Cap Dump Circuit

[Mario]

Hi Mike,

I've built various cap dump circuits over the last years, even with a perfectly driven fet by a fet driver hearing the click is normal. The sharper (faster) the fet turns on and off the louder it gets.
There can be cases where a click can come from a bad connection, a wire that's not connected well. But if everything is solid this is what I've found:

If you dump low capacities at low voltages you won't hear anything, but if you dump small capacity at high voltage, or very large capacity (talking 60'000uF up or so) even at low voltages you will hear the click, especially if your ride/fall times are in the nanoseconds range. With very large capacities you can hear the click through the wire and you can also feel it physically by holding the wire.

hope this helps

regards,
Mario

[stargate22]

Too many 'fets...

(1 or 2) 'fets, 1k from source to base ( each ) 1k to base ( each ) should get ya in the ball park....

...unless yer pulsing "Giga-Amps"

No two 'fets are exactly the same lab/spec and can work out of sinc with each other , thus work against each other.

J. Bedini talked about this in matching transistors, however what's bad for the "goose" can be the same for the "gander".

Also, ( 1 ) 'fet should more than handle what you are doing w/sink. If not, increase the 'fets "wattage" handling capability.

You shouldn't be hearing any sound at if firing correctly...

750 watts will run cool...$$$$

K.I.S.S. formula - "Keep..It..Simple...Stupid.

[Quigon10101]

In my professional opinion, that red bunny needs to get laid = problem solved.

[BroMikey]

Mosfet Firing Circuit

Hi Mike interesting. Can you please post a schematic of this?
Thanks.

Here is the rest of the circuit with the voltages.



Thank you for your reply.

Mike

[BroMikey]

Trigger Circuit

Hello Mike,

Just a simple question...are you using a dedicated resistor for each FET base besides the main resistor from signal out to base (you are saying you have a 160 Ohms one, and assuming that's the one from signal to base)?

When you are adding FET's in parallel, you must add also parallel resistors for each one you add as is provided to the first one.

A graphic of what you have would help as well...


Regards


Ufopolitics

Thanks for your reply to both UFO and Guruji

Here is my fun diagram of the trigger portion at 15vdc. I have not shown the negative of the cap going in and out at up to 90vdc.

I think I need to add resistance by putting a 5k pot after the plunger and just dial it up and down til she fires on the greatest amount of resistance?



Thank you for your kind reply.

Best regards, Mike

[Ufopolitics]

Hello Mikey

Hello Group Members

I need help. I am ganging up mosfet's in parallel and as I do the resistance drops across the bases I think. I am in the testing stage and when i dump the caps using the mosfet's I hear a tick each trigging. If I stay low at 12vdc it makes the tick sound more quietly and then for 30v dumps it is more audible.

Then the mosfet's short across, so I think my base resistance needs to go higher so I can not hear them dump .

It is a simple circuit with 160 ohms in series with the base leg plus a 10k across the source and base.

That's it then I throw 15vdc on it from a regulator and the bases all open.

I have 6 in parallel and I think with one the resistance is fine then with 6 it changes some. 6 in parallel must be lowering the resistance to the point I am going to need more to stop this TICK sound with every dump.

I am using a IRFP250 and I did not use a diode across the Drain and Source yet so maybe?

I will be done soon either way. Anyone who is an actual hands on guy and not just a arm chair scientist I welcome.

Thank you for your support.

Mike

Hello Mike,

Just a simple question...are you using a dedicated resistor for each FET base besides the main resistor from signal out to base (you are saying you have a 160 Ohms one, and assuming that's the one from signal to base)?

When you are adding FET's in parallel, you must add also parallel resistors for each one you add as is provided to the first one.

A graphic of what you have would help as well...


Regards


Ufopolitics

[Guruji]

Hello Group Members

I need help. I am ganging up mosfet's in parallel and as I do the resistance drops across the bases I think. I am in the testing stage and when i dump the caps using the mosfet's I hear a tick each trigging. If I stay low at 12vdc it makes the tick sound more quietly and then for 30v dumps it is more audible.

Then the mosfet's short across, so I think my base resistance needs to go higher so I can not hear them dump .

It is a simple circuit with 160 ohms in series with the base leg plus a 10k across the source and base.

That's it then I throw 15vdc on it from a regulator and the bases all open.

I have 6 in parallel and I think with one the resistance is fine then with 6 it changes some. 6 in parallel must be lowering the resistance to the point I am going to need more to stop this TICK sound with every dump.

I am using a IRFP250 and I did not use a diode across the Drain and Source yet so maybe?

I will be done soon either way. Anyone who is an actual hands on guy and not just a arm chair scientist I welcome.

Thank you for your support.

Mike

Hi Mike interesting. Can you please post a schematic of this?
Thanks.

[BroMikey]

Hello Group Members

I need help. I am ganging up mosfet's in parallel and as I do the resistance drops across the bases I think. I am in the testing stage and when i dump the caps using the mosfet's I hear a tick each trigging. If I stay low at 12vdc it makes the tick sound more quietly and then for 30v dumps it is more audible.

Then the mosfet's short across, so I think my base resistance needs to go higher so I can not hear them dump .

It is a simple circuit with 160 ohms in series with the base leg plus a 10k across the source and base.

That's it then I throw 15vdc on it from a regulator and the bases all open.

I have 6 in parallel and I think with one the resistance is fine then with 6 it changes some. 6 in parallel must be lowering the resistance to the point I am going to need more to stop this TICK sound with every dump.

I am using a IRFP250 and I did not use a diode across the Drain and Source yet so maybe?

I will be done soon either way. Anyone who is an actual hands on guy and not just a arm chair scientist I welcome.

Thank you for your support.

Mike