DeWalt 28v/flashlight build

[pwbset]

I don't know why I torture myself so over batteries, but this time I decided to try a DeWalt 28v build since they were so cheap from toolking.com. The lesson learned here (again) is that what you think you're going to do uber-cheap ends up costing you tons of money so you might as well just buy a frickin' pre-built headway or ping or cell_man these days. This lesson will sink in someday I swear. :x

Anyway.. 2s4p in packs and I wanted to use the existing flashlight's circuitry to protect the packs. Well.. all seemed to be going well during the build, but this afternoon I fired it all up and things were not as they seemed. I was reading around 53v, which seemed a little low though the batts had been resting a few days so maybe that's nominal/normal around 3.3v. As I was doing final tinkering I watched as the voltage crept down and down until it was around 51.2v when I actually hopped on to ride. I floored it and the voltage sagged loooooow down to the low 30s... hmm... that's not right.

My conclusion at this point is that somehow, despite my direct wiring, I'm only "seeing" 2s1p at the controller, which would explain the voltage sag. But.. when I removed all the batts one battery was still 29.2v and a few were at 27.7-28v so I think it's a connection/wiring issue I need to deal with first and then maybe bypass the flashlight circuitry and try again.

I also notice that I'm reading 3.5-4v even with all the flashlights "off" so there is some sort of parasitic drain from the flashlights.

What a bummer and a waste of money. Back to the drawing board for now.

 

[jag]

How did you do the wiring? Cut connections to bulb, then use these as pack outputs instead?

kfong and cyclomotorengineer have figured out how you "activate" the BMS controlled output in the packs. The flashlight obvioulsy odes this in some fashion also, but maybe not allowing as much current??

I've seen some post where the flashlight was used as a holder for the battery. Not sure what was done to the circuitry though.

 

[pwbset]

How did you do the wiring? Cut connections to bulb, then use these as pack outputs instead?

Yeah they are just little spade connectors. I'm going to be re-using some of the salvaged goosenecks in my camper van for internal lighting.

kfong and cyclomotorengineer have figured out how you "activate" the BMS controlled output in the packs.

Ironically money was initially the reason I didn't get the kfong adapters. Found the flashlights dirt cheap, but yeah now I wish I'd have spent the extra $$ & gone the kfong route and supported an ES member to boot. Hindsight is 20/20. :?

The flashlight obvioulsy odes this in some fashion also, but maybe not allowing as much current?? I've seen some post where the flashlight was used as a holder for the battery. Not sure what was done to the circuitry though.

Yeah, I wasn't even originally going to use the flashlight circuitry, but figured why not try it. Going to check all the wiring tomorrow to make sure it's not just a loose butt connector or splice. Been trying to keep this whole thing solder-free, but may cave for better connections. If all the wiring checks out then I'll just ditch the circuitry and use the packs LVC shutoff and CA limit.

 

[amberwolf]

Can you take one of the flashlight boards out and get good clear hires pics of front and back? I suspect there is something on there that is limiting current, as the flashlight would not need much (compared to tools) and it might be there to protect the lights themselves from pack failure.

Remember also that the BMS in the packs is always draining power from the cells inside, so if you're not using them maybe they ought to stay on the chargers. I've no direct experience with the DeWalt packs but this seems like the case from other builds that I've read over the last couple years.

I doubt the flashlight electronics have anything to drain the packs, but if they do any sort of active protection for the lights they might have only a "soft off", and could drain a few to a few dozen mA constantly.

 

[MitchJi]

Hi,

Have you considered building a solderless pack from the bare cells like this?:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=17912

Building cylindrical battery pack for Dummy!

…From that effort, I think I found a way for almost anyone with basic woodworking skill to build a battery pack in any configuration or shape. And when something is wrong with the pack, its easy troubleshoot and take out just the cell/string without disassembling entire pack.

 

[cassschr1]

I have been using 2s4p this year with kfong boards. The main problem for me was removing and reinstalling the packs for charging all the time, I only had 2 chargers.

Also if you tripped a bms you had to stop and unplug all boards to reset, a real PITA

 

[pwbset]

Have you considered building a solderless pack from the bare cells like this?:

Hi Mitch. Yeah, I saw that thread and that's my last case go-to option. I'm trying to keep it simple.. and in doing so complicate things a lot. Heh, heh. Going to peek at the flashlight circuitry and maybe get a high-res photo for amberwolf to look at, but in the end I'll probably just bypass the flashlight circuitry because it's unnecessary. I just wanted the flashlights for the connector plates anyway.

 

[pwbset]

:lol: Bwahahah! Sheesh... if only I had taken 5 seconds to look at the board before going through all this trouble. 3A fuses. No wonder. :lol:

 

[pwbset]

This just gets better and better. Snipped out all the flashlight circuitry and hooked it all up again.. 58.2v hot off the chargers.. that's more like it. Went out for a ride and had gobs of power. Sustained 2.5kw no problem. Okay cool.. ebiking again! Slurped about 3ah out of a theoretical 9.2ah bombing up and down local hills for a few miles. Max amps just shy of 75A. Got home and put the batts on the chargers and 4 of the 8 batts now register 0v and just cause the chargers to triple light blink. Nada voltage.. bupkiss. W? T? F? Triple checked all wiring and it's all good. The other 4 batts sat at 26.1v which makes sense. So essentially it looks like I blew 4 BMS or something equally stupid. So much for built in pack protection.

