Any Electrical Engineers?

[V4_AllTheWay]

It's a long shot, but maybe someone knows.

Say you have a temperature measuring circuit that is calibrated for a certain circuit operating voltage.
Everything works fine, temperatures are correct, but say you then lower the working voltage of the circuit, how does this affect the calibration? Will the measurements still be the same?

[simon1221]

Depending on what is used to measure the temperature, say if it was worked out using a temp sensor (or a termistor) and some resistance based circuit, then raising/lowering the voltage would lower/raise the resistance, giving you a different reading.

(Lets hope my A level pysics was correct)
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DNA50 (sorry) ->> TZR125l >> GPZ500S

[sickpup]

I'm pretty certain you get a gold star for that.

[V4_AllTheWay]

This then could explain the wierd temperature readings I am getting.

When spending prolonged periods of time in slow speed traffic and town areas the temperature gauge seems to rocket.
But whilst sitting at lights I notice a slight twist of the trottle at stand still will drop the temperature needle!!?!

My logic is this:
At low revs (<5k) the engine does not charge the battery (ref: Hanes). So after time in traffic the battery gets drained, and the voltage drops, hence affecting the reading on the temperature gauge which relies on a fully charged battery for correct result.
Bringing up the revs charges the battery slightly, increaes the voltage and corrects the temperature reading.

How does that sound?

I am thinking I either need a new battery or a new rectifier (NC30 ones are notorious for failure) or both new.
However could lack of charge storage just be the result of an old battery and not a broken rectifier?

[Ichy]

Isn't it more obvious that the bike is overheating when its standing still or moving slow so therefore less air flow?

If you have a multimeter and a good means of checking temperature then just start the bike and let it run. You should be able to check charging, if the rectifer is working, running temp to gauge, and normal voltage.

Working from memory, normal voltage should be above 11v, charging voltage shouldn't be higher than 15-16v.
I'm sure someone will put me right.

[V4_AllTheWay]

Yes, actual overheating must factor in, but what else would explain that picking up the revs gives instant temperature reading decrease?

[Bezzer]

Because at slow/stopped your waterpump is not doing much in the way of moving the coolant around and the fan if it's cut in is running slower so it's heating up and rising to to the higher parts which is usually where your temperature sensor is, you get a higher reading though it will be a bit cooler elsewhere. You start moving or revving and the pump flow increases,the fan goes faster and the water moves round evening the temperature out, so in a few seconds it's cooler at the sensor and shows on your gauge.

Edit - Missed the other bit - You'll find that the Haynes says MAXIMUM charging is at 5,000rpm not the start of it, it should be charging from tickover-ish upwards but won't reach the max until 5,000. To check it - multimeter set on volts, put it across the battery terminals and watch it rise as you rev it, should start around 13 volts and go to around 15v, if you look in your Haynes it will tell you the correct values.
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I used to be indecisive but now I'm not quite so sure.

[sep]

you can't really say, what the effect is, when you drop the voltage, search for the right datasheet... most will drop when you drop the voltage f.e. https://www.national.com/ds/LM/LM135.pdf

[Bezzer]

Think you'll find it's got bugger all to do with the working voltage of the gauge/sender and is purely what I put above, it happens on the majority of bikes just that not a lot of people take notice of it.
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I used to be indecisive but now I'm not quite so sure.

[the grim reaper]

That depends on whether the guage drops and stays low or drops when revving and then returns to the old reading when you stop. Revving a hot engine will help to cool it by circulating the coolant, as Bezzer said but the temp shoul slowly drop a bit and take time to creep back up.

Cheers

Grim
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Adverts don't always work: Remember that advert, where the army are running across the desert and they have a wounded man on a stretcher. They get to a ravine, the bridge is down and a caption pops up that says, 'What are you thinking?'. I don't know about you but I was thinking, 'Christ, I'm glad I'm not in the f***ing army'.

[V4_AllTheWay]

[sep]

last year I had to make sort of a big essay (don't know how it's called in english) with the topic: Watercooling of motors

you guys are right