# Question about power adapters, specifically 12V - 500mA



## jproffer (Feb 19, 2005)

This would be kind of a cross forum question I guess, but it has more to do with the electrical side than the other, so here goes....

I have a jump starter and have lost the original charger. The unit says it needs 12V-500mA...I know I could just buy one that's exactly that, and I will if I need to, but I dug around the house and found a couple that are close to what it needs. Found one that is a multi-voltage charger, 1200mA max...the lowest voltage it puts out is 3, so I'm assuming at 12V it would be 300mA. I also have one that is 12V-1A. So now finally to the question....

Would it be better to use (if either) the 12V-1A charger because the J/S is only going to draw what it needs no matter what the charger CAN put out?....or would it be better to use the (dial-a-voltage) 12V-300mA charger because it isn't over the J/S's rated amperage?

If you think it would be bad for the unit to use either one of them, I'll go buy a 12V-500mA charger...they're not expensive, but I figured since I already have these............


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## SemiRetiredEL (Nov 24, 2009)

I would go w/ the 12v 1A. You never know how their voltage selector will react to a 12V 1/2A load.


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## jproffer (Feb 19, 2005)

Sounds good....and makes sense. 

So is it safe to assume that the J/S will only draw whatever it needs??

I know in home elec. if you plug an appliance that only needs 5A into a 15A receptacle.....it only draws what it needs.......but is a DC battery pack the same?

Assuming that, theoretically I could use a 12V-5A or 10A and it wouldn't hurt anything?? Just thinking outloud....am I understanding correctly?


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## WarriorWithWood (Jun 30, 2007)

yes.


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## jproffer (Feb 19, 2005)

Good deal....I'll use the 1A.

Thank you gentlemen :thumbsup:


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## jproffer (Feb 19, 2005)

OK...another question regarding the same situation....

I also have (found) a 13.5V - 500mA charger...so now I'm wondering which is better...to be over a little on the voltage, or over a little on the amperage.?

Am I putting too much thought into this? LOL, probably so......just curious which is better as a general rule (short of having the exact right output).


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## Tinstaafl (Jan 6, 2008)

The big question I don't see being asked/answered here, is whether you need a _charger_ or a _power supply_.

Most commonly, the "wall wart" is just a power supply, and any charging circuitry is located in the device to be charged. If that's the case here, an extra volt or so, or excess current capacity would be quite acceptable. You just don't want to go smaller on either number. :thumbsup:


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## jproffer (Feb 19, 2005)

> The big question I don't see being asked/answered here, is whether you need a charger or a power supply.


Hmmmm....good question.....I think I know what you mean...a power supply would be similar to one for a laptop right?...one cord going in, then the magical box does it's thing, then another cord coming out.

I have what is shown in the picture...if I'm thinking right, the transformer is contained in the box or "wall-wart" as you called it (I like it BTW, lol).

Mine isn't exactly what is shown, the ones I have are either 12V or 13.5V and either 300, 500, or 1000 mA.


And to add this to the mix....that is what I have now. I don't remember what the J/S came with originally, but I would imagine it was similar to the one shown.


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## Tinstaafl (Jan 6, 2008)

jproffer said:


> Hmmmm....good question.....I think I know what you mean...a power supply would be similar to one for a laptop right?...one cord going in, then the magical box does it's thing, then another cord coming out.


A laptop/notebook power supply is similar in function to the pic you show, but normally has extra circuitry in it to produce well regulated and smooth DC. Wall warts (as in the pic) generally contain nothing more than a transformer and 2-4 diodes, producing "rough" DC.

If your starter:

(A) Has a jack labeled 12V/500ma
(B) Came with a wall wart like the pic

Then you can use a wall wart that provides 12-14V and 500 ma or more. The starter will contain internal circuitry to regulate the charging _current_, which is the critical element rather than voltage alone.

And yes, you're overthinking it. :thumbsup:


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## jproffer (Feb 19, 2005)

> And yes, you're overthinking it.


I figured I was...just seeking general info. Not that I want to mess up the J/S either, but was more interested in if my thinking was correct....(that amperage is a PULL by the device being charged....instead of a PUSH to the device - situation)

Thanks to all of you for the insight :thumbup:


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