# Help; I'm not sure what kind of power supply to get

#### Strahan

Joined Nov 25, 2018
10
Hi. I have a Wave n' Dry hands free towel dispenser. I was spending $25 on custom battery packs for it until one day I decided to cut the battery back open. I found it to be just six D cell batteries and a AA. I bought a battery bracket and made my own, much cheaper. However, after years of using it, I'm now tired of even that lol. It's annoying when the Ds are dying and the dispenser slows down. So I figured OK, it's DC current so it should be easy to find a DC wall-wart to replace it. Problem is, the way it's wired combined with my absolute void of electronics knowledge means I have no idea what power specifications I should be getting for said wall-wart. This is how the pack is designed: I assume the white wire is for powering the motion sensor and the red wire powers the motor. What kind of volts/amps should I be looking for? Also, I assume it would be bad to feed the higher power motor one into the sensor so I'll have to have two plugs for this machine. I'd rather avoid that. If someone has the know how to build a circuit that can take a single input and output both the motor and sensor current from that, please give me a price to build me one shipped to 17313. I tried to read up on making one myself but 1. I'm pretty electronics stupid and 2. I don't want to burn my house down lol Thanks! #### MaxHeadRoom Joined Jul 18, 2013 25,469 That shows 1.5v and 3v and the 1.5 +ve is 4.5v WRT the BLK common. Is this what you measure? Max. #### Hymie Joined Mar 30, 2018 1,082 Here is a circuit based on a 4.5V input with 2 diodes providing the volt-drop to give 3V. Due to the intermittent operation of the device, it is possible that the peak current draw is in excess of 1A. I would recommend that you buy a USB/charger wall-wart rated at 2.1A/5V with the connections as shown. Inputting 5V rather than 4.5V should not be an issue – the unit will perform as with a fresh set of batteries. The diodes D1, D2 should be capable of at least 1A continuous, such as 1N400X. Thread Starter #### Strahan Joined Nov 25, 2018 10 That shows 1.5v and 3v and the 1.5 +ve is 4.5v WRT the BLK common. Is this what you measure? Max. Don't know, I can't find my volt meter lol. Here is a circuit based on a 4.5V input with 2 diodes providing the volt-drop to give 3V. Due to the intermittent operation of the device, it is possible that the peak current draw is in excess of 1A. I would recommend that you buy a USB/charger wall-wart rated at 2.1A/5V with the connections as shown. Inputting 5V rather than 4.5V should not be an issue – the unit will perform as with a fresh set of batteries. The diodes D1, D2 should be capable of at least 1A continuous, such as 1N400X. View attachment 164411 That doesn't look too difficult. I googled for the 1N400X, I see IN4001, 4004, 4007, etc. What is the difference? I'm not sure which I should get, or does it not matter? Edit: Nevermind. I read the Wikipedia article on the 1N400X and I see it starts at 1 = 50V and as model goes up, voltage capacity goes up so being that this is 5V, 1N4001 is what I'll get. Thanks. #### LesJones Joined Jan 8, 2017 3,745 The last digit indicates the REVERSE voltage rating. In this application the junction will be forward biased so each diode will give a voltage drop of between 0.6 and 0.7 volts. So the two diodes in series will drop the 4.5 volts by between 1.2 and 1.4 volts. (So you will get 3.1 to 3.3 volts between black and red.) It does not matter which one of the 1N400x range of diodes that you use. Les. #### wayneh Joined Sep 9, 2010 17,167 Don't know, I can't find my volt meter lol. Unless you are very certain that the battery connections are just as you've drawn them, I'd take the time to measure the voltages and confirm it. You don't want to make an expensive mistake. The motor might have the voltage rating written on it, and that could also give you some confidence. If you need a multimeter, go find a Harbor Freight coupon and get one free. Be sure to look into safety considerations, ie. your local code requirements. It might not be cool to power that device from the mains in a "wet" environment. Code might specify that the wiring needs to be permanent, for instance in the wall or in a conduit. Thread Starter #### Strahan Joined Nov 25, 2018 10 I'm very sure about the battery wiring; I made the battery pack and can trace the wires I put on it. Worst case scenario it burns up the motor of the dispenser, but then, I'm only out$50. The dispenser is cheap

