Re: Instrument Voltage Regulator

Posted by HH56 On 2009/2/22 14:08:17

The constant 12v out on the old one is sure an indication the heater was burned out or not grounded so it couldn't function & operate.

Regulate is kind of a misnomer in this application, as it pulses so the voltage is either on or off but not regulated to a different level. The use of a capacitor, depending on size, would tend to smooth things out a bit and could result in a steadier lower voltage reading on a meter since the capacitor discharge would lag the pulses and tend to partially fill in the off gaps.

What makes things work in this situation is the gauges are thermal, each one has a heater coil which works on a bi-metallic strip. The IVR with it's short pulses, provides 12v to heat for an instant, then cuts off, then heats, then off and so on. The relatively slow response of the gauges to the on-off ensures you rarely see the pulsing yet the amount is calculated to be enough with the gauge response time and changing resistance in the senders to give periods of current flow for a fairly accurate reading. Hence the term regulate would be more for the pulse on-off time, not the voltage. There is an adjustment to control the time of cycles by varying the distance the strip has to move before making/breaking contact.

The senders are about 10 ohms when full, hot, or high pressure so less resistance equals more current flow through the gauge heater so it heats up more and gauge reads higher, conversely at about 80 ohms when empty, cold or low, less current so the gauge doesn't have enough heat to move very far.