Even Newer 4 to 24-cell Battery Management System (BMS)

[jorhyne1]

I have a quick question..I am planning to use this BMS with a large lifepo4 pack. I will be using this charger: http://www.bmsbattery.com/product_info.php?products_id=111&osCsid=2726a892cc5a75adbe3f1f57c9f3edd7
Data sheet here:
http://www.ecitypower.com/pdf/w3k.pdf?5a8729d658601922ad7447e28083cf65=c918d35f86836df3b488a1d58d46f4eb

I have been skyping back and forth with the owner of Ecitypower, Jack (very helpful and quick to respond to queries btw) and he is convinced that if I used this charger with the G/F BMS that it would trip the charger off accidentally, and the charger isn't capable of automatically turning itself back on. Here is what he said verbatim

The CV stage is often used for BMS balancing. It is long time stage. When one cell goes to 3.65V and one cell is 3.00V,I think your BMS will cut off the circuit for charger.

He says that the charger has built-in protection to turn itself off if the battery is removed while charging, and his concern is that the BMS would fool the charger into thinking a battery is not attached as it is balancing, causing the charger to shut off before balancing could occur.

Is there any merit to this? My understanding of the 4.0 BMS is that PWM controls the current to individual batteries, and that the batteries would never appear "disconnected" from the charger at any point. I could be completely wrong, but I'm sure one of you guys knows the right answer!

 

[alangsam1@me.com]

i could wind up with the same issue so interested in the response.

Also - how are we doing with the 4.0 in terms of when can we order?

 

[fechter]

When the highest cell reaches the set point, throttling will begin. Since the throttling takes place at a 20khz, the charger will simply see a gradual decrease in charging current. Most chargers will drop out when the current gets below a certain point.

The charger current will start out at whatever its bulk CC rate is, then taper down to a level that is slightly higher than the shunt current. At this point, the BMS will turn off and terminate the charge. As long as the charger doesn't cut off at a level that's equal to the shunt current, it should work fine.

V4 should work with a wider variety of chargers, but the charger output voltage should be a few volts higher than the pack voltage for best operation. Of course the only way to know for sure it to do an actual test.

 

[jorhyne1]

What is the exact voltage that shunting ocurrs? 3.65v?

So if I'm charging a 48 cell pack, it would be better to set up the charger to output 3.7 or 3.8 volts/cell to charge fully? So that would mean I would set the charger to 177.6ish instead of 175.2 (24*3.65)?

 

[GGoodrum]

The shunt current is defined by the shunt resistors used, so you could theoretically set it to whatever you want. Generally, the higher the shunt current, the quicker a pack will balance. Most of the less expensive, and even uber-expensive BMS boards I've seen usually only have shunt/balance currents of about 100-200mA. With our v4 BMS, we've been using a full 1A, mainly by providing active cooling, to move the heat out. This works quite well, actually, and is well above the cutoff point of any charger I'm aware of, including the eCityPower unit. I think your buddy Jack is making assumptions about our BMS, based on his knowledge of the other typical BMS boards, which is an honest mistake. Ours works differently, that's all.

As for when these will be available to order, I'm not going to make any more promises. We keep finding small issues that require more tweaks. We finished the control section, over a week ago, but now we're seeing small issues in the cell circuits. They aren't really problems, but it is more that we are learning/documenting the behavior of the circuit, over a wide variety of conditions. The circuit design is a bit different than the v2.x variants, and we are finding that parts like the LM/FAN431 work a little different with essentially double the shunt current that was practical with the old design. The set point is a little different, and we see a little more of a difference when the cells are connected than we used to. This has caused a couple of days delay, as the three of us (Richard, myself and Andy...) tried to come up with repeatable tests so we could figure out what the divider values needed to be to get the shunts to be fully on at selected points (4.15V for LiPo and 3.60V for LiFePO4...). Because we now share the single opto output for both the LVC and HVC/throttling functions, it has taken some further tests to get the point at which the LED comes on, and then when the opto trips, so that the LED is fully bright when the shunt is fully on, and then have the opto tripping be just about 20-30mV above that point. There were many changes in this area, over the last week or so. The reason is that I keep beating on Richard to reduce the parts count, not increase it, which has caused him to have to be ever more clever. We are both at the point our brains are hurting, pretty much 24/7, but especially his. Anyway, we went through the whole alphabet by yesterday, so now we've switched to numbers. The latest version is 3.9.4. When we are done, the "released" version will be 4.0, but we might have to go up to 3.9.xxx before we get there.

