Quick question about 12 Volt Power Supplies....

[30Hz.wav]

I am looking on here:

http://www.onlinecarstereo.com/products/68/Car_Batteries_and_Accessories/12_Volt_Power_Supplies.aspx

Each power supply is rated with a different "Amp". So what exactly is the Amp to Watts RMS Ratio?

I am looking to run roughly about 300 Watts RMS for a small home setup. Any help would be appreciated. Thanks

[Wicks]

Without more details, I'll ball park it.

Let's say the 300Wrms amp is 70% efficient = ~430W input.

With a 13.8V output. P/V = I. 430W/13.8V = 31A.

To not overstress the power supply you should up the current capacity to at least 40-50A.

If its for a home theater, you may be able to get by with less due to the dynamic nature of movies and such.

If you're listening to more constant bass heavy music/test tones then you need all of that 40A.

It'll be more expensive, but you'll want a linear power supply. A switching supply may not be able to handle the peaky current draw of the amp.

Don't forget a 50A fuse between the power supply and amp. In case something happens to the amp, you don't want a home fire.

The PS46kx (35A) looks to be a good choice. The PS64kx would be better, when you want to upgrade that amp in the future!

[30Hz.wav]

Without more details, I'll ball park it.

Let's say the 300Wrms amp is 70% efficient = ~430W input.

With a 13.8V output. P/V = I. 430W/13.8V = 31A.

To not overstress the power supply you should up the current capacity to at least 40-50A.

If its for a home theater, you may be able to get by with less due to the dynamic nature of movies and such.

If you're listening to more constant bass heavy music/test tones then you need all of that 40A.

It'll be more expensive, but you'll want a linear power supply. A switching supply may not be able to handle the peaky current draw of the amp.

Don't forget a 50A fuse between the power supply and amp. In case something happens to the amp, you don't want a home fire.

The PS46kx (35A) looks to be a good choice. The PS64kx would be better, when you want to upgrade that amp in the future!

Thanks for responding.

So I am going to actually be running about 268 watts. I have a 200 Watt Fosgate Amp and a stereo that puts out 17 Wattz RMS via 4 channels.

So would this put me at 19amps if I was running it full blast?

268W/13.8V = 19amps.

Would I be able to get by with the "Pyramid PS21KX" 20 Amp power supply?

It won't exactly be run full blast, it's just going to be a portable little system. Trying to keep it cheap as possible.

Edited February 9, 2012 by cccmaa

[Wicks]

Depends how efficient the amp(s) are.

If they output ~268W then they require an input of 268W/70% = ~382W.

Depending on the amp class (A, AB, D) and how its loaded.

Class A is maybe 50%. Class D is best at 70-90%.

So we're looking at about a 25A supply.

If you're not pushing the amp very hard then a 20A supply may work.

If you draw too much current from a power supply then the voltage droops just like in a car.

Too much of that and you could damage your amp.

You also don't want to run a power supply directly at its rating. Sure, it'll work for a while but you always want some headroom for dependability.

[30Hz.wav]

Depends how efficient the amp(s) are.

If they output ~268W then they require an input of 268W/70% = ~382W.

Depending on the amp class (A, AB, D) and how its loaded.

Class A is maybe 50%. Class D is best at 70-90%.

So we're looking at about a 25A supply.

If you're not pushing the amp very hard then a 20A supply may work.

If you draw too much current from a power supply then the voltage droops just like in a car.

Too much of that and you could damage your amp.

You also don't want to run a power supply directly at its rating. Sure, it'll work for a while but you always want some headroom for dependability.

Im kinda confused. You said it required an input of 382 watts. But the 20 Amp Power supply says its input is "450 Watts"

[Wicks]

Yup.

The amp will require ~382W of input.

The power supply is also <100% efficient so it requires more power at its input (AC wall power).

Power supply input = 450W.

Subtract inefficienies from power supply (heat) = ~380W to the amp.

Subtract inefficienies from amp (heat) = ~270W to the speakers.

Every piece of electrical equipment will have inefficiencies and give off heat. Therefore it inputs more power than it outputs.

These numbers aren't exact either. Depends on how the amp is loaded and ultimately how efficient it is.

PS. Running a power supply directly at its output will give off a good amount of heat so ventilation will be key.

Always a good idea to run a power supply at about half its rated power. Not necessary but good for reliability.

Edited February 9, 2012 by Wicks

[30Hz.wav]

Yup.

The amp will require ~382W of input.

The power supply is also <100% efficient so it requires more power at its input (AC wall power).

Power supply input = 450W.

Subtract inefficienies from power supply (heat) = ~380W to the amp.

Subtract inefficienies from amp (heat) = ~270W to the speakers.

Every piece of electrical equipment will have inefficiencies and give off heat. Therefore it inputs more power than it outputs.

These numbers aren't exact either. Depends on how the amp is loaded and ultimately how efficient it is.

PS. Running a power supply directly at its output will give off a good amount of heat so ventilation will be key.

Always a good idea to run a power supply at about half its rated power. Not necessary but good for reliability.

Ok thanks! Appreciate all the good info!

Why would the Pyramid PS21KX (20AMP) cost more than the Pyramid PSV300 (30AMP)?

Is the PSV300 something different?

It says "Fully Regulated Low Ripple

http://www.onlinecarstereo.com/CarAudio/p_22378_Pyramid_PSV300.aspx

Sorry for all the questions. Trying to get it right the first time.

[Wicks]

No problem, glad to help.

The 30A supply is a switching power supply. They use a different method to produce the power. Less expensive parts. Usually no large transformer/capacitors inside.

Here's some info on the differences:

http://en.wikipedia.org/wiki/Switched-mode_power_supply

I've played around with a cheap 40A switching supply on an amp and the power supply freaked out with the dynamic current pulses that the amp drew.

They're probably fine for constant and even power draw but when amps draw large current spikes, the cheaper power supplies may have a problem keeping up.

It may work fine but I'd hate for you to get it and it not work like you want.

If you go with a switching supply, I'd shoot for a higher current rating to make sure you don't have any issues.

Hmmm, looking around online, the prices sure jump up when you go over 30A. One of the reasons I haven't gotten a good bench supply either....

Is this one too much?

http://www.trcelectronics.com/Meanwell/psp-600-13.5.shtml

This has a little more headroom and has PFC (power factor correction) which may help the capacitive load that the amp will draw.

I don't see PFC in the manual for the pyramid and for the price, I doubt it does.

These simple encased power supplies will have better internals rather than the extra money for the flashy case.

Although it may need some extra effort to wire it up...

Options options...

[knowledge]

great info here

[tejarillo]

Why not just use a power supply for a pc that what im using in my home theater set up. Just use the yellow wires as positive and black as ground and solder the green and black wire that are connected to the motherboard and it should turn on