Jet Electrica blower fan ;file: mod.txt
From: Ron Freund rfreund@cup.hp.com
JET ELECTRICA (ESCORT) REAR BATTERY BOX BLOWER FAN REPLACEMENT
PROJECT
My Jet Electrica is pretty much stock, except for an upgraded
controller. Yet there is a persistent problem. For the benefit of the
many other owners, I documented my effort.

BACKGROUND: The DC motor that powers the rear battery box squirrel
cage blower draws about 3.2 A at 12.6V dc. This drain occurs whenever
my Lester charger is replenishing the drive pack, so it helps prevent
the 12 V aux. battery from ever really getting a full charge.

In winter weather at night with wipers, lights, and heater running,
and a stereo cranking, the 12V system gets a maximal load. Twice or
even three times per week I found that extra outboard charging was
necessary to keep my new marine duty 12V aux. battery "up-to-snuff".

GOAL: To replace the 12V dc motor with a similarly sized and rated AC
powered fan to reduce the extraneous loads on the 12V system during
charging cycles to something more tolerable.

METHOD: To minimize changes, I decided to use the 12V power feed for
this fan as the switched supply for a new fan power control relay. 
When the Lester charger timed out or the charge has tapered to the
point of "being done", this 12V is cut-off.

MOTOR: ITT Jabsco (the original blower manufacturer) faxed me the spec
on the old 3" flange mount motor blower assembly. Their maximum life
was approximately only 1000 hours! I needed the air rating, rotational
speed and the power consumption. They were: 105 CFM at maximum revs
(4000 rpm) pulling 4.4 A at 12V, in theory. So: (4.4 x 12) / 746 = 1
/15 HP. No monster motor here! 

Grainger (www.grainger.com) had a shaded pole motor (P.N. 3M548A) that
would fit (a bit deeper & heavier, but about the same diameter) -- yet
with 1 inch longer 5/16" shaft) for $28.XX. A shaded pole motor
develops max. torque at top speed. Just fine for a blower with back
pressure.

Specs were close enough! (Search their web site catalog for their
P.N.). Unfortunately it turned the wrong way! Not to be discouraged, I
carefully popped four clips holding the end cap, removed the rotor (a
solid core, no windings). Then using a 1/8" punch (from the inside of
the case) I relaxed the two dimples holding the field winding in
place.

On two flat 2x4's I repeatedly bounced the edge of the casing until
the coil could be extracted. I re-routed the AC feed wires through the
side of the coil body and re-inserted the coil (now backwards) into
the shell. Re-assembly and testing produced a smooth hum, and turning
in the opposite direction from before.

MOTOR MOUNTING: The new motor face has four studs (at 3,6,9, & 12
o'clock) which meant drilling the blower cover after a total
disassembly. I didn't want to completely block off the ventilation
inlet for the motor. To prevent leaks from the spinning squirrel cage
area, I used a circular 10 mil sheet of clear plastic (from a store
display box of a child's toy) to seal off the shaft access hole on the
blower cover.

I used duct tape on the edge to hold this sheet in place. Before
attaching to the blower cover, I placed an extra nut (about 1/8"
thick) flush with the motor body on each of the mounting studs. This
left some ventilation air clearance at either end of the motor body.
Without this the motor ran too hot. Assembly was the reverse, you know
the drill...

RELAY: The relay can be any 12V DC coil SPST, SPDT, DPDT, 3PDT, etc. 
relay. I chose a surplus Potter & Brumfield unit with an octal tube
socket base for clean wiring dress. Cost: $1.50 each. Try Alltronics
(www.alltronics.com) in San Jose, as they have lots of relays of
different sizes with bases.

This relay plugged into a chassis mount base with screw terminal
connections. DigiKey (www.digikey.com) sells that relay for $18.XX and
the base for $5.XX new. Part numbers from P&B are: KRPA-11DG12. Any
equivalent will do as long, as the contacts are rated at 10 amps. I
current limited the relay with a series 330 ohm 1/2 watt carbon
composition resistor.

This way, only about 9 volts is applied to the relay (so not to stress
it - for longer life), yet it is above the hold-in voltage by a safe
margin of over two volts. My DC load is now a mere 117 milliamps. 
YMMV, depending on your coil resistance. The series R is simply
screwed to an unused terminal (only 4 of 8 are really used: two coil,
and the normally open (N.O.) / wiper common pair for the switched AC
line).

AC SOURCE FEED: To get the 110 VAC for the new motor I had to pull off
the KWH meter face. This was the hardest task of all. It is awkwardly
placed and stubborn. With the plug fuses removed from my charger and
the meter open, I connected to the mains and measured the 4 lugs with
my AC voltmeter. From the two downstream lugs (either incoming phase
is fine) to car chassis I found 110 VAC. Viola!

Upstream from the meter means this new AC load doesn't get added to
the metered energy being pumped into the pack. I chose to measure
total power consumed. Your choice here. I popped a "knock out" for the
wire access at the meter's bottom. I used a short heavy old AC line
cord with male/female crimps to connect between the new AC motor
leads.

The other end was stripped and put underneath the #8 AWG clamps
holding the hot feeder wire, coming from the AC receptacle on the left
rear quarter panel. The return line was taken from the chassis ground
line inside the power meter. Testing with a voltmeter confirmed things
and the meter face was replaced and secured.

RELAY MOUNTING: I mounted the relay base using a Z shaped metal
bracket (distorted to nearly right angles) to one of the squirrel cage
housing assembly screws. Using crimp connections facilitated easy
removal for servicing or access later on. I was done.

That's it. Easy job and the new motor now runs noticeably more quiet
than the old one. Maybe over time this new one too will get louder! 
Questions: email to: rfreund@cup.hp.com
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