Author Topic: LM324 Power Supply with variable voltage and current  (Read 71930 times)

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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #875 on: June 20, 2021, 02:50:19 pm »
I removed C3 and now it look like that behavior of the led and relay disappeared.
By removing C3, one of the terminals of R7 remained unconnected.

Are there any other tests that I should do ?

LE: I tested with a 12V/20W light bulb (halogen) as a load, at a 14.4V output voltage. When I connected the load, the relay made a click and the led gone off and then again on, in a fraction of a second. Also, the CC led of the power supply was on while the red led was off. That was because the light bulb have a low resistance at room temperature...
« Last Edit: June 20, 2021, 02:57:09 pm by mike_mike »
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #876 on: June 20, 2021, 03:09:02 pm »
The purpose of R7 and C3 is to prevent the relay chattering while trying to switch from 15V to 30V while the PSU is at maximum load.
R8 and C2 cause a short fixed delay. R7 and C3 add no delay when the PSU output is shorted at high voltage. We don't want the output transistors having high voltage across them for too long.
 You could do some tests first to see if the chatter problem is there while C3 is removed.
Then maybe make some compromise by shortening the TC of R7,C3 and increasing R8,C2.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #877 on: June 20, 2021, 03:20:52 pm »
The purpose of R7 and C3 is to prevent the relay chattering while trying to switch from 15V to 30V while the PSU is at maximum load.
I did not understood exactly what you tried to explain in the above statement. Could you be more specific please ? How can I do this ?
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #878 on: June 20, 2021, 03:38:14 pm »
Set the PSU to 12V with close to maximum load. Then adjust up the voltage until the relay changes from 15V to 30V.
Repeat this while listening for relay chatter.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #879 on: June 20, 2021, 03:44:44 pm »
I set the output voltage to 12.5V, connected a 12V/35W halogen bulb and I increased the output voltage.
When increasing the voltage, the relay gone ON at 12.97V, and when decreasing the voltage the relay gone OFF at 12.74V.
There was no chattering, there were only normal transitions.
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #880 on: June 20, 2021, 04:02:32 pm »
I set the output voltage to 12.5V, connected a 12V/35W halogen bulb and I increased the output voltage.
When increasing the voltage, the relay gone ON at 12.97V, and when decreasing the voltage the relay gone OFF at 12.74V.
There was no chattering, there were only normal transitions.
That's good, no need for R7 and C3. I need a bit more time to rethink the R8,C2 delay. There might be a better way to do it.
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Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #881 on: June 20, 2021, 04:22:47 pm »
I would like to see how this version works before committing.
Leave C3 out.
« Last Edit: June 20, 2021, 04:26:08 pm by xavier60 »
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #882 on: June 20, 2021, 04:30:01 pm »
I will try this version and I will come back later with the results.
 

Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #883 on: June 20, 2021, 07:00:26 pm »
I tested the latest version, but it looks like it works like the previous version.
I made this test, and it looks OK:
I set the output voltage to 12.5V, connected a 12V/35W halogen bulb and I increased the output voltage.
When increasing the voltage, the relay gone ON at 12.97V, and when decreasing the voltage the relay gone OFF at 12.74V.
There was no chattering, there were only normal transitions.
But when I set the output voltage to 13V, and connect an 12V/20W light bulb then the PSU enters for a very short period into CC and the relay is going OFF then ON, also the led that is connected in parallel with the relay is flashing one time. Is this normal ?
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #884 on: June 21, 2021, 12:33:04 am »
But when I set the output voltage to 13V, and connect an 12V/20W light bulb then the PSU enters for a very short period into CC and the relay is going OFF then ON, also the led that is connected in parallel with the relay is flashing one time. Is this normal ?
Yes, that can be considered as normal.
The previous timer-latch circuit would not have worked properly in a situation where the input changes back to its original state immediately after a timeout. The output would also change back after a too short time.
The new C2 position and the diodes cause C2 to quickly charge to near 12V immediately after a timeout and output transition.
If the input immediately changes back, the output wont change until some time has passed, determined by R8 and C2, about 8mS.

Check that Q1 is handling the coil current ok.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #885 on: June 21, 2021, 01:40:51 am »
Q1 doesn't heat up, it looks like it handles the current OK, but probably it would be better to use a higher current transistor. The relay coil is consuming about 30mA and the LED about 10mA. So a totally of 40mA.

Probably I will change the relay with a better one, this is cheap chinese 10A relay.
« Last Edit: June 21, 2021, 01:44:06 am by mike_mike »
 

Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #886 on: June 21, 2021, 06:23:58 am »
I made a layout in Kicad for the tap switching circuit.
Please have a look and tell me what you think...
Dimensions 51x71mm.
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #887 on: June 21, 2021, 06:50:06 am »
Looks very compact. Are mounting holes needed?
It's not clear that C1's pad connects to pin 3 of the opamp. Do the tracks look wider than actual?
The tracks to the relay contacts should be wider.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #888 on: June 21, 2021, 06:53:21 am »
Mounting holes are not needed.
C1's pad connects to pin 3 of the opamp. The tracks are 1.2mm wide.
The tracks to the relay contacts are 3mm wide. I could make them wider, but those tracks will be covered with tin.
 

Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #889 on: June 21, 2021, 10:58:25 am »
I've built the circuit on the PCB, and it works, but I saw that my transformer has a secondary of about 17Vac and one of about 12Vac. I connected the tap switcher to the 17V secondary.
I found the following 2 things: when I increase the voltage, when the relay goes ON, then the CC led of the PSU lights for a fraction of a second. The second thing that I saw is that when the output voltage is very close to 13V (the switch point voltage) then if I turn off the PSU, after 2-3 seconds, the relay goes ON then OFF, also the relay's led (I used a amber led).

Edit: and the relay is chattering when powering the 12V/35W light bulb and when I increase the output voltage.
« Last Edit: June 21, 2021, 11:06:03 am by mike_mike »
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #890 on: June 21, 2021, 11:17:55 am »
I've built the circuit on the PCB, and it works, but I saw that my transformer has a secondary of about 17Vac and one of about 12Vac. I connected the tap switcher to the 17V secondary.
I found the following 2 things: when I increase the voltage, when the relay goes ON, then the CC led of the PSU lights for a fraction of a second. The second thing that I saw is that when the output voltage is very close to 13V (the switch point voltage) then if I turn off the PSU, after 2-3 seconds, the relay goes ON then OFF, also the relay's led (I used a amber led).
You have the 2 secondary windings of the main transformer in series. with the tap changer selecting 12VAC or 29VAC?
I cant imagine whey the CC LED should blink when the relay pulls in. Try tracing it with your DSO.
The regulated 12V in the tap changer serves as reference. As the 12V rail drops, the sense threshold voltage also drops. The relay will pull in for lower PSU output voltage.
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Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #891 on: June 21, 2021, 11:27:57 am »

Edit: and the relay is chattering when powering the 12V/35W light bulb and when I increase the output voltage.

Is the chatter brief or continuous?
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #892 on: June 21, 2021, 11:30:30 am »
You have the 2 secondary windings of the main transformer in series. with the tap changer selecting 12VAC or 29VAC?
The relay is selecting 17VAC or 29VAC. The CC led doesn't blink if I power the tap changer from another supply (for example another transformer or the LM324 PSU).
But if I power the tap changer from the voltmeter's transformer, then the voltmeter doesn't work anymore.

Is the chatter brief or continuous?
The chatter is brief.
« Last Edit: June 21, 2021, 11:32:12 am by mike_mike »
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #893 on: June 21, 2021, 11:41:02 am »
You have the 2 secondary windings of the main transformer in series. with the tap changer selecting 12VAC or 29VAC?
The relay is selecting 17VAC or 29VAC. The CC led doesn't blink if I power the tap changer from another supply (for example another transformer or the LM324 PSU).
But if I power the tap changer from the voltmeter's transformer, then the voltmeter doesn't work anymore.

Is the chatter brief or continuous?
The chatter is brief.
I assumed that the tap changer was being powered from a separate transformer to avoid unwanted current through the CS resistor.
Does powering from a separate supply stop the chatter? If not, try increasing the delay by increasing R8.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #894 on: June 21, 2021, 12:26:57 pm »
Does powering from a separate supply stop the chatter? If not, try increasing the delay by increasing R8.
Yes, by powering the tap changer from a separate 12Vac transformer, it stops the chatter.
Also, it stops the CC led blink.
« Last Edit: June 21, 2021, 05:41:25 pm by mike_mike »
 

Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #895 on: June 21, 2021, 08:44:43 pm »
Should I leave the circuit as it is, by powering the tap switcher from a individual transformer ?
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #896 on: June 21, 2021, 11:32:45 pm »
Should I leave the circuit as it is, by powering the tap switcher from a individual transformer ?
Yes. You could also test for chattering at a higher changeover voltage.
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #897 on: June 22, 2021, 12:40:16 pm »
I set the relay ON voltage (changeover voltage) at PSU output voltage of about 16.5V.
The chattering did not appear.
I used as load a halogen light bulb 12V/20W.
Now I am powering the tap changer from a separate transformer (12Vac) and the digital voltmeter from another transformer which is also 12Vac secondary.
 

Online xavier60

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Re: LM324 Power Supply with variable voltage and current
« Reply #898 on: June 22, 2021, 04:11:12 pm »
Did you try powering both from the same transformer?
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Offline mike_mike

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Re: LM324 Power Supply with variable voltage and current
« Reply #899 on: June 22, 2021, 04:41:29 pm »
Yes. If I power both tap switcher and voltmeter from same transformer, then the voltmeter show "1".

Where '1' means overload...
« Last Edit: June 22, 2021, 07:02:27 pm by mike_mike »
 


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