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?
--
Graeme

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.

Then Volts / Amps = R of the pump in Ohms, and place the same R in series.

Power rating of resistor Watts = Amps * Volts

Owain

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

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.

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

AB

On 21/06/2019 16:25, 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

Well maybe.

Or you could put a car light bulb in series, that will have low
resistance for starting and higher once it gets warm. I think I would
probably try a headlamp bulb for a start.

You don't say whether you have a suitable multimeter (I guess perhaps
not). There should be a current rating on the power supply, though,
which will assist us in doing sums. Or possibly a power rating. Is there
any "spec" on the pump?

On Fri, 21 Jun 2019 16:37:31 +0100, newshound
wrote:

On 21/06/2019 16:25, 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

Well maybe.

Or you could put a car light bulb in series, that will have low
resistance for starting and higher once it gets warm. I think I would
probably try a headlamp bulb for a start.

You don't say whether you have a suitable multimeter (I guess perhaps
not). There should be a current rating on the power supply, though,
which will assist us in doing sums. Or possibly a power rating. Is there
any "spec" on the pump?

I'm intrigued. Current rating on the PSU?

That's deep!!

Why the hell do people that are totally clueless pop up with their
stupid advice?

If you don't have a clue, post nothing, just read and learn.

AB

In message ,
writes
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.

Thank you all. This is potentially rather more complicated (and
expensive!) than envisaged. The pump is eBay item 283477907575, three
quid from China, including postage. It works perfectly, but too well
for my needs. I just want a fairly gentle jet of air to turn a fan
(don't ask), and whilst the pump works, it makes the fan spin rather
than gently rotate. I've tried various combinations of angle of jet,
moving the jet around etc., but the best results are when the pump is
running on 6 - 8v. I could try running the pump at 12v and restricting
the flow out of the pipe, but worry that could overload the motor?
--
Graeme

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

Just found a control valve for 99p which could be the answer. Worth
trying at that price, anyway.

--
Graeme

On 21/06/2019 16:08, 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.

Then Volts / Amps = R of the pump in Ohms, and place the same R in series.

Power rating of resistor Watts = Amps * Volts

Owain

Unfortunately thats not so good either as

(a) the resistor will get hot and (b) it limits stall current and
starting torque

Get a 6V supply

Or a 5-6V output downconverter.

That is something we use in the RC model world a LOT

https://www.amazon.co.uk/SODIAL-Hobb...dp/B00K67Y00S/


Is 3A enough to start the motor

Anyway search for UBEC to get similar products


--
Future generations will wonder in bemused amazement that the early
twenty-first centurys developed world went into hysterical panic over a
globally average temperature increase of a few tenths of a degree, and,
on the basis of gross exaggerations of highly uncertain computer
projections combined into implausible chains of inference, proceeded to
contemplate a rollback of the industrial age.

Richard Lindzen

On 21/06/2019 18:49, Graeme wrote:
In message ,
writes
On Friday, 21 June 2019 15:27:57 UTC+1, GraemeÂ* 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.Â* 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.

Thank you all.Â* This is potentially rather more complicated (and
expensive!) than envisaged.Â* The pump is eBay item 283477907575, three
quid from China, including postage.

**** Ive got doezens of those motors but all 6V 0nes for model planes


It works perfectly, but too well
for my needs.Â* I just want a fairly gentle jet of air to turn a fan
(don't ask), and whilst the pump works, it makes the fan spin rather
than gently rotate.Â* I've tried various combinations of angle of jet,
moving the jet around etc., but the best results are when the pump is
running on 6 - 8v.Â* I could try running the pump at 12v and restricting
the flow out of the pipe, but worry that could overload the motor?

Mm. RC speed controller + RC servo adjuster BUT you are spending WAY
mnopre than you want to


--
Karl Marx said religion is the opium of the people.
But Marxism is the crack cocaine.

Graeme wrote:

In message ,
writes
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.

Thank you all. This is potentially rather more complicated (and
expensive!) than envisaged. The pump is eBay item 283477907575, three
quid from China, including postage. It works perfectly, but too well
for my needs. I just want a fairly gentle jet of air to turn a fan
(don't ask), and whilst the pump works, it makes the fan spin rather
than gently rotate. I've tried various combinations of angle of jet,
moving the jet around etc., but the best results are when the pump is
running on 6 - 8v. I could try running the pump at 12v and restricting
the flow out of the pipe, but worry that could overload the motor?

