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  #1  
Old 03-11-2014, 08:51 PM
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Cap Dump Circuit

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
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Old 03-11-2014, 09:06 PM
Guruji Guruji is offline
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Quote:
Originally Posted by BroMikey View Post
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.
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Old 03-11-2014, 09:13 PM
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Hello Mikey

Quote:
Originally Posted by BroMikey View Post
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
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Old 03-12-2014, 03:40 AM
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Trigger Circuit

Quote:
Originally Posted by Ufopolitics View Post
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?

Attachment 14204

Thank you for your kind reply.

Best regards, Mike
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Old 03-12-2014, 03:58 AM
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Mosfet Firing Circuit

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Originally Posted by Guruji View Post
Hi Mike interesting. Can you please post a schematic of this?
Thanks.
Here is the rest of the circuit with the voltages.

Attachment 14205

Thank you for your reply.

Mike
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Old 03-12-2014, 04:09 AM
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In my professional opinion, that red bunny needs to get laid = problem solved.
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Old 03-12-2014, 04:31 AM
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Post 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.
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Old 03-12-2014, 07:31 AM
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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
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Old 03-12-2014, 09:25 AM
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High Regards

Quote:
Originally Posted by Mario View Post
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
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Old 03-12-2014, 09:27 AM
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Excellent advice

Quote:
Originally Posted by stargate22 View Post
(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
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Old 03-12-2014, 09:28 AM
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Time for all things

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In my professional opinion, that red bunny needs to get laid = problem solved.
Very funny, you never know huh?

Mike
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Old 03-12-2014, 09:45 AM
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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
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Old 03-12-2014, 10:58 AM
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Hi Mike,

Quote:
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
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Old 03-13-2014, 12:52 AM
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The only problem I see is with the switch. Wiley Coyote could never get the timing right ....
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Old 03-13-2014, 02:05 AM
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Thanks Mario

Quote:
Originally Posted by Mario View Post
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
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Old 03-13-2014, 02:26 AM
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Gate resistance danger

Okay Group Members I need to ask this.

Why would someone use 1000 ohms on the gate when 10,000 ohms opens the gate fully? Unless they were using a lower voltage? I mean some guys are using the same circuit and charging the same 36vdc battery packs and yet showing a 220 ohm gate resistance for fet irfp260.

The question I have is if 1000 ohms opens the gate fully and 10,000 ohms opens the gate fully won't the higher ohm resistor be easier on the fet and make it last longer?

Thanks again to all.

Mike
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Old 03-13-2014, 09:10 AM
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pulsing a mosfet hard

Quote:
Originally Posted by stargate22 View Post
(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.
Hello Stargate

I charged up my 120,000 uF bank just for fun to 65-70vdc and pulsed that through one big mosfet to a battery and that thing only worked once.

Maybe I will end up will 12 instead of 6 AAA?

But 1 or two? it's little legs just can't carry it.

My cap bank is set to deliver massive amounts of inrush to the battery.

By the way I did go down to 10,000 ohms of resistance on the base to get a full On so as to dump the entire load but that fet gave up the Ghost.

Just had to see. That pulse also burnt a tooth off of my gator clip so maybe the shorting out added resistance smoked the fet I do not know these things.

But one thing is sure the Wiley will always be my friend forever after that stunt. Yes big big inrush amps enough to blow the sulfation right of a huge battery plate.

I am going to pick up some 500 ah 4vdc cells in a few hours.

So I need this thing working come hell or high water.

Yeah 10k on the base gave me a "FULL ON" condition and it smoked that fet in a New York mil second.

Mike
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Old 03-13-2014, 09:45 AM
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Quote:
Originally Posted by BroMikey View Post
Okay Group Members I need to ask this.

Why would someone use 1000 ohms on the gate when 10,000 ohms opens the gate fully? Unless they were using a lower voltage? I mean some guys are using the same circuit and charging the same 36vdc battery packs and yet showing a 220 ohm gate resistance for fet irfp260.

The question I have is if 1000 ohms opens the gate fully and 10,000 ohms opens the gate fully won't the higher ohm resistor be easier on the fet and make it last longer?