The way it has turned out, the latest version also has one additional new feature. Now, when an LVC channel trips, the orange LED for that channel will lit up as well. In his "forced" cleverness, Richard has managed to figure out a way to do this without adding more parts. I've been a parts-count Nazi in this effort, but at the same time have whined like a 13-year old girl that it would be "really neat to have the LED light up when the LVC trips."

I'm continuing to work on the "production" layout, and have just been cutting and pasting in the new 6s cell circuits. Andy has a version that works, without the LVC/LED feature, but he still needs to put in the latest divider values. The latest version, with the LVC/LED feature, needs one last round of tweaks, to get the opto set point dialed in. I'm going to try and do that without having to wait for another order of proto boards to show up. Assuming I can, I'll put in the first "production" run of boards in the next couple of days, which would mean they might be available sometime next week.

-- Gary

 

[jorhyne1]

Thanks for the fast responses guys. The BMSs you have designed are fantastic and are a great service to not only the ebikers out there but electric motorcyclers and car guys too! I hope you guys are being properly compensated :wink: for your work!

One more question though, what is the ideal voltage to charge each lifepo4 cell to if using your BMS? 3.65? 3.7? Higher? From what I inferred from your earlier posts is that it might be beneficial to have the charger's voltage set to try to charge each cell to a little over the voltage that each cell is shunted at. I'm sure that it's come up earlier in the thread, but at 104 pages I don't know if I could find it!

 

[GGoodrum]

Thanks for the fast responses guys. The BMSs you have designed are fantastic and are a great service to not only the ebikers out there but electric motorcyclers and car guys too! I hope you guys are being properly compensated :wink: for your work!

One more question though, what is the ideal voltage to charge each lifepo4 cell to if using your BMS? 3.65? 3.7? Higher? From what I inferred from your earlier posts is that it might be beneficial to have the charger's voltage set to try to charge each cell to a little over the voltage that each cell is shunted at. I'm sure that it's come up earlier in the thread, but at 104 pages I don't know if I could find it!

Actually, what many have found is that it does seem to prolong the life of the cells if you pick a "full" point a little below the generally recommended charge voltage for each type. For LiPos, ithe recommended number is 4.20V and for LiFePO4 it is 3.65V. What I'm using for LiPo is 4.15V and for LiFePO4, 3.60V. This is what we are fine-tuning the fully on shunt set point to be at. For my 12s LiPo test setup, the total would be 12 x 4.15V, or 49.8V. What you want to set the charger voltage to is just a hair over that, to get the best results. We are trying to develop a simple calibration procedure, where you can determine the "shunt-fully-on" total, by simply connecting the BMS to the charger without the cells connected, because every setup is going to be slightly different, due to the 1% tolerances in the divider resistors. Anyway, with my test setup, it turned out I could get the best results when I set the charge voltage to 50.12V.

I disagree that it is okay to go "several volts" over the 3.60/4.15 x # of cells value, because although the throttling will take care of making sure no single cell goes over 3.60/4.15V, the farther over the "optimum" total voltage point the charger is set to, the more the throttling PWM logic will reduce the current. This is more of an issue with larger setups, and/or higher initial charge rates (20-30A...).

Anyway, back to my testing...

 

[gestalt]

jorhyne1 wrote:

Thanks for the fast responses guys. The BMSs you have designed are fantastic and are a great service to not only the ebikers out there but electric motorcyclers

I agree, I'm just about to embark on going over all these pages as the old tax return on its way and I'm in the bms market. From what I've seen so far I am really hoping when 4.0 comes out it will be a good fit with my components.

