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Convert old 49cc pocket bike to electric

Hello, I recently salvaged an old electric minibike from a junkyard. It had a 49cc motor that I wish to replace with an electric one. My goal is to try to be in the 25-30 mph range (I'm very light), and I'm not sure which voltage of motor to use, and what amp hour battery would be sufficient. I am also confused as to how the back sprocket should attach to the wheel. Is it needed to have a freewheel attached to the sprocket, as on many bikes, or can the sprocket be attached straight to the back wheel? I attached a few files, one being how the sprocket is attached, the other is the frame I have salvaged, and I also attached a file of what may be the original bike. Thanks in advance.

Hi Luca, A 1000 Watt motor should be able to move the bike up to around 27 MPH on flat ground. Drag (air resistance) will be the biggest speed limiting factor so if you sit straight up the bike will go slower and if you crouch down the bike will go faster. The Voltage of the motor has nothing to do with how powerful it is, only the Watts rating determines its power. A 36 Volt, 48 Volt, and 60 Volt 1000 Watt motor all produce the exact same amount of power.

Since the pocket bike looks fairly small a 36 Volt system might be best way to go so there are only three batteries on the bike, as opposed to four batteries for a 48 Volt system or 5 batteries for a 60 Volt system. For a 36 Volt 1000 watt motor the minimum battery size that I recommend is 10Ah to 12Ah. If you have room to fit larger than 10Ah to 12Ah batteries in the bike that will provide a longer ride time.

The rear sprocket can be bolted directly onto the rear wheel. A freewheel does not have to be used.

I see from the pocket bike's specifications that it has a 16" rear tire. I ran some gear ratio calculations for the bike with a 1000 Watt motor and here are the results:

Once you figure out what size batteries will fit in the bike then if you would like I can make kit out of all the part that are needed to electrify it. The dimensions of our batteries are located on our batteries page:

Thank you very much for your response. A kit with 15 ah batteries will work. I am also curious if with the you could include an 800w motor instead of the 1000w for mileage reasons. Also, will the predicted battery time /mileage be increased Significantly in general from coasting, and if so by how much? Also, I am unsure how to connect the fuse to the battery pack and in general, wiring the fuse, key switch, battery pack, and controller together. Details on this would be very helpful. Also, what are my choices for sprockets, to get the fastest ratio? I'm not too concerned about acceleration, but what's good for a higher top speed but still reasonable acceleration?

I can make the kit with a 800W motor instead of a 1000 Watt motor - that is no problem. With an 800 Watt motor the gear ratio should be lowered a little because it will not be able to power the bike to 27 MPH. If an 800 Watt motor is properly geared it will increase the ride time by over 20% compared to a 1000 Watt motor with the trade off being that the bike will have a 20% slower top speed. The amount that the freewheel will increase ride time is proportionate to the percent of time that bike is freewheeling when it is being used. If the bike is used only on flat ground then the freewheel will not increase ride time by much, however if the bike is being used on ground that is not flat then when going downhill it will allow the bike to freewheel with the motor off which will increase ride time.

If I make a kit then all of the parts will be put together in our shop with matching labeled connectors on them so all you have to do is plug them together. To choose the sprockets for the fastest gear ratio the power of the motor and speed that it can propel the bike need to be calculated. 

We have a grade power calculator that can help with determining what size motor to use:

If you play around on the calculator with the weight of the vehicle you will notice that it has no effect on the power that is required on flat ground to propel a vehicle at any speed. That is because it takes practically no power to move weight in a friction less environment. All of the power that is needed to move a vehicle goes towards overcoming drag (air resistance) on flat ground, and drag plus gravity on grades. Weight will of course effect acceleration though.

We have a top speed and gear ratio calculator which can be used to determine which size sprockets to use:

We also have a drivetrain parts selection guide which has directions and calculators for determining which motor and sprockets to use:

With that being said for an 800 Watt motor I recommend gearing the bike to go around 24 miles per hour. Here is a gear ratio calculation I made for an 800 Watt motor.

Sounds perfect! the only thing I have to mention is that with a freewheel, I'm not sure how I would attach it to the back wheel. There are no threads whatsoever to attach one to. Also another thing to mention in case it was missed is that the chain is on the left. The bike I have also has a much smaller gear on it right now and I believe it is a slightly smaller similar version of the bike pictured. Not sure what that is all about. A gear ratio on the slightly lower side would be appreciated as I am only around 95 lbs, so I don't think acceleration will be as much of a problem. Will you be open on Monday? I live over the mountains, so picking up the parts is fairly easy.

