Power gpu directly from car battery?

[DeinFreund]

Has anyone ever attempted this? I'm building a mobile desktop and am using a DC-DC supply for the mobo. I didn't find any compact dcdc supplies with 8 pin connectors, so I'm wondering whether I can just wire it up directly to the battery.

 

ATX specs allow voltages from 12.6 to 11.4 volts, so a slightly discharged car battery would fit in perfectly. I've also thought about using 3S LiPo batteries, but they're a little expensive for prototyping.

 

What's the lowest voltage that works for common GPUs? I wouldn't be astonished if modern GPUs only use 5v and lower anyway. The step down converters might not even need 12 volt in this case.

 

Here's my board if that's of any importance: http://www.asrock.com/mb/AMD/Fatal1ty X370 Gaming-ITXac/

 

PS: This is my first build.

[Hybris5112]

You would be better off with a marine or diesel deep cycle battery and top quality power inverter so you can use normal parts for the entire system.

[Mr.Meerkat]

So in other words, you trying to find something like this?  

https://www.aliexpress.com/store/product/X3-ATX-300-300W-High-Power-24PIN-DC-DC-ATX-Power-Supply-PICO-DC-DC-PSU/211500_1828902505.html

[Enderman]

You should use a 12V regulator.

Car batteries are 14-16v.

[DeinFreund]

@Mr.Meerkat that looks like a good fallback, thanks. Wouldn't that be too boring for Linus though?

 

@Hybris5112 I have that equipment, but it's not very portable.

 

@Enderman I'm using a sealed lead acid battery that usually stays around 11.8-12.8 volts under load. My question is more about how lenient GPUs are to varying input voltages, because I'd switch to a more portable lithium battery if this works.

[Enderman]

3 minutes ago, DeinFreund said:

@Mr.Meerkat that looks like a good fallback, thanks. Wouldn't that be too boring for Linus though?

 

@Hybris5112 I have that equipment, but it's not very portable.

 

@Enderman I'm using a sealed lead acid battery that usually stays around 11.8-12.8 volts under load. My question is more about how lenient GPUs are to varying input voltages, because I'd switch to a more portable lithium battery if this works.

You should be using a regulated power supply regardless of the voltage input range of a GPU.

Spikes in voltage can damage or kill the GPU, or cause programs to crash.

This is why computer power supplies aim to have very steady voltage with minimal ripple, only a few millivolts.

A 3s lipo can be anywhere from 9.something to 12.6v, and batteries also have voltage drop under load.

[IgorM]

10 minutes ago, Mr.Meerkat said:

So in other words, you trying to find something like this?  

https://www.aliexpress.com/store/product/X3-ATX-300-300W-High-Power-24PIN-DC-DC-ATX-Power-Supply-PICO-DC-DC-PSU/211500_1828902505.html

that's the most efficient and safe solution. 

[DeinFreund]

I can put a 10mF capacitor in parallel if you're worrying about ripples or spikes.. Is there any risk of damaging my board? Otherwise I could just put in an old 970 or even 660.

[Hybris5112]

1 minute ago, DeinFreund said:

I can put a 10mF capacitor in series if you're worrying about ripples or spikes.. Is there any risk of damaging my board? Otherwise I could just put in an old 970 or even 660.

 

In the short term probably not depending on how big the spikes are but I feel safe in saying that you will likely notice odd issues arise overtime. I think you are putting in a lot of work to save only a little bit of hassle.

[Enderman]

2 minutes ago, DeinFreund said:

I can put a 10mF capacitor in series if you're worrying about ripples or spikes.. Is there any risk of damaging my board? Otherwise I could just put in an old 970 or even 660.

*facepalm*

That's not how electronics works, you do not just put a capacitor in the circuit and magically you have constant voltage.

 

PS- you would put the capacitor in parallel if you wanted anything to work at all, not in series.

It sounds to me like you have a lot more research to do on electronics.

I highly recommend learning more before you try destroying hundreds of dollars of PC parts.

[DeinFreund]

@Enderman Sorry typo, also this was about ripples. Of course there will still be long term voltage changes. Anyway, I could just solder in a high power 12v step down converter if I wanted the easy solution. I came to this forum to ask for the more "experimental" approach. If it's completely pointless maybe I'll just leave it be.

[Guest]

1 hour ago, Enderman said:

You should use a 12V regulator.

Car batteries are 14-16v.

Alternators are 13.7 to 14.7V.  Car batteries are 11.4 to 12.6.

 

I still wouldn't power directly from the car battery.  Use a DC to DC PSU.  

 

Mini-Box will have what you need:  http://www.mini-box.com/site/index.html

 

[DeinFreund]

@jonnyGURU I've actually already ordered one. I just love trying out undocumented things. Apparently nobody has tried this before, so I may as well   

[Guest]

I have.  About 20 years before I knew any better.  It didn't work.

 

[Stefan Payne]

3 hours ago, DeinFreund said:

Has anyone ever attempted this?

No and you shouldn't!
 

Because Batteries are rather high impedance and not ATX conform.

So the voltage might drop very heavily under load.

 

And when we are talking about CAR Batterie and Car power, we are talking about ~14.4V from the generator...

 

 

So in the end it's not a good idea because no component you are using is designed for the use with a battery...

If we'd talk about Laptop, things would be different though...