Should I make a Seiko-based BMS?

[reagle]

As some of you know, I've been testing my S-8209 based BMS for quite a while now in my mower and so far it's been doing well, running its 24V DC motor.
(See http://endless-sphere.com/forums/viewtopic.php?f=14&t=18803&p=274105&hilit=seiko#p274107
for details)
So now I am thinking of spinning it into more of a product that others could use, and any wishlist features that might be useful.
What it does now is this: it looks at up to 8 LiFePO4 cells, detects over and under voltage and turns off charge or discharge as needed. It has a separate charge control FET and a separate load switch. It also does basic balancing. There is no voltage/current reporting or SOCI, just basic battery protection and balancing. The chips are factory trimmed to the LiFePo4 limits and are pretty accurate. They also use very little power. The current design is an 8S, but could be partitioned in any way necessary as the chips are stackable to a pretty large degree. So opening this for discussion and wishes.

 

[bigmoose]

If you purchase a quantity of the Seiko chips optimized for LiFePO4 chemistry (I believe the S-8209AAB-T8T1S), I would be interested in QTY(100) or so. If you need to split a reel let me know and I'll consider it.

 

[BatteryMooch]

I'd also be interested in at least 100pcs, depending on cost.

 

[grindz145]

This community needs this type of BMS very badly. I think that A replacement for the crude designs available currently would be welcomed.

 

[fechter]

After working with BMS circuits for years, I think the Seiko chip is the only thing that has all the features I've been trying to make, and it does it much better. Seiko uses the cascaded signalling setup I copied to eliminate the need for optocouplers and keep the current drain extremely low.

I'm looking at doing a version of BMS using these. It could shure cut the component count down and simplify a lot of things.

If we start talking large volumes of chips, Seiko can make them in any voltage we want.

I would combine this with a 'conduction cooled' resistor bank, possibly remote from the main board. I already have the designs for active and passive cutoff and charger current control that could be adapted to Seiko output.

Pending successful prototype testing, scaling up to fully automated assembly would be pretty easy. If the volume is enough, the end cost should be pretty reasonable.

I suppose if I go this route, we could end up in competition of sorts. This would not necessarily be a bad thing, but we should both be on the same page as to avoid any possible conflict. My goal has always been to bring an affordable, reliable and functional BMS to the market that works at high power levels. If you can do it first, the end users will ultimately benefit.

 

[reagle]

I suppose if I go this route, we could end up in competition of sorts. This would not necessarily be a bad thing, but we should both be on the same page as to avoid any possible conflict. My goal has always been to bring an affordable, reliable and functional BMS to the market that works at high power levels. If you can do it first, the end users will ultimately benefit.

Hi Fechter,
the way things are going so far, I don't see myself competing with you any time soon. I "scratched my itch" so to say and have a working thing I needed, but then it kinda slowed down,and moved to the "next shiny thing" projects If anything, a cooperative development would be a lot more likely. I still have about 10 samples of these chips in a slightly different voltage range (S-8209AAC-T8T1S) that I could share with you if you need them for prototyping.

 

[fechter]

Glad to hear that. I think we basically share the same goal.
I need to do a little thinking about the specific design I'm looking for, but most anything will resemble the app note.

 

[pelle242]

Might this new intersil device be an option?
http://www.eetimes.com/design/automotive-design/4211213/Monitoring-systems-ensure-Li-ion-battery-safety-and-efficiency?pageNumber=0&Ecosystem=power-management-design

 

[fechter]

That looks interesting, but perhaps overkill.
Interesting that they state the devices may be subjected to several times the normal voltage during transients. I think he had a fairly good description of the issues involved in a BMS.

I couldn't find a link to the datasheet there. I also didn't see any pricing information. I suspect it's still sort of vaporware at this point.

Maxim, Linear and TI have similar devices.

 

[BatteryMooch]

I was hunting around for info earlier this week for these Intersil devices...no luck.
IMHO, if there's no data sheet posted, these things aren't going to be available to us for many months.

[Edit] Added reference to Intersil

 

[webfootguy]

Here is a link to the datasheet and application note. Enjoy:

A series: http://www.sii-ic.com/en/product1.jsp?subcatID=5&productID=50231
B series: http://www.sii-ic.com/en/product1.jsp?subcatID=5&productID=50232

 

[BatteryMooch]

Thanks for the links!

I neglected to say though that I was referring to the new Intersil chip set.
I've updated my post.

 

[full-throttle]

Done!Testing them at the moment.. good fun.

 

[adrian_sm]

Awesome you final got the boards. Hope it all goes well. Sign me up for at least one 16s & 24s when your ready.

- Adrian

 

[bigmoose]

The question of the hour... where do we get the Seiko chips and how large is the minimum lot?

 

[full-throttle]

Adrian: not a problem, as long as they behave

bigmoose: PM sent

 

[fechter]

Done!Testing them at the moment.. good fun.

Nice!

What is the shunt current?

How is the current limiting implemented?

 

[full-throttle]

60-120A for the 24-cell, 40-80A for the 16-cell.

Current limiter based on rail-to-rail micropower comparator and Cu56Ni44 shunts.
Just a simple protection against accidental shorts and controller faults.
Auto restart after one second delay - no need to power cycle.

 

[CameraMan]

HI Guys,

I am new to this forum and I am delighted to see that you guys are interested in BMS.

The 16 cell unit built by full-throttle is most impressive. Will they be available to others ?

I have a 16 cell LiFEPO4 battery pack with 4 x 3.3v cells in series to give 15 Ah @ 13.2v. I then put 4 x 15 Ah packs in parallel to make a 60 Ah battery.

My biggest concern is cell balance. The intended charging source is a photovoltaic solar panel and the current draw from my device is unlikely to exceed 1000 mA.

Does anyone have any guidance for me in terms of cell management ? I have a Arduino board that measures the overall battery voltage and isolates the battery based on overall pack voltage for both over-charge (currently set at 14.6v) and over-discharge ( currently at 10v).

However, I need to manage the cells individually to maintain the cell balance.

Many thank for taking the time to read my post.