DC-DC converter for Desktops?

lukhangcheng · 8th November 2006, 11:22 PM

Is there something like this in the market?

Input 12-24V DC (actually anything in this range will do)

Output 12V,5V,3V (am i missing anything?)

about 65W total load,

ALSO, i would like if this powersupply could charge (drip?) a 12v SLA (sealed lead acid), and be able to use this 12v battery for emergency power?

This is in everyway similar to what a laptop does, but for a desktop, the peak power rating should not be a problem, as planning on running this with A64 2X 3600+ EE, and with laptop HDD and no optical drive.

Does anyone know anything similar?

Sadow · 8th November 2006, 11:40 PM

I have seen a 12vDC ATX PSU, think it was on this forum, but they didnt have a charger or battery backup capabilities.

lukhangcheng · 8th November 2006, 11:45 PM

Yeah i have seen similar stuff (no charging battery) for those VIA mini-itx boards. but they are generally quite expensive.

RILEYP · 8th November 2006, 11:48 PM

where are you going to get 12-24 vdc on the desktop from with the current capacity you are after for a start unless your in a vehicle
And no I dont believe ther is anything out there
The problem is this:
to change 24 dc to 12 dc or to 5 volt dc or 3 volts etc with the current capacity your after in a computer large amounts of heat are dissapated! Unless you convert the dc back into ac then step it down with a switchmode psu like in your desktop atx psu...
so basically what you asking for is a an invertor to convert 12/ 24 dc in to 240 ac to run the switchmode psu already in your pc as they dont make a switch mode psu for a 12/ 24 ac supply...nor do they make an off the shelf 12.24 dc to ac invertor that i know of..
But then again Im a sparky not an electronics guru that knows every gadget out there...
But if there is something I'd love to see it!
cheers rileyp

lukhangcheng · 9th November 2006, 12:09 AM

Quote:

Originally Posted by RILEYP

where are you going to get 12-24 vdc on the desktop from with the current capacity you are after for a start unless your in a vehicle
And no I dont believe ther is anything out there
The problem is this:
to change 24 dc to 12 dc or to 5 volt dc or 3 volts etc with the current capacity your after in a computer large amounts of heat are dissapated! Unless you convert the dc back into ac then step it down with a switchmode psu like in your desktop atx psu...

But then again Im a sparky not an electronics guru that knows every gadget out there...

I think you misunderstand something in my "requirements"
I am just after inputs of anything from 12v to 24v,
since if its less then 12v it would have efficenecy problems with DC/DC converter.
And 24v was just an arbertory upper limit.

True to some extends, that DC/DC is inefficent,
but would DC->AC->DC be more/less efficent?
(hard to say, i know AC/DC is efficient, but DC/AC isnt.?)

What i am after is similar to the result of using a laptop, if anyone have any ideas as to how it works in a laptop, then that is what i want

,

Current My laptop takes 18.5v input and has a 14.4v battery

RILEYP · 9th November 2006, 12:34 AM

Quote:

I am just after inputs of anything from 12v to 24v,

What do you mean by this?

dc/dc is inefficient
dc/ac is inefficient
ac/ac/ac/ac (as many as required)/dc is the way the entire planet is wired up and set up...
eg 220kv/22kv/240v/to dc
Less those horrid things we had to invent for to keep the pc's running when the generators failed called invertors!....
If there was a more efficient way of supplying your pc with power they would be selling them on every corner.....

SKiB · 9th November 2006, 12:50 AM

The M2-ATX does DC to DC and I believe meets your original specifications.

There's no reason why you couldn't use the 12v to trickle charge the battery. Unless of course you were using power from the battery to charge it. In which case the battery would just run flat over time.

Try this guide instead.

lukhangcheng · 9th November 2006, 1:01 AM

Quote:

Originally Posted by RILEYP

What do you mean by this?

dc/dc is inefficient
dc/ac is inefficient
ac/ac/ac/ac (as many as required)/dc is the way the entire planet is wired up and set up...
eg 220kv/22kv/240v/to dc
Less those horrid things we had to invent for to keep the pc's running when the generators failed called invertors!....
If there was a more efficient way of supplying your pc with power they would be selling them on every corner.....

