a123 developer packs (continued)

This is the email from Nick from the previous A123 Developer Pack Dewalt Pack Topic

Brian,

Thats sounds interesting. Basically I'm more interested in a low cost charge life po4 balancer than the dewalt cells themselves. I live in the UK and the dewalt packs are very expensive here after tax. But life po4 suppliers seem to be springing up all over the place for example (http://tinyurl.com/3agyws or http://www.goldenmotor.com/)

The problem is the BMS's are either unsuitable for ebikes, for example the golden motor lithium phosphate pack contains an unnecessary discharge BMS that might cause problems at high voltages or simply aren't available.
So it would be cool if the dewalt balancing modules could be used as a diy charge balancer. Especially if they could be modified to charge any number of cells in series, given a suitable charger.

The impression I get from your last post is that it is, so if I wanted to charger a 15s 48 volt nominal pack I could use 2 10 Series modules and leave 5 empty?

Many thanks

Nick

Nick: First, just to clarify:

a) I have no idea if you could get a Dewalt BMS module to work with a different charger. I believe nearly all the smarts for charging is in the BMS module, as per some R/C Airplane forum discussions. But how exactly the charger interacts with the BMS module is not clear.

b) I believe you could use the Dewalt charger and a Dewalt BMS Module as a low budget charger to charge a 10sXp pack made out of any brand (or cell size for that matter) of LiFeP04 cells, as long as they have the same basic cell voltage characterstics as the Dewalt A123 cells.

c) I didn't really mean to imply that you you could use the Dewalt BMS module to charge and balance any number of cells ≤10......

However, regarding point c - Maybe what you are getting is to use it as a balancer in the following way: You could split your pre-charged 48 Volt pack (I'll explain why pre-charged in the next paragraph) into a lower 10s pack and an upper 5s pack, and then take the upper 5s part and "carefully" tie it in parallel with any 5s section of the lower 10s part of your 15s pack. I say do this "carefully" here, because if the cells are too mismatched when you tie them in parallel, there may be too much current transferred for your connectors to handle - to avoid this you could make your connectors really beefy or you could put a bank of 5 series resistance between them, say .2 ohms or so and wait some time, before directly tying them) This strange and ungainly modified pack would still be 10 series cells that I believe could be balanced using the Dewalt charger and Dewalt BMS module.

I don't think you'd want to use the Dewalt Charger and Dewalt BMS module to charge this ungainly pack, since it would probably unbalance the double cell 5s2p section in the process....

Now that we are on the topic of charging a 48 volt pack using the 36V Dewalt Chager plus BMS module....Imagine that you had a 15s2p pack. If you wanted to use a single Dewalt charger and a Dewalt BMS module to charge it, you could split it up into three 10sp packs, and charge and balance them each separately. Or you could convert it into a 10s3p pack and charge and balance them all at once...as long as you were careful when you paralleled the potentially mismatched cell.

Interestingly enough, one really low budget way I have heard of to balance a pack of serial cells is to separate them and then to tie them together all in parallel, possibly through small, yet high power, resistors to avoid melting connectors...

Best Regards,

Brian

»

Thank you Brian, Chas for the wiring diagram of the DPDT switch! And also others who contributed...

I am not sure how to correctly wire it, pls let me know if this is the right way... Jojo

NOTE: This is a continuation from -
http://visforvoltage.org/forum-topic/batteries-and-chargers/578-a123-developer-packs?page=1

Looks right to me, and follows the wiring diagram I placed here for you.

Go 4 it,
Chas S.
My Bicycle Pages

Hi Jojo,

I agree with Chas, your diagram looks Good!

Just make sure that you have the + and - terminals of your batteries and charger matched up right according to Chas's diagram.

One tip: as a confidence builder, and to be careful, you can always verify exactly how the switch works by using an ohm-meter on it before you hook power to it.

Brian

Thanks for the explanation Brian.

Hi there,

This is my first post and although I'm a new member, I have been a returning guest for a little while now. Before I go any further let me say that, if while reading this you feel that it is misplaced or it would be more appropriate to start a new topic, please inform me and I'll do so right away. I'm a bit new to all of this, so thanks for your patience.

