(ET) Load values in amps...

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

I have been having a little correspondence with Neil Dennis about the 
shunt values for the load gauge.  Combined with some old data taken by 
Steve Naugler, I think we have a reasonable set of data about the load 
gauge on the ET.


Last week, I made the following request:

Anyone know the room temperature shunt resistance on for the power use 
gauge?  I don't have one apart or I would measure it myself.  I have a 
table (care of Steve Naugler) of current values off a gauge and want to 
prepare a table of actual currents based on that data for general 
reference.


Neil made the following reply:


> Larr, maybe the easy way is to calculate the resistance from the wire
> size and length, mine was always reading "pinned" under any load so I
> checked the length, it was about and  inch too long.  This is from the
> stated length in the manual - so I changed and now it works what I
> assume is right.


To which I replied:

> Yes, I have tables here for resistivity.  What is the gauge and length?  
> I don't have a manual here.
>


Neil promptly gave me the data:

On the E12, it is a 20" length of #6 AWG, When I measured, they had 20" + 
a little of wire and then the
terminals, I changed it to 20" center to center of the terminal mounting 
holes.  I don't see any
notation on the E15, just "shunt", probably all models used same part but 
hard to tell.


(Larry's note:  All of the ET's I have had, E10 through E15 have had the 
same gauges...  they all use the same basic set of batteries from E10 up)


With this data, I made the following calculations:


Thanks.  Great.  #6 AWG has a nominal resistivity at room temperature of 
.3952 ohms per 1000'.  20" is 1 and 2/3', or .001667 of 1000', so the 
resistance should be .001667 * .3952 or .000658667 ohms, or .658 mOhms.  
Now, the following are from Steve Naugler:

"
    The power gauge is actually a millivolt gauge measuring the voltage 
drop
across a shunt.  I took a loose but poor condition gauge and measured its
needle displacement vs. mV input.  Here is the data on that gauge:
1.  Bottom of green/0% = 0 mV.
2.  Top of green/bottom of yellow = 36 mV
3.  Top of yellow/bottom of red = 64 mV
4.  Top of red/100% = 90 mV
    This data is suspect because of the gauge condition, but within the
expected range.  (industrial shunts are usually rated 50 mV per full range,
and their mating meters are usually 50 mV at 2/3 scale and 75 mV at full
scale.
    Sorry this data is so poor.  My official factory shop manuals don't 
give
gauge or shunt data.  If I find better gauges I'll post data from them.

Steve Naugler
"

So, I get:

1.  Bottom of green/0% = 0 mV.                          (Still 0)
2.  Top of green/bottom of yellow = 36 mV               (54.66 amps)
3.  Top of yellow/bottom of red = 64 mV         (97.17 amps)
4.  Top of red/100% = 90 mV                             (136.64 amps)

I think these numbers are realilistic, based on how long 220 amp-hour 
batteries last on the application.  It's also a bit humbling as 760 
mechanical watts (and for a decent motor, 1000 electric watts) only puts 
out a single horse-power.  At 100 amps and 36V we are only doing around 
3600 watts; ~<4 hp of work!  I think that's about right.

Now, I would like to confirm these numbers with my clip-on hall-effect 
probe under load, but I would have to come up with a variable load.  
Perhaps the snow plow and a dirt pile.  I would like to confirm before 
this ends up on a faq list.  

I have not had time to confirm the values with a clip-on yet, but I think 
I believe them.  I don't think I slipped a decimal or did anything silly.

Combined with the more critical charge voltages, again from Steve Naugler:

1.  Needle just moves = 20 to 22 VDC.
2.  Bottom of red = 27 to 28 VDC.
3.  Top of red = bottom of green = "E" = 35 to 35 VDC.
4.  Top of green = bottom of white = "F" = 45 to 46 VDC.
Note:  Green zone is the normal operating zone.
5.  Top of white = bottom of upper red = 52 VDC.
Note:  White zone is the charge zone.
6.  Top or upper red = 54 VDC.

I think that legitimate tests of how the tractor should work are now 
practical.

Larry Elie