power supplys and amps

[bill2]

Can i run a solid state amp that calls for 12-16 volts with a 12 volt 47 amp computer grade power supply? I know it won't put out full power but any other things i need to know? Thanks.

 

[74IN]

If you starve an amp for voltage (what happens when it can't get the current it will need, voltage drops), the quality of the audio suffers.

Does the PS deliver 12V or closer to 14V?

12V is on the low side, most like about 14V, what a car typically gives.

 

[autotuner]

When you say computer grade supply, you don't mean one from a PC do you?

If it is a power supply from an old Mini (mine is from a Wang system) you may find there is an adjustment pot. Have a look at the regulator board.

The one I have allows adjustment from 11 to nearly 16 volts @ around 40 amps.

 

[BOOTY MONSTER]

those computer power supply wattage/amperage ratings are for the combined 12v 3.3v and 5.5 volt lines , the actual 12 volt amperage may be 1/2 of what the combined spec may be , or less .

 

[bill2]

When you say computer grade supply, you don't mean one from a PC do you?

If it is a power supply from an old Mini (mine is from a Wang system) you may find there is an adjustment pot. Have a look at the regulator board.

The one I have allows adjustment from 11 to nearly 16 volts @ around 40 amps.

I'am not sure but it looks like it may be from a hewlett packard computer. It's 11" long, 3" tall and about 2&1/4" wide switching type with one fan. It works the amp fine at 250 watts where it would do about 400 watts at 13.8 volts. I just want to make sure it can't cause any damage, and i will try and check to see if theirs any adjustable pot for volts.

 

[bill2]

If you starve an amp for voltage (what happens when it can't get the current it will need, voltage drops), the quality of the audio suffers.

Does the PS deliver 12V or closer to 14V?

12V is on the low side, most like about 14V, what a car typically gives.

I'll have to get a volt meter to check the output but i was told 12 volts.

 

[mackmobile43]

I'll have to get a volt meter to check the output but i was told 12 volts.

They're usually pretty close to either 12 or 5 volts depending which tap you use and I say this because they tend to use lower voltage value components such as capacitors.

 

[autotuner]

those computer power supply wattage/amperage ratings are for the combined 12v 3.3v and 5.5 volt lines , the actual 12 volt amperage may be 1/2 of what the combined spec may be , or less .

Yeh, hence my question if it was a PC type supply. Along with that they are usually pretty crappy build so I wouldn't be trying to run my good gear off one.

bill2, you wont do any harm at 12v, and to be honest the 15% difference between that and 13.8v only equates to about 40 extra watts. Hardly a bees dick of an S point at the other end.

But it is worth looking for an adjustment, it sounds to mine (wouldn't be surprised if it was a generic model used by a number of computer companies) and the pot is pretty obvious.

 

[Shockwave]

The 15% increase in voltage could actually equal a 30% increase in watts. Consider that when voltage rises across the load that current tends to rise proportionally. Power is your volts times your amps so a voltage change usually cause two times the change in power. If you take a 100 watt 110 volt light bulb and run it on 220 volts, it will be 4 times brighter and consume 400 watts until it quickly burns out.

If your computer supply is not causing objectionable interference in the receiver, you're probably not going to have problems from it. Almost all of them have termal protection, over voltage and over current protection. The current protection prevents you from drawing too many amps and blowing up the supply. The over voltage protection prevents a power supply failure from becoming a radio equipment failure.

It sounds like you have one of the power supplies from a main frame computer. They typically have discrete supplies for each voltage. If the 12 volt supply was 48 amps I bet the 5 volt supply was close to 200 amps on that computer! Most will have a group of 3 potentiometers inside that set the important operating limits. The first is the obvious output voltage. Then you have the over voltage protection setting and current limit setting.

The over voltage setting sometimes called the OV or crowbar is probably going to be of importance to you since you are increasing the voltage. Since the output voltage is set at 12, the OV is going to be set just above this point around 13. Once you set the output voltage control beyond this point the power supply will immediately shut down it's output voltage thinking the regulator has failed. Nice feature but you will have to increase the OV setting as well as the voltage output to reach the higher voltage.

The current limit should be checked while there is a full load on the power supply by placing a volt meter across the terminal of the power supply. If you see the voltage drop from the no load voltage, you will want to increase the current limit until the voltage holds constant under full load. If you don't go beyond this point, you will be offering your amp some protection by limiting the maximum current you can ever feed it. Nice if you ever run into a condition of over drive or shorted coax.

Now keep in mind we just asked this power supply to make more voltage and maybe more current then it was designed for. Since it is a switching supply we are just extending the duration of the on cycle to achieve the voltage. The supply was designed for continuous duty and intermittent communications service will extend the current capacity with it's cooling fan. I'd set it at 14 volts, check the current limit under full load and call it a day. You have little risk of damage to other equipment if the supply fails due to it's elaborate protection that would remain intact.