Power supply too weak, any danger?

Question

I have a car console that i wanna test on my work bench. It's rated at 10A DC max @ 12v, but I don't plan on driving any speakers, so the draw should remain fairly low. My power supply can only provide 3A DC @ 12 volts. If the console DOES exceed the 3A draw, will it just not function properly, or could i stand a chance of damaging my power supply?

Also see http://electronics.stackexchange.com/q/34745/4512 – Olin Lathrop Jul 15 '12 at 20:58 — Olin Lathrop, Jul 15 '12 at 20:58

Oli Glaser · Accepted Answer · 2012-07-15T19:32:46.067

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It depends on the power supply. Some have protection against overcurrent, and some don't - it should advise in the manual/datasheet (if it has one).
Most decent quality supplies will have some form of protection (current limiting, thermal cutout, fuse) and withstand at least temporary overcurrents, and a good bench supply should withstand an indefinite short circuit.
Without knowing anything about your supply though, it's impossible to say.

EDIT - so it's "a charger from some old gadget".
In this case without opening it up you can't really tell what it will do if overloaded. Probably the output will just sag or trip off for a while, but it may do nasty stuff like overheat and catch fire if you're unlucky.

However, if you are not running any speakers from the amp, I rather doubt you will use 3 amps. Depending on the amp type (class A, AB, etc) it may draw very little current when not loaded. This info may be (should be) available in the manual.
I would test the quiescent current with a multimeter to see what it draws, it maybe possible to use the bench supply if the current is low enough - maybe do this to start with.

edited Jul 15 '12 at 19:32

answered Jul 15 '12 at 19:18

Oli Glaser

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I should note that by "power supply" i mean a charge from some old gadget, so i'm not sure these kind of things were accounted for – Alexander Jul 15 '12 at 19:19
My bench supply doesn't go past 1A =/ – Alexander Jul 15 '12 at 19:20
Could you join me in a chat rather than spamming out comments? :P – Alexander Jul 15 '12 at 19:22
http://chat.stackexchange.com/rooms/4123/power-supply-too-weak-any-danger – Alexander Jul 15 '12 at 19:23
@XAleXOwnZX - I just edited the answer with a couple of suggestions. – Oli Glaser Jul 15 '12 at 19:33
The specs sheet on their website only lists the peak current =/ – Alexander Jul 15 '12 at 19:35
Should i just try it and hope for no magic smoke? :P – Alexander Jul 15 '12 at 19:35
Yes I would, try with your bench supply first. Sorry I can't seem to log into the chat rooms for some strange reason (off for tea in a second anyway, will check back later for updates) – Oli Glaser Jul 15 '12 at 19:41
Heh all PC power supplies are "suppose" to handle an indefinite short(at least on the 3.3V line)... unfortunately not all power supplies are equal – Earlz Jul 15 '12 at 20:19

score 4 · Answer 2 · answered Jul 16 '12 at 06:48

Depends on the design quality of your power supply.

In the unlikely case of no overcurrent protection it will get hot and after a short time components will start to fail in a cascading way, so that seconds after the first one fails the whole power supply is gone.

If it has common current limiting the output voltage will remain at 12 V until 3 A is reached. From then on current will not increase, the regulator will decrease output voltage to avoid a further current increase. In the event when the output voltage drops to 0 V the power supply has to dissipate a lot of power, but it should be designed to do so for some time. The input will probably be at least 15 V, then the dissipation may go to 15 V x 3 A = 45 W.

current limiting

A more advanced power supply will use foldback current limiting, which solves the dissipation problem. When there's overcurrent it won't just keep on pouring out 3 A, but will decrease both voltage and current, so that internal dissipation remains limited. Normally a power supply cannot recover itself from a foldback current limit, and needs to be reset. Usually it will have a button for that, so you won't have to switch it off and on again.

It was a case of voltage drop, thanks! I'm actually rather surprised that a simple dashboard media console uses >3A without driving any speakers, using the disk drive, or even having the touch screen turn on — Alexander, Jul 16 '12 at 19:46

score 3 · Answer 3 · answered Jul 15 '12 at 19:18

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Your bench supply may get hot and electro. caps degrade quickly and have must shorter lives. If exceeded they can fail. Consider using a small SLA or lead acid in parallel to charge and operate the surges.

As long as battery charge V = 14.2 max, it will operate like a car.

answered Jul 15 '12 at 19:18

Tony Stewart EE75

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I should note that by "power supply" i mean a charge from some old gadget, so i'm not sure these kind of things were accounted for – Alexander Jul 15 '12 at 19:41
a quick measurement of temp. max hot spot 85'C inside on any component and max voltage on a battery should answer your doubt but my solution is simple and old car batteries are cheap to wire under the work bench. – Tony Stewart EE75 Jul 15 '12 at 19:48

Power supply too weak, any danger?

3 Answers3