Cap Dump Circuit

[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

[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.

[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

[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

[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

[Quigon10101]

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

[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.

[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

[BroMikey]

High Regards

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

Thanks Mario

With high regards i am glad to hear these words, very deep into your work AAA? obviously you are and all of your words make perfect sense.

I failed to include other info such as 80,000 uf 250vdc caps charging up to 90vdc.

Also the circuit that controls dump down voltage needed more resistance in the bases at 16K each. Just finished testing this. What happened was this is my first time using mosfet's for a dump so large and I trusted others who told me 200 ohms.

When I decided that the diagram I had was wrong my fets were toast so I started with 20k and nothing got through then 10k and 6k worked and 16k worked the best so my other pot control works with it well.

Another aspect of the dump is............ when i first hook the batteries to the dump they charge up the cap bank backwards through the fets I think, maybe this is smoking my junctions.

Again when I hook the 36vdc charge bank up to the dump with empty caps the power some how back tracks and I think to fast and this maybe damaging things.

So I thought like car audio caps maybe I better have those caps charged up first or think up some other protection. Who knows maybe I had 1 or 2 trashed fet's by then. I am in a whirlwind of study. Gotta think back and keep trying.

These are my first conclusions and will grow in the process of failures.

Thank you so much for your excellent input.

Mike

[BroMikey]

Excellent advice

(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.

Thank You Stargate
Yes all true and some of that I forgot.

Mike

[BroMikey]

Time for all things

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

Very funny, you never know huh?

Mike

[BroMikey]

Learning Mosfet firing

Thanks for all of the input so far and here is my updated schematic.

mosfet firing3.JPG

I will be showing the entire circuit soon but I need a few more days to learn this stuff better. It is a little different than your standard transistor.

Mike

[Mario]

Hi Mike,

when i first hook the batteries to the dump they charge up the cap bank backwards through the fets I think, maybe this is smoking my junctions.

That is correct, mosfets have a built in body diode that will allow current to flow through it backwards, even when the mosfet is off. What I do when I first connect the batts is I connect them through a light bulb (depending on voltage) and let the caps fill, once full I connect them directly.
Or you can run your circuit and monitor the caps voltage, when they get in proximity of battery voltage connect your batts, but i would go for the first option.

What are you using to make the drive signal? Do you have a scope?

regards,
Mario

[ewizard]

The only problem I see is with the switch. Wiley Coyote could never get the timing right ....

[BroMikey]

Thanks Mario

Hi Mike,



That is correct, mosfets have a built in body diode that will allow current to flow through it backwards, even when the mosfet is off. What I do when I first connect the batts is I connect them through a light bulb (depending on voltage) and let the caps fill, once full I connect them directly.
Or you can run your circuit and monitor the caps voltage, when they get in proximity of battery voltage connect your batts, but i would go for the first option.

What are you using to make the drive signal? Do you have a scope?

regards,
Mario

Many thanks keep talking. I just love it when I run into folks who are pure at heart wanting to help. I wouldn't trade gold for it for it is priceless.

You guys are awesome.

Mike (Ps @Mario I just posted a small diagram check it out and tell me if you like it or you have another one better.

Mike