Cable query

[Rekusu]

I can relate to that but the last time I used the unit, they had not failed. In fact, it was working just fine.

Unless the suggestion is that total lack of use will cause them to fail?

What do I have to loose? It will either work again with new cable and reformatted capacitors, or it will be destined for the dump because what with cables and caps, it is not a viable repair job.

 

[SUNRAY]

Another thing I'd suggest is to connect a lamp in series with the mains to limit the current into the flash unit [edit:]while doing the reforming. Start with a small lamp <25W and when you've gone through the procedure change it for 100W and repeat.

edit: If the caps have/are failing I'll further suggest to place the unit inside several layers of of strong rubbish sacks as an exploding cap will fill a room with snow, mine was only 100μf at 25V.

 

[flameport]

I used the unit, they had not failed. In fact, it was working just fine.

No need to do anything then.

Electrolytic capacitors contain a wet electrolyte, which eventually dries out. As they fail, they get hot, which dries them out even more.
Then they either go open circuit and don't work as capacitors any more, or go short circuit internally and explode.

 

[Rekusu]

When I receive the replacement cable and have wired it up, I will do the recommended reforming, one for 1 second, off for minute until there is sufficient oomph for the ready light. But this will not be for a few weeks.

As an aside, what is the 'explode' business? As there is a bank of 16 caps within a ali frame, and the whole is fitting into a sealed ali box which is the flash unit, I assume that if it were to 'explode' it would be a bang/smoke contained within the unit and somewhere in the house, a fuse would blow? Or are we talking IED type of explosion?

As an aside, I have a 6k litre tank in the garden to collect rainwater for toilet flushing and garden use. Last year, the submersible pump stopped. I extracted the pump and dismantled. All was dry but the starting capacitor had 'exploded' or more specifically, its contents appeared to be bursting out. I replaced the cap and for the last year, all is good.

So is this 'explosion' likely to be a kinda oozing or a bang?

 

[JohnW2]

So is this 'explosion' likely to be a kinda oozing or a bang?

Electrolytic capacitors can 'ooze', but they also can 'go bang' (sometimes in a pretty dramatic fashion {true 'explosion'}, particularly if they are large)!

Kind Regards, John

 

[SUNRAY]

So is this 'explosion' likely to be a kinda oozing or a bang?

First of all the chances are it will be OK. You have raised another point worthy of inspection. On the insulated end of the caps there may be a pressure release hole covered with rubber like layer which may look like a little dip, have any turned into a 'bulge' or 'blister'?

It is more likely to be a bang and the entire contents of the cap will create a surprisingly large cloud of white and grey dust which will settle like snow and yes it will likely blow a fuse/trip too.
The act of putting it in several layers of bin bag could avoid significant spring cleaning.

My friend wanted something for a model railway layout and I tried exploding a cap unside a sealed [by knotting] tesco carrier bag, it made a hole in the first bag but on subsequent attempts it didn't get through 2 bags. In your case, being enclosed inside a box, I feel it would be for more for debris control rather than to contain a blast force.

Don't let me scare you, the chances of a bang are minor but simply bagging the unit could save a lot of work.

 

[SimonH2]

As above, effects can vary with the degree of "failed" and the type of capacitor. Modern caps tend to have formed weaknesses in the cans (eg the "Mercedes car logo" stamped in the top of many of them), but older ones often didn't.
With weakened cans, the can gives way before too much pressure builds up, and so the contents can blow out as fine confetti - I've only seen this with a small cap that I over-voltaged. With no weakness engineered into the can, pressure can build up until it "lets go" with a big bang. I've been told by old hands that these latter cases could be quite dramatic - one story involved the can of a capacitor exiting the wooden case of a TV through the hole it made for itself, and embedding itself in the wall the other side of the room

 

[Rekusu]

Again, many thanks for the explanations. Since the caps are housed within the unit casing, I don't think there will be any problem, but as a precaution, perhaps I will put in a bin bag and reform it outside. And maintain a healthy distance as I light the blue touch-paper!

 

[JohnW2]

.... pressure can build up until it "lets go" with a big bang. I've been told by old hands that these latter cases could be quite dramatic - one story involved the can of a capacitor exiting the wooden case of a TV through the hole it made for itself, and embedding itself in the wall the other side of the room

Albeit without the 'embedding itself in the wall' bit, I have, in the distant past, personally seen that happen with a plastic- (maybe bakelite-) cased TV.

Kind Regards, John

 

[bernardgreen]

For years I had a round dent in the ceiling caused by the can of an exploding electrolytic cap in an unboxed radio.

 

[flameport]

I will do the recommended reforming, one for 1 second, off for minute u

Waste of time.
If it's going to blow up, then it's inevitable.
Shove it outside, switch on and leave it powered for an hour.

 

[bernardgreen]

Reforming in best done by applying a low DC voltage, less than 1/10 of the operating voltage via a current limiting resistor and measuring the current flowing through the capacitor. The current should reduce as the oxide layer inside the capacitor reforms. When the current has dropped to zero ( or very close to zero ) the voltage can be increased to 1/5 of the operating voltage. Repeat unti lthe operating voltage is reached. If at any voltage the current does not eventually decrease then chances are the reforming is not working.

 

[Rekusu]

Thought I would give a heads-up on reforming the caps and the replacement of the cable.

Cable arrived from China and is very flexible. Silicone insulated and does not seem sufficiently resilient but I am sure that as it will not receive excessive use and abuse, will be more than adequate. Flash head rewired and currently reforming the caps.

Took all the advice from here and two others that I found; one used to work for the flash manufacturer, the other a flash repair expert. One advice was to on /off cycles with on for seconds, off for longer and increase the time. This apparently will not allow the caps to be stressed too much. The other was as given here, use a Variac or something similar and only use the 1/4 power setting first. Wired a 150w modelling light into the incoming live and gave is only seconds before turning off the power.

The unit was clicking, the bulb brightness gradually reduced and the ready light came on. No smoke or unpleasant smells! Turned off for minutes and did it again. Still lots of clicking and strangely, even when the ready light was on, there was still a click every 2 seconds for around 30 seconds, then the ready light went out.

This morning, tried again and the ready light stayed steady so hit the open flash button. Yippee!! Light (or a flash). More clicking as the unit recharged (still have the 150W connected) and tried again. All OK.

Left it off while we went for a coffee and on return, turned on to full power (150w still in-line) Ready light now steady and clicking stopped (apart from the first few seconds of recharge) and seems like full flash. So presently, leaving it live on full power. With the 150w in-line, it is taking around 15 seconds to full charge; probably be faster when the resistance is removed.

The flash repair guy told me that he usually repairs what are called mono-block units (these have the caps in the head and are stand-alone units, not requiring a power pack. he said that modern units with modern caps, generally have a no-use shelf life and after X years of non-use, would probably not work. But when my unit was made, the caps where more robust and he suspected that they could return to life.

Seems like that is the case.

 

[SUNRAY]

Thanks for the update.

 

[Rekusu]

Just thought I would give another heads-up.

Yesterday, as part of reforming the caps, having run the unit at 1/4 power, I switched to full and with the 150w bulb in series, it was taking around 13 seconds to fully charge with regular clicking.

Today, I removed the 150w bulb and it is charging to full in around 3 seconds, which is what I recall from when I last used it around 6 years ago.

So seems with the helpful advice, I have revived it and saved it from the skip. Next, replace the cable on the other two heads.