"Zephyr" - Finally, the "v4" Fechter/Goodrum/Hecker BMS...

[cor]

In continuation on the BMS issues list, one thing that is almost universally a fault detector is an overtemp sensor.
Whether it is a pack getting too hot (See the measurements taken of the "fake" Leadershobby LiPoly repackaged Tekocell packs) or the charger overheating; the charge-controller getting too much voltage and current to regulate or a large bank of shunt resistors shunting too long or in too high ambient. Even a motor controller getting too hot might be a reason to trigger a BMS event and reduce throttle, though it is actually outside the BMS context.

[cor]

BTW, what is the reason to put an AP431 in the BMS instead of the usual TL431? Was that a price or availability issue or is there a technical reason to go for the alternative manufacturer and type? I guess this is a question for Richard.

[fechter]

The TL431 has a slightly lower standby drain, but more importantly we found it has a slightly different turn on point that allows us to get closer to the desired set point with the available resistor networks.

One approach to signaling I looked at before is to use cascaded transistor switches instead of opto couplers. In this arrangement, if any cell triggers it trips the cell below and so forth to the end of the chain where it activates the HVC or LVC. This does a few things; the cell drain during activation can be much lower, a few uA, and there is a fail safe for any cell that becomes disconnected as this will trigger the chain. There is also no real limit to the cell count and there are fewer issues with creepage distance on large packs as the voltage differential from cell to cell is low. The Seiko chips use this kind of setup. Downside is way more parts per cell , possibly more susceptible to noise or contamination on the board and some propagation delay in the chain.

The Zephyr, being a centralized system, has little chance of a disconnection in the outputs of the optocouplers as they are all on the same board or in the same box in larger setups. Single failures of the tap wires (other than the end cells) will result in a pair of cells acting like one cell, but this still gives a fairly good level of protection.

All of the most recent Zephyr control boards have a temperature sensor that will suspend charge if the control board overheats. There is no provision for cell temperature monitoring, but that would be a desirable feature if it didn't take too many parts to implement.

[cor]

Hi Richard,
You chose the AP431 but you mention the advantages of the TL431, so I am confused.
I have been looking at combining multiple outputs to save on optos.
For a maximum of 8s you will have a max 8 x 4.2 = 33.6V which means that usual transistors and the TL/AP431 will allow combining 8 channels into single optos, which means that instead of 8x3=24 optos only 3 optos are needed for each 8 series cells.

I also like to make the LVC signal active, meaning that the throttle clamp or brake is held active unless the wiring is intact and the battery voltage high enough (above LVC), so that a broken LVC wire does not defeat the low voltage protection and you damage your expensive pack.
What this needs is an extra transistor to invert the clamp/brake signal at the throttle signal and turn the default active signal back into a signal that only clamps when there is a problem. Also a switched power input is needed, so that the BMS does not continue to draw power when the bike is switched off. This can actually reduce the power draw of the BMS to zero.
The last thing I like to do is shrink the whole BMS and Charge controller by making it SMD technology. There are plenty PCB houses that will supply a relative small number of (populated) PCBs for a reasonable price. I have dealt with PCBfabexpress in the past, I often pass by them on one of my commute routes.
I have a few sketches and drafts of how to add this to your BMS, let me know if you like me to share them.

[fechter]

All the '431 variants are pretty close in performance but as I mentioned, they have slightly different trigger points.

To combine multiple 431's into a single opto I think you'd at least need some diodes or transistors to prevent applying negative voltage to the output. You'd also probably need different resistor values for the series resistor feeding the opto. On the LVC side, the TC54 is rated for a maximum of 12v, so again you'd need level shifting transistors to go more than 3 cells. By the time you do all that, the cascaded transistor chain will have fewer parts.

The Chinese BMS just use a single transistor on the ouput of each cell circuit that pulls up a common line on the control circuit. These are coupled by 10M resistors to keep the drain low.
This approach works and is sort of a comprimise between the extremes.

I agree a fail-safe cutout is a good feature. The latest Zephyr circuit has an option for a mechanical relay output with both normally closed and normally open contacts. While the relay is power hungry (about 10ma) it makes it very easy to tie in to most any motor controller. The NC contacts can be used to complete the throttle power circuit or controller power circuit so that a fault in the wiring causes the power to stay off. Yes, you could also do this with a couple of transistors to save power.

The BMS really only needs to be active when the controller is on (discharge) or when charging. The Zephyr senses when the charger is active and automatically turns on the power hungry parts of the control circuit. The discharge side of things is always on.

