Spridget Tech Talk (MG Midget & Austin-Healey Sprite)
Hey guys my strip down is flying along and must say im really enjoying it so far! got all my lables done (with a sharpie!thanks guys!) anyway took my dash out today and was wondering what this was behind?
thats for your reply's as always!
im putting lables on everything! but im putting in a new loom so hopefully can just copy what came out, but my loom has been so chopped up that i dont know how i'll follow it!
More specifically, it is a voltage stabilizer for the fuel gauge.
When you put it back together, you might want to replace it with an updated solid-state stabilizer for a more reliable part. They are available from the usual suppliers for abut $16
god this is going to sound stupid! but here i go!! what does it do? Dont say stabilise the voltage, thank you!
I will give you the best explanation my non-science mind can provide.
The fuel guage works by a fluctuating resistance in the circuit by the sender in the tank... More resistance = more fuel, less resistance= empty etc.
this signal can vary as the fuel in the tank moves around and bouncer in the road etc... (and other electrical things that I can't explain) The stabilizer keeps it relatively steady, so there are no big spikes or drops and the gauge gives a reliable reading. without it, the needle on your guage would probably be constantly fluttering up and down. (in theory)
that's how I understand it anyway.
and whats the solid state one? hows that different? and also what a daft place to put it! thanx for the info!
As Chris said it stabilizes the voltage.
Your fuel gauge is set to run at 10 volts and this unit keeps feeding it 10 volts no matter what the system has. The electronic one does the same thing but just more accurately (and supposedly lasts longer).
It is not critical for your car, just nice to have for accuracy.
BillM
http://www.britishv8.org/Articles/MGB-Voltage-Stabilizer.htm
here's a pretty good write up of it and directions to make your own solid state stabilizer (but for the price I just bought one)
Basically the traditional stabilizer works kind of the same way as the flasher unit for your turn signal, by using a resistance wire and a strip of dissimilar metals as the metal gets hot it flexas and cuts off power, then it flexes back and power is restored like opening and closing a set of points, it basically flexes so rapidly from full power (12 volts) to no power 90 volts) that the net result is a relatively stable 10volts out to the gauge. This is fine until the metal wears to the point that it breaks or corrodes so it can no longer react as quickly as it should. modern solid state electronics just replace this basically mechanical moving part with an electronic resistor circuit. externally they are nearly identical.
In a word...progress
Think about it... Would you really want a 70 inch 3D HD 1080 dp big screen TV powered by vacume tubes???
The modernday stablizers are do the same thing... There just more reliable and less hassel...that said, i still have the one that came with the car... As im sure others do
Prop
Sorry Dave, couldn't remember who was the proper credit! ;)
The Lucas electronics are a bit unstable. If you overload the alternator you may pull the voltage down to less than 13V or so. At other times when you are not running lights, wipers and fan motor the voltage may be up near 14V. Imagine how that would affect the accuracy of your fuel gauge. It would dim with your lights.
The stabilizer, is more like a step down transformer. No matter how much the high voltage side fluctuates the low side output stays constant. Bill said at 10V, I thought it was 9V, but either way it is constant, therefore the fuel gauge doesn't fluctuate.
The solid state stabilizer should just be a more modern version and work better.
Bottom line, you need it.
everything JMac said, except for this: the voltage stabilizer isn't needed due to any shortcomings in the electrical system (or have anything to do with Lucas), it is just necessary for the reasons he said that apply to all cars with an electrical system (the voltage varies with engine speed/system load, so the voltage is stepped down below that for the most stable gauge needle). Modern cars have a voltage stabilizer for the gauges too.
Norm
Get a UA7810 voltage regulator from your local electronic supply store....the 10=10volts, they come in increments of 2, and you can get em to run 1amp...mount to heatsink, or small piece of aluminum...input, ground, and output...done and done
Mark
Correcto-mundo, Mark. Regrettably, folks this side of the pond likely won't find this component at Radio Shack anymore, since they are mostly a cellphone store now.
But, guys you can do this. Why pay $12 or whatever they charge for these voltage regulators? Buy the component off Ebay, straight from China, 10 for $3.54 postage paid. Search for "7810 voltage regulator".
This is the item right here, including the pinout. The black thing is a bit of plastic about 1/2" x 1/2" x 1/8" You put 12V into pin 1, Pin 2 goes to ground, and Pin 3 is your 10V output, it goes to the gauge. There's a little metal tab on top of the voltage regulator with a hole in it. Like Mark said screw a heatsink to the hole so the little bugger doesn't burn up. Simple, eh?
Charlie
Charles you have indeed impressed me Thanks for the tip
Toby
Aw shucks, Toby. I'm always learnin' neat stuff from you too. What goes around comes around. :)-D
Your fuel gauge needs a steady voltage in order to report accurate results.
The battery voltage will swing between 12 and 14 volts during normal operation.
The way the fuel gauge works is one volt= empty tank and 9 volts=full tank. So you cn see where if the voltage to the fuel gauge were allowed to swing from 12 to 14 volts, it would look like the tank was filling up as you step on the gas!
ok new guy here, im going to tell you exactly what my english freind said this part is and im including the photo i sent to him.
"that is a voltage rectifyier,it reduces voltage from the battery to the instruments which if memory serve should be around ten volts. This probably runs your turn signals and gas gauge if it were stock english. i dont know for sure how you creatons have it broke down,but here in the land of civilization,thats how we do it......lol"
mine does happen to run the turn signals and the emergency brake light,im not sure of the fuel gauge.
and heres the photo:
ps......he also said these things have a habit of becoming loose which results in a bad ground,make sure they are tight when installed!~!!!!!
