Why are DC-DC power supplied so expensive? - Page 2

twins22 · 10-22-1999, 09:12 AM

In reply to inmytree, why not use an inverter? Why not just buy a CD burner and make custom CDs for an aftermarket CD changer for your car? It's a whole lot easier than cobbling an old PC together, duct taping a case to hold it, stuffing it in some remote corner of your car, finding a place for a control pad and LCD, then screwing with software! It's the same principle! Why? The why to any of this home brew MP3 player stuff is the pride that comes from "I made that", not just the coolness of the system. It's the payoff of weeks of testing and trying that elicits the "Holy **** this thing really works!" response from the builder. The same is true for the DC-DC power supply, anyone can get an inverter, but building your own PSU is something else to be proud of! Before you knock someone else's idea, think about how you felt when your MP3 player started working. Besides inverters are very inefficient, you are going from 12-13VDC to 110/220VAC back down to +12/+5/-12/-5/3.3VDC. To me it's kinda of like backing up 30 foot to move ahead 40 foot. If you have to do it fine, but if there's a better way then why not take it! Besides, there are enough designs out there now that reliable DC-DC PSUs can replace the stock power supply with no effects on the computer.

LowLife · 10-22-1999, 06:20 PM

Ya I hafta agree with you twins22. =) I kinda wish I woulda made my own. I was just too afraid of ******* up my $400 motherboard. Maybe I will still try to make one, but find some cheap 486 board I have laying around to test it out on. hehe.

I guess all I was trying to say is, that for a little more money you can BUY a slick *** super small DC-DC converter that is way more efficient and a lot quieter than an inverter. Different strokes for different folks!

LowLife

<a href="http://www.sunflower.com/~jahelka/MobileMP3/">My Mobile MP3</a>

Alien8 · 10-22-1999, 06:50 PM

I have to agree with inmytree, I'm building my system with reusablility in mind also, thats why I decided to use an inverter, they are cheap, and if I ever get stuck and need to run some electrical device, I have an inverter in my car. Also I already had my inverter so it cost me nothing at all.
To further extended my reusability instead of cutting the cigarette lighter adapter from my inverter to wire it up in my trunk, I purchased an accessories adapter (like a cigarette lighter, but its only for accessories that use a cigarette lighter adapter) cost me $8 at cdn tire. So now I not only have a reusable computer, I also have a reusable inverter which gives me more options to run other equipment, It also gives me a nice accessories adapter should I decide to use something else =)

now if your going for fully involved professional with a custom case and all, then I'd say dc-dc, you have to look at the application.

sure inverters have loss. hell they draw current even when there is no load. Also they generate heat which can add problems if you live in a really hot area.

And for those Aussies that would be a major pain in the *** using an inverter ==))

inmytree · 10-23-1999, 12:21 AM

Firstly in reply to snake bite:

I also live in Australia and I don't consider $160AU for an 200W inverter from Jaycar Electronics a "****load of money".. to buy a DC-DC power supply costs a "****load" more than that.. I can tell you.. if you wanna make one.. sure.. but its gonna be a ***** and for no real advantage.. and as for your comment about inverters being "lossy".. thats just a load of crap.. my inverter stays pretty damn cool.. therefore there is no power loss via heat, so where else does all this power that is lost go?? Converting from AC-DC hardly looses any power at all..

And in reply to twins22:

Fair enough.. if you wanna have the satisfaction of making your own.. fine.. but the discussion started by talking about BUYING a DC-DC power supply.. which is an absolute waste of money.. the only ONE situation I can see it being an advantage is if you are really pressed for space.. but thats it..

And to Alien8:

As I said, I live in Australia and the inverter sure ain't a pain in the ***.. I just leave it on all the time, when my car gets turned on, the inverter and therefore the computer starts up.. when I turn the car off, the comptuer shuts off too.. its sweet..

