Author Topic: boost fets ..... is there an afterlife  (Read 21396 times)

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oztules

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boost fets ..... is there an afterlife
« on: April 24, 2006, 09:21:32 AM »
Well the dishes were done and tea was over what to do?


I had been pondering what Flux had said in his treatise of "matching the load" and decided to find out how the "boost converter " worked. I had built a few pwm devices before but they were offline devices for batt charging. Push pull, half bridge and two switch forward converters.... but a single switch converter....well I don't have any experience with these thinggyies so off out to the shed.


I grabbed a small pwm for driving tiny motors  tl494, and a totem pair  (bc139-140's) on the output. It was originally from a Silicon Chip article for a pwm driver. (Oatley electronics has circuit for this on their site the file is K098.pdf)


I fired it up, yep it still worked. It runs from zero to 90% and Flux mentioned that 50% should give me double voltage.  Soooo all that had to be done is wind a coil and off we go.


How much should we wind?  Well the boost inductor starts with defining the L min (limits the high freq ripple) . Next we define the no. of turns, the airgap length, ferrite core geometry, size and type for the specified power level, and finally the wire size and type are determined.


The minimun boost inductor value can be calculated as follows:

Lmin=Vout/4xfreqxLmax

and No of turns =LminxL1/AxBmax

L1=worst case inductor current at low input voltage

A=effective cross section of the core

Bmax=max allowable flux density of the core.


Armed with all of this I decided on a whim that 49 felt like a good number on a ETD39 core, and that the wire I had lying on the bench suddenly looked the right size...a match!


With gay abandon I whipped 50 turns on the core and loosly slipped in the ferrite cores( of course making sure they didn't meet in the middle to allow for my "Variable Air Gap System") Coz of course I didn't want to suffer the indignity of saturation  right off the cuff.


Scratched around and found some high current medium voltage diodes (just happened to have nine hundered and eighty D92 dual diodes hanging around from a miss-order some years ago.   plenty spare for testing I thought with a wry smile) 20A 200v (x2)


So how to do it?  A few days ago some one (on the board) wanted to charge a battery from another battery...a boost converter I said.. so here was a use I could test it on...battery charging.. albeit from another 12v battery, but that would give me a real test bed.


With the tiny (1.5x 2") pwm attatched to the 12v batt, the output in series with the new super power booster coil to ground, and a diode off to the second battery + and lastly neg to neg of the batts.   time to press the switch.


Well I poked the wire tentatively onto the pos terminal and bang.


It was a toss-up which bits flew the furtherest, the bits of ferrite, or the parts of the mosfets.


I'll post this and see if this diary business actually works and then continue the saga.... some one may learn something here. 12AX7 said that he felt robbed when he checked the diary of people and found nothing there, so this should satisfy him.


part 1 ........oztules

« Last Edit: April 24, 2006, 09:21:32 AM by (unknown) »
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Flux

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Re: boost fets ..... is there an afterlife
« Reply #1 on: April 24, 2006, 04:06:41 AM »
Charging a battery from another is not an ideal test. If there is nothing to limit the current you need a current feedback loop.


When operating from a wind generator you have a limited current input.


If you want to try with a battery source you would do better to start with lamps or resistors as a load until you have got things working.


Don't give up, start small keep current limited and you will get there.

Flux

« Last Edit: April 24, 2006, 04:06:41 AM by Flux »

oztules

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Battlefield description
« Reply #2 on: April 24, 2006, 05:15:18 AM »
Oh dear:


Well the dust had settled and the smoke cleared, and i sat and looked at a scene of carnage where once a tidy little converter had stood. The fets had gone to where fets go after they have been dealt with unfairly..... this bit I had half expected. The totempole transistors had been demolished and the tl494 was still looking alright. The circuitboard had blown a track, but apart from that all was chipper......egad.


Looking across past the PWM to the coil, the ferrites, so surprised by the massive currents of the dying fets passing through my super coil, both decided to try and take control of the middle ground at the same time. My variable gap went from 3/16th of an inch to zero in a fraction of a second. The deceleration was so severe that the ferrites destroyed themselves. this I hadn't expected.


Well, 2 more buk556 60A and some more bc 139 bc140 trannies later, the PWM was happy and functional (soldered up the vaporised track also) not connected to the "super coil"


Time to be not so cavalier...pull out the trusty scope. The square waves were picture perfect, control was perfect.... what happened. After looking at the circuit decided the constant voltage control (samples the output and adjusts the pulse width to compensate) was causing runaway with an effective short of the coil across the output, and so it opens up the pulse width to compensate for the zero output voltage and sends everything into orbit.