Something more like the CellLog would probably be a better direction to go. The CellLog just doesn't have a sleep mode that works and needs a provision for ganging more than one in series. Other than that, it seems to work well and a single MCU monitors 8 cells and can be programmed by the user. In theory, there should be a way to make the processor sleep most of the time during standby and take a measurment only once in a while. When the voltages start changing rapidly during charge or discharge, the MCU could stay awake.

[cor]

Hi Richard,
I was thinking more of using a key switch signal that also activates the motor controller, as signal to the BMS to make the LVC circuit active and the controller can deliver power to the motor as long as the "notLVC" signal is active. If a wire breaks or LVC is detected, then the controller will cut out. Some controllers have an automatic cruise control, so depending on the controller it also needs to affect the brake input (which will defeat the CC)

For the overvoltage signaling, to generate an "AnyHVC" signal it is only needed to connect a set of resistors to the TL431 (indeed different values for each cell and only up to 8 series to stay below the max 36V limit on the TL431. The "AllHVC" signal to stop the charging will require one transistor and for each cell two diodes to separate the cell circuits. For protection of the HC54 I could not find a way to do it with less than 2 transistors: one transistor plus a diode on each cell circuit and one transistor to drive the opto until one of the cells signals a LVC.
I am less concerned about the charge controller failing to stop charging, because I expect that BMS will typically get integrated with the charge controller and the charger should already have a max voltage to stop charging when all cells are full, so as long as the BMS keeps the cells balanced, the charger control should just be a secondary protection.

If one of the cells fails shorted, its LVC control signal will avoid the motor controller from drawing power so it is likely to be detected immediately and charging should not be attempted in such a case. I did not add a protection against charging if a cell has failed shorted, other than a test input for overvoltage detection test, where the resistor divider is bypassed to make the HVC circuit detect an overvoltage as long as the cell is above 3V. That test can detect a failed cell. When the BMS and Charge Controller PCB is integrated and done in SMT then the price of a transistor or diode becomes almost neglicible, but the optos due to their physical side and creep distance requirements will still be costly parts, that was one of the main reasons to add electronics to reduce the nr of optos. Also the automation of SMT production reduces the labor involved with building the boards, so as soon as nrs increase that is a requirement to keep supplies meeting demand.

[fechter]

Here's an example of a transistor chain arrangement, courtesy of Randomly. If any cell triggers, it 'breaks' the chain and triggers the output. If a connection comes loose or if a cell dies, it also breaks the chain. This gives a good fail-safe for connections. This also eliminates optocouplers all together. No problems with creepage distance if properly laid out.

I came up with a similar arrangement (but can't seem to find the file) that would have slightly lower standby drain and no real limitation on the cell count.

Randomly LVC3.jpg (105.63 KiB) Viewed 657 times

[cor]

Replace Q8 with an opto and you can have "unlimited" paralleled blocks for very high pack voltages

[jmmorgan]

I need help trouble shooting the Zephyr BMS lite charge controller. The kit was well packaged, but the instruction were very basic, but had good pictures. The assembly looked straight forward and was not hard. When I tested the unit the LED came on as described, but when the LED was green I still was measuring some voltage across the Pack pins. According to the instruction, I should not see any voltage. I have looked at the circuit too many times and I cannot see anything wrong. I elected to plug in the pack and see how the controller worked. Unfortunately, that was a mistake as the R1 resistor fried (the fuse was fine) and the controller no longer works, even when I replaced the R1 resistor. Any help would be greatly appreciated.
Thanks
John

[fechter]

I'll have to check those instructions. It would be normal to see some voltage across the pack connections even when the LED is green.

R1 is 1M and I can't see any way that should ever get enough voltage to burn up unless you're running over 300v. I suspect the wrong value was used for R1.

I'll PM you for more details.

[SlyCayer]

Hey guys, any news on the new version?

[dfar]

I am also anxiously awaiting news of the Zephyr BMS.

[chroot]

... bump

[SlyCayer]

Hmmm, this looks completely dead or it's only me? .

[fechter]

Sorry guys....

I'll try to at least get you an update on what's going on.
Basically both of our wives have prohibited us from working on the project anymore after wasting so much time and money with little hope of recovering it.

I'm literally working 3 jobs right now to make ends meet with 3 kids in college. I don't have lots of spare time these days.

I'm trying to work out some kind of alternate plan since the design seems to be finally worked out. It would be a shame to put so much into the thing and let it die at this stage.