Why not arrange a variable air leak? Put a tee in the output line,
near the pump, and a little plastic valve on the side arm of the tee
that you can open varying amounts to reduce the amount of air getting to
the output end of the pipe. Doesn't load the motor and can be varied
at will.
--

Roger Hayter

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.Â* 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?Â* Perhaps there is a
better way?


Is it 12V DC or 12V AC?

Diaphragm pumps are usually AC which limits what you can easily do.

"dennis@home" wrote in message
...
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?


Is it 12V DC or 12V AC?

Diaphragm pumps are usually AC which limits what you can easily do.

Easy to do a 2:1 transformer, but much cheaper to bleed some of the air.

On Sat, 22 Jun 2019 09:41:13 +1000, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:


Easy to do a 2:1 transformer, but much cheaper to bleed some of the air.

Trust me, my senile punching bag, I will make YOU bleed here yet a lot more!
LOL

--
about senile Rot Speed:
"This is like having a conversation with someone with brain damage."
MID:

On 21/06/2019 18:49, Graeme wrote:
In message ,
writes
On Friday, 21 June 2019 15:27:57 UTC+1, GraemeÂ* 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.Â* 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.

Thank you all.Â* This is potentially rather more complicated (and
expensive!) than envisaged.Â* The pump is eBay item 283477907575, three
quid from China, including postage.Â* It works perfectly, but too well
for my needs.Â* I just want a fairly gentle jet of air to turn a fan
(don't ask), and whilst the pump works, it makes the fan spin rather
than gently rotate.Â* I've tried various combinations of angle of jet,
moving the jet around etc., but the best results are when the pump is
running on 6 - 8v.Â* I could try running the pump at 12v and restricting
the flow out of the pipe, but worry that could overload the motor?

OK that does not look like a significant current draw.

How about this approach: get yourself a pack of silicon rectifier
diodes[1], and add a bunch of them in series with the power supply. Each
will drop around 0.6 to 0.7 volts, and unlike a resistor will not
exbibit a voltage drop that changes with load. You can then "tune" the
performance by adding diodes until you get the level of performance
required.


[1] https://ebay.us/SjzTP8

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In message , Roger Hayter
writes

Why not arrange a variable air leak? Put a tee in the output line,
near the pump, and a little plastic valve on the side arm of the tee
that you can open varying amounts to reduce the amount of air getting to
the output end of the pipe. Doesn't load the motor and can be varied
at will.

I like that. Thank you.
--
Graeme

In message , John
Rumm writes

How about this approach: get yourself a pack of silicon rectifier
diodes[1], and add a bunch of them in series with the power supply.
Each will drop around 0.6 to 0.7 volts, and unlike a resistor will not
exbibit a voltage drop that changes with load. You can then "tune" the
performance by adding diodes until you get the level of performance
required.

Another simple, straightforward approach (and cheap!). Thanks.
--
Graeme

In message , "dennis@home"
writes

Is it 12V DC or 12V AC?

DC.
--
Graeme

On 22/06/2019 06:54, Graeme wrote:
In message , "dennis@home"
writes

Is it 12V DC or 12V AC?

DC.

Just buy a universal PSU with adjustable outputs like

https://smile.amazon.co.uk/Panda-Pow.../dp/B00VIJZOB2

Or

use a buck converter like

https://smile.amazon.co.uk/Converter.../dp/B07H32G7CX

They are dirt cheap from china but you do need to solder and use a
voltmeter to set the voltage if you want to know what it is.

You still need a power brick to get the input.

Looking at the actual pump you have I doubt if it can over aerate even a
small tank left on 12V.

I'd imagine there is.
What you would need to know is the current used by the pump to do this by
resistor, but personally I'd just go out and get a 6v psu, indeed if its not
too much a 5v USB double output psu might do it.
I'm a little worried though why they would make a pump that runs too fast?
Surely most pumps rely on the flow to keep them unclogged to some extent.
Slowing one down seems to cause issues. I used to have a drill operated pump
for watering the garden from the rainwater but, and if you used a slower
speed the pump clogged.
Those I think were centrifugal pumps, I don't know what yours is.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Graeme" wrote in message
...

