Blinking DeWalt charger

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reikiman
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Over the weekend I finished the first stage of converting my Electra Townie 21 to electric. It's using a wilderness energy brushed 36 w/ 35 amp controller, which I already owned. And it's using a pack built from modified dewalt batteries. The pack is built out of five of the dewalt batteries.

It's constructed to bypass the BMS unit on discharge. For charging it's built to parallel the BMS units across the five batteries in the pack. I drop one of the batteries into a DeWalt charger and it charges all of them together. I haven't put the pack to use since building it this way.. however I'd used a smaller version of this pack last year.

Yesterday was the first serious use of both this bike and the pack.

I rode my usual commute.. about 7 miles total with no charging during the day. Since the dewalt charger is so large I didn't want to carry it with me.

When I got home the pack was still giving power enough so I could ride w/o pedaling and get decent speed, but the pack voltage had sagged to 26 volts. Eep, given it is 33 volt nominal that's a very deep discharge. I put the pack on the charger and of course it started blinking right away. Desparation time.. and I remembered I have a 36 volt soneil charger, used for my refurbished Vego 600, and got that. I connected it to the discharge connector of the pack and turned it on. It's charging the pack and it has recovered to 31.51 volts with nearly 7 ah of electricity put back into the pack.

Right now if I, disconnect the soneil charger, and then drop the dewalt pack onto the dewalt charger... it goes to two solid lights, and then starts blinking.

Any advice?

I remember reading someone saying the blinking happens when the charger thinks something is wrong -- such as the voltage being out of bounds (too low).

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- David Herron, Green Transportation Examiner, Green Transportation Info, The Long Tail Pipe, Electric Race News, davidherron.com, 7gen.com, What is Reiki
- Charger bike (rebuilt), Electrified Electra Townie, 1971 Karmann Ghia

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Jeffkay
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Re: Blinking DeWalt charger

This happened to me (among the other 50 horrible things I have done to the DeWalt batts). What is likely for you is one cell (or more) is lower than the BMS wants. It could be a bad cell also... The trick I have done two tricks to get it happy. One is discharge the other cells (figure out a method here) until it is closer to the bad one. Then you need to use another DeWalt or maybe your Soneil to bring the pack up until the DeWalt charger likes it again. The other way is to charge the single cell with a source like one cell off another pack until it gets around 2.6 or 2.8v. I have also "ticked" the cell with more voltage. By ticking I mean quickly tapping the wire you are using from a higher voltage source like a human pulse width modulator! This is not ideal but again, I have succeeded to satisfy the DeWalt charger this way. On another note, I have blown many DeWalt BMS units and feel the charger/BMS combo is pretty unfriendly for us EV'ers using the direct pack output. I have been looking into other ways to balance. I would like to know if anyone has found a way to get the 36v/3amps to come from the charger without a battery in it? If so, this is a good charger voltage source with some other kind of balancing. As far as auto-monitoring the low voltage cuttoff, the EV controller or a human looking at a volt meter can take care of that since you loose this function by bypassing the DeWalt BMS anyway...
Jeff K. "Bike to Future" and "Deep Cycle"

reikiman
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Re: Blinking DeWalt charger

Hmm.. clearly by "cell" you're meaning the M1 units inside the dewalt pack, not the individual packs in the overall pack. Interesting.

I remember on the visforvoltage.com forum some discussion about how the charging profile for these cells matched typical SLA charging profiles, except for the cutoff voltage. They mentioned the possibility of retuning a soneil charger for a lower cutoff voltage ... or else reconstructing the pack, breaking it down to individual cells, and constructing it to have a cutoff voltage compatible with a normal SLA charger. In such a case you would completely ignore the dewalt BMS units and the dewalt charger.

- David Herron, http://davidherron.com/

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- David Herron, Green Transportation Examiner, Green Transportation Info, The Long Tail Pipe, Electric Race News, davidherron.com, 7gen.com, What is Reiki
- Charger bike (rebuilt), Electrified Electra Townie, 1971 Karmann Ghia

reikiman
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Re: Blinking DeWalt charger

I haven't measured per-cell.. (btw, I never took off the black base part of the pack, any advice on how to do that? my attempts so far haven't worked)

But I measured each of the sub-packs and found the leads I'd soldered to one of them have fallen off and that battery sub-pack is at 20 volts. eep eep eep eep eep The others read a consistent voltage for each.

