# Cheap Volts!

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## Introduction: Cheap Volts!

http://www.macaulayaudio.co.ukThereis nothing more frustrating than finding out that your power supply isn't up to powering your latest gizmo. Especially on a rainy Sunday afternoon when your chances of buying any new components are zero. Well hereis a solution ,a simple circuit that provides a variety of dc voltages from the raw ac input of a transformer secondary.

That's exactly what this circuit does. It combines the functions of a voltage doubler, tripler and quadrupler . Connect your transformer secondary to its input and youll get 2, 3 or 4 times the input ac voltage as dc, dependent on where you take your output.

I've used this circuit to provide dc voltages between 18-200V dc with transformer secondaries from 6VAC-40VAC.40VAC is a practical limit to this board because of the voltage rating of the caps. Nevertheless I've operated relays motors and the odd valve circuit with this device.

## Step 1:

First the usual disclaimer. I accept no responsibility whatever for the way in which this unit is used and /or any injury or damage it might cause. Actually there's not a lot that can go wrong with it used in the way described here. To make life easier you can get a complete kit of parts for this project for £4.99 and yes we'll despatch it to anywhere in the world, airmail for £1, yes anywhere in the world. For more info visit my website. This is probably less than you would be able to make it for yourself considering minimum order prices and the cost of strip-board etc.
As you can see from the circuit diagram the device is a modified voltage quadrupler with multiple voltages taken from various points in the circuit.

## Step 2:

The parts youll need are listed below:-

D1,2,3 and 4 = 1N4007
C1,2,3,4 = 100uF/100V
Strip-board panel 11 strips x 22holes
6W Terminal block
3mm Thick plastic panel 55mm x 83mm
Wire
3 M3 x 16mm screw, nuts

The circuit diagram is shown below. AC power from the transformer secondary is fed through the Capacitor Diode network to produce rectified multiples of the input voltage. In fact the circuit consists of several half wave rectifiers in series. The only disadvantage of the circuit is that the ripple voltage tends to be a bit high but this can be helped by connecting a further smoothing cap(s) in parallel with the output terminals. When driving relays motors and other such devices this is irrelevant.

## Step 3:

So much for the theory, how about construction? To keep costs down Ive used a piece of 0.1 matrix copper clad strip-board measuring 11 strips by 22 holes across. Looking at the diagram this shows the layout. Note that 'X' indicates a break in the track and these should be made with a suitable cutter at the places indicated. This is the first task of construction. Next drill the hole in the panel at F13 to take a 3mm screw.

It's almost a must to mount the diodes first. Otherwise youll end up struggling trying to insert them between the caps.(take it from me! ) Also it makes life easier to temporarily hold components into position with a piece of masking tape to stop slippage when soldering. Note that the diodes are soldered the right way round. Polarity is indicated by the light band at one end of the component.

Next install the electrolytic capacitors C1-4. Again these are polarised as indicated both on the component body and layout diagram. At this stage the board is finished and can be put on one side while attention is turned to the plastic panel.

## Step 4:

The panel performs two practical tasks. Firstly and obviously it holds the project together but it also insulates the circuit from the outside world and making it easy to fasten into a metal case by means of a couples of M3 screws.

The plastic panels are available in most model shops in A4 sheets for a couple of quid and are easy to cut into smaller panels by marking them out and cutting along the lines with a scalpel. A Mechanical drawing is shown for the panel below. Simply mark out your plastic panel and drill the M3 clearance holes and this task is completed.

Lastly final construction. Attach flying leads to the board at the points indicated leaving these about 6(150mm) long. Mount the board with an M3 screw and tighten it down to the plastic panel. Similarly mount the terminal block and connect the ends of the flying leads as shown in the layout diagram. The project is now ready to use.

## Recommendations

• ### Large Motors Class

8,828 Enrolled

• ### Oil Contest

We have a be nice policy.

## Questions

nice, simple and elegant! How much current can this thing output? I've never been able to find a formula online for current output on voltage doublers/triplers/etc. I like the nice drawings, very proffesional *****

7 replies

Thanks for the complement. I did the drawings using 'Proteus' lite , Ares software. If you search you can get the lite version for free,sorry I dont know their address. Does good PCBs and circuit diagrams too.

a bit of a late reply:) but from what i gather on voltage doublers, they only work with ac.

You are both right. AC in DC out. DC in Bugger all out! Hope that clarifies it

formula one

Well the hard limit will be 1/2 or 1/3 or 1/4 of the input current depending on which multiplier you use, and there will presumably be a slight loss, but there might be other issues I haven't come across that further reduce the current you can draw. I would recommend you try perhaps the appropriate fraction for the multiplier you are using and halve it as a safe starting point, then cautiously try higher draws up to the theoretical limit watching out for overheating or weird output behaviour. If you happen to have an oscilloscope kicking around that would be very helpful, but excessive heat and voltage drop across the output (lower output voltage than you would expect) are two sure signs that you are overworking it.

I must admit I used the circuit for low current applications. Specifically as a substitute for valve HT batteries ( 12-20VAC input). I found it ideal for this application but my total current draw was <10mA. If you need more I would suggest upgrading the caps to a higher value. Remember that the voltage rating needs to be 3 times the ac input minimum. If not you'll fry the electrolytic. Not a nice smell!

I'm definitely not going to make this. I shocked myself horribly on a capacitor. In one arm, out the other. I almost passed out. Quite an enlightening experience.