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irishron40 Senior Member Joined: 22/09/2014 Location: IrelandPosts: 251
Posted: 04:36am 03 Jul 2016
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i just connected this yesterday. but the 330 ohm R7 restistor keeps burning out. I had no load connected and cant see an obvious fault . anyone any suggestions why that resistor could blow
thank you
ronEdited by irishron40 2016-07-04
Pete Locke Senior Member Joined: 26/06/2013 Location: New ZealandPosts: 181
Posted: 10:19pm 03 Jul 2016
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Did it smoke straight away, or did it happen as you wound the voltage up? Possible cause is you have the junction end of the resistor connected to the wrong side of the R7/R8 junction. That would negate the voltage feedback to the regulator chip. As with any new build, check the important connections twice. Then check them again after a coffee. I've let lots of smoke out of things by not doing that
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 10:23pm 03 Jul 2016
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You can buy that smoke in bottles now.There are only 10 types of people in the world: those who understand binary, and those who don't.
Pete Locke Senior Member Joined: 26/06/2013 Location: New ZealandPosts: 181
Posted: 10:25pm 03 Jul 2016
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Yep, I'll do you a good deal on a pallet load
irishron40 Senior Member Joined: 22/09/2014 Location: IrelandPosts: 251
Posted: 11:00pm 03 Jul 2016
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Pete ,i dont get what you mean. it starts smoking the moment i turn on the power , without a load connected.
I double checked , or trebled checked. I seem to have it as the diagram.
thx ron
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 11:12pm 03 Jul 2016
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Hmmm. It is just a voltage divider....on max volts would draw 40/450=88ma.
I^2R means .088x.088x330=2.5watts dissipation in the worst circumstance... would toast a 1/4 watter.... the 120r would burn up some .9watts so would not cook as fast as the 330r
The pin 4 is high impedance , so the divider has only one voltage drain... Gnd...
To test this use a 1k2 and a 3k3 resistor for R7, R8.... and this will give you time to find out what else is going on and work exactly the same without the burn ups...current will drop at worst scenario ( 40v) to 8ma or .02 watts... 100 times less because of the square function in the watt equation of I^2 and R for 10 times bigger R
ie now you can measure your Voc, and if high.......do you have a shorted transistor or a mounting problem with the rotten 3055 packages somewhere, poor insulation on the transistors to body of heat sink etc etc.
Voltage of the r7,r8 junction with respect to ground, and see if it works as expected.... if you have no control, then you have a problem somewhere else, making your output unregulated for some reason... is pin 4 short to internally?
...........oztulesEdited by oztules 2016-07-05Village idiot...or... just another hack out of his depth
irishron40 Senior Member Joined: 22/09/2014 Location: IrelandPosts: 251
Posted: 12:04am 04 Jul 2016
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thank you. they are 1/4 watt resistors i used.
pin 4 is connected between the 120 and 330 ohm resistors.
and between pin4 and pin 13 i used a small 100pf ceramic cap
I am after rebuilding it as I had the larges resistors on a stripboard, so being separated from that board it will eliminate melting the strips.
I didnt use 3055 transistors but 4 Tip41C transistors insted.
i see what happens when i power up the new layout.
thanks again.
Pete Locke Senior Member Joined: 26/06/2013 Location: New ZealandPosts: 181
Posted: 12:08am 04 Jul 2016
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O.K Did you have a volt meter connected to the output of the power supply when you turned it on? Trying to gather info on the fault from half way round the world is always interesting after a couple of beers and limited info about the symptom. So. What wattage is the resistor? The reason I suggested the connection between the two resistors is that that is where the regulator chip get's its reference from. So here's what I would do. If R7 is smoking but R8 isn't. Set the output voltage on the control to minimum. Have a volt meter connected to the output terminals. Turn it on. What voltage shows up. I'm guessing it's almost full voltage. This is assuming, from half a world away, that everything else is wired correctly. Also, how long does it take after switch on before the R7 starts to burn. It is a fairly simple circuit. But I would be looking at the junction of R7/R8, and making sure it's connected to pin 4 of the chip. Also, if there is an error in the wiring of R10 then the regulation of the output wont work. However. The issue of R7 smoking tells me that it's somehow connected between maximum voltage and ground. Solder bridges (no matter how small) can also be a cause.
Good luck
irishron40 Senior Member Joined: 22/09/2014 Location: IrelandPosts: 251
Posted: 04:59am 04 Jul 2016
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thx
Edited by irishron40 2016-07-05
VK2MCT Senior Member Joined: 30/03/2012 Location: AustraliaPosts: 120
Posted: 03:12pm 04 Jul 2016
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Which pins are you using on the Tip41C for Collector / Base / emitter ?
John
irishron40 Senior Member Joined: 22/09/2014 Location: IrelandPosts: 251
Posted: 03:26pm 04 Jul 2016
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Hi John.
Pin1 = base
Pin2 = collector
pin3 = emitter
thx
ron
irishron40 Senior Member Joined: 22/09/2014 Location: IrelandPosts: 251
Posted: 04:45am 05 Jul 2016
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Losing my patience here lol
I am after rebuilding it and have no shorts from veroboard.
when i connected it and put voltmeter on outputs it gave me from 2.5 to 24.8 volt
the moment i put on a load transistor no4 started smoking.
i then disconected that one and then No 3 started smoking.