Well as you said, DC to DC converters exsist, but at the cost of generating fair amount of heat (more heat = less efficient!)
AC/AC/AC/DC is perfect! (for a desktop)

I am after something that can make a whitebox (with my choice of lower power components), with laptop type power behaviour.
(so it can use a battery basicly)

In a laptop type system, u have a power brick that converts 240v AC to 12-24v DC (mine is 18.5v), which then in turn charges the battery and power your system, if your 240v disappear for some reason, the laptop runs on battery!

Also power bricks dont tend to have fans!

lukhangcheng · 9th November 2006, 1:07 AM

Quote:

Originally Posted by SKiB

The M2-ATX does DC to DC and I believe meets your original specifications.

There's no reason why you couldn't use the 12v to trickle charge the battery. Unless of course you were using power from the battery to charge it. In which case the battery would just run flat over time.

Try this guide instead.

Thanks SKiB,
I was looking at somthing similar, granted that u can use 14v to 12v on something like this.

But what of the 240v + the battery?

DIY UPS would be good, but usage time is still limited? and a bit expensive still

SKiB · 9th November 2006, 1:22 AM

I'd buy a $20 car battery trickle charger to get the 240v to 12v.

That'd keep the car battery charged.

But you could buy a 600W ATX PSU and charge the battery from the 12v rail. It'd also have enough steam to power the other PSU. That means the M2-ATX would be run from the big PSU, and when the power cuts out, the 12v battery would immediately start supplying the M2 with current. But doing it like this is just plain silly.

LethalCorpse · 9th November 2006, 1:37 AM

wow, you guys are talking some shit. It is not efficient to invert from 12VDC to 240VAC, back down to 12, 3, 5VDC. A DC-DC converter is able to achieve very high (>85%, at least) efficiency by using a simple single stage switchmode design. An inverter and ATX PSU has a far more complex switchmode circuit to convert the 12VDC into a modified square wave, then a transformer (inefficient) to get it up to 240VAC, then another complex switchmode circuit in the PSU to get down to the required levels. Add to this the fact that the modified square wave has a whole lot of high frequency harmonics which will, over time, demolish the filtering caps in the PSU, and you've got yourself a less than ideal power supply situation.

Lukhangchang, you can use the M2-ATX, or thisPSU to power the PC in the car. You can also set up a dual battery system for backup, however this is designed more to protect the main battery from going flat, so you can still start the car after playing warcraft all night instead of camping.

lukhangcheng · 9th November 2006, 10:16 AM

Humm yeah i think you guys are reading into this too much.....

wat i want.

240V AV -> 14V DC -> ATX power supply
<-> Sealed Lead Acid Battery

so that is 240V a one supply of power, and SLA as the other,

why step down to 14V?
to be able to charge the SLA battery.

LethalCorpse's suggestion is not bad, but not as elegant as i like.

RILEYP · 9th November 2006, 11:13 AM

Quote:

Originally Posted by SKiB

I'd buy a $20 car battery trickle charger to get the 240v to 12v.

That'd keep the car battery charged.

But you could buy a 600W ATX PSU and charge the battery from the 12v rail. It'd also have enough steam to power the other PSU. That means the M2-ATX would be run from the big PSU, and when the power cuts out, the 12v battery would immediately start supplying the M2 with current. But doing it like this is just plain silly.

1 You cannot charge a 12volt battery at 12 volts IE from the 12 volt rail of the computer ...It will always be almost dead flat...
2 For an lead acid battery the ideal charge voltage is~1.4-1.5 volts per cell
which means you would need 14 or 15 volts dc.
3 For your info.. a car alternators regulators is normally set at 14.4 volts..
4 Stationary batteries like in a telstra excahange etc are set at 15 volts...

That mini dc /dc convertor for $80 is very inpressive!

dakiller · 9th November 2006, 12:15 PM

Quote:

Originally Posted by lukhangcheng

Humm yeah i think you guys are reading into this too much.....

wat i want.

240V AV -> 14V DC -> ATX power supply
<-> Sealed Lead Acid Battery

so that is 240V a one supply of power, and SLA as the other,

why step down to 14V?
to be able to charge the SLA battery.

LethalCorpse's suggestion is not bad, but not as elegant as i like.

That is basically a UPS you want? Checkout this for some DIY action then - http://www.dansdata.com/diyups.htm

lukhangcheng · 9th November 2006, 3:42 PM

Yeah basicly want a UPS, but ... but one which supplies DC....
instead of AC.