- David Herron, http://davidherron.com/

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- David Herron, Green Transportation Examiner, Green Transportation Info, The Long Tail Pipe, Electric Race News, davidherron.com, 7gen.com, What is Reiki
- Charger bike (rebuilt), Electrified Electra Townie, 1971 Karmann Ghia

Jeffkay
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Re: Blinking DeWalt charger

Yes, I mean each cell should be measured. Here is a link to help you get the pack black back off. No need to remove the BMS. Most 2006 packs had yellow tape inside but now the 2007 packs have white tape and the BMS connectors have black goo on them like RTV sealant. You can measure the cells by peeling the tape back (it is pretty reusable) or simply poke your meter lead through it in the center of the big hole in the black plastic battery sides. Photos on the link will help you understand. Link: http://www.slkelectronics.com/DeWalt/packs.htm I doubt you killed cells so once you get the BMS/Charger happy again, leave it on the charger for a day in the three light-on mode. This is when balancing is done and the DeWalt balancer is not very good.
Jeff K. Burbank, CA "Bike to the Future"

reikiman
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Re: Blinking DeWalt charger

Hmm.. I just read through a bunch of postings all over the net; and made some links on my website, a123systems DeWalt batteries, with what I found. I'd of course seen that slkelectronics page before. Hmm...

I got the bottom parts off the packs (one of the pages showed me the trick I could never figure out... using a flat blade screwdriver, first pry the sides a little to loosen, then go to the end with the hole, and pry at each side to raise the cells up, do it a little at a time) ... okay, curiously in a couple of the packs some of the wires had melted themselves INTO the plastic of the case, and in one case the wires looked scortched. uh... The bike draws just 35 amps max, paralleled over 5 batteries is... uh?

In most cases the cells read 3.8 volts but in a couple cases they read less, including 0 volts. It's a little late but ...hmm... I do know how to read voltage with my meter, so I'll try again in the morning.

Some of the postings I found gave rather clear description to different ways to build packs from the raw cells. I'd read some of these before, of course, but some of these made it clearer than before.

- David Herron, http://davidherron.com/

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- David Herron, Green Transportation Examiner, Green Transportation Info, The Long Tail Pipe, Electric Race News, davidherron.com, 7gen.com, What is Reiki
- Charger bike (rebuilt), Electrified Electra Townie, 1971 Karmann Ghia

Jeffkay
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Re: Blinking DeWalt charger

Hey David, Thanks for your web collection of DeWaltisms! I really liked the charger ones. Here is what I found with bad cells. If the cell can be hand charged it may work again. It might have less capacity depending on the calamity that caused the mess in the first place. If no charge takes place and the cell remains at 0 volts it is most likely shorted and junk. You can solder in just one cell. There are usually single cells on e-bay for about ten bucks or other suppliers I guess.

I am still wondering if anyone has made the charger put out the full 3 amp voltage while no battery is in the socket?

Jeff K. "Bike to the Future" and "Deep Cycle"

reikiman
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Re: Blinking DeWalt charger

I rechecked my cell voltage readings. The cells are at 3.7 volts apiece except in most cases the positive-most cell of each pack reads 0. In one case the positive-most cell reads 3.4 volts. At 3.7 volts apiece they are slightly overcharged, no doubt because I used a 36 volt SLA battery charger and a couple times returned to the charging station to find it reading 41 volts (eek).

I traced the BMS wires and they all connect to the negative terminal of each cell. Except for the negative-most cell, and it's - is wired directly to a screwed-on connector on the BMS. It seems in the idea of connecting the packs in parallel, this negative-most connection got skipped. Hmm..

I did more researching and a123systems DeWalt batteries has more interesting links.

The a123 M1 Battery Pack Contruction Kit is interesting.. (direct) .. it's a method of building a 'stick' style pack, it has a central rod to which are attached plates, you insert the M1 cells between plates, and then screw the plates down tight. The plates provide electrical connections between cells and you build the pack circuit that way. We had discussed similar ideas on V.com last year, and many said a non-soldered connection doesn't provide enough connection to drive a significant current such as you'd see on a vehicle. But that context was more about using a tube to house batteries, and springs at each end of the tube to hold batteries in place. I think a plate with screws to hold everything together should give better contact, especially if you use an electrically conductive paste.

But I'm curious how to manage charging such a pack and haven't found a good pack charging solution.

