Digital readout power supply

[jem]

I have an Arceurotrade Verticalreadout bar, for my Mill, it works perfectly but it does eat button battries, so I would like to tap off the 24 volt ac supply on the mill. I have ordered a ac dc converter, and a dc "adjustable buck converter for Arduino replace LM2596" which converts 24 volts dc to the 3 volts that I require, or any other voltage.

My question is if I use this instead of the button battery, will there be any problem, ie when the mill is turned on will there be a voltage surge accross the readout bar to cause it damage?

best wishes

Jem

[springcrocus]

Jem, you probably enjoy tinkering and, therefore, relish the challenge but I would question whether you are likely to spend more than the cost of the adaptor if you continued to buy batteries, especially if you remembered to turn the read-out off at the end of each session? I have a similar vertical scale and am on my fourth battery (CR2032) in five years. About £2.00 so far...

Regards, Steve

[jem]

Thanks Steve, I am a tinkerer, and the cost of the bits is less than 5 pounds so worth a try, I was just worried about surge currents perhaps when I switch the miller on.

I have spent more than 5 pounds on batteries so far, in spite of turning it off all the time. the trouble is that it turnes its self on when ever I touch the quill handle!

best wishes

Jem

[SteveW]

Guys,
I have one of those Owl remote current monitors clamped across my house feed which transmits the readings to a kilowatt hour display in the hall. It uses three AA cells which seem to last a couple of months. Actually I have a second monitor on my solar feed so two sets of three AA cells randomly through the year to change.

A bright idea one day was to buy a three cell D cell battery holder and wire it to both monitors using plugs and sockets to allow some fiddling. So, now only one set of batteries to change and all the faffing about is now completed on a single session.

Have since lost track of when I did this and its all still going. A spare set of alkaline D cells is readied.

Years back Maplins would have been my source for the bits. They still exist in a form online but I now use CPC Farnell for all my bits. Once you're established with them they send a regular little special offers catalogue full of stuff you're unlikely to ever order. That said they are my source of domestic 18watt LED lamps and bulk AA and D cells and other odds and sods.

[cplmickey]

May 1, 2021 15:33:26 GMT jem said:

I have an Arceurotrade Verticalreadout bar, for my Mill, it works perfectly but it does eat button battries, so I would like to tap off the 24 volt ac supply on the mill. I have ordered a ac dc converter, and a dc "adjustable buck converter for Arduino replace LM2596" which converts 24 volts dc to the 3 volts that I require, or any other voltage.

My question is if I use this instead of the button battery, will there be any problem, ie when the mill is turned on will there be a voltage surge accross the readout bar to cause it damage?

best wishes

Jem

I can't imagine there will be any problem with what you're planning. Any inrush current will be on the mains power side to the motor. This may cause a slight voltage dip on the 24VAC depending on what type of power supply is used but minimal I would have thought. You've then got the added protection of the AC/DC converter. I'd be very surprised if any damage is caused. Ian

[chiptim]

Hi Jem,

your post's a little old now but in case this info is still useful...

A few things to consider.

1) - Minimum Load. Although the DRO 'eats' button cells, a button cell doesn't store much energy so the current consumption is likely to be low. Perhaps a few tens of mA at most? LM2596 is a 3A controller. You may find that with such a light load the output voltage is higher than set. A solution to this could be to add a 'ballast' resistor to draw more current from the supply.
2) - Converter Stability. A switched Mode Power Supply (SMPS) (so your 'Buck' circuit) regulates its output voltage using feedback to keep the output voltage stable when the load current and input voltage change. In response to a large input voltage disturbance such as when you turn on the motor, you will almost certainly expect the output voltage to dip and then overshoot momentarily. How much this overshoot is and whether that may damage the DRO is unknown. (The DRO, if it works from 3V may use 3.3V rated components that might be damaged with >4V say). There's a couple of things you can do. Firstly decouple the supply to your Buck converter to keep it more stable when the motor starts up. Use a series diode and resistor of a few ohms and a capacitor to ground. You could also connect the DRO to the output via a resistor of a few ohms, and place another capacitor after it with a breakdown diode in parallel to 'clamp' any voltage overshoot. (This may not be applicable if the motor has electronic control).
3) - Noise. The DRO being a precision measuring piece of electronics may be sensitive to electrical noise that you Buck converter emits. You may need a electrical filter between the Buck output and the DRO input and keep any wiring well away from the input cable to the DRO or the motor. Use Twisted Pair cable if possible.

Regards

Tim.

[jem]

Thanks very much Tim for your input. I have finished my mod, but not fully tested it yet, too hot in the workshop at the moment. I went to Banggood and bought their LM2596 DC DC step down power supply which I connected to a 12 v cdPWM 2-3 wire fan speed controller and adjusted it to read 3 volts output. I bought a second one to give 12 volts for some LED light strip to light the scale, the whole lot only cost 5 pounds. I hadn't thought about interference to the DRO, so must check this. otherwise it all seems to work very well.

After checking I will let you know how I get on,

very best wishes

Jem

[Gary L]

May 1, 2021 22:13:53 GMT springcrocus said:

Jem, you probably enjoy tinkering and, therefore, relish the challenge but I would question whether you are likely to spend more than the cost of the adaptor if you continued to buy batteries, especially if you remembered to turn the read-out off at the end of each session? I have a similar vertical scale and am on my fourth battery (CR2032) in five years. About £2.00 so far...

Regards, Steve

Go to your local pound shop Jem, or (down here at least) Proper Job. You can get a card full of these batteries for a quid. They might not be the best batteries in the world, but at that price, does it matter? They are fail safe too, whereas your PSU solution might not be.

HTH

Gary

PS: Proper Job’s Mellow Yellow is a very good, cheap handcleaner too.

[jem]

Thanks very much Gary, I have done a bit of testing, and all seems to work very well, so I am happy. The Batteries are not that expensive, but if I forget to switch the thing off, they don't last very long, and now it doesn't matter. They always ran out in the middle of a job!!

best wishes

Jem

[Gary L]

Jul 6, 2021 16:00:12 GMT jem said:

Thanks very much Gary, I have done a bit of testing, and all seems to work very well, so I am happy. The Batteries are not that expensive, but if I forget to switch the thing off, they don't last very long, and now it doesn't matter. They always ran out in the middle of a job!!

best wishes

Jem

They obviously vary a lot. I never switch mine off, and cheapo battery life is measured in months…

Gary

[Roger]

Jul 7, 2021 12:40:46 GMT Gary L said:

Jul 6, 2021 16:00:12 GMT jem said:

Thanks very much Gary, I have done a bit of testing, and all seems to work very well, so I am happy. The Batteries are not that expensive, but if I forget to switch the thing off, they don't last very long, and now it doesn't matter. They always ran out in the middle of a job!!

best wishes

Jem

They obviously vary a lot. I never switch mine off, and cheapo battery life is measured in months…

Gary

Mine only lasted a month or so with a battery, so I just used a linear voltage regulator and hooked it up to the 5V power supply in the cabinet. These things cost next to nothing. You don't need anything clever because the power consumption is so low. You could even use a pair of resistors to make a voltage divider.