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?
--
Graeme

Not that long ago, modern pwm controllers started to come in for Scalextric
and model railway speed controllers. These did not get very warm , so were
quite efficient, but fed the motor with 12v in short bursts. Thus no
decrease in power or torque but a slower running speed.
I've never tried one but suspect the modules mentioned are based around
similar devices.
You cold use a normal regulator chip but like the resistive approach they
waste power though heat generation, ie dumping the extra voltage by
dissipating it as heat.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"newshound" wrote in message
o.uk...
On 21/06/2019 16:25, 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

Well maybe.

Or you could put a car light bulb in series, that will have low resistance
for starting and higher once it gets warm. I think I would probably try a
headlamp bulb for a start.

You don't say whether you have a suitable multimeter (I guess perhaps
not). There should be a current rating on the power supply, though, which
will assist us in doing sums. Or possibly a power rating. Is there any
"spec" on the pump?

In article ,
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?

Not the best idea. Motors generally need a low impedance supply to develop
their best starting up torque, etc. PWM is probably a better way - but
likely to cost more than the correct PS.

--
*What boots up must come down *

Dave Plowman London SW
To e-mail, change noise into sound.

On 21/06/2019 18:49, Graeme wrote:

Thank you all.Â* This is potentially rather more complicated (and
expensive!) than envisaged.Â* The pump is eBay item 283477907575, three
quid from China, including postage.Â* It works perfectly, but too well
for my needs.Â* I just want a fairly gentle jet of air to turn a fan
(don't ask), and whilst the pump works, it makes the fan spin rather
than gently rotate.Â* I've tried various combinations of angle of jet,
moving the jet around etc., but the best results are when the pump is
running on 6 - 8v.Â* I could try running the pump at 12v and restricting
the flow out of the pipe, but worry that could overload the motor?

Could you reduce the efficiency of the fan by bending or clipping the
blades?

Bill

In message , Bill Wright
writes

Could you reduce the efficiency of the fan by bending or clipping the
blades?

Tried that Bill, but it doesn't make enough difference.
--
Graeme

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.Â* 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?Â* 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
--
Clive

On 22/06/2019 13:30, Graeme wrote:
In message , Bill Wright
writes

Could you reduce the efficiency of the fan by bending or clipping the
blades?

Tried that Bill, but it doesn't make enough difference.

Well how about a variable PSU? Too expensive I suppose.

Bill

On 22/06/2019 19:04, Bill Wright wrote:
On 22/06/2019 13:30, Graeme wrote:
In message , Bill Wright
writes

Could you reduce the efficiency of the fan by bending or clipping the
blades?

Tried that Bill, but it doesn't make enough difference.

Well how about a variable PSU? Too expensive I suppose.

Bill


Model plane ESC and a model plane servo tester will allow variable
control of the motor from nothing to full but you are talking over £10

https://www.robotbirds.co.uk/default...ushed-esc.html

https://www.robotbirds.co.uk/default/servo-tester.html


--
€œIt is dangerous to be right in matters on which the established
authorities are wrong.€�

ۥ Voltaire, The Age of Louis XIV

On Saturday, 22 June 2019 04:18:25 UTC+1, John Rumm wrote:
On 21/06/2019 18:49, Graeme wrote:
In message ,
writes
On Friday, 21 June 2019 15:27:57 UTC+1, GraemeÂ* 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.Â* 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.

Thank you all.Â* This is potentially rather more complicated (and
expensive!) than envisaged.Â* The pump is eBay item 283477907575, three
quid from China, including postage.Â* It works perfectly, but too well
for my needs.Â* I just want a fairly gentle jet of air to turn a fan
(don't ask), and whilst the pump works, it makes the fan spin rather
than gently rotate.Â* I've tried various combinations of angle of jet,
moving the jet around etc., but the best results are when the pump is
running on 6 - 8v.Â* I could try running the pump at 12v and restricting
the flow out of the pipe, but worry that could overload the motor?

OK that does not look like a significant current draw.

How about this approach: get yourself a pack of silicon rectifier
diodes[1], and add a bunch of them in series with the power supply. Each
will drop around 0.6 to 0.7 volts, and unlike a resistor will not
exbibit a voltage drop that changes with load. You can then "tune" the
performance by adding diodes until you get the level of performance
required.


