Building an EV motorcycle. Batteries: Need opinions.

[TurnNBurn]

Originally Posted by Daox

I'd highly suggest sticking with lithium. Their cycle life is rated around 3000 cycles under ideal circumstances. Under those circumstances you can use up to 80% DOD. With lead acid, you get at most 800 cycles at 50% DOD. So lets do some math:

65Ah lithium @ 80% DOD gives 52 usable Ah.
40Ah lead battery @ 50% DOD gives you 20 usable Ah. In order to get 52 usable Ah out of a lead acid battery, you actually need it to be 104Ah. That is a big battery, I know because I have four of them on my riding lawn mower.

Now, you have the same usable Ah, but you still have a battery that weighs a TON more, and is only going to last at most 1/4 as long as the lithium. Also, refurbished batteries won't have near the rated capacity of a new cell.

Thanks for the info. I understand the concept now, but I'm still confused as to what I should be looking for. I guess I don't understand the whole "40Ah isn't really 40Ah once it starts discharging" concept.

That and I'm just confused by browsing EValbum. I see people with 40Ah Lifepo4 batteries getting a 35 mile range and then I'll see other bikes using 70 Ah batteries getting 35 mile range. I do realize there's a lot of variables in play here, like sprocket size, controller, motor efficiency, etc... But is it really that complicated?

[Daox]

Everyone treats their batteries different. There are general rules to follow though:

- shallower DOD leads to longer battery life
- pulling less amps leads to longer battery life

You can squeeze a ton of range out of your batteries if you drive slow and take it easy. Some people quote this number in their EValbum page. Others, use a conservative number showing their normal usage to 50% dod or whatever and they use that as their rated range. There really are a lot of factors involved.

For a motorcycle, I would probably use 100wh/mile as my energy usage per mile (and in fact, I do have a spreadsheet made up that has this figure in it). Its conservative unless you're really moving fast. At 45-55 mph you're likely using less than this, at 75 mph you're probably using a bit more. So, if you planned on doing most of your riding around 75 mph, I would probably just bump the wh/mile up to 125 or 150 to be conservative. It never hurts you to have extra pack capacity. In the end that extra capacity is just going to make your whole pack last longer.

[TurnNBurn]

So it sounds like I should stick to the original plan. As much as it hurts, I'll need to fork over the $2000 for what my goals are. I wonder how much a soul goes for these days.

[Daox]

There is a reason EV bikes are not cheap.

[TurnNBurn]

Originally Posted by Daox

There is a reason EV bikes are not cheap.

Nope. They're not too bad, but the initial build is expensive.

[Daox]

I mean the commercially made ones:

https://www.brammo.com/buy/

Motorcycles : Zero Motorcycles, Electric Motorcycle and Electric Dirt Bike Company

[TurnNBurn]

Originally Posted by Daox

I mean the commercially made ones:

https://www.brammo.com/buy/

Motorcycles : Zero Motorcycles, Electric Motorcycle and Electric Dirt Bike Company

Yeah, those are outrageously expensive. I considered buying one, though, because it's easier to get a bank loan to finance one of those than to get a loan from a bank and tell them "I need batteries, BIG batteries."

[sheepdog 44]

Originally Posted by TurnNBurn

So it sounds like I should stick to the original plan. As much as it hurts, I'll need to fork over the $2000 for what my goals are. I wonder how much a soul goes for these days.

For electric motorcycles, batteries are already cost effective if you plan to put some good commuting miles on the bike. That $2k is good for about 150,000 miles more or less depending on efficiency. And it'll only cost several hundred a year to charge vs $1.5-2k+.

I have some questions to ask too based on the minimum specs i can get away with. Would a 48 volt electric motorcycle suffice for highway speeds, or should i look to 72-96 volts. I know a 48 volt system can have sufficient power to operate at highway speeds but will use more amps to compensate. Really is 72 volts worth it?

Secondly:

Originally Posted by Sheepdog 44

I was looking at the specs of the ME1115 PMAC motor and i came across this part about amps.

- Current: 125 Amps AC continuous (180 Amps DC into the motor control)
- Peak current: 420 Amps AC for 1 minute (600 Amps DC into the motor control)

ME1115 Brushless Motor 24-96V, 5000RPM, 12 kW cont, 30 kW pk

To find out the continuous power output of the motor at 96 volts, do i multiply by 125 amps AC for 12kw, or 180 amps DC for 17.28kw?

I don't understand why there are two different amp ratings?

Third question: Brushed DC motors, avoid them completely? Too much noise, friction, brush hassle?

[Daox]

Its almost always a good idea to go with a higher voltage. If I were doing a bike I would definitely go 72V or higher. Its just more efficient, and easier on the batteries (less amps).

Most of the DIY conversions use brushed DC motors. There isn't anything wrong with them at all. Their efficiency is not much worse than brushless motors, especially the permanent magnet brushed DC motors.

Sorry, I can't answer the current question. Suffice to say AC current and DC current are different.

[Ryland]

If you look at lead acid batteries, their capacity rating is often a 20 hour rating, they might also have a 5 hour rating but very few have a 1 hour rating, 6v Trojan T105 Golf Cart batteries have a 250amp hour rating if discharged over the course of 100 hours, at 20 hours it's 225amp hours but at two hours their they will only put out 146 amp hours and about 100 amp hours at 100 minutes! so is that 250 amp hour battery really a 250 amp hour battery???
That info all came from Trojan's own web site. http://www.trojanbatteryre.com/PDF/d...ata_Sheets.pdf

If you want highway speeds with 48v you are going to pull a lot of amps so you are going to need larger copper wires both between the batteries and in the motor, you are going to produce more heat all around and have more losses with more weight.
Always go with as high of voltage as you can afford, even if the motor is the exact same motor you can often program speed controllers to limit the peek voltage.

Brushed DC motors are cheap and common but they are less efficient then AC motors so with DC you have reduced range, reduced power per pound, more heat (motor cooling for long rides) and of course more parts to wear, brush wear is not a huge deal if your motor is sized right, heat is not a big deal if you don't ride very far and brushed motors are pretty quite, quiter then a chain on a chain driven electric motorcycle, on my shaft drive motorcycle the tires and wind are still the noisy part.
I would like a 3 phase AC motor on my motorcycle just because it would have better low end torque and would run cooler, but the motor I'm looking at would be close to $3,000 for the motor and speed controller, the motor I'm using right now I spent $200 on used.