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Greetings folks, first post.

First off my complements to the membership - while it does exist, the sticky thread concerning perpetual motion / over-unity et al. is only three pages long. :p

But the main reason I'm here.. very good friend of mine has asked for some tech support in converting a 1960s era (my guess) industrial tug (I believe it's 24VDC) from the current brute-force solenoid & resistor control to a modern, progressive PWM control.

The stock unit has two controls - a level for Rev / Off / Fwd and one for High / Low speed - that's it. The control hardware consists of a very large pair of SPDT solenoids (relays) and an equally large power resistor. The resistor has a tap at 1/3 and I'd make it to be around 400W or so, and probably less than one ohm. Haven't measured it yet.

So how do we go about converting this old, inefficient control setup to a modern PWM type controller? This seems like it would be cakewalk stuff for electric car guys, so here I end up asking you folks. FYI a tug is a lot like a forklift without the fork - it's meant for pulling.. tugging stuff.. rather than lifting.

Any and all input is appreciated. Hope this isn't too far on the OT fringe... if it is, any suggestions on where else to ask?

Thanks in advance - from both of us.
Take a look at the manual for one of these units. You'll need reversing contactors to go with it.

http://www.alltraxinc.com/Products_AXE.html
 

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Your existing F/R contactor's may work with the new controller. The manual has the wiring diagram which will clue you in.

You're likely talking about PM DC motors with 2 leads (terminals) which are reversible. Wound field DC motors (such as series motors) require 4 terminals to reverse. You must reverse the armature relative to the field or vise verse, but not both. Again the manual wiring diagram will show this.

Oh, a contactor is just a big relay, often called a solenoid in automotive lingo. And it does sound like you have a series wound motor.

major
 
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