LM 7810 voltage stabilizer
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Probably not. Most 3-terminal regulators need capacitors on both sides to maintain stability AND a load pulled from them to regulate.
Yeah, the old charger is probably a simple transformer, rectifier and some caps. You're better off testing off your car battery (especially since that's the end goal anyway). Those linear regulators are pretty robust, as long as you hook it up right and heat sink it appropriately depending on load. It's probably working fine.
Be sure there is an appropriate size fuse on the positive feed to any circuit you add to a vehicle.
If I were you I would be looking for a low drop out voltage regulator. The LM series requires something like 1.5 volts minimum from input to output. There are regulators out there that will stay in regulation with less than a volt input to output, though it might be hard to find one in a 10 Volt output.
You could take a 5 Volt low drop out regulator and add two equal value resistors in series to the output and connect the ground of the regulator to the junction of the two resistors to get the 5 Volt regulator to supply 10 Volts.
If I were you I would be looking for a low drop out voltage regulator. The LM series requires something like 1.5 volts minimum from input to output. There are regulators out there that will stay in regulation with less than a volt input to output, though it might be hard to find one in a 10 Volt output.
You could take a 5 Volt low drop out regulator and add two equal value resistors in series to the output and connect the ground of the regulator to the junction of the two resistors to get the 5 Volt regulator to supply 10 Volts.
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just wondering, but which gauges need 10V?
Originally Posted By: expat
Thanks guys, I will try it off a battery with a load.
I was also considering using a step down Buck converter.
Would that be better in my application?
I would stay away from any Buck converters.
Why do you want 10 Volts for your gauges. Is it to attenuate the brightness of bulbs that illuminate the gauges, and also make the bulbs last much longer.
The LM Voltage regulators are generally only good for up to one Amp. Be sure the total current draw for all of the loads do not exceed the current rating of the regulator.
If the use is to simply attenuate the brightness of the bulbs illuminating the gauges, I would not worry about the possibility of the regulator dropping out. It would not be a big deal.
If the only reason you want to use a 10 Volt regulator is to attenuate the lights on the gauges, you could get by with a power resistor. Be sure to get one that is rated for more than the wattage it will be dissipating, and mount it so it has plenty of air for cooling.
Thanks guys, I will try it off a battery with a load.
I was also considering using a step down Buck converter.
Would that be better in my application?
I would stay away from any Buck converters.
Why do you want 10 Volts for your gauges. Is it to attenuate the brightness of bulbs that illuminate the gauges, and also make the bulbs last much longer.
The LM Voltage regulators are generally only good for up to one Amp. Be sure the total current draw for all of the loads do not exceed the current rating of the regulator.
If the use is to simply attenuate the brightness of the bulbs illuminating the gauges, I would not worry about the possibility of the regulator dropping out. It would not be a big deal.
If the only reason you want to use a 10 Volt regulator is to attenuate the lights on the gauges, you could get by with a power resistor. Be sure to get one that is rated for more than the wattage it will be dissipating, and mount it so it has plenty of air for cooling.
Originally Posted By: expat
But when I test them with an old battery charger as a power source (14v) the output from the LM 7810 is only 7.7v
Try the 10V regulator hooked to your car battery.
But when I test them with an old battery charger as a power source (14v) the output from the LM 7810 is only 7.7v
Try the 10V regulator hooked to your car battery.
My gauges are Smiths, they require 10v, but they originally received 14v alternator out-put that was regulated on and off via a bi-metal contact to simulate a steady 10v.
Over the years those bi-metal contacts vary in their simulated out put.
Gauge lighting is full alternator power, regulated if need be, by a rheostat.
Why would a Buck converter not be suitable?
Over the years those bi-metal contacts vary in their simulated out put.
Gauge lighting is full alternator power, regulated if need be, by a rheostat.
Why would a Buck converter not be suitable?
Not sure on why not to use a buck, other than noise issues (which should not matter to the gauges, as much to your AM radio perhaps).