The rear wheel hub would need to have M35X1.00 or 1.375" x 24 TPI threads for the freewheel to mount onto it, and I see that it is not threaded to accept a freewheel so I so not know of any way to mount one to it.

The 36V 800W motor can be ran in both clockwise or counterclockwise directions so it can be used for a left hand chain drive bike. Using a lower gear ratio on the bike than I calculated would be no problem at all. We are open on Monday and you are welcome to drop in to pick up the parts. However if you would like for us to make a kit with matching and labeled connectors then that will take us a little while so you may want to call the order in ahead of time, or plan on dropping by to place the order and then come back in an hour when it is ready.

Ok, how would I request the kit, and would it be possible to review what its contents are? I'm fairly sure that's what I want to do. Are you saying that I would order the parts and you would create a kit from them? Or would you guys pick the parts to make sure they work?
I can make a kit and attach a link to buy it online or it could be purchased at our store using the kit's item number. I need to know which throttle and wheel sprocket you want to use to make the kit. Here is a list of the parts for the kit that I have in mind:
  • Motor - MOT-36800S
  • Motor Sprocket - (depends on wheel sprocket, motor includes 11 tooth sprocket for 8mm chain so if that is okay then no motor sprocket is needed for the kit)
  • Controller - SPD-CT660B9
  • Batteries - BAT-12V15Ah (3 quantity)
  • Charger - CHR-36V2.5AXLR
  • Charger Port - CNX-XLR05W
  • Throttle - THR-110K, Twist Throttle with 36 Volt Power Meter and Key Switch (is this okay?)
  • Chain - (depends on wheel sprocket)
  • Wheel Sprocket ???

How do these parts look to you?

Is the THR-110K throttle okay or do you prefer another throttle?

What wheel sprocket do you want on the kit? (I can make the kit without the sprockets and chain and you could decide on that when you pick the kit up if you want.)

Please let me know if you have any questions.

Thanks. I will order it in tomorrow. If it isn't too much work, would you mind creating a finalized part list? Would either SPR-2457 or SPR 2555B Work for a sprocket? If so, please include whicherver you recommend. Whatever #25 11 tooth sprocket fits with the motor will be good. Please include the back sprocket mounting scews as well. I need a #25 sprocket because the back wheel has a 3 hole mounting pattern. Also, The wiring diagram shows a fuse between the battery pack and motor controller. Can you please include this as well in the parts list? That throttle is perfect, everything else looks good. One last question, though. The rear tube is 145/50-10, I was wondering if any of your tubes could replace it.
47 or 55 tooth wheel sprockets may work as far as gear ratios go if the bike will be used on flat ground only, it is a little risky using that high of a gear ratio though because it could overheat the motor. If you want the bike to go up any inclines or grades then I recommend using a larger sprocket. Whether these sprockets will fit the rim depends on the center to center bolt hole spacing of the rim - our 3 hole sprockets have an adjacent bolt hole center to center distance 33mm (you could bring the rim into our shop and we could see if our sprockets will fit it). The wheel sprocket mounting screws depend on the diameter, pitch, and depth of threads on the rim which I do not know the specifications of - if you bring the rim into our shop we might be able to find some bolts that fit though, otherwise they could be purchased at a hardware store.

I will definitely include the fuse and fuse holder, in fact we add these parts to each kit that we make. I checked and we do not have 145/50-10 tubes.

If you would like I can make the kit without the sprockets and chain, and you can choose those when you pick up the kit?
Or I can include the sprockets and chain with the kit if you let me know which wheel sprocket you want to use?
I'll figure out the sprockets and chain when I pick up the parts.,

I made a kit without the sprockets. It is item # KIT-152 and here is the link to it:

If you order the kit online then please call us at 1-800-908-8082 during our business hours a couple of hours before you pick it up and let us know that you ordered the kit and need it made now so you can pick it up in a couple of hours.

I usually answer questions and help people in this forum in the evening, so if you let me know that you purchased the kit online through this forum I may not see the message in time.

Please let me know if there are any changes that you would like made to the kit.

hi ESP hey I have almost the same bike and would like to do the same electric conversation swap and would like  to know if over the past 3 years anything has been upgraded?

 also interested in the 1000 W motor and maybe a higher top speed, i recently called to verify you guys are still around and glad to find out you are !!

I'm up here in Orangevale, CA so it's pretty flat

We now have over 100 electric scooter power kits that will work equally well on pocket bikes. These kits range in power from 250 Watts up to 1800 Watts. 

Here is a link to the search page that they can be found on:

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