Curses magazine editors, writers, deliveryboys etc.


Time for an interesting trick with computer power supplies I designed years ago (the trick that is).


Most AT supplies are useless for anything because they trigger scr shutdown on current overload. As soon as you try and drive a low impedance load, zip.. nothing. (sometimes flipflop or some other shutdown system).


For some reason, all the supplies I had worked on had a similar trait of NOT using the second internal error amp. They always tie it off so it doesn't play any role in the PWM. This is very useful, as pin 16 is always earthed, 15 is connected to 14 (vref) and so is ready for expolitation. simply lift pin 15 out of the board, an rc network to pin 3 (feedback... say 10n 330R) a 47k from 14 to pin 15 and suddenly we have an active second control point. If we lift the secondary center tap of the power tranny out of the board, put 2-3" of wire in series to the board, we create a current resistor out of the piece of wire. We can then run a wire from the tap/wire interface to the pin 15 (via 1k trimpot), and we have a current regulator. Computer supply will now run like a normal low impedance power supply, fully current controlled. Will not trip on overcurrent as over current cannot occur(if it did due to fault, overcurrent in supply will load up deadtime to max and shut off)


So using that knowledge, i ran a 3" piece of wire from the PWM to neg. a wire from neg to (pull pin 15 as above), and suddenly I had control of my output. (so I think)


It is time. I hook it up, and tentatively prod the wire to the pos terminal and await the explosion.....all quiet on the home front...where is the whine? Oscillator freq is only 3k. should be able to hear it.....bloody ferrites forgot to replace them.


This time, replace the ferrites...and place 3/16" pieces of cardboard between the two E's so they cannot hit or move inwards and implode. Luckily have an abundance of these as well.


Try again,.... this time hear a whine ..hard then soft.....???? Now what??


The soft start is coming on then the current reg pulls it up...check the scope, hash everywhere, drawing 2amps, output 1 amp. Doesn't exactly glisten with rectitude.


Damn, the freewheel diode is still connected....grab the side cutters...exit freewheel diode.


It is testament to a crude current control that now I can do anything I please and no damage can occur even a dead short.


Try again, this time, I have full control of the current. scope shows a little ringing....no snubber but who cares(later..later), I'm charging the second battery now at 6.5A...now were cooking.


Some preliminary figures:

input    3.0A        36w      5.0A      60w       10A        120w

output   2.5A  12.8v 32w      3.6A 13v 46.8w      6.5A 13.5v  87w  


Note :looking back I should have measured the voltage of the donor battery as well. It's voltage  probably dropped under increasing load and the efficiency may not be as bad as it appears. I used nominal 12v for calc, but it is a 7ah batt, so at 10A draw, it may have fallen to 11.7 or less so. I should have checked. The recieving battery was 17ah a much heavier low inpedance device. damn and damn again.


So with a thrown together boost, 50T edt39 ferrite and 12v batt to 12v batt this is what I have gotten so far.


  2 fets sent to hell, 2 npn pnp trannies in the same direction, two Ecore shattered, and three hours later we have built our first boost converter, and so just as Flux said, a handful of components, a coil and presto a converter.


Now what to do to improve performance?


 1. stop the ringing with a snubber network


 2. May have to do the math and work out the correct coil turns and gap. It is just possible that "hunch coils" aint what theyre cracked up to be.


 3. Some heatsinks on the fets so we can turn it up a bit more (thats the only reason I stopped at 10A input no heatsinks). The efficiency dropped from 91 down to 67 over that range... that seems a bit ordinary I think the ringing may help explain this.


Any ideas welcome before testing tomorrow night.


will the fets meet their maker again?, or can we improve our "rail gun" ferrites.


............oztules


 

« Last Edit: April 24, 2006, 05:15:18 AM by oztules »
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oztules

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Re: boost fets ..... is there an afterlife
« Reply #3 on: April 24, 2006, 05:30:34 AM »
Now he tells me....mumble mumble mumble......


"If you want to try with a battery source you would do better to start with lamps or resistors as a load until you have got things working"  But that would be cowardace in the face of overwhelming odds.....


or then again, the real reason is I didn't think of it first myself.


