# 10v regulator for car

Discussion in 'General Electronics' started by James Carruthers, Jun 2, 2004.

1. ### James CarruthersGuest

Hi there,

On my Triumph Spitfire - and most British cars I assume - I have the
standard 10v voltage stabiliser designed in the 60s - but the things
are always blowing and not working - in short - theyre a PITA. They
provide the fuel and water temp gauges with 10v supply instead of the
12-14 that everything else gets.

Can someone give me some directions on how to build a modern solid
state version of this ancient device? Im pretty sure it must be easy
with a single IC - but I'd like some suggestions as to the most simple
way to do it.

James

2. ### NirodacGuest

I like to use the LM117 (LM317) voltage reg chip from National.

http://www.national.com/ds/LM/LM117.pdf

I've done this before on an American car (Chrysler) and it worked well (used
You are sure it's 10 volts, aren't you.

You should be aware that the thermal regulator that you are replacing was
designed to interrupt the current going to the gauges. Interruption
frequency is based on the current flowing through it. The gauges actually
only got an average voltage, based on the number of interruptions of the
current flow in a given minute. Automotive gauges of this era are typically
slow in responding to voltage changes, therefore you don't see the needle
move as the voltage is interrupted.
I'm not sure how you determined that the gauges needed 10 volts, but with
this solid state regulator producing a constant voltage, you may find that
the gauges read high, as the gauge won't be averaging out the voltage
interruptions. Simply lower the output voltage of the solid state regulator
to make the gauges read correctly.

The app note shows a precision 10 volt output. For older cars you do not
need this kind of precision. Just use the resistors on the ground (center
pin) as shown in the app notes. Adjust the trim pot for your output
voltage. Don't forget to put caps on the input and the output (it's all in
the app notes).

OBTW, mine got really hot when I used the Vreg., you may need a heat sink.
Gauges from this era tend to draw a lot more current than you may expect.
They were designed that way.

Yar

3. ### DboweyGuest

James posted:

<< On my Triumph Spitfire - and most British cars I assume - I have the
standard 10v voltage stabiliser designed in the 60s - but the things
are always blowing and not working - in short - theyre a PITA. They
provide the fuel and water temp gauges with 10v supply instead of the
12-14 that everything else gets.

Can someone give me some directions on how to build a modern solid
state version of this ancient device? Im pretty sure it must be easy
with a single IC - but I'd like some suggestions as to the most simple
way to do it.
----

I don't recall which car this was for, but I read a short piece many years back
suggesting a Zener diode to replace the electro-mechanical gizmo. I was
thinking of doing the changeover, but didn't need it at the time; it is
misplaced now.

I suggest you contact a MG and Triumph club. There are usually "Keepers of the
Obscure" in the clubs.

I think I was considering the conversion for my MGTD.

Don

4. ### no_oneGuest

remember that all the english cars used a positive ground, so you need a
regulator designed with that quirk in mind!

Many IC makers produce the LM7800 series three terminal regulators.
Radio Shack is a good source for these. There is not one specifically
for 10.0 volts, however, by placing a zener diode or series
combination of forward biased rectifier diodes in the ground (center)
terminal of these devices, you can alter the output voltage from say,
a 5 volt regulator (LM7805), to 10 volts using a 4.7 volt zener and a
forward biased rectifier or signal diode like a 1N4148 in series,.
The zener and rectifier will have a small current running through them
forcing a voltage drop of about 5.2 volts to appear across them. This
voltage drop biases the ground (or reference) terminal of the IC up by
that voltage so at the output, 10.2 volts will appear, and can provide
up to 1 amp of current, short circuit and over temperature protected.
There are 3 amp versions of these as well, but are not as common as
the 1 amp types. I doubt if your gauges will need more than an amp
anyway. Good luck!

6. ### James CarruthersGuest

I've found the perfect IC now!... 7810 - 10v regulator - the version I
have gone for is the 2A one (78S10 is what the one I have found is
called) - which should give me enough I think.

So the whole regulator will consist of 2 cables with a couple of spade
terminals on the end. It will ground to the speedo using the tag on
the top of the regulator... brilliant! This is an excellent solution I
think.

If it reads high then I will try a 9v regulator - more common than the
10v one too.

James

7. ### petrus bitbyterGuest

James,

Most standard types of 78xx regulators require at least 2V between in- and
output. So for the 78S10 the 12V battery voltage will be enough but you can
run into probles when that voltage falls below 12V. Some low drop types
require only 1V. Check out the datasheet of the regulator to avoid
unpleasant surprises.

petrus bitbyter

8. ### James CarruthersGuest

Petrus,

The standard voltage is about 12.6 and the regulator wants 12.5 - when
the car is charging on the alternator this goes up to about 14.5 - so
I should be fairly safe.

James

9. ### QuackGuest

So the whole regulator will consist of 2 cables with a couple of spade
with some of the regulator chips i have used (i cant remember
specifically which one right now), the tag on the top was Vout, not
gnd!. double check that.

Alex.