Author Topic: boost fets ..... is there an afterlife  (Read 21399 times)

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commanda

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Re: Battlefield description
« Reply #33 on: April 26, 2006, 03:22:58 PM »
Here's a few links that may interest some.


200w atx power supply.

http://www.pavouk.comp.cz/hw/en_atxps.html

This uses the TL494.


more info & circuits

http://www.smps.us/computer-power-supply.html


Amanda

« Last Edit: April 26, 2006, 03:22:58 PM by commanda »

dinges

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Re: Battlefield description
« Reply #34 on: April 26, 2006, 04:18:41 PM »
Never mind the previous question; in your photo-uploads the picture is perfectly clear.


But what's the 330ohm & 10n cap there for? Aren't they originally in the PSU? And if not, why do you add.


Thanks,


Peter.

« Last Edit: April 26, 2006, 04:18:41 PM by dinges »
“Research is what I'm doing when I don't know what I'm doing.” (W. von Braun)

oztules

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Re:Current control of psu supply
« Reply #35 on: April 26, 2006, 04:40:50 PM »
Hi Dinges, the voltage is controlled as you say, and will be slightly different for each supply maker.  This is only for current control which is the main drawback for the normal use of these critters.


The 10n and the 330r are there to complete the feedback loop for the second op amp. The "already in the supply " components going to pin 3 already only do the feedback for op amp one,


Op amp 1 and 2  outputs are joined internally via isolating diodes to pin 3 , so you still have to control the gain characteristics off the second op amp now that you have enabled it.


You have to control it, otherwise it will go click! click! click! no more no less......(insert evil grim here:-)


..........oztules

« Last Edit: April 26, 2006, 04:40:50 PM by oztules »
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oztules

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Re: boost fets ..... is there an afterlife
« Reply #36 on: April 27, 2006, 06:01:19 PM »
"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)"


GaryD, this experiment has run its course at the moment. It was done as an idle curiosity, and I have no use for this device anymore, as it was only a learning experiment. Flux has yet to get back to me regarding the power size I should be aiming for for an average windmill (4M), so I don't know where to take this now. I don't need to charge 12v batts from other 12 v batts, so until I can get some clear direction from the great man, or someone else, this project is dead in the water.


For your interest, it easily exceeds 300W input and output seems to be around 80-95%efficient. At low power (<3amps out) the efficiency is very high, and hard to measue (with the 30A meters I'm using to test with), it's only that unity is impossible that I don't say 100%, but with these meters it looks like 3 amps in at 12v and 3amps out at 13v...so measurement accuracy is bottom of the barel stuff here, and is rough as guts, but indicative none the less.


At higher currents, things got tricky as input V dropped dramatically as the small SLA batteries discharged rapidly and volts fell rapidly, conversly the output battery would rise dangerously fast at higher current (20A or more) and I was doing damage to the 17ah SLA, but more importantly I couldn't read all the meteras at the same time and write it down fast enough... so best guess at higher power levels was all that was done.


What is it that you are trying to achieve, I may be able to experiment in your direction, but I'm not sure what that is.


What I can say for now is the low power levels (<100w) it is very simple to make a boost control, and voltage input should not be too much of a problem. I havent tested the variable V over a large range, as I don't have a voltage source to emulate the windgenerator ...yet.


At higher power levels  the waveform started to deteriate a little, and probably due to the poor design (ratsnest on a desk)  and that the battery was dropping below a decent turn on voltage for the fets.


All in all it was interesting.


What range of voltages were you considering, and at what power levels, and doing what sort of job?


I may be able to help by doing experiments in that direction, but until I know what I'm aiming for, I don't have a clue where to take this further.


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


ps. And sorry, I'm no expert, just a hobby/hacker with a sense of adventure. There are far more knowledgable electronics people here. I think Commanda seems to have a far more electronic nouse than I will ever have and  is working towards a variable input PFC to condition and stabilise the voltage before a PWM system after that.  Flux's matching the load diary is the best thing I have seen yet to illustrate the problems and answers involved, and was the instrument I used to achieve this.

« Last Edit: April 27, 2006, 06:01:19 PM by oztules »
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vawtman

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Re: boost fets ..... is there an afterlife
« Reply #37 on: April 27, 2006, 07:02:42 PM »
oz,

 You seem to be overcomplicating things.I have that problem also.I just cant use the kiss method for some reason.Maybe the last s applies to me.No regrets though.


