Alkaline batteries overheating in flash. Causes?

[xkaes]

I was just given a like new flash. Looks new, so I finally got around to putting four new AA alkaline batteries in it. The familiar condenser WEEZ could be heard, but that was no surprise since the contacts look clean. After a minute, the READY LIGHT was still not lit, but I figured, the condenser probably was not "formed" for a long time -- and might take a little longer. After another minute, I picked up the flash to see if the test button would fire it. I never got to that point because the flash was VERY HOT.

After a few minutes, I removed the batteries -- but they were too hot to handle. The TEST light never illuminated.

I tested the batteries and they were basically drained.

Anyone else ever have this happen???? It's a first for me.

 

[Chan Tran]

Seems like a shorted capacitor. While it never happened with any flash I have but I have seen shorted capacitors often enough in other application. So the trick is can you open up the flash? I always have this problem. I can fix a lot of things if I can open it up and put it back together later.

 

[xkaes]

Thanks for the suggestion, but this flash is not worth trying to save. I was just curious if others had run across this problem -- like you, I never had.

 

[Chan Tran]

Yes haven't used a lot of my stuff for sometimes. Yesterday I checked out my Vivitar 283 and a Roleii flash unit both dead, not power up. I have the Metz SCA-3000c cable and the SCA-3402 dedicated module for Nikon and I don't know if the cable or the module is bad but the combo doesn't work. The jacket of the cable cracked. The Metz TTL cable for the Nikon F3 still work but the cable jacket cracked too. Gotta throw away some stuff.

 

[BobUK]

I was told a couple of times that flash guns can retain a nasty charge even when the batteries have been removed.

If this is genuinely the case, a few safety pointers would not go amiss from anyone that is knowledgeable in the workings of flashguns.

I have opened a couple to have a quick look for obvious faults, poke and hope, but never been successful at fixing one myself.

So how about some safety knowhow anyone.

Thank you.

 

[Chan Tran]

I was told a couple of times that flash guns can retain a nasty charge even when the batteries have been removed.

If this is genuinely the case, a few safety pointers would not go amiss from anyone that is knowledgeable in the workings of flashguns.

I have opened a couple to have a quick look for obvious faults, poke and hope, but never been successful at fixing one myself.

So how about some safety knowhow anyone.

Thank you.

It is genuinely the case that the flash gun retains high voltage when the batteries have been removed. The voltage typically 360V or so with some unit as high as 500V. But I am sure xkaes knew that so there is no need to warn him.

 

[BobUK]

Thanks Chan Tran

Methods of electrically discharging safely, plus the equipment to be used, with how-to information would be most welcome for those of us that don't know yet.
That would really be helpful if anyone knows how to safely.

Thank you.

 

[koraks]

So how about some safety knowhow anyone.

The actual capacitor(s) can retain charge for hours after powering off the unit. This voltage does not appear on the battery contacts, so as long as the unit isn't disassembled, there's no risk to the user. The voltage can appear across the trigger contacts (hot shoe), but this is so severely current-limited that again it poses no risk.

When opening up one of these units, care should be taken to avoid touching the circuit before any remaining charge has been bled off of the capacitors.

I'm not sure how relevant the warnings are, though. There are generally speaking two scenarios when someone approaches one of these units:
1: They know what they're doing, so they're also aware of the HV risk. They have a chance of troubleshooting the flash unit and perhaps even repairing it.
2: They are not aware of how a flash gun works, so they're poorly positioned to even start to troubleshoot, let alone repair the unit, and as such they have nu business poking around in the inside.

Of course there's always a category (3), which perhaps could be split up into 3A and 3B:
3A: has some basic knowledge of electronics and likes to pick things apart to learn. Or to make nice big sparks.
3B: is clueless, but will poke around anyway because hey, it's my flash unit, I OWN the thing, I'm entitled to my own...ZAPPPP

The way I see it, group 1 doesn't need to be warned. Group 2 neither; they'll generally not even start looking for a screwdriver. And group 3 can be warned until hell freezes over, but whaddayagonnadoboutit-eh!

All joking aside. Yes. The HV caps can hold charge. It's a nasty jolt. Mostly when you pick up an old flash unit, they'll have been discharged years ago.