Thanks again to all.

Mike
Mike, the higher the gate resistance the lower the turn on/off times will be. Yes it will turn on with high resistance, but instead of emulating a switch it will emulate a dimmer…. not what you want.

If you're using an opto to switch the mosfet it's not going to be as easy as driving a transistor. A mosfet needs at least 10V (better 15V) to fully turn on. You can find logic gate mosfets which turn on at 3V. So keep that in mind, the cap voltage minus the batt voltage will determine how many volts will be at the gate.
This is why I asked if you have a scope to monitor the turn on/off states. Otherwise you're never sure that the mosfet is completely on or completely off (this is important!), and you don't know your rise/fall times which directly depend on the resistors uses.
When I really want to get precise I replace the resistors with pots, I play with them until I see the perfect switching on my scope. Then I measure the pots and replace them with fixed resistors. I would start with about 47 ohms on the gate and 1 Kohm going to the source for a good turn off.

regards,
Mario
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Old 03-13-2014, 01:17 PM
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Being discussed elsewhere

BroMikey
your project is being discussed here also [member Seamonkey started a thread for this]

BroMikey's Capacitor Dump Circuit

Unfortunately the Diagrams you share here cannot be seen unless you are a member of this forum and signed in...[some are denied admission]

Good luck with your research .

Thx
Chet
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Old 03-13-2014, 07:15 PM
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Okay Okay here comes the scope

Quote:
Originally Posted by Mario View Post
Mike, the higher the gate resistance the lower the turn on/off times will be. Yes it will turn on with high resistance, but instead of emulating a switch it will emulate a dimmer…. not what you want.

If you're using an opto to switch the mosfet it's not going to be as easy as driving a transistor. A mosfet needs at least 10V (better 15V) to fully turn on. You can find logic gate mosfets which turn on at 3V. So keep that in mind, the cap voltage minus the batt voltage will determine how many volts will be at the gate.
This is why I asked if you have a scope to monitor the turn on/off states. Otherwise you're never sure that the mosfet is completely on or completely off (this is important!), and you don't know your rise/fall times which directly depend on the resistors uses.
When I really want to get precise I replace the resistors with pots, I play with them until I see the perfect switching on my scope. Then I measure the pots and replace them with fixed resistors. I would start with about 47 ohms on the gate and 1 Kohm going to the source for a good turn off.

regards,
Mario
Mario

You are the only guy who has got me digging my $20,000 scope out to see the switch. I knew someone would actually get me into the game and help me see what to do. I have the tools but many are unable to teach.

I have to go right now and will do tests when the scope gets setup in my new shop area. I understand you perfectly, keep talking when you do I go forward.

47-1000 it is.

I am thinking there will be some signs of distortion in the scope shot if....HUM?


Cap voltage minus the switch voltage is like 60- 80volts.

Got to think. There was something I was going to ask you.

Later for now this gives me something to think on and I just love learning new things.


Mike PS you are the only one Mario
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Old 03-14-2014, 02:57 AM
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Big Bank-O Batteries

Here is my new skid of batteries. They are fully charged excellent batteries I got from a power company who buys new ones every 5 years.

Sorry about the dark shots but not bad for no light pics.

They come 3 two volt cells per rack about 24X20X8 I have 4 now or a 24vdc bank.

It says it is a 870ah battery but I can't believe that yet. Maybe.

Will be pulse charging on Friday.

Attachment 14212

This is my appliance hauling trailer with the pallet of batteries.

Attachment 14213


I hooked them up fast and put them on my 200 amp roll around auto charger and they are at 14vdc already after 30 minutes.


That Acid has got to go soon. A toilet will take care of the acid, perfect

Attachment 14214

tonight I do scope shots, thanks Mario, you have no idea how excited I am to have someone coach me a little.

Mike
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Old 03-14-2014, 09:23 AM
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Hi Mike,

I wouldn't dump 80V into the batteries. It might ruin them. Go for twice the battery voltage. Say you have 12V batts dump the cap at 24V. Also, with voltages that high you risk frying your mosfet gate, unless you calculate the right resistances.