[1] https://ebay.us/SjzTP8

that's what I'd do, but diodes passing power drop nearer a volt each, sometimes more. 0.65v is the knee voltage not the running voltage at highish current.


NT

On 22/06/2019 23:01, wrote:
On Saturday, 22 June 2019 04:18:25 UTC+1, John Rumm wrote:
On 21/06/2019 18:49, Graeme wrote:
In message ,
writes
On Friday, 21 June 2019 15:27:57 UTC+1, GraemeÂ* 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.Â* 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.

Thank you all.Â* This is potentially rather more complicated (and
expensive!) than envisaged.Â* The pump is eBay item 283477907575, three
quid from China, including postage.Â* It works perfectly, but too well
for my needs.Â* I just want a fairly gentle jet of air to turn a fan
(don't ask), and whilst the pump works, it makes the fan spin rather
than gently rotate.Â* I've tried various combinations of angle of jet,
moving the jet around etc., but the best results are when the pump is
running on 6 - 8v.Â* I could try running the pump at 12v and restricting
the flow out of the pipe, but worry that could overload the motor?

OK that does not look like a significant current draw.

How about this approach: get yourself a pack of silicon rectifier
diodes[1], and add a bunch of them in series with the power supply. Each
will drop around 0.6 to 0.7 volts, and unlike a resistor will not
exbibit a voltage drop that changes with load. You can then "tune" the
performance by adding diodes until you get the level of performance
required.


[1] https://ebay.us/SjzTP8

that's what I'd do, but diodes passing power drop nearer a volt each, sometimes more. 0.65v is the knee voltage not the running voltage at highish current.


It would be better to use a regulator. Look he

https://www.ebay.co.uk/sch/i.html?_f...lator&_sacat=0

Select on that gives the more than the current you need at 6V

You could possibly try a 9V one, or look for an 8V one but they aren't
common.

I use versions of these regulators in several applications.







--
Always smile when walking, you never know where there is a camera ;-)

Remarkable Coincidences:
The Stock Market Crashes of 1929 and 2008 happened on the same
date in October. In Oct 1907, a run on the Knickerbocker Trust
Company led to the Great Depression.

On Fri, 21 Jun 2019 15:19:01 +0100
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?

Just get a 6V power supply with adequate current - it will probably
waste less energy as heat than any lash-up you're likely to cobble onto
the existing one.

On Fri, 21 Jun 2019 18:49:34 +0100, Graeme
wrote:

In message ,
writes
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.

Thank you all. This is potentially rather more complicated (and
expensive!) than envisaged. The pump is eBay item 283477907575, three
quid from China, including postage. It works perfectly, but too well
for my needs. I just want a fairly gentle jet of air to turn a fan
(don't ask), and whilst the pump works, it makes the fan spin rather
than gently rotate. I've tried various combinations of angle of jet,
moving the jet around etc., but the best results are when the pump is
running on 6 - 8v. 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?
--
Dave W

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...gen-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.
--
Dave W

On 22/06/2019 23:01, wrote:
On Saturday, 22 June 2019 04:18:25 UTC+1, John Rumm wrote:
On 21/06/2019 18:49, Graeme wrote:
In message
,
writes
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.

Thank you all. This is potentially rather more complicated (and
expensive!) than envisaged. The pump is eBay item 283477907575,
three quid from China, including postage. It works perfectly,
but too well for my needs. I just want a fairly gentle jet of
air to turn a fan (don't ask), and whilst the pump works, it
makes the fan spin rather than gently rotate. I've tried various
combinations of angle of jet, moving the jet around etc., but the
best results are when the pump is running on 6 - 8v. I could try
running the pump at 12v and restricting the flow out of the pipe,
but worry that could overload the motor?

OK that does not look like a significant current draw.

How about this approach: get yourself a pack of silicon rectifier
diodes[1], and add a bunch of them in series with the power supply.
Each will drop around 0.6 to 0.7 volts, and unlike a resistor will
not exbibit a voltage drop that changes with load. You can then
"tune" the performance by adding diodes until you get the level of
performance required.


[1] https://ebay.us/SjzTP8

that's what I'd do, but diodes passing power drop nearer a volt each,
sometimes more. 0.65v is the knee voltage not the running voltage at
highish current.

