Cable query

Rekusu · 25 Dec 2019

What ho one and all,

Sad that I should be writing this on Christmas Day, but what else is there to do?

In the past, I had a secondary income from photography and have a old(ish) studio flash pack with three lights. The pack is basically a floor standing capacitor. Having been asked to do some portraits after Christmas, thought I would check out the gear.

Unfortunately over the years, (and lack of use) the flexible rubber insulated cables from the flash heads have become so brittle that they are crumbling.

So my plan is to replace them but am having difficulty finding the right stuff. The cable is six core with an outer diameter of 11mm. Each core has an insulated diameter of 3mm and any twisted core (tinned copper, about 23 strands) is around 1mm o/d.

Simple maths reveals that the mm2 is 0.78mm2 so I presumably and cable with 0.75mm2 is correct?

The plug says 250V / 6A Again, a calculation reveals that with a max output of 800W (this would be full power to one head; use two and the output is halved to 2 x 400W) the amps is 3.2A.

And so to my question: I have found a supplier of 6 core, multi-strand tinned copper, 0.75mm2 and advised that the rated voltage is 450 - 750V. Is this likely to be OK?

One little 'but.' The old brittle cable has on o/d of 11mm; the new stuff has an o/d of 7.5mm. In itself, not a problem but would this imply that the cores are too small and I should go with the 1,,2 cable?

Thanks for toodle pip

RF Lighting · 25 Dec 2019

Can you post a picture of the existing cable?

Rekusu · 26 Dec 2019

Thanks for your reply. Images attached.

Grateful for any suggestions for the correct cable. Of the six cores, the blue and black go to a common terminal in the plug. Two are for the modelling light, which is switched; green is to the middle terminal on the plug so is presumably earth.

I'm not concerned about actually wiring both ends as i will just replicate how it current is. Just want to ensure I have the correct cable.

The plug says 250V / 6A and the mas flash output is 800W I should point out that max flash blam(!) is over in a faction of a second and then take around 3 seconds the the capacitors to recharge. So the 800W is not continuous.

Again, thanks and toodle pip

SimonH2 · 27 Dec 2019

Capacitors in the head or in the control box ?
I would hope that the inverter (voltage multiplier) and capacitors are in the head - these run at a "fairly high" voltage for which neither cable would be suitable

Assuming that bit is in the head, then I see no reason the cable wouldn't be suitable. The difference in diameter will be just a case of rubber being thicker - PVC is a better insulator and I would imagine more controllable in thickness during manufacturing.

Rekusu · 27 Dec 2019

Thanks for your answer but I don't understand.

"I would hope that the inverter (voltage multiplier) and capacitors are in the head - these run at a "fairly high" voltage for which neither cable would be suitable.
Assuming that bit is in the head, then I see no reason the cable wouldn't be suitable."

The first sentence implies that neither cable is suitable and the second implies that both are suitable.

Agreed that the difference in diameter is just the insulation.

This is pretty much the flash head. Image is a bit messy as it was taken as an illustration of the cable rather than the wiring layout. The model lamp socket is the black thing in the middle (Blue wire). The flash tube is not in this image, but the yellow (sheathed), red and black wires at the top go to the tube, which is mounted on a plate that screws onto the L shaped arm at the lower right (and similarly at the top.)

All other large capacitors are in the unit.

SimonH2 · 28 Dec 2019

There should be 3 wires to the flash tube - the HT supply, and a trigger wire.
From the sound of things, the HT supply for the flash tube goes up the multicore cable. To know whether a specific cable is suitable, you'd need to know the voltage used on the flash tube. However, I'd have thought it unlikely that the voltages would be within the specification of the cable you have been quoted. See https://en.wikipedia.org/wiki/Flashtube#External_triggering

Ah, on the other hand I was looking around at specs for flash tubes, and came across this trigger unit. I'm guessing that the device I first thought was a capacitor clamped in the top of the unit could be a trigger unit - does that thin red lead go to the flash tube trigger terminal ? If that is the case, then you may well be OK as the trigger voltage will be within the spec for the cable - the high voltage trigger pulse for the tube being contained solely within the head.

Rekusu · 29 Dec 2019

Again, thanks for your reply. Really do appreciate the advice.

