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Thought that I was imagining it, but I've noticed while riding on a fairly hot day (85F and up?) my Honda marine analog voltmeter reads lower than my normal readings. Below these temps, I can run down the highway and see around 14.2 volts fairly steady. In the hotter weather, it runs around 13.6-13.7 range. This is running at highway speed, no fans on with an "apples to apples" comparison. The hotter the temp, the lower it reads, but hasn't gone below 13.5 volts while riding at highway speeds. I first noticed this while riding a very hot interstate 75 in Michigan a couple of years ago. Since then I hardwired the gauge directly to the accessory connections at the fuse box, and its been much better.

Bottom line is, has anyone else noticed a reduction in voltage while riding in hotter weather? No other issues with bike, battery is 1 year old, battery connections are tight.....
 

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On a hot day my truck does it too, seems as the battery heats up, it don't want to take a charge as well as when it's cold.
 

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Could the analog meter's magnetic induction reacting to heat, but I have the Honda meter EC provides and it seems to be very considtent from cold to hot.

prs
 

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is it the system or the gauge reacting to the heat?

you may want to install a temporary voltmeter that is preferably calibrated to compare the readings...
 

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The internal resistance of a battery drops with temperature and it takes less voltage to fully charge a battery as the temperature rises. Some alternators use temperature compensation built into the regulator IC that automatically reduces the voltage a bit at higher temps. I don't know for a fact that the GL1800 regulator uses temperature compensation, but that might be what is going on.
 

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It's temp compensated, just like a Delphi (Compufire). Mine does the same thing, which is a good thing.
 

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Hot climate and batteries

What Fred Harmon stated is exactly right. Moreso,in hot climates,car/motorcycle batteries life is considerably shortened by hot climate exposure.I live in a tropical climate and is common to have batteries go south in a year. Of course we don't have winter ,therefore the heat exposure is 12 months a year. I change the battery in my 1800 every two years because it happens often that they don't last that long.The same with our emergency generator.
Also a car or bike with let's say 50,000 miles in this kind of year round hot weather acts in many respects of wear and tear as a vehicle double the mileage. Heat is bad for mechanical /electrical items. One good thing:we ride all year !!!
 

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This is an interesting topic and probably associated with the engine surge when coming to a stop as the rpms drop. I never associated it with a drop in temperature (more alt lead needed to charge the battery) but will pay more attention to that.
 

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Hot Weather Voltage

We have (2) 2008 1800 Navi's with digital voltmeters that read 14.2 volts at cruise speeds w/o variation based on load (lights, Gerbings, etc.), and they both drop 0.1 to 0.2 volt readouts (14.1 or 14.0) at cruise speeds at "hot" temperatures - say above 90 deg F. I have been curious about this and imagined aside from resistance changes, also could be the result on increased gap clearance within the alternator rotor/stator itself.
 
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