Computer Power Supply as a converter substitute

[working on it]

While researching computer case fans (in lieu of ac fans, or hi amperage dc fans), I saw that computer power supplies are pretty cheap compared to Deltran, Battery-Minder, and Schumacher 12vbattery trickle charger/maintainers, and much cheaper than the 110vac>12vdc power converters I've seen listed. For instance http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=422169&Sku=C13-2810 whose tech specs show 12vdc output @ 28amps, plenty of power to recharge a battery from shore power (and run all the 12vdc gadgets in camp), while the maintainers will only give a mere 5 amps or less. And the "converters" are priced double the power supplies, and have less features (surge protection, overload, etc.). Self-cooling also, with a built in fan. I was looking to have all 12vdc lights, fans, sound... powered by a Yellow top Optima, and have a generator standby (also to power the 5000 btu a/c), and a 400w inverter for possible further 110v needs. The battery is to be charged at home with a maintainer, and topped up if needed by 12vdc output from the generator, or by computer power supply/converter ?? where shore power is provided. Am I correct, in reading the specs on the web link? Or will the power supply not meet my reqirement? Several of you other forum members are quite knowledgeable about power hookups. Will the computer power supply work for me?

[pmowers]

There have been a number of discussions in the forum about using a CPS as a substitute for a 12 VDC converter. Computer power supplies (CPS) are designed to put out highly regulated 12 VDC with little variation. If memory serves, in order to charge a 12 V battery, you need to supply more than 12 V to the battery, ranging from 13.4-14.4 V so charging would be very slow, if it happened at all. CPS are also not designed to deal with voltage coming in through the output wires (from the battery), the newer switching supplies need to have a bit of a load for them to work correctly, and most have to receive a start-up signal to prevent the CPS from turning itself off.

I originally had your idea, but abandoned it when I really started looking at what I would need to do to have both 110 and 12 V in my conversion. It was much cheaper, neater and far simpler for me to buy a converter than the breaker box, fuse panels, 3 stage charger, etc. needed to "roll my own". I have a WFCO 8945 which provides me with space for up to 9 AC breakers, 45 A of 12 VDC, a 10 place 12V fuse panel, 3-stage battery charger/maintainer/rejuvenator- all in a space that is about 12.5x12.5x8 inches, easily mounted and accessible and warrantied. I paid $95 for it on ebay. All that I have left to do is figure out where my battery is going to go and run the wire to it. I think that a lot of members use either the WFCO or the American-made Progressive systems. When you look at the cost of a good quality battery charger/tender and the other materials, then the converter price seems pretty reasonable.

Pat

[olds-cool]

I'm not an electrical guru either so amps & watts elude me. That said, you may want to look at arcade power supplies. Similar to a pc power supply in that they offer 5v and 12 volt but no need for a startup signal, a simple household light switch can be used to turn it on/off. They can be had fairly cheap and most people don't know about them unless they are arcade junkies.

[working on it]

pmowers- Thanks for the input. I know that just 12vdc is insufficient to charge an automotive 12v battery (12.5 volts or more is the nominal voltage of a good battery). I posted hurriedly, without really delving into details.I was thinking about an article I had seen when researching fans, but couldn't find it again, to show why I wanted to try this method. It outlined a method to join various CPS voltage outputs to increase/decrease voltage to the case fans (to speed up/slow down). Here it is... I looked for several hours after reading your answer. http://www.overclockers.com/24v-cooler-overvolting/ I thought that, if it would work for fans, then why not other things (I love to re-purpose items). I was thinking of combining the 12v and 3.3v output to make 15.3v (a little high for battery charging, but not too much if monitored...I charged my dual batteries on my drag car at high amps and high voltage between rounds). And if this would be possible, then why not try it? The 15.3v combo would only be used for supervised quick charging, and the CPS would then be switched back to normal 12v for lights and radio, and 5v for usb charging, etc. only if the battery went under 50% (and shore power was available). And the 2500w generator would always be ready as a backup. I asked an IT tech at work if he could look into this for me.

[pmowers]

@olds-cool: Interesting article. I think that the major problem will be the amperage. The 3.3 V source is probably less than 1 A. The reason amps are important in this case is because you have to "replace" the amps in the battery. If you drain 50 amp hrs from a battery, you will need to replace them, at 1 A/hr, this would take 50 hours. This would be like trying to fill a pool through a soda straw. You may actually get more charging capability out of a trickle charger than the CPS. The arcade power supply mentioned is another option. The reason that you could get away with quick charging the dragster's battery is because you had a high potential difference (Voltage) and were probably pouring the amps to the battery- I imagine that the battery did not have a very long life expectancy.

Pat

[Shadow Catcher]

I understand the desire to save but the care and feeding of a deep cycle battery and its longevity are important. You can pick up a Progressive Dynamics 45A converter on Ebay for about $130. Buying the Chinese made converters is not a good idea, just way too many complaints from early deaths.

[webbaldo]

Im doing a live test now as we speak with two 12v CPS's (I work in IT and we have a few lying around)

They both will put out 15amp (180w) 12v which for me is enough, fridge is about 65w which is the only thing that will be running all the time and my tv etc and lights all running together would be about 120watts.

