Forming Phase Linear Power Supply Bulk Capacitors

Gepetto

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#1
Make sure you get quality caps when you replace them.

BE CAREFUL. THERE IS A VERY LARGE ENERGY HAZARD IN THESE CHARGED CAPS SO BE SURE TO OBSERVE PROPER SAFETY PRECAUTIONS!

Here is what I recommend once you get your new caps to "form" them properly before installation.

1. Using your PL700 frame power supply (unless you have a 100V DC power supply, unlikely), run a ground jumper clip from the copper ground bus bar between the 2 bulk caps in your amp to the minus terminal of your new cap that you intend to install.

2. Next using a jumper with a 2K ohm 2W resistor in series connect one end to the plus rail inside the Phase Linear amp power supply. Attach the other end to the positive terminal of your new cap that you intend to install.

3. Hook your DMM across the 2K ohm resistor with the positive DMM lead at the power supply end of the resistor and the negative DMM lead on the end of the resistor that goes to the cap being formed.

4. Apply power to the Phase Linear power supply.

5. As the cap being formed charges up you will see the voltage across the 2K ohm resistor start at a very high voltage and then gradually decrease as the cap reaches full charge.

6. Allow it to "form" for a long time. I run the caps that I sell for the PL400 for 2 days prior to shipping.

7. Once your forming time is complete, measure the leakage current for the caps at voltage by dividing the voltage observed across the 2K ohm resistor by the resistance (2000) to get the leakage current in microamps. Accept caps that have less than 50 uA of leakage at rated voltage and reject those that do not. 50uA translates to 100 mV across the resistor. You should see the voltage plateau at this very low level and stay there for many hours and only fluctuate a few millivolts, this indicates that the forming process has worked. If you see the current bottom out and then start rising again, this is generally not a good sign and you should watch this carefully.

8. Before removing the caps from forming, be sure to discharge them first by turning off the PL frame and letting the cap bleed down through the 2K ohm resistor. This takes a long time. Measure and check for near zero voltage on the cap being formed before you disconnect the test leads.

9. MOST OF ALL, BE CAREFUL. THERE IS A VERY LARGE ENERGY HAZARD IN THESE CHARGED CAPS SO BE SURE TO OBSERVE PROPER SAFETY PRECAUTIONS!

10. If all these steps check out, repeat for the next cap.

11. Once done, install the caps.


Forming is a process of building up the aluminum oxide coating on the capacitor foil inside the capacitor "jelly roll". The oxide acts as an additional insulator against capacitor breakdown and leakage. It is an electrochemical process that takes place when you do this. Once done and put into service, the capacitor will settle in at the voltage that it typically sees in the final application and adjust its oxide layer to suit. Caps that have been in storage a long time, especially at elevated temperatures tend to lose some of this oxide coating on the foil and leak more. These caps may take a longer time to properly form. Most recover fine but some do not. Those that do not should not be used.
 

laatsch55

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I thought cap forming was BS except for shiny new ones???? Thanks Joe. Nice procedure.
 

laatsch55

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unless you have a 100V DC power supply..............That's what variacs and BR's are for, when they are not bringing up amps.
 

Gepetto

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Hi Lee
It is a method of assuring that you have good, low leakage caps as well as bringing them up the right way the first time. All the major manufacturers have procedures hidden deep in their archives that describe this procedure in this or slightly different terms. Problem is that you really have to look hard to find them. Since this community uses so many large electrolytic caps, thought I would bring the data into a more accessible place.
 

mlucitt

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Joe,
We did this type of forming when we replaced our 80 VDC 35,000 mF caps in our SONAR power supply (and we had 180 of them) on the Navy ship. We did have a 100 VDC bench PS but your method is just as good using the amp as a PS. In step 4, do you reccomend the Variac to bring up power slowly?

Lee, how come your resistor is in parallel and not in series with the red wire?
 

laatsch55

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The resistor is waiting for a cap to form. Those are stress tested caps.

Also Joe , do you have a procedure for checking ripple with a scope??
 

orange

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That's pretty good reading there, Przem!
 

NavLinear

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Thanks Przem - some good stuff to add to Joe's procedures. I may have said this before but - nice rack.

