Dewalt A123 BMS battery interface solution

Batteries, Chargers, and Battery Management Systems.

Re: Dewalt A123 BMS battery interface solution

Postby kfong » Mon Mar 29, 2010 10:40 am

To charge with a normal charger, you can tap off the Negative fused output instead of the Neg FET output on my interface board. This is a direct connection to the battery with a protective 15amp internal fuse incase you have a mishap. I don't recommend parallel them this way unless you know the packs are equally charged. As long as you keep the same packs from a run, it will work charging them all in parallel this way, but you will need to make a charge cable separate since you are bypassing the isolation diode.

scriewy wrote:and after the interface board activates the BMS and the power is open can i charge the pack with something like iCharger or GT A8 while using same current rate as dewalt charger would ?
this question looks pointless, as if id use those chargers i can simply rout out few wires and let the charger do all the work, the question is in case i want to stay in safe framework of warranty and do everything through the BMS.
Last edited by kfong on Wed Mar 31, 2010 9:01 am, edited 2 times in total.
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Re: Dewalt A123 BMS battery interface solution

Postby Kevinator » Mon Mar 29, 2010 12:06 pm

I received my boards from kfong last week and the boards look great. Thanks for getting them out promptly!

I put an order in with digikey for the parts to build my boards. The premade one is working fine, and I can confirm these interface boards work with 28v dewalt packs. I haven't tested it on my ebike yet, but the interface board does power up the pack.
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Re: Dewalt A123 BMS battery interface solution

Postby Papa » Mon May 10, 2010 8:18 pm

kfong wrote:To charge with a normal charger, you can tap off the Negative fused output instead of the Neg FET output on my interface board.
Having just purchased a few 28v DeWalt packs, i'm also interested in your boards. However, having endured the "remove batteries - put in charger - reinstall batteries in bike" hassles on previous builds, I'd like to simply charge the batteries on-board. I'm planning 2p packs. Suggestions?
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Re: Dewalt A123 BMS battery interface solution

Postby kfong » Mon May 10, 2010 11:37 pm

You can charge the batteries from the 15amp fused negative power and postive power connection. You would need to use a hobby charger that can charge 10S A123 cells. This would take a while since you will be charging them all at once. The charging harness will need to be removed from the boards since you are now bypassing the diode protection circuitry. This can be easily done by using a multipin connector for the charge port. When the charge connector gets unconnected the wires to each 15amp fused connection and positve connection now gets separated. The only drawback to this solution is the BMS is always on and can drain the batteries if left for long periods of time on some of the older Dewalt batteries.

The Dewalt charger can charge a pack in less than an hour. I still find this the fastest way to charge the packs. I have 4 chargers and can get back on the road the fastest this way.
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Re: Dewalt A123 BMS battery interface solution

Postby pwbset » Tue May 11, 2010 12:07 am

kfong wrote:The Dewalt charger can charge a pack in less than an hour. I still find this the fastest way to charge the packs.


True, but these chargers are horrible at balancing so at least every so often leave them on overnight. I'm already seeing wild voltage swings between packs on the "one hour" charge method and one charger seems to want to bring my 28v pack to 30+v every time. Bad charger (or pack BMS)!! :twisted: Anyway.. so ironic that the best cells available were mated with complete DeWalt junk. :|
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Re: Dewalt A123 BMS battery interface solution

Postby kfong » Tue May 11, 2010 12:32 am

I have not even bothered to balance them, as long as I'm getting the capacity the chargers seem fine to me. I think the balancing stuff isn't that critical with the A123's. I'm going on 2 seasons now and have yet to worry about the packs. They are performing consistently for over 2000 miles. If Dewalt was that concerned, I'm sure they would have put in a better BMS. This is their top of the line tool so they must have done enough testing. I use A123's for my RC stuff, and I don’t even bother to balance those. Lipo’s on the other hand I do balance.


pwbset wrote:
kfong wrote:The Dewalt charger can charge a pack in less than an hour. I still find this the fastest way to charge the packs.


True, but these chargers are horrible at balancing so at least every so often leave them on overnight. I'm already seeing wild voltage swings between packs on the "one hour" charge method and one charger seems to want to bring my 28v pack to 30+v every time. Bad charger (or pack BMS)!! :twisted: Anyway.. so ironic that the best cells available were mated with complete DeWalt junk. :|
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Re: Dewalt A123 BMS battery interface solution

Postby pwbset » Tue May 11, 2010 1:38 pm

kfong wrote:I think the balancing stuff isn't that critical with the A123's. I'm going on 2 seasons now and have yet to worry about the packs. They are performing consistently for over 2000 miles.


