3-phase brushless

[VadimS]

Has any one used a brushes motor in their cart.
https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=5139

This one is good to 9hp at only $150.

There aren't any controllers available past 48V so this one
https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=8922
can be modified easily enough.

What do you think.

 

[VadimS]

What taking the weekend off.

 

[Kaptain Krunch]

sounds cool, expensive though, for that price i'd just make a gas kart.

 

[j.m.]

I too am interested in using the big brushless motors from hobby city...

But the issue of a motor controller capable of the amp draw necessary would indeed be expensive...

One could probably use this?
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10332

Link update on the motor:
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5139
(9.38 hp peak btw, @ 8640 rpm)

 

[VadimS]

That controller would be perfect.

 

[j.m.]

Maybe something with a bit more amp capacity would be better, but you could always buy two and add the fet board to another doubling it's capacity...

 

[VadimS]

That controller would be more then good enough for that motor, You can't use 2 3-phase motors on one controller and I have not seen any 3-phase motors that can draw more then 150Amps without melting. The only exception may be the electric of of a hybrid car but until they become more popular and parts can be cheaply salvaged that's not an option.

 

[j.m.]

You sound like you know what your talking about...

What's your background with brushless motors?

 

[oscaryu1]

Some guy on another forum put that on his electric GoPed.

Supposedly drains his 10/12 amp hour batteries in 6 minutes

Geared for around 40MPH... not bad. I don't like brushless though, burn up quick.

 

[oscaryu1]

http://img402.imageshack.us/img402/3784/photo16so.jpg

http://img407.imageshack.us/img407/6370/photo18r.jpg

 

[j.m.]

A properly designed brushless system is going to last many times longer than a brushed system........

 

[VadimS]

with J.M. a brushless motor will last much longer. The only thing that could fail is the bearings.

Brushless motors have all but taken over the rc world because they are more reliable and more efficient.

I have a fare amount of experience with an electric helicopter and taking engineering on college.

The best option for batteries right now is to pick up 3 deep cycle batteries and put then in series.

 

[j.m.]

Im in RC too...

For batteries I'd go with 4 or 5 12v Lead Acid's for the turnigy 80-100 and a 200 amp esc. For reliability, it's best to only run the esc at 60% of it's max rating for continuous draw with proper cooling.

Brushless systems may be considered 'unreliable' because people don't properly account for the increase in available power over a brushed system. Go overboard with esc ratings. You won't regret it.

 

[VadimS]

In this case you have 25% (200 amp controller and 150a motor)
But what you have to remember is the the only difference between a 10a and a 200a controller is ON resistance. The lower the resistance the less power is wasted in the controller hence less heat. So in this case just put a fan on the controller and it should be good to 250a or better. Replace the heat-sink with one out of a computer and it would probably be good to 300a. Manufacturers don't do this because heat-sinks are heavy and in a small rc vehicle that makes a big difference. Not so much in a go-kart.

This controller is only rated for 44v so you would be limited to 3 12v batteries in series. I would go with 3 series and 2 parallel, that way you could get it even (3 on one side 3 on the other).

With some nice deep cycle batteries you would be good for over an hour.

 

[j.m.]

In this case you have 25% (200 amp controller and 150a motor)
But what you have to remember is the the only difference between a 10a and a 200a controller is ON resistance. The lower the resistance the less power is wasted in the controller hence less heat. So in this case just put a fan on the controller and it should be good to 250a or better. Replace the heat-sink with one out of a computer and it would probably be good to 300a. Manufacturers don't do this because heat-sinks are heavy and in a small rc vehicle that makes a big difference. Not so much in a go-kart.

This controller is only rated for 44v so you would be limited to 3 12v batteries in series. I would go with 3 series and 2 parallel, that way you could get it even (3 on one side 3 on the other).

With some nice deep cycle batteries you would be good for over an hour.

Heat sinks are a good idea, as well as possibly a radiator of some sort.
The controller is actually able to go up to 50.4 v, so the max limit is probably about 55vdc.

As for brushless motors not drawing more than 150 amps, I've heard of motors many many times smaller than this drawing more than 240 amps (blowing castle creations HV240's) in vehicles much smaller than a go kart.

The only difference isn't just resistance, though that does help to keep temps down. The bigger ESC's generally have more mosfets. Some keep a small size by using higher quality FET's, but most keep the price down by using the least expensive versions (this is a budget esc, it's big).

There are three rows of fets on the board, one for each phase. So each phase has a capacity of 200 amps. If you take two esc's, and solder them together so that the three fet rows line up in series, you can increase the capacity to 400A per phase. Won't hurt for those hard accelerations and burnouts.

~Jon McLendon

 

[VadimS]

If you gear the motor to high it would be possible to fry the esc, but you would be putting a huge stress on the motor and if you used a larger esc it would fry the motor.

Putting more mosfets in parallel decreases resistance.

Amperage = Voltage drop / Resistance
Voltage drop * amperage = wattage

I reiterate my point the only difference is resistance.

It is possible to have a smaller motor capable of higher amperage but it would have a higher kv (kv = rpm per volt) and wouldn't be capable of as high a voltage, as it is this motor would freewheel at 6,500 rpm (180kv 36 volt).

The esc automatically disable itself if the voltage is above 51v at start-up.

Acording to my math the best way to utilize this motor is to re-wind it for a higher kv (240kv) or build an esc capable of 48 volt.

 

[oscaryu1]

Im in RC too...

For batteries I'd go with 4 or 5 12v Lead Acid's for the turnigy 80-100 and a 200 amp esc. For reliability, it's best to only run the esc at 60% of it's max rating for continuous draw with proper cooling.

Brushless systems may be considered 'unreliable' because people don't properly account for the increase in available power over a brushed system. Go overboard with esc ratings. You won't regret it.

Um... that guy was running I think 10/12aH batteries, he said he had a record of about 6 minutes before the batteries were down... lol... 5aH? XD

 

[VadimS]

That sounds about right. 37v, 12ah at 6 min = 120a draw.

 

[nevo]

don't forget that brushless motors and controllers like the ones you want to use are very well cooled from a contineous flow of air around and in them. the small motors that were said to work with 200 ampers move at 150 mph and more....
so when considering using these motors and escs i would highly recommend to stay within 50-60% of the maximum amp (it will gomuch higher when accelerating) and add cooling by ataching a fan (very small amp draw)
my 2cents

 

[Qmavam]

Putting more mosfets in parallel decreases resistance.

Amperage = Voltage drop / Resistance
Voltage drop * amperage = wattage

I reiterate my point the only difference is resistance.

It is not the only difference!
If you have have 100 amps through 4 FETs that is 25 amps through each. If you go to 8 FETs the amperage drops to 12.5 amps through each FET. The heat developed in each FET drops to half.
Mike