Running pico psu off car battery

[Badger906]

So I'm midway through my land rover defender restoration (better 4x4 than jeep to American folk ?)

 

And I plan to run a pc in the car off of a touch screen to handle entertainment and GPS. 

 

Now I know pico psu' s can run direct from a 12v source. However I also know that a pair of 12v batteries wired in parallel will dump 160amp straight to the psu...

 

So my question is.. how can I create a safeguard to only supply what is needed off a 12v supply?

I mean the simplest solution would be to wire up an inventor and run it off a laptop charger.. But that's more stuff to add and hide!

[Badger906]

10 minutes ago, CUDA_Cores said:

Snip

 

Yeah I get that. But surely that's up to a point. I thought devices have circuitry to protect against high currents.

 

[lieder1987]

you should go to mp3car.com and look around there. The entire site is based around putting a computer in a car.

 

I did it for a while using a Mac Mini and it was loads of fun. I had a full touchscreen in the dash, I had a gps receiver via usb...ah the good ol days.

[Badger906]

11 minutes ago, CUDA_Cores said:

The pico PSU itself should have over-current protection built in. Any modern PSU (even tiny ones like that) that are designed to supply power to PC components should have it already.

As per my understanding. But that current protection will have a maximum value. My guess would probably be about 16amp as that's as high as most household consumer units go other than off a cooker spur. Just incase a transformer failed and gave it a massive over voltage and over current.

 

But I'm talking 160amp, way higher than most supplies.

I'm probably wrong.. I just don't fancy burning my hard work to the ground because my pico didn't like high current!

[mariushm]

There's some confusion here.

 

The battery can give various devices a lot of current for brief periods of time. For example, when you start the engine, the process pulls tens of amps of current from the batteries... and the batteries would probably deplete in 5 minutes if you'd try starting the engine for so long.

 

A power supply will take only as much energy as it needs.

 

The problem you have is not the current but rather the voltage. You see, you don't really have exactly 12v in a car.

 

Just like a single AA rechargeable battery is around 1.1v when discharged and 1.35v when fully charged, so are the lead-acid batteries.... when they're fully charged, the voltage will be slightly higher than 12v, but they can discharge down to maybe 10.8v before they can be "damaged" (lead acid batteries don't like being discharged too much)

When the motor is running, the alternator of your car will continuously pump energy in the batteries trying to fill them up and in order to charge lead acid batteries, the voltage must be above the maximum voltage of the batteries. The alternators on cars usually charge the batteries with a voltage of around 13.8 -14v. 

Also worth mentioning that when you usually start an engine, the process takes so much power that for a few seconds the battery voltage will go down really fast down to around 11v, maybe even less and then once the motor starts and there's less current pulled from the battery then the batteries recover.

 

So there's two kinds of picoPSU power supplies.

The cheaper models which are powered directly from 12v don't do any filtering, don't process in any way the input voltage (12v) and just pass it along to sensitive components on your motherboard, to your hard drive and so on. These are dangerous since of course, once the motor starts your 12v could actually be above 13v and could damage hard drives and maybe even the motherboard..

The computer could also reset or freeze when the 12v drops below let's say 11v, for example if the battery is very discharged or maybe when you're turning on the lights on your car and the power consumption jumps up a bit.

 

So you'd need the kind of picoPSU that supports a wide input range , let's say 10v .. 20v and then from this will produce pure 12v and 5v and 3.3v for your computer.

 

And even those are not 100% perfect for cars because there's another issue with cars, voltage transients ... some quirks about electricity in cars where for very brief moments you can have spikes of voltage up to 20-30v or even negative voltages of let's say -14v 

 

Some picoPSUs that have wide input range don't handle well these transients, and you have special "auto" versions of picoPSU power supplies which handle them.

 

Something like this would be adequate for auto :http://www.mini-box.com/M4-ATX-HV?sc=8&category=981
 

Note the features on the right  :   6-34V wide input  , - Survives vehicle engine cranks , - Battery deep discharge prevention

 

---

 

But really, I would say it would be much cheaper to buy a quality inverter that produces 110v or 230v from 12v of your car.

 

Even though you're in UK, it would be easier on your batteries to use a 110v inverter (and would be a bit more efficient)

Most power supplies and laptop adapters  are designed to work on wide input voltage, something like 90v AC to 250v AC, so as long as you'd use the right AC plugs  you'd be able to plug those in your inverter and have everything working.