DeWalt BMSes have changed (for the worse)

ebinary

ebinary

100 W
Joined
Dec 12, 2007
Messages
145
So a week ago I wrote about a DeWalt BMS not energizing (activating its FET for discharge) and I figured I'd blown the BMS.

Not true... something has changed in dewalt land, and my bike (which uses unmodified packs) don't like it.

I just got two new packs (in blister packs) from ToolUp:


  • Hooked them to a DeWalt flashlight - works great...
    Threw them in the charger... charged great
    Hooked them into my bike recievers (which use a resister network to activate the BMS's FET) - CycleAnalyst blinks for a second and shuts down
    Hook to a Dewalt flashing again... still great
    Hooked up any of my four older packs to the bike... all of them start the bike right up

Something has changed on these packs... there is a new requirement for a softer startup or something. They are NOT the same packs. Four old DeWalts - perfect - Three new dewalts (from two different sources) - won't even start the bike.

I'll have a dewalt saw in a few days to test a high current tool on both types.
 
wrobinson0413 said:
I wonder if DeWalt has been receiving a lot of batteries back under warranty from non-DeWalt tool abuse and decided to nip it in the butt? I am waiting for one that I won off of EBay last week, I wonder if it is a newer or older generation battery? Can you take some pictures of the older and newer BMS modules that are in the batteries? I wonder how different they are and if you can see the difference between?
Click to expand...

Could be (I am still waiting after a month for a replacement).

I did a few more measurements.

  • The always-hot wires have 34V across - as expected
  • The BMS-enabled wires have 0V across when no resistor network - as expected
  • The BMS-enabled wires have 34V across when resistor network is used - as expected
  • If I start cycleanalyst with another pack, I can switch to a new pack and unplug the old and keep it powered
  • But, If I try to draw any juice from the controller, it shuts down
 
wrobinson0413 said:
Can you take some pictures of the older and newer BMS modules that are in the batteries? I wonder how different they are and if you can see the difference between?
Click to expand...

AFAIK, the bms is fully potted, so you can't see it without ruining it.
 
wrobinson0413 said:
Thats too bad about the potting. I have never had one to take apart yet. This is my first adventure or misadventure into the A123 world.
Click to expand...

They are great cells, just not the perfect package. As you probably know, you can draw power without using the BMS, although you will blow an internal fuse if you draw more than 15A that way. And you wouldn't be protected against over-discharging your cells (but that system is a tad flawed too).

I may be forced to go that route - maybe open them up and add an additional shunt to the fused side so I can get 30A-40A. Preferrably in a non-warranty-violating style, but the warranty service has been so slow (approved 28 days ago-still no sign) that I doubt I'll ever use it again.
 
wrobinson0413 said:
The only good thing is for my project I was only going to use the cells and not anything else. I am planning on building my own BMS for the pack when I get everything together. Now if I could only win another 3 packs off of Ebay :(

As for the potting, is it a hard potting material or soft? If it is soft, I may sit and do some picking to see what they did for a ballancing circuit.
Click to expand...

I think the only way to un-pot the board is to soak it in some toxic substance, which also disolves certain components.

Lots of good ideas on this board for BMSes w/o duplicating Dewalts' mediocre effort.
 
ebinary said:
I did a few more measurements.

  • The always-hot wires have 34V across - as expected
  • The BMS-enabled wires have 0V across when no resistor network - as expected
  • The BMS-enabled wires have 34V across when resistor network is used - as expected
  • If I start cycleanalyst with another pack, I can switch to a new pack and unplug the old and keep it powered
  • But, If I try to draw any juice from the controller, it shuts down
Click to expand...

Since you can start it up with another pack, it seems like your new Dewalt BMS is detecting the current surge as the Big Controller Cap charges up - One thing that would be easy to try would be to put a big inductor in line with your Controller Power input - It may slow down the spike in current enough to allow it to operate. I have done this on my Dewalt Power system to reduce the sparking damage when switching in direct power from my Dewalt's to the main power switch - I used a ferrite core I got from Radio Shack and wound 14 gage insulated solid copper wire around it.

Just a possibility.

Brian
 
mn_aerorider1 said:
Since you can start it up with another pack, it seems like your new Dewalt BMS is detecting the current surge as the Big Controller Cap charges up - One thing that would be easy to try would be to put a big inductor in line with your Controller Power input - It may slow down the spike in current enough to allow it to operate. I have done this on my Dewalt Power system to reduce the sparking damage when switching in direct power from my Dewalt's to the main power switch - I used a ferrite core I got from Radio Shack and wound 14 gage insulated solid copper wire around it.

Just a possibility.

Brian
Click to expand...

Great idea - are there any specs to that ferrite core, and about how many turns did you give it?

Thanks, Eric
 
used a ferrite core I got from Radio Shack and wound 14 gage insulated solid copper wire around it.
Click to expand...

will the rectangular snap-open style work? (pictured here):

http://www.radioshack.com/product/index.jsp?productId=2103979&cp=&sr=1&kw=choke&origkw=choke&parentPage=search

I've got a couple of those at home
 
Why don't you just tap the (+) & (-) from the cells and run it out to a pair of Anderson PowerPoles. That way you don't have to worry about the BMS and still keep your warranty intact. You can still use the stock Dewalt charger too, but I wouldn't recommend it as many of the cells were imballance.

Here's how mine look
chargersv9.jpg
 
I think you may be right .., my local service centre hasn't had any cells in quite a while .. the guy i know there even told me he thinks they may of fixed the problem ..

I hope not thou:p

-steveo
 
steveo said:
I think you may be right .., my local service centre hasn't had any cells in quite a while .. the guy i know there even told me he thinks they may of fixed the problem ..

I hope not thou:p

-steveo
Click to expand...

BTW - I finally got a real DeWalt tool (the saw, not just the flashlight) and it works fine with these "new" batteries. So its still DeWalt friendly, just not friendly to my particular eBike system :-(
 
ebinary said:
I think the only way to un-pot the board is to soak it in some toxic substance, which also disolves certain components.
Click to expand...

Actually, it's pretty soft, compared to epoxy. if all you're after is the fuse you can dig it out with a pair of dikes. I was planning on doing the resistor network but wound up bypassing the fuses for lack of time ( & laziness ). It would probably be safer to parallel another 2208 SMT fuse, but I just bypassed it and rely on external fuses for protection.

D_FS.JPG
 
Just to close the loop on this - If I start the controller with an old-style DeWalt pack, then add two new-style DeWalt packs, then remove the original pack (so - running on just new DeWalts) - everything works fine.

It is definately the inrush of current that is popping the new-style DeWalts.

I know of no way yet to identify the new DeWalts, but I date all my batteries whe they arrive, and the bad ones are all since July. The good ones were all up through January. Don't know exactly when the change occurred. All the old ones can start the bike from fully discharged - none of the new ones can.
 
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