Have you got a turbine plan?I know you where researching different types.

 Keep thinkin and good luck.

« Last Edit: April 27, 2006, 07:02:42 PM by vawtman »

oztules

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Re: boost fets ..... is there an afterlife
« Reply #38 on: April 27, 2006, 07:21:56 PM »
Its a sickness Vawtman....keeps life interesting. I don't need a boost at the moment, but the concept interested me.  Secondly Flux feels boost is a good idea, and thats enough for me.

If I was relying on this for power alone....two sticks and some animal skins ....


I have not finished with a difinative plan yet. DanB is in the right groove for sensible simple power generation.


Me, the more complicated, the more the chance for having to fix it up, more interesting on an ongoing daily basis.... tinker  tinker   tinker.... something to do.


If  I was relying on it for my only power... Danb all the way... nut for nut, bolt for bolt.


Now coming from a vawt enthusiast, I just know that max power for min effort is not your thing either.


I will probably build the standard Hawt first, just to get my feet wet. Then when boredom set s in (coz it's all been done before) it's time to take up a plank and hit my self on the head with it and struggle with vawts. This looks to be a life long -never get to the bottom of  it type of  interest....I can see why you do it.


Against all public opinion, I will do the pumper thing as well, should take years to finally give up and admit defeat there..... even Jacobs perservered for a long period of time with them before  he developed the 3 blade concept (and never looked back).


Keep the VAWT flag flying.... have you tried your HUGE induction conversion out on the 8 footer yet? or is the dreaded temp still to low....can't imagine that here.


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

« Last Edit: April 27, 2006, 07:21:56 PM by oztules »
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vawtman

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Re: boost fets ..... is there an afterlife
« Reply #39 on: April 28, 2006, 06:35:12 AM »
Ive been in a slump lately Oz.Im trying to figure a way to start the gen at a certain rpm and release it before stall.Since my plan is to go directly to heating elements I have no cutin.

 I plan building a much larger vawt once things get figured out.Cant blame it on the weather.Could use a boost.Good Day to you.
« Last Edit: April 28, 2006, 06:35:12 AM by vawtman »

oztules

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Re: boost fets ..... is there an afterlife
« Reply #40 on: April 28, 2006, 06:44:06 AM »
for testing purposes why not just a micro swith to relay triggered by a wind paddle, or a relay across the alt output, and retension the return spring in the relay so that you control what voltage it cuts in at. This will give it a heap of hysterisis as well, as it wont release until voltage drops a long way down (mag gap is now zero when closed small current only needed to hold it in)


I dont follow this bit "release it before stall.Since my plan is to go directly to heating elements I have no cutin." release before stall...... under what circumstances.. slowing down or over powering?


oztules

« Last Edit: April 28, 2006, 06:44:06 AM by oztules »
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TomW

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Direct to heater thought..
« Reply #41 on: April 28, 2006, 06:47:39 AM »
Vawtman & others;


I considered the direct to heater idea for awhile and the "always under load" part bothered me but I had this thought that you could use motor run caps on each feed line to a heater [or maybe transformer, too]. My thought was that the caps would essentially isolate the load from the DC pulses on startup and then pass the AC on through as the prop speeds up. No idea if it makes sense or will even work. It goes back to very basic circuit theory and the fact that caps block DC and pass AC. Sizing, etc would require some investigation. It seems if motor run caps can feed multi horsepower motors they could pass kilowatt class machine power. Motors not my thing so I may be cracked.


Cheers.


TomW

« Last Edit: April 28, 2006, 06:47:39 AM by TomW »

oztules

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Re: Direct to heater thought..
« Reply #42 on: April 28, 2006, 07:02:24 AM »
Perfectly valid concept Tomw ...(doesn't mean your not cracked though:-) )The voltage would lead the current and so a phase change will be evident, what that does to the vector product for the power needed to produce power out, I'm not certain, but it would certainly work. I use this for driving small control circuits from the mains into double insulated environments where isolation is not necessary . Appliance manufacturers use it as well  (insulated touch panel rangehoods etc)


I vaugely remember trying this one on the board sometime back, and there was some reason that it was knocked down, but I don't remember what it was.


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

« Last Edit: April 28, 2006, 07:02:24 AM by oztules »
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vawtman

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Re: boost fets ..... is there an afterlife
« Reply #43 on: April 28, 2006, 07:11:55 AM »
The blades will not start under load.The 5hp is too much for a turbine of this size has you stated some time ago.

