Hi Folks!
I've inherited an old "Electro Chemical Cleaner". As far as I can determine, it is used to de-rust items by electrolysis, which I've done for years using more modern equipment.

Inside is a rectifier which looks to be either a selenium or copper oxide type.
It has 5 plates and measures 2-1/4" long and each plate is 1-1/4" square.

For testing, the machine was connected to 120vac through a GFCI protection device & an isolation transformer. Powering the rectifier is a step-down transformer, delivering 7.14 vac.

I've never studied such a rectifier before, so I'm quite unfamiliar with these. My questions are:

The voltage drops from 7.14 input to 1.9 output across this device. I'm guessing this is normal for such an item. Or, is something terribly amiss?

The output frequency is zero. How do these devices do such a fine job of rectification?

This question may seal the unit's fate- Every 20 or 30 seconds, it will make a faint 'Pop" sound and a tiny spark will be seen between a plate. The spark location varies from plate to plate. It also smells like rotten eggs when energized.
Is this rectifier doomed?

If it is doomed, is there any way to judge the current requirement for a replacement bridge rectifier circuit? The transformer has no markings on it. My only clues are the size of the transformer matches a modern 60 va unit.
The wiring is all 16 gauge. But, it is old, so who knows?

In the photos, the wire on the right end, plus the yellow bus bar near the center are the DC outputs. The red wires are AC input and enter near the center of the rectifier.

Thanks you for any ideas or thoughts you have on the rectifier & sizing a replacement!
Paul

Here's an off-topic side note- This device came with a lead bucket which served as the anode. It would be filled with an electrolyte (Modern times- Water & Sodium Carbonate). Can you imagine how much lead is leached into the water or fumes off with the hydrogen & oxygen? Scary!

 

P=ie
60 = i (7.14)
i = 8.4

 

Thanks #12.
I phrased my post confusingly. I don't know the va of the transformer. It is physically about the dimensions of a modern day 60va.

 

Just get a 25A, 50V, potted FWB and throw it in there and don't quibble about whether it's supposed to be 9 amps or 11 amps.

 

Use a 25/35Amp 200V potted type like these...

http://www.ebay.co.uk/itm/KBPC3502-...al_Components_Supplies_ET&hash=item43b9117d5a

 

Thanks Guys Very Much!
I appreciate your advice.
Paul

 

Use a 25/35Amp 200V potted type like these...

http://www.ebay.co.uk/itm/KBPC3502-...al_Components_Supplies_ET&hash=item43b9117d5a

It should be noted these get hot even at just 5 Amps.
You need a heatsink by all means + forced cooling to use the full rating.

 

Thanks for the heads-up about heat.
This machine looks like it was built for convection cooling, so adding a small muffin fan should be a simple task. The air will flow perfectly across all components.
Paul

 

Thanks for the heads-up about heat.
This machine looks like it was built for convection cooling, so adding a small muffin fan should be a simple task. The air will flow perfectly across all components.
Paul

You still may need a heatsink for the bridge rectifier.

I have used a Pentium II heatsink for a bridge rectifier, attached it with thermal grease and "No More Nails" Silicone compound. This is not regular installation sillicone. It has proven to have excellent heat durability, the bridge recitifer was operated for 3 months with the sink turning very hot at times.

 

Just try it. I've done this and found that the sheet metal I bolted the rectifier to was enough for 3-4A. Just try it. If it gets hot, add a fan.

 

Thanks #12!
I'll give it shot.
There surely is a lot of metal to suck up heat. The case is made of 280 sq inches of 1/4" thick plated steel (or maybe iron?). I can bolt the FWB right to an existing tapped hole in the case. Almost too simple.

I test ran it with a small lamp for a load just to see the convection current from the heat of the existing selenium rectifier & transformer. It really does flow nicely in the bottom & out of the slots above the components. Seems like a nice design.
Paul

 

ps, you can put heat sink compound between the rectifier block and the 1/4" steel, which seems well equipped to carry heat away!

 

Thanks for reminding me. I would have forgotten.

I use that in my trade & have a big quantity (that I forget to use).
Step One- Open Jar
Step Two- Get compound on new, expensive arc flash shirt & pants
Step Three- Be certain to step in some & track it into the work truck

Thanks Again!
Paul