I have turned my old motorcycle into a dual sport and the original battery pack has failed. After shopping for a replacement battery and finding prices over 100 dollars for a replacement I decided to do some homework.
First things first I opened up the original battery and it looks to be a bunch Of Ni-Cad AA batteries with shrink tubing over them with a hot and ground wire, cant remember exactly but I believe there were 12 batteries.
The motorcycle has a voltage regulator that limits the voltage output to 14.5 volts max so now the part I need help with. I have 4 brand new Panasonic 18650’s with tabs on them. could I simply solder them together and add the hot and ground wires from my old pack and call it good or is there something else I would have to add to keep things safe.
The battery pack is located in a cutout in the foam in the underside of my seat so I don’t need to tell you what is located directly above the battery pack. Hence my fear of an exploding 18650.
Well, I’m not much of an engineer with regards to these matters but, let me explain:
A conventional 4S li-ion pack won’t be happy the way you’re intending it to work, total input voltage is too low (≈14’5V) so, they won’t hold much effective charge.
You need a suitable in-series cell balancing circuit. Either that, or sooner or later you could face some kind of nasty surprise.
4 “Panasonic” 18650’s in series? Are you serious? Even the now popular “top amps” 18650’s (LG HG2’s, 30Q Samdungs) would only do good enough to start very small engines…
DO NOT even try to solder batteries. You’ll need to heat them dangerously, and you will certanly damage them in doing so: a perfect recipe for a bitter end. Spot weld them or use some sort of smart trick like using hot glued strong disc shaped neodymium magnets pressing abundant strands of copper wire over the battery poles. Keep wires short, use adequate amounts of wire section.
Example:
If you want to make some sort of good, easy to build and implement cranking battery with newer technology, this is what I’d suggest: 4SxP LiFePO4s. That will do nicely with the vehicle regulator’s output, and deliver serious amps which is what you need for cranking: power output.
With 8 cells, 4S2P with up to 60A sustained. Getting two packs (4S5P) would allow it to deliver 150A.
Do you live in a cold climate? This may not be that much of a good idea in such a case, but wait for some other more experienced user in these issues to chime in.
There are forums specifically about electric bikes and similar, where they discuss this kind of stuff in detail. Not trying to get rid of you or anything. Just trying to help you find your answers.
One thing I’ve seen mentioned on an e-bike forum is the use of LiFePO4 cells without a BMS. The idea is that since LiFePO4 cells can be safely overcharged (just a bit), then you would design your circuit to overcharge them a bit as a method of balancing, since they will all come back down to operating voltage after a while. If you have 12 Ni-Cad cells now, then nominal voltage is 1.2V each for a total of 14.4V already. However, full charge voltage is 1.4V each, total 16.8V. LiFePO4 cells have a nominal rating of 3.2V. Five would give you 16V nominal. Full charge is usually 3.6V, so you’d have to charge them just a little beyond 18V to balance them. Please don’t do this unless/until you’ve read in one of the e-bike forums about how it is accomplished and you understand the method and the risks that may be involved.
Also, if you’re going to change from Ni-Cad to any lithium cell, you can use larger cells. In the case of the LiFePO4 cells, since you’re using just 5 instead of 12, you can probably use at least a 18500 instead of the 14500 (AA size) cells that are there. If there is extra room, maybe you can use an even larger cell, or double the cells, with the others in parallel. In other words, 10 cells would be connected as two parallel sets of 5 in series (5S2P). The main benefit of using more and/or larger cells is obviously longer run time.
Whatever you decide to do, let us know how it works out!
Edit: Hey Barkuti! Did you see where the OP said that the bike is now being run off 12x AA size Ni-Cad cells? If it can run off that, it could probably run off a single LG or Panasonic 18650 with a boost driver! Seriously, Ni-Cad are low power cells. NiMH have about double the capacity, and better current capability than Ni-Cad, and obviously lithiums can blow NiMH away. So, I don’t think the draw could be very much in this case.
You may want to consider paralleling 6S of those “D-Cell” Boostcaps to your existing 12AA battery.
I don’t have any advice on how to keep them in balance though. Some folks use passive balancing using LED’s. I like that idea, but would want LED’s with higher Vf’s then typical white LED’s.
Well, the only clue I can infer behind the reason to use 12 in-series Ni-Cd units would be to prevent excessive overcharging of the cells. Ni-Cd/Ni-MH need to be nannied with sophisticated dV/dt charging logic behind or unpleasant stuff can happen: a 10 in-series Ni-Cd pack would probably be consistently over-charged off the bike’s regulator.
Ni-Cd low power cells? LOL! Ni-Cds are power beasts, you’d have been smoked off the start had you put a Ni-Mh battery on your car in a RC classic race with pros (and maybe some of them would have called you “n00b”).
OOOPS! You’re right! I thought I’d read somewhere that Ni-Cad had both lower capacity and lower current draw, but I was wrong. The NiMH do have about double the capacity, but Ni-Cad is better at current handling, like you said.
I would love to have a battery for my drz400 dual sport like this, maybe powered by 30Qs
I would be too afraid of the venting situation, so I am stuck with a SLA battery that is always dead. I replaced it last year, and the bikes parasitic drains kills it in a week.
How in @#$% are you going to do that? You need to aim for a battery configuration which suits the vehicle regulator’s output, ≈14’4V, designed with 6S lead acid packs in mind. Forget about using conventional li-ion chemistries as good starting batteries, you’d need some sort of exotic and expensive DC-DC crazy high amperage converters inside the damned thing for it to work reliably, or a complete vehicle electric system redesign/overhaul. :person_facepalming:
Look at the info I presented above. It would not be that expensive to build a powerful custom LiFePO4 battery. Maybe I should get into that… :innocent:
Take care.
How in @#$% are you going to do that? You need to aim for a battery configuration which suits the vehicle regulator’s output, ≈14’4V, designed with 6S lead acid packs in mind. Forget about using conventional li-ion chemistries as good starting batteries, you’d need some sort of exotic and expensive DC-DC crazy high amperage converters inside the damned thing for it to work reliably, or a complete vehicle electric system redesign/overhaul. :person_facepalming:
Look at the info I presented above. It would not be that expensive to build a powerful custom LiFePO4 battery. Maybe I should get into that… :innocent:
I know it’s basically not possible, those ones you shower are quite expensive, there must be a way to make the same thing with a balancing circuit for a cheap price. I have seen another company that makes lifep04 batteries with the balancing circuit, and some have special balancing chargers. but it all costs money
If the alternator happily cranks the engine with no more than 400-600W of power, it will do.
If you don’t leave margin for errors, though, you may later regret on the “savings”.
This is a very interesting post. I have a failing car battery. Thinking 5P4S of those cells paralleled to 6S “D-cell” Boostcaps may be a nice replacement. Thanks for sharing this.
Any idea on how much parasitic drain the balancing circuit would have?
If you can get confirmation from the dealer as to these cells being genuine ANR26650M1As, looks good. Theoretically each one of these perform a tad better than 2 APR18650M1As (I have a couple of smidgeinly better Aliexpress deals for the last ones than the aforementioned eBay one above).
Two 10-packs of ANR26650M1As I'd say, ImA4Wheelr. How much cranking power are you aiming for? What can you tell me about those strings of superfarad caps?
Unceasingly learning tad by tad. :-)
Cheers
P.S.: no idea on what kind of parasitic drain for the balancing circuit (yet).