I think it could control overspeed.I plan on using belt drive with sometype of shaft speed sensor and relay to adjust belt tension.

 Say at 60rpms the relay would engage a clutch and disengage at 20rpms so in lighter winds the gen wouldnt drag the blades to stall.

 Talk about overcomplicating things.Geepers creepers Ill get it.Thanks for your input.

v.......
« Last Edit: April 28, 2006, 07:11:55 AM by vawtman »

Gary D

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Re: boost fets ..... is there an afterlife
« Reply #44 on: April 28, 2006, 08:08:13 AM »
Oz, my wants- not needs were to a doubler unit from 12 up to 24 volts. If I read and understood (doubtfull) Fluxes boost thoughts,it would add only the needed volts till the higher rpm's as a higher windspeed was achieved(then disconnect or be bypassed?). A 10 foot machine like Otherpowers produces (ballpark) 100 watts at 10 mph and gets up to 400 watts at 15 mph. Dan B. and friends were kind enough to build one for me (12 volter). If cut in is about 7 mph for 12 volts, just doubling that to 14mph would be 24 volt cutin. Dan F. writes for a publication(in his spare time?) That's where I got the approximate watts figures.

 At this time I feel I should go with 12 volts, just looking at cabling (battery bank)to the inverter of 280 amps seems kind of daunting. Also 16 trojen 105's (or their equivalent) is 8 strings to keep amp draw per string lower. I was hoping to "match the load" at the higher end (greedy), but I will be very pleased to get what I get. Down the road, will upgrade to a higher voltage (probably keeping this system)"if and when" a larger mill comes into my life. It is truely shamefull that I recieved the mill in January and it still isn't flying. I also have an 8 foot Winco unused (12 volter) just waiting to see air. My son is itching to see her spin, was too young to remember our 6 foot Winco back in the 80's. A skid full of missmatched old starter batteries were used on that system, did everything wrong, but still worked! Hanging my head (for good reason)....  Gary D.
« Last Edit: April 28, 2006, 08:08:13 AM by Gary D »

DingBat

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Re: Direct to heater thought..
« Reply #45 on: April 28, 2006, 10:00:19 AM »
I though with capacitors, current would lead voltage.

ELI the ICE man...


--DingBat

« Last Edit: April 28, 2006, 10:00:19 AM by DingBat »

RP

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Re: Direct to heater thought..
« Reply #46 on: April 28, 2006, 02:02:57 PM »
Should work fine going into a heater.  It wouldn't be good into a transformer or reactive load though.  Experimentation would resolve the correct amount of capacitance.
« Last Edit: April 28, 2006, 02:02:57 PM by RP »

vawtman

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Re: Direct to heater thought..
« Reply #47 on: April 28, 2006, 02:32:53 PM »
thanks for you input Tom.

 motor conversions have slight cogging even when they arent loaded.i think i have the same problem.LOL.

 anywho,my plan is to let the turbine freewheel until governed somehow.sorta like the hawts need to get to a certain speed before cutin.

 i would prefer not to use batteries.

 it will spin at 60rpms in a 10 mph wind and thats when the gen would start.

 i was thinking of using caps for awhile.thanks

 sorta like a brake that makes power.

« Last Edit: April 28, 2006, 02:32:53 PM by vawtman »

oztules

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Re: Direct to heater thought..
« Reply #48 on: April 28, 2006, 04:11:42 PM »
Ding you are correct. I don't know what I was thinking....not thinking perhaps


Thanks for the correction            


must take my tablets:).........oztules

« Last Edit: April 28, 2006, 04:11:42 PM by oztules »
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oztules

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Re: boost fets ..... is there an afterlife
« Reply #49 on: April 28, 2006, 04:56:52 PM »
So let me get this straight...

 1. DanB has supplied you with one of his beautiful machines cut in 7mph, 12v


 2. By 15mph, it would be doing 500W or so, and being greedy you wish to extract more power out at higher speeds at 24v and still get the benefit between 7 and 15 mph?


I'm happy with that, in this case greed is power.


Well looks like a doubler in the 500w range is what your after.


Ok, had another fiddle with it last night and decided the wave form under load was "shabby" and was the cause of my inefficiency. Rebuilt the current sensing system from the down and dirty to the not quite so dirty.


