Bowens capacitors

Two questions for Hans P Strobl.

I've been given two OLD Bowens 400 lights. (the two tone grey ones.)

One has a section of the power dissapation coil all burnt up and is "dead"

The other stays in the "pre-conditioning" mode, but starts smoking after a few

minutes - the same section of the power coil is overheating.

The section I refer to is the 25-34 ohm piece, partially under the temperature

cutout.

Is this overheating/burn-up due to the main caps being faulty? or should I

look elsewhere.

(I'm a qualified electronics tech, though studio lights are not my normal

fare.)

Also - in a previous article, you mentioned using the "right" type of caps to

replace old Bowens ones.

I recently acquired a box of brand new large electrolytic caps, and was

wondering if they might be suitable to use.

They are German made F&T brand - 1500uf @350volts DC - _40 to +105 deg C. -

stud mount, with screw terminals and top vent - marked: AL-Elko TypGH IEC384-

4LL.

Their physical size could be a problem, but if you think they might be

suitable, I'd "give them a go".

I would only be able to use two of them per flash, so would be operating on

reduced power (1500uf instead of 2000uf.)

Found all your technical repair articles most informative.

Cheers - Robin.

Hello Robin, please don't take it personal, but I definitely do not encourage persons without specific training on high voltage equipment to do repairs on hazardous equipment such as flash units, and I hope that equipment in need of repair is given into the hands of professional repair men specialised in such work. My answer to your question should not be interpreted by anyone as an invitation and guide for action of repair.

First off, it is not worthwhile to get the old Bowens Monolite 400 (with grey wrapper) repaired. These first generation compact studio flash units were built as early as 1968, and I personally think they should not be used any more because IMHO they constitute a threat to an operator's life and to our environment. Let me explain:

1. The dimmer circuitry of the modelling light has a not too effective filtering system, just a simple choke, and when a Monolite 400 is in operation it is feeding so much interference back down the mains supply line that I could wager a bet that listeners on the radio down the block can tell; or your neighbor may wonder why the door to his garage is opening and closing once and a while without him having pushed any buttons on the remote control.

2. Whereas there are laws against polluting the environment with radio interference, there are none to keep you from ruining the flash sync circuitry of a modern camera or wireless trigger unit with the sync voltage of 200-250 V as found on a Monolite 400.

3.The flash power section is made up of 2 pairs of 350 V capacitors connected in series to each other to enable operation on 640 V. Because of ageing the individual capacitors may have experienced a degrading of the aluminium anode oxide film used as a dielectric, liquid electrolyte and separating paper layer. This may upset the balance of capacitances in the system, and unless special action is taken to restore this balance, capacitors may be driven into an over voltage condition, resulting in excessive heating of capacitors and the chance of activating the safety valves to relieve the pressure produced by hydrogen gas.

4. I am questioning the electrical safety of the old Bowens Monolite 400, and saying the least, it is definitely not to standards applicable to equipment nowadays. Later models like the 400 E had a separate ground wire from each of the metal sections of the body, including wrapper and flash tube assembly, running to a common solder lug connection on the back of the unit. The original Bowens Monolite 400 had not. Some importers of those units had to modify them to obtain national electrical safety certification requirements of their countries.

5.The funny non-standard 3-prong Bowens plug and socket system for the mains supply is made from a plastic material that can't take much abuse and it can easily be broken when dropped or stepped-on. Replacements are not available any more, and users are most inventive in finding methods for repair of broken plugs and sockets, sometimes creating hazardous conditions.

6.The capacitors of the Monolite 400 are probably using an electrolyte which contains PCB (Polychlorinated Biphenyls). To my information, one should assume that any capacitor or transformer manufactured before 1976 may contains PCBs, and manufactures of flash capacitors made extensive use of PCBs well into the '80s of the last century. These chemicals are listed as a carcinogenic substance. Body contamination can cause long term health problems with the skin, eyes, hair and liver.

Though a capacitor is normally sealed, when it goes bad it may heat-up or even explode emitting gases and vapours which are extremely dangerous when inhaled. Old capacitors are first rate canditates for that.

----- Often a beginner in studio photography will want to start out with second-hand equipment. If she or he is on a low budget even equipment of the very old types may look attractive because of the price. However, because it is really easy to fall prey to a seller peddling his/her "oldies", hiding the truth about the real age of equipment, condition, properties and performance, a person interested in buying older units had better get as much information as possible before making a decision in order to avoid paying too much or getting stuck with a piece of useless junk.

Some time ago I observed an internet auction for a Bowens Monolite 400 of vintage 1968-1976 which was won by a poor sucker with a highest bid of EURO 175 (that's BP 115 or US$ 210)!

The person who put this item on auction was using sweet words about how good and reliable flash equipment made by Bowens is. He (or she) failed to mention the true age of the unit on auction, covering-up with words like "I bought the unit 6 years ago". Sure, but this didn't mean the unit was merely 6 years old. There was no information saying that the Monolite was probably already 30 years old when she/he bought it, and that it sported a sync voltage of 200-220 V! I knew, and now you will also, but evidently the highest bidder didn't.

My entry to this forum may help to avoid a rip-off when this

junk appears on the market.

Robin, please excuse what may appear like a crusade against the old Bowens Monolites 400. I am most willing to help others, but I think that I owe it to the community to write these words. I am aware of the fact that these words are very well suited to spoil the trade for some in the future.

Now to your technical questions: The symptoms you describe are typical for faulty capacitors. If the unit was not used for a long time, the capacitors may have degraded partially, and should have been reformed before turning-on the unit in order to avoid dielectric breakdown.

The F&T "GH" caps which you have are electrically top of the line, but they are probably the 50x100mm type and won't fit physically. The Monolite 400 can only accommodate caps 85 mm high.

If you want to have more information about your flash units, you can contact me by email. You can get the address through photo.net.

Hans

Hi again :)

No problem with comments.

I'm not new to high voltage equipment - I daily have dealings with high-powered electric fence controllers (400 to 550 volts.) - microwave ovens (1900 to 2300 volts @ 700mA.) - colour tv sets (over 25,000 volts eht.) I've also had plenty of dealings with large old valve power amps, running a plate voltage over 750v. (been "in the game" over 30 years now.)

Re the odd power plugs used, I recently got given a small bag of these plugs - brand new. (would you believe.)

I'm not repairing the old grey 400 series for any customers - purely for myself. Partly as a technical challenge, to resurrect them and partly to have some working lights for my own useage.

If the caps are showing any signs of leakage, I ditch them.

So far, the grey Bowens I've looked at all have had extra earth wires fitted in them, to the various internal metal components - maybe it's something to do with local electrical requirements here.

I look at them as a technical challenge - to get them flashing again.

I just managed to get a second one working perfectly yesterday - it wasn't charging - small micro-switch on control pcb had a hole burnt through side of it - caps appeared to have been replaced recently and were in mint condition.

Appreciate the concern - looking forward to further comments - will let you know how I get on with other two dead ones I have here.

Thanks - Robin.