Had a look inside the head again today and this is how it is laid out:

Black and Red go to the flash tube.
Blue is to the modelling light, with another length of blue to the switch.
White goes to the modelling light switch (so blue and white are only for the modelling light)
Green is earth.
Yellow is to one side of what is presumable the HT Trigger. On the same side, there is a brown coming out of the HT.T that wraps around the flash tube.
The other side of the HT.T has a red and yellow that go to earth.

It is not too difficult to rewire, just need to know that the 1mm2 cable rated to 750V is correct? The insulation is slightly less than the existing (which is why the possible replacement is smaller diameter) but maybe current insulation is better than that from 30 years ago?

Any thought greatly appreciated.

SUNRAY · 29 Dec 2019

The important question which hasn't been answered yet is:
What is the operating voltage of the flash tube and capacitor?
If it is signifacantly below 750V then the cable should be suitable.
What is the 'voltage rating' of the capacitor in the main unit? that will give us a clue.

Rekusu · 30 Dec 2019

I will have a look and report back. But the plug on the end of the cable that I would like to replace, although not specific to this product, does say 250V / 6A.

SUNRAY · 30 Dec 2019

Rekusu said:
I will have a look and report back. But the plug on the end of the cable that I would like to replace, although not specific to this product, does say 250V / 6A.

Yes but the flash tube wires have been given an extra layer of insulation within the head unit and I wonder why.

Rekusu · 30 Dec 2019

That I don't know, but I can confirm that only the cores of the perished cable is rubber / silicone insulated. All other wires in the unit and head are PVC insulated and appear to be in good condition. Perhaps the extra insulation is just a belt and braces approach?

Cannot see any notification on the flash tube itself and nothing inside the heads. On top of the power pack, 200 / 250 V 50 Hz; 800 w/s.

Inside there are 16 main electrolytic capacitors and a bunch of smaller ones that I cannot get visual access without a major dismantling. For what it's worth, 15 are the originals, and one is newer but was replaced some time before I bought the unit.

From what I can see using mirrors and an endoscope, they are all made by DALY / 500uF / 450v DC / and have PF 350 450 written on them. Other markings FTL 61 / 12 WKG and the newer one has L00 B36S (or it may be LOO B36S?)

My unit is number 1586. These where never major professional units, designed for rugged everyday professional, location use. It is an amateur / studio / occasional use flash unit, but obviously the internal power is still sufficient to give one a serious blast.

To be honest, I would have thought it unlikely that Courtenay had special cable made for them so I would assume the cable was something readily available; but what do I know?

SUNRAY · 30 Dec 2019

Rekusu said:
That I don't know, but I can confirm that only the cores of the perished cable is rubber / silicone insulated. All other wires in the unit and head are PVC insulated and appear to be in good condition. Perhaps the extra insulation is just a belt and braces approach?

Cannot see any notification on the flash tube itself and nothing inside the heads. On top of the power pack, 200 / 250 V 50 Hz; 800 w/s.

Inside there are 16 main electrolytic capacitors and a bunch of smaller ones that I cannot get visual access without a major dismantling. For what it's worth, 15 are the originals, and one is newer but was replaced some time before I bought the unit.

From what I can see using mirrors and an endoscope, they are all made by DALY / 500uF / 450v DC / and have PF 350 450 written on them. Other markings FTL 61 / 12 WKG and the newer one has L00 B36S (or it may be LOO B36S?)

My unit is number 1586. These where never major professional units, designed for rugged everyday professional, location use. It is an amateur / studio / occasional use flash unit, but obviously the internal power is still sufficient to give one a serious blast.

To be honest, I would have thought it unlikely that Courtenay had special cable made for them so I would assume the cable was something readily available; but what do I know?

You're right, they are unlikely to have cable made but they are so many cables out there to chose from the chances are anything within reason can be sourced.

That said I'l now make the assumption that with the caps rated at 450V the maximum operating voltage is likely to be well below this and a 750V cable should be more than adequate.

This is my remote assessment which I can of course not guarantee without hands-on inspection/testing.

Rekusu · 30 Dec 2019

Was speaking with a gentleman today, who not only lives local(ish) but was employed by the flash manufacturer when they existed in Dorking. He said that they did have the cable specifically made, and that as far as he recalls, the red and black cores were a larger diameter.

