# The compromise



## Amberwolf (May 29, 2009)

Well, first, which DC motors did you find, and from what?

Remember that the radiator fan motors I used, even with just a friction drive, did pretty well at 3x their "rated" voltage. Better motors would certainly have worked better, cooler, and would last longer than I expect those fan motors would have if I'd kept using them. 

AC motors I can't help you with, as I don't know enough about them.
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## carl2.0 (Jun 26, 2009)

ok so I was sceptical at first but I got myself a radiator fan motor n Im lookin to run it at 36v... Next issue is that i cant get small deepcycle batteries here only huge golfcart sized...so Im wondering how would this affect the build besides dead batteries in 2 months 


Plan to import LiFePO ones soon tho


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## Amberwolf (May 29, 2009)

It depends on what motor it is, and it's power capabilities. Does it have any labelling? Do you have any photos?

I have had fan motors that were pretty wimpy, which were more the cylindrical type, and then the pancake style I ended up using. I *think* the larger diameter of the rotor coil arrangment, and larger diameter magnet (plus it being an ironless axial flux style, perhaps) is what gave it more capability than the cylindrical type (which I assume were radial flux but I never took one apart). 

What were the other motors you found? If they were wheelchair motors, it's quite possible they're capable of even more than the fan motors, being *designed* for high continuous power dissipation. (at least, the ones I have from Invacare seem to be, especially the 4pole one).
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## major (Apr 4, 2008)

carl2.0 said:


> Im thinkin AC now. I have access to a couple air conditioning fan motors..im told they are about 1100 rpm at 120v n about 20 pounds... Could this be used for a small electric bike ? perhaps with a 1000w inverter with 36v worth of SLAs ?


Hi carl,

I doubt it, but stranger things have been done.

Sounds like the 120Vac fan motors would be single phase. If so, they would have crappy starting torque. For an AC drive you need 3 phase.

1000W inverter? Sounds like you mean those DC to AC inverters which run at 60 Hz single phase only. Not what is needed for a vehicle drive. You need a variable frequency 3 phase motor control inverter.

Regards,

major


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## carl2.0 (Jun 26, 2009)

Ok I just finished cleaning up the fan motor so i could finally read it this is the writings that was on it I googled it and got Johnson electric company... still dont have any detailed specs on it tho

GATE-S.p.a-ASTI 
12v 6E (or L)

MP8020

Its a 4 inch diameter motor, here are the pics


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## Amberwolf (May 29, 2009)

carl2.0 said:


> GATE-S.p.a-ASTI


This appears to be the Italian company it was made by, as part of Johnson. Johnson makes motors for a lot of people. I have a tiny one of their motors in my Ryobi lawn string-trimmer.
http://goliath.ecnext.com/coms2/product-compint-0000515958-page.html
The homepage listed on that page appears to be dead (or inaccessible right now). The Internet Archive (archive.org) only has copies up to 2005, so they might be long-defunct. 
http://web.archive.org/web/20051221090249/www.itagruga.com/Benvenuti/UK_benvenuti.htm
http://web.archive.org/web/20050824143249/www.itagruga.com/prodotti/UK_prodotti+.htm
Apparently they made fan motors up to 700W, and they could be 2pole or 4pole (4pole would be better for your application, as they'd run slower and have more torque, but take more current). 



> MP8020


 I couldn't find any good info on that model, except some of the cars it was used in. 




> Its a 4 inch diameter motor, here are the pics


If it is 4" diameter of the main case (not including the flanges for the bolts and stuff) then that's a decent size, and probably can do some decent torque. You'll need to test it with say, 24V to see what happens. First test it at 12V and see if it makes any noises like bearing problems, etc. 

Do you have a couple of car batteries you can use for bench testing? That will get you pretty far in making sure things work at lower voltages and get you enough torque without having to first buy the batteries you're going to use on the EV itself, and build the whole thing. Testing in stages is a good idea (I've wasted lots of time on blind alleys because I built a whole thing before testing any part of it). 


The case looks fairly weatherproof, and also kind of heavy. It may be a tough motor; I don't know what it's insides are like.  Hopefully you'll never need to open it up but it looks like it would be simple to do so if bearing or brush service is required.
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## carl2.0 (Jun 26, 2009)

Ok so I got the motor n did a couple of tests on a normal car battery to see how it was functioning listenin for anything unusual n things seems ok , this battery was a higher current that i expect to be using for the project tho (12v 300amp slas). 