As for it drawing a current when there is no load.. it does, but its very very small and pretty much insignificant..

snakebite · 10-24-1999, 01:24 AM

Inmytree, you are obviously very passionate about this inverter thing so Ill leave it alone. However I do tend to agree with twins22, if you are capable of putting a DC-DC together then do it. (mine cost me ~$30AUS and 2-3 hours to build, thats $130 cheaper than Jaycar.....$130 thats more than 4 cartons of beer).

inmytree · 10-25-1999, 09:22 AM

Yep.. fine.. if you can build one for that price then it is a much better alternative.. I'll swap my inverter for your DC-DC power supply along with 3 cartons of beer anyday.. although the beer is main concern

CivicMinded · 10-25-1999, 12:08 PM

While were on the topic of dc-dc power converters. Does anyone know of a website that sells dc-dc'c with working -5v? Also, if anyone has any websites with affordable inverters, could you please list em. Thanks in advance!

jjohnson · 10-25-1999, 05:53 PM

How many of you can keep your car MP3 player running WHILE starting the car? I'm just curious because when I used to use an inverter, the voltage would sag too low and the computer would hang or reboot.

It was kind of a pain to shut the system off, start the car, and then boot it up again after the engine was running if I was sitting in the car with the engine off listening to my MP3s waiting to pick someone up, for instance.

Obviously this doesn't apply if you have the computer tied to the ignition switch

Just curious...

--Jason
http://jump.to/m2pc

Probedude_2000 · 10-25-1999, 11:59 PM

To address just this issue, I made a board for a friend's powermac based MP3 player. It monitors the car's ACC line and only activates the onboard relay if the ACC is on solid for 5 seconds. This is to help prevent his mac from booting during cranking. The relay feeds the computer/inverter.

Once the relay is activated, a 'powergood' signal is sent to the mac's serial port. If the ACC line goes dead for 8 continuous seconds, a "powerfail' signal is sent, and after 30 more seconds, the relay is turned off. This way using UPS software, his Mac will shut down properly. The 8 seconds delay before sending the powerfail signal is to prevent his MAC from turning off if he stalls his car and needs to restart the engine.

I've since tried the same board with APC's powerchute software on NT and Windows95 and it works well! Another guy is using my same board for his Linux based MP3 player, but he isn't currently using the Powergood/fail status line, just the smart relay controller portion.
Dave

snakebite · 10-26-1999, 04:33 AM

I know this is getting right off the subject but....jjohnson, something that has always worried me (not enough to look into though) is, could there be any problems with back EMF from the starter motor when leaving audio stuff on during cranking? next,... Probedude_2000, Ive been trying to get hold of that powerchute software for ages, I saw a site back when I was building my player where someone used the powerchute software and a simulated low battery input to shut down their player. Do you know where I can get the powerchute software?

jjohnson · 10-26-1999, 12:16 PM

I never thought about back EMF... I do know that some car devices (cell phone chargers and CD player adapters) say not to have them on while starting the car. I'm not sure if this is because of the voltage sag that occurs or if it's because of back EMF. Hehe, you could always wire a transient suppressor (MOV) across the coil on the starter, or even a diode to short back EMF spikes to ground.

Hmm... another feature to add to my car!

--Jason
http://jump.to/m2pc

LowLife · 10-26-1999, 05:29 PM

I'm using the ACE-865, the one you can get from Arise. Starting the car doesn't kill the computer.

LowLife

LowLife · 10-26-1999, 05:32 PM

Oh, and for all those that think its convinent to have a AC power supply and an inverter in their car so they can bring it into the house and work on it easy...

All I do is plug the 12v out from an AC power supply (that is sitting behind the computer desk in my room) straight into the 12v input on my DC-DC Mobile. Works great and doesn't take up hoards of space.

Probedude_2000 · 10-27-1999, 12:39 AM

I got the powerchute software from the APC website itself about 3 weeks ago.

Did you try them?

If anyone is interested in looking at what my powerup/powerdown board, go here
http://www.dschmidt.com/autooff.html

Dave

jjohnson · 11-01-1999, 02:53 PM

I have an old Camaro (1970) with a big V-8 engine. While cranking the battery voltage sags below 9V

That would explain why my computer would go crazy if I left it on while starting the car. But a custom electrical system and DC-DC will solve this

I'll be using a separate battery for the computer and onboard electronics, so I won't have to worry about this kind of thing anymore.

--Jason
http://jump.to/m2pc

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