 

[Kick Gas Coop]

when will the next batch of boards be ready? I have not noticed anyone offering to build these. Would anyone in California or Southern California be interested in building a board or two for us in San Diego?
Jason

 

[jorhyne1]

when will the next batch of boards be ready? I have not noticed anyone offering to build these. Would anyone in California or Southern California be interested in building a board or two for us in San Diego?
Jason

Please go to the page before this one and read Gary's (GGoodrum) post. He already addressed your question. Forum member AndyH runs rechargeablelithiumpower.com which sells the current version of this BMS and will offer a completed version of 4.0 when it is ready.

 

[Lock]

Check with AndyH here... he's in the Lone Star State:
http://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=6551

His site:
http://www.rechargeablelithiumpower.com/oscommerce2/catalog/index.php

Latest word:

Jan 14th: We're currently out of stock on the V2.6c battery management boards. Our first shipment of the new BMS boards arrived today. We'll start building our prototype and report back. Once the BMS is ready to go, we'll move it from 'development' to the active store area and start building a BMS for you!

I'm a happy customer. Bought v2.6 from Andy just B4 Christmas
tks
Lock

 

[j3tch1u]

gary can you provide exact dimensions of the new boards including location of the mounting holes? it would help some of us that are designing boxes with your bms in mind. standardizing the form factor for hot-swappable upgrades might also be something to keep in mind for the future. looking forward to seeing the smd version as well. great work and many thanks.

 

[sterling]

I'm a newbe, so maybe this is an old question: I'm building an electric car, so I need a charger on-board, which charges the 12v SLI battery from the 144v traction pack, while driving. I am an analog circuit designer, so I have a circuit for 90 amps. Cheap. Does anyone know of a forum for this discussion, and is there anyone interested in joining with me. Open-source, of course. Please respond to my e-mail for any comments not in the general interest: smithclydew@live.com Kindest regards to all.

 

[jonescg]

"...so I need a charger on-board, which charges the 12v SLI battery from the 144v traction pack, while driving."

Sounds like you will need a very long extension lead

I'm guessing you mean a 144 V to 12 V converter?

 

[fechter]

I'm a newbe, so maybe this is an old question: I'm building an electric car, so I need a charger on-board, which charges the 12v SLI battery from the 144v traction pack, while driving. I am an analog circuit designer, so I have a circuit for 90 amps. Cheap. Does anyone know of a forum for this discussion, and is there anyone interested in joining with me. Open-source, of course. Please respond to my e-mail for any comments not in the general interest: smithclydew@live.com Kindest regards to all.

Analog designers seem to be a dying breed. Glad to see there are some left.
You could start a new topic under the E-Vehicles General Discussion forum, and you may also want to check out the EVDL listserver. http://www.evdl.org/archive/index.html where there will be more people interested in full sized cars.

Being the cheap/lazy person that I am, I would suggest using a bunch of cheap switching mode power supplies in parallel to get 90A. Almost any switching power supply made for 120vac will run fine off 144 vdc.

 

[alangsam1@me.com]

Gary, i noticed you are now out of your trick LVC setup? when will you have more. i fried one of my turnigys while waiting for the 4.0 BMS?

3/4/5/6-Channel LVC + 3p/4p Parallel Adapter
Details

New
3, 4, 5 or 6-Channel LiPo Low Voltage Cutoff Protection Circuit + Parallel Adapter Kit.
Provides two functions, individual low voltage protection for each of channel (3-6 channels), and provides a convenient way to connect the balance plugs and main pack leads for up to four Turnigy/Zippy LiPo packs in parallel.The PCB can contain three, or four, onboard JST-XH connectors with 4/5/6/7-pins, and one matching output pigtail, plus up to four sets of 4mm bullet plugs. This is a very easy way to build 10, 15 or 20Ah packs, and provide cell-level low voltage protection at the same time..