Ic got also warm and resistor R7 burned out again.
I have no variable voltage ,just max voltage at 37volt
but when i disconect power to main transistors i do have 2,5 to 24.8
Edited by irishron40 2016-07-06
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 02:28am 07 Jul 2016
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I can not see what the problem is, i am unable to make any solution from your picture as it tells me nothing, maybe a matching photo of the bottom side of the strip board may help.
My gut feeling is you have a short to ground somewhere.
Do you realise that the heat sink is live to V+ supply voltage unless the transistors are isolated from it.
It would seem you have a short somewhere between the emitter pin of 1 or several of the 3055 transistors and ground, there is no way they should blow if the current is going through the ceramic resistors.
Are you 2000% sure you have the transistors wired the correct way around, Base Emitter, collector?
You should be able to do a test as i do with connecting the output leads together as a dead short and then wind the voltage up and it should current limit to the setting of the output current.
Your circuit is not doing that so you MUST have a construction error, Gismo and many others built the circuit and it worked, so it can only be a error in your circuit.
Pete.
Sometimes it just works
irishron40 Senior Member Joined: 22/09/2014 Location: IrelandPosts: 251
Posted: 05:39am 07 Jul 2016
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thank you for your reply.
i have the bd139 connected 1 emiter 2 collecter 3 base
the transistors are isolated from heatsink and double checked it with tester
transistors i used are tip41c
pin 1 is base
pin 2 is collector
pin 3 is Emiter
emiter from bd139 i have connected to base from the tip transistors
collector from bd139 is connected to supply at the large capacitor
base from bd139 is conneted to pin 10
tip pin 1 to emiter bd 139
tip pin 2 to supply from capacitor
tip pin 3 emiters are all 4 connected separete to each of the 4 large resistors
I looking at it for 2 days and realy want it to work. I also tested all the circuits on the board, and there is no short shown
Thank you Pete
Edited by irishron40 2016-07-08
irishron40 Senior Member Joined: 22/09/2014 Location: IrelandPosts: 251
Posted: 07:44am 07 Jul 2016
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ok just seen that all 4 tip41c and also the bd139 were blown. i relaced the bd139 and only connected 1 tip for testing.
nothing blowing lol ,
yesterday i had 2-24.5 volt
now i have 4.3- 25.9
when i connected a wiper motor , just the transistor blew again.
restistor didnt burn this time.
I did however used the continou tester to check was any of the legs from tip and bd139 making contact with neutral. and they didnt
it seems to blow when i connect something. like i said i am also confused why output range is different now
back to drawing board.
gosh i love this new hobby lol
Edited by irishron40 2016-07-08
irishron40 Senior Member Joined: 22/09/2014 Location: IrelandPosts: 251
Posted: 11:19am 07 Jul 2016
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right just changed r7 and r8 to 1k and 3.3k resistors as oztules mentioned to me in other thread.
voltage range was lower . when i connected motor again the tip41c exploded
I double checked neutrals and positives again, but cant find the problem
ron
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 12:08pm 07 Jul 2016
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The change in voltage is because you have changed the ratio as well, the 1k needed to be 1k2... but thats not relevant to whats happening.
You are exceeding the current the tip41 can run. Start up of a motor from a wiper can be in the high 20a range, and you have a 6 amp transistor, capable of transients of 10a.. it is a baby in this case.
I hope you are not trying to use this for motor control... it won't cut it for that motor without loads of heat from a lot of transistors... use a pwm version, linera ones are not viable.
I would also probably use the tips for the driver.
Try a 5w parklight globe first, then go to blinker globe ( 18w). It should run them ok.
This should get the thing working, and you can test it out to see if it is all fine.
Next is to test the current foldback system. It looks like it takes a sample form the 0r5 resistors to override the voltage signal, and attenuate in over current conditons.
Test it to see how many volts are required to see this happen, and calculate the current across the load resistors and see if that will trip it to save the blow ups.
I think your asking way too much from it from my experience with these types of linear power supplies.
With tip35c,we can squeeze 10 amps/transistor if you can keep it cool... those tip41's are small comparatively.
You may have done nothing wrong except drive it way over the top.
.........oztulesVillage idiot...or... just another hack out of his depth
irishron40 Senior Member Joined: 22/09/2014 Location: IrelandPosts: 251
Posted: 12:24pm 07 Jul 2016
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this wiper motor draws 2.5 amps
i am just wondering oztules can a shortend bridge rectifier cause it to blow each time also?
thanks ronEdited by irishron40 2016-07-08
irishron40 Senior Member Joined: 22/09/2014 Location: IrelandPosts: 251
Posted: 12:32pm 07 Jul 2016
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yesterday it blew all 4 tip41c transistor and also the bd139
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 02:41pm 07 Jul 2016
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2.5a when running... what is the instant surge when starting though...
How many ohms does it report on a measurement, that will give you the max amps it will draw on instant start up.
Try the resistive globes first to ascertain if you really have a problem... then increase power.
The fact is does not blow under no load tells me your transistor connections are probably ok, but there is a problem with your current control. we know the voltage controls alright, so it must be somewhere else..... try globes first and see if it heats up dramatically.
.........oztulesVillage idiot...or... just another hack out of his depth
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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