Re: (ET) lift motor thoughts

["Elie, Larry \(L.D.\)" <lelie ford com>]

Some thoughts on lift motors...  I have designed a LOT of
electromagnetic coils.

Number 1-- When you design a complex device (i.e. lots of parts from
different vendors), you try and use 'cheap' parts whenever you can.  If
someone already has something in bulk production, they can make if for
you VERY CHEAP compared to finding an exact fit.  For example, we don't
make tie rod ends, we buy them.  When someone else needs a similar sized
tire rod end, they shop around and probably will get them from the same
company.  That's why you may find the same tire rod end on a Ford,
Toyota and Honda.  It wasn't a matter of an exact fit, it's a matter of
money pure and simple.  The exceptions are if you actually have a plant
making that part, like GE, Delco (now Delphi) or Ford Electronics (later
Visteon now Ford again).  Since GE didn't have an exact fit, they used a
Delco part that was 'good enough'.  Later New Idea found a different
vendor, probably after going over warranty data.  The cost difference
was probably only a few dollars in bulk.

Number 2-- The torque from any motor depends on the CURRENT and NOT the
VOLTAGE.  You want torque, you have to pay with current.  Because of
ohmic losses (wire resistance), you have to pay for that current with
voltage.  The window motor is a 'nominal' 14V motor at something like
50% duty cycle.  That means if you ran it 100% of the time at 14V it
would burn up eventually.  It gets hot.  Kids on trips burn them out all
the time; they hold the button up on the stalled motor.  Actually,
usually the switch burns out first; it is designed as a poor-man's fuse.
The resistance of the motor at operating temperature determines the
current, and it just isn't made to be run 100% of the time.  Putting it
in a system at 18V (actually almost 21V at full charge) will bring the
current up dramatically, and increase torque by far, but will also lower
the duty cycle to something like 10-20%.  The lift stinks at 12V.  If
you try and lift the mower deck, and it doesn't quite come up, holding
the switch for say a half minute WILL overheat the motor.  Even
rewinding with a higher temperature insulation (I use 190C on motors I
wind here) won't help much as the brush springs will lose their tension
and the bearing grease will boil before you get to 190C, and that wire
DOUBLES the price.  You can't protect it by just using a smaller fuse
either; the motor really DOES draw over 20 Amps in this application, but
it should do so only briefly.  This is a bigger problem with the tiller
where you use the lift a lot.

Number 3-- Use pulleys to keep the load low; you don't want to use the
motor until it stalls.

Oh, and watch how the system is stored.  My kids heard a noise once in a
rain storm.  I found it.  Water had dripped onto the rear lift switch
and shorted it out.  The lift raised the tiller, broke the strap clamp
and had merrily spun until it was too hot to touch.  It hadn't burned
out... yet.

Larry Elie


-----Original Message-----
From: elec-trak-bounces cosmos phy tufts edu
[mailto:elec-trak-bounces cosmos phy tufts edu] On Behalf Of Christopher
Zach
Sent: Sunday, November 20, 2005 6:36 PM
To: Elec-trak list
Subject: (ET) lift motor thoughts


Ok, I'm getting together a few Delco motors and am thinking of going 
into the "fix the $#@&& lift motor" repair business. :-)

It looks like the major sources of failure are torched armatures/fields,

  burned out circuit breakers, and burned common wires. The last one 
seems to be everywhere; those wires use el-cheapo insulation and are 
just too small a gauge (14-16 or so) for 30 amps. Some motors actually 
get to the point of wearing down the brushes.

So here's my thought: I'll replace parts with Delco parts, and replace 
the long ground wire runs and the little jumper wire to the field with 
10 gauge THHN-2 wire. THHN-2 is expensive, but unlike normal wire (40 
degree C rating) and THHN (60 degree C) THHN-2 has a 90 degree 
insulation rating. That coupled with being 10 gauge should stop the 
smoking wire problem. On the ones with Delco frames I can just put a 
hole in the back, seal it with epoxy, and run the common wire to a nice 
connector. On the Elec-trak motors I suppose I can just put a connector 
on the back.

Now for the question: What is it worth to the list? Anything? Probably 
be an hour a motor, so my time is never going to be compensated (labor o

love, whatever) and there is the cost of parts. But what would people 
reasonably pay for rebuilt lift motors?

Or should we just find something else?

Chris


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