Didn't mean for it to be so darn long. If you don't want to read the whole thing, basically my question is this: could someone very kindly walk me through every step the process of wiring dewalt 36v's together, 2s Xp, so I can charge them each in individual chargers (to retain a 1 hour overall charging time) while making use of the BMS, and use the pack to power an electric motorcycle / is this even possible? I'm thinking 2 hours would be easier (and cheaper) based on the 2s part and the DPDT switch, but I really am aiming for 1 hour. I'll gladly buy the necessary parts from someone here (I recall seeing someone was hoping to recoup their losses).

I'm sorry if this seems repetitive or unintelligent, but I've read (several times over) through every topic on these forums regarding the Dewalt packs, and I still can't figure out how to do what I'd like to do. This probably stems from my lack of experience with these batteries and electrical work in general, but I am dedicated to the idea of a home-built electric motorcycle and I'm trying very hard to learn as much as I can. I've read up on the basics, but my actual experience is slim to none. I'm planning out an electric motorcycle, but I'm never going to get anywhere unless I start asking questions to the people who know the most.

The goals:
- use Dewalts in series/parallel, 2s Xp with a 72v motor and appropriate controller and so on.
- keep the charging time at 1 hour (so, basically, keep the battery to charger ratio at 1:1)
- have only 1 (preferably retractable) cord to plug into a normal 110v AC wall outlet for charging.
- have everything fairly permanently in place (no constant swapping of batteries -- only after years, when they need changing), with each battery strapped into its own charger, and the charger plugged into a power strip.

I'm thinking that multiple power strips would be needed to accommodate all the chargers (based on desired range / # of batteries in parallel with their own chargers), and I'd be plugging extra power strips into each other as necessary to create both a complete circuit and enough outlets for the individual battery chargers. I would like to take advantage of the engineering put into the balancing systems in place to keep my batteries in good shape, so I'd rather not bypass those units unless my batteries could be otherwise balanced.

Everyone here seems pretty nice, but please be kind if I missed some horrible logical flaw or you feel like I should be able to figure this out on my own. I need to start somewhere. I can't have fun until I'm riding, I can't ride until it's built, and I can't build it until I've planned it. I can't plan it until I have a better understanding of some basic principles, so I better start working on that understanding, right?

I did see mention of charging the dewalts in parallel "in situ", but that topic just pointed me towards the main thread. Just a few posts up there is info on a DPDT charging switch and even a wiring diagram for it, but I can't quite figure out what that all means or how it would impact the whole BMS system of these battery packs. I also read about using diodes to protect the BMS, but I don't know what kind of diodes you guys were talking about, how this would be wired, or how basically how it would work.

I'm also confused by the mention parallel-izing of the BMS units. Does this mean just wiring the batteries themselves in parallel will inherently balance them? Do I have to wire the battery terminals in parallel and the BMS units in parallel separately?

Thank you everyone in advance for your help, and I look forward to many discussions and much sharing of experience in the years to come. When I do finally get to building my electric motorcycle next summer (I'm back to college again in 2 weeks, but hey, that gives me about 8 months to plan, right?), I'll be sure to document the whole process and take pictures and everything fun like that.

-- Mark

Hi Mark, Some quick thoughts n your post: First, leaving the chargers with you is not a huge deal but leaving the batts on the charger could be. Also, be aware that not opening the batteries to get the + and minus power directly at the cells means that you would be using the power after the BMS module. This module has a fuse on the negative side at 15 amps. It is VERY easy to blow and I am sure a 2SXP bike situation will blow it. So your first step might be to tap the power at the cells and then when depleted, simply reach into the battery bag and connect it to the charger. Next, the parallel-izing will not be needed because each charger will balance the 10 cells in each of the two packs. For your 72 volts (remember it will be less due to the Dewalt fictitional 36 volts--it is really about 33.3 nominal) all you need to do is connect one pos to one neg and use the string like this. If you have no draw (ontactor or switch open for "bike being off mode", then you can still charge them without breaking the middle battery connection...
Jeff K.

