Calculating the size of a resistor
 

On 23/06/2019 09:42, Graeme wrote:
In message , Dave W
writes

I could try running the pump at 12v and restricting
the flow out of the pipe, but worry that could overload the motor?

It seems to pump air not water, so instead of restricting it, perhaps
you could add a hole in the tube to let out unwanted air?

It does indeed pump air, and I assume, although haven't looked, it is
just a basic 12v DC motor driving an impeller.

They are usually diaphragm pumps. The Brrrrrr sound is the give-away.
May be a motor and crank, may be like a door-bell, i.e. a solenoid with
a breaker switch on the arm. Screen washers are often impeller, note the
higher frequency sound.

Calculating the size of a resistor
 

In message ,
newshound writes
On 23/06/2019 09:42, Graeme wrote:
It does indeed pump air, and I assume, although haven't looked, it
is just a basic 12v DC motor driving an impeller.

They are usually diaphragm pumps. The Brrrrrr sound is the give-away.
May be a motor and crank, may be like a door-bell, i.e. a solenoid with
a breaker switch on the arm. Screen washers are often impeller, note
the higher frequency sound.

Excellent, thank you.
--
Graeme

Calculating the size of a resistor
 

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

Calculating the size of a resistor
 

On 21/06/2019 16:32, Archibald Tarquin Blenkinsopp wrote:
On 21 Jun 2019 16:25:07 +0100 (BST), Theo
wrote:

wrote:
On Friday, 21 June 2019 15:27:57 UTC+1, 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?

You need to know the current taken by the pump.

...which will almost certainly not be constant. When the pump tries to
start, it'll take a big gulp of current. The resistor will thus drop the
voltage to very low, and it won't start.

A switching converter might help - things like these:
https://www.ebay.co.uk/itm/Durable-6.../113655869520?
https://www.ebay.co.uk/itm/5A-DC-DC-...K/312565786982
https://www.ebay.co.uk/itm/9A-DC-CC-...V/312612183383

but we don't know what the pump's ratings are to make any better
suggestions. You're probably better off with a PWM speed controller, for
example:
https://www.ebay.co.uk/itm/DC6-60V-1...w/401782991554
https://www.ebay.co.uk/itm/DC-PWM-Mo...V/202657320802

Theo

You are quite correct. The only thing I would suggest though is that
if the pump is happy at starting and running on 6V DC, a three
terminal regulator would be cheap.

From the following line we assume you mean a 5V 3-terminal regulator.

A couple of caps and lift the ground terminal up with two diodes. 6.2V

But 6V regs are just as cheap as 5V ones + 2x diodes.

Calculating the size of a resistor
 

On Wed, 26 Jun 2019 07:58:46 +0100, Grumps wrote:

On 21/06/2019 16:32, Archibald Tarquin Blenkinsopp wrote:
On 21 Jun 2019 16:25:07 +0100 (BST), Theo
wrote:

wrote:
On Friday, 21 June 2019 15:27:57 UTC+1, 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?

You need to know the current taken by the pump.

...which will almost certainly not be constant. When the pump tries to
start, it'll take a big gulp of current. The resistor will thus drop the
voltage to very low, and it won't start.

A switching converter might help - things like these:
https://www.ebay.co.uk/itm/Durable-6.../113655869520?
https://www.ebay.co.uk/itm/5A-DC-DC-...K/312565786982
https://www.ebay.co.uk/itm/9A-DC-CC-...V/312612183383

but we don't know what the pump's ratings are to make any better
suggestions. You're probably better off with a PWM speed controller, for
example:
https://www.ebay.co.uk/itm/DC6-60V-1...w/401782991554
https://www.ebay.co.uk/itm/DC-PWM-Mo...V/202657320802

Theo

You are quite correct. The only thing I would suggest though is that
if the pump is happy at starting and running on 6V DC, a three
terminal regulator would be cheap.

From the following line we assume you mean a 5V 3-terminal regulator.

A couple of caps and lift the ground terminal up with two diodes. 6.2V

But 6V regs are just as cheap as 5V ones + 2x diodes.

Times have moved on....!??

I bit my teeth on 7805's. I seem to recollect a 7812, but never went
to those ginagerous Voltage levels.

7805,s littered the toolbox as they do to this day, 'same for silicon
diodes.

AB

Calculating the size of a resistor
 

On Wednesday, 26 June 2019 16:07:25 UTC+1, Archibald Tarquin Blenkinsopp wrote:
On Wed, 26 Jun 2019 07:58:46 +0100, Grumps wrote:

On 21/06/2019 16:32, Archibald Tarquin Blenkinsopp wrote:
On 21 Jun 2019 16:25:07 +0100 (BST), Theo
wrote:

wrote:
On Friday, 21 June 2019 15:27:57 UTC+1, 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?

You need to know the current taken by the pump.

...which will almost certainly not be constant. When the pump tries to
start, it'll take a big gulp of current. The resistor will thus drop the
voltage to very low, and it won't start.

A switching converter might help - things like these:
https://www.ebay.co.uk/itm/Durable-6.../113655869520?
https://www.ebay.co.uk/itm/5A-DC-DC-...K/312565786982
https://www.ebay.co.uk/itm/9A-DC-CC-...V/312612183383

but we don't know what the pump's ratings are to make any better
suggestions. You're probably better off with a PWM speed controller, for
example:
https://www.ebay.co.uk/itm/DC6-60V-1...w/401782991554
https://www.ebay.co.uk/itm/DC-PWM-Mo...V/202657320802

Theo

You are quite correct. The only thing I would suggest though is that
if the pump is happy at starting and running on 6V DC, a three
terminal regulator would be cheap.

From the following line we assume you mean a 5V 3-terminal regulator.

A couple of caps and lift the ground terminal up with two diodes. 6.2V

But 6V regs are just as cheap as 5V ones + 2x diodes.

Times have moved on....!??

I bit my teeth on 7805's. I seem to recollect a 7812, but never went
to those ginagerous Voltage levels.

I have a 7806, 7809 and I had a 7824 somewhere.

I also have the 79 series which are negative regulators and the L series which were 100ma, niether of which we use much now.

Now I have 78S05 too which are rated at 2 amp rather than 1 amp.
some variable voltage like the LM317K, LM317T & LM317LZ.

and some LDOs which only need about 0.5V rather than 2+V on the i/p.
LD1117 which are 3.3V @ 800ma and even a surface mount 3.3V @ 250ma version.

The fun thing with the older 7805 is that if used above about 250ma they get very hot and without a heatsink they shutdown, cool and startup again.
The surface temperature gets to around 110C, it's amazing just how robust these sorts of things are.

Until a student gets hold of them ;-)





7805,s littered the toolbox as they do to this day, 'same for silicon
diodes.

AB