Indeed, but its hardly an exact science in this case - we don't really
know what voltage the motor is going to work at the required speed and
still start under load etc. Adding or subtracting cheap diodes should be
a fairly quick empirical exercise in finding the optimal number.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 23/06/2019 00:44, John Rumm wrote:
On 22/06/2019 23:01, wrote:
On Saturday, 22 June 2019 04:18:25 UTC+1, John RummÂ* wrote:
On 21/06/2019 18:49, Graeme wrote:
In message
,
writes
On Friday, 21 June 2019 15:27:57 UTC+1, GraemeÂ* 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.Â* 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.

Thank you all.Â* This is potentially rather more complicated (and
expensive!) than envisaged.Â* The pump is eBay item 283477907575,
three quid from China, including postage.Â* It works perfectly,
but too well for my needs.Â* I just want a fairly gentle jet of
air to turn a fan (don't ask), and whilst the pump works, it
makes the fan spin rather than gently rotate.Â* I've tried various
combinations of angle of jet, moving the jet around etc., but the
best results are when the pump is running on 6 - 8v.Â* I could try
running the pump at 12v and restricting the flow out of the pipe,
but worry that could overload the motor?

OK that does not look like a significant current draw.

How about this approach: get yourself a pack of silicon rectifier
diodes[1], and add a bunch of them in series with the power supply.
Each will drop around 0.6 to 0.7 volts, and unlike a resistor will
not exbibit a voltage drop that changes with load. You can then
"tune" the performance by adding diodes until you get the level of
performance required.


[1] https://ebay.us/SjzTP8

that's what I'd do, but diodes passing power drop nearer a volt each,
sometimes more. 0.65v is the knee voltage not the running voltage at
highish current.

Indeed, but its hardly an exact science in this case - we don't really
know what voltage the motor is going to work at the required speed and
still start under load etc. Adding or subtracting cheap diodes should be
a fairly quick empirical exercise in finding the optimal number.


By th time you have bought all those resistors and diodes it would be as
easy to buy a model plane controller with a servo tester.


--
€œProgress is precisely that which rules and regulations did not foresee,€�

€“ Ludwig von Mises

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. A cheap inline
restriction valve is on the way, and the plan is to cut the tube and
insert a three way connector, with the valve connected to one of the
outlets, to control the amount of air exiting the business end.

There have been some interesting suggestions (thanks!), and I like
John's pack of silicon rectifier diodes, as they will be useful
elsewhere.

The pump is picking up power from a 12v bus bar, and I would prefer that
option, although could run a dedicated variable supply via a toy train
controller or similar, but am trying to avoid that option.

--
Graeme

On 23/06/2019 08:46, The Natural Philosopher wrote:
On 23/06/2019 00:44, John Rumm wrote:
On 22/06/2019 23:01, wrote:
On Saturday, 22 June 2019 04:18:25 UTC+1, John RummÂ* wrote:
On 21/06/2019 18:49, Graeme wrote:
In message
,
writes
On Friday, 21 June 2019 15:27:57 UTC+1, GraemeÂ* 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.Â* 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.

Thank you all.Â* This is potentially rather more complicated (and
expensive!) than envisaged.Â* The pump is eBay item 283477907575,
three quid from China, including postage.Â* It works perfectly,
but too well for my needs.Â* I just want a fairly gentle jet of
air to turn a fan (don't ask), and whilst the pump works, it
makes the fan spin rather than gently rotate.Â* I've tried various
combinations of angle of jet, moving the jet around etc., but the
best results are when the pump is running on 6 - 8v.Â* I could try
running the pump at 12v and restricting the flow out of the pipe,
but worry that could overload the motor?

OK that does not look like a significant current draw.

How about this approach: get yourself a pack of silicon rectifier
diodes[1], and add a bunch of them in series with the power supply.
Each will drop around 0.6 to 0.7 volts, and unlike a resistor will
not exbibit a voltage drop that changes with load. You can then
"tune" the performance by adding diodes until you get the level of
performance required.


[1] https://ebay.us/SjzTP8

that's what I'd do, but diodes passing power drop nearer a volt each,
sometimes more. 0.65v is the knee voltage not the running voltage at
highish current.

Indeed, but its hardly an exact science in this case - we don't really
know what voltage the motor is going to work at the required speed and
still start under load etc. Adding or subtracting cheap diodes should
be a fairly quick empirical exercise in finding the optimal number.


