Dave W wrote:

On Sat, 22 Jun 2019 17:24:05 +0100, Clive Arthur
wrote:

On 21/06/2019 15:19, Graeme wrote:

I have a 12v aquarium pump supplied by a 12v power supply, but, for my
purposes, the pump performs ideally when running at 6v. Can I just put
a resistor between the power supply and pump, to reduce the voltage, and
if so, how do I calculate which resistor I need? Perhaps there is a
better way?

6V zener diode. I have a shed load of surplus 3.3V 5W zeners, two in
series would get you down to 5.4V. I could send you some if I knew where...

Cheers

I found this alternative supplier who rates the pump at 12V 250mA:
https://www.deltakit.net/product/12v...-vacuum-pump-f
or-aquarium-tank-oxygen-circulate/ So assuming it would take 125mA at 6V,
the zener would dissipate 750mW so a 1W zener would do. 3V zeners don't
have very sharp voltage curves so I wouldn't recommend them.

I have no direct experience, but I would expect a diaphragm pump to be
lime a buzzer - a very non-linear device both in current and output lfow
terms. Below a certain voltage it will probably draw more current than
usual and get hot, with zero output. And as the voltage rises it will
start working with near full current (or more) and output.

--

Roger Hayter