Randy also said this;
"I had first hand experience with early voltage regulators that would stick closed causing voltage spikes, so I wanted the Runtz to be "dead on" accurate and able to accept those voltage spikes without damage."
He is right and you were right to point it out. "Load Dump" is a factor. This can cause high voltage. I removed my comment. (strikethru). I should have done more research. Supposedly, there can be big spikes, I have not had this happen or know anyone who has on non solid state vehicles. As far as I know, the ground on the IC Randy used should redirect a large spike to ground to protect his IC. That is what I thought the ground wire is for. The device also has thermal overload protection and shuts down temporarily to protect the gauge.
Randy was a member here "Fifthave". Quite a prolific poster too. Here is the story about spikes from Randy.
Ok sorry for the vacation guys but i have been like the one armed paper hanger these past months....shop expansion and related....
As for the part time Runtz.... The Runtz has a built in circuit protection to protect the dash gauges from voltage spikes and shorts in wiring harnesses. If the Runtz detects a voltage spike it will shut down like a fuse until things cool down then will come back. It will do that about 4-5 times before it acts like a fuse and stops the flow of current completly.
This case sounds like enough of a voltage spike to just barely trip the Runtz.
That is why it is important to be sure the power to the ignition switch comes directly from the battery post of the battery and not from the amp gauge or starter solenoid as per original.
When the starter switch is closed to crank the engine a voltage spike is created that travels thru the electrical system ....about 300 volts worth. By powering the dash gauges thru the battery, the battery will "eat" those voltage spikes and protect the dash gauges from the voltage spikes.
This is important because the Runtz is a solid state device and is very accurate. If you notice most new positive battery cables already have a 10 gauge wire moulded into the battery clamp. That is what that wire is for.....to power the ignition.
All of this is also true for things like cell phones plugged into cigar lighters, and modern stereo radios... all need to have direct battery power.
Have you seen modern radios installed in old cars and soon after the LED lights are burned out and you cannot figure out what station they are on? A voltage spike is what took out the LED lights and soon ennough the radio itself will be next.
So the important lesson here is be sure the power to the ignition switch and any solid state accessories comes directly from the battery....
Class dismissed....
Randy
