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wall wart

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i am monster

New Member
is a "wall wart" just like a thing that plugs into the wall that converts ac to dc like a video game system uses or a batterey charger that you can then plug into a bread board and use instead of battery cells
 

MikeMl

Well-Known Member
Most Helpful Member
This is a wall wart
 

Torben

Well-Known Member
is a "wall wart" just like a thing that plugs into the wall that converts ac to dc like a video game system uses or a batterey charger that you can then plug into a bread board and use instead of battery cells
Yes, pretty much. Some wall warts just step the voltage down and output AC though, so be careful.

Wall wart - Wikipedia, the free encyclopedia


Regards,

Torben

[Edit: Also be prepared for the fact that many are simple unregulated linear supplies, so while it may say "9VDC output" on it, you'll find that it's only actually putting out 9VDC when loaded with its rated load. If you measure the output when it's unloaded, you'll see something more like 13VDC.]
 
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giftiger_wunsch

New Member
I'm using a 230VAC/6VDC wall-wart to power a processor + prototyping board with a rating of 6-14V, is there a reason I shouldn't be using a wall-wart to do this?
 
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i am monster

New Member
thanks for all this info..
so i can just use this 9v 250ma charger that i got and cut off the connector and strip the two wires?
also about whats the avage mA you should have for a breadboard power supply? just the higher amps the wall wart the better?
cuz if so i also this gamecube one thats 12v 3amp
 

giftiger_wunsch

New Member
Well the higher the amps on the wall wart the more you'll be able to power with it, but I think it's unlikely you'll need a 3A supply. Depends what exactly you're powering.
 

Hero999

Banned
Wallwarts aren't always AC-DC, you can also get AC-DC and the SMPS type will do DC-DC conversion as well.
 

Torben

Well-Known Member
Well the higher the amps on the wall wart the more you'll be able to power with it, but I think it's unlikely you'll need a 3A supply. Depends what exactly you're powering.
Yeah--you probably don't want to run 3A on a breadboard anyway. :)


Torben
 

i am monster

New Member
whats the max amount of amps you can run on a breadboard with out damage?(just for furtue referance)

also do they sell wall warts that are designed for breadboards with like varible voltages and varible mA settings?
 

giftiger_wunsch

New Member
I'd think the answer to that would be specific to the breadboard: see if there are any max power ratings listed. I haven't used one before (though I plan to use one soon now that I have found out that they are ;) ) but given their function it seems more likely that the components in use are more likely to be damaged by excessive current than the breadboard itself: from my understanding of it it's just a low-resistance board which enables circuits to be constructed easily and changed easily. It's a bit like asking the max current for a wire: i'd imagine it varies.

I'd recommend waiting for someone else's reply though, as my signature states, I'm an electonics noob :p
 

confounded

New Member
I think you'd need a bench top supply or you'd need to build your own in order to get variable current limiting.

If you just want a cheap variable DC voltage source, this power supply is switchable between 1.5, 3, 4.5, 6, 7.5, 9 and 12V DC

--|MWS893UK|ADAPTOR, REG ADJ 300MA UK | CPC

but if you want to get anything from cpc you got spend over £45 (ex vat) or pay delivery and handling charge

(and they show prices ex vat)
 
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MikeMl

Well-Known Member
Most Helpful Member
Just to clear up some confusion: Assume that your load (breadboard or whatever) is rated at 12V, 500mA. You could run this load with a power-supply rated at 12V 100A, or a car battery (which is about 12.6V) but capable of delivering 1200A (Cold Cranking Current rating) and your load would still only DRAW a maximum of 500mA!!!!

Think of it this way: 12V is the CAUSE, 500mA is the EFFECT. The load knows nothing about how much current the supply can DELIVER, it only draws what it needs off the supply. The supplies' job is to keep the voltage constant at 12V, and for that to happen, it needs to deliver a minimum of 500mA.

Nobody cares if the supply is capable of delivering more than 500mA, unless you accidentally create a short circuit or miswire your circuit. That is why supplies used for lab work usually have built-in current limiting, so that you can set the current limiter a bit higher than your circuit under test will draw, thereby limiting the amount of smoke in case you screw up!
 

giftiger_wunsch

New Member
Just to clear up some confusion: Assume that your load (breadboard or whatever) is rated at 12V, 500mA. You could run this load with a power-supply rated at 12V 100A, or a car battery (which is about 12.6V) but capable of delivering 1200A (Cold Cranking Current rating) and your load would still only DRAW a maximum of 500mA!!!!

