Today's Message Index:
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1. 07:10 AM - Re: Problem with the Harbor Freight Carbon Pile battery tester (Robert L. Nuckolls, III)
2. 07:48 AM - Re: Carbon Pile battery tester (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Problem with the Harbor Freight Carbon Pile battery |
tester
At 06:25 PM 12/23/2012, you wrote:
>
>I've used this unit a few times without a problem. Then it suddenly
>stopped working. I couldn't seem to apply a load though the exact
>symptoms I don't quite remember.
is it failing to APPLY a load or failing to
INDICATE what that load is? Does the voltmeter
behave as expected? Can you depress the voltmeter
reading and get it to smell hot by cranking the
load knob down?
>Today, I pulled the unit apart and found
>1) a fuse on a small circuit board which had not blown (not easily
>replaceable either)
>2) the carbon disks that presumably supplies the variable resistance
>seem to be stacked between two steel plates but the carbon disks
>appeared to be loose or askew.
Those are classically not tightly captive.
A carbon pile rheostat is a PRESSURE device
wherein once the slack is taken out of the
stack height by the first turn of load knob
rotation, the pile doesn't physically move
much after that. It's behavior is a response
to pressure not motion.
>If I screw the big knob down and shake things a bit, I can get the
>stack of carbon plates lined up and it seems that increased
>resistance results from placing more pressure on the stack.
>
>Does that sound right?
No, the resistance between the fat wires to hte
battery should drop markedly. To load a battery
to 500A at 8 volts requires a resistance on
the order of 16 MILLIOHMS.
>Furthermore, it would seem for consistent operation, it would be
>best to lie the unit on its back to insure the carbon plates remain flat.
Doesn't matter.
>Tomorrow I will attempt to use it again to see if it works now that
>the plates are back in position.
>
>Any insight or tips welcome. I will report further tomorrow.
I've got two of these critters and they've
performed as expected for 5+ years. Sounds
like something may be unhooked. Tell us what
behaviors you see on the voltmeter while trying
to get the load increased.
Bob . . .
Message 2
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| Subject: | Re: Carbon Pile battery tester |
>Don't know about your unit, but traditional carbon piles *decrease*
>resistance as you tighten them up, pushing the pack into better
>contact, or decreasing the total electron path length, depending on
>how you'd like to think about it. Relaxing pressure *increases*
>resistance, as the carbon gets further away from each other, at
>least microscopically.
>
>At least, our 1937 2400 volt AC generators' excitation current
>control widgets work that way... technology may have marched on in the interim.
Yeah, those were the good ol' days.
http://aeroelectric.com/Pictures/Regulators/Carbon_Pile_1a.jpg
A carbon pile regulator had no contacts to burn. It could
be taken apart and refurbished. Adding a separate
offset winding to the regulator provided an opportunity
to make two generators parallel onto one bus.
http://tinyurl.com/cf8b43e
It's one of my favorite examples of creativity in
electronic controls from the era of copper, steel, rubber
and Bakelite.
http://tinyurl.com/d9nyju4
This control device came out of a steam turbine
power plant, one of many shepherded by one of
several favorite uncles. Throughout this assembly
one can identify a/d converters, d/a converters and control
logic that presided over line power quality for
hundreds of thousands of Kansans. Uncle Bill received
this piece with a plaque on it commemorating his
decades of service to the only job he ever held after
graduating college.
I'm pleased that he saw fit to pass it on to me.
Bob . . .
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