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Old 01-26-2009, 06:19 PM   #1 (permalink)
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More smaller batteries vs. Less bigger batteries

I have two motorcycles, an '81 Suzuki GS850 and a 2001 Buell Blast. I'm considering converting one of these to electric.

It seems to me that you can only fit 2 to 4 "normal" size batteries in the space normally occupied by the engine/transmission. I don't really want to resort to hanging them off the sides like a saddlebag.

It also seems to me that if the batteries were half the size, I could fit more than twice as many on the bike. For example, the Blast has a plastic shell over the actual gas tank. I think I could fit a battery under that once the tank is gone. It also has the muffler mounted under the frame. If I could find batteries that were only 4-5 inches thick, I could put some where the muffler used to live. I imagine I could fit one under the pillion too, if memory serves. I'm in Wisconsin and it's in storage right now, so I'm working from memory.

But you see my point, right? I could fit MAYBE 3 normal size batteries. But if the batteries were half the size I'm pretty sure I could fit more than 6, possibly 8 or 10.

Are there physically smaller batteries that would provide more usable power assuming you can fit a greater quantity in the vehicle?

Thanks for your responses, I'm quite interested to hear what you all think.

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Old 01-26-2009, 06:56 PM   #2 (permalink)
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Hawker makes (or at least made) good small EV-type batteries. The only problem is that the cost per watt-hour is much higher, since the smaller batteries cost almost as much as large batteries. Also, consider the voltage: if you use smaller 12V batteries, you'll need to either go higher voltage or use something like buddy pairs or multiple strings (all of which contribute to balancing issues.)
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Old 01-26-2009, 06:59 PM   #3 (permalink)
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Oh, and there's also the BB600 military surplus NiCads which are 6V and fairly light, if you can find them. Only problem is that they're flooded (not sealed), so if you dump your bike, you could end up with electrolyte spilling.
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Old 01-29-2009, 02:42 PM   #4 (permalink)
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Buells are great, i own 4.

sorry for the hijack.
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Old 01-29-2009, 06:39 PM   #5 (permalink)
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OOoo-OOOOoo!

I know the answer.

Use as many small batteries as you can cram in there. The more you run in series, the higher your system voltage = the faster your bike goes.

Also, higher voltage means fewer amps for the same amount of work, so it's easier on on batteries and their lifespan. You can also use thinner cabling. High amps need thick cables.

Higher voltage parts tend to cost more. The cut-off points for chargers, controllers, etc, tend to be: up to 48V, up to 72, and above 72.

My cycle goes 45 mph on a 48V system. 72 would be a great system voltage for a cycle, or even higher, if you can afford it.

Use sealed batteries on a motorcycle, as tipping a bike is NOT that hard to do. I had mine tip over once on a trailer when I didn't have it tied down right. Also, vibration is a big issue on cycles. You don't want your batteries getting shaken to death and spilling.

If you haven't read it before, you might want to check out:
http://ecomodder.com/forum/showthrea...rsion-599.html
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Old 01-30-2009, 10:41 AM   #6 (permalink)
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Ben,

You say higher voltage makes for the same work at lower current. This is true, P=VA... but isn't the force generated by an electric motor ONLY proportional to current? If i recall correctly from electromagnetics class (way back), F=cAT (c is a constant, Amps, Turns).... (I'm really sketchy on the electromagnetics details).

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Old 01-30-2009, 12:40 PM   #7 (permalink)
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You know what? I am NO Theorist.

Instead, lets use a real-world example.

On my motorcycle, I have basically had in in three different configurations. No, wait, the damaged YellowTop would count as another. Four configurations then.

When I first rigged up my cycle, it ran on three small SLA batteries in series. So, that's 36 volts, but you can't pull very many amps from them. Speed was decent, acceleration was OK. Range was poor (low Amp-hour batteries)

When I switched to three Optima Yellow Top batteries, the speed really didn't change at all, but acceleration was greatly improved (these batteries can handle much higher current) and range was greatly improved as they were 55 AH batteries instead of 18 AH batteries.

Then, I added a fourth YellowTop. This increased my system voltage to 48 volts and increased my top speed from 35 mph to 45 mph (made it to ALMOST 55 down a big hill once...)

However the acceleration felt like it was still about the same.
Still, my top speed and range both increased - both of which tend to be important to motorcycles.

