# Looking for a small bms for 12VDC and 24VDC pack



## dimitri (May 16, 2008)

maybe this will fit your bill?

http://www.tppacks.com/products.asp?cat=26


----------



## COS (Dec 23, 2008)

dimitri said:


> maybe this will fit your bill?
> 
> http://www.tppacks.com/products.asp?cat=26


 
Hmmm...
Thanks but that's a little too much DIY for me. Although I have 15yrs in assembly from HP, I am old bastard now and my eyes will give me trouble. Besides, i'm a lazy DIY'r. Im just looking for a board (already assembled) that I can solder the leads on that will do as I explained. 
I hope there's something out there. I have been looking at two items. 
One from BatterySpace: 
12.6VDC 100A: http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=4879

25.2 50AVDC: http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=4060

The other from All-Battery: 
12.6VDC 30A: http://www.all-battery.com/protectioncircuitmodulefor3cellslifepo4batterypack-2.aspx

25.2VDC 30A: http://www.all-battery.com/protectioncircuitmodulefor3cellslifepo8batterypack-1.aspx

What I found strange from battery space is the PCB they have are set to a 2.0V LVC and I can't find a LifePO4 they sell that matches it. Most cells they have spec out a 2.5V LVC.
For the All-Battery PCB, it has a 2.2V LVC and they do have a descent cell 10AH (http://www.all-battery.com/32v10ahlifepo4lithiumironphosphaterechargeablebattery.aspx) that it's obviously designed for where the cell LVC is 2.0 and the board is set to 2.2V for LVC.

fyi, I am building my son's battery pack for his go cart and scooter. I know I can buy already made ones but I'm a tinkerer and want to DIY it.
________
MARGOSHA_


----------



## AndyH (Jun 15, 2008)

COS said:


> I was wondering if anyone knows where I can get a small BMS for 12VDC and 24VDC pack? I would like it to manage OV Protection, LV protection and OC Protection. For the 12VDC pack it needs to handle at least the 60A burst (3C) rate and for the 24VDC pack at least 150A or better 300A to handle burst (3C) rate. Both need to balance as well.
> Is there such a board? I just want to make the packs "Standalone" in the sense that all I have to do is plug it into the charger and never have to put it on a balancer while charging.
> 
> I'm lazy.


COS - tell us a bit about your pack and we should be able to find you a solution that works for you. Battery type, number of cells, cell capacity in Ah? What size and type of charger do (or will) you use?

Andy


----------



## COS (Dec 23, 2008)

AndyH said:


> COS - tell us a bit about your pack and we should be able to find you a solution that works for you. Battery type, number of cells, cell capacity in Ah? What size and type of charger do (or will) you use?
> 
> Andy


 
Weird, my reply didn't post....

Well, I'm building a couple of packs. One pack is a 12.6VDC using 4 cells from: http://www.all-battery.com/32v15ahlifepo4lithiumironphosphaterechargeablebattery.aspx 3.2V 15AH and I will use their PCB here: http://www.all-battery.com/protectioncircuitmodulefor3cellslifepo4batterypack-2.aspx that has a OVC=3.9V and LVC=2.2V at max 30A. Which is fine because the cells can only produce burst 45A. I will make two of these and plug them in in series for a 25.2VDC pack.

The next pack I will buy 8 Thundersky cells from JungleMotors: http://shop.junglemotors.com/product.sc?categoryId=2&productId=15 but I do not know of a simple BMS board rated at 150A that will do all of the following: Balance during charging, protection of OVC=3.9V, LVC=2.5V. From what I understand, brining the LVC to 2.5V is like the cells going through a "Near Death Experience".

Any ideas? I would also like a matching charger too.
________
Lesbian Webcams


----------



## AndyH (Jun 15, 2008)

COS said:


> Weird, my reply didn't post....
> 
> Well, I'm building a couple of packs. One pack is a 12.6VDC using 4 cells from: http://www.all-battery.com/32v15ahlifepo4lithiumironphosphaterechargeablebattery.aspx 3.2V 15AH and I will use their PCB here: http://www.all-battery.com/protectioncircuitmodulefor3cellslifepo4batterypack-2.aspx that has a OVC=3.9V and LVC=2.2V at max 30A. Which is fine because the cells can only produce burst 45A. I will make two of these and plug them in in series for a 25.2VDC pack.


What's the space limitation for this application? Do you have to break the pack into 2 12V nominal packs or will there be room for the entire pack in one lump? When considering the battery compartment, include a sturdy box or package for these cells - they are very easily punctured. (I've only found one guy that's used the Tenergy cells - you may want to contact him.)

If space allows, you might consider the 12V20Ah modules from Elite Power Solutions. Each is less expensive than than a four-pack of Tenergy cells, has an extra 5Ah of capacity, is 3C (60A) continuous and 10C (200A) burst. Elite is the N.A. distributor for Thunder Sky. They're in Arizona. I've bought from them and will do again.

There may be other cell options that will fit and could save you a few dollars and give better performance (which side-steps the need for discharge protection from the BMS).



