Is there a way to safely run a system off 240V power?

[savage1987]

I remember reading somewhere that there's a way to set up your car's electrical system to run off a 240V power inverter (right word? long time since I studied electrics lol) so you can run an extension lead to your car and run the stereo all night without worrying about the battery (or batteries).

Is there a way or am I dreaming??
Sam

[Phreddy]

Actually Sam, an "inverter" is more generally used to go the other way - ie. from 12V to 240AC, to run household appliances etc from your car battery.

You could use a heavy duty 13.8V regulated DC power supply (powered from 240VAC), but I would suggest that there are some potential problems there as well. If you just hook that up straight across the battery, you could possibly end up overcharging the battery. It would definitely NOT be a good idea to hook up a battery charger that was rated at lower current than your stereo system draws - for example, if you have external amps and stuff trying to pull 40A or more at high levels, then you try and pull that out of a 10A battery charger, you'll probably blow it up!

It's a good theory, but really if you want to run a sound system off 240V, then you should use a system designed to run from 240V.

[savage1987]

Dammit. Thought there might be some sort of hell expensive but safe way to do it... Looks like it's time for another battery.

[azzfox]

what do they use at car shows then? they run their systems all day. all iv seen is power cables leading under the cars, so not sure what they use.

[Phreddy]

Sorry, I should have said that there are ways to do it - a suitably high current rated battery charger would work, but that wouldn't be cheap. A high current regulated power supply would work as well, but if it was me I would disconnect the battery while this was connected for reasons I stated above. Then again, I could be wrong too!

[kopper69]

Phreddy isnt totally correct.

"40A or more at high levels, then you try and pull that out of a 10A battery charger, you'll probably blow it up!"

Not completely true. The battery will supply the current, the power supply will just keep supplying power to the battery. It shouldnt be a problem. It would drain your battery pretty quick though. When the battery got too low, you would start to cause problems to the charger and possibly blow a fuse or 'blow it up'.

What you want is a power supply. This will convert mains 240Vac to a nice smooth 12 (13.8/14.4)Vdc. You first need to work out how much current your gear is drawing. If you are only wanting to run the radio and a set of speakers, you have many options and wont cost the world. If you want to run your amp/subs etc you are going to need something that can supply a bit more current, or your just going to be running your battery flat.

So what do you intend to run?

[kopper69]

Jaycar sell a 13.8V 40A power supply that should cover you. Just go to jaycar and search MP3089

That is a whopper. I would imagine that it could get warm so it would be a good idea to monitor it for a while to make sure it isnt getting too hot and put it in a spot that it wont set fire to anything. You could also look at using a computer power supply to. You would have to make sure that the car was never NEVER started while the power supply was connected up.

Here is a bit of reading:

Powering car amplifier from wall outlet - Audio - Forums - www.atomicmpc.com.au

But let us know what you intend to power and we can go from there.

[savage1987]

Powering a deck, front 6" splits, rear 6x9s and two 12" Alpine Type S subs running off a 450W monoblock. For now. It will, of course, be upgraded as bits and pieces fail I blew my first type S with that amp and put 2 of them in instead Also have plans to amplify cabin speakers at some stage.

Thanks guys
Sam

[Phreddy]

Yeh, you're right there kopper - if a battery charger was to blow up by trying to pull excess current from it, then it wouldn't be very well designed. Also, when you hook up a 13.8V regulated supply across the battery some charge current would flow, but when the battery approaches full charge that current would drop away due to the battery voltage getting very close to what's applied.

Maybe I shoulda connected my brain to my fingers before I replied...

[feistl]

Hey mate,

Could you use a standard PC power supply? You could get a PSU which supply's 80A+ on 12v...

I honestly dont know, just an idea....

[Tom_1569]

Hey mate,

Could you use a standard PC power supply? You could get a PSU which supply's 80A+ on 12v...

I honestly dont know, just an idea....

I honestly dont know the answer to your question, but i dont think you could without alot of work.
One thing most modern PSU need to be plugged into a motherboard to run, which makes it expensive for computer technicians, and myself who has to by a special power supply tested for over 100bux. Also it wouldnt be the safest option and would have to be directly wired. May work in the sense of bench testing a headunit though.

[kopper69]

Hey mate,

Could you use a standard PC power supply? You could get a PSU which supply's 80A+ on 12v...

I honestly dont know, just an idea....

A cheap/second hand computer power supply cannot put out 80A at 12V unfortunatly. You would need to spend some good money to get one that could put out that much current. And you dont need to connect a computer power supply to a motherboard to get it to work. As long as you take precautions there are no reasons why its not a 'safe option'. It is a sealed box and with a minor modification the power supply will work without a motherboard. Phreddy, theres nothing wrong with throwing ideas up too, everyones input is always welcome and it sounds like you know your stuff too.

