2.4v PSU for electric screwdriver

[CapLeaker]

Re: 2.4v PSU for electric screwdriver

if you back up and read the thread you will see we did the DX stuff.

I see DC to DC converters, not AC to DC.

[Agent24]

Re: 2.4v PSU for electric screwdriver

You can probably find a wall-wart etc the right spec 2nd hand on eBay if you wait a while and keep a lookout.

[SteveNielsen]

Re: 2.4v PSU for electric screwdriver

Such a wall-wart may come my way. In the meantime I have screws to deal with and hands that don't like it so I'm using the old Delta ATX PSU. Installing an AC switch, cut off unused wires at the PCB, install pwr-on light, etc. It's all old parts I have, I have no money to spend so it's all good and better than collecting dust in boxes.

Concerning the ac-dc converters, those I've seen are low ac input, not suitable for this.

[SteveNielsen]

Re: 2.4v PSU for electric screwdriver

BTW, mod'ing the PSU I've wanted to do anyway because I already use it as a general purpose DC voltage source on my bench so I may as well at least give it a proper on/off ac switch and an on LED anyway. I think I'll hook up the LED and resistor to pwr ok line and make use of that wire.

[stj]

Re: 2.4v PSU for electric screwdriver

if it has a preset on the pcb to ajust the output, replace it with a pot and you may be able to screw the 3.3v rail down to 2.4v!!

[SteveNielsen]

Re: 2.4v PSU for electric screwdriver

That's an interesting tidbit, thanks. There is a micro pot on the board but don't know what it does (yet). It is located in the primary side of the smps region of the board so I'm thinking it may adjust all output voltages. I'll have to try and see It's a Delta DPS-145PB-117 REV 00.

Even so, I am ok with using the diode I've got to drop the 3.3v down to 2.4v. I don't what else I might want to use this diode for and it's a perfectly suited use for it, it nailed the target voltage right on the money.

[stj]

Re: 2.4v PSU for electric screwdriver

you usually find 2 pots.
one is the voltage ajuster,
the other sets the maximum current before the safety trips the supply off.

[SteveNielsen]

Re: 2.4v PSU for electric screwdriver

Well I bone-headed this one already. I was checking out different LEDs for a pilot light and after the umpteenth time of flipping the pwr switch I got an arcing short between the hot and ground lugs on the back of the ac jack with the help of a solder drip/blob between them. No major damage to the jack.

That opened up the 5A line fuse as well as trip the GFI in the mains. I saw a flash and a bit of magic smoke from the back of the ac jack. I did solder a wire to the hot lug for the ac power switch so it is my fault. Obviously I didn't check that good enough, which is out of character for me as I usually check & double check everything I do and those lugs tend to have too much solder blobbed on them anyway. I did a double bone-head by using a 3A switch instead of at least 5A. I thought it was 5A but my bad again.

So after a dozen or so switch uses the 3A switch arced enough to increase the current draw thru the ac jack enough to make the sloppy solder arc. I don't see any other damages and no shorts. I knew I should have used a blue LED dammit.

[stj]

Re: 2.4v PSU for electric screwdriver

here are some tips from me doing similar mods for my worktop test-bricks.

1: fit an led-fan to know when it's on - no drilling and it looks really good.
(it also means your not trusting an old fan)

2: use heatshrink over any mains soldering like switches.

3: use a capacitor across any mains switch to reduce or stop arcing.

[SteveNielsen]

Re: 2.4v PSU for electric screwdriver

Those are good tips, thanks.

[kc8adu]

Re: 2.4v PSU for electric screwdriver

i put an 18650 li-ion and a cheap tp4056 board in mine.
soon all the shop screwdrivers will be modded.microusb to charge it

[SteveNielsen]

Re: 2.4v PSU for electric screwdriver

I found a 5v 3a inline type psu in my wall wart box and it works to power the screwdriver. Kinda fast, the diode knocks it down to 4.2v but still a bit fast. I suppose I could get used to it and hope I don't burn out the motor.

[Agent24]

Re: 2.4v PSU for electric screwdriver

Add more diodes?

[SteveNielsen]

Re: 2.4v PSU for electric screwdriver

Don't have any more 3 amp diodes. I tried 1 amp diodes and they heat up pretty fast, as one would expect.

[SteveNielsen]

Re: 2.4v PSU for electric screwdriver

Mission accomplished. I scrounged up another 3A si diode from an old oddball ATX PSU and the two diodes in series drop the free-running motor voltage down to about 3.1v which produces a very usable RPM for me.

I also found that the position of the motor was irrelevant, the factory soldered the red and black wires reversed on the switch and must have swapped them at the board to correct for the mistake instead of re-soldering to the switch, which makes sense since it is mostly plastic construction that wouldn't stand up well to repeated soldering.

Sideline: Concerning the other ATX PSU I was using that popped the fuse, I was reading about arc suppression in ac line switch contacts and found the attached PDF. Apparently using only a capacitor suppresses the arc when the contacts open and actually increases arcing when they close from the cap discharging. Better to use an RC circuit.