Yes thanks for that Flux, it completly eluded me until I generated world war three on the bench. As the explosions were ringing around me I felt that you may have neglected to mention something to that effect... I think I must have missed it in the fine print.


Is there anything about the coil that needs mentioning?.... or snubbers... did you use any?


Thanks for your words of encouragement.


Just another wayward pupil.......oztules

« Last Edit: April 24, 2006, 05:30:34 AM by oztules »
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Gary D

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Re: boost fets ..... is there an afterlife
« Reply #4 on: April 24, 2006, 07:27:21 AM »
oxtules, could you add 2 extra fets to "share" the load (less heating per fet)? It's well over my head what you are doing. I searched in vain for non-ferrite inductors thru several sites and no matches were found.

 If you don't mind, are you winding two coils of the same gauge wire (inner and outer) for a boost 12 volts to higher 12 volts before attempting eventually going to a doubler circuit that can handle multiple amps? I'm not trying to muddy the waters, just wondering what your hopes are. Definately hoping this may be the beginnings of a boost circuit that can handle multiple amps, unlike what seems to be on the market now....in any case, Good luck with your trials  Gary D.
« Last Edit: April 24, 2006, 07:27:21 AM by Gary D »

dinges

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Re: Battlefield description
« Reply #5 on: April 24, 2006, 07:54:02 AM »
Been reading your story but not sure I understand; a quick hand-drawn schematic can do wonders; one picture vs. 1000 words etc.


Also, I'm interested in that feedback loop with the TL494, where you used one of the free opamps. Hurray for schematics!


Good fun to read your stories though. Nowadays I wear safety glasses when working on electronics. There's a reason for it :)


Peter.

« Last Edit: April 24, 2006, 07:54:02 AM by dinges »
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willib

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Re: boost fets ..... is there an afterlife
« Reply #6 on: April 24, 2006, 07:58:43 AM »
Riveting reading , thanks !

btw thanks for the chuckle, love the commentary !

« Last Edit: April 24, 2006, 07:58:43 AM by willib »
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dinges

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Re: boost fets ..... is there an afterlife
« Reply #7 on: April 24, 2006, 08:09:19 AM »
I think he meant to say the FETs went to Silicon Heaven. And no, not California :)


Peter.

« Last Edit: April 24, 2006, 08:09:19 AM by dinges »
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12AX7

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Re: boost fets ..... is there an afterlife
« Reply #8 on: April 24, 2006, 08:40:11 AM »
Hey Oztules!

"felt robbed"?

Come to think of it...  I may have said something like.

Perhaps I could have expressed myself better!


how about...   visiting an empty space/diary..  is more akin to...  checking out a bank for a loan, and finding that their as poor as you are.

hummm...   gonna have to think about that.


hope your safty glasses are resting on your nose...  during the next "power-up" of your test circuit!  


I was wondering...   do Gainclones explode?


my el34's never have!

« Last Edit: April 24, 2006, 08:40:11 AM by 12AX7 »

commanda

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Re: Battlefield description
« Reply #9 on: April 24, 2006, 08:45:15 AM »
« Last Edit: April 24, 2006, 08:45:15 AM by commanda »

WXYZCIENCE

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Re: boost fets ..... is there an afterlife
« Reply #10 on: April 24, 2006, 10:40:32 AM »
This is unbelievable Oz, My brother was working on a single switch forward converter yesterday. It works perfectly! It has adjustable input and is running at 92% efficient. We put 6v in we get 13.76 volts out. First tests yesterday. I am pressing him to hurry up with the circuit diagram. I am excited! The gennies I bought put out 6 volts at 700  rpms. And I can now charge a 12 volt battery with them. He will post later on today if I can put enough fire under his chair. Joe
« Last Edit: April 24, 2006, 10:40:32 AM by WXYZCIENCE »

coldspot

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Re: boost fets ..... is there an afterlife
« Reply #11 on: April 24, 2006, 02:10:04 PM »
"Riveting reading , thanks !

btw thanks for the chuckle, love the commentary !"

""ing willib

One of many reasons my computer sits @ otherpower

:)

« Last Edit: April 24, 2006, 02:10:04 PM by coldspot »
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oztules

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Re: Battlefield description
« Reply #12 on: April 24, 2006, 03:01:07 PM »
Sorry Peter. I would very much like to put said pictures into story, I am the first to grizzle when people dont put in circuits.... so why didn't I


Well the sad story is that with speed dropping down to 7-800 bps, and frequent drop out, uploading any size at all usually fails. Internet banking can take an hour for a single transaction.....usually includes two or three re-starts.