I'd think an LM7810 would be fine with engine-on. Drop out is like 1.5V or so. A couple of 10uF caps would be good. Heat is a bigger issue; dropping 4V at an amp would make for some problems getting the heat out.
How much of a load are the guages?
I'd think an LM7810 would be fine with engine-on. Drop out is like 1.5V or so. A couple of 10uF caps would be good. Heat is a bigger issue; dropping 4V at an amp would make for some problems getting the heat out.
How much of a load are the guages?
I've seen these things used to power a small 12V amplifier in a 24V vehicle. the gauges will have much lower load, and much less voltage drop over the LM78
MolaKule
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Originally Posted By: expat
My gauges are Smiths, they require 10v, but they originally received 14v alternator out-put that was regulated on and off via a bi-metal contact to simulate a steady 10v.
Over the years those bi-metal contacts vary in their simulated out put.
Gauge lighting is full alternator power, regulated if need be, by a rheostat.
Why would a Buck converter not be suitable?
The voltage drop across the regulator X the current "through' the regulator is the power your regulator will have to dissipate as heat, so it most likely will have to be heatsinked.
Buck converters are switching regulators and unless they are filtered properly, will generate noise that will be sent throughout your electrical system, including the PCM.
I think what you really need is an LM317 adjustable regulator in a TO-220 package on a heatsink.
http://www.ti.com/lit/ds/symlink/lm317.pdfhttp://www.ti.com/lit/ds/symlink/lm317.pdf
If interested, I can show you how to determine the R2 resistance.
My gauges are Smiths, they require 10v, but they originally received 14v alternator out-put that was regulated on and off via a bi-metal contact to simulate a steady 10v.
Over the years those bi-metal contacts vary in their simulated out put.
Gauge lighting is full alternator power, regulated if need be, by a rheostat.
Why would a Buck converter not be suitable?
The voltage drop across the regulator X the current "through' the regulator is the power your regulator will have to dissipate as heat, so it most likely will have to be heatsinked.
Buck converters are switching regulators and unless they are filtered properly, will generate noise that will be sent throughout your electrical system, including the PCM.
I think what you really need is an LM317 adjustable regulator in a TO-220 package on a heatsink.
http://www.ti.com/lit/ds/symlink/lm317.pdfhttp://www.ti.com/lit/ds/symlink/lm317.pdf
If interested, I can show you how to determine the R2 resistance.
The 7810 will work fine in your application. The key to survival for the thing is to put a small - a few ohms will do, maybe 2.7 or 3.3 - in series with the input power and a fairly fat 24 volt zener across the input to common after the resistor. Automotive electrical systems are full of transients, and the 7810 is pretty robust but it's 35v input limit needs to be respected. The zener protects the 7810 and the resistor protects the zener. As others have said, you'll have to have capacitors across the input and output. 1 mfd polycarbonate is probably a good choice - they can take the heat. Electrolytics don't last well in that environment.
I did this on my old 1 series Volvo with an LM317. All suggestions up the thread are good, but I will emphasize you will want a heatsink. The old gauges with the thermal voltage regulator draw quite a bit of current and you will be dissipating several watts in that regulator. It took many days for the TO220 tab sized burn to heal on my index finger when I poked it up behind the dashboard to feel if the reg was getting "warm".
can you not bolt it up to the car's metal somewhere?
Originally Posted By: Jetronic
can you not bolt it up to the car's metal somewhere?
7810? Yes. Tab is Gnd.
LM317? No. Nothing is Gnd.
On mine I built a little board to directly replace the plug in reg so I just added a small aluminium heatsink on that.
can you not bolt it up to the car's metal somewhere?
7810? Yes. Tab is Gnd.
LM317? No. Nothing is Gnd.
On mine I built a little board to directly replace the plug in reg so I just added a small aluminium heatsink on that.
that's what I did with the LM7812, use the car (bus in my case) as a heatsink
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