If you have trouble controlling the mosfet with the opto method there's another option. You could use a small dc-dc isolation converter (i'm talking 1 or 2 watts power), say 12V to 12V, powered from your primary batt or from whatever source you want. With that you can run your timing circuit and use proper mosfet drivers so that your mosfet gates will always switch on and off properly, fast and with the correct voltage.

regards,
Mario
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Old 03-14-2014, 10:08 AM
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Scope Setup

Quote:
Originally Posted by Mario View Post
Hi Mike,

I wouldn't dump 80V into the batteries. It might ruin them. Go for twice the battery voltage. Say you have 12V batts dump the cap at 24V. Also, with voltages that high you risk frying your mosfet gate, unless you calculate the right resistances.

If you have trouble controlling the mosfet with the opto method there's another option. You could use a small dc-dc isolation converter (i'm talking 1 or 2 watts power), say 12V to 12V, powered from your primary batt or from whatever source you want. With that you can run your timing circuit and use proper mosfet drivers so that your mosfet gates will always switch on and off properly, fast and with the correct voltage.

regards,
Mario
Hey Mario

I dump 30vdc for a 12vdc battery that will rise to 15-16vdc for a full charge and right now my battery array upstairs is a 36vdc system so miuimum 75vdc dump voltage.

Here is my favorite circuit.

pulsing594.JPG

Also I wanted you to know that I setup my juicy scope and am trying to get use to it again. Oh I remember now I said and this scope does not show you so much as it tells you everything.

It is like a running program it is the old HP54100A/D one can store images and print. To bad for me cause I don't know what i am looking at yet.

But I can get my rise and fall down to 3 or 4ns well i got that much tonight out of it just watching the amp meter and using 50ohm 100ohm 1000ohm didn't find the pot yet but I will.

The big bank in the yard is at 14.1 and from what I know about the AGM batteries she is in need. It works out perfect. Buy half dried out brand new industrial batteries and hit them with ALUM and they will and have become better than ever.

Thanks Mario for helping figure this all out. I am in burnout mode the last 3 days and better get back quiet for a few ZZZZ

Let me know what to look for, should i use 2ns or 200ns? The resistor on the bases seem to open the gates but the real story is being told on this super awesome digital scope. This scope practically walks and talks.

Mike
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Old 03-14-2014, 11:27 AM
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Mike, it's impossible to get into the nanosec switching range with an opto setup. The H11d1 has rise/fall times of 5 microsecs minimum if I recall well, so even if you do really well on matching the resistors to the gates that's the fastest you can switch. With the mosfet driver option I described earlier it's another story, but I wouldn't worry about that too much for now. Get some experience first. And I would work with a small system first..

What I would worry about is getting a control signal that let's you narrow the ON duty cycle down to the 1% range. If you use a simple 555 circuit with 50% On time you discharge the cap but for a much longer time your charging source will go right trough the cap and mosfet and charge your batts directly. You don't want that. You only want a very short pulse long enough to discharge the cap down to almost the batt voltage.
Even better is to make a circuit that shuts the power supply down during the cap dump. But you can worry about that later…

Here you can see a way to control the 555 duty cycle, page 44.
http://www.free-energy-info.co.uk/Chapter12.pdf

regards,
Mario
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Old 03-14-2014, 08:33 PM
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1% On Time

Quote:
Originally Posted by Mario View Post
Mike, it's impossible to get into the nanosec switching range with an opto setup. The H11d1 has rise/fall times of 5 microsecs minimum if I recall well, so even if you do really well on matching the resistors to the gates that's the fastest you can switch. With the mosfet driver option I described earlier it's another story, but I wouldn't worry about that too much for now. Get some experience first. And I would work with a small system first..

