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[OM] Re: T-28 cable extension anyone?

Subject: [OM] Re: T-28 cable extension anyone?
From: "Johann Thorsson" <johann@xxxxxxxx>
Date: Fri, 2 Mar 2007 21:21:08 -0700
Thank you for your hints, they are really helpful.  I usually solder all 
wires together anyway and then use crimp tubes to insulate them.  It takes 
longer but you feel better afterwards knowing that the connection is robust.

J


>
> You are not going to blow any common guage wire even with a relatively 
> thin guage because duration
> is only at the few mS level and heat is spread out over length.  However 
> it takes away light
> output directly from flash:
>
> A reasonable approximation for ignition resistance value for small tubes, 
> is something of the
> order of 60V at 150A. Which translates to about 60/150 or say 0.3 Ohm. 
> This means the light drops
> 10% for every 0.03 Ohms added wire and connector resistance you add.
>
> common small connectors are specified as capable of 6-12A continuously 
> with a specified maximum
> resitance < 10/1000 Ohm (typ more like 5ea).  This means for two 
> connectors on an extension cable
> at the worst case values, the light would drop 20/300 or ~7%.
>
> You can look up wire tables to determine resistance (remember wire goes 
> there and back, so 2X the
> resistance for whatever ext length is used).  Calc the resitance and do 
> the same exercise as above
> to determine losses for the wire length and guage you choose.
>
> I would solder, not crimp wire for the connections, although crimping 
> works well when done right.
> In fact you can crimp and then solder for even better connection!
>
> Tim Hughes 


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