The improvement was quite startling. Because of the totally unacceptable layout (long current carrying wires ratsnested all over the bench), the original current limiter was high gain by definition. This meant that it was susceptable to poor layout in a big way, and the more power going through it, the more the waveform suffered from interference from it. This led to the inefficiecies.. I thought i'd be smart and just add more fets and diodes (your suggestion I think), it worked, but it only hid the underlying poor design and layout. Temp was down, efficiency was also.


So having decided to do something about it before I scrapped this experiment, I had to solve this "noise"..... just because...


I used a tiny current sense coil 1 turn: 200 turns (spiderweb thick 200 turns) on a very small ferrite.. The whole coil 1/2"cubed. This gave my over the top control voltages..(over 50v peak), so we have gone overboard again. This was rectified and fed into the op amp, and suddenly the waveform was stable over a very large range (0-30A) No degradation occured at all. Completly stable even with my rats nest.


The interesting thing from this is that with just two mosfets with no heat sink at all, at 50w it stayed stone motherless cold. I couldn't calculate the efficiency to within 5-10% of what was true, as the amp meters were so coarse in their scale that the figures from sight reading came out at 100% which is nonsense, but there was no denying that there was no heat discernable at all in the fets. The new waveform must be close to perfect.


At 120w the two fets only got to luke warm, and once again the efficiency readings were useless as they were so close to unity that with these meters I could not measure what really was going on. But with less then 1 sq cm of cooling on the fets, they stayed very cool.


Up at 30A, there was no appreciable temp rise (only for short periods, as the battery being charged was suffering badly V=18.6 after only 10 seconds.


If you want I will go further with this and try it on the big batteries in the Grader, then I should be able to check the watts without them changing radically at higher powers.


If this goes as planned I will post the circuit etc. Should get away with building it for peanuts.


Is this the kind of thing your after.


For the grand finale, I will try and post a pic of the scope output at 300W (approx)


It looks like more power is simply more fets and diodes. The design seems very stable regardless of my crummy build


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

« Last Edit: April 28, 2006, 04:56:52 PM by oztules »
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Gary D

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Re: boost fets ..... is there an afterlife
« Reply #50 on: April 28, 2006, 06:30:35 PM »
Oz, it is quite up to you how far to take this. It would seem that many people are starting out with either Hugh's 8' or Dan's 10 foot designs. That is why I thought it might be a usefull circuit. I am gratefull you have persued this as far as you have. Hopefully others can see that with your sweat time, and Flux's explanations gains in power could be tremendous; especially thinking along the lines of the 14' and above machines, with furling at the same windspeed. Winding a machine for 24 volts (lower resistance) for a 48 volt system could become the new norm, or a magic bullit? Many thank you's are deserved! Gary D.

« Last Edit: April 28, 2006, 06:30:35 PM by Gary D »

willib

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Re: Battlefield description
« Reply #51 on: April 29, 2006, 08:45:44 PM »
great links amanda..

oh btw , your email addr isnt working.
« Last Edit: April 29, 2006, 08:45:44 PM by willib »
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willib

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Re: Battlefield description
« Reply #52 on: April 29, 2006, 11:35:34 PM »
yes you seem to have left out the L..

it should be aLwynne at bla bla bla.
« Last Edit: April 29, 2006, 11:35:34 PM by willib »
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Flux

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Re: boost fets ..... is there an afterlife
« Reply #53 on: April 30, 2006, 01:47:42 AM »
Oz.

You are only needing to deal with the power below about 12 mph as the machine will be able to run direct above that.


At the change over point you will not be much above 200W and your converter will be phased well back, you will only be boosting a volt or two in the last stages.


I am not sure what frequency you are chopping at, but if you keep it above 20kHz I think you have more turns than really necessary on your inductor. If you have means to measure it, 1mH should be plenty.  I think you could come down to about 20 t and it helps to use several wires in parallel to reduce eddy currents. Core gap of 1 to 1.5 mm should be enough.


If your layout is good, 100v fets should be ok but there are some higher voltage ones around with reasonable Rds on. No good me quoting numbers from here, if you can't get them at a sensible price it won't help.


I think you are about there, it's just a question of making sure you have a good layout and make sure you have fast diodes and polypropylene pulse capacitors directly across the output as close as possible, you can use low esr electrolytics in parallel with that and the connections to them can be a bit longer, the polyprops will take the sting out of the spikes.


If the efficiency is ok at cut in, it should be ok as you start to phase back as the % boost is falling all the time.

