12V DC Transformer

[gemini5362]

Really.. you havn't seen many... You walk or ride a bike alot? what about an auto transformer?

You know, for a basic example..... and ignition coil and a set of breaker contacts with a condensor across them.? ring any bells?



Some other forums.. but not here. lots of sharp people here.. and if you make a blanket statement like that and leave a big loophole in it.. someone will call you on the rug pretty quick.. Like I said.. had i said all xformers are run off AC.. it would'nt have taken very long for someone to post about autotransformers. After you have experienced enough 'power rebuttals' for omitting a seemingly insignificant yet valid fact.. you learn to CYA when writing posts of a technical nature.. etc..

Actually I was making a joke.

I am aware that points and a coil on automobile ignition system is a pulsed dc.
I have not seen a lot of Autotransformers and the things I saw that were labeled as autotransformers in the military were still AC. But the overwhelming majority of cases where you use a transformer is for AC

I am editing this because I went back and looked up autotransformers since I thought I knew what they were and could not figure out how they were a dc application I now realized that you were talking about AUTO transformers not autotransformers.

 

[jtlee]

from 32 - 55 amps take your pick

Atwood Power Converters | RV Supply Warehouse

oops forgot you said inexpensive heres some cheaper

20, 30, 40 Amp Power Supply for DC chargers from Hobby Lobby!

 

[gemini5362]

from 32 - 55 amps take your pick

Atwood Power Converters | RV Supply Warehouse

oops forgot you said inexpensive heres some cheaper

20, 30, 40 Amp Power Supply for DC chargers from Hobby Lobby!

Nice job finding those. to me for roughly the same money you get a lot safer product than a battery and charger.

 

[rich_ncal]

jtlee listed some good sources. 12volts is also an output voltage for the power supplies used in many computers.

350W ATX 12V P4 Power Supply

or

Buy.com - Corsair TX 750W ATX 12V Power Supply - CMPSU-750TX

Ham radio operators also like to use 12v supplies to operate mobile equipment at home. So you will find 12volt power supplies at ham radio swap meets.

Or at ham radio stores

Pyramid, Astron, Turbo Power Supply Pacific CB Radio

 

[RayCo]

Nice job finding those. to me for roughly the same money you get a lot safer product than a battery and charger.

I strongly agree. This is most likely the route that I'm going to go. Thanks again jtlee!

 

[mbrule]

That's rather brilliant! Especially since I have about 10 old power supplies sitting around!

I think you would find that you will need those 10 and probably 20 more to get 30 amps from computer supplies. I don't know just what the 12 volts is rated on a typical computer supply, but a "large" computer supply is 250 Watts, they have 5 volt, 3.3 volt, and + / - 12, and volt outputs I think. The 12 volts is probably only a few amps.

The hobby supplies look like a pretty good choice.

Were it me, I would use a cheap low power (10 - 20 Amps or so, supply) For the radio and cell phone chargers, and use a battery when working with high power things such as automotive power seats. It sounds as if you want to wire your whole shop. To handle 30 amps without huge voltage drops, you will need 4 or 6 gauge wire, and expensive interface terminals. Wire is expensive!!! Also remember that most automotive stuff typically runs at 14.5 volts, so any voltage drop will be an issue.

Even for 10 amps you may need 10 gauge wire depending on the length of your runs.

just more to think about!

Matt

Matt

 

[RayCo]

Were it me, I would use a cheap low power (10 - 20 Amps or so, supply) For the radio and cell phone chargers, and use a battery when working with high power things such as automotive power seats. It sounds as if you want to wire your whole shop. To handle 30 amps without huge voltage drops, you will need 4 or 6 gauge wire, and expensive interface terminals. Wire is expensive!!! Also remember that most automotive stuff typically runs at 14.5 volts, so any voltage drop will be an issue.

Good valid points. Thank you Matt.

 

[Wood_Butcher_Dav]

I'll help muddy the waters with my 2 cents:

Computer supplies are 'switchers' which means they would need some small pre load, most likely on 5 volts. As mention, usually the +- 12v is only rated 1 or 2 amps.

Below is excerpts from Belden Cable Co.
Current carry capacities of 3 conductors in raceway, conduit, cable;
ambient @30C (86F) Polyethylene/Neoprene insulation
18awg 14amps
14awg 25amps
12awg 30amps
10awg 40amps
8awg 55amps

I could only find these resistance values;
18awg Solid = 6.6ohms/1000'
18awg (19/30) = 5.5ohms/1000'
16awg solid = 4.2ohms/1000'
16awg (19/29) = 4.3ohms/1000'
14awg solid = 2.6ohms/1000'
14awg (41/30) = 2.5ohms/1000'

 

[PILOON]

Same situation for me.

I found some old Army surplus power supplies that were used to power up Tank radios on both 12 and 24 volts DC. (also adjustable and filtered)

They came from the surplus market at about $100. and could handle even 40 amps.
Heavy brutes at about 75 lbs or so but you could actually weld with them!

Today there is probably more value in copper content than I paid for them but I have actually boost started my tractor with it.

I would offer one for sale but the shipping would surely exceed the sell price.

Sombody suggested a RV unit and probably that would be best solution.

Why not build one!
Basically it is a transformer with a full wave bridge to rectify ac to dc and it would be a fun project to boot.

 

[Soundguy]

sorry.. thought that mighta been evident since we were talking a dc application here.. specifically pulsed dc..

soundguy

I am editing this because I went back and looked up autotransformers since I thought I knew what they were and could not figure out how they were a dc application I now realized that you were talking about AUTO transformers not autotransformers.

 

[texbaylea]

Hi
You might consider a power supply from an old computer
Charlie.

You need to go back before the IBM PC to when computer power supplies were linear not switched. The supplies for 8" floppy drives were about 12 amp on the 12v line if I remember correctly. If you can find an old moss back like me who was fiddling with microcomputers back then, he might have an old linear power supply stuck on a shelf (again like me). The floppy power supplies were well regulated, those for an S-100 computer were not.

Vernon

 

[BigE_]

I'm looking at a "standard" 600W power supply for a PC. It has two 12V supplies in it, both rated at 22A. I believe this was around $40 new. "Older" 350W power supplies would be closer to 20A on one 12V rail.

PC Power supply manufacturers play a little game where if you multiplied all the voltages by their corresponding currents, you would exceed the specified power supply rating. Each output can provide the specified current, as long as the total power doesn't exceed the rated power.

Bear in mind that PC power supplies are among the cheapest out there, and therefore also some of the "dirtiest" in regards to noise due to all of the switching, so you'd likely need to put some filters on the supply to run a radio off it.

Regards,
-Steve

 

[Soundguy]

You need to go back before the IBM PC to when computer power supplies were linear not switched. The supplies for 8" floppy drives were about 12 amp on the 12v line if I remember correctly. If you can find an old moss back like me who was fiddling with microcomputers back then, he might have an old linear power supply stuck on a shelf (again like me). The floppy power supplies were well regulated, those for an S-100 computer were not.

Vernon

I have some old CPM boxes.. and their power supplies are HUGE!

soundguy