Good to know thx. Admittedly I'm only a few cycles into my 28v pack ownership, but seeing resting pack voltages off the charger ranging from 28v up to 29.8v isn't inspiring confidence in me yet with these chargers. :wink: I will say that I sucked 8.8ah out of 4p packs yesterday and they still felt fairly strong so if I'm getting 2.2ah/pack already after only 5-10 cycles out of cells from 2007 I'm a happy kid.
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Re: Dewalt A123 BMS battery interface solution

Postby kfong » Tue May 11, 2010 2:12 pm

Resting voltage won’t really indicate balanced cells. These batteries have a surface charge that gets depleted rather fast. If you have older abuse cells the surface charge drops rather quickly. Because of this the resting voltage can vary quite a bit. The load voltage is what is more critical of cell performance. After you deplete the surface charge and then measure the pack. You will see a more consistent number. They should hold steady 3.3-3.0 volts all the way to the end of cycle depending on how much load you are drawing.
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Re: Dewalt A123 BMS battery interface solution

Postby pwbset » Tue May 11, 2010 5:26 pm

kfong wrote:They should hold steady 3.3-3.0 volts all the way to the end of cycle depending on how much load you are drawing.


Again.. good to know thanks! Slurped 7.4ah this morning on the way to work and I just checked and after 6hrs the pack is sitting at 52.4v / 16s = 3.275v/cell. Works for me. :D
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Re: Dewalt A123 BMS battery interface solution

Postby The Mighty Volt » Thu May 13, 2010 4:30 pm

Hi, do you have any interfaces available, and if so, how much are you charging for them. Please feel free to PM me. Many thanks indeed.
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Re: Dewalt A123 BMS battery interface solution

Postby kfong » Thu May 13, 2010 4:53 pm

Yes, I have plenty. I just did a new run, since they have been popular. The pricing is found on the first page of this thread. Just PM, or email me at kinf@embeddedtronics.com

The Mighty Volt wrote:Hi, do you have any interfaces available, and if so, how much are you charging for them. Please feel free to PM me. Many thanks indeed.
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Re: Dewalt A123 BMS battery interface solution

Postby Mike B » Sat Jun 19, 2010 12:53 pm

Kfong, great solution! Looked at this thread a few times.

Question, will the interface allow regenerative charging? Lots of hill here, up and down. The 4011 motor on a previous bike would hit 20 amps of regen going downhill (had two Watts Up meters wired head to head to read this once I figured out why the one meter's voltage was going high on downhills). But your board has a diode. So I think not....
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Re: Dewalt A123 BMS battery interface solution

Postby kfong » Sat Jun 19, 2010 7:20 pm

Your right the diode would prevent it. I think the BMS might have problems with it as well. Not much info on the Dewalt circuitry to know. The amount you get back from what I've read isn't enough to be very practical. It does seem to make a good electric brake, something I want to try on my 10x6 motor I've acquired recently.

Mike B wrote:Kfong, great solution! Looked at this thread a few times.

Question, will the interface allow regenerative charging? Lots of hill here, up and down. The 4011 motor on a previous bike would hit 20 amps of regen going downhill (had two Watts Up meters wired head to head to read this once I figured out why the one meter's voltage was going high on downhills). But your board has a diode. So I think not....
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Re: Dewalt A123 BMS battery interface solution

Postby eBikeStore » Wed Jan 19, 2011 3:09 pm

Hello,

There may already be a thread on this, but I haven't been able to find it.

Does anyone know a safe testing process to determine the health of a dewalt battery? I am looking for a process that would not involve using kfong's adapter (to start). I am trying to determine if my batteries have enough life in them to make buying kfong's adapter worthwhile.

Thanks!

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Re: Dewalt A123 BMS battery interface solution

Postby kfong » Mon Feb 21, 2011 9:00 pm

If you keep it under 15 amps and have an RC charger that can cycle your batteries like the 1010B, you can test the capacity. Most RC chargers don't have much of a current load so the 15 amps isn't really much of an issue. You will be able to just tap into the two outer terminals.
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Re: Dewalt A123 BMS battery interface solution

Postby jag » Sat Oct 22, 2011 3:14 pm

kfong wrote: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.