Here is some news. Originally, I was thinking how great it is that you could take a Dewalt pack back if you tapped into it. What I mean is, aside from soldering to the cell before the BMS unit to get full current, Dewaltcould not tell you were "inside the case". Assuming if they knew, they could void the warranty. Well, the latest '07 batteries I have opened now have black goo (silicone?) over the BMS multiconnectors. Just thought you might like to know. Also the Kapton tape changed from Yellow to a white one that looks obvious if tampered with. Frankly, I am surprised Dewalt did not put a seal on the case, though they probably assume not everyone has a security-star tool to open the pack.
Jeff

Hi Jeff,

I'm concerned about the black silicone goo you mentioned that is now in these 07 packs. I don't have a great concern about the warranty, but how hard is it to remove this "goo" and then remove the male connectors and then access the two female bms connectors built into the packs? Do you end up destroying the male end to do it? The reason I ask is that I am currently using these to build self-balancing into my multi-parallel 33 volt 5-pack ...

Thanks,

Brian

No Brian, They will seperate and be usable. You can scrape most of goo off. I doubt warr will be an issue for me now that I am done killing cells. Do you have any new schemes for the self-balancing? I did it in my 12v pack. It is cool.
Did you see my post about new DeWalt packs? If not, you may want to view that in "Batteries and Chargers". Also, the EV Cobra project guy has made balancing circuit boards with LEDs but I know not if he will offer them to others....
Jeff

Charger guts out of DeWalt one hour charger case will be "onboard".

I accidentally dropped 10 cells connected by tabs at approx 4 ft high, making a hard impact to cemented floor in the garage. Is there some damage to the cells? Checked the voltage, it remains the same...

Damage from dropping? If able, check that no tabs popped off the welds. They are not real strong I have noticed. If the volts are good you are probably okay all around. Talk about a "voltage" drop! Sorry

Hi,
I built an ebike in Sept. with a Crystalyte 406 and 3 SLA's in series. The SLA's have since gone south and I am going to go with 3 Dewalt 36v batteries in parallel.

I'm planning on bypassing the BMS's on each of the 3 Dewalts for the output.

I bought (haven't received them yet) 3 Dewalts and 2 chargers. If I get another charger, Is it feasible to have the three connected in parallel with each battery sitting on it's own charger? The idea being that I could charge all the batteries in one hour.

Would I have to disconnect the individual batteries to charge them on their own chargers? Or could I just leave the batteries in parallel and turn the controller off and plug in the chargers?

Thanks for any help. ltan

Hi Itan,

I don't know of anyone who has tried to use more than one charger to charge packs in parallel. I have charged 5 in parallel, but only using one charger.

However, it will probably work because these chargers do act like fairly ideal current sources, as shown by their ability to charge 5 packs in parallel in 5 times the charging time.

The only potential "catch" would be if they intefere with each other during the balancing cycle. The hope would be that they would work together and balance them as fast as a single charger and a single pack...

If I were you, and wanted to take the risk of experimenting with this, I would first just try to do two packs in parallel on 2 chargers at the same time, to limit the scope of any damage that might occur. You might want to track how well the balancing cycle works through the process.

Best Regards,

Brian Lee

It does not work. I tried it. One charger becomes "king" of current and then the others just sit there. I did it with two in this "load sharing" mode and it did not work--maybe others have got a trick. Jeff

Interesting result Jeff.

I wonder how the non-dominant charger can tell that the dominant charger is attached to the same batteries? This charger must be sensing something on the line?

What happens with the lights on the non-dominant charger? I get the impression that nothing happens...

Does it make any difference what order you plug the paralleled batteries into their respective chargers, as to which battery dominates?

Thanks,

Brian Lee

I wondered the same thing. Perhaps it senses the other charger's higher voltage as cutoff...

Hi Jeff,

What really throws me is how can these charging modules sense or measure anything significant additional or lower voltage across these batteries when the two battery packs are each only 10x10 milli-ohms of resistance? These two packs should only see about 100 mV of charging voltage while charging these batteries, unless the internal connections and charging wires are adding significant resistance?

