# Chroming Rectifiers



## piperunner (Aug 22, 2009)

Well i guess this is for electro plating check the input what ever you need 
480 volts 3 phase AC power or single phase ?
Your rectifier must have its own transformer built in yes no ?

Is output 3 ph or single phase ?

I see at least 125 kw just a guess on the input for test power if single phase ?

You need a meter thats high freq to test like a fluke there good up to 400 hz.

Open it up check wiring and look at the caps for leaks cracks inside look at the rectifier diodes look at the buss inside clean it .

With out seeing is the unit ready to turn on you tell me go with 3 ph or 1ph 480 volt and you do have the correct input feeder for this ?

Just check it with a dummy load bank DC power is DC power nothing special about it check your DC coming out off rectifier first . Yes use a scope on the DC to see output is clean this will check your freq also .

Then check your SCR output DC 3/1 phase. Load it up 
a little at a time if it doesnt blow your good check rotation if its not in the rotation or out of sync whats the output 3 phase good your done . If is single phase then just put the meter on the DC output .

One thing your meter will read a lot higher on the DC buss so you may see 550 plus volts dont flip out its fine. 
Check freq what ever cycles 50 cps cps125 cps 60 cps 300 cps 400 cps 35 cps or what ever you need run it up or down while its loaded .

Show us the unit put up a photo nameplate some info . 

And be carefull inside after its off its still has power in the rectifier you say 10k amps thats normal for plating .


----------



## l0sts0ul (May 7, 2011)

piperunner said:


> Well i guess this is for electro plating check the input what ever you need
> 480 volts 3 phase AC power or single phase ?
> Your rectifier must have its own transformer built in yes no ?
> 
> ...


Ok, here are some answers I know so far. Input power is 480vac 3phase. Service is 600v, I have to install a 480v service to supply the equipment. 

Out put would be single phase 12vdc. ( I'm assuming single phase because there is only one set of buss bars coming off the unit and hey aren't separated. Into groups. 

I was going to isolate and test the caps ( but I have no idea what the rating is because the label is non existent. 

I would have to rent a load bank as I don't have one. 

These units are extremely old, but due to the lack of moving parts, I have some faith they are acceptable for use.


----------



## JRaef (Mar 23, 2009)

l0sts0ul said:


> Out put would be single phase 12vdc. ( I'm assuming single phase because there is only one set of buss bars coming off the unit and hey aren't separated. Into groups.


Ummm... DC means there are no "phases".



> I was going to isolate and test the caps ( but I have no idea what the rating is because the label is non existent.


Not sure what the caps would be for, it will depend on whether they are on the AC side or the DC side. On the AC side they may have been PFC caps because of the inductive transformer load. if on the DC side they may have been smoothing caps for the DC ripple from the rectifier, although ripple current on a resistive heater element is rarely a problem. But either way if the unit has been sitting somewhere unused and un-powered for more than a year, chances are the caps are bad now. If so, you might be able to rescue them by doing what's called a "reforming" procedure. If you Google 'capacitor reforming" you will see various instructions on doing it. 



> I would have to rent a load bank as I don't have one.


May not be necessary to test it at full load, at least not for basic functionality. Most likely the design is that the 480 goes into the SCR controller, which varies the voltage. That goes into another transformer that takes the variable 0-480V down to something like 0-10VAC, but 48X the current. That then goes into a rectifier bridge to give you DC output, which goes to the heating elements. So basic ohm's law applies, which means if the unit is capable of 10,000A at 12VDC, the resistance of the heater elements is 12/10,000 = 1.2 milliohms. If you put in a 40W 12V light bulb (like from an RV store) which is 36ohms, that will test whether or not the control works if you can safely vary the intensity of the bulb, but without drawing any real current. The only thing more that loading it to 10,000A would do is to stress test the power devices, but really if the SCRs are shorted, the low power test will show that.



> These units are extremely old, but due to the lack of moving parts, I have some faith they are acceptable for use.


Again, it will depend on the caps more than anything el;se, and without knowing why they are there, it's hard to say.


----------



## l0sts0ul (May 7, 2011)

JRaef said:


> Ummm... DC means there are no "phases".
> 
> Yes, you are right, I saw that after I submitted and forgot to delete it lol. Thanks
> 
> ...


Sigh, iPads suck


----------



## John (Jan 22, 2007)

A couple things you need to know.the output needs to be as close to to battery DC as possible. Chrome plating is real fussy and will not plate well if there is any AC present in the DC output. The caps are for removing any ripple in the DC and you may need a choke as well.
It would be best to hook them up somewhere where you have 480 V and test the output with a scope and/or quality DMM. Check for both AC and DC on the output side with the DMM. This will save you the PITA of installing them and then find out they are no good
If there is any corrosion on the electronics or electrical, it will need to be cleaned up an checked. Plating and corrosion go hand in hand and it is a constant problem.


----------



## John (Jan 22, 2007)

Here is a DC plating choke.......it was about 10 years old at the time of the picture. 
When you are dealing with any kind of plating equipment...you can expect corrosion. 
View attachment 21410


----------



## JRaef (Mar 23, 2009)

John said:


> A couple things you need to know.the output needs to be as close to to battery DC as possible. Chrome plating is real fussy and will not plate well if there is any AC present in the DC output. The caps are for removing any ripple in the DC and you may need a choke as well.
> It would be best to hook them up somewhere where you have 480 V and test the output with a scope and/or quality DMM. Check for both AC and DC on the output side with the DMM. This will save you the PITA of installing them and then find out they are no good
> If there is any corrosion on the electronics or electrical, it will need to be cleaned up an checked. Plating and corrosion go hand in hand and it is a constant problem.


Well that explains the caps then, good info. :thumbsup:
I have no experience with plating systems, didn't know ripple was such an issue.


----------



## John (Jan 22, 2007)

Here you go.....


View attachment 21432


----------



## l0sts0ul (May 7, 2011)

Thank you. Very much


----------



## Tom45acp (Sep 6, 2011)

A quick test I use on my customers plating rectifiers is to measure the ripple frequency on the DC bus. Six SCR's translate to 360 Hz if all of them are working. You would have to disconnect the filter capacitors to do this test.

The rectifiers I work on do not have capacitors, the ripple does not seem to affect the quality. But if one of the SCR's is shorted & letting AC through, you can sure see it on the finished product.


----------



## l0sts0ul (May 7, 2011)

if the %ripple listed on the nameplated is 5%, its safe to assume the unit has the capacitors on the DC side right? 

would you recommend PFC for an install of approximately 400A @ 600V? keeping in mind the main transformer is only capable of about 500A @ 600v. So, im concerned about the power quality as well.


----------



## l0sts0ul (May 7, 2011)

Also, in calculating the branch cct conductors, fusing and disconnect sizes, should I just follow the 125% rules (motors for example) or is nameplate ratings fine... I realize there is a transformer inside, but its stepping down, and I believe quality would be affected more than current draw. I have also considered PFC could reduce current draw, but they are listing the PF at 0.9 already on a couple of the units... 

also, there is 5 or 6 rectifiers ranging in size from 2000ADC to 10000A DC. I have heard before more of the smaller units are usually used for stripping.


----------

