Johann,
Sorry there is a bit more to this which I forgot to mention in my quick
reply.
The trigger wire gets a high voltage of about 4kV briefly.
That means the connector and wire must have enough insulation to handle this:
Unfortunately most common connectors are only rated at less than 1kV (typically
300-600V). In
practise they will take a lot more than 300V transiently but 4kV is way too
much for them and it
is fairly likely they will at least partly break down cause flash misfiring.
You could try a
multipin connector with plastic shell and remove intervening pins to get a
large airgap between
trigger pin and any other metal/pins.
The second problem is wire insulation (even if you don't use connector). Most
commonly available
wire is insulation rated to 300-600V or so. One exception is a single wire, so
called "test lead
wire" which is rated at 4-5kV, that you could combine with conventional 2 pair
wire (which is fine
for 330V of flash cap). In reality a lot of insulated wire is good to quite a
few kv transiently
(although 4kv is high), but the vendors are worried about degradation at hv and
pin holes which
are hard to control and so can't guarantee any sort of hv breakdown in pvc.
Another special wire that is really good at high voltage is "corona resistant"
teflon coated wire
but it is not so easy to get,is expensive (>$1/ft) and is rather stiff and easy
to break at solder
joint. It is good to 10kV continuously which means good to probably 20kV
transiently. This is what
I often use, as I have a large supply from surplus. I have often used it when
designing medical
instruments for high voltage patient safety isolation circuits.
If you don't need a very flexible wire you can just take a piecs of convention
pvc insulated wire
for the trigger lead and slide a piece of Kynar shrink (black type) over it
(don't need to shrink
it). Although only rated continuously at 900v or so, common 18/1000"
polyolefin/kynar is actually
good to > 5kV and pin holes are not a problem. Again combine with common 2wire
pvc for remaining
leads. (You need to know which is trigger lead obviously) The polyolefin shrink
is better than the
pvdf shrink tubing for voltage and durability.
Tim Hughes
--- Johann Thorsson <johann@xxxxxxxx> wrote:
>
> 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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