VAL Digest V1 #138

VAL Digest          Sunday, January 25 2004          Volume 01 : Number 138




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Topics in Today's Digest:

[VAL] Re: VAL Digest V1 #127 Trailer frame grounding
[VAL] Re: VAL discussion on 120VAC via inverter
[VAL] Re: VAL Digest V1 #137 - Trailer Parking Brake
Re: [VAL] Parking Brake Security Lock
Re: [VAL] Parking Brake Security Lock
[VAL] Vintage Airstream Club Website update - no airstream.net email

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Date: Sat, 24 Jan 2004 03:00:16 -0600
From: waymark1@xxxxxxxxxx.com
Subject: [VAL] Re: VAL Digest V1 #127 Trailer frame grounding

The 115VAC black wire is "HOT".
The 115VAC white wire is "NEUTRAL".
The 115VAC green or bare copper wire is "GROUND".

The 12VDC (usually white or red) wire is "HOT".
The 12VDC (usually black) wire is "NEUTRAL" and "GROUND". (12VDC color
codes are not standardized or reliable.)

The 115VAC white wire and green/bare wires should not be connected
together anywhere before the land (shore) main power panel's
neutral/ground bus. Of course we have no control over the park wiring.
The 115VAC panel's neutral bus in the trailer should not be grounded to
the trailer frame or body (metal). It is not reliable as a true ground.

The potentially main source of trouble is in the RV park's wiring, which,
especially if outside city limits and the reach of a city electrical code
department, may have been wired by an amateur, or have been repaired or
modified by an amateur who didn't know what he was doing. If the polarity
is reversed, the "HOT" of the land power would be connected to the
frame/body of the trailer and the "NEUTRAL" and "GROUND" of the land
power would be connected to the "HOT" (black) wire of the trailer wiring.
That is what the green and red lights on the voltmeter box that is on
many RVs is supposed to detect. 
Not only would this make the step and body of the trailer have 115 volts
relative to the ground (dirt the trailer is parked on), it would connect
the 115 volts to the 12VDC "GROUND/NEUTRAL" wire in the trailer, which is
supposed to be grounded to the frame/shell. Not good.
So the RV electrical code was revised to isolate the 115VAC wiring
completely from the trailer body/frame.

The trailer body/frame should have its own separate ground strap with a
big alligator clip on it, clamped to the land power pedestal, conduit (if
metal) or some other known good ground, like the water spigot IF it is
iron (galvanized) or copper, NOT plastic.

The only time it's "legit" to have the "GROUND" and "NEUTRAL" wires
connected is at the land power main panel's neutral bus bar, which is
SUPPOSED to be properly grounded.
Also, in old houses that have only 2-wire wiring with no ground wire
(like "12/2 with ground") sometimes the ground receptacle, the round
opening in a replacement 3-prong outlet, is strapped with a little piece
of bare wire to the "NEUTRAL" screw of the receptacle when the old
2-prong receptacles have been replaced with 3-prong receptacles. This is
better than leaving the ground receptacle unconnected to anything and
giving the impression that it is good just because it's there. The proper
thing to do is rewire the house wiring with 2-conductor plus ground
romex.
Al

> ------------------------------
> 
> Date: Wed, 14 Jan 2004 01:21:47 +0000
> From: hex-n-tex@xxxxxxxxxx.net
> Subject: [VAL] Grounded to Frame, GFI's and Hypothetical Scenarios
> 
> Dr.GJ wrote:
> 
> >In general since 1950, three wire circuits (hot/neutral/safety ground)
are the norm with neutral and ground isolated. The modern code calls for
more outlets (and hardly any place ever has too many), ~~SNIP~~ 
> 
> >The power inlet cable ground wire is attached to the ground bus in the
main panel, an that ground bus is attached to the trailer frame and metal
shell with a substantial conductor.
> 
> >Gerald J.
> ~~~~~~~~~~~~~~~~~~~
> 
> What is meant by "neutral and ground isolated" ...isolated from what?
each other? hasn't that always been the correct way i.e isn't that the
ONLY way to do it? Or is there some legit application where they touch?
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Hypothetical:
> The trailer is correctly wired with safety ground "circuit" going to
the ground buss and that buss going to frame. Mama accidently drops her
portable mixmaster (locked in the ON position) in a sink full of water.
The mixmaster  was plugged into a three prong circuit without any GFI
receptacles.The mixmaster has a 3 wire plug. Junior is coming back from
the pool and it has been raining, the soil around the trailer is
soaked,Junior, barefoot, has stopped at door to say goodby to a friend
and has one hand on the assist handle, one bare foot on the aluminum fold
out step, and one bare foot on the wet soil. He is in this place at
precisely the time Mama drops her mixmaster.
> 
> I assume the mixmaster shorts and a charge spikes back thru the "third
rail safety ground circuit" to the frame...??? Right ???
> 
> Does Junior get a hotfoot or does he assume room temp?  Why?
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> There are only 2 or 3 circuits in our Airstreams. One or two should
have a GFI anyway, so by just adding enough more to make the first
recepticle of each circuit GFI'd (Ground Fault Interrupted) wouldn't we
solve the grounding  problem in all but the rarest of occurances? 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  BTW (and I suppose it is obvious) I admit freely to being kilowatt
challenged.
> 
> ++HeX++

