Electronics > Beginners

which type of capacitor for pulsed discharge

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T3sl4co1l:
:palm: That's literally half the application. Can you please tell everything?

Tim

tautech:

--- Quote from: LaserTazerPhaser on April 04, 2019, 03:43:33 am ---
--- Quote from: tautech on April 03, 2019, 01:08:32 pm ---
--- Quote from: LaserTazerPhaser on April 03, 2019, 12:58:55 pm ---Are there any motor run caps above 100uF?
--- End quote ---
Never seen one more than 60 uF.

--- Quote ---Only the noname brands seem to go above 100uf which can be just motor start listed as motor run.

--- End quote ---
Yes and if you use a Start one in a Run application they let out the magic smoke.  :scared:
Don't ask me how I know.  :palm:

For just the few $ they are I'd try some of the Chinese Run caps and see how they perform. If they get too warm you might have to use proper Pulse rated caps at more cost.
I looked at getting some a while back for a sick electric fence I scored but the cost was something like $30 ea IIRC and I needed a couple.
Found a crowd in NZ that manufactured them for the few electric fence manufacturers we have here that export worldwide.

--- End quote ---

Was it a no name brand cap? Those probably have inadequate or no safety measures implemented.

--- End quote ---
The one I smoked was a start cap....they have a short duty cycle and the motor centrifugal switch removes them from circuit after a second for two at the most unlike motor run caps that are connected to mains while the motor is running.
In short (pun intended) a motor start rated cap is not rated for continuous connection like a run cap.
They may both look the same but are for different purposes.

Gyro:
Typically, Motor start capacitors are 'thermally under-rated' bipolar electrolytics (to get the high capacitance) whereas Motor Run are metallized film, usually Polypropylene these days.

LaserTazerPhaser:

--- Quote from: tautech on April 04, 2019, 07:12:11 am ---
--- Quote from: LaserTazerPhaser on April 04, 2019, 03:43:33 am ---
--- Quote from: tautech on April 03, 2019, 01:08:32 pm ---
--- Quote from: LaserTazerPhaser on April 03, 2019, 12:58:55 pm ---Are there any motor run caps above 100uF?
--- End quote ---
Never seen one more than 60 uF.

--- Quote ---Only the noname brands seem to go above 100uf which can be just motor start listed as motor run.

--- End quote ---
Yes and if you use a Start one in a Run application they let out the magic smoke.  :scared:
Don't ask me how I know.  :palm:

For just the few $ they are I'd try some of the Chinese Run caps and see how they perform. If they get too warm you might have to use proper Pulse rated caps at more cost.
I looked at getting some a while back for a sick electric fence I scored but the cost was something like $30 ea IIRC and I needed a couple.
Found a crowd in NZ that manufactured them for the few electric fence manufacturers we have here that export worldwide.

--- End quote ---

Was it a no name brand cap? Those probably have inadequate or no safety measures implemented.

--- End quote ---
The one I smoked was a start cap....they have a short duty cycle and the motor centrifugal switch removes them from circuit after a second for two at the most unlike motor run caps that are connected to mains while the motor is running.
In short (pun intended) a motor start rated cap is not rated for continuous connection like a run cap.
They may both look the same but are for different purposes.

--- End quote ---

You didnt mention the capacitor branding. Maybe epcos, kemet, avx or some other brandname makes entirely film wound start caps for long service life and low disintegration rates.


--- Quote from: T3sl4co1l on April 04, 2019, 05:52:12 am ---:palm: That's literally half the application. Can you please tell everything?

Tim

--- End quote ---

I suppose I didn't include load impedance which varies with thermals from 0.35R - 0.45R aside from that not sure what else you were looking for. Capacitor will be discharged into this load which is nearly identical as placing a screwdriver across its terminals due to the low impedance of the load. But the load wont be spot welded as a screwdriver would be since its attached to a large barrier terminal block.

StillTrying:

--- Quote from: LaserTazerPhaser on April 04, 2019, 03:43:33 am ---I was considering which capacitor is ideally suited for https://www.analog.com/en/products/lt3751.html massively powerful cap charger set to with 3.5amps peak 1.2amps rms at the secondary (shunt set to 9.8mR) it will run for hours and electrolytics might have disfavorable features for this application in which they cease to perform as a capacitor and in an ideal situation they have adequate safetey measures implemented. Its actually far more than 0.74Hz mentioned earlier with the 9.8mR shunt is nearly 1.9607Hz which puts even more of a load onto the capacitor. I just need >300v >32j per discharge cycle.

--- End quote ---

A constant 1.2A charges 1000uF to 300v in 250ms, with only ~144mW dissipated if the ESR is 0.1R. Even at 2Hz it's less than 100mW average in the cap. so I don't think you need to worry too much about the cap dissipation during charging, just the discharging. :)

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