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Old 18 Aug 2012
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Thanks for your detailed post, Ian. Good idea re: the voltmeter. I'll get one.
Is your replacement alternator bigger and did you notice an effect on mpg/power?
They dont make anything for my bike and from what you say it could lead to other issues so I've decided to minimise my consumption instead.
Like John I've swapped my backlight and indicators for LED and have just got a Rigid Ind. LED front light from Zen.
My bike (GS500) is a permanent headlight jobbie, though I plan to disable that and maybe turn the headlamp off to rely on the Rigid lamp if running the vest on cold nights with the voltmetre sagging. All this is hypothetical at the moment. My bike's output may be fine though I read it's 235w @ 8000 which doesnt sound too promising. Never get anywhere near 8000.

Chris S
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Old 18 Aug 2012
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Originally Posted by IanJ View Post
3) Voltmeter - As other people have mentioned fitting a voltmeter is the best thing you can do to see how well the bike charging system is working at a given engine RPM.
Originally Posted by Chris Scott View Post
Thanks for your detailed post, Ian. Good idea re: the voltmeter. I'll get one.
I use an LED voltage monitor. It's a single LED fitted somewhere visible to the rider, wired to a switched live and earth. It changes colour according to the system voltage - green is (from memory) 14V and up, then amber, red and flashing red. Overcharging is indicated by alternating red and green flashes. I got mine from Sparkbright products on eBay - one man operation, very professional and a super guy to deal with. I think they were 10GBP plus postage. Good value and much easier to locate on the bike than a dial instrument. All my bikes are going to have these in future. Highly recommended. No connection except as satisfied customer, etc.

Here's the monitor:

And here it is on my XT (strapped to the idiot lights with ins tape):

2006 XT660R daily ride, 1994 XT600E about to be reborn, Blog: http://goingfastgettingnowhere.blogspot.com/
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Old 19 Aug 2012
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I've seen those for sale on ebay and they look very good - a lot neater than the version I made myself about five years ago which only cost a couple of quid less and involved hours of soldering and fiddling around trying to fit it all into a small box. Over the last five years the device has proved its worth a few times and I've caught a number of electrical problems before they proved terminal (). One time in France the main battery earth came loose on the engine and the change in light pattern warned me early enough that something was wrong that I could find it before I ground to a halt. My latest project bike is only 6v though so I've now got to find or make a 6v version.
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Old 19 Aug 2012
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Originally Posted by Chris Scott View Post
Is your replacement alternator bigger and did you notice an effect on mpg/power?
Yes the new alternator is 400W the old one was around 230W, I don't notice any difference with power/mpg

Originally Posted by Chris Scott View Post
My bike's output may be fine though I read it's 235w @ 8000 which doesnt sound too promising. Never get anywhere near 8000.
If you have a look at the link below it shows a graph detailing alternator output versus engine RPM for a BMW R100GS with an Endurolast alternator (I couldn't find a graph for a GS500 and from what I understand this is typical for all alternators). The curves level off so that after a certain engine speed the output doesn't change all that much. So an output at 3000 RPM may not be all that much lower than at 8000 RPM.

BMW Electrical & Maintenance Parts | Moto Guzzi | Ducati Motorcycles | EuroMotoElectrics.com

But it sounds like your option of lowering consumption is a good idea. The link below might be worthwhile to confirm what capacity you can get from the alternator.

Calculating Excess Electrical Capacity - Learning Center - Powerlet Products

I like those LED voltmeters I will have to get one of them for testing.

All the best

Ian J
Always have plan B, and maybe plan C
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Old 31 Aug 2012
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Alternative headlight - 36 Watts?


Load reductions.

Your indicators, brake lights are only 'on' for short periods of time so reducing the load here is not that effective.

Your headlight
  • * may be on all the time the bike is running. Putting a switch here is a very good idea, even if legally in some countries you cannot use it while travelling! You can, in any place, use it while starting the engine - when the battery load is highest and you may need that little bit of extra energy to get going. And in places where you may turn it off while travelling you then have that option.
  • * Scooters use a 36 Watt light - some 20 Watts less than the common bike lights of 55/60 Watts. They have a similar base to the H4 globes in common use ... but you'll need to modify something to make them fit (I'd go for the the mounting in the headlight rather than the globe as the next globe would also need modification). This saves you 20 Watts. Of course it won't be as 'bright' as the 55watt globe, but then you could always swap it back if seeing rather than being warm matters? I do not recommend this if running at night, but for use during the day I think it is fine. As any traveller knows, travel at night will take you through the best scenery of your trip when you cannot see it.

Heated vests consume about 60 Watts on full blast, most of the time you only need 20 Watts or less. So get and use an efficient regulator for it.
Same goes for other heating things.

Shunt regulators, as has been said, remove the excess energy from the charging system by dissipating it as heat. This is very efficient when high loads are present. They will get hot with small loads.
Series regulators limit the energy flow through them from the charging system to suit the load. Very efficient for small loads. They will get hot when used with large loads.

Unless you know what you are doing leave your system alone, or have large pockets to pay for your mistakes.

Voltmeter! An extremely good idea, particularly if running close to maximum load.
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