To get the CPS to stay on all the time, you just permanently join the green and one of the black ground wires on the ATX connector.

My two concerns were mainly heat based, during usage and also someone mentioned they can overheat on zero load (nothing connected.)

So I have one right now running nothing, but switched on

The other is powering a 50watt mini fridge.

Im leaving them running from 9am till 2pm (5hours) today UK time.

Ill post my results when the test is finished.

Im not bothered about battery charging as I just want everything in the Van to run off 12v, makes wiring everything easier and a little safer. The camp sites I plan on using will have mains hookup and I wont have an onboard battery so charging issues wont affect me.

I'd need a 12v psu anyway for items like my 12v tv/fridge and electric tap/pump. It also means if I ever did want to go down a battery route in the future, all the 12v infrastructure is already there.

[webbaldo]

OK so results after 5 hours

2 bog standard 180w computer power supplies, rigged to run all the time

1 with nothing connected after 5 hours was fine and cool to the touch, so it doesnt overheat when switched on but nothing connected

1 with a mini fridge connected, after 5 ours was barely warm to the touch. Fridge itself was working fine.

Therefore for someone whos after a 12v 240/110v transformer (and isnt bothered about battery charging) a PC PSU is an ideal low cost choice!

[working on it]

webbaldo- Thanks for testing the PC powersupplies; my IT guy was involved on another project. I intend to try to rig my own "test to destruction" of a battery charging PC power supply when I finish the trailer (using a conventional 12v battery charger (alas!, sigh) and inverter/shore power/deep cycle 12v battery set-up in the meantime). I'm trying to get my TTT road ready in a month, so I'll have to forgo extra expense and time-consuming projects now (I've made more progress in the last week than in the 6 months before).

[Hillmann]

The CPS's will not charge a battery, I have one that I rewired into a desktop power supply. It can run the accessories in a car(if you try to start it with the power supply attached the power supply will shut off. It won't charge because it is only 12 volts and a 12 volt battery actually is closer to 14 volts. Although when I was looking in to how to rewire the power supply I read that they can be hooked in either parallel or series (I don't remember which) but if they can be hooked in series it may be possible to to hook 3 of them together and hook there 5 volt outputs in series giving you 15 volts. Although 15 volts may be too much for a battery. If you get them used you can get the computer power supplies for $5 each and another $.50 in parts to rewire them so they can stay on all the time so you could try it and find out.

[Hillmann]

Just found this.
http://www.mp3car.com/power-supplies/31 ... upply.html
I will have to see how much a 5K pot costs. If it is only a couple buck I may play around with it and see what happens.

[GuitarPhotog]

The CPS's will not charge a battery, I have one that I rewired into a desktop power supply. It can run the accessories in a car(if you try to start it with the power supply attached the power supply will shut off. It won't charge because it is only 12 volts and a 12 volt battery actually is closer to 14 volts. Although when I was looking in to how to rewire the power supply I read that they can be hooked in either parallel or series (I don't remember which) but if they can be hooked in series it may be possible to to hook 3 of them together and hook there 5 volt outputs in series giving you 15 volts. Although 15 volts may be too much for a battery. If you get them used you can get the computer power supplies for $5 each and another $.50 in parts to rewire them so they can stay on all the time so you could try it and find out.

I don't know why you would want to jeopardize the health and life span of an expensive deep-cycle battery to save a couple of bucks on a charger. A four-stage Battery Tender will set you back about $50, or about 1/4 the cost of a good battery, Why cheap out on something with so much impact on your electrical system.

I can see using a computer PS instead of a 120 VAC - 12 VDC converter for LED Lights and accessories, but trying to make it/them work as a battery charger is asking for a dead battery.

<Chas>

[eamarquardt]

I don't know why you would want to jeopardize the health and life span of an expensive deep-cycle battery to save a couple of bucks on a charger. A four-stage Battery Tender will set you back about $50, or about 1/4 the cost of a good battery, Why cheap out on something with so much impact on your electrical system.

I can see using a computer PS instead of a 120 VAC - 12 VDC converter for LED Lights and accessories, but trying to make it/them work as a battery charger is asking for a dead battery.

<Chas>

Yup! Gus

[working on it]

I am convinced that the battery charging will best be left to conventional charging means, but I still think I'll get a CPS to run the 12v lights and fans when 110v is available, to lessen the usage of the battery. Of course I'll have to have a battery disconnect when the CPS is being utilized, but no problem seen there. I guess that if something looked that easy to do, I would've heard about it before now!

[GuitarPhotog]

I am convinced that the battery charging will best be left to conventional charging means, but I still think I'll get a CPS to run the 12v lights and fans when 110v is available, to lessen the usage of the battery. Of course I'll have to have a battery disconnect when the CPS is being utilized, but no problem seen there. I guess that if something looked that easy to do, I would've heard about it before now!

So, if you are going to have a battery charger also, why bother with the computer power supply in the first place? Why not just use the battery charger to charge the battery and to supply 12VDC for accessories when shore power is available?

Why use two devices when one will suffice?

<Chas>