Adjustable Voltage Regulator Step Down Power Supply

[cctransuk]

As I outlined a single resistor change will restore 300 degree pot rotation and hence even finer control, should that be desired

 

Please could you indicate - in terms and diagrams as simple as those provided by Brian (above), exactly what I need to replace with what?

 

Reference to the images of the regulator at https://www.aliexpress.com/item/LM317-Adjustable-Voltage-Regulator-Step-Down-Power-Supply-Module-With-LED-Meter/32618386190.html?spm=a2g0s.9042311.0.0.svpAoZ would, for an electronic numbskull like me, be most explanatory.

 

Sorry to be a nuisance; thanks in anticipation.

 

Regards,

John Isherwood.

[Junctionmad]

Please could you indicate - in terms and diagrams as simple as those provided by Brian (above), exactly what I need to replace with what?

 

Reference to the images of the regulator at https://www.aliexpress.com/item/LM317-Adjustable-Voltage-Regulator-Step-Down-Power-Supply-Module-With-LED-Meter/32618386190.html?spm=a2g0s.9042311.0.0.svpAoZ would, for an electronic numbskull like me, be most explanatory.

 

Sorry to be a nuisance; thanks in anticipation.

 

Regards,

John Isherwood.

Sorry I can't determine the actual resistor as the AliExpress picture isn't the right angle. What should be obvious will be a resistor from the pot to the ouput of the lm317

 

Perhaps you might take a picture of the board looking directly down on it

[cctransuk]

Sorry I can't determine the actual resistor as the AliExpress picture isn't the right angle. What should be obvious will be a resistor from the pot to the ouput of the lm317

 

Perhaps you might take a picture of the board looking directly down on it

 

Will do - thanks.

 

Regards,

John Isherwood.

[dhjgreen]

I can actually read the the values in the pictures. The pot is a dual 10k which they describe as a design feature, giving 5 k as they are in parallel. The design does use the datasheet recommendation and the reference resisitor is 240 ohm (can't read the colours, but the value is screen printed on).

If you replace the dual 10 k with a dual 5k you will have a regulated 14 V supply ( provided you meet Crosland's head room suggestions)

Edit to add: before you embark on building your transformer box, do read this

[cctransuk]

Sorry I can't determine the actual resistor as the AliExpress picture isn't the right angle. What should be obvious will be a resistor from the pot to the ouput of the lm317

 

Perhaps you might take a picture of the board looking directly down on it

 

Junctionmad - below are two images of the regulator - I trust that they will provide the information that you need.

 

 

 

dhjgreen - you indicate that I should replace the pot; junctionmad seems to be indicating that I should replace a resistor between the pot and the output.

 

I'm easily confused on matters such as this - are you both talking about different modifications?

 

Thanks,

John isherwood.

[dhjgreen]

I think it has been said earlier to retain the max current out you need to keep the 240 ohm so the variable resistor needs changing from twin 10k to twin 5k. If you are happy to accept a lower output current you can change the 240 ohm to 470 ohm.

 

So the same mod from different directions. It is the relative values of the 2 that decides the max voltage.

Edited October 16, 2017 by dhjgreen

[cctransuk]

I think it has been said earlier to retain the max current out you need to keep the 240 ohm so the variable resistor needs changing from twin 10k to twin 5k. If you are happy to accept a lower output current you can change the 240 ohm to 470 ohm.

 

So the same mod from different directions. It is the relative values of the 2 that decides the max voltage.

 

Thank you for that explanation - I take it that the 240 ohm resistor is the blue component with the black / black / black / yellow / red stripes, above to the 1000uf component?

 

In order to replace the pot, I assume that I will need to obtain either a desoldering pump or some desoldering braid?

 

Regards,

John Isherwood.

[Gordon H]

Thank you for that explanation - I take it that the 240 ohm resistor is the blue component with the black / black / black / yellow / red stripes, above to the 1000uf component?

 

 

Looks like you are reading it in the wrong direction.