The R/C hobbyists seem to prefer the LiPoDapter (direct). Also the Astro "Blinky" Battery Balancer for A123 Cells (direct) looks like an interesting addition.

- David Herron, http://davidherron.com/

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- David Herron, Green Transportation Examiner, Green Transportation Info, The Long Tail Pipe, Electric Race News, davidherron.com, 7gen.com, What is Reiki
- Charger bike (rebuilt), Electrified Electra Townie, 1971 Karmann Ghia

proton
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Re: Blinking DeWalt charger

If I may respond with a query...
Why are people going to the trouble of using the Dewalt packs when it would be so much easier ( at the same price )
to just buy LiFe cells from a supplier ?
So - you find a pack on ebay or wherever at say, $100 + $15 shipping. At 36V / 2.3 Ah, you will need 4 units so you dont over blow the BMS.
That = $460 for 36V 9.2 Ah. Which = $50 per Ah... am I right ?

then figure out how to hook them all up and charge them AND to stay balanced. ( w the $100 charger )

9.2 amp hours aint settin' the world on fire either and your limited to 20-25 amp controllers ?
Straight cells allow you to go to 40+ amp controllers.
Personally 12Ah would be my minimum to go anywhere. Which = $50 per cell and $50 per Ah. Same as Dewalt.
falconev will have these in Nov. along with a balancing charger
What am i missing here ?
thanks

3_2V12Ah_LFP-1.jpg

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reikiman
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Re: Blinking DeWalt charger

1) When I started on this a year ago, dewalt was the only LiFePo battery source.

2) DeWalt has designed a BMS and charger which work together, and I want to reuse their engineering talent.

3) I bypass the BMS on discharge so my current to the controller is limited by the wiring. FWIW the spot-welded connectors DeWalt uses probably won't withstand really high discharge, but for my electric bicycle that's okay.

4) the pictured cell you show has no BMS or charger... you say Falcon will be offering one, so I'll take a look when that becomes available. It's not available today, and it wasn't available last year.

I agree with you, diddling with DeWalt packs isn't exactly my idea of fun but as I said it's been the available choice and they do already offer a well tested charger and BMS combo.

- David Herron, http://davidherron.com/

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- David Herron, Green Transportation Examiner, Green Transportation Info, The Long Tail Pipe, Electric Race News, davidherron.com, 7gen.com, What is Reiki
- Charger bike (rebuilt), Electrified Electra Townie, 1971 Karmann Ghia

reikiman
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Re: Blinking DeWalt charger

And.. you say eBay has sellers of LiFePo batteries. Can you suggest a search string to find them? I just tried a few and couldn't find any. FWIW electric motorsport has thundersky LiFePo cells available but they're too large for my electric bicycle. They would go great on my Lectra motorcycle though.

- David Herron, http://davidherron.com/

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- David Herron, Green Transportation Examiner, Green Transportation Info, The Long Tail Pipe, Electric Race News, davidherron.com, 7gen.com, What is Reiki
- Charger bike (rebuilt), Electrified Electra Townie, 1971 Karmann Ghia

reikiman
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Re: Blinking DeWalt charger

I did some more research and found Is my a123 battery dead? (direct) ... this is a forum discussion with someone having an A123 M1 cell that's gone to 0 volts. The suggestion someone gave was to "zap" it with 12 volts a few times and see what happens, he tried that and the cell recovered. Soooo....

I have a 12v SLA battery on my work area ... I first tried the skinny 22 gauge jumper wires I have, but those heated up to burning hot immediately. But the battery cell did take on some voltage from that. I ended up with some medium duty jumper cables I built, connecting them through a massive 300W rheostat I have so it would limit the current keeping the cables cool. After a few minutes with 12v directly connected to the cell it started reading at 2.8 volts, and after a few more moments it read at 3.1 volts. I disconnected the battery and have let it rest for awhile, and it's dropped to 3.0 volts. Looks good.

With the battery pack disassembled I don't like the look of the plastic parts dewalt built. For instance the BMS wires connect to the battery cells with a "spring" which doesn't seem terribly reliable to me. So I'm pondering an alternative way to connect the BMS, which I think will be far more robust.