 

[koraks]

Methods of electrically discharging safely

1: Set unit aside and wait 24 hours. -OR-
2: Place a 2W 10k resistor across the capacitor's contacts, using an isolated pair of pliers to hold it there. Wait half a minute.

Verify before further work is done if the voltage across the capacitor's contacts is <40V or so. If not, repeat 1 or 2.

 

[Andreas Thaler]

It also depends on the path the current takes through the body.

If I touch both terminals of a high-voltage capacitor with one finger, the current will probably take the shortest path through the finger. This is painful, maybe there will be a burn.

If I touch the terminals with one hand each, the current can flow diagonally via the heart, which is dangerous.

The amount of current flowing will also depend on the respective skin resistance. And on the charge.

You should also know that an electronic flash can generate high voltage from a few AA batteries that are harmless on their own. You might not suspect this.

If I didn't know about these things, I would stay away from an electronic flash.

 

[xkaes]

Yes haven't used a lot of my stuff for sometimes. Yesterday I checked out my Vivitar 283 and a Roleii flash unit both dead, not power up. I have the Metz SCA-3000c cable and the SCA-3402 dedicated module for Nikon and I don't know if the cable or the module is bad but the combo doesn't work. The jacket of the cable cracked. The Metz TTL cable for the Nikon F3 still work but the cable jacket cracked too. Gotta throw away some stuff.

I had a recent "DEAD" flash -- NOT the one that overheated. I left it ON for around an hour or two, and it came back to life on it's own.

 

[xkaes]

It is genuinely the case that the flash gun retains high voltage when the batteries have been removed. The voltage typically 360V or so with some unit as high as 500V. But I am sure xkaes knew that so there is no need to warn him.

Oh yes. I would not get need a flash capacitor. They are HIGHLY charged, and stay charged for quite a while after being turned OFF. I've read that discharging them when you turn them OFF, is not a good idea. For some reason, it's better to leave them charged. Same thing with rechargeable batteries.

 

[xkaes]

Thanks Chan Tran

Methods of electrically discharging safely, plus the equipment to be used, with how-to information would be most welcome for those of us that don't know yet.
That would really be helpful if anyone knows how to safely.

Thank you.

I've seen a couple of flash service manuals that tell you how to discharge the flash before servicing, so it's obviously CRITICAL.

 

[xkaes]

2: Place a 2W 10k resistor across the capacitor's contacts, using an isolated pair of pliers to hold it there. Wait half a minute.

Could a similar approach be used to drain a battery?

 

[koraks]

Could a similar approach be used to drain a battery?

In principle, yes, but it takes much longer. And usually it's not necessariy or even a particularly good idea.

 

[Chan Tran]

By the way both of my flashes had the same symptom as your flash Koraks. It draws high current and ready light not coming on. Last night I hooked them up to an external power supply, setting the current limit to 2A and turn the flash on. For half an hour the flash would draw the full 2A and the power supply voltage had to drop to 2V to limit the current. If it maintained 6V the current would be a lot higher. After half an hour the current dropped gradually allowing the power supply voltage to raise. The ready light finally came on and the flashes started to work fine. With 283 when the ready light is on it just cycling on and off drawing between 1A and 0A. With the Rollei flash it draws 0.5A.

 

[ic-racer]

Before discharging the capacitor, measure the voltage. If it is low, you know that the capacitor is leaking and needs replacement.

One can use a resistor to drain and cycle NiMh batteries but I usually use a light bulb.

 

[xkaes]

One can use a resistor to drain and cycle NiMh batteries but I usually use a light bulb.

Thanks, this might solve my problem, and will be easy to set up.

 

[ic-racer]

What type of flash?

On many Nikon speed lights the capacitor discharge or testing points are easy to access.

 

[kl122002]

All I can say is, when doing with electronic flash, make sure your desk, and equipments are organized. Flammable stuff like alcohol, glue should be away and we'll covered. Statics from high voltage can trigger fire.

Insulated tools are necessary, especially when you are unsure with whether the parts has been charged. Treat them as if charged for the best precaution.

Older flash have very high trigger voltage be careful with it.


For battery heat up with failed flash charging, most likely because the charging process has been draining in high current , over the alkaline batteries could support. Some capacitors could gain back to life after charging , but mostly not.

As far as I could recall, not all old flashes have current protection circuit installed. And this why back in the early electronic flash the batteries are over heated when the flash used continuously.