First Electric Motorcycle, General Questions

Hey everyone,

I'm trying to find out some basic information and build a motorcycle for a specific commute.

Requirements
45+ mph
15+ miles range
seating for 2 (I know it won't get max performance w/ passenger)
Florida - Minimal hills

Frame: Sport Bike - I've found a few within my price range.

I'm currently looking at the Mars Brushless motor, and need to know what kind of power I need.

48 Volts would be Ideal (less weight and lower CG)

72 Volts if necessary

How does the AH constant affect the performance of the bike?

If the batteries are in Series to achieve 48 volts, do they need to be (theoretically) 100 Ah each to get 4800 watts or does the controller somehow do this?

Thanks for any input, especially on those last two questions.

I'd recommend 60v or 72v. The Mars will have a tough time getting you to 45mph at 48v.

The Ah of the battery really only affects range. More Ah = more range for a given voltage.
Higher Ah batteries can supply higher current more efficiently though.

The controller will try to pull as much current as it needs from the battery. The 13Ah batteries in my scooter can put out over 100 amps, so no sweat there.

Snoop around and look at the other cycles built by people (Malcolm's comes to mind).

Funny you say malcolm, I was reading his stuff before I posted...

So running smaller batteries to get the higher voltage at the same weight and comparable would be a good idea?

Wha? No I didn't do it, honest! Ohhh, you're talking about motorbikes...

Should be fairly easy to achieve your goals.
First of all though, if you haven't already got your bike I'd recommend looking around for the lightest bike you can find. Weight saved at this stage is worth its weight in lead.

Just to get the basics out of the way (apologies if I'm stating the obvious):

Power = Volts x Amps = Watts

Batteries are rated in Amp hours. This is a measure of the amount of charge they hold (so a 100Ah battery can deliver 1A for 100 hours, or 100A for 1 hour theoretically. In real life, the higher the current you draw from them, the less of the theoretical capacity you actually get. In the case of lead acid, at the currents you're interested in, you will only ever get around 60% of the rated capacity.

Energy capacity = Amp hours x Volts = Watt hours. So a 12V 100Ah battery has a theoretical energy capacity of 1200 Wh, but in practice you only get around 60% of this, so actual capacity is 720 Wh.

Energy consumption is usually measured in Watt hours per mile.

Like Link said in the other thread, I'd take a look at the Etek RT and think about running it at 60V. It's a brushed motor and the design is well-proven. The Mars brushless is attractive and a couple of people here are trying them out, but it seems difficult to get the full potential from them with the available controllers.

My bike weighs around 130 kg and averages around 80 Wh/mile taking things easy, or around 110 Wh/mile if I ride two-up, so say 100 Wh/mile for the sake of calculation. That means I need 1500 Wh actual capacity to get 15 mile range. So for a similar setup and lead acid batteries you'll need around 2500 Wh (remembering that you only get 60% of nominal capacity). Dividing by 60V gives just over 40Ah. So you're likely to need 40 or 50Ah batteries.
The batteries I use are just 28Ah and I can just manage 15 miles if I take things very easy.

If you can afford it consider a perm 132, very well made motor
You'll want around 1500watt hour battery pack to get your 15-20 miles range, thats 30AH at 48v, or 20AH @ 72v. Again, if you can afford it, get a lifepo4 pack (a123 or LifeBatts), youll get 95% of the rated AH.

So if I go the lead route, I'll need 72v 30Ah batteries? (for range)
will this also allow for the 45 mph cruise? 150-200lb bike + 170 rider + batts + motor and controller
Have you seen any deals on, or cheap lead or gel batteries?

Maybe closer to 35AH, you'll see alot of sag on them batts. YEs though, that should handle 15 miles cruising at 45mph. 40AH might give you more current available for better acceleration.
Cant help on the SLA's...only hunt for life batts these days

Jozzer said:

If you can afford it consider a perm 132, very well made motor
You'll want around 1500watt hour battery pack to get your 15-20 miles range, thats 30AH at 48v, or 20AH @ 72v. Again, if you can afford it, get a lifepo4 pack (a123 or LifeBatts), youll get 95% of the rated AH.

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The Perm 132 is a little to pricey for me...

If I were to do 40-50 Ah batteries, could I use 4 x 12volts (48V) and get the same performance? Would it still be able to cruise at 45+mph and have the same range?

What about using the ME 0709 Mars motor?

125 amps continuous VS 100 amps for Brushless. The controller would allow the 300amp max as well, giving me over 17 hp at 72v, I think.

Controller is cheaper, so motor + controller, they cost about the same.

I don't know your budget, but I'll recommend at least looking at your options in lithium. What are Ping's packs, ~$0.75/Wh? Expensive, compared to lead, but I'm worried you'll have a heavy cycle with not much range. Then again, I have no idea how much lead you can get into a sportsbike.

It is my understanding that the Etek is a much better-made motor than the Mars, and that despite being brushed it is in fact more efficient than the Mars. Can anyone back that up?

lazarus2405 said:

I don't know your budget, but I'll recommend at least looking at your options in lithium. What are Ping's packs, ~$0.75/Wh? Expensive, compared to lead, but I'm worried you'll have a heavy cycle with not much range. Then again, I have no idea how much lead you can get into a sportsbike.

