• Ian Watts

Volt / Amp meter - Test display

At the outset I decided it would be really handy to be able to see battery voltage and motor / controller current primarily for test purposes but also whilst riding, however, because I hadn't found a relatively in-expensive meter and because it was simpler at the time and because I really had no idea where I would fit such a meter on the bike and because I didn't want to 'invest' in 'just' a V/A meter without knowing if I would later wish for more (power, temperature and maybe speed...) and because... because... because...

all I did was fit a 100A shunt and a 5 pin test port (both of which I had) ;

pin 1 = Gnd

pin 2 = 12V (DCDC converter

pin 3 = 72V (Battery pack)

pin 4 = Shunt 'A'

pin 5 = Shunt 'B'

All in all a really simple 'test port'...


Later on down the line, I found a volt / amp meter on eBay (about 10 euro) using the same 20mV shunt. Needless to say, I ordered one and here it is cabled up and plugged in to the test port :

Now though, some 6 weeks into the build, I've arrived at this point and I really think I'm going to need to see this stuff whilst riding. So, whilst I had the covers / fairings off (to add an earth cable to the charge IEC socket) I revisited my 'test port' idea and ran a multi-core, screened, cable from the port up to the instrument panel and terminated it with a standard cable socket. In fact, at the same time, I ran a second multi-core, screened, cable from the port up to the instrument panel although not having any immediate real use for it - I'm bound to want it later and, if not, nothing lost !!


Keeping to my original, circa 800Euro costs, I still couldn't find a waterproof V/A meter, that could be retro-fitted on the scoot and be seen whilst riding, for any reasonable price. There was, however, a clock built into the instrument panel... maybe I could remove it and re-task the vacated space for the new V/A meter...

Anyways, like I said, I already had all the covers off again, so I removed the instrument panel and stripped it; 3 screws and it was off, 4 more screws and it was opened up, 2 more screws and disconnect 3 cables and the clock was out. No damage done...

Unfortunately, no matter how I tried I couldn't fit the V/A meter in it's place - it was simply too tall. What I came up with though was to split the two 3-digit displays into two, and site them separately.

I left the voltmeter on the PCB - it fitted just fine in the available space - and, after painting the front face of the PCB black, added 100mm of cable between the, now removed, 3-digit display panel (Amps) and the original solder pads on the PCB. The original Volts / PCB panel was fitted to the internal bezel.

I then re-sited (with a little help from Sketchup and the 3D printer) the Amps 3-digit display within the housing...

I then fitted a matching cable plug to the previous one I'd fitted on the end on the new cable from the controller / battery area to the instrument panel, connected it up and tested it all out...

Result !


All's good... ready for testing !


So... back onto the motor 'stutter' and clutch...


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© 2017 Ian Watts