Now Im at that dreaded section the controller ! Its no surprise that I cnt get one here so Ive been doin a lil research to build one I think Ill go with a PWM ...seems the easiest right ? Can anyone steer me in the right direction here and also I know this is a noob question but what is the advantage of controller/pwm over a variable resistor ?


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## Amberwolf (May 29, 2009)

> Ok so I got the motor n did a couple of tests on a normal car battery to see how it was functioning listenin for anything unusual n things seems ok , this battery was a higher current that i expect to be using for the project tho (12v 300amp slas).


Since it works on that, do you still have the fan that came on the motor? You will want to keep the metal hub out of it and the bolt or nut that held it on anyway, but having it attached to the motor, bolt the motor to a table securely, then put on some leather gloves and hold the fanblades with one hand, ready to move your hand out of the way if you feel you can't hold them (very unlikely).

What you are going to do is test the torque of the motor at 12V. It will probably be minimal, and likely require 24V or 36V to do significant work. 

While holding the fan, turn on power to the motor. If you feel it pulling really hard, you're in luck and have an even better motor than mine. If it doesn't do much, you will have to test it at 24V, or even 36V to see if it will do better. If it does not have much pull at either of those, then you need to find a different one. (they are not all capable of much power, and the pancake ones seem best at it, given my extremely small sample size). 




> Now Im at that dreaded section the controller ! Its no surprise that I cnt get one here so Ive been doin a lil research to build one I think Ill go with a PWM ...seems the easiest right ? Can anyone steer me in the right direction here and also I know this is a noob question but what is the advantage of controller/pwm over a variable resistor ?


If you try to use a variable resistor to control that much power, you will need one that is bigger and heavier than your motor, and possibly your battery.  Otherwise it will get so hot so fast that it could melt or burn up, depending on the type. 

I have a very high power (1000w?) stage lamp dimmer here, and it is extremely heavy and bigger in diameter than my spread out hand! It's just a giant wirewound potentiometer, basically. I wouldn't recommend using one for motor control. 

PWM is very efficient, with little power loss in the controller, especially at lower voltages like what we use on bikes, typically.

It is also easy to make, even with just transistors (lots of wiring, though). If you have an electronics junk source, especially for industrial stuff, you can find LM339 quad comparators in a lot of things, including industrial power supplies (which may also have giant MOSFETs and diodes you could use). 

I have the very basic schematic someone drew up of my ScootNGo controller, which worked for my radiator-fan bike just fine, with the larger MOSFETs and driver transistors I used (it would not have worked as it originally came), but I did no actual circuit modifications, just replaced small-power parts with bigger ones. 

After I find it, I can scan it in and post it here--it's a hand-drawn schematic, but it is usable to build and/or troubleshoot the controller from, if you know electronics. 

If you do not, you'll probably need a more direct visual representation of how the parts get connected, and that would take some time for me to draw up, of which I have little right now (trying to make ends meet). 

I have posted the same reply to your new thread, in case you miss this one. 

FWIW, it might be a lot easier to get relevant replies if you kept your project in a single thread, instead of starting new ones. Then others can see what you already have, what you know, what limitations you have, without you having to re-explain yourself every time. 
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## carl2.0 (Jun 26, 2009)

Great, the drawn schematic will be greatly appreciated I wouldnt want to steal any more of your time with a detailed drawing, I have a friend who should be of great assistance with such things so Ill have him help me with the schematic.


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## carl2.0 (Jun 26, 2009)

Ok so I managed to started some of the torque tests you were suggestin (only 12v so far). The motor has a decent torque for its size tho i could still hold it back with a couple fingers. Mostly Ive been spending my time reading up on motor control I was considering building a PWN motor contol circuit with current limitin prolly using one of (those 555 timer chips ? ) ...quite a bit of research I have to do to fully grasp the whole thing honestly. since i dont think it be able to find a controller on the shelf this seemed to be my only option then it hit me cant I just use the controller from a golf cart ?


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## Qer (May 7, 2008)

In short, it might look like it's easy to build a controller (one year ago I thought the same). It isn't. And it isn't cheap as well. You'll blow some transistors, spend lots of time figuring out why, reconstruct, test, blow up some more transistors, scrap the whole design, redo major parts, rethink the strategy etc etc etc.

It's not cheap, it's not easy and it's definitely time consuming (and if you think otherwise, your pre-study sucks).

My suggestion: Buy a second hand Curtis on E-bay or join forces with the group around M. Paul Holmes and contribute to their controller. They've spent some serious time and effort on their controller and have got something that actually works, seems pretty reliable (and getting better) and has performance that seems competitive with your average mid-size Curtis or Kelly.


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