What I would worry about is getting a control signal that let's you narrow the ON duty cycle down to the 1% range. If you use a simple 555 circuit with 50% On time you discharge the cap but for a much longer time your charging source will go right trough the cap and mosfet and charge your batts directly. You don't want that. You only want a very short pulse long enough to discharge the cap down to almost the batt voltage.
Even better is to make a circuit that shuts the power supply down during the cap dump. But you can worry about that later…

Here you can see a way to control the 555 duty cycle, page 44.
http://www.free-energy-info.co.uk/Chapter12.pdf

regards,
Mario
Hey Mario

This is a great doc for guys to freshen up with, somehow I missed this one.

Dc to dc conversion and shutdown the supply WOW all great proposals and I was thinking of some way to throw a (HUGE) resistor in between the bank and supply to slow the bank charge time alittle but better to let it charge fast and shut her down.

Yes I need brushing up that is for sure. My circuit with the 555 timer I showed you has both the standard 555 timer 50% duty and the extra knob is for cutting off dump time.

This means that my LED will flash like the blinker on a cars turn signal and is adjustable all the way down to an ever hastening (faster) cutoff time than can be seen with the naked eye.

I must have read the scale wrong but I was varying my timer circuit up and down and the scope was showing 5 ms to 50ms or whatever the division.

Okay I know this the button I push is "RISE TIME" "FALL TIME" well all of it can easily be read I just need more time. Last night I was out of it.

Yes all of the things you are saying, right down to the nicer controlling drivers and smooth supplies have lodged in my thinking.

I have not missed anything you have pointed out or I would come right out and ask you about it.

Keep talking

Here is that circuit

timeropto.JPG

Many people miss the fact that a standard timer circuit can easily be altered to control the duty cycle without going the the 556 dual timer with separate sections one for timing and one for duty cycle.

This circuit is working on 2 of my other cap dumps that are in use now and allow me to dump caps down to any voltage I like.

For instance this circuit was running lat night and I charged the caps up to 45 volts and cut off the dump time to 35 volts showing on the meter.

I can dump at 60 and start recharging at 55volts or I can dump at 30v and stop at 25volts if I want to.

I have more to learn about the difference in using a LM741 or a NAND gate but I could start if needed.

Let me play with this scope some more and I will tell you for sure what I am getting.

I have been controlling dump down voltage and charging batteries this way for 1 year as I said with the smaller units.

In fact I am about to take my small bank of 60,000uF out to the trailer so I can get it charged up more, it is just that I wanted to use Mosfet's on a bigger system.

The one I use now has 4 deflection transistors in it and they never blink.

They run cool and are very stable.

Thank Mario for helping me use Mosfet's. Among other things of interest.

It is not like mosfets are the only way of doing this.

Mike
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Old 03-14-2014, 10:54 PM
lotec lotec is online now
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I found this one helpful
https://www.youtube.com/watch?v=10R0Mrqwjuo

I liked the little pnp for draining the gate fast.
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Old 03-15-2014, 11:21 AM
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BroMikey BroMikey is online now
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Great Help

Quote:
Originally Posted by lotec View Post
I found this one helpful
https://www.youtube.com/watch?v=10R0Mrqwjuo

I liked the little pnp for draining the gate fast.
Thanks for the help.
I rebuilt my fet bank and this time I used 560ohm on the bases but will need more at 90vdc dumping.

Sg Oscillator to dump to industrial AGM ALUM converted batteries - YouTube

You guys are all helpful and so i will get up to speed.

I spent 4hrs on my scope and can see waveforms now.

Mike Ps the book on this scope is hundreds of pages long
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Old 03-16-2014, 09:41 AM
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BroMikey BroMikey is online now
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Measuring the switch

Quote:
Originally Posted by Mario View Post
Mike, it's impossible to get into the nanosec switching range with an opto setup. The H11d1 has rise/fall times of 5 microsecs minimum if I recall well, so even if you do really well on matching the resistors to the gates that's the fastest you can switch. With the mosfet driver option I described earlier it's another story, but I wouldn't worry about that too much for now. Get some experience first. And I would work with a small system first..