Flux

« Last Edit: April 30, 2006, 01:47:42 AM by Flux »

oztules

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Re: boost fets ..... is there an afterlife
« Reply #54 on: April 30, 2006, 07:20:22 PM »
Thank you for that Flux.


I have since played with this thing, and reduced the fets to 3, the diodes to 2xd92 (4diodes@200v 20A)


Somewhere down this diary is a scope directly accross the coil (or fet drain source). It is very close to perfect at 300W. The heat loss in the diodes and fets is surprisingly low, and the efficiency at lower power (<200w ) is excellent.


Current switching is at 3khz. I can hear it at this freq, and layout is more forgiving.


I will vary the frequency upwards to test the wave form of this setup at higher freq, if it degrades, I will keep it low.... kind of agricultural.


How many uf for the poly caps. I have some 2uf 600v greencaps will these be ok?


In your story, you made mention that you used the current in the line to the batteries (all input current from all sources) to modify your switcher.

 unt.


If I load up the prop at full current when it is just starting out, It would stall? In which case do you current limit the output at start according to the system size (prop) and drop from there as the current into the batts gets suplemented and then the main alt takes over?


I'm a bit confused over the characteristic that needs to be built into the switcher


ie I have voltage control at the output 0-60v  i have current control at the output 0-40A..... how should i use them?


Your circuit seems to indicate you start high current and work your way down.. linearly is that correct.?


Thanks.................oztules


I'm putting the cart before the horse here I know, but others may decide to go it alone long before I get the mill up in the air.

« Last Edit: April 30, 2006, 07:20:22 PM by oztules »
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Flux

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Re: boost fets ..... is there an afterlife
« Reply #55 on: May 01, 2006, 12:46:15 AM »
Running at 3kHz is ok and I still have one unit working at a low frequency. It does mean a bigger inductor, but with your core that is not a problem.


It probably does make layout easier but the switching edges are still fast and long leads will still result in serious spikes. Low frequency is convenient in that you can hear it working.


The idea of the polypropylene capacitors is that they have a low impedance to the fast rising edges. To be effective they need to be able to handle fast rising pulses so you are looking for types designed for pulse duty. I use the Evox-Rifa PHE series but Epcos and others make suitable things.


The thing to look for in the data is a high dV/dT rating. Those not designed for this duty will not have a quoted dV/dT rating. Class x suppressor capacitors and normal metalised film capacitors designed for low frequencies will not stand this duty, the pulse current seems to break the metalising and they eventually loose capacitance.


Some types of ceramic capacitor would also do but again there are various types and you need ones specified for pulse duty.


Regarding the control, the circuit is basically a constant current regulator with very low gain. As current starts to flow, the pulse width starts to fall and if the gain was high the thing would current limit at very low current but because of the low gain the current continues to rise until the converter pulsed disappear at a point when the machine is producing a useful charge directly.


I will give you a simpler circuit using a hall effect sensor, I have just got to draw it. The circuit I gave before would be ok but was used on a different type of machine where all the current went through the converter and there was a schottky diode across the shunt to reduce dissipation at high current.

« Last Edit: May 01, 2006, 12:46:15 AM by Flux »

Flux

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Re: boost fets ..... is there an afterlife
« Reply #56 on: May 01, 2006, 02:09:08 PM »
Here is the simpler circuit using the LEM LTS 25-NP hall sensor. There are others that will also do.




.


P1 sets the mark/space ratio and determines wind speed at cut in. Start at 50% on scope.


P2 sets gain and decides the wind speed where the converter pulses stop and the machine carries on without boost.


There is little interaction between the pots if you build it my way.


If your machine is big and the gain is too high just increase R1.


If you choose to use something other than the MC33060A you may have to do some mods.


These chips are designed for switchmode power supplies and the input op amp is meant for high gain and an input near the 5v reference. Many of these chips have op amps on their input with very strange characteristics. I used to use the 3525 as it has mosfet drivers but the input amp will only work over a range near 5v and if you over drive it pulses come back when it should be hard shut off. The 3524 is earlier and may be even more awkward but you can always work round these quirks.


The idea is to get a cut in at about 7 mph and get the converter to pull out as soon as the main machine is working well with direct connection. Leaving the converter in longer causes stall and also lowers the efficiency as the alternator is forced to make more amps at lower volts.