- David Herron, http://davidherron.com/

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- David Herron, Green Transportation Examiner, Green Transportation Info, The Long Tail Pipe, Electric Race News, davidherron.com, 7gen.com, What is Reiki
- Charger bike (rebuilt), Electrified Electra Townie, 1971 Karmann Ghia

Jeffkay
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Re: Blinking DeWalt charger

I have found REALLY dead cells that act like a short and will not take charge... I have built a 4S6P pack using tubes and rubber foam "springs". The wire used at the ends is flat 12 ga. speaker wire. I used the pack over 20 times with no problems powering an Etek motorcycle at up to 150 amps! Maybe it would show problems later but no problem at all so far. \Jeff K. Burbank, CA "Bike to the Future" and "Deep Cycle"

CGameProgrammer
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Re: Blinking DeWalt charger

I'm seeing a lot of misinformation in this thread regarding A123 batteries.

A *single* A123 cell is capable of 30C continuous discharge. That means a *single* cell can safely deliver 70 amps continuously! This is because A123 cells are NOT regular LiFePO4; they use that chemistry but are what A123 calls "lithium nano-phosphate" because the physical molecular structure is such that it's capable of far greater charge and discharge rates than regular LiFePO4. A123 has no direct competitor.

On the other hand, the DeWalt BMS is not capable of much and I think it should be bypassed for discharge and only used for charging/balancing.

reikiman
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Re: Blinking DeWalt charger

CG, I agree the dewalt BMS should be bypassed for discharge. I've read it's fuse is 15A and will blow easily in an EV.

I have some good news to report in that I've worked out a system which will work.

I'd pulled the batteries completely out of the box and took a good look. I absolutely do not like the way the DeWalt designed the connections for the balancing part of the BMS. They used a pair of black plastic sheaths, into which were inserted bare wires routed through channels, and ending in springs connecting to the batteries. In my case the bare wires in most cases melted the plastic around them and were just a horrid mess.

What I've decided to do is... I've mapped out the wiring for the BMS unit to the cells, and have soldered 5-conductor cable to the cells. Those 5-conductor cables are brought out to a screw-down terminal block. Then I have another pair of 5-conductor cables which end in the female version of the connector that's on the BMS. This way I'm implementing the BMS-battery cell connection compatibly with how DeWalt did it, but can parallel one BMS over more than one battery. You also have to make sure to connect the + and - on the BMS to the battery, and for good measure I'm connecting the wire that's in the corner of the BMS to the negative-most terminal.. simply because DeWalt made that connection.

I've done this with one battery pack right now, and found it works. So I have four more to do it to.

I've taken pictures and will be writing it up on my website and will post links soon.

- David Herron, http://davidherron.com/

__________________

- David Herron, Green Transportation Examiner, Green Transportation Info, The Long Tail Pipe, Electric Race News, davidherron.com, 7gen.com, What is Reiki
- Charger bike (rebuilt), Electrified Electra Townie, 1971 Karmann Ghia

Jeffkay
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Re: Blinking DeWalt charger

David, Good luck but keep in mind the BMS is extremely easy to fry! I guess you will have a supply of them from the batteries not using it or re you keeping them on all batteries? If you go parallel, I think you can have just one for 5 or six batts...
Jeff

reikiman
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Re: Blinking DeWalt charger

If you go parallel, I think you can have just one for 5 or six batts...

Yes, that's my plan .. is to parallelize the batteries and reuse the dewalt BMS for charging/balancing. The plan I outlined above is v.2 of the method. Right now I have 1 BMS in use and four left-overs.

In my research it looked to me that the "LipoDapter" would be a good alternative to using the DeWalt BMS. But I didn't find a clear how-to-tutorial on wiring a lipodapter.

- David Herron, http://davidherron.com/

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- David Herron, Green Transportation Examiner, Green Transportation Info, The Long Tail Pipe, Electric Race News, davidherron.com, 7gen.com, What is Reiki
- Charger bike (rebuilt), Electrified Electra Townie, 1971 Karmann Ghia

Jeffkay
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DeWalt charger report:

DeWalt charger report: I just charged 7 packs with one charger. It only has BMS on one. The rest just share the plus and minus main leads. Charged from 28.2 (pack depleted volts) to full in 7 hours. Charger was not unusually hot or upset in any way. If doing this, please check your balanceness of the other 6 packs before and after...
Jeff K. "Bike to the Future" and "Deep Cycle"

efreak
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Re: Blinking DeWalt charger

a volt meter on the discharge line is what I have to remember to install before testing here is one of the topics talked about a bit here at the sphere

http://endless-sphere.com/forums/viewtopic.php?t=2498

good luck

efreak

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