By th time you have bought all those resistors and diodes it would be as
easy to buy a model plane controller with a servo tester.

No need for resistors, and the ebay diodes come in a pack of ten for
under 2 quid.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Saturday, 22 June 2019 23:34:46 UTC+1, Brian Reay wrote:
On 22/06/2019 23:01, tabbypurr wrote:
On Saturday, 22 June 2019 04:18:25 UTC+1, John Rumm wrote:
On 21/06/2019 18:49, Graeme wrote:
In message ,
writes
On Friday, 21 June 2019 15:27:57 UTC+1, GraemeÂ* 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.Â* 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.

Thank you all.Â* This is potentially rather more complicated (and
expensive!) than envisaged.Â* The pump is eBay item 283477907575, three
quid from China, including postage.Â* It works perfectly, but too well
for my needs.Â* I just want a fairly gentle jet of air to turn a fan
(don't ask), and whilst the pump works, it makes the fan spin rather
than gently rotate.Â* I've tried various combinations of angle of jet,
moving the jet around etc., but the best results are when the pump is
running on 6 - 8v.Â* I could try running the pump at 12v and restricting
the flow out of the pipe, but worry that could overload the motor?

OK that does not look like a significant current draw.

How about this approach: get yourself a pack of silicon rectifier
diodes[1], and add a bunch of them in series with the power supply. Each
will drop around 0.6 to 0.7 volts, and unlike a resistor will not
exbibit a voltage drop that changes with load. You can then "tune" the
performance by adding diodes until you get the level of performance
required.


[1] https://ebay.us/SjzTP8

that's what I'd do, but diodes passing power drop nearer a volt each, sometimes more. 0.65v is the knee voltage not the running voltage at highish current.


It would be better to use a regulator. Look he

https://www.ebay.co.uk/sch/i.html?_f...lator&_sacat=0

Select on that gives the more than the current you need at 6V

You could possibly try a 9V one, or look for an 8V one but they aren't
common.

I use versions of these regulators in several applications.

better in what way?

On Sunday, 23 June 2019 00:44:49 UTC+1, John Rumm wrote:
On 22/06/2019 23:01, tabbypurr wrote:
On Saturday, 22 June 2019 04:18:25 UTC+1, John Rumm wrote:
On 21/06/2019 18:49, Graeme wrote:
In message
,
writes
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.

Thank you all. This is potentially rather more complicated (and
expensive!) than envisaged. The pump is eBay item 283477907575,
three quid from China, including postage. It works perfectly,
but too well for my needs. I just want a fairly gentle jet of
air to turn a fan (don't ask), and whilst the pump works, it
makes the fan spin rather than gently rotate. I've tried various
combinations of angle of jet, moving the jet around etc., but the
best results are when the pump is running on 6 - 8v. I could try
running the pump at 12v and restricting the flow out of the pipe,
but worry that could overload the motor?

OK that does not look like a significant current draw.

How about this approach: get yourself a pack of silicon rectifier
diodes[1], and add a bunch of them in series with the power supply.
Each will drop around 0.6 to 0.7 volts, and unlike a resistor will
not exbibit a voltage drop that changes with load. You can then
"tune" the performance by adding diodes until you get the level of
performance required.


[1] https://ebay.us/SjzTP8

that's what I'd do, but diodes passing power drop nearer a volt each,
sometimes more. 0.65v is the knee voltage not the running voltage at
highish current.

Indeed, but its hardly an exact science in this case - we don't really
know what voltage the motor is going to work at the required speed and
still start under load etc. Adding or subtracting cheap diodes should be
a fairly quick empirical exercise in finding the optimal number.

indeed. Just don't go with an initial estimate that leaves the motor no power.


NT

On Sunday, 23 June 2019 00:06:25 UTC+1, 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.Â* 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?Â* 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...gen-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.

Motor starting current is many times run current. You can't overload zeners like that & expect them to last long if at all.


NT

On Sunday, 23 June 2019 12:56:05 UTC+1, John Rumm wrote:
On 23/06/2019 08:46, The Natural Philosopher wrote:

No need for resistors, and the ebay diodes come in a pack of ten for
under 2 quid.

Next time keep some e-waste and you won't need to spend or wait.


NT