Like some other people in this thread I had problems that the DeWalt BMS would cut when connecting to my controller. The current peak to charge the controller input caps was too high. I started winding an inductor (had bought the toroid from Kin just in case). Then it occurred to me why not use an NTC resistor as inrush current limiter of the type used on many switched power supplies. I had used these on the input side of my own controller project (http://endless-sphere.com/forums/viewtopic.php?f=7&t=19993&start=15#p292906) just for this purpose (They are the two black discs in the bottom left corner of the PCB from the previous link), but commercial controller manufacturers seem to not be so careful.

Here how it looks on a kfong board. Note the much smaller footprint of the NTC resistor compared to the inductor.
DSCF9555_sm.jpg
DSCF9555_sm.jpg (82.05 KiB) Viewed 1553 times


The NTC I used is rated for 15A. Gets warm (as it is supposed to do) running near the rated current. Tried it both with the controller from the cellman 350W geared kit and a crystallyte 20A. Works great to prevent startup BMS tripping (and sparks on connecting the wires) for both.

I was looking to try this on some higher amp controllers, but had a hard time finding a suitable part number on digikey. Instead I was thinking of using higher ohm, but low current NTC for startup only, like this one:
http://parts.digikey.com/1/parts/1521264-cur-limiter-inrush-50-ohm-1-6a-sl10-50002.html
Then when caps are charged just short the NTC out of the circuit. I'm curious if you think this would work on the Castle HV160? The HV160 does some "motor twiddles" on bootup that are probably pretty high current. Can those be turned off in the programming somewhere? Or the NTC has to survive that?

Mike B wrote:
Question, will the interface allow regenerative charging? Lots of hill here, up and down. The 4011 motor on a previous bike would hit 20 amps of regen going downhill (had two Watts Up meters wired head to head to read this once I figured out why the one meter's voltage was going high on downhills). But your board has a diode. So I think not....


I run w/o the diode. I haven't purposively used regen, but my 9C often puts 100-200W backwards when backing off the throttle, and the DeWalts seem to survive that.

Another "feature" (not sure if accidental or not) is that on a 2s pack, when the BMS triggers at the end of capacity of one it seems to allow current though, so I can keep riding on half the voltage on the remaining pack without any reconfiguration. B.t.w. I get about 2Ah of the rated 2.3Ah from my 2007 toolking 24V packs.
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Re: Dewalt A123 BMS battery interface solution

Postby kfong » Sun Oct 23, 2011 9:10 pm

Jag that looks like a nice solution, but the current output from the FET driver is usually 20-25amps. Need to find one with a higher rating to make full use of the current. I've never used these, but isn't the resistance a little high? The 25 amp version has a 5 ohm value at 25'C. I think the Toroid still works out to be better.

The diode is to protect batteries with different capacities. If you plugged a fully charged pack and left an empty pack plugged in as well. You end up with one pack tying to fast charge the other. Not a good situation. If you keep the packs together all the time, then the diode can be omitted.
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Re: Dewalt A123 BMS battery interface solution

Postby jag » Sun Oct 23, 2011 9:59 pm

kfong wrote:Jag that looks like a nice solution, but the current output from the FET driver is usually 20-25amps. Need to find one with a higher rating to make full use of the current. I've never used these, but isn't the resistance a little high? The 25 amp version has a 5 ohm value at 25'C. I think the Toroid still works out to be better.


You mean for instance this 25A one:
http://www.digikey.com/es/en/products/M ... -ND/749869

Before connecting the controller it is 5Ohm. This helps limit the inrush current when connecting the battery to the controller.

The point is that when connected and in use it will heat up from the current in just milliseconds. Since it is an NTC the resistance goes down when temp increases. At full current, 25A, the resistance is only 0.03 Ohm, so it adds negligible resistance compared to the DeWalt pack itself.
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Re: Dewalt A123 BMS battery interface solution

Postby kfong » Sun Oct 23, 2011 11:02 pm

Yep that's the one. I'll have to give it a try. Neat solution.
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Re: Dewalt A123 BMS battery interface solution

Postby CyclemotorEngineer » Thu Jan 26, 2012 10:59 am

Kfong et. al.,

Nice work with the hack circuit. My circa 2006 packs are still going strong, after over 1000 charge cycles. I've attempted to start a discussion of what to do about the change to our beloved DC9360 packs. (They no longer contain A123 or equivalent cells!!) Title was Open-source alternative to DeWalt DC9360 since Stanley shaft. I would think this to be of interest to all who built this hack. Details repeated below:

