12V Power Supply

I have a need for a circuit for a 12 volt, 30 amp DC regulated power supply. Does anyone no of the existence of one or the availability of an off shelf supply with same specification? Any help would be appreciated.

30A is too much current for 12VDC, may be 3A will work please confirm

Total Rubbish!!!

3 amp is not enough, I'm working on a hydrogen fuel project and require higher amps

Where are you? This is about $250 for 64 Amps 12V. But: I guess it will cost you to get it shipped anywhere but the UK.

http://cpc.farnell.com/jsp/Batteries+&+Power+Supplies/AC+to+DC/AKASA/AK-P085FG/displayProduct.jsp?sku=CS15619&_requestid=248370

If you do go for this you'd better check the spec. I can't figure why it's called an ATX supply.

Thanks Randall for your interest and the information. Regards, Warrenh

Randall, I suspect it is because it is a high power ATX (pc computer) power supply. The kind you have in your PC in front of you. They have a soft start 5v switching system and output multiple voltages, not just 12V. Probably not what he was looking for.

Yes it's a PC supply, but, it claims to have two 12V 35A outputs:-

http://www.overclockers.co.uk/showproduct.php?prodid=CA-026-AK

It may be the cheapest way of getting what he wants (might have to supply the power good signal back from the "motherboard"). I have used PC supplies in the past instead of very expensive proprietary supplies.

You can try with vicor power supply. Go to www.vicorpower.com

Any problem is half-solved if you know the problem or how to put it. 12V/30A DC doesn't say much. Take a 12V battery and short it with a .4Ω resistor and you'll get 30A.

You should specify the input of the needed power supply, such as 120Vac. You may have other AC voltage input or a DC, in which case you might need a DC-DC converter. Who knows?

Nobody here is a mind reader.

Warrenh,

Do you need 30 VDC+/_ ?? V --at the output terminals IRRESpective of whether you draw out 0>30 Amps ?

If that is what you -- please reply -- What is "??"

There may be - and may not be - EXISTING models-- depending on What is ??

In any case - there are Solutions. So do spell out.

Thanks for your input Mukulmahant. I would like 12v dc 30a out at the terminals. I want that to be the constant maximum possible current draw.

If you search globalspec, you can specify that your current to be no more than 30 amps,I have done the search for you with a result of almost 4000 products if I don't specify the input voltage, which you don't give.

Alternatively you can get a supply with a higher current rating and limit the current via ohms law with a very hefty 0.4 ohm 360 watt resistor that can also be found on globalspec.

Hope this will help you:

That was a Huge block of nothing for me! What was it supposed to be????

A car battery will do that just fine.

Hello Warrenh,

You are looking for a power supply circuit of less than 1ohm, precisely, 0.4 ohms.

It will be difficult, if practicable, to realise such circuit.

Cheers,

Ethobil

Easy, got one in my garage. Came out of a Silicon Graphics Workstation circa 1998. Wanna buy it? It'll cost an arm and a leg to ship, the thing is a freakin boat anchor. But it DOES work.

Thanks Rorschach, sounds like its a monster. How physically big is the power supply and what selling price? Once I know that I can make a decision.

Regards, Warrenh

Yeah, it is definitely a monster. When I grabbed it out of the scrap heap I wasn't sure what I'd ever need that much power for, I just knew that if I did, it would cost an arm and a leg so I figured what the hell... Actually there were two of them and I gave one to a coworker who liked to tinker too. I'm going from memory at the moment since I don't have the unit in front of me, but it is probably on the order of 8" x 10" x 14-18" lg. It probably weighs 40-50 lbs. It is a triple output unit. It puts out +5, -5, and +12VDC if memory serves, the 12V side puts out so much current that instead of a plug, it has a 3/8" stud terminal (the rack had some pretty huge fans in the system, plus hard drives in a RAID array). It probably will put out more current than you need. As to price, I'm pretty flexible, I haven't used it in ages and it is just taking up space. Make an offer and we'll talk. Meanwhile I'll try to get you some more specific specifications and get back to you.

Warren, I really should learn to not trust my memory, it is not as good as it used to be.

I have the unit sitting here in front of me and I was mistaken on the outputs.

It is a 4 output unit, not 3.

