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Old 06-11-2013, 12:54 PM
heatmizr heatmizr is offline
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Default New Guy, researching an e-Kart build

*I didn't realize there was a section for electric stuff yet, so I am pasting my intro post here. Looking forward to perusing all the threads here!*

Good day to all from heatmizr, aka Todd...
I've just begun browsing and gathering some basic ideas. I suppose I got started when I scarfed an electric motor out of my neighbor's electric mower who's controls crapped out. I wanted to see if it is big enough to drive a small kart for my sons. They are only 1 & 3 so far, so I have plenty of time to think ahead.

I looked up a similar mower online to estimate the specs and I believe it is a 36v, 50amp motor, which I calculate to be 1800w. I hope to keep this kart small, and geared down for limited speed, so from my limited browsing I think this should be sufficient.

One thought I had was to build the kart a bit bigger so that we can share - maybe with removable interchangeable seats that I can swap in to fit either them or me. With that in mind I may power it with only 2x12v batteries at first, with the option to add a third battery if I end up with something that I want to drive too.

For now, I am just gathering info, ideas, and the costs involved, and looking for a way to economize on this first kart while gathering experience. I am eager to learn more about alternative sources for controllers, throttles, stock and other parts as I don't have dedicated funds for this (accountant wife).

I'll be at a crossroads soon methinks; either looking for a cheap used frame/completed kart to build on, or getting serious and purchasing a welder for a more homegrown approach! I don't have many fabrication tools so this approach while far more fun might get me in trouble.
Comments welcome...
Todd Glasier in Charlotte

PS - where is the "getting electrocuted" smiley?
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Old 06-12-2013, 06:14 AM
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landuse landuse is offline
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Welcome to the forum Tod. There are not too many electric guys on the forum (me not being one of them) so you might have to hold on for a reply to your questions
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Old 06-13-2013, 03:20 PM
oscaryu1 oscaryu1 is offline
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50 amp continuous?!
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Old 06-13-2013, 03:29 PM
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50 amps continuous is very dangerous I hope you know. Thats more than 3 times the average rating on a house's copper wiring and would generate a TREMENDOUS amount of heat. You would need THICK wires for something like this and I am telling you that it is not worth it. Your batteries would definitely be drained quickly with that rating and for sure, would over heat to an extreme amount.

Also, if young children are going to use something like this, I suggest hiding the wires inside of the metal framing itself to prevent damage from the wires and even preventing the children from getting shocked. It may not be very possible but it is just for safety; you don't want open wires of that much amplitude (Assuming that is even the proper amplitude) operating near children out in the open. Can you post some detailed pictures of the engine as possible? Along with any other information that you may have about it? The one online may not be the same one you have.
  • 1-10 Milliampers: Person will feel little or no electrical shock effects or sensation.
  • 10-20 Milliampers: Painful shock will occur like a jolt, but muscle control will not be lost at this amperage.
  • 20-75 Milliampers: This shock is more serious. You'll receive a a painful jolt and muscle control will be lost resulting in the inability to let go of something you may have grabbed that is shocking you.
  • 75-100 Milliamperage: As the current approaches 100 milliamperes, ventricular fibrillation of the heart occurs and damage is done.
  • 100-200 Milliamperes: Ventricular fibrillation occurs and death can occur if medical attention is not administered quickly.
  • Over 200 Milliamperes: Severe burns and severe muscle contractions occur. Your heart can stop during a shock because the chest muscles put pressure on the heart. Internal organs can be damaged at this stage and in you survive, a painful recovery can be expected. What may surprise you about this level of shock is that through this clamping effect on the heart, ventricular fibrillation is avoided and the chances of a person's survival is good if the victim is removed from the electrical circuit.

I hope you know those are rated in Milliamperes and not actual amperes, like what you are stating.

You also said it was an 1800W machine, which is also the same as a household receptacle. In fact, that is the max (Average) a household circuit can hold safely without activating the fuse.
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Old 06-13-2013, 05:07 PM
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I have to comment on this...

While most of the above is true, especially when viewed from an AC perspective, I don't believe its much of a cause to ring the alarm bells on a well built DC motor circuit.

Some DC motor applications at lower voltages can draw hundreds of amps. Build the circuit properly, and in accordance with good electrical practices, and it'll be fine.

Food for thought- under the right circumstances, a car battery can kill you.
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Old 06-25-2013, 02:12 PM
heatmizr heatmizr is offline
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Phaseman you are scaring me!
Just because the motor is rated up to 50amps doesn't mean that much will be pumped into it, does it? I checked the motor and can't find any specs listed on it. It came out of some name brand e-mower, a good sized one not a small cheapie. The specs I listed came off the inter-webs from a similar mower I found online, which gave the 36v and 50amp. I calculated the 1800 watts (similar to a hairdryer).
If that is dangerous how are they selling mowers using this setup? It didn't have large wiring. So I will temper what you're saying with ToyStory's comment... that DC is a bit different.
With an e-kart the motor is so small that the battery can be located right next to the motor behind the seat. So the only wiring will be to the throttle controller. That can be run under the frame for safety.

Oscaryu1 - Being that it IS a lawnmower motor, I am assuming that means continuous? Not sure, but does it matter? The point is if it can run on 3 12v batteries in the mower that I took apart, then it can do the same in a kart.
Only diff being that the mower runs fully on for the duration, while the kart will have lots more stop-n-go. This may increase load & heat and shave battery life, but by overbuilding my battery/motor side, I should be able to compensate. Also not looking to complete any long-distance competitions.

Thanks for the excellent feedback so far! Keep it coming pls.

I have an acquaintance that works in a loading dock so he is going to put me in touch with the company that services their forklifts. Hopefully this turns into a good source of used parts.
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