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AC to DC converters

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Alec_Hood View Drop Down
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    Posted: 29 June 2013 at 12:04pm
Looking to buy a converter so I can run my 800 watt JVC car amplifier off 240V house power.

Can someone please link me to one that is cheap and will give me max wattage.

FIY, I only need enough power for 250 RMS for the sub, and two 40 RMS for the speakers.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lost eden Quote  Post ReplyReply Direct Link To This Post Posted: 29 June 2013 at 1:23pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alec_Hood Quote  Post ReplyReply Direct Link To This Post Posted: 29 June 2013 at 1:46pm
Alright thanks man
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alec_Hood Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2013 at 2:23pm
Isn't it made for LED lights? They would't use near as much power as speakers would?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2013 at 3:28pm
I reckon that supply might cut out/blow a fuse if you try and turn the amp up; it is quite beefy, but if your amp tries to develop 800 watts into the speakers, assuming 80% efficiency that means it will be trying to take 1000 watts or 83.3 amps from the supply - almost three times its rating, pretty much guaranteed to make it unhappy. 
In addition, not all SMPS are equal; there is the concept of rise-time to think about. In essence this means that some supplies, like that one, are designed to supply a constant current without sudden large changes in demand. LED lights are a constant load. Audio amplifiers are not. They require a different type of supply designed to cope with large changes in demand from one microsecond to the next. The "steady" type of supply may become unstable if presented with a large transient load, and this may make the amp unhappy too; the worst case scenarios are that the current spike causes a voltage oscillation and temporary over-voltage leading to damage to the amp or blown fuses, or that the amp and supply get into a fight leading to low-frequency oscillation in the speakers, as the supply dips and bounces back continually; this could easily break your speakers.
If it were me I'd use a car battery and trickle charger, and let it recharge while I wasn't using the system. It's a lot simpler, and probably cheaper too.
Studio45 - Box Builder Commotion Soundsystem -Mobile PA
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2013 at 5:18pm
Have a look at this link to Ebay for a Voltcradt SPS 1525 PFC 15V 25A Switch Mode Bench PSU
This does 3 to 15 Volts DC at up to it's current limit of 25 Amps

Others are available but this may give you an idea of what to look for; otherwise go for the 'Battery with Charger' also suggested

Mik

Edited by audiomik - 01 July 2013 at 5:19pm
Warning! May contain Nuts
plus springs, washers, screws, etc, etc.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Audio_AL Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2013 at 6:19pm
Originally posted by Alec_Hood Alec_Hood wrote:

Looking to buy a converter so I can run my 800 watt JVC car amplifier off 240V house power.

Can someone please link me to one that is cheap and will give me max wattage...


I was in this same boat (only with 110v power). I used a large computer power supply to power my car amp. It worked fine until I cranked it up. It played loudly for about 10 minutes then it caught on fire Ouch

In hind-sight I would have just bought a cheap pa amp to power the car subs. It would have been cheaper in the end. The thing to watch for here is the impedance of the speaker. Car subs are often 2ohm (mine had dual 1ohm voice coils). Be sure to wire in a way that the amp wont mind.
Make it loud!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2013 at 6:41pm
Originally posted by studio45 studio45 wrote:

I reckon that supply might cut out/blow a fuse if you try and turn the amp up; it is quite beefy, but if your amp tries to develop 800 watts into the speakers, assuming 80% efficiency that means it will be trying to take 1000 watts or 83.3 amps from the supply - almost three times its rating, pretty much guaranteed to make it unhappy. 
In addition, not all SMPS are equal; there is the concept of rise-time to think about. In essence this means that some supplies, like that one, are designed to supply a constant current without sudden large changes in demand. LED lights are a constant load. Audio amplifiers are not. They require a different type of supply designed to cope with large changes in demand from one microsecond to the next. The "steady" type of supply may become unstable if presented with a large transient load, and this may make the amp unhappy too; the worst case scenarios are that the current spike causes a voltage oscillation and temporary over-voltage leading to damage to the amp or blown fuses, or that the amp and supply get into a fight leading to low-frequency oscillation in the speakers, as the supply dips and bounces back continually; this could easily break your speakers.
If it were me I'd use a car battery and trickle charger, and let it recharge while I wasn't using the system. It's a lot simpler, and probably cheaper too.


Never tried it myself, but you could very well be right about the instablilty stuff ....

OTOH - if that "800W" is Chinese/marketing watts .... well that'll likely be into 1R or 2R load(s). And then don't forget that power rating will be at 14.4V power rail ... if you use 12V it'll cut down your power yield by 30% or so .... so "800W" could very easily be more like 200 real watts.
REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 01 July 2013 at 9:16pm
I wouldn't directly import any mains equipment like that. There's no saying its built to UK standards and might not be safe. Best buy high technology switchmode stuff from a european supplier.
Kevin

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SMP Quote  Post ReplyReply Direct Link To This Post Posted: 02 July 2013 at 12:48am
not too sure what all the song'n' dance is about with this...It seems to me to be fairl simple although would like to know the exact application for the amp.
But simple enough to deal with any power change requirements  just get yourself a fairly hefty Car Battery charger add a large 16Volt Capacitor very often find ex-equipment ones from older Computer server PSU do the job nicely as they are often very high values of 56;000 uF 
this is a very cheap way of power for 12Volt systems to run on 240Volt AC supplies
The charger is not a hard find and generally give high enough supply under load but make sure it is not an Automatic type as they do not behave as needed
of course failing this a large Transformer a Rectifier and a Capacitor  the amp will be a PWM powered type for the DC/DC converter which will have sufficient filtering on board
I have used similar setups to power Car Audio on the bench to test after repair with good results
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Edd Jordan Quote  Post ReplyReply Direct Link To This Post Posted: 02 July 2013 at 1:12am
I do a sideline in ply wood wheels.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 02 July 2013 at 7:32am
Just realised I have a large-ish transformer here ... chunky thing - designed for LV lighting I think ....
12V rated at (I think) 300 or 350VA or so .... yours for a coupla beers .... but I _ain't_ shipping it .... collect from London E2.

REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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