Reducing RPM on heating pump.

[wonderdust]

At the moment we have a Johson 12v magnet motor pump ( C010P5-1 ) for the central heating. This is not to noisy but on occasions when you want a bit of quite it can be distracting.

 

What I'm hoping for, is to find a way to slow the rpm on the 12v pump? I have tried a PWM from Maplins and although it does slow it down there is a high pitch noise doing this, has anyone tried this method, is there a fix for this problem?

 

I have thought about a pump by-pass as used on domestic systems but don't want to drain and cut into the pipework only to find it does not reduce the noise.

 

Or does anyone have any other suggestions.

 

Thanks in advance!

[koukouvagia]

At the moment we have a Johson 12v magnet motor pump ( C010P5-1 ) for the central heating. This is not to noisy but on occasions when you want a bit of quite it can be distracting.

 

What I'm hoping for, is to find a way to slow the rpm on the 12v pump? I have tried a PWM from Maplins and although it does slow it down there is a high pitch noise doing this, has anyone tried this method, is there a fix for this problem?

 

I have thought about a pump by-pass as used on domestic systems but don't want to drain and cut into the pipework only to find it does not reduce the noise.

 

Or does anyone have any other suggestions.

 

Thanks in advance!

 

Try sitting the pump on a foam pad - it'll cut down the whine considerably. Also my pump is noisy if there's any air in the system.

[WJM]

Mine makes a bit of a drone too. Would you not be worried that the boiler would overheat if you are drawing the water through it more slowly?

[wonderdust]

Mine makes a bit of a drone too. Would you not be worried that the boiler would overheat if you are drawing the water through it more slowly?

 

I don't see a problem slowing it down, at the moment it pumps about 12l per min. Thermo systems without pumps seem to manage ok.

[Keeping Up]

You can slow it down by wiring a 12 volt lightbulb in series with it. Sure it wastes a bit of power in the bulb - although it saves more than it wastes, as the current drain will still be less than with the full 12 volts across the pump.

 

Without knowing the rating of the pump I can't say what size bulb you need, but should easily be able to get about 6v across the bulb and 6v across the motor if you use a bit of trial and error. I'd suggest start with a bulb that is rated at about the same as the pump and work from there (it's not a simple calculation, the effective resistances of both the bulb and the pump are a complex variable of the applied voltage). Or just try any old bulb that you can and see what you get!

[WJM]

I am not an electrical engineer but; isn't that something you can do with a resistor or some other electrical device, thus avoiding the drain of running a light bulb needlessly?

[chris w]

What I'm hoping for, is to find a way to slow the rpm on the 12v pump? I have tried a PWM from Maplins and although it does slow it down there is a high pitch noise doing this, has anyone tried this method, is there a fix for this problem?

The whine you are hearing is the PWM frequency. It's chopping the 12v into square waves at a high frequency (probably around 500Hz) and varies the width of the pulses as you rotate its knob ( ) so that the average voltage is lower. So, if a pulse is 50% ON and 50% off, the average voltage is 6v rather than 12v. If it's 30% ON and 70% OFF, then the average voltage is around 4V and so on.

 

The advantage of a PWM is that it is highly efficient - usually around 95% - so no power is wasted; it's either switched fully ON or fully OFF. This means its output transistors are either fully ON so delivering high current with no volts across them (= zero power) or are switched fully OFF so having 12v across them at zero current (= zero power). So, the output transistors run cool and don't waste power in heating up.

 

The problem is that with poor design, you will hear a whine because something is vibrating at the PWM frequency - either a component (maybe an inductor) in the PWM device itself or something inside the motor. You didn't say from which one the whine is coming.

 

Allan's idea with the bulb will solve the problem of the whine at the expense of less efficiency. - you pays yer money etc....

 

Chris

 

I am not an electrical engineer but; isn't that something you can do with a resistor or some other electrical device, thus avoiding the drain of running a light bulb needlessly?

Using a resistor will be the same as using a light bulb - they are both resistors. The resistor will dissipate power as well and get hot.

 

Chris

[Gibbo]

.................. there is a high pitch noise doing this, has anyone tried this method, is there a fix for this problem?

 

Is the noise coming from the controller or the pump?

