Car battery regulator to 12v/4.5a output?

[alexs415]

Hello there,

I am looking to create a simple circuit to regulate the output of a car battery to 4.5amp.

I need to power a monitor for a long period of time, it has a 12vdc input at 4.5amps using a 4pin xlr.

I would also like to implement some sort of cut off switch which the battery reaches less than 40% as I hear it can damage your battery when constantly charging and discharging below this amount?

Should I also be worried about a car battery's voltage being to high when fully charged and concentrate on regulating this to avoid damaging my monitor?

Any help would be muchly appreacited!

Many Thanks

Alex

 

[simonbramble]

You need a buck boost converter. This will reduce the voltage when the input voltage is higher than 12V and increase the voltage when the voltage is too low

Have a look at the LTC3789
https://www.linear.com/product/LTC3789
When your car is cranking, the battery voltage can go down to 6V. When the alternator kicks in, the battery voltage will go up to 14V. You could use a linear regulator, but this would dissipate too much heat.

Despite the fact that this sounds simple, it is more complex than would first appeaar

 

[colin55]

Simply connect the monitor to the battery. It will have internal regulation. Buy a $2.00 stopwatch and keep track of the hours.

 

[Llamarama]

I spotted this a few weeks back as I was after the same sort of thing. Here's what I was going to use. I'm afraid I've not built it yet (Exams... ) but as long as the transistor is heat-sinked it should be able to supply that current no problem.

Link https://www.electroniq.net/power-supply/12-volts-voltage-regulator-car.html

As for the 40% problem, you could use a resistor voltage divider and a comparator to trigger a relay once the voltage has dipped below a certain point. This page may be of use too; https://www.mpoweruk.com/soc.htm

Good luck with your project.

 

[colin55]

The circuit will not work:

**broken link removed**

The voltage between the base and the supply is 0.1v

The current through the 1k resistor will be 0.1mA

The transistor will amplify this current and provide 10mA output !!!!!

This circuit has never been tested.

 

[irishape]

I am new here but if the monitor has internal regulation as Colin55 says, what is wrong with putting a trickle charger on the bat. to keep at level volt? Unless monitor uses more v than charger can put out which seems unlikely.

 

[alexs415]

Thanks for all of ur posts guys.

I have been doing some research and was thinking maybe some sort of IC might do the trick. Would something like an LM338 work?

**broken link removed**

Do u think this could handle the high currents of a car battery or is there a better alternative?

I forgot to state earlier the battery will not be in a car. I just want to use something like a car battery/leisure battery externally.

Many thanks.

Alex

 

[Reloadron]

A DC / DC ATX typr PSU can be had relatively cheap. Something along these lines.

Depending on some variables, like temperature a 12 volt SLA (Sealed Lead Acid) car/truck battery works out close to these numbers:

12.65 V = 100%
12.45 V = 75%
12.24 V = 50%
12.06 V = 25%
11.89 V or less = discharged

When fully charged about 2.1 volt/cell.

I believe people here were looking at this initially as an automotive application where battery voltages can vary between 12.6 to as high as 14.5 or greater system voltages.

You have a 12 volt monitor and a 12 volt battery and as Colin mentioned early on why do you want to regulate any voltages?

Do u think this could handle the high currents of a car battery or is there a better alternative?

The fact that the battery can source hundreds of amps means nothing. The load will only draw its rated current at its rated voltage. A 12 volt monitor rated at 4.5 amps likely will not draw that full current but a little less. Actually 4.5A X 12 Volts = 54 Watts which seems high to me for a LCD Monitor, even a 23 inch monitor. Mine typically draw about 23 to 30 watts.

Anyway, I would just run it as Colin suggested. If you really want 12 volts regulated from a 12 volt source then consider what I linked to. The only merit being most have automatic shutdown when the battery voltage drops below about 11.8 volts.

Just My Take
Ron

 

[4pyros]

[QUOTEI am looking to create a simple circuit to regulate the output of a car battery to 4.5amp.
][/QUOTE]
You dont need to regulate the current. The monitor will only take what it needs.

 

[audioguru]

An LM338 adjustable 5A regulator needs an input of at least 14.8V for its output to be regulated 12.0V at 4.5A.
A 12V lead-acid battery will be boiling if it is charging at 14.8V.

 

[Llamarama]

Oh well, thanks for the heads up Colin!