A computer power supply could work in certain situations with some effort. I wouldnt be expecting too much though. Lets say we have a 550 watt power supply. The 12V rail is probably rated at 30A max. And it is 12V too, not 13.8/14.4V.

Let me explain a little. The way that you would want to run this is so that you run power to your car battery. This way it works as if the alternator is charging the battery, as in when the car is running. The alternator/power supply supplies the power to keep the battery charged. The battery provides the power to the system. To keep the 12V battery charged, the alternator normally puts out about 14.4V. The problem with a computer power supply is that it is 12V, and a nice 12V at that. The voltage isnt high enough to charge the battery at all.

The problem there is that you cannot use a battery. You would have to run the power supply straight to the stereo system. If the stereo system had a big thump of bass or loud moment where is needed an extra kick of power, it would blow a fuse or blow the power supply. There are ways to modify a computer power supply to output a higher voltage, but its really not worth the effort.

Lets get some more idea of what we are trying to do savage1987. The stereo that you are trying to run - its in the car and works in the car? You just want to keep it running for an extended period of time while the car is off? If so, can you work out the approximate current draw of the system by adding together the power (in rms) of each bit of gear. I think our best option may be the power supply from jaycar. Would you be happy to pay that sort of $ or are you looking for a cheaper alternative?

For anyone who is wanting to run a car head unit out of the car, say you have an old one laying around and a couple of speakers spare, you can run them from an old comptuer power supply.

[Tom_1569]

You would need to spend some good money to get one that could put out that much current. And you dont need to connect a computer power supply to a motherboard to get it to work.

Could you explain how to do this, im doing cert IV and an extra hardware course via correspondence and i have been told with all new motherboartds their is no way to test them without being connected to a motherboard, theirfor you cant test the motherboard plugs, with out a PSU tester, the only problem i can see is the on/off switch is actually controlled by the motherboard.
Could you please explain if testing motherboard plugs is possible, or even getting the PSU to run without it being connected to a motherboard. Oh im talking about P4 ones, not the older ones i know how to do them.

[one_and_only2004]

last year i had a similar setup running in my room. I had 2 250w RMS soundstream subs running off a 800w RMS Tarantula amp. I ran them off a p4 500w psu quite easily. Myself being an electrician, thought the best way to get it working was to connect a 80mm fan up, and randomly connect 2 pins of the mainboard plug together. I have no idea which pins it was but it worked anyway - for a while. Eventually the fuse popped in the psu and i gave the stuff to a friend...

[commsirac]

A high powered battery charger may be all you need, one rated at 6A may be enough to meet the average draw of just one amp and a head unit, that is just playing background music.

What is important to consider is that battery chargers are generally just 240V ac rectified, and regulated to 14Vrms. Apparently, the 100Hz pulsing is an advantage in actually charging a lead acid battery.

Connecting a battery charger to a sophisticated piece of electronics without a car battery to smooth the output should be avoided, it may simply causes a mains hum type prob, or something more sinister.

[garfa]

really how long do you want to run the system and what are the power requirements?
as for the whole PSU idea, com eon people. how thick is a wire rated at 80A@12V? a LOT thicker than the PSU cables! get your actual requirements with a clamp meter and then start looking.
also it depends if you have all month to play with the setup. a 2nd batt is great, it will be quick to setup and run for even if you have a 40A system! lol

[kopper69]

as for the whole PSU idea, com eon people. how thick is a wire rated at 80A@12V? a LOT thicker than the PSU cables!

You doubt there is a computer power supply that can output 80A? There are supplies out there that can supply even more. They use mulitple wires and can supply that current.

Tom_1569, youre right, modern power supplies disable most of the outputs until connected to a motherboard. You just need to trick it to see a motherboard. This may be what a 'tester' is doing (havent seen one before). I havent done it personally yet but I have seen many that have.

Have a read of this :Computer power supply - Wikipedia, the free encyclopedia

"PS-ON wire, which can be shorted to ground to turn on the PSU outside the computer" If you have a look at http://www.formfactors.org/developer...public_br2.pdf (page 36)this pdf you can see that ps_on pin location. Normally a green wire. This only needs a momentary short to simulate the power button being pushed.

Test ATX Power Supply

Computer power supplies also require a load to operate, so some people use large power resistors connected to a voltage rail - the 5V rail I think.

