Batteries

This motorcycle is powered by four off-the-shelf batteries. They are Optima Yellow-Tops, rated at 55 amp-hour capacity, and cranking current of nearly 900 amps. They are AGM - absorbed glass matt. That’s a style of lead-acid battery that is sealed up and the electrolyte is soaked into coils of fiberglass matting. They cannot leak, spill, or slosh around.

While there are other types of batteries available, this seemed to be the best combination of price and performance for my project. “Flooded” lead-acid batteries are really not acceptable for a motorcycle. Besides being challenging in adding water, the movement and possible tipping-over of a motorcycle would not be good for flooded batteries.

Sealed lead-acid batteries (VRLA) would also be fine, as would gels. However, neither of those can crank the power as well as an AGM can, which is what gives the cycle good acceleration. Lithium batteries are excellent for weight, capacity, and power, but are currently only for those with higher budgets. If you use lithium batteries, everything else about the project is the same, except for a different battery charger and a battery management system.

Figuring Range
Going back to some simple math, we can get an estimate of motorcycle range. I have four batteries, each of which is 12 volts, but they are wired up in one series string of all four of them, so it’s really 48V in total.
The batteries are rated at 55Ah.
So, in theory, 48V x 55AH = 2640 watt-hours capacity. 100 watt-hours per mile is a typical ball-park number for energy consumption per mile on an electric motorcycle. (Of course that does vary by weather, speed, riding style, etc.) But this is just a rough estimate.
2640/100 = 26.4miles
Just a real rough estimate, but it’s good enough to say “Will this vehicle meet my needs? Will it perform the way I want it too?”
In this case, yes. I only live a couple miles outside town, and the next town is ten miles away. I can use this cycle to drive all over locally, and head to the next town over and back on one charge.

In real-world driving tests, the single-charge range of the cycle came to 23 miles if I drove full-tilt, and 32 if I was doing easy acceleration and in the city 25 mph zones.

Mock-ups and CAD
Lead batteries are NOT light. It helps to make a mock-up from foam or cardboard, so that you have a LIGHTWEIGHT, easy-to-handle version of the battery to experiment with. I like to think of this as the poor-man’s C.A.D.

If you are into computer design, there are many great programs out there to help you create 3D images and think in three-dimensional space. Google Sketchup seems to be getting fairly popular. Still, you really can’t beat an actual, physical object in your hands. I just prefer something that weighs less than lead.

In my earliest version of the cycle, I had three batteries in it. Then I moved up to four (for more range and higher top-speed.) I was never sure how to fit four inside the frame in a way that fit well and looked good. By using cardboard mock-ups, I was able to experiment with various arrangements of batteries until I found one that I liked. In this case, the fact that I could mount these batteries turned on end allowed me to come up with a configuration that I liked.

Once the size and number of batteries are decided on, they need to be physically mounted inside the motorcycle, and solidly connected to the frame.

Here’s a little video for you explaining one way to use cardboard to make your life easier designing and working on your electric motorcycle.

Next: Battery Rack —>

{ 8 comments… read them below or add one }

1 Érick Thomas May 7, 2013 at 9:10 pm

Hey! I liked this design …. I am a college student and would like to reproduce this design …. I’m Brazilian, so now I’m sorry for my vocabulary ….. I have a question for you …. Only 26.4 miles? I think there must be another way for the use of battery life, so that the engine go to be better, I wonder if lithium is a good idea to improve performance, 26.4 miles is not legal. Do you can response for me?

2 Ben N May 8, 2013 at 9:58 am

The RANGE or distance the motorcycle is designed to travel is between 20 and 30 miles per charge. The top speed it is designed for is 45 miles-per-hour. I don’t know how the RANGE can be illegal. In the United States, there are speed restrictions on major high-speed roads, such as Interstate Highways. Lithium batteries would allow for longer range. They are also more compact. By adding more batteries to the cycle, you would increase the system voltage, and on a DC (Direct Current) motor, such as this cycle uses, higher voltage means higher speed.
It would also be possible to simply change the gearing, without changing anything else. That would allow higher speed, but in exchange for range. I use my cycle in an area with 25mph and 45mph speed-limits, so I geared the cycle for a 45mph top speed and a useful amount of range. If your requirements are different, you can build your cycle with lithium batteries, higher voltage, larger capacity batteries, and different gearing.

3 James Evans August 26, 2013 at 12:27 am

I went to the Optima battery website. It seems that the blue top batteries would be more applicable, as they are marketed for trolling motors and such, whereas the yellows are meant for starting cars. Do you have any input on that?
at 219 dollars for the 12 V 50 Ah, 1000 cranking amps model, the price seems comparable to yellow tops of similar rating

4 James Evans August 26, 2013 at 12:33 am

shoot, I am mistaken, I spoke too soon, the Blue’s are not meant for deep cycle, never mind!.
I like the saddle bag idea though. Giant saddle bags with 4 batteries on each side of the wheels would be quite the sight with quite the range!
most of my commute is interstate (college to home to college) so I am always dreaming of long haul EV’s

5 admin August 26, 2013 at 7:13 am

Red-Tops are the starting battery. My understanding is that both the Blue-Top and Yellow-Top are internally the same, they just have different power connections on them and are marketed differently.

6 admin August 26, 2013 at 7:15 am

There are diminishing returns with the size of any lead-acid battery pack. It makes more sense to go to lithium batteries than really loading up with lead. I built the motorcycle about five years ago, and lithium battery costs have really come down since then. On the other hand, you can get lead-acid used/cheap and it’s great for learning, experimenting, and a practical local vehicle.

7 Ben diaz August 3, 2015 at 5:56 pm

Hi I’ve been watching your videos and it has really inspired me to build an electric motorcycle I’d like to try and hit around a 40 to 50 mile range. I want to use the same 4 yellow top battery set up that you have and I am wondering is it possible hook up smaller sized 12 volt batteries to the bigger yellow top ones so that I can get a little more range and it would be easier to find room for a would extra smaller batteries. Is something like this possible?

8 admin August 5, 2015 at 7:52 am

For a 40-50 mile range, you probably want to go with lithium batteries. They keep coming down in cost, and the smaller cells are easier to fit to the shape of a motorcycle frame.
If you are using lead acid, you want to keep the batteries all the same size. Batteries of different sizes have different capacities, which which will make them harder to charge. If they are in series, the smaller batteries would limit how much capacity of the larger batteries you could use.

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