It seems to be the 30 kilometers of  electric fences inbetween me and the exchange that causes the "clicking" on the line, and so interferes with the protocols and so final bps.


 I have not yet managed to take pictures under 50K. Will try and find a way to downsize and do something about it today.


I will do another diary for you to describe (hopefully with piks and circuit) to do the conversion of the comp supplies. They become a very useful tool when you can control 0-20A at very precise steps (.01A). They are also excellent then for testing this kind of experiment as you cannot blow up the "experiment " as the current would be limited to predetermined amount. A trim pot on the voltage and you have a laboratory spec power supply.... for nothing. 0-15v.... more if you replace the filter caps to a higher voltage.


soon I hope.............oztules

« Last Edit: April 24, 2006, 03:01:07 PM by oztules »
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dinges

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Re: Battlefield description
« Reply #13 on: April 24, 2006, 03:31:40 PM »
Ah, the computer conversions with current limiting. Now we're talking. Am alert now. Hope you figure out the problem with your net connection soon :) Maybe that way I can get rid of the big stack of computer PSUs. Let's just call it my share of reducing pollution of our environment, LOL.


Commanda, thanks for the schematic. A motorcontroller is one of the projects that was (is) still on my to-do list. The parts I already have (all used), just need to connect them together.


Peter.

« Last Edit: April 24, 2006, 03:31:40 PM by dinges »
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oztules

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Re: boost fets ..... is there an afterlife
« Reply #14 on: April 24, 2006, 03:43:29 PM »
"oxtules, could you add 2 extra fets to "share" the load (less heating per fet)?"


oxtules?..... ok, yes adding extra Fets would reduce the resistance of the switches and the heat would be shared over more silicon, but the important point from this is that my efficiency went down markedly, and this is where the heat is coming fron. I would prefer to treat the disease in this case, rather than papering over an obvious shortcoming.


 In it's current configuration, it should easily do 200W without much heating ..IF I get the efficiency up. At 67% I would have to get rid of 66W at 200Winput.   If we get back up to 90%ish we only have to deal with 20W @ 200W, and we put an extra 40w into the batts. Some of this is disappated in the coil also. This is the direction to go I feel. We can add extra fets later when we fully understand what didn't work properly.....then power... and more power....and..


"If you don't mind, are you winding two coils of the same gauge wire (inner and outer) for a boost 12 volts to higher 12 volts before attempting eventually going to a doubler circuit that can handle multiple amps?"


This is not an offline converter and insulation from primary to secondary is not a concern, it is a simple boost converter. As such it has a single coil (of too many turns I think) and no secondary. The theory  can be found thru "Matching the load" by Flux, where he points to some sites that explain this more fully.


The circuit already handles 120W .....poorly, but it is also driving a very low impedance load. If it was running off 6 volts, driving 12 volts, it would probably perform a little better, but clearly it's not good enough .....yet!


...............oztules

« Last Edit: April 24, 2006, 03:43:29 PM by oztules »
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oztules

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Re: Battlefield description
« Reply #15 on: April 24, 2006, 03:55:35 PM »
Before I tried to blow mine into next week, it was a very nice little motor controller. It's limit is the top end though. There is an internal deadtime built into the chip which makes it less than straightforward to get 0-100% pwm. It can be done though. If you add the current limiter i used last night it becomes very very useful, as it will drive any load to it's max, rather than only small motors.


Ritchee Burdette has information regarding it in his Testla circuits. Don't remember the URL but he can be found through the teslta users.... a regular guru.


Yes you will look at the pile of psu's in a new light.


.......oztules

« Last Edit: April 24, 2006, 03:55:35 PM by oztules »
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oztules

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Re: boost fets ..... is there an afterlife
« Reply #16 on: April 24, 2006, 04:02:05 PM »
It's good the share the trials and tribulations. Others can learn what not to do by my example.... but it's all fun.
« Last Edit: April 24, 2006, 04:02:05 PM by oztules »
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oztules

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Re: boost fets ..... is there an afterlife
« Reply #17 on: April 24, 2006, 04:09:44 PM »
"I was wondering...   do Gainclones explode?"....... I know somebody who has done that. There is only so much you can squeese out of those things, particularly when you use them in motional feedback loops.....know him very well actually....very very well.


