Reforming Capacitors For A V.F.D.

I picked this power supply up from a recycling centre, a TITAN plus Electrophoresis Model 1503 220v 0.5A. It outputs 0v to 850v D.C.
Is this suitable for reforming V.F.D. capacitors or would using the variac method be a better way of reforming capacitors.

Jim

Jim Kennedy said:

I picked this power supply up from a recycling centre, a TITAN plus Electrophoresis Model 1503 220v 0.5A. It outputs 0v to 850v D.C.
Is this suitable for reforming V.F.D. capacitors or would using the variac method be a better way of reforming capacitors.

Jim

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This is a first for me and I've been around electronics and electrics now for more than 60 years. What is reforming capacitors?

Sure, no reason it would not work.

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Seems like it will do fine, 230V or 460V. It has a voltage display right on it, which is convenient.

Apparently you cannot set the max current, so it may be necessary to use a resistor to limit current in case of a fault. The basic unit can supply up to 120 mA, which is more than should be required for any reforming.

Here is what passes for a manual.

http://www.helena.com/Operator Manuals/Titan Plus Op Man D6500002D.pdf

Don't be surprised if the main capacitors need replacement. Main caps in VFDs are a common failure point.

steve-l said:

This is a first for me and I've been around electronics and electrics now for more than 60 years. What is reforming capacitors?

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Reforming Electrolytic Capacitors

rons said:

Reforming Electrolytic Capacitors

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Well, I learned something, but I now know why I never heard of it...........'cuz it's stupid. New caps are cheap, a lot cheaper that the time expended to do this reforming.

When you have a 3 year old drive new in the box - way less effort and cost to reform the caps than replace - especially when you are set up to do it and you do a few dozen a year as part of a spares maintenance program.

We provide maintenance for a local waste water treatment facility including spares maintenance - it would be ridiculous to replace caps on all the spare 20, 50, 100 and 200 HP drives they have in spares every few years.

Between maintenance contracts and service calls - I bet we have reformed caps on over 200 drives in 20 years and thus far we have not once ever had a situation where we had to replace a cap.

It is not stupid. If you understood the chemistry in an electrolytic capacitor you would think differently.

This is for caps that have been setting for several years, not just a casual think I'll do this today thing.

In a large VFD, you could would probably end up with several thousand in capacitors plus the additional labor required to remove the old ones and mount the new ones.

Well---------It has been over 72 years since I assembled my first crystal set (with massive assistance from a neighbor), and I have reformed lots of capacitors over the years.

When two conductors are brought near each other and one is given an excess or depletion of electrons, if there is a source or sink available, electrons will be attracted or repelled in the other conductor. The closer the conductors, the stronger the interaction of the fields. The reason that electrolytic capacitors can have larger capacities than ones with conventional insulation is that they form an aluminum oxide layer (the same compound sapphires and garnets are made of). Because aluminum oxide is an excellent insulator, a thin layer formed on the surface of aluminum foil will withstand high voltages. The capacitor is made of two sheets of aluminum with a membrane soaked in an anodizing electrolyte and the formation process is the same as anodizing parts. The electrolyte is a conductor and forms the negative plate connecting to the negative foil. The problem is that the electrolyte tends to dissolve the oxide layer over time. Applying a small current between the foils will form new oxide, restoring the capacitor. Too high a current will burn spots causing permanent damage. The procedure is to apply a small voltage that starts to break down the layer slightly so the resulting current flow generates new oxide. A current limiting resistor is not required but is a good idea as a safety measure.

Almost any adjustable DC supply that covers the range will work. I put a milliammeter in one lead to monitor the current. I bring the voltage up until the meter shows a small current and watch it fall off as the new oxide forms. When it has dropped to almost zero, I raise the voltage again and repeat until it has reached the rated voltage of the capacitor. The increments and current values depend on the capacitor ratings.

You do not need an external supply to reform VFD capacitors because one is provided. As mentioned in the op, connecting a Variac to the AC input will work fine. It would be a good idea to unhook one capacitor lead and insert a milliammeter. The supply shown would also work. Disconnecting from the rest of the VFD would also be desirable.

The hookup only takes a few minutes and a few spins of the electric meter and if you have the equipment, the cash cost is zero. Once running, you only have to look at the meter once in a while and adjust the voltage.

I particularly reform on antique radios where exact replacements may not be available and I want to preserve originality. Besides, I can set up in less time than it takes to order a new one or go to buy one.

Bill

Oh no mr. Bill, 72 yrs ago? how old was the little Marconi inside you when you did that?

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mike_kilroy said:

Oh no mr. Bill, 72 yrs ago? how old was the little Marconi inside you when you did that?

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I was hatched in the fall of 1935. In the summer of 1944 I went to visit some cousins who had a farm near Springfield, IL. One of their daughters had a high school physics book, which I started to read. I was fascinated and they let me take it home. When I got home, a neighbor who was a ham and worked for a local electronics store had given me some old transformers and related junk. Then he helped me with a crystal set, mostly built it himself, then collaborated on a one tube amplifier. From there on I was totally hooked.

