Dewalt A123 BMS battery interface solution

[kfong]

I don't plan to make a kit since the parts are easy to obtain from Digikey. I just wanted to cover part of the cost of my run. The next batch will be priced higher $8-10 if there is still enough people interested for me to do another run.

[kfong]

Here is the partlist.

(1) 7.7k 1/4watt resistor 7.15k can be substituted since digikey has a minimum order of 5 resistors. cat# 7.15KXBK-ND
(1) 8.5k 1/4watt resistor 7.15k can be substituted
(1) 1k 1/4watt resistor 1.00KXBK-ND
(1) V30100S-E3/45 DIODE SCHOTTKY 30A 100V TO-220AB
http://search.digikey.com/scripts/DkSea ... E3/4WGI-ND
(3) Keystone Electronics quickfit male #1265 Digi-Key Part Number 1265K-ND
http://search.digikey.com/scripts/DkSea ... e=1265K-ND

The rest is just wiring to your motor controller. Just use the NEG FET and POSITIVE output for power and parallel packs for current. 3 packs should cover most ebikes using hard accelleration. That's 60amp * 32Volts = 1920 watts

[kfong]

Here is how simple the wiring gets. I plan to use this on a scooter. I won't have to worry about the batteries. As you can see it's all connected. I plan to use two packs to get a useful 10mile range
Video of the test.
http://www.youtube.com/watch?v=8n_q0ax1RM8

[morph999]

How many dewalt packs would I need to get 15 mile range on 5303 hub motor? Assuming 36v? and then also assuming 72v?

[kfong]

I don't have a 5303 motor to be able to tell you that. It really depends on how much the average amp draw of the motor is at the speeds you want. The dewalt batteries are rated at 2.3ahr, you would need to parallel them to get the amp hour needed, but to keep them happy, it's best to run them to 80% of capacity. A rough general rule is an amp hour a mile for bikes. Of course if you pedal assist you can increase you miles as much as 30-40%.

A scooter is much more efficient due to the smaller wheel giving it a better range. Making them a great alternative to bikes.

How many dewalt packs would I need to get 15 mile range on 5303 hub motor? Assuming 36v? and then also assuming 72v?

[kfong]

I did some more testing with the boards. Looks like capacitive spikes are a problem. It will shut down the BMS, an inline inductor of 300uh and a diode across the batteries will be needed. This is what was in the original circuit. I was hoping to avoid using them. I will have to do more testing.

[kfong]

Update, looking for a suitable inductor. The one I found, I wasn't happy with the wire gauge, so I looked around and found a ferrite toroid, and started wrapping wire around it. I ran out of wire, but felt it would be good enough for the test. Worked better than I expected. It just goes in between the battery and the speed controller. No bms shutting down from the capacitive discharge coming back from the controller. I left out the reverse protection diode, but will probably add that across the inductor as well. Here is a picture of the inductor I made, the ferrite toroid should be easy to find, search on ebay if you can't find one locally. Just find one that is big enough to wind a bunch of wire around it. They work like noise suppressors. Amazing how well it works. I was able to run on two packs without it shutting down and the combined current of 40amps from the two packs was sufficient enough to keep the bms from tripping as well and if the current does trip, it just goes into momentary off state and comes back on again. You get a stuttering effect if you keep on the throttle. Once I have 3 or more packs in parallel, current won't be an issue.

[mhz128]

Kin,

Your interface boards are awesome! Using an e-bike as transportation, with 6-8 Dewalt packs with your boards, how could I charge all the packs using only 1 charger? So I wouldn't have to carry multiple chargers, and dismantle the entire pack for charging.

For example; ride to work, charge entire pack with one connection, then ride home

A very simple, expandable, plug and play solution using these Dewalt packs would be ideal! I think you have achieved this to 70% by building your interface boards.



Thanks, and keep up the good work!
MHz

[kfong]

I provided access to the 15 amp fused connection. This goes directly to the negative side of the battery. The other side of the enable pin goes directly to the positive side of the battery. You could create a charger with protection diodes to charge each pack individually. Since you don't know the state of charge each pack has, you need to keep them all isolated, since one pack could try to charge another and create large currents that could do some damage. One solution to this is to protect the packs with a 5 amp fuse on the charge connects to all the batteries. Then if you want to charge all the packs together, provided they were closed to each packs capacity, meaning you’ve been keeping all packs charged and discharged together. You can parallel them all together at the end of each run. The fuse will blow if one pack is significantly different from another protecting each individual pack. If there is a slight difference, the 5 amp fuse should be easily handled by the batteries. Now you have all packs in parallel with your fuse charge cable and can charge them with one charger.

Here is a schematic of the charge cable,

It might even be possible to leave this cable connected in the bike all the time as long as you keep all the packs together. I'm not sure how the BMS will handle this, but I suspect it will be ok with it. Then all you have is one connector to deal with. I don't advise this since I have not tested this out and don't plan too since I will be using packs in 2, 4 or 6 depending on my ride distance so the packs might not be the same at times. I will be using 2 packs most of the time since everything is so close, so the 1 hour dewalt charger is ideal for me. A drawback to leaving it installed all the time is one bad bms could take out the rest of the packs. Safer just to use an external charge cable and connect them together with some mutipin connnector.

I've been quite happy with the dewalt bms setup. I’m just running 2 packs till I get the bike finally wired. I had a nice late night ride last night to cool off from the day’s 90 deg heat and rode the packs to empty. I was close to home and just pedaled the rest of the way. I don’t have a lighted wattmeter and it’s a distraction to have to worry about the batteries anyways. Great just to enjoy the ride and let the batteries take care of themselves.