I don't know about his recollection, but when twisted together, all the cores are the same diameter. However, as the cores measure 1mm, a simple calculation reveals the mm2 to be around 0.75mm2. He feels that any cable that is 1mm2 will be more than adequate.

What he did warn me about is that capacitors, not used for some time, so need to be 'reconditioned.' Apparently this is done by plugging into the mains, and hitting the switch for 0.5 seconds, on / off / on / off etc. Basically gradually build up until they should hold a charge.

So I guess I will get one 5m length of cable first and see how it goes. If OK, then buy sufficient to replace the cable on the other two heads.

Thanks for the hand holding advice, and patience related to my 'stupid' questions; it is much appreciated.

Toodle pip and Happy New Year

Rekusu · 3 Jan 2020

Happy New Year to all,

I will post a report when / if I get the unit up and running again; in the meantime, I have ordered via eBay 5m of multi-strand tinned copper, 6 core rubber insulated cable with a 1mm2 section and rated for up to 750v.

Difficult to envisage how I could go wrong with this, but I will find out in due course.

The other issue mentioned above is the re-formatting of the capacitors. A web search brought up this site:

https://www.photo.net/discuss/threads/will-advise-on-bowens-monolite-monoblocs.131350/

and one of the posters wrote the following, which when I have the cable reinstated, I will try.

Electrolytic power/storage capacitors begin to change their characteristic values after a certain period of time of non-use. This process, called "unformatting", begins to be measurable after about 2 weeks. Practically, this means that the capacity and, more troublesome, the maximum voltage it can operate on is greatly reduced. So, after long periods of non-use, and whenever you are not certain how long the unit has been idle, you have to take specific steps to avoid the unit going up in smoke.

The following procedure applies to Bowens Monolites only, because the power capacitors of these units are always, regardless of power setting, charged to maximum voltage.

Determine the exact type first, and select the correct procedure, A or B:

A. Formatting of power capacitors for Bowens Monolite 200, X 200, 400, X400 and 750 S only (the ones with the silver grey housing and the slow charge feature).

1. Do not connect the unit to the mains as yet.
2. Make sure that the power switch is in the off position (so it's NOT pointing towards the flash tube symbol)
3. Connect the unit to the mains. Do not turn it on as yet.
4. Now, the next exercise is to turn the unit on for the duration for TWO SECONDS only.
So take a deep breath, throw that switch ON and turn it OFF after 2 seconds, and leave it OFF !
5. Wait for approx. 5 minutes.
6. Now repeat step 4. But this time, leave the unit on for FOUR SECONDS. Then turn it off.
7. After 5 minutes, turn the unit ON. It should start out in SLOW CHARGE and change to READY after 8 seconds. Leave it on for at least ? hour before you trigger the flash.
There is no need to trigger the flash needlessly! The discharge of the capacitors always puts a strain on them, especially right after the formatting procedure. So, avoid popping off needless flashes----the gas in the tube doesn't need formatting--- it just makes dealers peddling replacement tubes happy.

B. Formatting of power capacitors for Bowens Monolite 200 B+E+D, 400 B+E+D, 800 B+E, (the ones with the black housing and without the slow charging feature):

1. Do not connect the unit to the mains as yet.
2. Make sure that the power switch is in the off position (so it's NOT pointing towards the flash tube symbol)
3. Connect the unit to the mains. Do not turn it on as yet.
4. Now, the next exercise is to turn the unit on for the duration for ? second -ONE HALF SECOND- only. This means "on" and "off" real quick!!!
So take a deep breath, throw that switch ON and OFF, and leave it OFF!
5. Wait for approx. 5 minutes.
6. Now repeat step 4. But this time, leave the unit on for ONE SECOND. Turn off.
7. After 5 minutes, turn the unit ON. The READY light should come on after 2 seconds. Leave the unit on. Do not trigger the flash before at least half an hour has gone by. Like I wrote before, there is no need to trigger the flash needlessly!

Different flash units call for a modification of procedure.

Can't imagine the capacitors in my unit would be significantly different, and will report back when I know more.

flameport · 3 Jan 2020

Rekusu said:
The other issue mentioned above is the re-formatting of the capacitors

Failed capacitors need to be replaced.

Attempting to 'reform' them using such methods might enable them to work partially for a while, but ultimately failed capacitors are failed, and can't be fixed by any method.

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