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> From: Dave <dhaupt@bewellnet.com>
> To: amps@contesting.com
> Subject: Re: [AMPS] High current filament circuits
To: <amps@contesting.com>
> Date: Thursday, November 12, 1998 4:27 PM
>
>
> Scott, before abandoning crimps in favor of solder, or swapping out #10
> for #2 welding wire, you should be able to actually measure where the
> drop is happening. On your bench arrangement, try baring the wire on
> either side of one of those crimps and put the voltmeter leads on each
> wire - if you've got 0.1volt drop across the connection it'll read
> that. To see how much drop is in the #10 wires, put a voltmeter lead on
> each end of a wire. Sounds a bit odd to measure the voltage between the
> ends of a piece of wire, but it works. The wire is conducting 30 Amps,
> but the voltmeter leads are conducting no more than microamps.
>
> Per the 1987 handbook, six feet of #10 has 0.0061 ohms (I'm assuming
> your six feet is three feet each way), and at approximately 30 amps,
> should be approximately 0.183 volts drop. Notice, however, what that
> resistance is - six thousandths of an ohm. Crimp connections can easily
> add hundreds, if not tenths, of an ohm. When I pass tens of amps
> through connectors, and I care about voltage drops of tenths of a volt,
> I always use many parallel pins to reduce the total voltage drop. A
> crimp assembly rated at 30A means it won't burn up at that current, but
> it does not mean it won't drop voltage. 30A crimp connections are
> probably rated assuming 120V or 240V systems, where a 0.5V drop is
> negligible. Again, you can confirm where the drop is happening using
> your voltmeter.
>
snip
> 73, Dave W8NF
>
Agree. We shouldn't be too quick to blame crimp connections for high
losses. I recall from my early days working at Collins radio as QC engineer
that "properly" crimped crimp connections have higher reliability than
soldered connections. That's why they are (were?) used extensively in
avionics and other MIL spec equipment. A good crimp actually cold welds the
joint. This of course assumes the correct tool, wire and connector are
used.
Cheers
.......................................................
Graham W Jones
Supervising Engineer
Upper-air & Marine Telemetry
Instrument Engineering Section
Observations and Engineering Branch
Australian Bureau of Meteorology
>
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