Think of it this way: 12V is the CAUSE, 500mA is the EFFECT. The load knows nothing about how much current the supply can DELIVER, it only draws what it needs off the supply. The supplies' job is to keep the voltage constant at 12V, and for that to happen, it needs to deliver a minimum of 500mA.

Nobody cares if the supply is capable of delivering more than 500mA, unless you accidentally create a short circuit or miswire your circuit. That is why supplies used for lab work usually have built-in current limiting, so that you can set the current limiter a bit higher than your circuit under test will draw, thereby limiting the amount of smoke in case you screw up!

Very well explained, I apologise if my comments caused confusion about this.


As MikeMl says, using a 3A wall-wart isn't an issue; the voltage is the important factor, since the 3A indicates the maximum that the wall-wart can deliver: the actual current passing through your breadboard is determined by the voltage provided by the wall-wart, and the resistance of the circuit, as defined by ohm's law. It just seems unnecessary to use a wall-wart with a 3A max output unless you know that a particular component will require a current approaching this value.

As I said, check to see if you can find a max power rating listed on your breadboard.
 

im_in_asia_now

New Member
What kind of transformers are used in wall warts?

pic:

DSC00541.JPG

DSC00542.JPG

Are they simply iron-core transformers? why do they generate so much heat? Thanks

edit: I'm talking about step down transformers in AC-DC wall warts.
 
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MikeMl

Well-Known Member
Most Helpful Member
They are made with loose magnetic coupling from primary to secondary. As part of UL/CSA certification, they cannot catch fire if the secondary is shorted, so to limit the primary and secondary current, the coupling coefficient is purposely reduced way below what a "normal" power transformer would have...
 

Torben

Well-Known Member
Just to clear up some confusion: Assume that your load (breadboard or whatever) is rated at 12V, 500mA. You could run this load with a power-supply rated at 12V 100A, or a car battery (which is about 12.6V) but capable of delivering 1200A (Cold Cranking Current rating) and your load would still only DRAW a maximum of 500mA!!!!

Think of it this way: 12V is the CAUSE, 500mA is the EFFECT. The load knows nothing about how much current the supply can DELIVER, it only draws what it needs off the supply. The supplies' job is to keep the voltage constant at 12V, and for that to happen, it needs to deliver a minimum of 500mA.

Nobody cares if the supply is capable of delivering more than 500mA, unless you accidentally create a short circuit or miswire your circuit. That is why supplies used for lab work usually have built-in current limiting, so that you can set the current limiter a bit higher than your circuit under test will draw, thereby limiting the amount of smoke in case you screw up!
Hi Mike,

Just to clear up my own confusion (please humour me :) ):

Is it not also the case that while the above is very true, you can still damage a circuit by using an apparently appropriately-rated power supply which both a) has a sufficiently higher amp rating than needed and b) is unregulated? In this case it would seem to me that that voltage would not sag to the rated level when presented with the too-light load, and the load would then see too high a voltage and could be damaged (or at least operate incorrectly).

Say a basic 9VDC unregulated supply rated at 1A was used to power a circuit requiring 9VDC but only 30mA. The voltage would then be well over 9VDC.

I'm thinking this might not be a problem in a lot of cases, but could be something to look out for.

Am I totally hooped here?


Regards,

Torben
 

audioguru

Well-Known Member
Most Helpful Member
Say a basic 9VDC unregulated supply rated at 1A was used to power a circuit requiring 9VDC but only 30mA. The voltage would then be well over 9VDC.
I think the voltage will be 10V to 12V.
If the wall-wart was small with a rated current of only 100mA then its voltage without a load or with a low load will be 18V or more.

A high current transformer is strong with low resistance windings which allows it to have pretty good voltage regulation.
A low current transformer is just a very thin wire with lots of resistance so has poor voltage regulation.
 

Torben

Well-Known Member
I think the voltage will be 10V to 12V.
If the wall-wart was small with a rated current of only 100mA then its voltage without a load or with a low load will be 18V or more.

A high current transformer is strong with low resistance windings which allows it to have pretty good voltage regulation.
A low current transformer is just a very thin wire with lots of resistance so has poor voltage regulation.
Hey, thanks! That actually makes sense to me. I'll need to do some more reading but I think I see where you're going with that.

So my '1A' implied that the transformer in the supply would have better regulation because it would tend to be beefier, and that the danger is actually greater when using a supply with a lower-rated (i.e. smaller but still over-rated for the load) transformer. Non-intuitive but good to know.

Transformers and inductors are still a bit of a black art to me so this kind of info is golden.


Thanks again,

Torben
 
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