Output1: 5V @ 120A

Output2: 12V @ 15A

Output3: 12V @ 15A

Output4: 5V @ 5A

It is a ACDC electronics (division of Emerson) model number REV804B-2332-000-9004 SN# AF9947

Input: 115V/230V 15A/8A 50/60 Hz total power 800W

Is this still something you can use?

Hi Rorschach, No, it does not give me quite what I need. I'm looking for either a circuit or an off the shelf power supply: 12V DC in and a constant 12V DC 30A out, it needs to be regulated so that it will not deliver greater than 30A. Many thanks for your help. Regards, Warren

Warren, I'm sorry I don't recall seeing where you were saying that you wanted a 12V input. I thought you were wanting a 120VAC to 12VDC supply.

Wouldn't a simple circuit breaker or fuse suffice?

No, The project I'm working on is the generation of Hydrogen as a fuel suppliment and I don't want to shut off the power but to regulate it to deliver a constant 12V DC 30A. I've mostly got the rest of the gear, but just struggling to find a suitable power supply. I have used an experimental setup but only had 15A, it was a bit messy but it did work, now I want to get up to the 30A which is where I thinkl I need to be but I want the project to not only work but to look professional and as though someone cared about it. Experimentation and improvisation is OK up to a point, then one has to move on and tidy things up and make it all looks good. Again thanks for your interest and help. Regards, Warren. PS - Where are you and what time of the day is for you? It is 06.45 here for me.

Warren, had you looked at my user profile alongside my posts you would see it shows me in Spring (just outside Houston) Texas. It is 1:50 in the afternoon here. You should go to your user profile and fill that information out for yourself.

You still have not clarified what you want. Do you want to limit the maximum power you can deliver to 30A without changing the voltage input? So what do you want to happen if you short the system, do you want the voltage to drop to maintain the 30A? Do you want the Amperage to drop to maintain the 12V output? You DO understand Ohms law right? You also understand the third law of Thermodynamics right? TANSTAAFL also applies.

If you want the current to remain the same and let the voltage sag, you have what is called a constant current regulator. If you want the voltage to stay the same but let the current sag, you have a constant voltage regulator. But either way you slice it, the regulator is going to dissipate power and will reduce the output voltage by some number, there are some low dropout regulators on the market that can operate with as little as .7V difference between the input and output, but they generally are very low current devices. Most high power devices need about 2-3V delta between input and output to regulate. The most efficient switchmode power supply I've ever heard of is only about 95% efficient, but most are closer to 70-80%. Most Linear supplies are far less efficient. They waste a lot of power in the form of heat.

I think you need to re-think what it is you are asking for and make yourself much clearer.

BTW, I have done some Fuel Cell work in the past myself. What technology are you using? We were playing with PEM type fuel cells for distributed power generation fueled by cracked (reformed) Natural Gas. We got 8kW out of our cell stack (and met our target), but the reformer we would have used and the inverter electronics would have burned 21kW in the process. The team working on the reformer did not come CLOSE to hitting their efficiency target, nor their size target. The reformer alone was the size of a small minivan. The whole system was supposed to be no bigger than a 4-6 ton AC compressor unit. The inverter was only about 70% efficient and we just could not seem to get much better than that.

edit: if you can let the output voltage sag, then the simple thing to do would be to put a very low resistance resistor in series as others have suggested. It will act as a current limiter, but it will need to be able to handle almost 400W of power and it will need to be very low resistance.

You are absolutely correct. And yes there are things that I don't understand with the whole power thing. I'm applying a current to water and drawing off the Hydrogen and oxygen which is then fed into a motor through the air intake as a fuel supplement along with whatever fuel the motor is running on. So far the results experienced have been an increase in motor torque and an extra 40 kilometers to a tank of fuel. I had previously used a headlight globe as a resister with a 15A supply. I will share your thoughts with my electrical colleagues here at work. Regards, Warren

But at the cost of having to lug all that water around and use alternator power to diassociate the water. You basically gained less than a gallon of gasoline's worth of distance for your trouble, you could have added an additional gallon of gas to your tank a whole lot cheaper and easier and take up less space. Remember TANSTAFFL always applies. There is no such thing as a free lunch.

Absolutely correct, but it is fun keeping the mind active and having a play.