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Date: Sat, 24 Jan 2004 02:45:36 -0600
From: waymark1@xxxxxxxxxx.com
Subject: [VAL] Re: VAL discussion on 120VAC via inverter

A while back there was a little discussion that involved why we do not
run air conditioners when we are not connected to 120 (or 240) VAC land
line.
If everything was 100% efficient, it would take 10 times as much current
at 12V as at 120V. For example, my 13,500 Btu A/C draws 16 amps running
at 115VAC. For this to be operated from the batteries thru a 100%
efficient inverter it would draw 154 amps from the batteries.
This is bad enough, but in reality it's much worse. Inverters are not
anything close to 100% efficient. According to 
DEEP CYCLE BATTERY FAQs 4.4, by Bill Darden, at
www.uuhome.de/william.darden/dcfaq4.htm,
"A common application in recreational vehicles is using a DC to AC
inverter, which is used to convert 12 VDC to 120 (or 240) VAC power. It
takes between 12 and 14 amps of 12-volt DC power to make one amp of 120
VAC power (or one-half amp of 240 VAC power), so large deep cycle
batteries are normally used with inverters."

The only practical way to run an A/C when not connected to land power is
by a generator.

Al Grayson

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Date: Sat, 24 Jan 2004 01:59:39 -0600
From: waymark1@xxxxxxxxxx.com
Subject: [VAL] Re: VAL Digest V1 #137 - Trailer Parking Brake

One potential problem with a trailer parking brake is the same as that
with parking brakes of motor vehicles that are left sitting for long
periods. The shoes may stick to the drums from rust. I have had a car
that sat for years with the parking brake on, and when it was to be moved
the brake refused to release. The mechanism or cable wasn't jammed; it
was the shoes stuck to the drums. Clutch disc linings sometimes do the
same.
I suggest that if your trailer is going to be sitting for a long time
without moving that the wheels be chocked and the  parking brake
released.

Electric brakes are largely self-energizing, that is, the torque of
braking applies the shoes against the drum with much more force than the
lever presses the shoes against the drum.
Most drum brakes, electric or hydraulic, are partially self-energizing.
Al

> ------------------------------
> 
> Date: Fri, 23 Jan 2004 11:09:47 -0500
> From: Rick Langer <farreach@xxxxxxxxxx.net>
> Subject: [VAL] Parking Brake Security Lock
> 
> The recent thread on the Dexter axle with parking brake got me thinking
that such a brake would be a great security device, if it were lockable
or even if it's controls were hidden somewhere.  From where do you
control the brake?   I wonder if I could rig a parking  brake on my '66
GT?  My experience with parking brakes on cars with drum brakes is that
the shoes are expanded via a cable and lever that exits the assembly
through the backing plate. Could something be rigged mechanically  or
maybe electrically? Do electric brakes need continuous current to stay
engaged?
> Thanks,
> Rick Langer
> #3847, VAC, TCT
> 
> ------------------------------
> 
> Date: Fri, 23 Jan 2004 13:42:17 -0500
> From: Matt Worner <wornmatt@xxxxxxxxxx.net>
> Subject: Re: [VAL] Parking Brake Security Lock
> 
> Rick Langer wrote:
> <snip> Could something be rigged mechanically
> Probably, but as Dexter already has maybe loaded backing plates can be
fitted?  I have seen smaller cargo trailers (military 1/4 and 1-1/4) with
parking brake levers, so the technology is out there.
> 
> or maybe electrically?  Do electric brakes need continuous current to
stay engaged?
> No and yes.  Electric brakes are actually mechanical brakes with the
lever being pulled by an electromagnetic "puck" on the inner face of the
drum.  Sort of a "half disk" arrangement.  Not only do they require
current to work, but constant current will burn out the puck windings. 
> The classic "lose/lose" situation.
> 
> Matt
> 
> ------------------------------