Every technically oriented kid should have the incredible good fortune I had, to have four neighbors who would work with me projects.

Bill

Thank you to everyone for your comments.

JST, would you give me a resistance value you think would work with this power supply.

Jim

really great description of how and why, thanks Bill. (just a tiny quibble, garnet is a different "species", not just aluminum oxide, ruby is tho, and sapphire of corse)

obviously not all capacitors are electrolytic either, but most of the type we are discussing probably are ( multi-microfarad "cans" capable of storing some "meaningful" charge)

are all electrolytic caps aluminum? Tantalum caps, for instance, are also metal/oxide, but tantalum oxide being much more stable and "self healing" don't have an electrolyte in them I presume?

it's been a long time since I busted one open, and it's not that obvious that there is an electrolyte in there on an aluminum cap either...

It sort of depends on how you will do the reforming..... The best way is to disconnect the internal low voltage supply, because it draw current, but that is usually not possible nor practical. So that means you need to supply more current than is needed to re-form the capacitors.

One of the best resistors is probably a small light bulb, of the old incandescent type. Since your supply can produce 120 milliamps, and the voltage may be as much as 350V or so, A good option might be three 120V 25W bulbs in series.

Light bulbs are low resistance until they get hot, so they will pass low current, butif something is pulling a lot of current, they will increase in resistance and limit current.

In the world of vintage radio, it's quite understood that bringing a long-unused piece of electronics of whatever type up,
you need to do so slowly for exact this reason - to reform the oxide on the aluminum plates in the capacitors. Do it
wrong and you can wipe out the really expensive parts, like the power transformer. Two most common approaches
are indeed variac on the input power, or a small wattage incandescent lamp in series with the power leads.

Interestingly physics worked just fine, even 72 years ago.

Heck he's probably forgotten more physics than you or I will ever learn.

Make fun of wisdom at your own peril.

JST said:

One of the best resistors is probably a small light bulb, of the old incandescent type. Since your supply can produce 120 milliamps, and the voltage may be as much as 350V or so, A good option might be three 120V 25W bulbs in series.

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Since Jim will be dialing up the voltage as he goes, one bulb should be plenty; the visual indication of brightness will tell him when to stop and wait. If he was inclined to just turn it full on then 3 bulbs needed and no fancy neat PS; but that does not seem to the reason he bought the PS.

jim rozen said:

In the world of vintage radio, it's quite understood that bringing a long-unused piece of electronics of whatever type up,
you need to do so slowly for exact this reason - to reform the oxide on the aluminum plates in the capacitors. Do it
wrong and you can wipe out the really expensive parts, like the power transformer. Two most common approaches
are indeed variac on the input power, or a small wattage incandescent lamp in series with the power leads.

Interestingly physics worked just fine, even 72 years ago.

Heck he's probably forgotten more physics than you or I will ever learn.

Make fun of wisdom at your own peril.

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Having destroyed a plate transformer by not reforming the old electroytics is costly! Custom Peter Dahl replacement was a lot more expensive than if I had just done it right to begin with!

Luckily I was wary on my last project (National HRO receiver wax paper capacitor replacements) and found the shorted electrolytic before it smoked another transformer.

Reforming is good!

mike_kilroy said:

Having destroyed a plate transformer by not reforming the old electroytics is costly! Custom Peter Dahl replacement was a lot more expensive than if I had just done it right to begin with!

Luckily I was wary on my last project (National HRO receiver wax paper capacitor replacements) and found the shorted electrolytic before it smoked another transformer.

Reforming is good!

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My HRO 50T1 was always poor on single sideband. No matter how carefully I did it, the result was distorted, worse than the standard "Donald Duck". I replaced the two 6V6 audio output tubes and the plates on the new ones went red hot. It turned out that the coupling capacitors to their grids had failed, apparently over a long time and the excessive current burned the tubes down to where they were so weak that they only drew about normal current, even with the grids so positive. They still functioned after a fashion, but the result was hardly "Hi Fi". With new capacitors and tubes I had a normal receiver.

I think I have had more papers fail than electrolytics.

Bill

cyanidekid said:

really great description of how and why, thanks Bill. (just a tiny quibble, garnet is a different "species", not just aluminum oxide, ruby is tho, and sapphire of corse)

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Of course you are correct. This is an example of an aging brain. The first symptom has been difficulty remembering names, even ones I have known for years. In that statement I normally would have said ruby and sapphire but ruby would not come up and I substituted garnet without really thinking about it.

I don't know much about the newest capacitors. Edwin Armstrong may have known almost everything there was to know about radio in 1920, but now no one brain can begin to cover it. I do know that the new electrolytics are far better than the old ones. I have a 20s battery eliminator used to power the old sets with rows of 01As. The capacitor has to be reformed every time I turn it on, which I naturally don't do often.

Bill