[Noisebridge-discuss] How close do I need to get with amperage?

[Steve Castellotti]

On 12/21/2012 10:42 AM, Andy Isaacson wrote:
> On Thu, Dec 20, 2012 at 07:32:37PM -0500, rachel lyra hospodar wrote:
>> I have a piece of audio gear (roland micro cube) that requires 9v & 185 mA
>> .  I scored a power supply that supplies 200 mA but am wondering if it's
>> safe to use or if it might fry the amp?
> With off-the-shelf power supplies you are fine up to at least 2x.  The
> reason is, the power supply is designed to reliably run very close to
> the rated voltage.  The current is variable depending on the load to
> preserve the accuracy of the voltage level.
>
> There is an alternate kind of power supply known as "constant current"
> which varies the voltage instead.  The nice "bench" power supply at
> Noisebridge can operate in this mode, and there are some kinds of
> circuits that need it, for example somebody told me that EL wire
> transformers are constant current.
>
> Any commercial power supply that says "9 volts DC, 200 mA" is a constant
> voltage supply.
>
> If your load is *really* low, like if you try to use a 2000 mA (2 amp)
> supply to power a device that only uses 10 mA, then you might see
> problems (voltage variations mostly).  A sufficiently fragile device
> might be damaged that way.

     Late reply to the thread but just wanted to state that a year or so 
ago I blew through several batteries for a radio-controlled helicopter 
by using an AC/DC adapter which had too high of an amperage. I don't 
have the bits handy at the moment but I'm pretty sure it was less than 
50% over what the charger was rated for.

     It was the kind which would use 4 AA batteries to power the 
charger, or there was a AC/DC power source optional. I had the voltage 
right for certain but didn't know anything was amiss until my 
helicopters wouldn't fly and I noticed the batteries were getting swollen.

     I ended up sticking to only charging from the AA's and have been 
fine since.


sc