240 Ohms would be red, yellow, black, black (+ tolerance band) in four banded terms.

[cpman46]

Looks like you are reading it in the wrong direction.

240 Ohms would be red, yellow, black, black (+ tolerance band) in four banded terms.

The board is marked 240. I think you will find the resistor in this case reads RIGHT to LEFT i.e. red, yellow, black, black with the fifth band (tolerance) actually brown (1%). The LM317 data sheet shows this resistor as 240R.

[kevinlms]

The board is marked 240. I think you will find the resistor in this case reads RIGHT to LEFT i.e. red, yellow, black, black with the fifth band (tolerance) actually brown (1%). The LM317 data sheet shows this resistor as 240R.

Handy of the PCB maker to be helpful with the markings, often they just label them as R1, C2 etc.

[Junctionmad]

The resistor is an easier change , just change it for a 560 ohm , the only issue is at higher resistances , ie as the pot approaches it's maximum value , the current flowing in the feedback falls below the minimum required to keep the lm317 functioning

 

A simple expedient of tacking a 2K ohm resistor between the board output and GND will suffice to ensure the LM317 operates

 

Easier then sourcing a dual wiper pot imho

[cctransuk]

The resistor is an easier change , just change it for a 560 ohm , the only issue is at higher resistances , ie as the pot approaches it's maximum value , the current flowing in the feedback falls below the minimum required to keep the lm317 functioning

 

A simple expedient of tacking a 2K ohm resistor between the board output and GND will suffice to ensure the LM317 operates

 

Easier then sourcing a dual wiper pot imho

 

I now have 470 ohm resistors to hand, plus a dual wiper 5k pot; I will have a trial soon and report back.

 

Thanks,

John Isherwood.

[Junctionmad]

Hi These are not really dual wiper pots , but in essence conventional " dual " pots i.e. two independent pots , They are connected on the board in parallel to in effect give a pot of half the stated value .

 

If you have a dual 5K pot, then I suggest you JUST use that mod as it gives you around 14.7 volts which less two diode drops will work out about perfect and as the overall value of the feedback resistors is lower then before, the LM317 will have no issue with its operating current ( which is around 5mA, with these resistor values ) and doesnt need any further modifications 

[cctransuk]

Hi These are not really dual wiper pots , but in essence conventional " dual " pots i.e. two independent pots , They are connected on the board in parallel to in effect give a pot of half the stated value .

 

If you have a dual 5K pot, then I suggest you JUST use that mod as it gives you around 14.7 volts which less two diode drops will work out about perfect and as the overall value of the feedback resistors is lower then before, the LM317 will have no issue with its operating current ( which is around 5mA, with these resistor values ) and doesnt need any further modifications 

 

I have just realised that I have not given feedback on the project - in short, it works!

 

I have replaced the double pot with a 5K one, but decided in the end not to bother with the diodes - though I did try them.

 

I have fitted a coiled four-core lead, terminating in a five-pin DIN plug, so that it can use the same baseboard sockets for 19V AC input, and track output, as used for the H&M Walkabouts.

 

In operation, there is initially a time lag as the pot is rotated until the starting voltage for the individual motor is attained; then control is smooth and effective up to the maximum voltage output, after which further rotation of the pot does not increase speed.

 

Nonetheless, the effective rotational range of the pot is more than sufficient, and could be limited by mechanical rotation stops at the lower and upper points of control.

 

All in all, this project has been well worthwhile, and offers me a cheap and effective alternative when and if the H&M Walkabouts give up the ghost.

 

Meanwhile, I am using the prototype controller to drive my shunting plank, and I have a stock of the electronic components necessary for production of a small batch.

 

Regards,

John Isherwood.

[Penlan]

Following information posted at ... and that I have some VR's in stock,
plus the fact I've had a couple of Controllers play up, after some 40+ years. I thought "let's try it".
Apart from some self inflicted dry joints, and the pot and a on/off switch are in a separate walk-about handheld unit, all went well.
Many thanks for this John.