The dispenser isn't in the kitchen, which is what I assume you mean by wet. It's just outside the kitchen and it's a regular living room type environment, no water. Of course, I already have a bunch of stuff powered by mains right next to a sink lol. Can opener, vacuum saver, microwave, waffle iron, etc. If those are cool, I doubt it would be a problem for this.

Thanks!

#### wayneh

Joined Sep 9, 2010
17,167
The dispenser isn't in the kitchen, which is what I assume you mean by wet.
I was thinking of a bathroom.

#### Strahan

Joined Nov 25, 2018
10
Here is a circuit based on a 4.5V input with 2 diodes providing the volt-drop to give 3V.

Due to the intermittent operation of the device, it is possible that the peak current draw is in excess of 1A.

I would recommend that you buy a USB/charger wall-wart rated at 2.1A/5V with the connections as shown. Inputting 5V rather than 4.5V should not be an issue – the unit will perform as with a fresh set of batteries.

The diodes D1, D2 should be capable of at least 1A continuous, such as 1N400X.
View attachment 164411
OK, so I got the parts today to try to build this. Bear in mind, I have like zero electronics experience lol. I bought stripboard, IN4001 diodes, a USB female plug and some solder and stuff. I hooked it up I believe matching the diagram. Measuring the positive input line I am getting +5DC, that's good. But when I measure the line the last diode outputs to, the meter reads millivolts and jumps all over. Not sure what I did wrong. I illustrated it in a video:

What did I mess up?

#### Hymie

Joined Mar 30, 2018
1,082
Just for clarification – you are measuring mV (varying) between the zero volt line and the cathode of the diode (which is to be connected to the red wire in the final assembly), is that correct?

Looking at the circuit construction, it appears correct – I suspect the problem is a dry-joint on the PCB at one or more of the diode connections on the strip board.

I would suggest you give each diode solder joint another go with the soldering iron and a small amount of solder and see how you get on.
Although prolonged heating with a soldering iron can destroy the diodes – they can take quite a bit of abuse.

#### wayneh

Joined Sep 9, 2010
17,167
OK, so I got the parts today to try to build this. Bear in mind, I have like zero electronics experience lol. I bought stripboard, IN4001 diodes, a USB female plug and some solder and stuff. I hooked it up I believe matching the diagram. Measuring the positive input line I am getting +5DC, that's good. But when I measure the line the last diode outputs to, the meter reads millivolts and jumps all over. Not sure what I did wrong. I illustrated it in a video:

What did I mess up?
I believe that is not strip board, but protoboard. That means that the rows and columns - and each of the individual dots - are not connected by default. You need to bridge across a few of the dots to actually complete the connections. You can double check my hunch with your multimeter - you should see that there is no continuity between adjacent dots.

#### Hymie

Joined Mar 30, 2018
1,082
Note that when you are reading the 5V with your meter, it is actually displaying minus 5V, are you sure that you have the polarity from the USB output correct?

#### Strahan

Joined Nov 25, 2018
10
Just for clarification – you are measuring mV (varying) between the zero volt line and the cathode of the diode (which is to be connected to the red wire in the final assembly), is that correct?

Looking at the circuit construction, it appears correct – I suspect the problem is a dry-joint on the PCB at one or more of the diode connections on the strip board.

