looking to convert from gas to electric, please help!

[scoker54]

I am looking to convert a gas operated go cart to electric. I figured you might be the people to talk to. The cart weighs about 200lbs today and I would expect about 400 to 500 pounds total weight with rider. I am looking for this thing to do about 10 to 20 mph for about 45 - 60 minutes before needing a charge. Since it will be driven mostly by kids I am not looking for anything much faster than that. Could you recommend a motor size, battery type/number, and any additional things I might need for it… costs estimates would be great too.

Gas "toy cars" are illegal here, but golf carts on streets marked 35mph or less is ok

let me know what you think and if you have any suggestions or perhaps there is something I haven’t thought of.

It currently has a 3hp gas motor in it

this is a pic of what it looks like. You can see why I don't want it to go too fast.

http://i.ebayimg.com/00/s/NjEyWDgxNg==/z/SXUAAOxydlFS0z02/$_57.JPG


Thanks,
Steve

 

[itsid]

Welcome!

judging by the weight and the wheel size,
I think your best bet is an electric golf cart. (broken ones are cheap and contain all you need with more than enough power for what you want)

it will move with just a my1020 36V 1000W motor, but I don't think it can climb the slightest angle with it.
I cannot recall the math from the top of my head right now;
but My best guess is, you'd need about 1500W to climb a 5% inclination with wheels & weight like that.

I'll let you know within a few hours when I find the formula

'sid

PS please fill in your profile to let us know where you are.. that'll help finding sources etc.

 

[scoker54]

Thanks sid. I was thinking golf cart as well. I guess that is the next thing I need to research. Any links or additional direction you can offer is great. I am just a touch green to all of this
I did find the simple guide on the main page very helpful, but will need to keep looking for a post that is similar to what I am looking to do.

Thanks again!
~Steve

 

[itsid]

Math-time...

So it's even easier than I thought it was
Allow me to use metrics since imperial values are basically crap

F = m * g * sin alpha
500lbs = ~227 kg
gravitational force = 9.81m/s²
maximum road inclination alpha = 5°
F = 227 * 9.81 * sin(5) = 194
So you need 194 Nm to move the Kart up a 5° inclination.

To move uphill at 7m/s (~15 mph) that'll result in
Pm = 194 Nm * 7m/s = 1360 Watts mechanical power
(ah well.. not too bad a guess previously)

BUT: 5° is not much actually.. so a little bit of hilly terrain and you'll need more like 10°
or 387Nm
even at a lower speed of just 4m/s (~9mph) that's already 1547 Watts
trying to hit 7m/s it'll require 2707 Watts.

And that is mechanical power!
power at the rear wheels...
Now an electric motor (a good one) has an efficiency of about 90% in his prefered powerrange, down to 50% in it's peaks.

So I think a 2000 Watt motor is a good idea.
That shouldn't be too fast for your kids, nor to weak to move up a hill at a reasonable speed.

BMC should have something that matches your needs:
http://www.bmcus.com/bldc.htm
(13130-2 for example)

'sid

 

[scoker54]

Wow! thanks for the information. That is all very helpful.

I took a peek at the site you listed, but I didn't see any prices. Any idea about how much that motor is?

Before I got your post I was looking at a 48v, 1000w.

http://www.monsterscooterparts.com/...t-11-tooth-8mm-05t-chain-sprocket-my1020.html

I liked it because at the time I thought it was enough watts and it came with the mounts and sprocket. The price didn't make me cry either

Let me know what you think. BTW, the 500lbs or 227kg is probably a worst case scenario. 350lbs is probably the day to day on it.

thanks again for all your help!

 

[itsid]

Well the BMC 13130 have a keyed 7/8" shaft, you'll find a #35 sprocket for that I'm sure
IIRC the 2kW BMC motor should be around 250 $
but I don't know any retailer to check.
which leads me to the next problem..
you'll have to ask BMC for a retailer near you (or on the internet) yourself.
I'm sure they can help you find one.

