Sorry, I’ll be a bit more practical! Might seem a bit boring, but hey ho!

I did a lot of calculations when I got the bike and this is what I found…

The connected load (everything within the electrical system) for the Z is for argument’s sake about 300W or 21A, which pretty much matches the peak alternator output. However, this does not include the starter motor circuit, but we’ll ignore this for a minute as it is effectively a direct load on the battery rather than the alternator because it is drawing current only when the engine/alternator is not running.

The demand load is what the bike’s system uses at any given time (dipped headlight, side lights, fuel pump, ECU, ignition, instruments etc), which is unlikely ever to be as high as the connected load. The demand load on the Z is about 105W (7.5A) when the bike is running in standard trim at 5000rpm (slightly less if you’ve got LED side/number plate lamps fitted). This equates to a maximum of 195W (14A) of spare capacity in the alternator, but only assuming the demand load does not increase, which it of course will when random and cyclical loads such as the brake lights, indicators, radiator fan, horn, headlamp flash are used. This extra demand can be up to 195W (14A), using all of the spare capacity, but it is unlikely. It is important to consider the effects of starting now; the battery 20-30 minutes after starting will have a fairly high current draw itself to bring it back to a stable voltage, increasing normal demand load above 105W (7.5A) .

There is no exact formula to work out what you can actually safely use of the 195W (14A) spare capacity, you can assume that third will be need to be called on at any one time (more after starting). This leaves approximately 130W (9A), but you still need to add a further margin of safety for battery recovery.

A pair of 55W spots (8A) will use up all the spare capacity and allow no margin for extra demand load. I run Vision X Solstice LEDS, which are 20W (1.5A) the pair, so leave a good 110W (7A) spare. Add grips 30W (2A), GPS 15W (1A) and there’ll still be 4A (56W) spare for other accessories and the recovery time of the battery.

What’s the current draw of your vest Keith?

At the end of the day this may help, but it still involves a lot of assumptions and variables.

Note: Calculations based on 14V assuming charging voltages between 13.6 and 14.4V)

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