Does anyone here have any electrical/electronics experience?

[ghouck]

I have a little project I'm trying to get figured out, and I need a little help. I have a snowmobile, which has no battery (pull start). It does have a stator / regulator-rectifier that powers all the lights, gauges at ~14 volts. I installed another set of gauges that are electronic (exhaust gas temperature gauges). The problem is that when the engine is shut off, or the RPMs get too low for the system to put out full voltage, the EGT gauges shut off. My plan was to install a small (0.8 or1.2 amp/hour) 12v battery, with a diode so the system will charge it, but the diode will prevent the battery from draining back through the electrical system (Charging system -> Diode -> Battery -> EGT Gauges in the + side). That all seems to be OK, ,, but, , the machine's charging system at ~40watts will charge that small battery too quickly, as that sized battery is reccomended to be charged at around 4-6 watts. It is my understanding that a resistor could be used to limit the current to the 0.3 - 0.5 amps it should be limited to, but I don't know a) if a resistor will work in this capacity, or b)  how to calculate the ohms of said resistor. I'm also not clear on what to look for in the diode as far as a spec that will give me what I need, other than it must have a breakdown voltage of at least twice the power used (so it must be at least 24 volts breakdown). Any help will be appreciated. Thanks.

[CheezeFlixz]

The stator might be going to bad, like a bad alternator on a car or your idle might be to low. You could "rig" it, but I'd check the stator first. Rigging always leads to problems. Not knowing the type of stator you have I can't say for sure, you might be able to rebuild it, might just have to replace it. They don't last forever. Check your spec see what the output should be and check it with a multimeter. Based on what you said that would be my first guess.
I'd think in AK it could get more junk (dirt, salt, moisture) in it being a snowmobile, than you'd get on a street bike. Don't know just a guess.

[ghouck]

The stator is fine, it's just that since it's a 2-stroke and run when it's cold, the Rs go up and down a bit until it's warmed up. That's what makes the gauges go on and off. The problem with adjusting the idle, is that when you adjust it so it idles a little high when cold, it screams when it's warm. But, when it's warming up is one time one should watch the temps, in case the engine is leaning out from an iced carb or something.

It turns out that a resistor and a couple of diodes is all that makes up the circuitry I am looking for. A 24 Ohm resistor will limit the charge to the battery to a half an amp or so if the battery is fully discharged. As the voltage difference between the charging system's 14 volts and the battery drops (IOW, when the battery is charged), , the current drops, , so that's good. One diode prevents the battery from draining back through the charging system when the engine is off, the other allows battery power to bypass the resistor when the gauges are running off the battery and the engine is off.

Thanks though. The part that was confusing me is how to apply the I=V/R (Current = Voltage / Resistance).

[CheezeFlixz]

The stator is fine, it's just that since it's a 2-stroke and run when it's cold, the Rs go up and down a bit until it's warmed up. That's what makes the gauges go on and off. The problem with adjusting the idle, is that when you adjust it so it idles a little high when cold, it screams when it's warm. But, when it's warming up is one time one should watch the temps, in case the engine is leaning out from an iced carb or something.

It turns out that a resistor and a couple of diodes is all that makes up the circuitry I am looking for. A 24 Ohm resistor will limit the charge to the battery to a half an amp or so if the battery is fully discharged. As the voltage difference between the charging system's 14 volts and the battery drops (IOW, when the battery is charged), , the current drops, , so that's good. One diode prevents the battery from draining back through the charging system when the engine is off, the other allows battery power to bypass the resistor when the gauges are running off the battery and the engine is off.

Thanks though. The part that was confusing me is how to apply the I=V/R (Current = Voltage / Resistance).

Well that's Ohm's Law and based on a algebraic equation you have two of the variables. I=V/X X=?