Ya see, I never blew up  thermionics, tried hard enough, 1000v on the plates, watching 6v6 anodes glow red everytime the morse key was pressed....At least with valves you only blew the end off the screwdriver, not the devices themselves.


Watch that paddle wheel and keep well.................oztules

« Last Edit: April 24, 2006, 04:09:44 PM by oztules »
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oztules

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Re: boost fets ..... is there an afterlife
« Reply #18 on: April 24, 2006, 04:15:46 PM »
"This is unbelievable Oz, My brother was working on a single switch forward converter yesterday. It works perfectly!"...........damn perfectionists.......:-)


Joe, don't you realise that it isn't properly road tested until it has been driven to destruction at least twice?...... once by accident, and once by "lets see what she'll do mister".


Fortunately for you I have done the destruction test for you so you can tick that box off.


Well done, look forward to seeing the results


...........oztules

« Last Edit: April 24, 2006, 04:15:46 PM by oztules »
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Gary D

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Re: boost fets ..... is there an afterlife
« Reply #19 on: April 24, 2006, 06:02:16 PM »
AHHHHH, Oztules..... My mistake! Glad you have a sence of humor... I even proofread my posting and missed it!  My apologies...Gary D.
« Last Edit: April 24, 2006, 06:02:16 PM by Gary D »

WXYZCIENCE

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Re: boost fets ..... is there an afterlife
« Reply #20 on: April 24, 2006, 08:56:05 PM »
...........damn perfectionists.......:-
Oz, Joe here. I think my brother was an electronic genius, but he is all right now. This is a top view of his desk on a good day.

I like the  Buffalo skinning knife in the front. Joe.
« Last Edit: April 24, 2006, 08:56:05 PM by WXYZCIENCE »

12AX7

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Re: boost fets ..... is there an afterlife
« Reply #21 on: April 24, 2006, 10:11:40 PM »
Hello Oztules!


"so much you can squeeze out of those"...


Some may see it that way.  

Others say that your "trying to shove too much in"  (expecting more out)

cept their not planning on it being "smoke".


The paddle wheel is on temporary hold. (but may be coming back strong)..

been playing with a "prop like" device inside a 55gal drum (ends removed).

Broke down and gone digital.   (camera that is)

Got some pics of the location..  working on some way to show depths.


So.. ANYWAYS..   truth be known,  I've not been following the controls side of re..

Your looking to match the 'z' of the genny to the load..  or directly to battery charging?

« Last Edit: April 24, 2006, 10:11:40 PM by 12AX7 »

oztules

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Re: boost fets ..... is there an afterlife
« Reply #22 on: April 24, 2006, 11:39:47 PM »
How on earth did you get a picture of my desk on a monday.


Your brother is obviously a super star and all round good bloke. I particularly like the neat and carefully prepared work area. The only dfference between his and mine, is the birds that sneak into the shed and aim at my my keyboard. Have to clean the crap of every other day.... bloody starlings.  ( a smart person would cover it up...i always forget)


update: had a fiddle around today and put the fets on heat sinks, and the D92's on heat sinks... much more fun. over 200W at around 89%.


Seems to be some instability at high power levels, but I think that has more to do with the careful layout... it would take up 1/4 of your brothers desk. The parts are small. it's the rats nest joining it all together... and the two batteries, and the charger  (from flattening the donor battery 7ah does not last long at 200w or more. (I have seen 30amps at times.....as I was quickly sutting it down to protect the cells)


Will try and stabilise it at higher power levels, and give some figures. Will have to use bigger batteries, at these levels the voltages change by the second, even in short bursts... 12v shoots up to 15-16v in seconds on one and 12.5 down to 9v on the donor real quick.


Looks like might just work.


Keen to hear about your brothers.....he should be able to rustle one up off the desk without getting up to find parts.....beautiful system there.


..............oztules

« Last Edit: April 24, 2006, 11:39:47 PM by oztules »
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oztules

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Re: boost fets ..... is there an afterlife
« Reply #23 on: April 24, 2006, 11:55:52 PM »
Greetings 12AX7


"The paddle wheel is on temporary hold. (but may be coming back strong)..

been playing with a "prop like" device inside a 55gal drum (ends removed)"


How the hell are you going to sit back and have a cooling ale on a sunny afternoon beside "a prop in a 55 gallon drum" :)


  If you must do that, at least put an ornate looking reasonable facsimilie of a paddlewheel on top of it. even if you have to use the power from "the prop in the drum to turn the paddle wheel"


No, not matching the z at the moment, i haven't even got a prop in a drum at the moment. My carefully crafted wooden blades are still on the Mainland, and I will build some new ones here.


