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smartalec
04-03-2010, 01:15 AM
Hi all,
i got a switchmode power supply that is 20amp at 24v.
now this power supply has a tweek voltage which i have turned so now i have 28v comming out of the power supply,
My Question is? how many amps would i have?

im taking a wild guess an thinking like maybe 18amps? at the 28v level

This is DC im talking about..

thanks alec.

budude
04-03-2010, 01:19 AM
Well - assuming it's a linear output you would go by total power output which would be 24 x 20 or 480W. So - 480W / 28V = 16.6A - with a strong 'probably'... :p

smartalec
04-03-2010, 01:29 AM
Well - assuming it's a linear output you would go by total power output which would be 24 x 20 or 480W. So - 480W / 28V = 16.6A - with a strong 'probably'... :p

thanks for that, i didn't realise the math i had to do.
thanks heaps

another question, would doing this shorted the life of the power supply?

budude
04-03-2010, 01:47 AM
thanks for that, i didn't realise the math i had to do.
thanks heaps

another question, would doing this shorted the life of the power supply?

It might depending on the components used - I would say it definitely wouldn't lengthen it's life anyway... I should have mentioned before that I'm assuming the 20A number you gave is the maximum ouput so you wouldn't want to run at full load - that will definitely shorten its life. A good general rule of thumb is to go to 80% - so using 28V you're probably really looking at 13.2A or so... This is a definite YMMV situation.

aussiephil
04-03-2010, 03:08 AM
Depending on just how good the design is, adjusting it within it's valid range should not shorten it's life.
Nor should running it close to it's rated output, that's what ratings are for.

Cheers

budude
04-03-2010, 03:33 AM
Normally I would agree with you but as this is going to be used for the lighting power it will be going through huge transients depending on the sequencing and if you are running to the edge it may put some hurt on it. You also hit on the other part of - how good the design is and also how old the supply is.

Anyway - I wouldn't go full load myself but if you have spare supplies - then go for it...

smartalec
04-03-2010, 04:03 AM
well it was brand new, but i did get it off ebay.
not alot of info on the site. (never is)

DC Power Reyed® 480w 24V 20A Switching Power Supply



Model: RYD-480A
AC input: 220V ±15%
Output: 24V , 0 ~ 20A .
Auto on/off cooling fan.
High Efficiency, Low Temperature.
High reliability .
LED indicator for power on
Built-in EMI Filter.
Over Load and Short Circuit Protection.
Over Voltage Protection .
Auto-recovery after protection .
Size: 225mm x 112mm x 58mm .
Weight:1330g.

so i reckon i might set my max load of 15amps or less on my amp meter.
(visual way of seeing what im pulling)

ErnieHorning
04-09-2010, 08:10 AM
The 20 amps isn't necessarily a fixed value. The transformer used for input will supply more than the supply would output. I wouldn't doubt that it still puts out the 20 amps at 28 volts.

If it's a reparable manufacturer, I would expect that it puts out the rated current all day without failure. The parts would be over rated probably double or triple. Unless its from China, nobody is going to choose parts that fry at the rating.

I've qualified power supplies before and we test for the manufatures specs and they put out what they said they would. I was told that they had a lot more headroom if the circuit was allowed.

To put out at the maximum you may need cooling or special mounting though.

IdunBenhad
04-09-2010, 09:10 AM
Hi:
From the specifications you posted:

Model: RYD-480A
AC input: 220V ±15%
Output: 24V , 0 ~ 20A .
Auto on/off cooling fan.
High Efficiency, Low Temperature.
High reliability .
LED indicator for power on
Built-in EMI Filter.
Over Load and Short Circuit Protection.
Over Voltage Protection .
Auto-recovery after protection .
Size: 225mm x 112mm x 58mm .
Weight:1330g.

The power supply has overcurrent protection. The tolerance from the nominal rating of 20 amps is not listed, but probably will be 5%, so the overcurrent protection would shut down the PS at 21 amps.

It is rated at 480 watts. This is a maximum rating and applies to either an output voltage of 24 volts or 28 volts. 17.14 amps x 28 volts =480 watts: 24 volts x 20 amps=480 watts. I would not exceed that current at either voltage.

A watt is a watt is a watt, no matter how you get it. If the power supply is rated at 480 watts, then that total power should not be exceeded. The manufacturer sets the ratings and he is the authority.

If you want to exceed these specifications, that would be at your own risk. However, in this case, you are protected by the overcurrent/overvoltage circuitry, so there should not be too much to worry about.

Cooling is not an issue here, as the PS has its' own automatic fan.

Momentary spikes above the maximum ratings will probably be tolerated, but then again, it may automatically shut down. This is an unknown, as that is not in the specs. 17-20 amps is a lot of current and will run a lot of lights.