 

Either way it can be fixed.

 

Gibbo

[wonderdust]

Is the noise coming from the controller or the pump?

 

Either way it can be fixed.

 

Gibbo

 

Gibbo, the noise comes from the pump and changes pitch as you turn the pwm dial.

[Keeping Up]

Allan's idea with the bulb will solve the problem of the whine at the expense of less efficiency. - you pays yer money etc....

Precisely.

 

I'm a cheapskate so I'll always find the cheapest solution.

[chris w]

Gibbo, the noise comes from the pump and changes pitch as you turn the pwm dial.

Try attaching 2 x 470uF capacitors between the pump's positive connection and ground.

 

Chris

Edited December 16, 2008 by chris w

[Gibbo]

Gibbo, the noise comes from the pump and changes pitch as you turn the pwm dial.

 

OK. That's easy to deal with.

 

You need a biggish value inductor in series with the output. It needs to be low resistance. The low voltage secondary of a discarded transformer (insulate the primary) springs to mind for a cheapskate solution.

 

Then put a capacitor across the motor terminals. A big 'un. Maybe 25,000uF or higher. Whatever you can lay your hands on. It needs to be at least 50 volt rating.

 

The only slight problem here is that doing this, depending upon the quality of the transformer you find, may just move the whining noise form the pump to the transformer

 

Gibbo

[chris w]

.................... depending upon the quality of the transformer you find, may just move the whining noise form the pump to the transformer

 

Gibbo

I'd lay money on it

Edited December 16, 2008 by chris w

[Keeping Up]

Personally I'd go for the light-bulb solution to see if it achieved what I wanted, and then decide whether to go for something more sophisticated after I'd run it for a while. Being me I'd probably then try all the clever solutions, spend ages getting them working, then decide I could use the PWM and other components more usefully elsewhere and put the lightbulb back in.

[chris w]

Personally I'd go for the light-bulb solution to see if it achieved what I wanted, and then decide whether to go for something more sophisticated after I'd run it for a while. Being me I'd probably then try all the clever solutions, spend ages getting them working, then decide I could use the PWM and other components more usefully elsewhere and put the lightbulb back in.

The advantage of the light bulb over a resistor is that its cold resistance will be very low and so there is no danger of the pump's not starting, as there might be with a resistor.

 

Chris

[smileypete]

Gibbo, the noise comes from the pump and changes pitch as you turn the pwm dial.

I'd try a smallish resistance between pwm controller and pump.

 

Edit:

 

If that doesn't help I'd add a largeish capacitor across the pump.

 

cheers,

Pete.

Edited December 17, 2008 by smileypete

[chris w]

I'd try a smallish resistance between pwm controller and pump.

 

cheers,

Pete.

What's your thinking here? A resistor will purely limit the drive current to the pump. The PWM frequency will still be present.

 

A 12v pump looks like about 1 ohm anyway so sticking a resistor between the PWM and the pump will just act as a potential divider and severely limit the pump's speed. You wouldn't need the PWM then. Confused of Tunbridge Wells

[smileypete]

What's your thinking here? A resistor will purely limit the drive current to the pump. The PWM frequency will still be present.

 

A 12v pump looks like about 1 ohm anyway so sticking a resistor between the PWM and the pump will just act as a potential divider and severely limit the pump's speed. You wouldn't need the PWM then. Confused of Tunbridge Wells

 

Something like 0.1 - 0.25 ohms, a length of thin speaker wire should do for a try-out.

 

If there's still a whine then I'd add a 470uF - 1000uF capacitor across the pump.

 

If it works OK it should give a decent compromise between energy saving, controllability and quiet pump running.

 

cheers,

Pete.

[chris w]

Something like 0.1 - 0.25 ohms, a length of thin speaker wire should do for a try-out.

 

If there's still a whine then I'd add a 470uF - 1000uF capacitor across the pump.

 

If it works OK it should give a decent compromise between energy saving, controllability and quiet pump running.

 

cheers,

Pete.

I still don't see why the resistance will make a difference to the whine? The capacitor, I understand...... I recommended the same thing earlier, above.

 

Chris

[Gibbo]

Something like 0.1 - 0.25 ohms, a length of thin speaker wire should do for a try-out.