[dnmun]

don't be sorry, not for the tourists anyway.

you and gary did a great thing, i still think this is the best thing to come out of the sphere. a lotta people know how much you guys have done.

so elegant and capable design, i was amazed you guys could devote as much time to it as you did.

really, you cannot imagine how the work you have done over the years has inspired me to learn some electronics finally in my old age. from the original hacking of the C'lyte controller, the puma/infineon solution and all the time you guys devoted to making the premier BMS solution. not once but twice, and all of it open source.

you guys should be proud. not sorry.

maybe some of the tourists will finally wake up and start studying electronics enuff to help out instead of whelping.

[megacycle]

I'm fairly a newbie, with no cred here, but If the membership could send you a dollar or more 10K+.
Need to have a whip round to get you home.

[chroot]

... RIP Zephyr...

Otherwise I understood your situation.

[fechter]

... RIP Zephyr...

Otherwise I understood your situation.

Not quite dead yet, just sleeping.
If I could find a source of funding, I could possibly get some bare boards made.
They won't be cheap though.

[Alan B]

PC Boards $5 per square inch for three boards:

http://dorkbotpdx.org/wiki/pcb_order

[megacycle]

The ES fund donation area should be for helping innovation like this
Is there anyway of funding this idea on mass
Who personally is gonna miss a few dollars, can't understand it .

[SlyCayer]

help out instead of whelping.

Don't get me wrong, my last post was not to whelp, but I was only noticing, I adore these guys for everything they have done, if I would be in a better financial position myself, I would certainly pay for the boards to be manufactured...

[fechter]

PC Boards $5 per square inch for three boards:

http://dorkbotpdx.org/wiki/pcb_order

That looks interesting. It might be a little cheaper than ExpressPCB, but looks a lot more complicated for me to get an order in, as all my layout files are in ExpressPCB format, not Eagle or Gerber.

I took donations in the past and burned through all of it without a lot to show. I really didn't feel good about this, especially since the end goal was for me to make some money, even it it's like minimum wage.

If you compare what a Zephyr board does to something like Method's HVC/LVC boards and the pricing per cell, I'd have to charge quite a bit for it to be comparable (for fully built boards). There's no way I'd have time to build these, so at best I'd be able to offer bare boards with a parts ordering list and some instructions.

In the past there were some people who built up the boards and offered fully built units. If you're organized and have reasonable soldering skills, it could probably be done fairly efficiently wth some practice, but there is still quite a bit of labor to fit the box, heat sinks, packaging, shipping, bookkeeping etc., so the labor cost would still be high. Could be a good side job for someone with the right skills.

I'll have to try and come up with a cost estimate for bare boards. This will have to be the actual board cost plus quite a bit extra to go toward repaying the immense development cost.
But one of my main objectives is always to make products that not only work but are affordable enough to be widely adopted. Any bozo can build a fancy BMS for $1,000. That's not what I want to do.

[megacycle]

Would'nt feel bad about burning through supporters dough if your putting all that effort in.
Especially now you guys are near a completion.

Some people we know get a lot for doing next to nothing.

[Alan B]

ExpressPCB is nice for their easy to learn software and their 2.5 by 3.8 inch low cost miniboard (which is still almost $7 per square inch for three boards with no silkscreen or solder mask, so not a bargain but it is delivered fast). I have made many of those and a few commercial boards of other sizes from ExpressPCB. But their pricing is much too high for what you're trying to do. And to get their prices down you have to order way too many boards for a small operation, and they never get reasonable at any quantity.

It does require learning another software package, but using other services like BatchPCB or dorkbotpdx for cheap but slow prototypes (or expressPCB for expensive but fast prototypes), and then get panels from goldphoenixpcb.com at 155 square inches for $110 each so less than $1 per square inch. No need to buy 100 boards and invest big bucks. Buy one panel at a time.

I've tried several packages and not been happy (Kicad, Eagle, FreePCB). Diptrace is next on my list and has a lot of good reviews. ExpressPCB is nice but pretty weak and keeps your design from being moved to a better package and a better PCB supply place.

BatchPCB has an interesting feature in that you can put your PCB design up for "sale" there. Folks can log in and have some boards made for them, get the fairly low BatchPCB pricing, and you can get a royalty on it. So you don't even have to handle the boards. Just register them and advertise your designs with a link so folks can get them made. It might be good to make boards a panel at a time to start, and when demand slows down or you get tired of it put it in batchpcb so folks can still get it even when you don't have any left, and the design stays available after you move on to other projects.