The primary of the hall sensor is linked for 1 turn and is in the battery positive lead. If pulses phase forward rather than backwards the primary leads need reversing.

Flux

« Last Edit: May 01, 2006, 02:09:08 PM by Flux »

dinges

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Re:Current control of psu supply
« Reply #57 on: May 01, 2006, 03:44:35 PM »
Hi Oztules,


Did a bit more of study w.r.t. the schematic of Amanda. Learnt a lot by that. One thing that had me worried a little was the 2ndary power supply in that schematic, that feeds the TL494. Also, the TL494 is fed off a diode via the +12V. If this goes to +29V, the TL494 should survive though (can stand +40V). But I think it would be better to remove the diode D completely and supply power to TL494 only by the 2ndary PSU.


Some questions I still have before I dive in:


-pin16 of the TL494; should it be left as it was, i.e. if grounded leave grounded and if at +Vc left at +Vc? It's a bit unclear from your schematic.


-is there overcurrent protection in Amanda's schematic? I can't spot it, unless it's there in the overvoltage protection.


-pin4 deadtime control. I think this can be completely bypassed (I'm not interested in overvoltage protection here; it's not like I'm going to be feeding boards full expensive logic-ICs. It would be used for regulating drill motors etc. So I can probably simply disconnect the PCB from pin4, I think, without side effects?


-how do you disable overcurrent protection?


-that 330ohm resistor is much less than the feedback resistor of the other opamp (which is 27k, IIRC). You sure this is correct?


voltage control should be straightforward, as you've already pointed out. Only if it goes below a certain level (+7V) it becomes too low for the TL494; in that case, I assume the secondary powersupply (standby PSU) kicks in? Don't know if it is rated for that kind of continuous duty (feeding TL494) though.


As you can see, lots of questions (one idiot can ask more questions than ten wise man can answer, as they say over here :) ) Then again, I'd hate to have my face above an exploding switch-mode PSU.... :0


Peter.

« Last Edit: May 01, 2006, 03:44:35 PM by dinges »
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dinges

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Re: Battlefield description
« Reply #58 on: May 01, 2006, 03:52:14 PM »
I've noticed that deadtime control in the TL494 datasheet.


Does this mean that, in the standard PSU configuration, you can only control pulse-width up to 50% (as it says in the datasheet)? Then again, this should be enough for +12V at 10A, I assume? And +24 at 5A? etc.


You mess around with the deadtime control too? Thinks that would be a little bit over the top/too much for me though.


Will checkout the 'guru' you mentioned.


Peter.

« Last Edit: May 01, 2006, 03:52:14 PM by dinges »
“Research is what I'm doing when I don't know what I'm doing.” (W. von Braun)

commanda

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Re: Battlefield description
« Reply #59 on: May 01, 2006, 05:02:26 PM »
Standard psu is push-pull. That 50% is for each switching device.


Disabling deadtime control is likely to let all the magic smoke escape.


In the single-switch converter, you tie the 2 TL494 outputs together. This way you can get 90 something percent pwm, with deadtime enabled.


Amanda

« Last Edit: May 01, 2006, 05:02:26 PM by commanda »

dinges

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Re: Battlefield description
« Reply #60 on: May 01, 2006, 05:10:08 PM »
You sure about that deadtime control? From the looks of the circuit (the first one you posted) I think pin4 is used only externally when over-voltage conditions occur? I don't see any other feedback-loops going to that pin4.


http://www.pavouk.comp.cz/hw/en_atxps.html


I notice D11 from overvoltage control and a control line from the stdby on/off switch. Nothing to suggest that the deadtime-control of pin4 is used as an active feedback loop. Or am I missing something here?


This is all assuming 'my' PSU is the same as in that schematic, of course. Which is doubtful.


I'm not that bad in electronics, just not an expert on switch-mode PSUs (though I've repaired a few).


Interesting stuff BTW, am learning a lot about switchmode PSUs the last few days.


Peter.

« Last Edit: May 01, 2006, 05:10:08 PM by dinges »
“Research is what I'm doing when I don't know what I'm doing.” (W. von Braun)

oztules

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Re: boost fets ..... is there an afterlife
« Reply #61 on: May 01, 2006, 06:21:39 PM »
Very useful information thank you Flux. I will try this out, but will have to blend in some chips I have on hand. Due to a quirk of history , I find myself on an island with many hundereds of  3825 and 4990 pwm chips ( only a couple dozen 494's) Both have direct fet drives in them and both are curent control types.