Magnets are still in the box and wire on the reel.....until the Boss gives me the go-ahead to play. (haven't finished the house yet).


This is just a curiosity to see what can be done, and will influence the cutin speed i design for later....not much good designing for high cutin, and then not having a decent boost.... like a valve without a heater string.


If all goes well, then time for z match.


..........oztules

« Last Edit: April 24, 2006, 11:55:52 PM by oztules »
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12AX7

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Re: boost fets ..... is there an afterlife
« Reply #24 on: April 25, 2006, 12:40:44 AM »
Hello Oztules!


"temporoary"   when applied to me..  is kinda like "steady, by jerks"


The paddlewheel..  will happen.  like ya said..  I just GOTTA watch it go round d round.


I'm thinking of building it in the "back yard"..  it may spend a few years...  with a garden around it..  (enough wind and high enough water table) to spin it...

once I got a way to "guard it"..   and drop it in place...  splooch.. in da river she goes.


Besides,   think I mentioned that come winter... the river.. she gets mighty hard.

(under the ice...   she still flows)  gotta have parallel planning/thinking!


ah..   and then..  there is the "boss".. isn't there?

shudders    enough said!


You DO...  run your heaters with dc...   !..  don't you?


"z" match..   ah...  now there's a critter not easly caught!    and if caught,   sure to get away from you...  the moment you turn your eye!  and then..  there were times where I caught him...  but found out later..  I just had one of his harmonic sisters!


VSWR..  power transfer..sure has many hats.  

I just stumbled onto three 2kva  220-480/ 120vac control transformers.

Thinking of hooking them up to a old servo motor..  should beable to tie the three to the delta configured motor..  and do both "z" matching and..   converting the delta to a "Y" output.  


come to think of it...   I really have 4 of these 2KVA transformers.. the fourth one..stripped off the 220/480 primary..   using the 120 secondary as the primary..  a very nice hunk of iron..wrap my own secondaries..  (dual)   for the next set of gainclones..  L

« Last Edit: April 25, 2006, 12:40:44 AM by 12AX7 »

elvin1949

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Re: boost fets ..... is there an afterlife
« Reply #25 on: April 25, 2006, 05:09:21 AM »
Joe

How does he manage keep it so neat.

later

elvin
« Last Edit: April 25, 2006, 05:09:21 AM by elvin1949 »

oztules

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Re: boost fets ..... is there an afterlife
« Reply #26 on: April 25, 2006, 05:11:31 AM »
I can't envisage a climate where the rivers freeze over. Whats snow? I don't know how you folks prosper in that environment...super people I guess.


Mild year round here.


She-oak for heating, not DC....sometimes eucalypt.


2kw for gainclones????  and you think I'm cruel to the 6v6's... good grief. Are you going to use it to break up the river ice ? or start some snow slides.... egads


...........oztules

« Last Edit: April 25, 2006, 05:11:31 AM by oztules »
Flinders Island Australia

Norm

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Re: boost fets ..... is there an afterlife
« Reply #27 on: April 25, 2006, 09:46:07 PM »
  Just read in the latest issue of Popular Science

"The invention machine" you tell it what you want

and it figures it all out keeps working and adapting and evolving into the perfect machine.

  This is just what you need...Right?

   LOL !!

                   ( :>) Norm.
« Last Edit: April 25, 2006, 09:46:07 PM by Norm »

oztules

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Re: boost fets ..... is there an afterlife
« Reply #28 on: April 25, 2006, 10:50:32 PM »


Hi Flux


Some questions if I may regarding my poorly designed but still working booster.


How many watts should i be shooting for, to cater for a 48v 4m turbine ( wound for 24v I think would be your suggestion)? (dual axial flux )


Currently it seems happy in the 20 - 200 watt range is this enough? I'm guessing it will do a bit better driving a 48v load from 24v or so than driving a 12v battery from a 12v source battery.... or am I being hopeful here? (can't begin to guess how to mimic the dynamics of the real world here)


Managed about 18A into the second batt. higher for short periods at this stage.


The coil set up is currently standing at


 50 turns 1.8mm wire aound etd 39 core.more/less?


 4mm gap Bigger/smaller? didn't seem to make much difference...?


