5 Minute SLA to LiPo Battery Conversion for the DIY Electric Bicycle (Video)

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I pulled a couple 4Ah 3S LiPos from my tricopter’s stash and soldered together a little series adapter to give me an effective 4Ah 6S LiPo pack. The effective range has been cut in half to around 5miles compared to the original 13lb 10Ah SLA pack, but that’s still plenty enough to get someone around a college campus.

Click here to read more about how to build the DIY electric bicycle.

Here’s a video of the updated e-bike taking a quick spin around the block: Be sure to continue reading after the break for more info.

The current carrying capacity of these batteries are completely overkill (40-50C). Each one is capable of delivering a constant 160A of current with a maximum burst of 200A. The bike only draws an average maximum of 10A to 13A.

I also put a battery alarm/monitor on one of the packs to ensure I don’t go below their minimum voltage. Otherwise they would loose their capacity quickly over time.

Additionally, for safe and proper charging, I have to remove these LiPo batteries from my bike and put them on my tricopter’s charger since the scooter’s original SLA charger is not designed to charge LiPos. I’m sure it’s possible for one to find a small LiPo charger that can be embedded in the bike though. That would enable the user to charge it simply by plugging it into the wall without hassle.

24 thoughts on “5 Minute SLA to LiPo Battery Conversion for the DIY Electric Bicycle (Video)”

  1. Dude so cool!

    Is the throttle twist?

    I want to make one and use out on flat dirt trails running my Red bone coon hounds.
    I usually drive behind in truck but this would be way better.

  2. Hey Mike, thanks for the new post!

    I haven’t started building yetbut this is pretty cool. A lot less weight and size for the battery.

    In theory this should make it easier to upgrade the bike for longer distances while sacrificing less weight correct?

    Is this just as safe?

    1. As long as the LiPo batteries are handled and charged properly, there is no danger. They are a bit more expensive and a lot lighter then SLAs for the same capacity too.

  3. Dude so cool wherecan i buy the parts im planing to make a foam boat but if i can install this system in a paddle boat that set dont need nothing else .

    1. I used two Turnigy 4Ah, 3S LiPos in series to give me one 6S battery pack. 4Ah is a measure of the battery capacity and means the battery can deliver approximately 1 amp of power for 4 hours, or 4 amps of power for one hour. 3S or 6S tells you how many cells are in series within the battery. Each cell is between 3.7 to 4.2 volts. Just multiply that by the “S” number, and you have the nominal battery voltage of about 12 volts for a 3S, and 24 volts for a 6S.

    1. 4Ah is a measure of the battery capacity and means the battery can deliver approximately 1 amp of power for 4 hours, or 4 amps of power for one hour. 3S or 6S tells you how many cells are in series within the battery. Each cell is between 3.7 to 4.2 volts. Just multiply that by the “S” number, and you have the nominal battery voltage of about 12 volts for a 3S, and 24 volts for a 6S. If you want to learn more, read this detailed write up: http://www.rcgroups.com/forums/showthread.php?t=209187

    1. Well that depends a lot on how you drive the bike. Are you going to assist it by peddling? Are there hills in your area?

      With my 300W bike, a 24v 10000mAh SLA pack got me about 10 miles on flat Florida ground after primarily assisting it when accelerating from stops.

      If you use 2 3S 5000mAh LiPos in series, you will effectively have a single 6S (22-24v) 5000mAh pack. With a 400W motor, you might get around a 5 miles range. Again that would be heavily dependent on how much you make the motor do the work.

      1. Sorry Mike for not responding in 2015. I thought I had made a post (in Oct. 2015) and was waiting for an answer (which I wasn’t aware that you did give an answer!), but thought maybe there was a glitch in the system and that I didn’t make a post. Thanks for giving the hypothetical. I was thinking of using one of two Turnigy motors (D2836/8 1100KV Brushless Outrunner Motor, or NTM Prop Drive Series 35-42A 1250Kv 600W [I copied the text verbatim from hobbyking]). I live in the Bronx, NY and there are many inclines. I weigh about 185 and I want to be able to ride at least 70-80 minutes before needing to give the LiPo a charge.

        Two points that I want to ensure I cover:

        –I wouldn’t mind if I have to charge for an hour and be able to go 30-35 minutes on that charge.

        –I would be interested as to what batteries I would need to do that (I want to use a 24V system) with the two motors mentioned (or is your motor better?).

        Thanks in advance 2 times! and thanks for your response

  4. Hi friend I like to this. Can you tell me how did you find this motor. How I find a motor like this.Please reply answer to my quection soon…………………………………

    1. I got mine from an old Razor E300 Electric Scooter that I had previously. You can buy the motors for that scooter on eBay or Amazon. Just search something like ‘razor e300 motor’ or ’24v 280w motor’. Amazon has a couple (in the US) for less than $42.

  5. The SLA batteries I bought for my project will be fine for proof of concept, but I am absolutely saving up for something with the word “lithium” in it. Clean republic has a 12v 10 AH LiFePO4 at a fairly reasonable price (still four times more than the SLA package I got however).
    I’ll really have to keep my lead acid babies charged. Bikes are not a good vehicle for the purpose of transporting bricks if you have to pedal.

  6. hey Mike, I am really impressed by your project, I was wondering if you used any DC motor driver? or its just the variable throttle directly connected with the motor
    any BMS for LiPo batteries? or any other device except for motor, LiPo and throttle?
    and nice neighborhood, which place is this?

    1. The motor’s speed is infinitely variable with a 24v motor controller; the same that was used in the Razor E300 scooter I tore apart to make this. It does not support LiPo battery monitoring, a separate voltage alarm/cutoff is needed. That video was filmed near Coral Springs, Florida.

  7. Question
    What did you use or how did you make the shaft that connects thru the skateboard wheel? Did you press a shaft thru it or connect bolt thru the hole to a snug fit?

    My second question would be using a motor with 500 to 600W to much torque for a street bike or aluminum if you know or have tried in the past?

    1. I used a motor arbor to connect the skateboard wheel to the motor shaft. A motor arbor clamps on the motor shaft with a couple set screws and in turn has a bolt thread on the other end that can clamp on to any skateboard wheel without bearings.
      I only have this 24v, 300w motor. I have not tried anything else.

  8. I use 6, six cell lipos. Three sets of two batteries in parallel, for a total of 48 volts, because i only charge to 4 volts per cell. I only discharge down to 3.75 per cell. I hardly ever peddle except to get rolling and I get great millage. All the research I have done says that I can get at least double the battery life, which is about 1000 to to 1200 cycles per battery. Only time will tell.

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