It is my understanding that the Etek is a much better-made motor than the Mars, and that despite being brushed it is in fact more efficient than the Mars. Can anyone back that up?

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If I'm going to have to run 72 volts, lithium batteries are going to be insane... I saw 3v lithium batteries for 100 bucks a piece, that's a little much.
What affordable routes are there with lithium?

What are Ping's cells good for, 2c and 4c burst, being generous? They're cheap Chinese LiFePO4, and have pretty crappy discharge rates. To get 1500wh, at 60v, you'd need 25ah. That's 50a, 100a burst. I really don't think that would be anything like enough power.

E-MOLI cells are the next best option, at ~$1/Wh, good for 10c continuous/15c burst. You could build your own pack of these from Milwaukee power tool batteries, for ~$1500. In a similar setup, they'd be able to provide the hundreds of amps you'd want.

There are then a123 cells. They'll last longer, and they can discharge faster, but being the best lithium cells you there, they're expensive, at $1.70/Wh.

There are also LiPos, but I don't know prices on those. They'd be a lot lighter, close to the same price, aad have a chance to explode if you crashed.

On second thought, I'd say build it with lead now and start saving up for lithium. It's quite a large investment for a first build.

Yea... you are going to want to go to Lithium Iron Phosphate ASAP ... but you can fake it for now with lead acid.

Another option might be a trailer with three big RV batteries in series ... that will get you there cheap until you can build a proper cell with Lifebatts or A123s.

Ping packs are great for bicycles ... but the prismatics just don't put out enough amps to run a motorcycle properly.

kbarrett said:

Yea... you are going to want to go to Lithium Iron Phosphate ASAP ... but you can fake it for now with lead acid.

Another option might be a trailer with three big RV batteries in series ... that will get you there cheap until you can build a proper cell with Lifebatts or A123s.

Ping packs are great for bicycles ... but the prismatics just don't put out enough amps to run a motorcycle properly.

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I think running a trailer would be more along the lines of 'faking it' lol.

Just found some Deep Cycle Marine 12v 75Ah batteries for $55 a piece at wal-mart, I only need 35Ah or so, so 6 x 40+ Ah 12v batteries total weight of about 180-200 lbs will weigh a little more than the old motor and transmission. At the rates for what I saw, the batts would be less than $300. I'd save maybe 100 lb by switching to Lithium, not worth $1200. By the time I have enough money for those (they'll be cheaper by then), I'll be building a much better motorcycle/EV.

Well, I'll point out that weight isn't the only benefit of lithium over lead, but your plan looks good.

Puting the weight in perspective with the engine/tranny really helps. It should handle fine.

Run those batts hard; beat them up. When they die out in a few years, you'll be working on your next build. The lithium then won't just be cheaper, but safer, more energy dense, have a longer lifespan, and have higher discharge rates. That's based on what's happened with them in the last few years. With even more R&D going into battery technology now, I think it's fair to expect at least the same in the mid future.

Back to the motor. I'd stick with the Etek and as high of power brushed controller you can get. It'll be harder to feed a Mars as much juice. All things considered, performance should be more or less similar, and the controller options might make more of a difference.

You will want to consider regenerative brakking. On bikes it's more or less a curiosity, but with a cycle you'll have a lot more energy stored in the greater mass, and loose less of it because of the far better aerodymics.

lazarus2405 said:

Well, I'll point out that weight isn't the only benefit of lithium over lead, but your plan looks good.

Puting the weight in perspective with the engine/tranny really helps. It should handle fine.

Run those batts hard; beat them up. When they die out in a few years, you'll be working on your next build. The lithium then won't just be cheaper, but safer, more energy dense, have a longer lifespan, and have higher discharge rates. That's based on what's happened with them in the last few years. With even more R&D going into battery technology now, I think it's fair to expect at least the same in the mid future.

Back to the motor. I'd stick with the Etek and as high of power brushed controller you can get. It'll be harder to feed a Mars as much juice. All things considered, performance should be more or less similar, and the controller options might make more of a difference.

You will want to consider regenerative brakking. On bikes it's more or less a curiosity, but with a cycle you'll have a lot more energy stored in the greater mass, and loose less of it because of the far better aerodymics.

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The weight will also be lower with an empty gas tank and no battery in stock location.

I'll be graduating college in less than a year, should do fine 'till then.

mars 0709 = brushed e-tek replacement, kelly controller = regen

Safety note:

Be sure to include a main contactor that can completely disconnect the batteries in the event of a controller short. This is particularly important for brushed motors since a controller short can cause full output to the motor. The cutoff switch should be in a easy-to-reach position, like the kill switch on a regular motorcycle.

fechter said:

Safety note:

Be sure to include a main contactor that can completely disconnect the batteries in the event of a controller short. This is particularly important for brushed motors since a controller short can cause full output to the motor. The cutoff switch should be in a easy-to-reach position, like the kill switch on a regular motorcycle.

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I was planning on running a contactor to the ignition cylinder, so you can just turn it off if that happens and have a way to disconnect power when the bike is sitting.