I just finished buiding an Aleph 0. For the power supply I uesd Hitachi 22.000/100V industrial grade elco's.
The power supply connections were tripple checked and then again checked by a friend of mine. All was wired correctly and the amp fired up and working like a dream!
After about 20 hours of operation, one of the caps exploded. The whole plate with screw terminals came off the can.
So now I'm really puzzeled as to what happened here. I verified all connections again OK. I can not see or measure any problem with the amplifiers. After I cleaned the channel with the blown cap, I hooked it up to the other channels power supply and it again was working.
The problem is that I'm still hessitating to put a new cap in and operate in in my living room when I do not know why this cap exploded.
Suggestions...Anyone?
Thanks.
The power supply connections were tripple checked and then again checked by a friend of mine. All was wired correctly and the amp fired up and working like a dream!
After about 20 hours of operation, one of the caps exploded. The whole plate with screw terminals came off the can.
So now I'm really puzzeled as to what happened here. I verified all connections again OK. I can not see or measure any problem with the amplifiers. After I cleaned the channel with the blown cap, I hooked it up to the other channels power supply and it again was working.
The problem is that I'm still hessitating to put a new cap in and operate in in my living room when I do not know why this cap exploded.
Suggestions...Anyone?
Thanks.
What voltage do you have across them?, usual causes for 'exploding' are connected wrong way round (unlikely as it wouldn't last 20 seconds, never mind 20 hours), or too high a voltage across them. Older electrolytics had a little reserve in their voltage rating, but modern ones are VERY narrowly specified, if you put 101V across a 100V electrolytic, even for a short time, it may well blow.
I may have an explanation if the caps were NOS, they might have need "reforming" before use.
Reforming elco is putting a current controlled tension to the cap, to rebuild the oxyde isolation of the aluminium foil inside. Because this isolation tends to dissolve into the electrolyte as time goes by.
The process is more sensitive with higher operating voltages.
When you use directly an old elco, losses are hifh and the cap heats up. When the electrolyte boils, pression builds up to the "explosion".
Do you intend to use elco from the same source? If yes, just power le power supply without load (amp) with a 2-5W 1k resistor inserted after the bridge and before the caps. If the current is low (less that, say 1V accross the resistor, that makes 1mA), it is OK.
hope this help.
Reforming elco is putting a current controlled tension to the cap, to rebuild the oxyde isolation of the aluminium foil inside. Because this isolation tends to dissolve into the electrolyte as time goes by.
The process is more sensitive with higher operating voltages.
When you use directly an old elco, losses are hifh and the cap heats up. When the electrolyte boils, pression builds up to the "explosion".
Do you intend to use elco from the same source? If yes, just power le power supply without load (amp) with a 2-5W 1k resistor inserted after the bridge and before the caps. If the current is low (less that, say 1V accross the resistor, that makes 1mA), it is OK.
hope this help.
Hello,
Be sure to disconnect all the caps and reform them all to be sure. The last post from France is right i think. Even if your working voltage is very far from the one stated on the cap it can get you into trouble after they have been on the shelf for several years. I remember that somebody told me that some surplus caps are coming from companies that are not allowed to use them anymore after they have been on the shelf more than 5 years just incase an accident will happen and the insurance will start looking for a cause greetings, Eduard
Be sure to disconnect all the caps and reform them all to be sure. The last post from France is right i think. Even if your working voltage is very far from the one stated on the cap it can get you into trouble after they have been on the shelf for several years. I remember that somebody told me that some surplus caps are coming from companies that are not allowed to use them anymore after they have been on the shelf more than 5 years just incase an accident will happen and the insurance will start looking for a cause greetings, Eduard
Forgot to mention 
If the losses are high, just let it on.
Check some time to time the tension across the resistor, it should lower little by little (may need few hours, even days).
If there is a short in the cap, its over, just throw it away.
Always stay around, il case of failure, if you have to leave, shut it down, all reforming already done is not lost.
If the losses are high, just let it on.
Check some time to time the tension across the resistor, it should lower little by little (may need few hours, even days).
If there is a short in the cap, its over, just throw it away.
Always stay around, il case of failure, if you have to leave, shut it down, all reforming already done is not lost.
Tarasque said:
I understand that the exploding of caps is due to heat generation,
and the heat generation is coming from three reasons:
1. Over-voltage
The over-voltage application provides excessive leakage current
across the cap. Then power dissipation happens according to I(leak) x V.
2. High ripple current
The high ripple current creates the power dissipation according to
Ir x Ir x ESR.