DeWalt = Piece of Shit

To be honest I'm thinking of selling the whole kit and kaboodle at a loss just so I can get a turn-key pack and be riding. I'm over it. At least the chargers are good and there would be 64 loose cells. Make me an offer. :wink:

 

[webfootguy]

I think you need to stop and post some details on what your wiring is. A lot of folks are having good success doing what you are trying to do. You should not have packs that are at zero volts if others are nearly full. The 28v DeWalt BMS will protect the cells on discharge unless you bypass it (you can at the interface). Details please.

 

[pwbset]

I think you need to stop and post some details on what your wiring is. A lot of folks are having good success doing what you are trying to do. You should not have packs that are at zero volts if others are nearly full. The 28v DeWalt BMS will protect the cells on discharge unless you bypass it (you can at the interface). Details please.

I'm just using the flashlight housing adapters +/- at this point. Bypassed. 2 packs in series, 4 in parallel. Got rid of the flashlight circuitry since the boards had 3A fuses x 4p = 12A tops... not nearly good enough. I'm pretty sure my problem was that I was assuming, based on other threads I read here, that the 28v packs could handle 20A+ per pack instead of the normal 15A like the 36v packs. I had set my CA to 80A max and was riding around hard and saw ~75A max and blew 4 BMS so clearly the 28v packs are probably 15A max as well or maybe there are two versions of BMS. :lol: I've cracked open the 0v packs and they read ~29v at the +/- so the cells are fine. At this point I'm probably going to go the leamcorp route and harvest the cells and make a copper strip pack like he does. Or else sell the whole kit and kaboodle and go with a more simple solution like a cell_man pack or something. I just can't seem to stop tinkering and it always costs me time and money, but sure is FUN! :wink:

 

[webfootguy]

I've got tons of the 28v BMS cards around if you want some replacements. I've never seen the insides of the 28v flashlights but I would hope they take power from the right place. The connection to the battery has two ways to connect. One is via a 15 amp fuse directly to the cells and the other is via a FET that the BMS controls. If you are just taking power through that fuse, it may be that you are blowing the 15 amp fuse. Have you decoded the flashlight circuit? If not, can you post pictures so we can decode it for you?

 

[MitchJi]

Hi,

I think you should build a leamcorp style pack.

At this point I'm probably going to go the leamcorp route and harvest the cells and make a copper strip pack like he does...

Wow, this is great. I have been playing around with trying to find simple "bolt together " solutions for building a123-based packs for, well, for years. This is about as simple as it comes, great job.

A couple of suggestions. You might want to use brass strips, instead of copper, as they won't oxidize. Also, I agree that a single wider strip might be a bit better, connection-wise, but the single strips will certainly work fine. I would put connecting strips on each end, though, to even out the load.

I just can't seem to stop tinkering and it always costs me time and money, but sure is FUN! :wink:

Very easy,it won't take much time, you already have the cells so it won't cost much and you know you want to do it :wink:

 

[pwbset]

you know you want to do it :wink:

Heh, heh.. you're right of course. The only thing holding me back is balancing and I'd need yet another charger. For now I'm thinking of paralleling 4 packs to one that has the BMS/connector and then use the DeWalt charger for those and check the "extra" 3 packs balance every 5th time or whatever. 2 of those "4 packs" will take 4hrs+ to charge then, but on the other hand I can then sell 6 of my chargers and all the flashlight bits and try to re-coup some costs.

If I do go the Leamcorp Packâ„¢ route I'll post a photo though. It would be a 16s4p obviously. I have a 75v charger that I might be able to dumb down to 58.4v somehow. Or I suppose I could series two of the DeWalt chargers pretty easily.

 

[MitchJi]

Hi,

If you can live with 2 amp charging you could get 16 of these and use CellLog's for LVC:
https://p10.secure.hostingprod.com/...talog/product_info.php?cPath=3&products_id=60

This is the quantity price for 10 or more of these Single cell LiFePO4 chargers .

Purchase in quantity and save!

Note: The price is $10.95 for each charger if you purchase 10 or more.

IMO a better idea (assuming it happens this year ) would be the Gary/Richard V4 BMS with a couple of Meanwell 27v 350w (12 amp) Power Supplies. Probably sell your Dewalt chargers for enough to cover the costs.

 

[pwbset]

Commuted 3 times to work this week up the mountain loving it and this afternoon was at a friends and he was like, "c'mon lemme ride it". Well seeing as he donated his old Jamis as my ebike 3 summers ago how could I refuse. He guns it outta his driveway and disappears down the street with a huge EV grin while I talk to another buddy for awhile in his driveway. After a few minutes we're like.. hmm.. and then see him pedaling slowly back to his house. He says, "I think I broke it". :lol: Sure enough.. nothing.. no go juice. Pedal back to my garage to find out he'd blown 3 more pack BMS's. Doh. Despite that I had a 60A limit in my CA he peaked it at 144A before the CA had a chance to catch it and dampen it. Shoulda told him not to full throttle from a dead stop. Oops. Damn.

Now I have 1 good BMS left out of 8 packs so it's to bare cells I go already. What a pain. Leamcorp Pack for Dummiesâ„¢ here I come. Or I sell the lot of it at a steep loss, learn my frickin' lesson and buy a turnkey cell_man 16s15ah that I *know* will give me enough go juice. *sigh* $$$ Hindsight certainly is 20/20.. and cheaper to boot.

 

[webfootguy]

I have plenty of 28v bms replacements if you want some. PM me.

 

[pwbset]

I have plenty of 28v bms replacements if you want some. PM me.

I already did... waiting for a total price so I can pay you. Hehe. :wink:

 

[RoughRider]

what was the price for the batteries?

 

[pwbset]

what was the price for the batteries?

Got them from toolking.com for $40/ea. They are stamped 2007. After like 5 full cycles I've slurped as much as 2.2ah out of each pack so I'm happy with that.