You might want to examine your "connectology" for shared higher resistance lines between the BMS modules, and if you have a DVM, you could measure your in-line resistance.

Maybe you've already done this , but the best that could be done would be to send the current from the 2 BMS modules through separate low resistance wires to the individual packs, and connect the packs in parallel through a separate set of low resistance wires. I think this would limit the amount of interaction between the charging packs.

I don't yet have my battery pack setup to charge from two different modules. When I do, I may try to test my setup like you did.

Brian

Brian, I think you might have something with the lower resistance wire idea. I was using small jumpers. I was only using the "main" outs of the second charger. Regardless, I have changed my whole method of using these batteries as I believe the BMS/charger from DeWalt is not a good solution anyway... Also, my pack voltage will not be a multiple of "36v" either. So what am I up to? I am harvesting the A123 cells from the DeWalt packs. Then, I am making interesting 10P sub-packs. These use individual, equal-length wires that terminate in a lug. The equal-length wires help "flow" current for longer cell life and the differences caused by each cells resistance. There are 2 lugs per brick, so looks like battery. Each sub-pack goes into a string for the pack voltage (currently 36 for testing. As you know, this is really 39v in DeWalt due to deWalt marketing-speak. The 4 subpacks charge in the string from a 12v smart charger at 6amps. This brings them up for the bulk charge in about 1.5 hours. Then, a small 3.6v charger will take over and do the "final", topping charge.

The above describes one concept but I plan to go further using my gigantic 40 or 80amp 3.6 volt CV power supplies to charge ALL cells in at the cell voltage level. Then, in use on the motorcycle, I will use the string but during coasting and stopping or rest, all cells will be switched (by custom contactor) so ALL cells are in paralell. This will "balance" the pack using its own power and gaining the most AH from the setup.

So far, I have tested 1 of the 10p4S sets mixed with lead-acid on the motorcycle and it perfored perfectly! The other advantage to my sub-pack design (which I plan to post details of soon) is the fact that the cells are held in by pressure, not tabs or solder. Somewhat like a power-tube system but not using tubes. I made a tube prototype that worked well though.

The advantage of this design is that at any time I can open a sub-pack and test all cells individually on my CBAII tester to confirm health or make repairs, etc.

You and others should see this info on individual cell charging at http://endless-sphere.com/forums/viewtopic.php?t=2586&sid=72b899eb809b336236dd5c0f7230342d

Jeff K. Burbank, CA "Bike to the Future" and "Deep Cycle"

Jeff and Itan, and whoever might be interested - I finally got around to nearly finishing my Dewalt multi-pack and was able to test the concept of using Multiple Chargers...

I was able to use two Dewalt Chargers in Parallel to simultaneously charge 6 "paralleled" Dewalt Battery Packs. Charging proceeded normally from a slightly discharged state - one light on and one light flashing in each, to two lights on and one light flashing, to a full charge with all lights on. No warning flashing even after the balancing cycle overnight! These chargers have no idea that they are sharing the battery load from 6 packs

My configuration: Two Fully Intact 36V Dewalt Battery packs (with BMS modules in place) with main power and the 9 BMS lines routed externally and wired in parallel to 4 other 36V Dewalt Batteries (without BMS modules). The intact Battery packs, used to plug into the chargers, were located on opposite ends of the parallel string.

Itan - This leads me to believe that there is a good chance that you could use 5 Dewalt chargers to charge 5 Dewalt packs wired in parallel and charge them all in 1 hour.

I myself am happy with being able to charge 6 packs in 3 hours - it only cost me about $60 for these two chargers on eBay. Others have pointed out that the Dewalt chargers don't do such a great job of balancing, but I am hoping that the multiple parallel packs will compensate by self-balancing. How well this will work in practice is still TBD... I won't know until the snow melts here in Minnesota, so I can start riding.

Best Regards,

Brian

That's handy. Probably the end to end idea helped. I have two used like new chargers to sell anyone interested...PM me.
Jeff