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as alwaysthanks
From: Randall <TR3driver@ca.rr.com>
To: 'Frank Fisher' <yellowtr3@yahoo.com>; 'Triumphs List' <triumphs@autox.=
team.net>=20
Sent: Thursday, July 2, 2015 3:25 PM
Subject: RE: [TR] gas gauge and voltage regulators
=20
>=C2=A0 the purpose of the voltage regulator is to stop the ups and=20
> downs of the voltage caused by alternator as engine revs?=20
Yes.=C2=A0 At idle, the stock Lucas alternator (or generator on the TR4/4A)=
puts out almost nothing, so the battery voltage can droop
quite a bit under heavy load (eg headlights on).=C2=A0 The gauges used on T=
R4-6 work on heat, and so are very sensitive to changes in
voltage (power and therefore heat is related to the square of the voltage).
> what then is usual output? ie 13/14 volts in----? volts out.
The stock "voltage stabilizer" doesn't actually change the voltage.=C2=A0 I=
nstead, it interrupts the voltage output part of the time,
such that the average is 10 volts.=C2=A0 The technique is commonly known as=
Pulse Width Modulation (PWM) and is still quite common today.
But, modern devices use solid state switches (transistors) that can switch =
very quickly.=C2=A0 Transistors back then were expensive and
fragile, so Smiths (or whoever owned them by then) used a simple mechanical=
switch that only operated a few times per second.
Pretty ingenious really, but like so many other things on our cars, strange=
and poorly understood today.
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.=C2=A0 So,
it's more or less impossible to check the original VS accuracy with a voltm=
eter or DMM.=C2=A0 Smiths' suggestion was to hook up a "known
good" gauge along with a dash light bulb in series to a regulated 10v sourc=
e, note the resulting reading, then hook it up to the VS
to be tested and compare the reading (after waiting for it to settle each t=
ime).
But in my limited experience, the usual VS failure modes are either that th=
e heater burns out (meaning it supplies input voltage all
the time), or the contacts go bad.=C2=A0 You can check the contact resistan=
ce with an ohmmeter.=C2=A0 Or just pull the wire off the
temperature sender and connect it to a test lamp (with the other side of th=
e lamp grounded).=C2=A0 If you can see the light blink on and
off, the VS is working, and probably reasonably accurate.=C2=A0 Unless you =
are chasing a fairly subtle error in gauge reading, the
problem is not the VS.
> any one have a list of what smiths gauges require a voltage=20
> stabilizer and those that don't. have not been to see the car=20
> yet, but id like to be prepared.
Sorry.=C2=A0 I had a partial list, but can't seem to find it at the moment.=
=C2=A0 But all of the fuel and temperature gauges originally used
on TR4-TR6 (as well as Stag, 2000 and so on) require a VS.=C2=A0=20
-- Randall=C2=A0=20
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<html><body><div style=3D"color:#000; background-color:#fff; font-family:He=
lveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;fo=
nt-size:16px"><div dir=3D"ltr"><span>as always</span></div><div dir=3D"ltr"=
><span>thanks</span></div><br> <div style=3D"font-family: HelveticaNeue, H=
elvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px=
;" id=3D"yui_3_16_0_1_1435879145015_4115"> <div style=3D"font-family: Helve=
ticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font=
-size: 16px;" id=3D"yui_3_16_0_1_1435879145015_4114"> <div dir=3D"ltr"> <hr=
size=3D"1"> <font size=3D"2" face=3D"Arial"> <b><span style=3D"font-weigh=
t:bold;">From:</span></b> Randall <TR3driver@ca.rr.com><br> <b><span =
style=3D"font-weight: bold;">To:</span></b> 'Frank Fisher' <yellowtr3@ya=
hoo.com>; 'Triumphs List' <triumphs@autox.team.net> <br> <b><span =
style=3D"font-weight: bold;">Sent:</span></b> Thursday, July 2, 2015 3:25 P=
M<br> <b><span style=3D"font-weight: bold;">Subject:</span></b> RE: [TR] ga=
s gauge and voltage regulators<br> </font> </div> <div class=3D"y_msg_conta=
iner" id=3D"yui_3_16_0_1_1435879145015_4113"><br>> the purpose of =
the voltage regulator is to stop the ups and <br clear=3D"none">> downs =
of the voltage caused by alternator as engine revs? <br clear=3D"none"><br =
clear=3D"none">Yes. At idle, the stock Lucas alternator (or generator=
on the TR4/4A) puts out almost nothing, so the battery voltage can droop<b=
r clear=3D"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=3D"none">voltage (power and therefore heat is related to the squa=
re of the voltage).<br clear=3D"none"><br clear=3D"none">> what then is =
usual output? ie 13/14 volts in----? volts out.<br clear=3D"none"><br clear=
=3D"none">The stock "voltage stabilizer" doesn't actually change the voltag=
e. Instead, it interrupts the voltage output part of the time,<br cle=
ar=3D"none">such that the average is 10 volts. The technique is commo=
nly known as Pulse Width Modulation (PWM) and is still quite common today.<=
br clear=3D"none">But, modern devices use solid state switches (transistors=
) that can switch very quickly. Transistors back then were expensive =
and<br clear=3D"none">fragile, so Smiths (or whoever owned them by then) us=
ed a simple mechanical switch that only operated a few times per second.<br=
clear=3D"none">Pretty ingenious really, but like so many other things on o=
ur cars, strange and poorly understood today.<br clear=3D"none"><br clear=
=3D"none">Since the gauges are so slow to respond, they don't follow the co=
nstant up and down from the VS, but any voltmeter or DMM will. So,<br=
clear=3D"none">it's more or less impossible to check the original VS accur=
acy with a voltmeter or DMM. Smiths' suggestion was to hook up a "kno=
wn<br clear=3D"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=3D"none">to be tested and compare the reading (after waiting fo=
r it to settle each time).<br clear=3D"none"><br clear=3D"none">But in my l=
imited experience, the usual VS failure modes are either that the heater bu=
rns out (meaning it supplies input voltage all<br clear=3D"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=3D"none">temperatur=
e sender and connect it to a test lamp (with the other side of the lamp gro=
unded). If you can see the light blink on and<br clear=3D"none">off, =
the VS is working, and probably reasonably accurate. Unless you are c=
hasing a fairly subtle error in gauge reading, the<br clear=3D"none">proble=
m is not the VS.<div class=3D"qtdSeparateBR"><br><br></div><div class=3D"yq=
t8541498650" id=3D"yqtfd19863"><br clear=3D"none"><br clear=3D"none">> a=
ny one have a list of what smiths gauges require a voltage <br clear=3D"non=
e">> stabilizer and those that don't. have not been to see the car <br c=
lear=3D"none">> yet, but id like to be prepared.</div><br clear=3D"none"=
><br clear=3D"none">Sorry. I had a partial list, but can't seem to fi=
nd it at the moment. But all of the fuel and temperature gauges origi=
nally used<br clear=3D"none">on TR4-TR6 (as well as Stag, 2000 and so on) r=
equire a VS. <br clear=3D"none"><br clear=3D"none">-- Randall <=
div class=3D"yqt8541498650" id=3D"yqtfd52573"><br clear=3D"none"><br clear=
=3D"none"></div><br><br></div> </div> </div> </div></body></html>
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