Steven - How'd you get the titty bumpers to stick?
 

orange

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Not my photo, it seems to be making the rounds on the 'net and I found her being employed by a seller on eBay Australia.

THOSE are 45 adaptors! If you look at the lower left corner you'll see she was part of a magazine cover (see the DirecTV logo)?
 

NavLinear

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And here I was waiting for a cool story about how you got 'em to stick! Never seen a 45 that big though.
 

laatsch55

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Hi Lee,
When I was working on my PL700II I came across this set of manuals – worth of reading…
Przem

P.S.
Upload File Manager here and Mac OS X don't work along too well ;-)
Thanks Przem!! Glad to see you posting!!
 

orange

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It's a cut-out magazine picture some bloke either sized or was lucky enough to match her bosom...those are standard sized adapters.

Gone now.
 

NavLinear

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Just yanking your chain Steven. I liked her! Hope you didn't change your avatar because of my smart ass comments!
 

WOPL Sniffer

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Hi Lee,
When I was working on my PL700II I came across this set of manuals – worth of reading…
Przem

P.S.
Upload File Manager here and Mac OS X don't work along too well ;-)
This is an excerpt from that Mil-C document which isn't very ancient when compared to the rest of our Military References. It would seem, from the military at least, if you are using NEW capacitors, reforming is not necessary. Just my take on the document provided.

6.4 Reforming of dielectric film. Caution should be exercised in using capacitors which have had an idle shelf life

of more than 4 years. Users should refer to
MIL-HDBK-1131 “Storage Shelf Life and Reforming Procedures for

Aluminum Electrolytic Fixed Capacitors†for inspection and reforming procedures.




4.3 Inspection frequency. MIL-C-62 and non-military grade - At the end of 6 years, or 4 years from


the date of manufacture, depending upon storage conditions (see 4.2) or 3 years from the last inspection


period, capacitors should be inspected (see 4.6) to determine if the dc leakage requirements of the

applicable procurement document can be met






5.2.3 Capacitor reforming time. The leakage current which an electrolytic capacitor will pass increases


with temperature rise. Heat is generated in the electrolytic capacitor during the reforming process.


Accordingly, leakage current measurements made immediately after reforming will be higher than at


ambient temperature. If leakage current measurements taken immediately after reforming are within


specified limits, the capacitor should be considered acceptable. The capacitors should be reformed for a

maximum period of 1 hour or for a shorter period where the leakage current measurements fall within


specified limits. Where the limits are still exceeded after the 1-hour period, the capacitors should be


removed from the voltage source, held for approximately 24 hours, and the leakage test performed again.




 

Gepetto

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This is an excerpt from that Mil-C document which isn't very ancient when compared to the rest of our Military References. It would seem, from the military at least, if you are using NEW capacitors, reforming is not necessary. Just my take on the document provided.

6.4 Reforming of dielectric film. Caution should be exercised in using capacitors which have had an idle shelf life

of more than 4 years. Users should refer to
MIL-HDBK-1131 “Storage Shelf Life and Reforming Procedures for

Aluminum Electrolytic Fixed Capacitors†for inspection and reforming procedures.




4.3 Inspection frequency. MIL-C-62 and non-military grade - At the end of 6 years, or 4 years from


the date of manufacture, depending upon storage conditions (see 4.2) or 3 years from the last inspection


period, capacitors should be inspected (see 4.6) to determine if the dc leakage requirements of the

applicable procurement document can be met






5.2.3 Capacitor reforming time. The leakage current which an electrolytic capacitor will pass increases


with temperature rise. Heat is generated in the electrolytic capacitor during the reforming process.


Accordingly, leakage current measurements made immediately after reforming will be higher than at


ambient temperature. If leakage current measurements taken immediately after reforming are within


specified limits, the capacitor should be considered acceptable. The capacitors should be reformed for a

maximum period of 1 hour or for a shorter period where the leakage current measurements fall within


specified limits. Where the limits are still exceeded after the 1-hour period, the capacitors should be


removed from the voltage source, held for approximately 24 hours, and the leakage test performed again.




correct not required on brand new caps but never does any harm
 
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