 

If there's still a whine then I'd add a 470uF - 1000uF capacitor across the pump.

 

If it works OK it should give a decent compromise between energy saving, controllability and quiet pump running.

 

cheers,

Pete.

 

Er............

 

This PWM controller is probably running at about 1kHz with relatively fast rise and fall times. Probably in the order of 10nS.

 

At 50:50 M:S ratio on 12 volts into a 1000uF cap with a series resistance of 0.25R what current do you think the cap will have to tolerate?

 

How much power will be wasted?

 

A 1000uF cap on the output of that PWM controller will almost certainly blow the controller to pieces unless it's designed for about 30 amps. If not it will be wasting a few hundred watts which has to go somewhere. Probably into smoke in the capacitor.

 

Adding the series resistance will make no difference to the noise in the pump. The noise is caused by the windings vibrating in sympathy with a triangular waveshape corresponding to the current waveform.

 

He needs an inductor as I posted originally.

 

Gibbo

[John Orentas]

Hi Wanda.

 

It is usually a big mistake to use any kind of series resistor with a DC motor.. Almost inevitably the motor will stall at some point and immediately burn itself out.

 

The only way to control the speed is using a 'stepped DC' bit of circuitry, effectively the motor is switched on and off very rapidly with the on and off periods being controllable.

 

The most common use of such things is with model railways, very smooth starting and stopping can be achieved.

Edited December 17, 2008 by John Orentas

[smileypete]

Er............

 

This PWM controller is probably running at about 1kHz with relatively fast rise and fall times. Probably in the order of 10nS.

 

At 50:50 M:S ratio on 12 volts into a 1000uF cap with a series resistance of 0.25R what current do you think the cap will have to tolerate?

 

How much power will be wasted?

 

A 1000uF cap on the output of that PWM controller will almost certainly blow the controller to pieces unless it's designed for about 30 amps. If not it will be wasting a few hundred watts which has to go somewhere. Probably into smoke in the capacitor.

 

Adding the series resistance will make no difference to the noise in the pump. The noise is caused by the windings vibrating in sympathy with a triangular waveshape corresponding to the current waveform.

 

He needs an inductor as I posted originally.

 

I'd just try a small series resistance first of all.

 

It's by far easier to actually try out, than debate endlessly about whether it should work

 

cheers,

Pete.

Edited December 17, 2008 by smileypete

[Keeping Up]

Once again, the virtues oif the light-bulb solution spriing to mind. Not only cheap, with no hum, and as Chris says it will switch on with a low resistance when cold so the pump is almost guaranteed to start; but if something stalls the motor, the bulb will light up brightly and its increased resistance will limit the current to reduce the chance of any damage occurring. It will even give you a visual warning of any such problem. And while it is maybe less efficient than a PWM, the setup does still consume less power than the existing directly-connected pump.

 

Just thought, it also has a further protection function; if you connect it to too many volts, the bulb will act as a fuse and once again save the pump.

 

If I was a marketing man I could put it inside a box so that nobody knew what it was, and market it as a truly wondrous multi-functional device. To satisfy the techno-freaks I'd write the word "digital" on the box, which would actually mean only that you can pick it up with your fingers.

[Gibbo]

I'd just try a small series resistance first of all.

 

It's by far easier to actually try out, than debate endlessly about whether it should work

 

Well.............

 

You can try it to see if it works. If that takes you five minutes then it's five minutes longer than it took me to know it won't work

 

Gibbo

 

If I was a marketing man I could put it inside a box so that nobody knew what it was

 

Just a hunch this but I have a nasty feeling that the light and/or heat coming from the box may give the game away. Although you could mount it in a finned aluminium extrusion with extra fans nailed onto the outside, insist that's it's highly efficient and put out sales blurb that it's specced at 40 deg C instead of 25 deg C

 

 

Gibbo

[Sir Nibble]

I have to disagree with Gibbo and John. I would go for the series resistor, especially given that this is a permanent magnet motor and the field density will be unaffected. You might want to consider the resistor pack used to speed control a car heater blower and even though it will not apparently work, it will give you 3 or 4 non working speeds to try out.

I had the same problem and moved mine into the engine compartment.

Edited December 17, 2008 by Sir Nibble