# What about these lithium batteries to run a etek?

I got this bike

A Etek motor on its way

And have a source for these batteries, just want some opinions on the batteries and how many i should buy to reach my 35-45mph max speed and get around 30+ miles to a charge.

Bit hard to read but the battery packs are 4.25v 40ah

dimensions 190mm x 140mm x 45mm

And have a source for these batteries, just want some opinions on the batteries and how many i should buy to reach my 35-45mph max speed and get around 30+ miles to a charge.

How fast do you want to do the 30 miles? The answer for 30 miles at 10mph will be a lot different than 30 miles at 45mph. I know little about Etek motors, but it sounds like all you really want to know is how much current the Etek consumes at a given rate of speed. Of course if you had those numbers, and throw in some fudge factors for wind resistance and friction, isn't the rest of it some rather simple math?

alright cool your going all the way. here are some examples

http://www.electricmoto.com/BladeXT.html

the E-tek is rated for 48v but it will do 60v.

They're probably closer to 3.7v per cell under load. I'd go for 12 - 14 cells.

From other users, so far the experience with these has been pretty favorable.

Todd at Electric Motorsport uses the 40ah cells on the Derby Motard.

Here's a pic of some 90ah cells made by the same company:

cajunjay:

And have a source for these batteries, just want some opinions on the batteries and how many i should buy to reach my 35-45mph max speed and get around 30+ miles to a charge.

I'll assume you want to run the etek at 48v. From the thunder sky spec sheet if you scroll to the bottom where it shows the discharge graph you can see that the nominal voltage (which is supposed to be the average voltage during discharge) is close to 3.2v at the 1C rate.

Where do you plan to ride? Is it going to be used for off or on road? If it is on road than I can say with reasonable accuracy that the power consumption might be around 80 whrs/mile in that speed range. If the batteries deliver 90 % of their nominal calculated energy (48v * 40 ah) than thats 1728 whrs in energy with 15 of the cells. Divide that by 80 whrs/mile and thats 21.6 miles. This is a rough calculation of the range until the batteries are dead. The practical range would be about 17-18 miles to have a safety margin.

This is my best guess based on what I've seen other bikes consume, and my own from average riding conditions in the city. Obviously if you have a 300 ft rise hill to scale your not going to get 21.6 miles, or if you put a 400 amp controller in and pin the throttle to accelerate as fast as you can from every stop.

If you want 30 miles than you may want to consider the 60 ah cell. All other things being equal this would increase the range by 1.5 times or about 26 miles with a few miles safety margin.

If you absolutely have to have 30 miles and no less than I can figure out how many cells you need then figure the voltage from there:

Each cell has a nominal voltage of 3.2v and nominal ah of 60ah (if you used the 60ah cells) so thats 192 whrs nominal * .9 = 173 usable whrs * .8 (safety margin) = 138 whrs per 60 ah cell.

At 80 whrs/mile for 30 miles you will need 2400 whrs / 138 whrs/cell = 17.4 cells. Since I was generous with the safety margin we'll figure 17 is good enough. 17 * 3.2 is 54.4v and I'm sure the etek can handle this fine.

You may think it convenient to remove the safety margin calculations and the fact that the batteries may only deliver 90% or less of their nominal calculated energy but this is just being realistic. And 80% DOD cycles are much easier on the batteries than 100% especially if you are not using a BMS system. In real world conditions there are a lot of factors that are changing all of the time so if you want to guarantee a certain amount of range you need to put in generous safety margins.

cajunjay - what's your source and cost for the cells? Those are the cells that electric motorsport cells for $100 each. Do you have a better price/source? Also, what are you doing for a Batter Management System (BMS) and a charger?