I had a look at the Dan's Data site but just reakon this could be more easily/cheaper done?

8th November 2006, 11:22 PM	#1
lukhangcheng Member Join Date: Sep 2002 Location: Melb, AU Posts: 311	DC-DC converter for Desktops? Is there something like this in the market? Input 12-24V DC (actually anything in this range will do) Output 12V,5V,3V (am i missing anything?) about 65W total load, ALSO, i would like if this powersupply could charge (drip?) a 12v SLA (sealed lead acid), and be able to use this 12v battery for emergency power? This is in everyway similar to what a laptop does, but for a desktop, the peak power rating should not be a problem, as planning on running this with A64 2X 3600+ EE, and with laptop HDD and no optical drive. Does anyone know anything similar?

8th November 2006, 11:40 PM	#2
Sadow Member Join Date: Dec 2001 Location: Brisbane, Springwood Posts: 590	I have seen a 12vDC ATX PSU, think it was on this forum, but they didnt have a charger or battery backup capabilities. __________________ Shuttle SN95G5, A64 3500+, 2GB Geil Ultra-X, 200GB Seagate SATA, Pioneer DVR-108, ASUS V9999GT 6800GT

9th November 2006, 12:50 AM	#7
SKiB Member Join Date: Aug 2002 Location: 37°48'28.8S 145°7'8.04"E Posts: 840	The M2-ATX does DC to DC and I believe meets your original specifications. There's no reason why you couldn't use the 12v to trickle charge the battery. Unless of course you were using power from the battery to charge it. In which case the battery would just run flat over time. Try this guide instead. __________________ All Glory To The Hypno-Toad

9th November 2006, 1:22 AM	#10
SKiB Member Join Date: Aug 2002 Location: 37°48'28.8S 145°7'8.04"E Posts: 840	I'd buy a $20 car battery trickle charger to get the 240v to 12v. That'd keep the car battery charged. But you could buy a 600W ATX PSU and charge the battery from the 12v rail. It'd also have enough steam to power the other PSU. That means the M2-ATX would be run from the big PSU, and when the power cuts out, the 12v battery would immediately start supplying the M2 with current. But doing it like this is just plain silly. __________________ All Glory To The Hypno-Toad

9th November 2006, 1:37 AM	#11
LethalCorpse Member Join Date: Mar 2003 Location: Harris Park, NSW Posts: 3,799	wow, you guys are talking some shit. It is not efficient to invert from 12VDC to 240VAC, back down to 12, 3, 5VDC. A DC-DC converter is able to achieve very high (>85%, at least) efficiency by using a simple single stage switchmode design. An inverter and ATX PSU has a far more complex switchmode circuit to convert the 12VDC into a modified square wave, then a transformer (inefficient) to get it up to 240VAC, then another complex switchmode circuit in the PSU to get down to the required levels. Add to this the fact that the modified square wave has a whole lot of high frequency harmonics which will, over time, demolish the filtering caps in the PSU, and you've got yourself a less than ideal power supply situation. Lukhangchang, you can use the M2-ATX, or thisPSU to power the PC in the car. You can also set up a dual battery system for backup, however this is designed more to protect the main battery from going flat, so you can still start the car after playing warcraft all night instead of camping. __________________ Sig Of Shame removed.

8th November 2006, 11:45 PM	#3
lukhangcheng Member Join Date: Sep 2002 Location: Melb, AU Posts: 311	Yeah i have seen similar stuff (no charging battery) for those VIA mini-itx boards. but they are generally quite expensive.

9th November 2006, 10:16 AM	#12
lukhangcheng Member Join Date: Sep 2002 Location: Melb, AU Posts: 311	Humm yeah i think you guys are reading into this too much..... wat i want. 240V AV -> 14V DC -> ATX power supply <-> Sealed Lead Acid Battery so that is 240V a one supply of power, and SLA as the other, why step down to 14V? to be able to charge the SLA battery. LethalCorpse's suggestion is not bad, but not as elegant as i like.

9th November 2006, 3:42 PM	#15
lukhangcheng Member Join Date: Sep 2002 Location: Melb, AU Posts: 311	Yeah basicly want a UPS, but ... but one which supplies DC.... instead of AC. I had a look at the Dan's Data site but just reakon this could be more easily/cheaper done?