Workbench DC Power Supply Project.....sounds feasible?

[partyanimallighting]

Thanks themadhippy! I just want to be sure that I order the correct part. So 50K 3 Pin Linear Taper Potentiometer it is.

[richardash1981]

You also used to be able to get x10 (and more!) geared reduction drives to mount onto a standard (1/4" shaft) potentiometers, so the knob went round multiple times but the pot only turned once. Would be more complex / messy to mount however, because I think the drive went on the panel and the pot had to be supported behind it.

[Jivemaster]

Sometimes a control has  coarse and fine knobs. It's just two potentiometers wired in series. The fine pot is 5 to 10% of the value of the coarse pot.

[partyanimallighting]

So richardash1981, this reduction would give you even more precise control of the output? And Jivemaster, the smaller pot in series would do the same? Interesting........

Edited June 18, 2023 by partyanimallighting

[Jivemaster]

I've seen the geared drive used on amateur radio controls, I have a bench psu with two series pots in the voltage control section.

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[pmiller056]

Panel mounting 10 turn pots can be expensive to buy. If you have the front panel space for two pots, a much cheaper way is to use a dual track pot as a 'coarse' control and a normal single track pot as a 'fine' control. See the image below. This works well if the pot is used as a voltage divder and the end-to-end resistance of the pot track is not critical (most cheap mass-market pots are typically +/-20% anyway). The values shown are appropriate for a 50k pot. Scale the values for your application. This idea only works where a linear-taper pot is needed in the application.

Edited June 19, 2023 by pmiller056
Tidy-up.

[themadhippy]

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Panel mounting 10 turn pots can be expensive to buy

wouldn't class £3.83 expensive,especially as you can pay that  for a bog standard dual pot

The problem I have with course/fine is the constant juggling act needed to get things just were you want them course down a bit fine up a bit course down a smidge,oops to far.

Another thought,if you've the space is to add in a dual fixed supply,its the most used part of my power supply set up,no pots to mess with,just a switch to swap between voltages.

 

 

[partyanimallighting]

Well madhippy, I bought a case after countless measuring and remeasuring so everything WILL HAVE to fit! My intention for the build is as follows: a True Con connector on the back panel with leads going to two individual switches mounted on the front panel, one switch feeds a 12V 20A PSU, the other switch feeds a 24V 15A PSU. The outputs from these PSU's will feed two individual volt/ammeters, also on the front panel along with individual banana plug inputs. A separate feed off the 24V PSU will feed yet another switch on the front panel then onto a small buck DC to DC converter and the 50K pot, then to yet another meter and on to this third feed's banana plug inputs. So banana input 1 ~ 12VDC, banana input 2 ~ 24VDC and banana input 3 ~ 24VDC ~ 60VDC. 🤔 .......hopefully........

[partyanimallighting]

Well, I'm back after a two week trip/holiday and work seems to be progressing smoothly on my power supply. The PSU's fit neatly into the project case but the space is a little tight so I'll have to use right angle spade terminals on the power switch (I went with only one main switch instead of individual switches for each output) and the most difficult task was cutting the knockouts for the meters. Trying to control a drill nibbling tool on such small holes was stressful to say the least so I opted for a rotary tool and hand file. I'm also short one meter so here's the next question. The meters I bought are volt/ammeters and they're rated at 10A/100V so they'll work fine on the 12VDC and 24VDC outputs. However........I'm using a DC ~ DC buck converter, fed of the 24VDC PSU, to feed the variable output supply and neither of the two meters I have available will work because, despite being rated at 0 ~ 100 volts, the pamphlet states voltages over 30 volts will burn the meter. So my question is, why do all the meters I've searched for (same size as what I have for conformity) state 0 ~ 100V when they can only read up to 30 volts? 

[Tom Baldwin]

The small V A panel meters I have seen normally have separate connections for a supply to make the meter electronics work and for the system to be measured.

So you would feed the meter supply connections with something less than 30V, while the other connections (for measuring) can cope with up to 100V.

Do you have a link to the meters you've bought?

[themadhippy]

I've use several voltcraft 230rn, on various projects ,a few quid more than the ebay cheapys,but the measurement inputs are separate to the supply (9v) plus  you can configure them to show additional characters including  V A m u, set were the decimal point is. With a bit of clever switching they can be used for both voltage and current measurement with the appropriate  unit also displayed.You can find  the datasheet at  https://static.rapidonline.com/pdf/126564_an_ml_01.pdf

[partyanimallighting]

Well, here are the basic specs listed on the web page:

Specifications:
Working voltage of Meter itself:DC 4 - 30V(The maximum input voltage can not exceed 30V. Otherwise the meter will be burned)
Working current of Meter itself:≤20mA
Voltage Measuring range: DC 0 - 100V
Current Measuring range: DC 0 - 10A
Voltage resolution (V): 0.1V
Current resolution (A): 0.01A
Measure accuracy: 1% (± 1 digit)
Display: 0.28" digital tube, Two color blue and red
Refresh rate: about 300mS / times
Dimensions:48mm*29mm*26mm
Operation Temp: -10°-+65°

Package Include:
1pcs x Mini Digital Voltmeter Ammeter DC 100V 10A Panel Amp Volt Current Meter Tester 0.56" Blue + Red Dual LED Display

[partyanimallighting]

I'm basically letting my OCD flow uncontrolled with this little project. Red meter with red wiring for 12V, blue meter with blue wiring for 24V and yellow meter with yellow wiring for >24V and I'm almost done. The 12V and 24V meters seem to be correctly wired (thin red and yellow to banana socket+ output from PSU+, thick black wire from PSU-, thin black wire ignored and thick red wire to banana socket-). I tested with a LED PCB and diode plate and the voltage readings are correct and I'm getting what I assume are correct Amp readings. I just have to sort out that meter issue (+30VDC on the variable voltage output) and sort out this new issue with the replacement rotary pot.  I followed the advice from themadhippy and I removed the 3296 503 50K pot from the buck converter and wired in the 50K panel mount pot and tested but I'm not getting a voltage increase on the output. Possible faulty solder job??

Edited July 20, 2023 by partyanimallighting

[partyanimallighting]

OK, I went at it again with the variable voltage output. As I mentioned above, I removed the 3296 503 50K pot wired directly to through holes for the 3296 on the  PCB but the pot didn't work. So I pulled another buck converter, removed the original pot  and soldered on a 3 pin Molex connector to the pot terminals. I then wired the 50K rotary pot to the female Molex and powered up. The output voltage is 24VDC but again, I am not getting any increase in voltage off the DC to DC buck converter via the 50K pot so I'm either doing something wrong wiring wise or the pot is not compatible (???). I wired according to the pin numbers on the 3296 (pin 1 to red wire on rotary pot etc) but no control. I then tested another converter with the original 3296 pot and this pot functions fine so I'm sort of stumped here.

 

 

 

[DrV]

Did you drill out the holes in the PCB to fit that connector, or otherwise damage the tracks so that the pot is not actually connected to the circuit? Looking particularly at pin 1 where I think I can see untinned copper.