How to... make a peak voltage meter
To get a precise fix on the AC voltages in your bike’s electrical system. It’s not that tricky
Make a simple plug-in to help your multimeter
IF YOU HAVE a multimeter you will no doubt be smitten by its indispensability. However unless you’ve opted for a top-of-the-range, fully functional multimeter with a three-figure rather than two-figure price tag, you might find that it has the odd limitation here and there. One such is the inability of the average multimeter to record peak AC voltage from the likes of generator and ignition windings. The simple fact is that the voltage
fluctuates so wildly and quickly that the meter can’t keep up – blink and you’ll miss the key figure.
A peak voltage adaptor is the solution. In a nutshell it uses a diode to rectify the AC to DC, charging up a capacitor which acts like a little battery. Your multimeter can then measure the AC voltage as a DC voltage stored in the capacitor. You can also use one on intermittent DC feeds such as indicators. Peak voltage adaptors are expensive to buy – about £78 for a Fluke one – but cheap to make. We went on the internet and looked at some diagrams before amalgamating a couple to make our own version.
A resistor across the capacitor allows it to discharge slowly so you don’t get an electric shock off of the leads should you inadvertently pick them up soon after testing. We also fitted a push-to-make switch to allow the capacitor to be instantly discharged for quick retesting.
All you need are the tools listed above followed by a quick trip to Maplin for a handful of common and cheap components.