Please check my BMS order options.

[Parf]

Hi guys, it's my first post. I rode a Giant Twist Freedom the other day, and liked the way it zipped around.

After doing some research here, I decided to build an electric bike with pedal assist, so I am going to install E-Bikekit.com's 350w geared kit on my 2002 Gary Fisher Mamba mountain bike. I need to make a battery kit for this thing that will get me to work, and I want to build my own pack.

I think I will order 3 Thunder Sky LiFePO4 12v 20ah packs to get to 36v20ah. $360+shipping from ElitePowerSolutions.com .

I also plan on ordering a BMS. I am looking at the ECityPower Smart BMS S5-13 supports 5~13 cells. I think I will order it from BMSBattery.com for $18.50+shipping. They want me to fill in some blanks, and I would like to have my answers checked out by the experts.

Smart BMS S5-13 supports 5~13 cells:

1. Battery Type: LiFePO4

2. Overvoltage: 4.2

3. Charge Overcurrent: 3C (is this right? “C” and “S” I'm still trying to figure out. Does this mean 3 amps continuous?)

4. How many cells in series?: 12

5. Undervoltage: 2.7

6. Continuous Discharge Current: 10Amps (the batteries webpage says - Max Discharge Current: 2C (continuous) / 10C (impulse))

Does this look like a good safe setup that will last a long time and not give me too much trouble? Will I be able to plug in one cord into the pack to charge the whole thing up?

What charger should I get? Think easy, safe, and reliable.

I think I am going to go onto the BigBlueSaw.com and create a nice aluminum enclosure for the whole pack, and the BMS.

Does this sound right? Thanks for any help and suggestions.

 

[morph999]

I'd put the overvoltage at around 4.1v and under voltage at 2.5v . When I use my cells, it's pretty typical for them to sag to about 2.8v per cell under a 2C discharge current. Your probably using a 1C current but you'd probably still want to set it at 2.5v or 2.6v.

Charge overcurrent: probably 20 amps ...since I think 1C is the maximum charge current recommended by thundersky

continuous discharge current: 30 amps

 

[morph999]

Like this:

1. Battery Type: LiFePO4

2. Overvoltage: 4.1

3. Charge Overcurrent: 20 amps

4. How many cells in series?: 12

5. Undervoltage: 2.5

6. Continuous Discharge Current: 30 Amps

You want it to still work and not cut out so you need undervoltage at 2.5v and continuous discharge current at 30 amps. It looks like you might have to solder stuff, though, to get the BMS thing to work. Is that right? I've never bought one but I don't see any wires coming from the circuit board.

 

[cell_man]

I do not think that BMS is sufficient for your needs. You stated 10A continuous discharge current. That's not enough. Typically the HVC on most BMS from China are 3,9V which is reasonably safe. Can't see why you would want to go above that. LVC is generally set to 2.0V for most BMS but better you don't actually hit that routinely. If it's set too high you will easily trip it once the cells are below about 30% SOC (30% remaining capacity), 2.5V isn't overly high though.

 

[Parf]

Thanks for the replies! I don't want to solder on the BMS if I don't have to. Could you guys point me toward a BMS that would be more what I need?

 

[pgt400]

Check out the Signalab V2.5 I've been using it for about 1 month and it is excellent. Has SMD leds that light when 3.6v is hit. Turns off the charger if any cell hits 3.9v. Comes with the cell wires so it is very fast to install. I'm using it with a 16S3P A123 pack. They have 8,12 & 16 cell versions.

 

[yopappamon]

I have the same thundersky batteries and just ordered a BMS from High Tek Bikes.

http://www.hightekbikes.com/BMS.html

 

[morph999]

parf, how many miles do you plan on going with the battery pack? If you never plan on going over about 15 miles on your pack then a BMS isn't something that is really all that necessary. It's possible to do without one if you are careful.

For these Thundersky 36v20AH packs

1) keep your discharge current to 25 amps or less peak
2) never use more than about 10AH or go more than about 15 miles

If you do those two things and carefully charge them, you can do without a BMS.

 

[Parf]

I plan on going 10 miles to work, so a 20 mile round trip. I'm a pretty big dude, 325 lbs , so I worry that the ride home involving about a 500ft elevation change will crush the batteries. I am going to use this as a pedalec as much as possible so that should help out.

 

[morph999]

yeah...especially if you have any kind of elevation, you'll want some kind of BMS or cell log monitor. Where I'm at, it's pretty flat.

 

[morph999]

you could get two of the Cell log monitor 8s from hobbyking. They are $15. Then you could either mount them on your handlebars or connect an alarm to it but that might involve some soldering to do that (the alarm). The connector wires cost about $10 each so that's another $20. $15 x 2 = $30...+ 2 wire connectors ($20) = about $50. Then add in a alarm if you want that. That's another $10. About $60 - $80 to do it.

 

[Parf]

I think I am going to go with the hightekbikes BMS. The signalabs v2.5 looks a lot easier to hook up, too. I will have to have one of the end panels of my battery enclosure made out of clear polycarb so I can see the leds. I'm thinking a 15 inches long x 7 inches high x 5.25 inches wide aluminum box, tight on the batteries, with an internal partition where I'll stash the BMS, and put all the bulkhead connectors or grommets coming out of the poly end.

 

[Parf]

The BMS is going for $70. Going with the cell logs, I will have to charge each cell independently, right? With the BMS I can just plug the whole shebang in and charge it all together, right?

Man, I think I jumped into the deep end of the pool.

 

[cell_man]

I'm not sure what the situation is for tying into the 12V Thunder Sky Cells. These will have 4 series cells internally but I don't know if there is an easily accessible place to get to the balance points between each cell. With the standard 3.3V Thundersky cells you could tie the BMS wires with ring crimps directly onto the terminals of the cells.

In response to your PM, the 12S 30A constant BMS I stock will work out to about 70USD including EMS shipping to USA. Small parcels work out relatively expensive for shipping I'm afraid. You should be charging 12S LiFePO4 at between 43.8V and 44.4V BTW. If you just want a plug and play solution a BMS is advisable IMO. If you don't mind monitoring the cells and putting some more effort into the charging/discharging, running without a BMS is also fine. However for what you are planning the cost saving for going without a BMS is not so significant if at all when you add up all the other bits you will require.