[eSharo]

Hi suk,

Not bad Here's a couple of comments. Refer back to your #1 post for quote context.



Not necessarily. Many 36V motors work out well for guys on 72 or 96V systems, some even higher. That usually requires advance (shifting the brush position).



Unless you go way overboard, I doubt you need to worry about a few motor pounds subtracting from your range.



HP is HP Electric motors and gas engines are rated differently w/r/t HP. And they have different torque curves. But one HP from an electric motor shaft is exactly the same as one HP from a gas engine shaft at the same RPM

Regards,

major

Hi Major,
One thing that I have a hard time to understand. Many folks on this site are suggesting to use a forklift DC motor to replace the original combustion engine. But as you say, an electrical motor HP and a combustion engine HP is the same... So, if I want for instance replace a 100 HP combustion engine and look at the 100 HP electrical motors outthere, they are a lot bigger than the typical forklift DC motors. And for some reason, these forklift motors are not showing the amount of HP they are providing on any nameplates that I looked at. So, how can you size a "good" forklift DC motor to fit your expected output power?

Thanks,
eSharo

 

[eSharo]

Thanks a lot guys.

Waiting for your replies, I educated myself in parallel and found out many interesting things on the subject on this forum and on the net.

What I understand better now is that the required starting torque for a DC motor is not an issue since the lower the RPM, the higher the torque for a DC electrical motor.

My main concern now is the higher speed torque peaks required for say hill climbing or higher speed acceleration. For a given voltage supply, the generated HP will be the same so that for higher RPM, I will get a lower available torque. But on the other hand, I can configure the controller to supply higher voltage to generate higher HPs (raise the "speed-torque curve") therefore, higher torque for a given RPM. But in this situation, the dissipated heat may be a problem but as Ducan said, a fan installed on the motor shaft would help a lot.

I figure out that I will not be able to anticipate completely the behavior of a given DC motor to replace my current engine while designing my system but as a general rule, I will choose the highest possible HP rated motor available with the ability to install a fan on its shaft if not already equipped as such. I will also plan for a controller that will allow to supply higher voltages (higher than the nominal voltage of the motor) at higher RPMs. Since I will keep the current transmission in the vehicle, my sweet spot RPM for a 100 KMH speed will be around 2000 RPM as it is now. So, I'll have to keep a fairly good acceleration (torque) beyond this RPM until say about 2500 RPM. The rest of the story will be a try and "error" workbench test plan making sure that I will not let the motor to overheat not to damage it.

Any other comment from the community would be welcome!

Thanks!
eSharo.

 

[eSharo]

Thanks again Duncan. I got you... But regarding the 100 KMH at 2000 RPM, there is nothing I can do since it is the current built in mechanism characteristics. But I will try to find a controller to have the ability to cope with it and, as I said before, provide a battery pack that will supply higher voltage than the nominal voltage of the motor. This will leave the controller to adjust the voltage to cope with the torque (current) demand at higher RPMs. Sounds good?

 

[eSharo]

Makes very good sense to me... Thanks a lot!

 

[eSharo]

Makes very good sense to me... Thanks a lot!

But thinking at loud, if the lower gear RPM is too high, I may end up with a mechanical problem. But I am sure you have a point, I will have to fine tune the selected gear with the proper RPM to take down the supplied current while cranking up the RPM. But my point is that it will not be a tuning based on "the the highest RPM is the best" scenario because of mechanical restrictions. I will figure out all of this on my workbench.