I would suggest you give each diode solder joint another go with the soldering iron and a small amount of solder and see how you get on.
Although prolonged heating with a soldering iron can destroy the diodes – they can take quite a bit of abuse.
I had the meter's negative lead on the USB negative strip and the positive lead is what I was touching to the various points to check. I bought a de-soldering iron as well, so I'll desolder and start over. Of course, I have like 30 boards and 100 diodes so I guess it's not the end of the world even if I start all new lol

I believe that is not strip board, but protoboard. That means that the rows and columns - and each of the individual dots - are not connected by default. You need to bridge across a few of the dots to actually complete the connections. You can double check my hunch with your multimeter - you should see that there is no continuity between adjacent dots.
Good point. OK, I switched the meter to continuity and checked, the row is connecting. Whew! I was afraid I got 30 of the wrong board hehe.

Note that when you are reading the 5V with your meter, it is actually displaying minus 5V, are you sure that you have the polarity from the USB output correct?
Good catch, I totally didn't see that. Anything is possible, lol. I'll go measure and put my black lead on what I thought was the positive from USB and test.

Yep, that was it, it was backwards. Desoldered the inputs and reversed. Readings positive now. After fixing that, the straight input row C is 5.09V, first level diode strip E is 4.94V and second level diode strip G is 4.71V. Voltage dropped, but not as much as it should...?

It's ~.2 V drop per diode. I suppose I could just put 10 diodes in, the board is large enough. Or did I perhaps mess up another thing?

#### LesJones

Joined Jan 8, 2017
3,745
I can't see a connection between the cathode of the first diode and the anode of the second. I can't be sure as the board was never held steady when the camera was looking at the solder side. I am not even sure if the card is strip board or just copper dots round each hole. A good focused still picture of the copper side would be a great help.

Les.

#### Hymie

Joined Mar 30, 2018
1,082
If all is correct, once there is a current draw through the diodes, they will give the desired voltage drop.
If you have a resistor of around 100 ohm, you could wire it from diode D2 cathode to 0V – you should then see around 0.7V drop per diode.

#### Strahan

Joined Nov 25, 2018
10
I can't see a connection between the cathode of the first diode and the anode of the second. I can't be sure as the board was never held steady when the camera was looking at the solder side. I am not even sure if the card is strip board or just copper dots round each hole. A good focused still picture of the copper side would be a great help.

Les.
Ah sorry. Here:

#### Strahan

Joined Nov 25, 2018
10
If all is correct, once there is a current draw through the diodes, they will give the desired voltage drop.
If you have a resistor of around 100 ohm, you could wire it from diode D2 cathode to 0V – you should then see around 0.7V drop per diode.
Ohhhhh so just metering it doesn't tell the story, it has to be under load? Okie doke.

PS, whilst waiting replies I said what the hey and started a 10 diode board. I think my soldering is starting to slightly improve, more of them look like the "Hershey kiss" type joints than the.. uhh... chocolate covered raisin cluster joints lol

#### wayneh

Joined Sep 9, 2010
17,167
Ohhhhh so just metering it doesn't tell the story, it has to be under load?
Correct, and it doesn’t take a lot of load. The delta-V will increase as the current increases, up to maybe 0.75V before it blows.

#### Strahan

Joined Nov 25, 2018
10
EUREKA!!!

Thanks so much everyone, you guys rock This is so awesome, I'm giddy lol. Now I just need to run to the hardware store cuz the USB female jack is a bit thicker than the thin plastic wall of the dispenser so gotta get some washers or maybe a PVC pipe I can cut to make a large single washer so it doesn't stick out of the chassis. That and gonna make a new board with the components tighter together and cut it down. For now, I'll wrap in electric tape but probably order one of those little plastic project boxes for later.

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,088
"Hershey kiss" type joints than the.. uhh... chocolate covered raisin cluster joints lol
Funny!

Your first time soldering looks good. I remember I guy that contracted my services and he was "dripping" solder on etched brass for his business. I turned him on to "resistance soldering" which he really liked. See the company American Beauty.

Copper boards develop an oxide, Some have a coating. I don't think yours does. You can use sandpaper (e.g. 400 grit) to make the surface shiny. A mix of vinegar and salt will also remove the oxide. The pads should solder better.