Blinking DeWalt charger
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.
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).
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"
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"
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"
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 ?
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"
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.
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...
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"
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