nuckolls.bob(at)aeroelect
Guest
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 Posted: Mon Dec 24, 2012 7:10 am Post subject: Problem with the Harbor Freight Carbon Pile battery tester |
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At 06:25 PM 12/23/2012, you wrote:
| Quote: |
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.
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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?
| Quote: | 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.
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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.
| Quote: | 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?
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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.
| Quote: | 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.
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Doesn't matter.
| Quote: | 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.
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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 . . .
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