Cap Dump Circuit

[BroMikey]

Scope Setup

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.



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

[Mario]

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

[BroMikey]

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.



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




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



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

Mike

[BroMikey]

Okay Okay here comes the scope

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

[RAMSET]

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

[Mario]

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

[BroMikey]

pulsing a mosfet hard

(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

[BroMikey]

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

[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

[ewizard]

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

[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

[BroMikey]

Learning Mosfet firing

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



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

[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]

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]

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