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New Voltage stabilizer for a TR4A - which to use?


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Folks, I want to replace the VS on my TR4A (negative ground). My initial plan was to get one of the new solid state units from either The Roadster Factory, or Moss (US). However several folks on the Triumph Experience forum have said the VS units being offered by the US vendors are very trouble prone (one gentleman had 4 bad units in a row from Moss). Have you gents had better luck with any of the VS units offered by your suppliers?

thanks

Jim

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Hello Jim

Make sure that the electronic solid state version you get is marked -GND on the back for negative earth cars. A while ago over here in UK, Moss were selling +GND units but using the wrong part number for the negative ground units. From their data sheet I got it states

131-555 negative ground

131-556 positive ground

The older original non solid state units work regardless of polarity. I have one of those. 

Here is a link to a thread I started 3 years ago on this topic

https://www.tr-register.co.uk/forums/index.php?/topic/66848-voltage-stabilisers-for-tr4-and-4a-are-different/

Keith

Edited by keith1948
link to earlier thread
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Hello All

              I just bought a few of these and fitted them inside the original can (Negative for Spitty) been working for 10+ years

LM7810ACT Onsemi, Linear Voltage Regulator, 7810, Fixed | Farnell

Roger

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Hello All

              This what I fitted in Spitty ,Vitesse and TR6 some negative and some positive.

They are a cheap as chips and easy to fit!

6 X Regulator Voltage L7810CV LM7810 7810 10V 1,5A - Voltage Regulator TO-220 692685035738 | eBay

Roger

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As the two Rogers say, it is easy to build one into an old casing:

The LM 7810 works for negative earth cars, the LM 7910 is for positive earth.  The connections are very simple and it only requires a couple of other components. These are  0.22uf ( 220nf ) capacitors from the input terminal to earth and  from the output terminal to earth to help with noise isolation. The voltage rating of these is not important as long as it is higher than 50 volts, most such capacitors are higher. 

These ones are fine: 

https://www.ebay.co.uk/itm/263756115737?hash=item3d6916ef19:g:CG8AAOSw1u5bIYJz&var=562973822517

blank2.png.df38d647e297abefbfe744b3613a7f3b.png

Some makers may fully encapsulate the chip including the mounting tag.  In that case a wired earth connection is required to the centre pin. 

 

 

Edited by RobH
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The 78 and 79 series regulator ICs do get hot, so they need to be firmly clamped to the metal case with a smear of heat sink compound.

In the late 70s I was involved with developing solid state voltage stabilisers for the company I worked for, who were trying to get into automotive electronics, and we found there was a lot of difference between different manufacturers in terms of reliability and ability to handle high temperatures and voltage transients. Sadly I can't remember which ones were good, but it's probably all changed now anyway. I think I was named on the patent application, but I never did receive any royalties!

Pete

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You are right they need clamping to metal but they shouldn't get terribly hot in this application Pete -  the gauges don't draw much current  - around 200mA total - and the regulator is dropping less than five volts max, so the dissipation is only about 1 watt. 

 

 

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10 hours ago, RobH said:

You are right they need clamping to metal but they shouldn't get terribly hot in this application Pete -  the gauges don't draw much current  - around 200mA total - and the regulator is dropping less than five volts max, so the dissipation is only about 1 watt. 

 

 

Agreed Rob, but 1W is rather a lot for an enclosed TO220 package.

Pete

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15 hours ago, stillp said:

found there was a lot of difference between different manufacturers in terms of reliability and ability to handle high temperatures and voltage transients.

Hello Pete

                 I must have bought the good ones as still ok after 10years! I did clamp it to the aluminium case probably with a smear of heat paste?

Roger

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My TR6 fuel and temperature gauge have always seemed to read low. Measured my TR6 V.S. yesterday, using an AVO model 8 analogue meter. Oscillates about every second between 7 to 9V dc at 12.5V input . I believe I read somewhere that it can be adjusted with a screw that increases or decreases the gap to the thermal bi-metallic strip.

Is this true, as could be reason gauges read low?

Colin.

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See this. Most don't have the adjustment screw available:

http://www.mgb-stuff.org.uk/ivs.htm

Your AVO reading is only approximate and depends on the inertia of the needle as it wobbles between zero and 12v.  To get a proper reading you need to smooth the voltage using an RC network as shown at the end of that link.  

 

The output from the bi-metallic stabiliser is a square wave switching between 0v and supply voltage  with variable mark-space ratio depending on the value of the supply. The car meters average that output thermally and you either need a true-rms reading meter or a smoothing network to read the right value.  An AVO only reads true rms on the ac volts range for a sinewave input. 

Edited by RobH
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53 minutes ago, c.hydes said:

Thanks Rob, I will remeasure with the RC network firstly and if necessary see if it has the adjustment screw fitted.

Colin.

Hi Rob, what's the series diode for in the circuit, surely this will drop 0.7v on the charging cycle?

Colin

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Hmm  -  good point Colin I hadn't looked closely at that.  The diode shouldn't be there.  

With that in circuit there is no discharge path and the voltage will just 'pump' towards the peak which isn't what you want to measure.    The reading on the meter will take a few seconds to settle at the average. 

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5 minutes ago, RobH said:

Hmm  -  good point Colin I hadn't looked closely at that.  The diode shouldn't be there.  

With that in circuit there is no discharge path and the voltage will just 'pump' towards the peak which isn't what you want to measure.    The reading on the meter will take a few seconds to settle at the average. 

Yeah diode not logical, for both reasons, so will leave out.

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3 hours ago, c.hydes said:

Yeah diode not logical, for both reasons, so will leave out.

Just retested with the smoothing circuit (no series diode) Rob. 10K and 10uF still pulses, but with 100uF is fairly smooth with AVO or digital at about 8V dc.

So assume that's why gauges read low?

Colin.

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