Mostly Academic Hornet Electrical Question

[TaeKwon125]

So my Honda hornet has a 12V battery with a rating of 7 Amp Hours. I believe this means it can deliver 7 Amps at 12V for one hour. This is 84 Watts over the space of an hour or 302,400 Watt seconds or Joules.

I was wondering what the starter motor power is, as if I knew this I could work out the amount of energy required to start the bike. Given this, and the alternator output (333W according the the Hornets Nest forum), I could then work out how long the engine has to run to return power to the battery that is lost during start up.

I was wondering this as my commute to work is only about 1.2 miles so I was wondering over a long time would this drain the battery?

Cheers, Olly

[nowhere.elysium]

[TaeKwon125]

By all means correct me if I'm wrong but,

This link:
https://www.migweb.co.uk/forums/engines-transmission/167433-how-much-current-does-starter-motor-draw.html

Appears to show that a car starter motor can take up to 325 Amps at 12V for a V8 engine. Even if my starter motor used the same then that's 3900W. With a 333W alternator output the alternator would only need to be on for 12 times as long as the starter motor is used to recharge the battery.

I know the battery is also running the lights and spark plugs etc at that time but I'm not convinced it will kill it as quickly as you believe or at all.

[map]

[gavbriggs]

1.2 miles will probably kill your engine before your battery. Go the long way round, fit a temp sensor(if not already present) and don't arrive at work until it's warmed up properly.

Battery and engine will last longer!

Next question!
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Recent bikes: Varadero 125 - Mod 2 3/2/14 - Bandit 1200 SK4

[nowhere.elysium]

[Timmeh]

I have done this very experiment, because I was bored.

I fully charged my gixxer's battery, and then disconnected the reg/rec from the stator. It was reading 13.2v when I started.

I did about 10 miles around our site at about 20mph, with no lights as it was daytime.

When I got back, the reading was 12.8v.

This was a brand-new battery. Obviously higher speeds require more sparks so it'll run down quicker and lights will take their toll too, and a well-used battery will have less capacity than a fresh one.

In a real-world situation, running total loss, I reckon you wouldn't get more than 15 miles out of it before it went flat. I suspect that it would start to misfire at high RPM and then get more and more sick as your plug's performance dropped.

I agree with the others though; 1.2 miles isn't nearly enough time to get to get the engine warm; your plugs will coke up and you're running the risk of accelerated engine wear. It takes my bike 3-4 miles before the temp gauge even starts to move, and before that time I limit myself to 50% of the available RPM and short-shift so there's less stress on the engine.

I'd walk.


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GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[Baffler186]

Depends what other riding you do besides your 1.5 mile commute. I'd say a good 45 mins/hour on the motorway twice a week will do lots of good, both in terms of your battery and your engine.

Might also be worth fitting some charging leads (with waterproof ends) so you can trickle charge when not riding the bike, especially useful if the battery is hard to get at
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Current: 2009 SV650 S, 1990 Kawasaki GT550
Previous: 2009 CBF125, 1998 GSF600, 2004 FZ6 Fazer, 1978 CB400a Hondamatic

[map]

It's not really the distance ridden it's a combination of that and the revs used.
The bike manual may contain the optimal revs for charging the battery.
IIRC it's usually in the 4-5K range for the majority (see, someone will post exception).

Just leaving the bike on idle/tickover will do nothing. As will thrashing it to the redline not charge the battery as well.
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...and the whirlwind is in the thorn trees, it's hard for thee to kick against the pricks...
Gibbs, what did Duckie look like when he was younger?

[Andy9934]

100% get a pushbike or walk. By the time you've geared up you'd be there on a pushbike and halfway walking.
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Surrey
Honda Varadero XL125

[Lord Percy]

1.2 miles is tiny and can be walked in any weather all year round, no matter where you live.

[P.]

[G]

[TaeKwon125]

G, thanks for your reply.

I had a go and came to a similar conclusion, the difficulty is the sheer number of variables (how long is the engine at certain revs for, does the battery also loose power when idling etc.).

I usually go for at least two longer rides per week and my battery hasn't died just yet.

If it does I'll let you know!

Cheers