400 volt capacitor how to know its leckage or damaged

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newone
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400 volt capacitor how to know its leckage or damaged

Post by newone » Fri Jan 20, 2006 1:00 am

400 volt capacitor how to know its leckage or damaged


one day my own digital satellite reciver not working

itry but not fix

i went to technican and he only change the 400 volt capacitor

my capacitor was like new one


my question is how to know its leckage


i have analog and digital meter

which is best for capacitor
new

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Chris Smith
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Re: 400 volt capacitor how to know its leckage or damaged

Post by Chris Smith » Fri Jan 20, 2006 3:20 pm

Charge the cap with a voltage.

Measure the voltage with any V meter for volts.

Watch it drain slowely, hopefully.

If it charges up, If it holds the charge for a given time based on the cap value, then its most likely ok.

However, if it acts like a dead short, wont charge, or doesnt hold the charge for any reasnoble amount of time, its most likely bad.

These are JUST the basics. Read op on caps, the web has plenty to impart with you.

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Edd
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Re: 400 volt capacitor how to know its leckage or damaged

Post by Edd » Sat Jan 21, 2006 1:41 am

Just these observation and assumptions:

The sole information supplied is a “400 volt capacitor”
Type of capacitor ???

“one day my own digital satellite reciver not working”

From that information, of it being “digital”, we can assume the equipment not being a very old unit , since old analog units can go back to the ‘80’s

“ went to technican and he only change the 400 volt capacitor”

I can only see a 400 volt capacitor rating being used in that receiver in two places.
One place would be for “X” and/or “Y” rated ceramic or poly capacitors used in the AC line input of the unit.
The second place would be as the raw DC filter electrolytic capacitor of a line powered supply that is to further feed into a switch mode power supply portion for current modern receivers. BUT in the order of only 250-300 volts would be the rating of that capacitor, should this be for 120 VAC line power operation. A 400 volt cap rating would suggest a 220VAC line supply. With your “neotion” info I might guesstimate a locale of either just east of Marseille or in the Shanghai China area…with the English sentence structuring and the “yuytutfg “ , I would heavily suspect the latter . Which I believe to be a 220/230 V service area.
If your receiver experienced one of the X Y capacitor failures, it typically would be apparent with a visual inspection or an ohmmage check. A bolt of lightning hit to the AC power line is the typical failure mode for those units.
Should that capacitor be an electrolytic type, I could only suggest a relative comparison between two like units.
Specifically, you said:

“my capacitor was like new one”

By that , I interpret that he returned to you the old capacitor unit that was in the set and that you couldn’t tell any difference between the old cap and the new unit Assumedly that old one looked as good as the new one , and also, that the whole receiver unit is probably not very old.
The way I see to confirm that would be to just check and see if both units acted the same in a like testing. (This is assuming that you have nothing more than your mentioned meters to perform testing with.)
In that case, you would initially take the “old” electrolytic capacitor and connect a jumper test clip lead across it to assure that it is totally discharged. Then take your analog meter, set to its 500VDC scale range, and connect its positive lead to a jumper test clip lead and the other end of that lead goes to the negative term of the electrolytic. Another jumper test clip is to be connected to the to be tested electrolytic capacitor to its positive terminal and its other end will go to the only source of a like voltage that you would have available to you, the positive terminal of the replaced electrolytic in the receiver. (Naturally, after the receiver housing has been opened for access.) Next you would observe the 50 VDC position on your meters scale.
Also view / locate the position of the negative terminal wire of the receivers new electrolytic. Lastly, have a watch at hand with a seconds timing capability.
To test :
This sequence will be done. Power up the receiver to have its raw DC power supply functioning. Observe the watch until it is at the minute changeover point, at that instant the loose meter negative lead is held onto the negative terminal of the receivers electrolytic while the analog meters pointer is observed flying up to the charge voltage level of the supply voltage. The pointer then will start reversing as the cap takes on its full charge with a progressively diminishing voltage shown. When the appointed voltage reference of 50 VDC is reached, check the timer and take note of the seconds elapsed for that charge to have been made, and log it down.
Now you are up to the moment of having to exchange the places of the “old” capacitor with the new one on the equipment.
Initially test to see if the replaced capacitor that you have is not showing a dead short with your ohmmeter in low ohms scale and placing the ohmmeters probes across the caps terminals. I certainly don’t expect it! Then you will see the like action of the meters pointer as the cap takes on its charge, but with the much lower voltage from the internal voltage supply of the meter. Considering that you have what seems to be a normal cap in its cap charging action then power down the receiver and wait and measure until the caps voltage has discharged down.
Then exchange the caps. Next power up the receiver and see if operation is normal.
If so, you might be wondering why that unit is working with a “bad” capacitor.
If it is inoperative , then you did have a bad cap and that is it. Otherwise, assuming that the unit instead, seemed to be working normal.
The procedure then would be then to hook up the pulled new electrolytic capacitor and test it in the same manner as the first one.
In that manner you would be comparing two like capacitors in their charge time….related to their capacitive value and somewhat in their leakage characteristics.
As far as a universal leakage formula for all electrolytics, that would be asking too much, as capacitor type, capacitance value, voltage levels, temperatures, and many other variables enter into being able to prescribe a precise leakage definition.
But, the comparative procedure above should let you evaluate two like units
Should you have found the charge timing of both units to that chosen 50 VDC reference level to have been alike , the meter could have been dropped on down to its lower ranges as the changing voltage approached them and eventually the meter will stabilize and quiver at a low voltage level. The capacitor of the two that will maintain the lowest voltage will be the one with the lowest internal leakage.
Considering that “old” capacitor is working now, the other possibility would be that the unit could have an intermittent inter connection problem in its wire lead to foil interconnection within the casing. Usually a flexing of the wire leads at its entry point into the casing will sometimes detect a bit of “looseness” in one lead, for that condition. Another test is to subject the unit to vibration with a firm tapping action to the case while observing output.
Another visible indication is loss of electrolyte around a leads seal, but that is accompanied by a capacitance loss and a case temperature increase.
Lastly is one thing that is not be expected in an electrolytic filters use at 50/60~ line freq is ESR. That would be more apt to be found deeper into the power supply in the Switch Mode Power Supply portion operating in the typical 20-85Khz switching speed ranges. All of the electrolytics on that supply transformers secondary are subject to that stressing. Also there might be one or two low capacitance start up / feedback electrolytics at a high voltage rating used in the front side of that SMP supply. I could only assume that, if you came back with precise specifications info on the mystery “400 Volt capacitor”.

On the topic of leakage on non electrolytics, my like test procedure is to have a DC power source available for the max voltage to be evaluated and then go through the same procedure with an analog meter and switching it on down to lower scales as they are approached until the lowest one is reached If I happen to have a higher voltage capacitor that is to be used in a tube grid circuit , I am wanting to see no leakage whatever. That is also what one will experience on just about all capacitors except the old wax sealed (cracked) paper capacitors, where moisture creepage enters. Also high voltage ceramic or mica units that have experienced a dielectric voltage punch through path.
The analog metering is my choice in these applications, by virtue of a changing voltage needing to be continually observed.
Had there been a need to take a final precise stable reading the digital would have been the choice…..or setting an adjustment to a precise 14.1414 VDC.

I commend you on the English second language effort that you are confronted with in your learning experiences…..with your English--- ???? dictionary and its translation. It is sure to get a work out on all of this text.
Alas, I could not framework technology into “See the boy run” simplicity.


73's de Edd
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<small>[ January 21, 2006, 02:38 AM: Message edited by: Edd Whatley ]</small>

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