Monday 10 March 2014

The poor man's Cycle Analyst

The Cycle Analyst is a comprehensive instrument for electric bikers. It tells you everything you might ever want to know about what's going on, and also helps you control things.

I was trying to decide whether to get version 3 or version 2.3, at a cost of $125 vs $155. Although I wanted a temperature readout, I knew that wouldn't work for me because my motor doesn't have a sensor - likewise many of the other features wouldn't be useful to me. So then I concentrated of version 2.3, looking at the features there, when suddenly, I realised that maybe I didn't want a Cycle Analyst at all.

So what do I actually want?

I'd like to know the voltage of the battery, the amp-hours used and the speed I'm moving at. But I already have those, via various things already installed. It would also be nice to know the current being pulled at any time, and that's the big piece of information that I was missing.

When I was testing bike.4, I temporarily installed an ammeter by running four big cables between the battery and the handlebars. 4 mm sq so that they could carry the big current (42 amps) without putting a lot of resistance in the circuit. But I didn't feel that this was really practical.

So I went to Ebay and had a look at ammeters that can go up to 100 amps. And there's loads of them, all really cheap, but with the disadvantage that you have put add an exterior shunt.

Hang on. That's not a disadvantage. That's a big plus!

I can put that big shunt down at the battery end of the bike, then I need only a couple of small wires, capable of carrying up to 4 amps (10 if I want to go up to 100 amps) up to the handlebars.

So, here's the Poor Man's Cycle Analyst, giving you a handlebar readong of volts, amps and speed, and when you stop and have a look at the battery end, you can see amp-hours and watt-hours, and peak current usage.

It starts off with one of these. £8.89 and that give you amp-hours, watt-hours and peak amps. Plus some other stuff that isn't so useful. That installs at the battery end, and will handle 50 amps (100 amps peak) at 60V. That's plenty enough for me. When my battery is exhausted, and I dismount to change battery, that tells me how many amp-hours that battery gave me. I expect 4.5 (these are 5 Ah batteries). If it's a lot less, then that battery has a problem, and I'll need to replace it.

I want to have a voltage display on the handlebars, because that gives me a good idea of how much power is left in the battery I'm using. £1.83 gets me a voltmeter that goes up to 120 volts, and uses only two wires (the three-wire voltmeters need a separate power supply, slightly less convenient).

I want a speedometer/odometer, to tell me my speed and how far I've biked. £2.08.

And I want an ammeter, but I don't want to run big cables from the back of the bike to the handlebars. The shunt goes at the back of the bike, the meter itself mounts on the handlebars, and those two cost me £6.03. The wiring from the shunt to the meter, only has to be able to carry a tenth of what's being measures. So, if I know that my maximum current will be 40 amps, I need wires that can carry 4 amps,

So the total is £18.83; the Cycle Analyst is £76.

Of course, the Cycle Analystdoes a lot more, and you need to read the description to decide if you want the additional features.

But I don't think I do.

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