 6 buk455 60b fets rdson=.0.028/6=.0046ohms


 4 d92 diodes (makes 8 diodes). =200v 20A each


max I set at 30A  input.


effeciency seems around 80-90%..


Higher for low currents ie 3amps approx 93%, 10A 85% although hard to nail it properly... 30A scale on the meters...analog types,and battery voltage changing quickly at higher drive levels.


For 48v system, should I go for higher voltage fets...eg FP40N10L 40A 100v


Does this seem about right?


What parameters should I work towards, as you have the field experience that beats the hell out of my best guesses.


Thanks for your inspiration Flux.


...............oztules

« Last Edit: April 25, 2006, 10:50:32 PM by oztules »
Flinders Island Australia

SmoggyTurnip

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Re: boost fets ..... is there an afterlife
« Reply #29 on: April 26, 2006, 06:42:14 AM »
That's what this board is doing, ... just slower.
« Last Edit: April 26, 2006, 06:42:14 AM by SmoggyTurnip »

Gary D

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Re: boost fets ..... is there an afterlife
« Reply #30 on: April 26, 2006, 06:56:07 AM »
Dang Norm, have to clean the Pepsi off the screen! With such a machine our brains would get cobwebs much more quickly.... And my waistline would grow exponentially too... Where can I buy one- or a dozen  ;-)

Hopefully Oztules has this close, I struck out with my first expert, seems it isn't a standard thing being taught( Varible input voltage and fixed output voltage at high amps pass thru with high effeciency) Kudo's to Flux and Oz for trying this...

        Gary D.
« Last Edit: April 26, 2006, 06:56:07 AM by Gary D »

oztules

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Re: Battlefield description
« Reply #31 on: April 26, 2006, 11:31:14 AM »
Ok Peter, I have battled with a multiplicity of drawing programs ( I never draw anything) and have struggled to come up with this...It may be as clear as mud, but hopefully you will get the idea for comp power supplies. The ones I have worked on are all of chinese origin I think, and all have pin 16 to earth, and pin 15 to vref (pin 14). As I said, this makes our life easy. Pin 15 will have to be lifted out of the board as it will in all liklyhood be on a large land... difficult to cut from pin 14.


The idea is simple, pin 14 through the 47K provides a positive bias to the opamp input (pin 15) the trimpot (2k) from the flying lead out of the secondary CT of the transformer sees an increasingly negative current with respect to ground (which is now 2-4" of resistance above it) as the current through the wire resistor increases, the tiny voltage drives the pin 15 below ground potential, thereby driving the op amp on and so decreasing the pulse width. The 330r and 10n provide a modicom of feedback to set the opamp parameters. So two resistors, a capacitor and a trimpot and you have a down and dirty current controlled power supply.


To vary the voltage it can be a little trickier as there is a multitude of designs getting around that load up pins 1 and 2 in very cunning ways. That said, I have usually found a pair of resistors in parallel (perhaps so they can fix the R closer to a perfect value..can't see any other reason for two) or a trimpot (rare) on the board.


Anyway, you are looking for the last voltage divider before the tl494 to effect the voltage.


However, there is only a small range you can use before the overvoltage sensing system picks up that you are fiddling where you should not, and this may require disabling, or more usefully... fooled into playing your game, this will still enable the safety shutdown to function....all depend how far you want to go.


This mod is simple and a long way from perfect, but gets the job done. It will denature the waveform slightly (you have wires draped over the board from the power tranny secondaries at high current feeding a sensitive op amp).


Now taddah... will the hard fought for diagram actually load? If it does thanks to Commanda.


Comments (good or derogatory) and improvements welcome Peter and others. This is how I have done it for some years now


...................oztules

« Last Edit: April 26, 2006, 11:31:14 AM by oztules »
Flinders Island Australia

dinges

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Re: Battlefield description
« Reply #32 on: April 26, 2006, 01:07:02 PM »
Thanks, Oztules.


Not really sure about that 10n cap and the 330ohm resistor; how are they exactly connected? That screen capture & re-resolution seems to make some lines disappear. Please clarify.


Looks like an easy enough mod though. I assume this is only for the current control; voltage control is via the usual divider-resistors and a de-functional overvoltage protection SCR?


As far as drawing goes; how about good old pen and paper, and scanning it in? That's my quick & dirty method...


Peter.

« Last Edit: April 26, 2006, 01:07:02 PM by dinges »
“Research is what I'm doing when I don't know what I'm doing.” (W. von Braun)