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Old 23rd September, 2001, 03:17 AM
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Yo Colin,

I just don't get it. What's the real advantage to using a variable linear voltage regulator instead of just using a 25Ohm rheostat? Both just work like a resistor, so were do you gain anything?

Seems to me a variable step down switching supply might have some advantages (less heat, more efficient), but just can't see it with a linear design.
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Old 23rd September, 2001, 03:19 AM
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i have no idea what that meant maybe you can explain??
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Old 23rd September, 2001, 03:40 AM
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Quote:
Originally posted by phiber
i have no idea what that meant maybe you can explain??
A rheostat is a variable resistor that you can use to regulate fan speed, but they do get a little hot overtime.

A linear voltage regulator is like a variable resistor that adjusts the voltage to the preset automaticaly as input voltage varies and load varies. You can use external circuitry consiting primaraly of a potentometer to make the regulator variable.

A switching supply regulates voltage via a pulse width modulator(PWM), it is either on or off, but it switches on and off so quickly that an inductor coil and a filtering capacitor can transform it into a smooth steady current. You can modify, again with the addition of a potentometer, the error amplifiers sampling circuit to make a switching supply variable.
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Last edited by dimmreaper; 23rd September, 2001 at 03:42 AM.
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Old 23rd September, 2001, 04:19 AM
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Quote:
Originally posted by dimmreaper

A rheostat is a variable resistor that you can use to regulate fan speed, but they do get a little hot overtime.

A linear voltage regulator is like a variable resistor that adjusts the voltage to the preset automaticaly as input voltage varies and load varies. You can use external circuitry consiting primaraly of a potentometer to make the regulator variable.

A switching supply regulates voltage via a pulse width modulator(PWM), it is either on or off, but it switches on and off so quickly that an inductor coil and a filtering capacitor can transform it into a smooth steady current. You can modify, again with the addition of a potentometer, the error amplifiers sampling circuit to make a switching supply variable.
i have so many things yet to learn
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Old 23rd September, 2001, 05:58 AM
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While a rheostat will do the job, a voltage regulator is better suited to the task. They dissapate the heat without relying on a mechanical contact. Pump a lot of current through a mechanical contact and it needs to be real beafy. The solid state voltage regulator provides a more reliable way to deal with this and more long term stability. The price is you loose about 1.5 volts. For fan regulation, an easy way around this is a SPDP switch. One position is for off, one for the full 12 volts and one for the voltage regulator.
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Last edited by Colin; 23rd September, 2001 at 06:01 AM.
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Old 23rd September, 2001, 06:08 AM
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Quote:
Originally posted by Colin
While a rheostat will do the job, a voltage regulator is better suited to the task. They dissapate the heat without relying on a mechanical contact. Pump a lot of current through a mechanical contact and it needs to be real beafy. The solid state voltage regulator provides a more reliable way to deal with this and more long term stability. The price is you loose about 1.5 volts. For fan regulation, an easy way around this is a SPDP switch. One position is for off, one for the full 12 volts and one for the voltage regulator.
Ahhhh, forgot about the whole solid state advantage. And I just bought a solid state relay for my water pump too
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Old 23rd September, 2001, 06:50 AM
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Yeah I think I am going to a solid state relay for my next rig too.
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Old 23rd September, 2001, 07:17 AM
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Quote:
Originally posted by Colin
Yeah I think I am going to a solid state relay for my next rig too.
Your "next rig", what you going to do with the one you have now, give it to the wife?

Anyway, this is the relay I just bought, 25A ought to be plenty enough:
http://www.allelectronics.com/cgi-bi...03U&type=store
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Old 23rd September, 2001, 08:34 AM
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only thing is solid-state or optically-isolated gear is just sooooo expensive compared to the mechanical equivalents. that s-s relay is about 20 times what you'd pay for a mechanical one!
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Old 23rd September, 2001, 08:42 AM
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I hear ya Paul, solid state ain't cheap. But on the up-side it will last forever(or at least long enough for you to forget I said that), it takes less input current to close the circuit, and it is a bit safer too . . . . .
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Old 24th September, 2001, 11:58 AM
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Quote:
Originally posted by Colin
The price is you loose about 1.5 volts. For fan regulation, an easy way around this is a SPDP switch. One position is for off, one for the full 12 volts and one for the voltage regulator.
Personally, I'd prefer to see a switch mode regulator rather than a linear regulator. Switch mode regulators give you better low-speed stability, superior low-voltage spin-up and dissipate less heat. Designed correctly, they can also give you higher output voltages for fans that will tolerate 15-16 volts.

The downside? They're more complex to build.

Áedán
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