Overclocking a pump?

[Áedán]

Has anyone tried to overclock a pump yet? If so, how did you do it?

AidanII

[Uncle Bob]

Never done it with a PC water pump, but in the field, we just crank up the voltage. It really depends what pump you are trying to oc. Most good ones now are using an magnetic field and only a shaft as the rotating part. So if you increase the field strength, theoretically it should spin faster. There are other things to consider as well, NPSH (net pump suction head) is another. Putting two pumps in line isn't a bad way to go, We do it all the time in our business, they are simply called 'booster pumps' and they can typically increase flow rates by 50% of given gpm of 'booster pump'.

[Áedán]

Originally posted by Uncle Bob
Never done it with a PC water pump, but in the field, we just crank up the voltage. It really depends what pump you are trying to oc. Most good ones now are using an magnetic field and only a shaft as the rotating part. So if you increase the field strength, theoretically it should spin faster. There are other things to consider as well, NPSH (net pump suction head) is another. Putting two pumps in line isn't a bad way to go, We do it all the time in our business, they are simply called 'booster pumps' and they can typically increase flow rates by 50% of given gpm of 'booster pump'.

Most good ones use a magnetic field, indeed. Unfortunately, the design is such that the motor is a synchronous motor. That means that the magnetic field generated by the coil appears to the shaft to be a rotating field. Hence the speed of the shaft is governed by the frequency of the powerline.

(And hence, if you take such a pump designed for 60Hz operation, and run it off 50Hz, it'll run 17% slower!)

Yes, if you bring up the speed of the shaft, you'll also need to increase the power to ensure that enough power is going into the system to stop the shaft from falling behind! If the shaft falls behind, it's out of sync with the magnetic field, and you don't get any power transmission!

AidanII

[Uncle Bob]

Ahhhh. are you of the 50hz?
Well, you could always get a freq generator? Pretty darn spendy, tho! LOL

[Áedán]

Originally posted by Uncle Bob
Ahhhh. are you of the 50hz?
Well, you could always get a freq generator? Pretty darn spendy, tho! LOL

Yeah, tell me about it. I've looked into it a bit more and there's some interesting things that can be done.

AidanII

[Áedán]

I was looking at building a circuit that provided a 12V sine wave, and then feeding that into a transformer running backwards, so that it came back out at 230V. T

he biggest problem with this is that the transistors on the output would get hot (worst case about 25W of heat), and a big transformer for the 25W worth of power.

It's the simplest way of doing it, but it's inefficient.

AidanII

[Áedán]

Another alternative would be to use a square wave - that way the transistors are either on or off, so don't dissapate much power.

The problem with this is that the pump motor will not run wonderfully well on a square wave. It'll tend to consume more power, but not push more power into the shaft. This can only mean that the pump gets hot instead!

That's easily, cuz things don't get so hot, but doesn't work very well.

AidanII

[Uncle Bob]

Which also brings to mind that this is a cooling system and any heat generated by the pump is directly transferred to the cooling medium! There is a tradeoff point I suppose. It yould be nice to have a small turbometer such as we employ to show online gpm!

[Áedán]

Next step appears to be looking at synthesising a sinewave using a square wave. This has the advantage that the square wave is much more efficient on the transistors, but after filtering, the load sees a sinewave.

Using a technique called Pulse Width Modulation (PWM), we can actually generate a sinewave simply by using pulses (the square wave). By changing the width of the pulse, we can make it look like the average voltage is higher or lower.

The easiest way of synthesising the correct width PWM pulses is with a sawtooth wave and the sinewave we want. When the sawtooth wave is at the start of a tooth, we start our output pulse. As the sawtooth ramps up in voltage, we compare it to the value of the sinewave. Once the sawtooth gets to the level of the sinewave, we stop the output. Now, this requires the sawtooth wave to be higher in frequency than the sinewave. This probably doesn't make much sense, but here's a picture so you can see!

The top wave, is a 180 degree section of a sinewave. Underneath is the sawtooth wave, at approximately 80 times the frequency of the sinewave. Lastly is the approximation of the PWM wave that would represent the sinewave.

http://www.hawks.dircon.co.uk/aoa/pwm.gif

The output is a bunch of pulses, where the width approximates the sinewave output. Filtering this by passing it through an inductor, and you have a sinewave.

Unfortunately, this is more complex, and requires more parts...

It needs an inverter to generate +230V, and then four transistors connected in a bridge to control the PWM pulses.

By seperating the inverter from the power output, we can control the voltage easily - we turn down the inverter, but continue the same PWM frequency. That way the voltage goes down, but the frequency remains the same.

The inverse is also true. Just by changing how quickly we send the PWM pulses, we can change the frequency with changing the voltage at all.

I'm thinking of building a digital controller for this on a testbed initially, to see how it works at 12V. I it works well enough, I'd like try it on the 230V generated by an inverter. The inverter would take the power from the 12V line, so no real mains will be available. This will also isolate the pump from the mains, so that a massive pump failure won't cause live mains to appear in the water cooling system!

Yes, I know it's complex, but I'm hoping it'll work. I'm thinking that the PWM waveform will be stored in a ROM as a table, and that a counter can just step through the ROM. If I change the speed of the counter, the frequency output changes.

AidanII

[GaulHahn]

Here is good mod using 3 pumps inline so its kinda like overclocking a pump. view it here. You'll need to be a member of OCAU to view it though.

But here are the pictures in the thread.

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Edit:

And hullo from my first post

[surlyjoe]

thats awesome

[Uncle Bob]

Very nice crafstmanship! What were the individual pump ratings and what do you project the final will be?

[SiGmA_X]

Welcome to the Forums, GaulHahn!! Hope you enjoy your stay with us

That's some nice work there.. Yours?