<html><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px"><div dir="ltr"><span>as always</span></div><div dir="ltr"><span>thanks</span></div><br> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;" id="yui_3_16_0_1_1435879145015_4115"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;" id="yui_3_16_0_1_1435879145015_4114"> <div dir="ltr"> <hr size="1"> <font size="2" face="Arial"> <b><span style="font-weight:bold;">From:</span></b> Randall <TR3driver@ca.rr.com><br> <b><span style="font-weight: bold;">To:</span></b> 'Frank Fisher' <yellowtr3@yahoo.com>; 'Triumphs List' <triumphs@autox.team.net> <br> <b><span style="font-weight: bold;">Sent:</span></b> Thursday, July 2, 2015 3:25 PM<br> <b><span style="font-weight: bold;">Subject:</span></b> RE: [TR] gas gauge and voltage regulators<br> </font> </div> <div class="y_msg_container" id="yui_3_16_0_1_1435879145015_4113"><br>> the purpose of the voltage regulator is to stop the ups and <br clear="none">> downs of the voltage caused by alternator as engine revs? <br clear="none"><br clear="none">Yes. At idle, the stock Lucas alternator (or generator on the TR4/4A) puts out almost nothing, so the battery voltage can droop<br clear="none">quite a bit under heavy load (eg headlights on). The gauges used on TR4-6 work on heat, and so are very sensitive to changes in<br clear="none">voltage (power and therefore heat is related to the square of the voltage).<br clear="none"><br clear="none">> what then is usual output? ie 13/14 volts in----? volts out.<br clear="none"><br clear="none">The stock "voltage stabilizer" doesn't actually change the voltage. Instead, it interrupts the voltage output part of the time,<br clear="none">such that the average is 10 volts. The technique is commonly known as Pulse Width Modulation (PWM) and is still quite common today.<br clear="none">But, modern devices use solid state switches (transistors) that can switch very quickly. Transistors back then were expensive and<br clear="none">fragile, so Smiths (or whoever owned them by then) used a simple mechanical switch that only operated a few times per second.<br clear="none">Pretty ingenious really, but like so many other things on our cars, strange and poorly understood today.<br clear="none"><br clear="none">Since the gauges are so slow to respond, they don't follow the constant up and down from the VS, but any voltmeter or DMM will. So,<br clear="none">it's more or less impossible to check the original VS accuracy with a voltmeter or DMM. Smiths' suggestion was to hook up a "known<br clear="none">good" gauge along with a dash light bulb in series to a regulated 10v source, note the resulting reading, then hook it up to the VS<br clear="none">to be tested and compare the reading (after waiting for it to settle each time).<br clear="none"><br clear="none">But in my limited experience, the usual VS failure modes are either that the heater burns out (meaning it supplies input voltage all<br clear="none">the time), or the contacts go bad. You can check the contact resistance with an ohmmeter. Or just pull the wire off the<br clear="none">temperature sender and connect it to a test lamp (with the other side of the lamp grounded). If you can see the light blink on and<br clear="none">off, the VS is working, and probably reasonably accurate. Unless you are chasing a fairly subtle error in gauge reading, the<br clear="none">problem is not the VS.<div class="qtdSeparateBR"><br><br></div><div class="yqt8541498650" id="yqtfd19863"><br clear="none"><br clear="none">> any one have a list of what smiths gauges require a voltage <br clear="none">> stabilizer and those that don't. have not been to see the car <br clear="none">> yet, but id like to be prepared.</div><br clear="none"><br clear="none">Sorry. I had a partial list, but can't seem to find it at the moment. But all of the fuel and temperature gauges originally used<br clear="none">on TR4-TR6 (as well as Stag, 2000 and so on) require a VS. <br clear="none"><br clear="none">-- Randall <div class="yqt8541498650" id="yqtfd52573"><br clear="none"><br clear="none"></div><br><br></div> </div> </div> </div></body></html>