RE: (ET) E20 lacking power

["Markus Lorch" <mlorch vt edu>]

Hmm, you know what.. I guess the field of the smaller
motor has a different resistance. I will measure 
tonight. The control card components (3 20 Ohm resistors
and 1 10 Ohm resistor) are tailored for the 18 Ohm
field of the E20 motor. 

If I calculate the voltages I should see on the field
for the 18 Ohm field of the E20 then this should be
something like
            
0 Ohm FW        34.5V
20 Ohm FW       32.0V
40 Ohm FW       16.2V
60 Ohm FW   10.8V
70 Ohm FW    9.3V

(not certain that my calculations are correct)

I suspect that the E15 motor field is somewhere around
12 Ohms ... thus stronger field ... which would also 
explain why it is a slower running motor and has a 
larger pulley (4.5" than the 3 7/8 pulley of the E20 
motor). 12 Ohms would about explain the voltages
I see. 

I'll measure tonight. 

Markus

> -----Original Message-----
> From: Christopher Zach [mailto:czach computer org] 
> Sent: Thursday, February 24, 2005 9:33 AM
> To: Markus Lorch
> Cc: 'SteveS'; 'et'
> Subject: Re: (ET) E20 lacking power
> 
> 
> You have something seriously screwed in your field current. 
> Field should 
> be about battery power; it should never drop that low on 
> speeds 7 and 8; 
> that's basically using the compensation windings as a field.
> 
> Chris
> 
> Markus Lorch wrote:
> > Thanks for all your replies. 
> > 
> > Based on Steve's suggestions I did some measurements
> > this evening. The following table shows the voltages 
> > I measured in the different speeds with the transmission
> > in neutral. I later measured under load and the only 
> > major difference was the armature voltage that caved 
> > in on heavy loads mainly in speeds 1-3, which was 
> > expected.
> > 
> > Speed    Armature     Field    Battery
> > 1         29.8        34.5      37.5
> > 2         30.6        34.4      37.3
> > 3         31.6        34.4      37.3
> > 4         33.6        33.4      37.0
> > 5         35.5        33.2      37.0
> > 6         35.5        11.7      36.7
> > 7         34.7         8.1      36.7
> > 8         34.4         5.5      36.5
> > 
> > I was puzzling why the field current is lower
> > than the battery. The voltage drop from the 
> > diodes shouldn't be that much (0.7V, right?). 
> > So maybe I should revisit that circuit to make
> > sure I provide a high enough voltage to the field.  
> > 
> > The performance of the tractor while driving it around
> > seemed a bit better than yesterday. Maybe the field
> > connector wasn't seated right and had a high resistance.
> > Running in D2 is now mostly in the yellow area
> > except when going up inclines. 
> > 
> > Markus
> > 
> > 
> >>>Also poor motor performance and large currents is usually 
> >>
> >>associated 
> >>
> >>>with a weak (or missing) field. You may want to hook up the 
> >>
> >>voltmeter 
> >>
> >>>across the field terminals and check that it's 36V when in 
> >>>cruise mode - 
> >>>actually I guess anything below the field weakening setting 
> >>>should be 36V?.
> >>>
> >>
> >>These are good points. Too low a field could really be the 
> problem and
> >>I haven't measured the field voltage after I fixed the 
> >>diodes, so I think
> >>this is a good thing to check. 
> >>
> >>Thanks
> >>
> >>Markus
> >>
> >>
> >>>SteveS
> >>>E20
> >>>
> >>>
> >>>
> >>>_______________________________________________
> >>>Elec-trak mailing list
> >>>Elec-trak cosmos phy tufts edu
> >>>https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
> >>>
> >>
> >>
> >>_______________________________________________
> >>Elec-trak mailing list
> >>Elec-trak cosmos phy tufts edu
> >>https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
> >>
> > 
> > 
> > 
> > _______________________________________________
> > Elec-trak mailing list
> > Elec-trak cosmos phy tufts edu
> > https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
>