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# 12 volt stabilizer/regulator (high current) Answered

Hi, I need something that's able to regulate the car voltage that vary from 10.2 to 14.7 (with lower voltages at startup that's not relevant)
to a stable 12v with a tolerance of 1-2% at high current (need at least 35A but I don't want to full load it too often then 40A would be better).
I saw something like a lm317 with some external transistor that's able to put out something like 15A but it required a 30V input and it was a too much low current.
can you link me an image of a circuit that's able to do what I want?

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You certainly can't use a linear regulator as it always has a voltage gap between input and output. So if you feed it 12, you can only get less. Since your voltage drops to 10.2, that way doesn't seem plausible.

The alternative to linear regulators is switched regulators. Although extremely efficient, I don't think they too can increase the voltage. You can implement them and they will probably cut off at 12V.

What I think you need is a buck-boost convertor, since you need to convert both higher voltage into lower and lower into higher: https://en.wikipedia.org/wiki/Buck%E2%80%93boost_c...

I'm not sure if there are any of those which can provide 480 watts you need. If you do find one, it might be very costly.

Lastly, are you sure you need exact 12 V? Such huge current is mostly required by heavy duty devices like motors or multiple lamps, instead of logic devices(which are voltage sensitive). These devices are very forgiving about the range of voltages you supply and 10-14 volts should be acceptable by most 12V ones.

the 480 watts are about my pc peak consumption, I want to power it while i'm traveling with car. unfortunately pc components have a maximum tolerance of 5% then i can't power them directly.

I know that powering a pc this way may seem stupid but it's an experiment.

I've already seen buck-boost converter but they are usually low current (3-5A)

p.s. yeah I already excluded linear regulator because of such power they will emit too much heat

A typical car battery is around 40Ah, can be upto 60Ah. Even if you place a 60Ah one, assuming you only run the PC off the battery and not the car, your battery will last only (60*60/480) = 7.5 minutes

You can get a car power outlet 12V to AC inverter which can give a whopping 500 watts like this: https://www.amazon.com/ENERGIZER-Inverter-cigarett...

Then plug in your typical SMPS which will power your PC. That should keep your PC safe from fluctuations and voltage drop. Just be sure to do this with a spare or your car won't start...

I didn't want to use it when car wasn't on. I excluded inverters because of their high inefficency usually and the problem related on the square wave.

a dc-dc transformer was the solution but the ones I found were like 260-300 watt.

and then I decided to find a circuit that's able to do what I want.

p.s. for the battery if it can supply 40A if I consume 40A it should last for about an hour.

p.p.s my battery anyway is 85Ah :P

7° line: if it can supply 40AH ...

Ah sorry my bad. I totally mixed up amps and watts in my calculation. It should have been 40Ah/40A = 1hour. So you're right, it will last an hour. Your 85Ah will last 85Ah/40A = 2.125 hours if you completely discharge it(which you certainly shouldn't).

I think you have 3 options:

1. Buy a costly DC-DC convertor for 50A:

https://www.victronenergy.com/dc-dc-converters/buc...

http://power.murata.com/en/products/dc-dc-converte...(they seem to have a lot of options. See if they have one fitting your need)

2. Use a DC to AC inverter and connect your PC's SMPS to convert it to 12V.

3. Put 2 car batteries in series. You get a range of 20.4V-29.4V which can be easily converted to 12V by a switching regulator which is very efficient.

sorry, do you have any schematics of a high current buck-boost converter that I can build? I wanted to do something myself for experiment and that dc-dc converter 50A seems pretty expensive :/

And, the second link you sent doesn't have an high current converter that outputs 12v :P

Else if you don't have any schematics thanks anyway :D