And yes the my1020 is a nice motor, but I'm afraid it won't be up for the task at all times.
Maybe in a dual motor config, but I'm not too sure that this is a good idea
synchronising two motors (and thus two controllers) can be a real pain.

IIRC the BMC 13280-1 is rated at 1500W and a little cheaper,
which would be good enough for the 350lbs day to day experience;
but then again, maybe the price difference isn't big enough to loose the additional power

For the ease of computing possible motor values, just simplify the values:
convert
speed: mph * 0.447 = ~ m/s

F ~= 0.78 * (weight in lbs)
F * (speed in m/s) = Power needed

multiply weight in lbs with 0.78 to get the approximation for the force in Nm.
multiply that with your target speed in meters per second and you end up
with the mechanical power in watts you need on your driven wheels.
Since all values are already rounded up, it's basically the poweroutput of the motor you would want just get the next bigger available motor and you're good .

for 350 lbs and just 10mph you still end up with about 1250 Watts.
(half of that for just 5° inclination [~650W motor] )
And it's down here in performance when the my1020 starts to make sense for you

'sid

 

[scoker54]

sold! BMC 13130-2 it is! I was thinking about it and I remember as a kid always having to get a friend to jump out and help push on the big hills. I wouldn't wish that on my kids I will get a hold of them and track one down. I couldn't tell from their schematics, but is it 24v or 48v? Is it strange that the only thing on the internet about those motors is just their site? I would have figured others would be using them too. Are they sold under another name?

So, with that figured out, I guess my next question is about the controller. There are so many different ones it is a bit overwhelming. I was recommended an Alltrax 4834 by someone, but the price seems like a lot. Being programable does have its advantages though.

Currently the go-kart also has a cable driven pedal, so I was thinking something like the Curtis PB 8 pot box would work for that.

http://www.ebay.com/itm/Curtis-styl...TER-0-5K-/111036822018?_trksid=p2054897.l4275

This leaves me to the coil and the batteries. I was looking at the yellow tops, for no other reason than they are what was recommended in the forum guide. I guess once I figure out the 24v or 48v that will answer the coil type as well. Again, if you have an opinion on the matter, please share as I don't.

Again, thank you for all the help!
~Steve

 

[itsid]

I'm starting to feel sorry, that I even mentioned BMC...
those things are just hiding away from me...
There are other makers of similar motors but still, all that are in the poweroutput range you need are playing hide and seek.
the 13130 is officially a "lawn mower" motor. maybe that's a start for a new search

So I have to keep the statements more general.. again
It's quite possible that the motor is neither 24V nor 48V
it can be 36V or even 72V depends on the windings I think they made different layouts.
just like the my1020 for example there are two versions with 1000W that I know of, one 36V and the other 48V.

And that is the bright part, we're about to get in the blurry foggy zone now
controllers.
As far as I know some BMC have an internal controller.
attach batteries and a throttle and you're done.
If the 13130 is one of those I cannot tell. (it was a quick pick from the net; I don't own one or even touched one in person)
If it doesn't come with a controller you can choose of a variety of good controllers
that match the motor specs.
Generally I tend to point to kelly controllers, they're reliable and have a decent price
(cheaper than most other controllers in that powerrange being still a good quality)
some are programmable (which is nice especially for limiting the kids top speed) others are not.
As soon as you know the voltage rating you know what controller specs you need.

The only thing I can almost guarantee you is:
you'll need a hall effect throttle.

I don't know any controllers that rely on potentiometer throttles,
some accept them, most don't.
All I know accept hall effect throttles.

and for the batteries.. gel if you can whatever color the top may have
(I'm on another continent, so colors/brands/names are likely to be different )
If you want to spend more serious amounts LiPoly;
but be sure to have a melting fuse temperature guard.
you don't want your kids anywhere near an overheating lithium battery.

I'll try to find out what mowers have a motor like that and in case I find out I'll let you know

'sid