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Discussion Starter #1
I'm thinking about building an alternative lithium battery for my 650R/ER-6F (using A123 LiFePO4 cells), but I need to know the current draw of the starter motor so I know how many cells in parallel are necessary. I've googled, but I can't find this particular piece of data. Any ideas?
 

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You would want to build a pack that could deliver "at least" 200 amps. But that may be the least of your problems.
Can you build a series/parallel pack that comes up with the required 12 volts?
Is the motorcycle charging system the correct charging voltage and sophisticated enough to handle A123's? I doubt it.
How would you handle cell balancing?
That is one nice thing about LA, it can be brutalized and take it.


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You may want to check some of the military sites before embarking on your journey. There's a reason the battieries go through rigorous testing before being allowed in military equipment. If you've ever seem even a small one explode it's pretty impressive. LiB's are much more senstive to overcharging and in particular discharge rates than other batteries. They're also highly reactive to water and should be in a sealed compartment in case there's a lithium leak. Good luck.
 

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Discussion Starter #4
I'm very aware of the dangers of LiIon and LiPo cells, which is why I'm planning on using LiFePO4 ones, which are completely safe - there's a video somewhere of a dude sawing them in half with no consequences whatsoever.

200 amps?! Yow! I thought this is what cars draw! Figured the bike would be closer to 60 or so... if the 200 amp figure is right, this stops my plan right here...
 

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Cars, of course depending on the engine, draw anywhere from about 100 to as high as 250 amps, or more. But the kicker here is, that the batteries are rated for usually 2 to 4 times starter draw.
That is why I said a pack that can deliver 200 amps. If you build one that just supplies what you need, the capacity will be low, the internal resisitance probably too high, the heat will be great!
But I think that the satisfactory recharging would be more of an obstical.
It would certainly be an interesting project, but as far as cost and practicality goes,
hmmm, the jury just might be out on that.
If you go ahead, be sure and post back with your results as I am curious!
 

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Discussion Starter #6
Cars, of course depending on the engine, draw anywhere from about 100 to as high as 250 amps, or more. But the kicker here is, that the batteries are rated for usually 2 to 4 times starter draw.
That is why I said a pack that can deliver 200 amps. If you build one that just supplies what you need, the capacity will be low, the internal resisitance probably too high, the heat will be great!
A123 LiFePO4 cells are of a fairly low capacity, but they can be discharged at a massive 60C burst rating (30C continuous). This means that a 1.1Ah pack of four 18650-sized cells could deliver 66 amps for the time necessary to start the engine. And, again, even if I were to overdischarge them way too hard, LiFePO4 cells are completely incapable of catching fire.
I wouldn't be able to leave the bike unused for extended periods with a 1.1Ah pack because the parasitic draw of the electronics would discharge them fairly quickly, but I use the bike almost every day so it shouldn't be a problem. As for recharging, I'd probably have to come up with a charging circuit. Before I do that, however, I need to know how much current the starter motor draws, so I know if this project can even be done without going way over budget on battery costs.
 

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Kinda hard to figure stating current as many variables to calculate: 1. compression or engine(high or low),2. weight of engine oil, and 3. ambient air temperature.

Most motorcycle starter wiring is comparable to 8 gauge wire using the American Wire Gauge(AWG). In some situations it might be closer to 6 AWG. Using the wire charts should not be hard to figure out current draws.
 

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Discussion Starter #8
I hoped the motor had an official figure for current draw. Surely it has specs printed on it? I can't take the engine apart to see, but someone who's replaced one ought to know...
 

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Why don't you measure the current draw of the starter? A clamp on DC ammeter clamped around either the battery positive or negative lead will give you the info you want. If you don't have one, or want to buy one, then usually someone at the local auto repair shop has one.
 

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Discussion Starter #11
Clamp-on AC ammeters are cheap; clamp-on DC ones aren't. Still, I might just try asking the shop to measure it - or heck, just ask them for the draw, the mechanics there must have the specs ready. If that fails I'll try contacting the two linked places.

Thanks :)
 
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