How do I make a standby power supply that will power the remote control reciever and a relay (about 50mA total)? My main goal is efficiency. I see that Digikey carries the BPS 1/4 to 2W supplies which are 50% minimum regardless of load, but that's $10 + as much for shipping, so $20. There's got to be a cheaper way to do a copule of watts power supply that will do that current at about 9V.
Go to a pawn or resale shop and find a wall wart.
Integrate the guts or even the whole thing into your design.
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Don't you have something like this laying around? I usually have at least a couple of random wall warts @ the house. Ask your friends and neighbours and coworkers. Someone is bound to have one.
Integrate the guts or even the whole thing into your design.
/edit
Don't you have something like this laying around? I usually have at least a couple of random wall warts @ the house. Ask your friends and neighbours and coworkers. Someone is bound to have one.
Hmm. I hooked up a small transformer ripped from a broken wall wart (about 5 to 7 VA) to the mains and with a DMM set to AC current, it measures almost the same current drawn by the primary (about 25 mA) whether there's a load on the 9V secondary or not. Plus the transformer gets fairly warm, without any load. I don't know the phase between voltage and current so I can't calculate power. But it seems a good deal of power is going into heating the transformer. Is there a way to measure the power use without an actual power meter?
No, it's not hot, but quite warm (maybe 50* C). Probably it's just a crappy transformer with lots of parasitic losses.
Any way to roughly measure power without a power meter? Maybe some simple circuit that can be made? I guess I could just measure the heat given off but that's pretty hard to do without a lab.
Any way to roughly measure power without a power meter? Maybe some simple circuit that can be made? I guess I could just measure the heat given off but that's pretty hard to do without a lab.
Wall warts get warm. Yes. It is a large reason for a large electrical bill for someone who uses a lot of them. If you want a transformer to not draw current at load-idle, get a switch for the mains. Wasteful little transformers are a way of life for the modern small-electronics user. For grins, have you measured the idle current of a bigger transformer that you may have laying around for comparison?
If this is standby for a 500W dissipation monster, then a couple of watts at idle is relatively speaking ~peanuts~. If it really bothers you that much, make up a little PWM supply.
If this is standby for a 500W dissipation monster, then a couple of watts at idle is relatively speaking ~peanuts~. If it really bothers you that much, make up a little PWM supply.
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