Good link, so you don't over do it with wiring size. Just follow chassis wiring guidlines.
http://www.powerstream.com/Wire_Size.htm

[kfong]

Here is something I just discovered about the Dewalt packs. Not all of the Dewalt BMS are the same. There must have been design changes. I’ve been using the packs on my scooter. viewtopic.php?f=12&t=12031 and found I did not need the inductor, but 2 of my packs would shut off every time on this scooter. I then put the inductor inline and they worked fine. I took the 4 packs that did not need the inductor and tried them on my ebike. They worked fine without the inductor on the ebike. Unfortunately there isn’t any easy way to tell which Dewalt pack require the inductors. Digikey sells the inductors as well as the rest of the parts for the boards. I’m currently just selling the bare board and spacers. If you are using the boards, you might check to see if you can omit the inductor.

[nightowlgk]

Very nice work, What about a simple connector interface for Bosch Fatpacks that includes a diode for matching different numbers of packs?

[kfong]

Sorry, I only have Dewalts to play with. No plans on using any other packs since the Dewalt have been very reliable. I will be getting the Dewalt 28volt packs, and will verify if those will work.

[kfong]

Here is a picture of the battery carrier. You can make something similar out of just wood and flat aluminum rails for the support. I used a generous amount of epoxy to glue and position the circuit board. I had a spare empty battery case for positioning. Once the glue sets you can slide out the battery, ensuring perfect alignment.

[sharkmobil]

What is R5 there for? (the BMS MOD schematic)

[kfong]

It is not used, I put it there to use a pot instead of resistors to experiment with. Best to use the resistors.

[nightowlgk]

Sorry, I only have Dewalts to play with. No plans on using any other packs since the Dewalt have been very reliable. I will be getting the Dewalt 28volt packs, and will verify if those will work.

Yeah, but at $50 each!!!??? Bosch are much more attractive for multi setups.

[kfong]

I've found a problem with some of the Dewalt batteries. Some of the older Dewalts when enabled have a rather high discharge current when in standby mode. This is not problem when the pack is charged since it takes a very long time to drain a pack when full, but when the pack is empty and left plugged in, it will fully discharge due to small constant drain on the batteries. I don't recommend leaving the packs installed after discharged because of this, unless you verify you have one of the newer bms designs. On my setup, I usually take the pack out to charge after a run and have them in my charger ready for my next ride, so this isn't a problem I need to worry about. For those of you who plan to have the batteries permanently part of the bike, you will need to disable the enable line and add an opto circuit to turn them on. I'm working on an opto board to do this and should have the boards sometime next week.

[Tony]

I'm going to be using the Dewalt 28v packs with your boards, would the same resistors and diode be used as the 36v pack?

[kfong]

I have the 28volt packs to play with now. Seems to work, will be doing further testing. Been busy lately with other projects, but I did plug it in and was able to see the proper voltage reading at least. The only change would be the resistor values, but I suspect that won't even be necessary since it's probably setup for 20amps, similar to the 36volt version.

[Evereste38]

Hello,

I'm try to use the 28V pack too, but I'm not able to activate the BMS with the 3 resistors like on the 36V pack.
I blew the fuse and shunt it by a external between the BAT- inside and the output Pin outside, ratter to dig into the pack to change the SMT fuse, does it a problem ?
Do you confirm your pack in 28V is working with the same resistor network ?

Thanks.

[webfootguy]

Did you blow the fuse before or after trying to use the interface board? I just got the rest of my parts to build 2 interface boards today and I have lots of 28v packs so I will give it a try fairly shortly.

[Tony]

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Re: Dewalt A123 BMS battery interface solution

Postby kfong » Sat Jun 20, 2009 10:02 am
I did some more testing with the boards. Looks like capacitive spikes are a problem. It will shut down the BMS, an inline inductor of 300uh and a diode across the batteries will be needed. This is what was in the original circuit. I was hoping to avoid using them. I will have to do more testing.
Last edited by kfong on Sat Jun 20, 2009 8:02 pm, edited 1 time in total.
1st ebike (Diamond Back, 650w cylcone, 3 dewalt packs)
viewto ... f=3&t=6348
2nd ebike (Motobecane DS, 600w BMC torque, 10S8P Konions)
viewtopic.php?f=6&t=12654
Outback Mountainboard
viewtopic.php?f=12&t=11137
X-Treme Electric Scooter

Dewalt interface board
viewto ... 14&t=10986

My website http://www.embeddedtronics.com/
RC blog http://www.rcgroups.com/forums/member.php?u=23712

kfong
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Have you tried this? maybe it will prevent the BMS from shutting down.I'm waiting for all my parts to arrive too for the 28v set up, should be testing soon-

[kfong]

I finally got around to testing the 28volt packs last night. They work fine with the interface board. Here is the chart of the cutoff, as you can see the BMS shuts down at around 21volts. I put one pack on the bike this morning to do a current test. The max current I was able to pull was close to 25amps. This is actually a higher setting than the 36volt setup. This was a pleasant surprise. I verified this with a second pack. Note: you need the inductor to keep the BMS from shutting down due to the current spikes. I’m guessing since the voltage is lower, Dewalt increased the current limit to make up for the power.

[kfong]

Doesn't sound like you are using my boards since I just verified that it works with the 28volt packs.

Hello,

I'm try to use the 28V pack too, but I'm not able to activate the BMS with the 3 resistors like on the 36V pack.
I blew the fuse and shunt it by a external between the BAT- inside and the output Pin outside, ratter to dig into the pack to change the SMT fuse, does it a problem ?
Do you confirm your pack in 28V is working with the same resistor network ?

Thanks.

[webfootguy]

kfong, I'm about to finishing building mine and test them as well on the 28v packs. What inductor do you recommend and where should it be inserted in the circuit? I'm assuming either the + or - pack would be ideal. Does the inductor have to be rated at +25 amps? Those seem spendy. Can you suggest a part to experiment with?