What I would worry about is getting a control signal that let's you narrow the ON duty cycle down to the 1% range. If you use a simple 555 circuit with 50% On time you discharge the cap but for a much longer time your charging source will go right trough the cap and mosfet and charge your batts directly. You don't want that. You only want a very short pulse long enough to discharge the cap down to almost the batt voltage.
Even better is to make a circuit that shuts the power supply down during the cap dump. But you can worry about that later…

Here you can see a way to control the 555 duty cycle, page 44.
http://www.free-energy-info.co.uk/Chapter12.pdf

regards,
Mario
Hi Mario

I am finding my head with both hands learning this scope functions.

I had the wrong probes out of 4 probes I own. Now when I sit down it pops right on to the place where I left off.

I can go down to 107ms rise and fall is 33ms

Don't know what that means.

Mike
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Old 03-16-2014, 11:31 AM
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Quote:
Originally Posted by BroMikey View Post
Hi Mario

I am finding my head with both hands learning this scope functions.

I had the wrong probes out of 4 probes I own. Now when I sit down it pops right on to the place where I left off.

I can go down to 107ms rise and fall is 33ms

Don't know what that means.

Mike
Hi Mike, it means that if you have a square wave the rise time is the time it takes to go from off to on (low to high) and the fall time is the opposite, meaning the time it takes to turn off.
Is that millisecs or microsecs?

regards,
Mario
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Old 03-16-2014, 08:48 PM
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Rise and Fall

Quote:
Originally Posted by Mario View Post
Hi Mike, it means that if you have a square wave the rise time is the time it takes to go from off to on (low to high) and the fall time is the opposite, meaning the time it takes to turn off.
Is that millisecs or microsecs?

regards,
Mario
Hi Mario

Yes I realize that it means what you just said but what I should have said was I do not know how 107 ms relates to a possible 1% figure that you mentioned as a target.

Okay the div/ms on a scope humm....... not sure........ all I know is that a 107 ms flash on my led is faster than the blink of my eye.

Eyes blink at 150 ms miliseconds. I think.

Are we looking for micro-seconds?

As I dial up and down the LED will get lazy looking at 900 ms humm.........

I better research this as it really was a question of mine when I read that value.

Well at least I am getting my head on straight a little

Maybe these pulses are in mili-seconds and if so that is very slow.

Is it possible that a 560 ohm base resistor would slow the rise time down that much?

I see data showing Mosfet's switching much faster. I just don't know what a 1% switching means in relation to seconds.

I thought that mili-seconds = (mS) microseconds=(uS) and nano-seconds =(uS)

I better stop being afraid to lower base resistance, it looks like huh?

Of course I am switching at low level voltages 20-25vdc and amp pulses are

at 1-2 amps so I will go up to 90vdc at 20 amp pulses first to see if

switching time is effected dramatically or no.

This was in my mind from the beginning and so far I am studying the function

of the scope and now can see some point of reference.


This is my first day. Today is the first day in years that I wanted to get

myself in the know concerning switching times.

Thank you so much for your continued patience helping me crawl in slow

motion. Patience is a virtue I am told and is probably quite true.

I have heard your instruction on using a pot from 1000 ohms down to 47

ohms till you get what you want.

Now that I can read the scope in a small way I will complete my test at the elevated power levels as mentioned above and them go back to a single FET to test again.

Last night was the first time in my life that I sat down in front of my scope

and the reading was exactly the same as it was the day before.


Just so you know Mario 2 days ago I had the wrong high frequency probes

hooked up and I had power supply hum and you know the drill, I mess of

signals entering my view even from my own hand touching things, so I am

not totally scope illiterate.

I know very little, this is my first day to see that with the high frequency

probes I better use my 2 regulated supplies for a clean view of switching

times.


I have dozens of tiny 12vdc batteries so I hooked them up to get my cap at

24vdc and dumped the power to another battery of 12vdc using a separate

12vdc battery to run the timer/trigger circuit.


All clean voltage, no hum.

Now that I see this difference it has become quite clear that my bench

battery chargers will not work here.


I recently learned how to fool a tl594 chip found in PC switch mode power supplies and have an extra 0-24vdc regulated supply.

I also have a 0-15vdc +- 5vdc+- variable 1 amp dc supply.

My bench needs cleaning and the shelves are going in now.


It is an exciting time for me.

Mike
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