> ------------------------------
> 
> Date: Fri, 23 Jan 2004 22:51:55 -0600
> From: "Dr. Gerald N. Johnson, electrical engineer" 
> <geraldj@xxxxxxxxxx.net>
> Subject: Re: [VAL] Parking Brake Security Lock
> 
> I suppose some sort of a cam or cable could be arranged to pull on the
electric brake operating arm. The biggest problem would be a nice access
hold for the cable through the backing plate. Rear brakes on cars and
trucks tend to have the backing plate formed so the cable comes straight
through. It would be difficult to add that without warping the plate. 
> 
> Perhaps a little pulley could be set into a hole in the place so the
cable outside the brake pulled mostly towards the middle of the trailer
and the pulley turned the corner to make it pull on the brake arm.
> 
> In any case there'd need to be a sleeve that the cable went through
with a clamp beyond the sleeve so the electric brake actuator could move
the arm without needing to move the cable. And probably a retracting
spring so the weight of the cable didn't make the brakes drag.
> 
> Often car and truck rear brakes have a separate actuator arm for the
parking brake, though that varies from brand to brand.
> 
> Gerald

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Date: Sat, 24 Jan 2004 11:02:47 -0500
From: "Joy Hansen" <joytbrew@xxxxxxxxxx.net>
Subject: Re: [VAL] Parking Brake Security Lock

Hi Dr. G.J.,

The Dexter has an outside the backing plate arm that will take a yoke type
cable fitting.  I'm of the mind to take the cable assembly from a junk yard
auto along with the cab operator.  Could fit it on the "A" frame with a lock
for security.  For those worried about long term use, I wouldn't use the
brake in storage, or would I?

Regards,           '69 Safari, Joy

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Date: Sat, 24 Jan 2004 11:10:21 -0600
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxxxx.net>
Subject: Re: [VAL] Parking Brake Security Lock

I think I'd start with a length of cable, say 3/16" inch diameter and
some yokes to fit the plate arms. Say McMaster-Carr 6071K12 (quarter
inch pin, 1/4-28 internal thread). I might ignore the threads and run
the cable through the threaded hole and bring it back around with a
couple ordinary cable clamps. Might use a simple clevis for that such as
McMaster-Carr 3561T44. There'd need to be a couple guides at the sides
of the frame forward from the axle so the pull on the arms is parallel
to the frame. Then I'd go over to the middle at the tongue. The guides
could be pulleys or short bent pieces of steel tubing lined with teflon
tubing. At the front, I'd run the cable through the closed hook of a
sturdy tension spring. That would allow axle motion up and down with the
brake applied without releasing the brake an allow the brake handle to
have a full stroke without compromising the brake's full application.

A brake handle from a 50s vintage chevy (pull to lock, rotate to
release) or a brake lever from a 60s vintage heavy duty truck that
operates the brake on the back of the transmission would work, as would
a vintage plow or side delivery rake handle with a latching arch. Or an
over center lever like on the sliding door latches on my machine sheds,
or some rotary ratchet mechanism like on a ratchet strap or ratchet
cable come-along. Maybe a chain load binder. Or maybe a simple lever
with a pin hole that I could stuff a latching clevis pin (McMaster-Carr
# 90222A112 or 92384A033) into a hole to hold it braked or released.

By summer I hope to have space to park my Airstream inside, so braking
wouldn't be needed there for security and the wind won't get to rock the
chocks loose. I do have that problem with the chocks outside in the
winter.

Without chocks or a parking brake mechanism the single axle trailer is
hard to park, depending only on the tongue jack for positioning. I know
there are better single axle chocks than the simple plastic chocks, but
they are fairly expensive and a pain to haul.

Gerald J.
- -- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.

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Date: Sat, 24 Jan 2004 11:15:16 -0800 (PST)
From: Toby Folwick <toby_folwick@xxxxxxxxxx.com>
Subject: [VAL] Vintage Airstream Club Website update - no airstream.net email

Just wanted to let everyone know a couple things.  The
Vintage Airstream Club website is back up and
functioning!

The down-time was a result of a continuous stream of
unsolicited SPAM email (upwards of 100,000 emails an
hour) that was taxing not only our bandwidth and our
users, but other users of the same host.

as a result, all airstream.net email addresses have
been removed from the system until further notice.  If
you have one of these addresses, please notify your
contacts of another way to contact you.  I wouldn't
expect to see them available any time real soon.

I'm sorry for the inconvenience, it had to be done.

Toby Folwick
VAC Webmaster.

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Do you Yahoo!?
Yahoo! SiteBuilder - Free web site building tool. Try it!
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End of VAL Digest V1 #138
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