Now here's a weird one. Shortly after increasing to 48 volts, I damaged one of the YellowTop batteries. OK ok. I melted the post completely off.

I then tried repairing it myself, but the cycle never had the same acceleration after that. I think what happened was that my poor repair limited the amperage that could get fed through the battery.

Later, my home repair eventually failed. I removed the 4th battery, and was now running on only 36v. But guess what? The bike got its pep back! Suddenly, I had my zippy acceleration again.

Later, I found a battery place that repaired my post (free of charge! Great guys! ) So, now the cycle is running 48 volts, with good range, speed, and acceleration.

So, getting back to MazdaMatt's question, it's my opinion that Acceleration (is that the same as Force? or Torque?) is proportional to amperage.

Using 36 or 48 volts didn't seem to make a difference in acceleration, just speed. Using a different style of batteries, which couldn't pull as much current didn't change the system voltage, or speed, but did effect acceleration.

A damaged battery also didn't effect voltage, but seemed to limit amperage, and acceleration was poor at that time as well.

Now here again is something of interest.
Some batteries don't handle amperage as well as others. AGMs are very good, and a nice choice for motorcycles.

When you use higher voltage, you pull less amperage to do the same amount of work. At a certain point, amperage is limited by the characteristics of the batteries - their size, chemistry, state-of-charge, etc.

Running batteries in series can reduce the amperage needed and thus keep the amps below the "wall" of what the batteries can keep up with.

I think that on the motorcycle, the controller (300 amp 48V) is the limiting factor because I have some very nice batteries that can keep up with that.

On my Electro-Metro, I believe the batteries are the limiting factor. At the end of a drive, it's uphill and the highest speed limit of any where I drive. In third gear, I can have the pedal to the metal, and the ammeter won't budge past 250 amps. I can upshift to increase this, but then the battery voltage drops like crazy - ie. the batteries are NOT happy.

If I had 12 batteries in series, instead of 6, only half the amperage from each battery would be needed. I believe that this would then mean that I would have more amperage available from the batteries, and could accelerate a bit more to get to that higher top-end speed.

So, in summary. My real-world experiences do seem to indicate that amperage has pretty much everything to do with acceleration. Howerever, higher voltage has lots of other advantages, including keeping your batteries happy and higher speed.
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Old 01-30-2009, 12:50 PM   #8 (permalink)
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THANK YOU!!!

So the moral is - More batteries is better, always. 12 battereis in series will be happy batteries and give you high speed. 12 batteries in two six-battery strings will give you less-happy batteries and mad acceleration.

So to answer the OP... the infamous "it depends". Check on the series resistance of those smaller batteries and the output current rating and compare to the same on the other side... then choose acceleration vs speed.

For me, i'm interested in a vehicle (cycle or car) that can take me to work along an 80km/h road, so i would need the highest possible system voltage that i can muster up.
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Old 01-30-2009, 01:16 PM   #9 (permalink)
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Quote:
Originally Posted by MazdaMatt View Post
So the moral is - More batteries is better, always. 12 battereis in series will be happy batteries and give you high speed. 12 batteries in two six-battery strings will give you less-happy batteries and mad acceleration.
.
I THINK that more batteries is always better, with few exceptions.

1) Weight - you just can't keep adding weight to a vehicle and expect it to perform the same

2) Voltage limitations of existing charger, controller, and motor
If you already own a 72V charger and a 72V controller, it may not made sense to upgrade to 144 volts, if you just have to buy new of each. Instead, it may make sense to do "buddy-pairs" of batteries to add the additional range, although no more speed, to the vehicle without having to upgrade everything else.

12 batteries in 2 6-strings most likely won't give you mad acceleration. Most likely, you would be limited by your controller, unless you are using crappy used batteries like I am in the car.

Also, those electric drag racer guys (NEDRA, etc) get really picky about exactly battery size, capacity, configuration, chemistry, - but they aren't designing eco-grocery-getters...
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Old 01-30-2009, 01:43 PM   #10 (permalink)
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Sorry, i'm an engineer... i don't live in this "real" world... I was considering if someone were to be building a new vehicle, not taking existing controller into account.

So when you say 'buddy pairs" do you mean that typically you would not use 2 strings of 2 batts, instead you'd use 1 string of 6 pairs of batts? I suppose that makes more sense for balancing.

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