Educate me!

General BVS related area
Tom Thomson
Posts: 64
Joined: Fri Aug 31, 2007 12:48 am

Educate me!

Postby Tom Thomson » Thu Sep 06, 2007 10:26 pm

I have an '82 Dodge Ram 50 (Mitsubishi) pickup running 72V (lead acid) with a D&D series wound motor and an Alltrax 7245 controller. I should add that I have installed rather small tires - 21 1/2" standing height. It will max out, with the pedal floored, on a level road, at 30 mph while drawing 90A (shunt at the battery neg). The controller is capable of 400A and will show this briefly when accelerating from a standstill. My question is, why will the system not show 400A at 10 or 20 or 30 mph with the pedal floored?
Your curious friend,
tommyt

Tom Thomson
Posts: 64
Joined: Fri Aug 31, 2007 12:48 am

Postby Tom Thomson » Sat Sep 08, 2007 12:48 am

I just put some larger tires on the back and as expected the truck goes faster and pulls more amps. I think I learned something but I don't know what.

Tim
Posts: 38
Joined: Fri May 18, 2007 10:32 pm

Postby Tim » Sun Sep 09, 2007 4:31 pm

Hello Tom,

What's the maximum RPM of your motor, at what RPMs does it generate peak power and torque, and what road speeds do those RPMs equate to?

Tim

Tom Thomson
Posts: 64
Joined: Fri Aug 31, 2007 12:48 am

Postby Tom Thomson » Mon Sep 10, 2007 12:18 am

Tim
As a series wound, the motor has no max rpm. It will keep right on spinning til it scatters itself. The motor speed that I am getting appears to be abt 3500 rpm. I say appears because I have no tach at this point; the speed is calculated from road speed.
tommyt

electric cat
Posts: 11
Joined: Sun Sep 09, 2007 10:31 am
Location: London

Postby electric cat » Mon Sep 10, 2007 1:19 am

Hi Tom,

If you had access to a programmer - or the programming software for the controller you would be able to up the max rpm - but you should first find out the reccomended value for the motor!

The max amps are pulled just as you start - especially if you are facing up hill with a heavy load. As the revs pick up the motor generates a back EMF so the amps drop away.

Good luck

Tom Thomson
Posts: 64
Joined: Fri Aug 31, 2007 12:48 am

Postby Tom Thomson » Thu Sep 13, 2007 12:16 am

Hey Cat;
Thanx for the reply. The back emf reasoning makes sense, I had not thought of that. Is the emf dependant on rpm, current or both? If both, in what proportions? Can it be overridden with increased voltage? My truck goes faster with 72V than it did with 36V and I'll bet it would be faster yet with 96 or 144. I am using an Alltrax (which I regret buying) and the distributor tells me that the controller has no rpm control. Maybe he's right, maybe not. BTW what is your preference on lead acid battery chargers?
tommyt


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