COS said:


> The next pack I will buy 8 Thundersky cells from JungleMotors: http://shop.junglemotors.com/product.sc?categoryId=2&productId=15 but I do not know of a simple BMS board rated at 150A that will do all of the following: Balance during charging, protection of OVC=3.9V, LVC=2.5V. From what I understand, brining the LVC to 2.5V is like the cells going through a "Near Death Experience".


What will you use for a motor and controller for the scooter? If this is a commercial unit that you're converting from lead to LiFePO4, you probably don't need a BMS with discharge control, as the controller will limit the load. For example - the X-Treme XM3500Li uses 40Ah Thunder Sky (T-S) cells to power a 3000W motor. The max draw from the controller is 80A - a modest 2C. The XM5000Li spins a 5000W motor thru a 100A controller. The 60Ah T-S cells only see a 1.6C max discharge. (I have one of each of these in my garage.)

The Thunder Sky Battery Manual gives excellent info on what the BMS needs to do to keep these cells happy. Like all LiFePO4, minimum normal voltage is 2.0V, maximum is 4.3V. T-S does say to keep the voltage between 2.5 and 4.3 for a 2000 cycle life. You'll get a bit longer life keeping things down to 3.65/3.70V at the charged side. So - no near death experiences if you routinely discharge to 2.5V!

I'm not surprised that you're having trouble finding a BMS solution that matches the cells! I'm a battery vendor and have been digging for a supplier of BMS boards for the PSI 40138 cylindrical LiFePO4 cells I import. A number of board vendors have submitted solutions to PSI and they've all failed. Most of the readily available boards are small and designed for the electric bicycle market. The boards include discharge current protection because, frankly, they're designed to protect the 1C and 2C cells that are common in inexpensive ebike packs. You might check ebay for one of two vendors - PingPing and Cammy_CC. They have excellent prices on 1C and 2C packs and will make a custom pack in any size with BMS and charger for a very good price. There are a number of their customers on the Edless-Sphere forums

I'm using the Fechter/Goodrum board that Dimitri referenced earlier to manage the 21 cells in my 5000Li. The board can be built to handle from one thru 24 cells on one board, and boards can be daisy chained to support more cells. It was designed as a group project on Endless Sphere with A123 and PSI cells in mind. (Here's a board I build last month for a customer in Canada.)

Charge is managed with shunts which keep the cells between 3.65 and 3.72 (parts tolerance). The low voltage is set to 2.1V using a TC54 voltage reference and signals the controller thru the brake inhibit line. The LVC can easily be moved to 2.7V by using a different TC54. While the manufacturer does make a 2.5V TC54, they're not stocked by the parts houses...and the 2000 part minimum order is a bit pricey. I would be happy to build a board for you with either a 2.1 or 2.7V low voltage cutoff.

Charging is pretty easy. LiFePO4 uses the same constant current/constant voltage charge profile as sealed lead acid. The cells do not want to be trickle charged or 'desulphated'  so the dumber the charger the better. If you use the DIY BMS, it was designed to throttle an SLA or a bench-type power supply, so you don't need any intelligence in the charger at all. There are excellent chargers available from Soneil ($$) and HighPower that are very solid. I have another batch of HighPower chargers on a boat somehere now, but I don't normally stock 24V chargers. The Thunder Sky TSL series chargers 'protect' the pack by limiting charge to about 3.6V per cell - this is in line with a typical SLA charger. So - undercharging is a factory approved management method. 

There's another option for charging and balancing, and that's to use a number of single cell chargers. I have a dozen of the 2A 'wall wart' chargers from VoltPhreaks (cheaper for 10 or more). These are isolated and can be used on adjacent cells. The beauty of these is that you can charge and automatically balance the pack with these. You can connect the chargers together into one connector (Molex Minifit JR?) and connect with one plug. If you chose that option, all you would need is low voltage protection as current would be limited by the controller.

Again, for LVC-only you're back to Endless Sphere and Gary Goodrum. Here's a 16-cell board he's made. He also has a run of 1-24 cells 'break away' boards that aren't on his site yet.

There are other options for charging and balancing - like the range of devices used for radio control model packs. Here's another charging option - 3.7V DC-DC converters fed from power supplies.

Sorry for all the words - we can narrow this down a LOT with a few more details of the devices you're running.

Andy


----------



## COS (Dec 23, 2008)

AndyH said:


> What's the space limitation for this application? Do you have to break the pack into 2 12V nominal packs or will there be room for the entire pack in one lump? When considering the battery compartment, include a sturdy box or package for these cells - they are very easily punctured.


For my son's scooter, there will be two 12.6V packs. both packs will fit snug in the original compartment but i'll have to "Fan" them out to spread evenly to fit. This one's no prob. Thanks for the heads up on the packaging. I'll ordere the protecting package for them as well then.




AndyH said:


> What will you use for a motor and controller for the scooter?


I paln on using a PWM for motor controller. Hobby grade though, I don't need anything fancy, just stop and go.
For space on my scooter, well, I'll just duct tape the batteries wherever.....lol. Duct Tape RULES!

What I am really looking for then, after reading your post, is a managment board that triggers a cut off when a cell(s) reaches the cells threshold voltages. Do you have one? These TS cells spec out an LVC of 2.5 and OVC of 4.something. Is going down to 2.0 for LVC ok to do?
________
Colorado Dispensary


----------

