Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

[SOLVED] can capacitor incur damage from beta isotopes

Status
Not open for further replies.
Z

Zak28

Advanced Member level 2
Joined
Aug 19, 2016
Messages
579
Helped
6
Reputation
12
Reaction score
6
Trophy points
18
Activity points
4,681
Recently tried to get a spark gap to break over using spark plug shortened to closer than 1mm with 390v by placing SR-90 and Po-210 in the vicinity of the gap. Then after a short duration the high voltage filter capacitor on the inexpensive boost 390v module was destroyed then flamed out, the can was propelled outwards with no safety vent functioning.

I didn't measure the 12v input current to module to determine if the isotopes caused the gap to break over but it seemed either isotopes caused emi noise in the module or the gap did infact break over. Could the isotopes induce a form of EMI or other noise which would damage the capacitors? The isotopes from www.spectrumtechniques.com and were at least 8 inches away from the module. Might replace the damaged capacitors to repeat this and measure input current to the module when isotopes are in vacinity to the gap.
 
Last edited:

Seems unlikely to me, I have done a fair bit of radiation testing
and never seen a discrete capacitor let go. However these are
generally not in high ripple current applications and I derate at
least 2X the expected applied voltage. But there is no way that
the beta flux from these samples is going to heat the capacitor
to the point of failure - they would have self heated noticeably
as a large portion of alpha or beta never make it out of the
source mass before stopping.

I think it's more likely that the ionization from the radioactive
material let you start a spark-gap arc easier, so as to then
put more ripple current through the converter's filter cap
(which in-the-moment is the only source of arc step-current)
and cook it by repeated I^2*R (boil the electrolyte and you
are done).

Might suggest you look for alternatives to, or supplement the
boost converter's output capacitor that will tolerate more
ripple current (we're not talking the ripple from the boost
supply, but the ripple from the spark's negative differential
resistance behavior when it's kicked off).
 
  • Like
Reactions: Zak28

    Z

    Zak28

    Points: 2
    Helpful Answer Positive Rating
dick_freebird said:
Seems unlikely to me, I have done a fair bit of radiation testing
and never seen a discrete capacitor let go. However these are
generally not in high ripple current applications and I derate at
least 2X the expected applied voltage. But there is no way that
the beta flux from these samples is going to heat the capacitor
to the point of failure - they would have self heated noticeably
as a large portion of alpha or beta never make it out of the
source mass before stopping.

I think it's more likely that the ionization from the radioactive
material let you start a spark-gap arc easier, so as to then
put more ripple current through the converter's filter cap
(which in-the-moment is the only source of arc step-current)
and cook it by repeated I^2*R (boil the electrolyte and you
are done).

Might suggest you look for alternatives to, or supplement the
boost converter's output capacitor that will tolerate more
ripple current (we're not talking the ripple from the boost
supply, but the ripple from the spark's negative differential
resistance behavior when it's kicked off).
Click to expand...

It seems you are absolutely correct in regards to ripple causing the destruction to the capacitor. The trouble remains finding that cap which flew out and cleaning the module of the remnants from the capacitor.

https://pasteboard.co/Id4fU2U.jpg https://pasteboard.co/Id4g2JG.jpg

The module was operating after the capacitors destruction as was evidenced by the transformer switching noise which incured after capacitor was destroyed. The spark plug has a 5k resistor can you explain how a gaps negative resistance increases ripple into the capacitor?
 

That certainly is an unusually inventive experiment you tried. However it's doubtful 390V can spark in ordinary air with help of nuclear radiation...
unless your strontium and polonium are strong enough to give you radiation poisoning.
Even my geiger counter needs a power supply more than 800V inside the GM tube containing inert gas.

Do you think the capacitor was perforated by emissions from your radioactive sample (strontium-90 and polonium)? How close was it?

Or do you think over voltage caused the capacitor to explode? I once caused a capacitor to shoot like a bullet to the ceiling, as s I inadvertently exposed it to 3 times its rated voltage. It took less than a second to happen.

With no load a boost converter's output voltage can soar higher and higher within a few cycles, unless its regulation immediately steps in to halt oscillations. Can you verify whether overvoltage, destroyed your output capacitor? Be sure to monitor output voltage next time.
 
  • Like
Reactions: Zak28

    Z

    Zak28

    Points: 2
    Helpful Answer Positive Rating
BradtheRad said:
...I once caused a capacitor to shoot like a bullet to the ceiling, as s I inadvertently exposed it to 3 times its rated voltage. It took less than a second to happen....
Click to expand...

I was testing safety mechanisms of several electrolytics by simply overvolting them in with reverse voltage including a few soviet electrolytics and it turns out the very small electrolytics' cylinder shoots off even from a reputable brand such as Lelon. The larger capacitors vent out in this case it appears the brand was of poor quality and cylinder flew off as would a rocket.

BradtheRad said:
...Or do you think over voltage caused the capacitor to explode? I once caused a capacitor to shoot like a bullet to the ceiling, as s I inadvertently exposed it to 3 times its rated voltage. It took less than a second to happen.
Click to expand...

I did measure far higher voltages than the module is supposed to support on occasion and it appears the capacitors were destroyed from overvoltage. I didn't know they need a load to not be damaged. Ceramics and large can film capacitors are likely far more dangerous than these small electrolytics. But there might have been some heating from ripple as I occasionally shorted the output while the device is powered in which case the transformer makes audible noise from large switching current. Its unlikely the isotopes did damage to capacitors since these capacitors have a rather thick cylinder to protect it from deforming or evaporating.
 
Last edited:

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top