dc series motor and rpm

[iceman10]

Is there any way to determin the relationship between load and rpm on a series dc motor? I am converting a Zamboni from gas to electric and while I would like to have a 90 volt 20 hp dc shunt wound motor, I am unable to locate one. So I am looking at a series wound dc motor which are easily obtained. The motor will be driving a sundstund hydrastatic transmission with a hydraulic motor piggybacking on the end. Today I connected a 36 volt series 4.5 motor at 72 volts and the machine operated and with load changes the motor slowed down, I can deal with a small change in rpm but before I purchase a larger motor I would like some idea on how the series will respond.

All comments welcomed and appreciated
Ellery Deuville

 

[Skogsgurra]

A very unusual problem, indeed. Are you saying that you can get series wound motors for low power testing - and then for the real application with about 20 HP? But no shunt wound motors?

The general relation between speed and load is that speed is k/torque. So the speed varies inversely with torque. That's why you shouldn't run the motor without load - it will self destroy.

Shunt wound motors are available. I think that you should widen your search. The Web is a good start.

Gunnar Englund

http://www.gke.org

 

[iceman10]

Thanks Gunnar, I live in Nova Scotia Canada, and while I have looked extensively on the web and through local motor companies a 20hp 90 volt dc shunt wound motor running at 3000 rpm is nowhere to be found, I have had a responce from a company in england that will get one at a cost of $5000. The last one that I obtained was a free motor from a junked german forklift type machine with a shunt wound 90v,10hp, 2400 rpm which I have on a converted Zamboni that I used for the last two years on our rink.
I have an explosion proof motor from a forklift that is a series wound 4.5 hp at 36 volts. I also have an industrial charger that gives me 12,24,36,48,and 72 volts at about 200 amps.I tried the 36 volt motor at all the voltages and found that the 72 seemed to give me the rpm I needed, however at 200 amps I believe that I would toast the motor after a while. I do have a great duty cycle as the machine will operate for 10 minutes out of the hour( the time it takes to flood the rink) and then rest for 50 min. I use 13 deep cycle batteries that get recharged after each flood, the batteries have lasted for about two years. The reason for the conversion was to eliminate the toxic gasses that go along with a gas machine. I also have two Curtis Dc controller that I could use to control a series wound however I would prefer to just have a relay. I am hoping that I can get a series that would give me the needed RPM with not much change when the loads are applied. If you have a source for shunt wound I would sure appreciate it. Also the series motor has two small wires coming out with the larger wires which made me think that the motor may be a compound wound with a seperate field winding, the tag states that it is a series wound. I have tested it with nothing connected to the wires and the motor works great??????
Thanks again for your comments
Ellery

 

[Skogsgurra]

Understand your special needs. But there should be some forklift motors and similar animals available around your location. I did a quick google search and found some motors on e-bay and such places.

They are not exactly 90 V DC, but you can probably get very good results with a 110 or 120 V motor, which are more easily available.

On the other hand, a series wound motor isn't bad at all. It will give good acceleration and the series characteristic is like a hydraulic automatic transmission with speed going up when load is reduced and going down (with increased torque) when load goes up.

BTW: the two thin wires are probably a temperature sensing thing. Klixon, PTC, Pt100 or something like that.


Gunnar Englund

http://www.gke.org

 

[itsmoked]

iceman; I commend your creativity! Have you "ebayed" for forklift motors??!??

http://search.ebay.com/forklift-motor_W0QQfkrZ1QQfromZR8

 

[iceman10]

Hi itsmoked, most things on E-bay are traction series motors which I can obtain locally, or higher dc voltages then I want to meet with batteries as I am restricted to the number of batteries. Here is a link to my present conversion

http://www.austinev.org/evalbum/576.html

The shunt wound motor is ideal as it maintains it's rpm. The Zamboni was recommended to operate the gas engine at between 2400 and 3000 rpm. I am thinking that a series motor may operate in those rpm range. When not using the augars or moving the machine the rpm would be 3000 and when under full load be 2400, but am unsure of this prediction. I do know that the 36 volt series motor that I did try (at 72 volts) did not runaway but I do not have a way to tell rpm I think that will be my next step (finding a way to tell rpm)so I will know more precise numbers
BFN
Ellery

 

[PowerfulStuff]

iceman10,
Do you have a motor rewind facility nearby? They would be able to remove the series field and replace it with a shunt to give the performance that you want. It depends on their level of experience though.

 

[iceman10]

Not real confident in the local shops may have to go to Halifax and check out shops there.

 

[itsmoked]

Stumbled across this motor list.

http://www.austinev.org/evalbum/advdc.html

 

[iceman10]

Thanks again itsmoked, am aware of this site however they cannot help me with a shunt wound motor, great selection of series but would need a controller, See anything else let me know
Ellery

 

[raisinbran]

Iceman,
I am not sure that this will help, but I have seen series wound motor applications that separately excite the series winding with low voltage and high current. With this approach, you can get results similar to those of a shunt wound motor - i.e. constant excitation on the "series" winding and a variable voltage applied to the armature circuit. This may be a better alternative that rewinding a good motor. Saminco (

http://www.saminco.com)

has made such drives for the mining industry, although they are in the 250 volt range.
Good luck,
Raisinbran