The LVC function provides an opto-coupled 2-wire output signal that can be connected into the ebike controller's ebrake input, that goes active anytime a block of paralleled cells goes below 3.0V. This will cause the controller to temprarily cut the throttle input, which removes the load. Simple, but very effective and estremely reliable. A two-wire JST-BEC set of male and female pigtails are provided, which can be used to "daisy-chain" the opto outputs from multiple LVC/Parallel Adapter boards, and/or for connecting into the controller's brake input. New to this version is an added feature that allows the LVC cutoof to cutoff the throttle directly. There is a 3-wire input from the throttle, and a 3-wire output to the controller's throttle input, via a current-limiting resistor.

Complete kit, including all parts shown, and a complete set of illustrated instructions. A fully assembled and tested option is provided.

# of Cells per Pack:
# of Parallel Packs:
Assembled/Tested:
Price: $40.00

 

[GGoodrum]

I'm re-doing the LVC-only boards as well, using the revised circuit from the new BMS. I also have some new 6s4p parallel adapters that now have pads for the same Molex Micofit 3.0 connectors that will be on the new BMS boards. Anyway, all of these will be available at the same time as the new 4.0 BMS units, as the boards are going to be made at the same time.

I just finished building and testing a new 12s test unit, which is fitted in one of the Hammond extruded aluminum boxes, and uses the new end plates, with two fans on one end, and holes for the LEDs on the other. I'll post some pictures in a little bit. Anyway, the last thing I want to verifyis the set point turn-on for the shunts and for the HVC opto signal. At that point, as far as I'm concerned, we are done. I will then put in the production order for the boards.

-- Gary

 

[GGoodrum]

Here's some pics with the lid off:

View attachment 12s BMS-09.jpg
View attachment 12s BMS-10.jpg
View attachment 12s BMS-11.jpg
View attachment 12s BMS-12.jpg


The fans are oriented in a push-pull arrangement, one blows air into the box, and the other one sucks hot air out of the box. There are "Popsicle stick" air dams/guides, running about 2/3 of the way down the length, in between each of the three PCBs.

The latest version has a few changes to the fan end plate, mainly to add some inter-box connectors, for the LVC/HVC opto signal, and for the fans.

More later... (after the Super Bowl... :lol: )

-- Gary

 

[Arlo1]

Super what? I never herd of it could be the big lack in Horse Power and speed lol. But sometime after the super thingy I will take 2 12s balancers like in the pictures with lvc and all set up for lipo.

 

[__Tango]

Looks great. I can't wait to get my hands on the new design.

Just a quick question...is it possible to use this BMS along with something that will show/record cell voltages like a PakTrakr (http://www.paktrakr.com/) or a CellLog 8S (http://www.rcgroups.com/forums/showthread.php?t=1055820)?

Thanks!

 

[GGoodrum]

Super what? I never herd of it could be the big lack in Horse Power and speed lol.

Let's see... this coming from a place where two fat guys pushing a squished bowling ball with a handle across the frozen tundra with a broom is considered a sport.

 

[Arlo1]

Super what? I never herd of it could be the big lack in Horse Power and speed lol.

Let's see... this coming from a place where two fat guys pushing a squished bowling ball with a handle across the frozen tundra with a broom is considered a sport.

Haha there is still not enough HorsePower in that to intrest me. Although I made my own curling rock for my shop.

 

[ryan_lirui]

Those Hammond extruded aluminum boxes look really slick. I suppose they're no use for anyone planning to use a 24s2p combination though right?

 

[j3tch1u]

Super what? I never herd of it could be the big lack in Horse Power and speed lol.

Let's see... this coming from a place where two fat guys pushing a squished bowling ball with a handle across the frozen tundra with a broom is considered a sport.

LMAO :lol:

 

[j3tch1u]

Looks great. I can't wait to get my hands on the new design.

Just a quick question...is it possible to use this BMS along with something that will show/record cell voltages like a PakTrakr (http://www.paktrakr.com/) or a CellLog 8S (http://www.rcgroups.com/forums/showthread.php?t=1055820)?

Thanks!

ya, just make a parallel y-adapter:

MOLEX (f)
--> 2 x 9P-JST (f) <-- 2 cell-logs
--> MOLEX (m) <-- pack balance taps

now you can log charge/discharge