3. Reverse bias
The reverse bias creates heat due to the internal chemical reaction.
I guess when they made the fake, they did wrong printing of the
polarity indication on the plastic cover...
The most probable reason could be item 3...
I can't be 100% sure of it tho...
I think I found the reason for the problem. I looked at reverse polarity by using a power supply with current limiter and connect the cap both way. This was not the problem
I checked the ripple current in the application and found that this is within spec as well.
The most interesting thing was seen while reforming the caps @ 95% of the voltage rating and charging them with a constant current. the current should drop when the max voltage is reached. Some caps however would show an increase of the leakage current after initial drop.
lowering the max voltage to 85% wold not show the increasing leakage anymore.
As the power supply where the cap exploded is running on 90% of the voltage rating, I suspect that there was one weaker cap that exploded as a result of elivated operating temperature, increasing leakage, and elevated stress due to ripple current.
I checked the ripple current in the application and found that this is within spec as well.
The most interesting thing was seen while reforming the caps @ 95% of the voltage rating and charging them with a constant current. the current should drop when the max voltage is reached. Some caps however would show an increase of the leakage current after initial drop.
lowering the max voltage to 85% wold not show the increasing leakage anymore.
As the power supply where the cap exploded is running on 90% of the voltage rating, I suspect that there was one weaker cap that exploded as a result of elivated operating temperature, increasing leakage, and elevated stress due to ripple current.
I finally figured out what lead to the explosion of teh cap.
There were a couple of issues:
1. Nigel was thinking across the correct lines. As these caps are now confirmed as fake Hitachi's and are Chineese clones, the voltage handling of these ones is not sufficient for my application. The idle voltage of teh PS ws 99,3V and only 1 in 3 of the fake caps could take this voltage.
When looking at the leakage current (DC source) I found that the current exponentially increases when the maximum voltage FOR THAT CAP is passed. So in my case 2 out of 3 caps were below spec. and showed this behaviour above 89V.
2. The needed to be reformed. Having omitted this step added to the dissipation of the cap and is lowering the limit.
So hereby a warning when you buy Hitachi caps, make sure that they are produced by Hitachi.
Also when you use caps close to their limit, it is advised to test if the caps are fitted for the application. This is especially true for overstock caps.
There were a couple of issues:
1. Nigel was thinking across the correct lines. As these caps are now confirmed as fake Hitachi's and are Chineese clones, the voltage handling of these ones is not sufficient for my application. The idle voltage of teh PS ws 99,3V and only 1 in 3 of the fake caps could take this voltage.
When looking at the leakage current (DC source) I found that the current exponentially increases when the maximum voltage FOR THAT CAP is passed. So in my case 2 out of 3 caps were below spec. and showed this behaviour above 89V.
2. The needed to be reformed. Having omitted this step added to the dissipation of the cap and is lowering the limit.
So hereby a warning when you buy Hitachi caps, make sure that they are produced by Hitachi.
Also when you use caps close to their limit, it is advised to test if the caps are fitted for the application. This is especially true for overstock caps.
Tarasque,
By reforming gently (I mean current controlled and low current), you can slowy increase the maximum admissible voltage. I've done it with 450VDC rated caps, reformed to 530VDC. But tube supply is much lower current, so dissipation by ripple current is by far, not the same.
So, you replaced the fake caps with what caps?
Can we know your fake source, in case it is on eBay? Just to avoid it.
Cheers
Trung
By reforming gently (I mean current controlled and low current), you can slowy increase the maximum admissible voltage. I've done it with 450VDC rated caps, reformed to 530VDC. But tube supply is much lower current, so dissipation by ripple current is by far, not the same.
So, you replaced the fake caps with what caps?
Can we know your fake source, in case it is on eBay? Just to avoid it.
Cheers
Trung
Hi Trung,
I'm concidering the EPCOS caps.
In my view the source is not important, it should be enough to know that there are fake Hitachi's out there. I will place a pic of the print when I have time.
I use these caps in a Nikko Alpha 2000 amplifier (2x330W)
The original Nippon Chemicon caps can not be found anywhere.
When you know a source for 15.000/100V caps, let me know.
I still have to replace some.
I'm concidering the EPCOS caps.
In my view the source is not important, it should be enough to know that there are fake Hitachi's out there. I will place a pic of the print when I have time.
I use these caps in a Nikko Alpha 2000 amplifier (2x330W)
The original Nippon Chemicon caps can not be found anywhere.
When you know a source for 15.000/100V caps, let me know.
I still have to replace some.
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