Author Topic: DIY 0-30V 0-3A ...Again  (Read 15809 times)

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Offline m3vuv

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Re: DIY 0-30V 0-3A ...Again
« Reply #50 on: November 27, 2019, 04:57:28 pm »
u3 voltages are as follows,this is with the output set at 6v in cv mode pin1:-5.2v pin2:0.0002v pin3:10.05v
pin4:-5.12v pin5:-5.22 pin6:22.61v pin7:23.69v pin8:0.2v,pin 3 doesent vary smoothly with the cc pot but
sits at 10v cc led off,0v led on,its like on or off,no smoth varyation but a sudden jump,hope this helps.
 

Offline floobydust

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Re: DIY 0-30V 0-3A ...Again
« Reply #51 on: November 27, 2019, 06:00:36 pm »
CC setpoint at U3 pin 3 should smoothly go from 0.005V to 1.5V as you rotate the pot. Using values P2 10k, R17 33R, R18 56k. You are getting 10V which is way too high.

Either the potentiometer P2 is defective or wired up wrong, or R18 or R17 are the wrong value.
 

Offline m3vuv

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Re: DIY 0-30V 0-3A ...Again
« Reply #52 on: November 27, 2019, 07:06:53 pm »
well sorted it,it was the pot u/s,replaced it and its working fine,cheers all m3vuv.
 

Offline xavier60

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Re: DIY 0-30V 0-3A ...Again
« Reply #53 on: November 27, 2019, 07:59:47 pm »
well sorted it,it was the pot u/s,replaced it and its working fine,cheers all m3vuv.
What sort of Pot is it? I have had 2 cheap 10T Pots from ebay do the same thing. Real scary when it's the CV Pot.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline JwillisTopic starter

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Re: DIY 0-30V 0-3A ...Again
« Reply #54 on: November 28, 2019, 12:11:03 am »
Wow .Never thought this thread would pop up again.
Anyway the supplied pots in the kit are crap. One was faulty at start and the other failed soon after.
Yes I finally got this Kit to work properly by reducing the transformer voltage to 20 Volts.  Also replace the pots with  WXD3-13-2W 10K 10 Turn Potentiometer .

The  2X 0.25 5W resistors in series made little difference to the final operation. Added a small 40mm X 40mm heat sink and 40mm 12v fan supplied by the onboard 12v regulator. Regulator only required a small 10mm by 20mm heat sink.
All in all it works fine. 
 
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Offline floobydust

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Re: DIY 0-30V 0-3A ...Again
« Reply #55 on: November 28, 2019, 12:39:43 am »
Did you mean these green potentiometers that come with the kit are crap? I found they work OK.
 

Offline xavier60

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Re: DIY 0-30V 0-3A ...Again
« Reply #56 on: November 28, 2019, 12:42:52 am »
My failed Pots are fake Bourns 3590S series,10K via ebay. The resistance wire breaks.
There are a lot of Bochen WXD3-12 Pots about. I hope they are not fakes.
Looks like they are 5 turns which I think I can live with.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline JwillisTopic starter

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Re: DIY 0-30V 0-3A ...Again
« Reply #57 on: November 28, 2019, 05:53:37 am »
Did you mean these green potentiometers that come with the kit are crap? I found they work OK.

Maybe I just have bad luck  :(
 

Offline m3vuv

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Re: DIY 0-30V 0-3A ...Again
« Reply #58 on: November 28, 2019, 01:36:04 pm »
With mine i used a 2n3055 for q4 driven by a bd139,this in turn drives  6x tip35 trannys,the transfo is one from a 30amp ham radio psu with 5 more turns on it,r18 is a selection of 3 different values selectable on a 3way rotary switch,the current sense resistor is 0.8ohm 25 watt wirewound,goes from 0-29v and 100ma to 20a ok,also quadrupled the size of the filter caps and used a 50a bridge rectifier,its working well,the heat sink is 8" square with a 12v quadbike radiator fan bolted to it runing from a thermo switch and relay,it has a cv led as well and a digital volt/amp meter with a 90a shunt.
« Last Edit: November 28, 2019, 01:38:06 pm by m3vuv »
 

Offline xavier60

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Re: DIY 0-30V 0-3A ...Again
« Reply #59 on: November 28, 2019, 11:02:46 pm »
 Has anyone tried any mods to enable T2 to also function as a fast current limiter?
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline JwillisTopic starter

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Re: DIY 0-30V 0-3A ...Again
« Reply #60 on: November 29, 2019, 08:27:31 am »
 I've only done in depth tests and measurements on a modified circuit using the OP445.Of course all the transistors are of higher ratings than the original circuit.
As far as I can tell, when messing around with the circuit , Q1/T2  is a current dump for when the circuit is turned off. Without it, the output voltage shoots up to the charged voltage in the filter capacitors then slowly drains off . Even when voltage and current  is set to 0V before shut down.In my case the out put would shoot up to 40 volts.
On tests I noticed that when power is on, the base ofQ1/T2 is at a negative volltage equal to the negative rail.Around -25 volts.  When power is switched off the base goes positive and dumps any voltage at the output to ground.But the filter capacitors remain charged for a period of time until they to drain off. I did put a similar circuit to also discharge the capacitors and it worked pretty much the same way, but later removed it to simplify things for further testing and design.The breadboard was getting crowded.
 

Offline xavier60

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Re: DIY 0-30V 0-3A ...Again
« Reply #61 on: November 29, 2019, 09:12:34 am »
I've only done in depth tests and measurements on a modified circuit using the OP445.Of course all the transistors are of higher ratings than the original circuit.
As far as I can tell, when messing around with the circuit , Q1/T2  is a current dump for when the circuit is turned off. Without it, the output voltage shoots up to the charged voltage in the filter capacitors then slowly drains off . Even when voltage and current  is set to 0V before shut down.In my case the out put would shoot up to 40 volts.
On tests I noticed that when power is on, the base ofQ1/T2 is at a negative volltage equal to the negative rail.Around -25 volts.  When power is switched off the base goes positive and dumps any voltage at the output to ground.But the filter capacitors remain charged for a period of time until they to drain off. I did put a similar circuit to also discharge the capacitors and it worked pretty much the same way, but later removed it to simplify things for further testing and design.The breadboard was getting crowded.
Have you measured the size of the current spike when the output is short circuited?
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline JwillisTopic starter

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Re: DIY 0-30V 0-3A ...Again
« Reply #62 on: November 29, 2019, 09:50:12 am »
On the original or modified version? The original I have not . I could set it up later and test it. but I can't imagine it being much higher than the 3 amps I was getting on load test.
On the OP445 version it has a maximum current output of well over 20 amps shorted .But I only tested that once because it set the boards on fire and could not get an accurate measurement . :-DD .Right now its limited to just 10 amps until I can modify the bread board setup with heavier rails for current.
 

Offline xavier60

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Re: DIY 0-30V 0-3A ...Again
« Reply #63 on: November 29, 2019, 10:13:43 am »
The concern is what the current spikes to in the first few hundred microseconds. Because output BJTs are usually used at a fraction of their maximum ratings, it might seem that the BJTs are safe even if the spike is very large. Maybe they will never fail.
What bothers me is not being able to figure out how much SOA derating to allow for at high temperature.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 


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