an in-line mic, then by-pass using the built-in mic in the gadget, which prolly makes more sense if wearing on belt.

Interestingly though, the whole circuit is so tiny (and the housing comparatively big) and you could put this circuit into another device where you need hands-free DECT telephony! (perhaps a PC keyboard!) I'm pretty sure it would even fit into a geeky looking large wrist-watch at a push ;-)

Here's some pictures of it. They sell for £25 on eBay, only one seller (in the UK) sells them. I was going to buy 100's of them for my business with my own custom brand on (glad I never now!) as I was offered a good bulk discount in China. The guy on eBay seems to be stuck with them and tried to sell me his remaining stock.

 

[Deleted member 4366]

I purchased a new LiFePo4 3.7v cell for it which are available cheaply on eBay from China, thinking the cells might be degrading due to long shelf-life (I bought two of these gadgets) but replacing the battery cell hasn't helped the problem (much).

LiFePO4 is 3.3v and runs between 3.65v and 2v, though most of its charge is between 3.3v and 2.8v. If your original battery was 3.7v, the BMS will control it to between 4.2v and 3.1v. A LiFePO4 one would therefore not give much charge because it has virtually no charge above 3.3v and you'd be cutting it off at 3.1v long before it's empty.

 

[KirstinS]

Actually I rather meant the indicator setup you designed

The dect stuff. It's very cool butt rather niche as you say

 

[morphix]

LiFePO4 is 3.3v and runs between 3.65v and 2v, though most of its charge is between 3.3v and 2.8v. If your original battery was 3.7v, the BMS will control it to between 4.2v and 3.1v. A LiFePO4 one would therefore not give much charge because it has virtually no charge above 3.3v and you'd be cutting it off at 3.1v long before it's empty.

D8veh do you recommend I use a higher current charger then (at the same voltage)?

This is why I need you on our new CycleCharge "Battery Recycling, Research & Development Team"

 

[morphix]

Actually I rather meant the indicator setup you designed

The dect stuff. It's very cool butt rather niche as you say

Oh! I did wonder.

Well here's goes the indicator lights story..

I bought a set off eBay (an integrated brake light and two amber indicators, with a wired handlebar switch, and it runs off ultrabright LED's and 3xAA).

At < 5 quid I wasn't expecting much. And like many things from China, it was shockingly bad, not only were the lights very dim and unsuitable for indicator lights in daylight, but the whole thing fell apart.

HOWEVER, the housing matched and fit the end of my eMezzo rack perfectly and it looks great. So I thought, why not strip the insides out, source some 12v LED's use a voltage stepper and a 555 timer chip (even the indicator lights flashed too quick on the original circuit).

So basically that's what I'm building! I have everything now. I got some mega bright 12v LED's but I'm still not convinced they will be bright enough in daylight. We'll see. I may have to build some better reflective background.

As soon as I get time I will happily share my project and post pics and videos along the way.. In fact, I might do some now of the device before I strip it out, like a 'before and after'

The other thing is.. I don't like the idea of adding more wire over the bike/switches on the handlebar. I was thinking of perhaps doing a Bluetooth option and making a simple app (I have a Bluetooth wrist watch and also a holder for mounting a smart phone on the bike itself). Bluetooth might not be safe though/reliable enough and would require a lot of testing.

But surely, anything is better than sticking your arm out on an electric bike! It's not ideal or very safe really is it, when moving under power? Especially if using a throttle!

I'd welcome any other ideas on different approaches re automating or making the indicator lights wireless? The brake light is actually wireless (to an extent) it uses a crappy little switch which is near the device and intended to be attached to the rear brake lever at back of the bike, when you squeeze the brake it closes and the big red light in the middle comes on. The lights are intended to be mounted on the seat post I think.

Picture of the device..

At the bottom is a breadboard with a 555 timer chip on it, and just above that two of the 12v
LED's I sourced from China (notice how they're flat with FOUR LEDs on each panel. I powered
one up from a 12v DC battery I have, they're very bright indeed and very cheap, only about a quid for a pack of 4 I think.

At the very top is the rear brake light switch, and the handlebar switch is at the bottom which is 3-way for indicators, and an electronic horn that is also built into the device (actually plays 7 silly melodies so clearly this is more of a toy, aimed at the kiddie market than a serious indicator light).


Upper right is my little key-ring camera. I thought perhaps this (or something like the wireless fob switches used to open garage doors) could be used to turn the indicator lights on/off using radio frequency.

 

[morphix]

LiFePO4 is 3.3v and runs between 3.65v and 2v, though most of its charge is between 3.3v and 2.8v. If your original battery was 3.7v, the BMS will control it to between 4.2v and 3.1v. A LiFePO4 one would therefore not give much charge because it has virtually no charge above 3.3v and you'd be cutting it off at 3.1v long before it's empty.

If I understand what you're saying correctly then, switching to a Li-Ion battery makes more sense? It might provide a more stable power source and more reliable charging?

The original battery was indeed marked 3.7v 240mAh and I replaced it like for like.

 

[Deleted member 4366]

You need a Li-ion battery for your charger and BMS - not a LiFePO4. A LiFePO4 battery is probably too low voltage for your system to work too, so no point in getting the correct charger and BMS.

I'd like to come and se you to discuss some things. Am I right that you're in Redditch?

 

[morphix]

You need a Li-ion battery for your charger and BMS - not a LiFePO4. A LiFePO4 battery is probably too low voltage for your system to work too, so no point in getting the correct charger and BMS.

I'd like to come and se you to discuss some things. Am I right that you're in Redditch?

Yes I'm in Redditch, where are you? What did you want to discuss?

It's a bit early yet for us to start planning repairing and developing e-bike batteries, but ultimately that is what I'm planning to do with CycleCharge and it will be a big part of future activities. For now, we need to do feasibility studies and make the case, and some testing/safety checks need carrying out on the 'budget' CycleCharge branded batteries we're supplying, and the laptop-style chargers (these are supposed to have CE approval and I've seen a lot of Chinese safety certificates etc, but it means nothing to me, I need knowledgeable people here to check these, both for pricing, safety, and repair/recycling feasibility).

I'd like yourself to head this side of it if you're interested, and several other volunteers to work with you who have put their names forward and shown willingness to together as a team (remotely)... some doing development work (on a new battery design), some assembly work (of the new batteries), some doing recycling/repairs (on the existing budget batteries). There will be funding available for your time and materials/equipment provided, but this will take some time and first we have to do feasibility studies, and finish the website/make a business plan.

 

[KirstinS]

As it happens I played around with one of those exact units a couple years back ! I powered with a 18650 instead of 2xaa and it made a good difference to brightness

Ultimately not enough and the switch for use is hateful in practice

Good luck with it!