The 4990 is single ended with current mode control, so is probably the one of choice.


Layout will be of some importance, and so some experimentation is in order here. This could provide some useful experience.


The 26NP is a ? (LH side)


The sensing of a smooth signal (b+) should ease most instability problems, as I have been sensing with a spiked current and voltage. After 300-350W my system was starting to get spurious waveforms imposed on the output.


Thanks for your tireless question answering Flux. Your solution to the problems of load matching are probably the best combination of simplicity, efficiency, reliability and redundency. The mppt solution that is bandied around is too complex for the not that much better result that you have achieved with a simple boost....


If i can show that a complete idiot can get one of these up, then maybe Danb may just give it a shot, and then more mainstream acceptance will ensue, as I'm sure he will make a good fist of the endevour ( should he try it)


Until then, it will remain a curiosity, which it shouldn't be.


Hopefully I will help those of us who are less electronically literate to cross the barrier and make these devices, and so harvest the resource better, and make better use of the stator.


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

« Last Edit: May 01, 2006, 06:21:39 PM by oztules »
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oztules

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Re: Battlefield description
« Reply #62 on: May 01, 2006, 06:33:29 PM »
The circuit you are referring to is an ATX not an AT which was the type I was describing. The intergration of the small switcher to provide sleep functions, complicates the mix quite a bit, and also uses the second op amp. This doesn't preclude it's use, just muddies the water from simple.


The deadtime is usually used as a soft start, and once running the O/Voltage circuit causes Q5 to conduct which pulls pin 4 up to vref. This pulls deadtime to 100% ie shutdown.

« Last Edit: May 01, 2006, 06:33:29 PM by oztules »
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oztules

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Re:Current control of psu supply
« Reply #63 on: May 01, 2006, 07:20:00 PM »
Hello Peter,


  1. Yes, psu2 can supply the necessary juice. Nn need to modify the circuit from the main secondary feed, as it is diode isolated, so as Vout (main supply) drops below 12v, psu#2 should take over like a ups.
  2. Pin 16 left alone. This is at gnd potential. Our aim is to pull pin 15 below ground when current rises up, thereby turning on the op amp. A triangle wave is compared to an input voltage from op amp 1 and two. (diode isolated inside the case). As the signal voltage increases, so the pulse width is lowered. (draw a triangle wave, and slide a ruler up and down the y axis (ruler parallel with x axis). The size of the triangle thats left as you ascend up the y axis gets less and less. The width across the base of the resultant triangle is the width of the output wave. )So as we increase the output from op amp 1 or 2, we decrease the output wave. This is what we have to achieve by any number of methods. If you are the lucky one and have a circuit, it makes it that much easier.
  3. No....but somehow in the myriad of interrelated diodes, zeners, resistor bridges over at the O/voltage circuit, it also senses the o/load of the device. I think by undervoltage, but have never followed it through.
  4. Amanda has stated a very important thing...magic smoke. However Pin 4 need not be used but it would be handy to use it for a soft start. (cap 10uf to + and 100k resistor to ground.  Overcurrent protection is tangled up in the overvoltage networks to pin 4.
  5. 330r and 10n....no not certain, but it works for me. You may find better values or feedback systems. I didn't spend much time on this, just made it work. I would be happy to see a better approach to this loop.


I don't see the tl494 using huge amounts of power, and the aux should be good for a few watts.  


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

« Last Edit: May 01, 2006, 07:20:00 PM by oztules »
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Re: Battlefield description
« Reply #64 on: May 01, 2006, 07:25:18 PM »
Peter I'm sorry I was looking at the wrong thing disregard post #62


.........oztules

« Last Edit: May 01, 2006, 07:25:18 PM by oztules »
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oztules

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Re:Current control of psu supply
« Reply #65 on: May 01, 2006, 07:42:05 PM »
One more thing, As per Amandas warning about magic smoke. The genie will arise if you disable the deadtime circuits  before you achieve stable active current control. If you don't get the current control under control before you fiddle with the voltage circuits (pertaining to pin 4), then magic smoke is a certainty. It is the only protection you will have until you can knowingly stop the current from running away and going feral. There is no margin for error with this part.


Whilst the pin4 network is properly active, shut down is usually the only disaster to befall you when you are mastering the current control.


wear glasses for eye protection please...


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

« Last Edit: May 01, 2006, 07:42:05 PM by oztules »
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