Short, semi-chronological background to the shaft: A123 develops the best all-around battery, which is cycle-life-cost-competitive with lead-acid, and has best power density along with very good energy density. DeWalt incorporates these into their DC9360 packs. This poster designs simple hack to unleash the DC9360 for alternative uses. Kfong expertly develops and sells hardware to implement this hack. Stanley buys B&D/DeWalt. Short-sighted Stanley surreptitiously substitutes Samsung cells for A123. Hackers and more legitimate customers lose out.
http://www.youtube.com/watch?v=ZqPX46RX3gY

Meanwhile, A123 develops 7Ahr 32157 cells more appropriate for e-bike use. Also, back at Endless-Sphere, open-source BMS and chargers are developed.
http://www.a123rc.com/goods-474-LiFePO4 ... 57%29.html

I haven't scoured the hundreds of pages on this forum for details about the open source electronics, but am wondering: Has there been a discussion of developing charging and discharging hardware specifically for the 7Ahr 32157 A123 cells, in 10 to 20 cell series packs? Could this hardware be made available to all of us as SEEED project?
http://www.seeedstudio.com/propagate/

(moderator edit: fixed your second link; it didn't copy/paste from your other post correctly due to phpbb shortening displayed text of long links)
Last edited by CyclemotorEngineer on Thu Jan 26, 2012 1:25 pm, edited 1 time in total.
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Re: Dewalt A123 BMS battery interface solution

Postby PeteCress » Thu Jan 26, 2012 11:17 am

CyclemotorEngineer wrote:My circa 2006 packs are still going strong, after over 1000 charge cycles.


How many Ah do you get out of a pack now?

I'm down to about 2 from 2.2 - but more like 100 than 1,000 charge cycles - and wondering if that is normal wear-and-tear.
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Re: Dewalt A123 BMS battery interface solution

Postby CyclemotorEngineer » Thu Jan 26, 2012 1:33 pm

I'm getting about 15% less capacity on the 2s2p DC9360 setup. Probably being shut down by the worst pack, and I haven't bothered to test individually on a dummy load.

How old are your packs? There is a stamped date code next to the recycle tag which is six numbers corresponding to a year and week. Mine are all between 200618 and 200637.

Also, as kfong noted, it is important to pull packs from discharge circuit when not in use.
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Re: Dewalt A123 BMS battery interface solution

Postby PeteCress » Thu Jan 26, 2012 2:08 pm

CyclemotorEngineer wrote:How old are your packs? There is a stamped date code next to the recycle tag which is six numbers corresponding to a year and week. Mine are all between 200618 and 200637.


I only have 2 packs and they are stamped "2009 09-U0" and "2009 12-U0".
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Re: Dewalt A123 BMS battery interface solution

Postby CyclemotorEngineer » Thu Jan 26, 2012 8:09 pm

Pete,

It may be that your packs have degraded with age. I don't recall seeing specs for shelf life. Some chemistries, like NiMH, are not tolerant of disuse. It may not matter for A123s, but just to be conservative, I try to cycle mine at least once a month in winter.

So, pertinent questions include: Are you charging/discharging regularly? Did you buy these new? Are you keeping them out of the discharge circuit when not in use?
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Re: Dewalt A123 BMS battery interface solution

Postby biohazardman » Thu Jan 26, 2012 8:31 pm

CyclemotorEngineer wrote:I'm getting about 15% less capacity on the 2s2p DC9360 setup. Probably being shut down by the worst pack, and I haven't bothered to test individually on a dummy load.

How old are your packs? There is a stamped date code next to the recycle tag which is six numbers corresponding to a year and week. Mine are all between 200618 and 200637.

Also, as kfong noted, it is important to pull packs from discharge circuit when not in use.


It is known that the DeWalt packs with their BMS and charging suffer with some problems when used together. They do not charge evenly and over time some cells become weak and eventually the pack will not charge at all. It would be good if you could test the cells individually. I have purchased such packs and after removing a faulty cell or two, always the same cells, all other cells were healthy and are still serving me well two plus years later. Although I have not checked the tag you speak of I have a bag of the cases and did not to mark the info on my packs. Thanks for the thought that even these my favorite cells will eventually die :shock: it brings much remorse to my otherwise miserable existence. :wink:

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