How to Convert a Computer ATX Power Supply to a Lab Power Supply - wikiHow

Testing a Computer Power
Quick Shot review 18: Connectland ATX Power Supply Tester
Testing power supply

There is a heap of info out there, just need to google a bit. Hope that helps. If your doing it a bit though you could probably find use with something like:

LCD Power Supply Tester for ALL ATX PSU Voltage Display - eBay Standard ATX, Power Supplies, Components, Upgrades, Computers. (end time 21-Apr-08 14:21:36 AEST)
or
ATX Power Supply 20 24 Pin PSU Diagnostic Tool Tester - eBay Other Power Supplies, Power Supplies, Components, Upgrades, Computers. (end time 02-Apr-08 22:53:26 AEST)

[savage1987]

Thanks for the info guys, much appreciated. Might just look into the dual battery setup if I decide to pursue this idea. Could just be a waste of money though..

Sam

[Astranomical]

You could use an old-skool AT power supply (NOT ATX, which is what most 1998 -> current PCs use), found in most post-1998 PCs, which have a real on/off switch, and therefore don't need a PSU tester or a motherboard to run. Cheap, and easy to find - just find someone with a 486 or early Pentium they want to unload, and strip it for the PSU. Just make sure it puts out enough watts for what you want.

[kopper69]

You could use an old-skool AT power supply (NOT ATX, which is what most 1998 -> current PCs use), found in most post-1998 PCs, which have a real on/off switch, and therefore don't need a PSU tester or a motherboard to run. Cheap, and easy to find - just find someone with a 486 or early Pentium they want to unload, and strip it for the PSU. Just make sure it puts out enough watts for what you want.

Read above mate. A computer power supply wont work with a battery meaning you would have to run the system solely on the power supply. The amplifier would kill the power supply on the first bass note. Older power supplies have a lower output too, which means an even lower chance of running. As I mentioned above it is fairly easy to enable an ATX power supply output - but thats not a solution to the problem.

[feistl]

Could you explain how to do this

Jump the green wire to black. PSU starts .

(Watch though, make sure you have something plugged into it, turning it on with no load = dead PSU).

Sorry to stir so much discussion... I currently work in IT, and know quiet a bit about PSUs etc.

Anyway i remember a while back needing a strong source of 12v power for a model train set (G scale for those in the know)... most seemed expensive, however with minor modifications a PSU was able to be used. I know you can get decent power on a 12v rail, although is below the 14v you actually want. Again, just an idea....

[Tom_1569]

Jump the green wire to black. PSU starts .

(Watch though, make sure you have something plugged into it, turning it on with no load = dead PSU).

When you mean no load, do i just stick a cd rom on it or something. My main reason is i want to be able to test the voltages of the motherbored plug mainly for research purposes. I will probly stop being such a tightass and just by the digital tester.

To the other bloke who posted a **** load of links, thanks heaps i will have a look through them when i have more time, it is all appreciated. Also those digital testers are the ones the TAFE want us to buy (for correspondance course) and their about 100 bux through them, ill just get one off ebay im sure their the same, either way they do the same job.

[feistl]

When you mean no load

PSUs/electronics dont work so well if you power them up with nothing using the power. Most ATX PSUS require a minimum of 2A to be drawn through them, otherwise you seriously risk damaging them. A CDrom isnt great as once its checked for a disk, it uses very little power. A HDD/Fan is a better option, as the power draw is consistent.

In saying that, i have a box of ATX PSUs here if you want em, just use them till the blow and then throw them out.

[Tom_1569]

PSUs/electronics dont work so well if you power them up with nothing using the power. Most ATX PSUS require a minimum of 2A to be drawn through them, otherwise you seriously risk damaging them. A CDrom isnt great as once its checked for a disk, it uses very little power. A HDD/Fan is a better option, as the power draw is consistent.

In saying that, i have a box of ATX PSUs here if you want em, just use them till the blow and then throw them out.

Ok that makes sense, Where are you located i may be interested in a couple of PSU's saves blowing good ones up lol.

[kopper69]

When you mean no load, do i just stick a cd rom on it or something. My main reason is i want to be able to test the voltages of the motherbored plug mainly for research purposes. I will probly stop being such a tightass and just by the digital tester.

I personally would grab one of the ones off ebay for $20 or whatever they are. Then use a multimeter to measure the exact voltage. If your looking to save yourself some $ you simply need two resistors which you could pick up from jaycar/dick smith. One of those testers (that connectland one) simply uses two large power resistors (the white rectangle things). The site is down at the moment, so I cant see what values they are. When the site comes back up Ill have another look for you - but you can just walk into dick smith and ask for these two resistors, which will probably cost $0.70 for both. They just get connected between the 12V and ground and 5V and ground.

If youre planning on testing power supplies often its probably just as easy to get an old motherboard in a case. You should come across these relitively easy or even grab a faulty one from a generous computer shop. Just connect the power switch up and turn it on, use your mulitmeter to measure the voltages. There is a guide here:

OC-Hades: Article / Testing your PSU with a multimeter

My apologies to everyone for turning a car forum into a computer forum