Controlling Aquarium Air Pump Output

Ok. I can see how that would be best. However from what little I know that's a complicated procedure requiring (relatively) expensive equipment - and that's just to output square wave.

Yep. There's 'fixed overhead', a small amount of air needed for valve opening/closure. It's not a lot as a fraction of volume at mains voltage but I see that it would become a larger fraction as the voltage dropped.

Interesting. I hadn't even considered that such a thing is possible. LOL, n00b alert!!!

Going by the youtube video that Clive did these are leading edge 'dimmers' (Clive calls them 'power regulators' and says they seem to be industrial control equipment.)

This model (assuming that mine is the same as the one Clive reviewed - and I'll check that as soon as I get it) has a clever diode bridge arrangement and "it doesn't go unstable" especially at lower settings and keeps the output symetrical. He says transformers and motors don't like non-symetrical AC and get hot.

He says "the advantage of this is that if you're controlling inductive loads like transformers or motors you're not going to go into a dodgy situation where you end up with a slightly non-symetrical wave form. Most standard incuction motors and transformers hate if the sine wave is being half-wave triggered or not quite symetrical it creates a bit of heat in the transformer...."

This is why, after watching the video

I asked him in the comments if it would do the job I want it for (after I'd started tis thread) and he said I'd be better to restrict the air output (but I don't think he knows about rubber diaphram air pumps, the only air pump he's reviewed has a close-tolerance ceramic-coated piston.) He also said that the air pump "wouldn't be a high enough load for a dimmer" but he might be thinking it's a little 5W thing.

I thought this might be easier as I have some 7.5W, 0 - 5l/min air pumps that are adjustable. They have a pot (variable resistor?) and a small PCB. The PCB has two resistors, one a 1/4 watt and a big one (22 long x 7mm diameter), a small diode, two 0.1uF capacitors, a trimpot and a Z0102 transistor. I'd use one of these pumps but they're noisy compared with the big 30l/min pump.

I can't find Phils answer in this thread. :(

All I know is that there's quite a bit of damping of the arm movement cause by the rubber pivot bush and that 'arm' type reciprocating air pumps tend to give (usually quite a bit) less than 1litre/min per watt whereas the double-ended type start at over a litre/min per watt and go up to more than twice that. They're also a lot more expensive but are much more reliable.

Cheers,

Yep, my bad - I meant series. Parallel wouldn't do anything.

Yep, hence my questions here.

Indeed.

I would like to know the answer to this.

Thanks for the reply.

In theory it wouldn't be any more complicated electronically than the controller you've bought. It would just require detecting the zero-crossing of the AC waveform, then using a logic circuit or microcontroller to turn off the output for every cycle after a certain interval. Eg. every 2nd, 3rd,

The zero-crossing detection and SCR switching circuit are (hopefully) common with your controller. The difference that will complicate things is that I'd guess many of your controller's functions are performed by one of the various Phase Control ICs available, whereas with a frequency controller the main functions may have to be designed and built separately, unless a suitable IC is available.

The Audio amp and power transformer method I would consider to be more of a test set-up than a permanent solution. If nothing else, it won't be power efficient. However a PC could be used to produce the sine wave, in order to save building a custom oscillator to feed the amp.

A variable frequency drive $80 delivered on aliexpress for one with a case, $55 for a used one - needs a case both are marked 220V so may not be reliable on Aussie 240V

much cheaper to buy a new pump.

just needs a new plug fitted.

Nah, it's not. it's a triac circuit, the bridge rectifier (used for current steering, not rectification) only passes the timing currents.

a ring generator (telephone ring voltage generator) might be just the thing might not be cheap though

or perhaps a curcuit that passes every third half-cycle

_ _ _ _ _ _ / \ / \ / \ / \ / \ / \ _/ \_/ \_/ \_/ \_/ \_/ \

_ _ _/ \______ ______/ \_____ ______ \_/ \_/

_ _ _ _ ___ / \___/ \ ___ / \___/ \ _/ \_/ \_/ \_/ \

You might need to update your thinking on this score.

In 2000, Australia converted to 230 V as the nominal standard with a tolerance of +10%/?6%.,[10] this superseding the old 240 V standard, AS2926-1987.[11] As in the UK, 240 V is within the allowable limits and "240 volt" is a synonym for mains in Australian and British English.

One problem is that I doubt those devices would be designed to switch at the zero-crossing of the AC waveform, and doing otherwise is likely to cause inductive spikes and their associated problems.

I'm having trouble imagining how cutting half-cycles would be any easier to implement. Nice ASCII waveforms though.

They generate about 90V AC at 16.67Hz seems about right to run a pump at

A triac with the right drive, not sure what the crcuit to do that is though.

Oh I see, I was thinking on the wrong track. Yeah, if it can survive the unusual load conditions it might just work. No doubt somebody sold one on Ebay once. :)

Yes, though a Triac could also be used to cut a whole cycle:

_ _ _ __/ \ ______/ \ ______/ \ ____ \_/ \_/ \_/

A basic implementation for fixed 1/2 division of the supply frequency may be as follows:

|ZERO CROSSING| |FLIP| | SCR | | |---|FLOP|---| | | DETECTOR | | /2 | |(TRIAC)|

The Flip Flop divides the signal from the Zero Crossing Detector (which produces a pulse on every 0V transition of the mains waveform) by two. This signal activates the SCR (which powers the compressor) for one of every two mains cycles.

Mains Waveform to Zero-Crossing Detector: _ _ _ _ _ _ */ \* X/ \X */ \* X/ \X */ \* X/ \X _/ \_/ \_/ \_/ \_/ \_/ \ "*" & "X" Indicates pulse from Zero Crossing Detector "*" = SCR Triggered "X" = SCR Disabled

SCR Output Waveform to Compressor:

_ _ _ __/ \ ______/ \ ______/ \ ____ \_/ \_/ \_/

A variable division of the Zero-Crossing signal would be desireable to allow further reduction of the supply frequency if required. A counter which disables the SCR for just one cycle after a certain count of zero-crossings may be used instead of the divide-by-two Flip-Flop for frequency reduction less severe than 1/2 division.

Oops, out of time. I'll have to hope all that made sense, no time for a final check!

Yep, I can see how it would work now. However while possibly being cheap (I've got a few amps kicking around) it's not exactly elegant. ;)

As Jasen says it's a diac-triggered triac system. The bridge rectifier is used instead of discrete diodes to discharge any partial charge in the triggering capacitor when the phase changes to make it operate more smoothly at lower settings rather than have charge build up from seperate peaks and result in an unstable, non-symetrical waveform output.

Or something - I'm trying to learn as I go.

I got the unit I ordered a few days ago and opened it up to check it wasn't going to let any smoke out when connected. It's indentical to the one Clive strips down (except mine doesn't have the un-soldermasked power tracks and legs of the triac left on to beef up power connections). However the labeling is wrong going by Clives schematic. What Clive calls input is labeled output, both on mine and his units so I asked him but no reply to that one yet. Worrying as I haven't studied further to see if they can be swapped.

Then reading down the comments I saw this; "I have the same device, but it came with a 100 ohm in the snubber. If you want to do inductive loads, best swap in & output, so the fuse is on the output. Otherwise a fuse break will almost definitely damage the triac. Also, mod it like this for better inductive control

So I guess the fact that they're labeled differently to Clives schematic doesn't matter - or (whisper it) Clive's wrong.

I still haven't applied mains AC to my device yet. Life can be demanding like that. ;) However I don't use radios and my TV is digital (and only used for a maximum of 20minutes day for news headlines and weather). I could always add a large choke, I have a bunch of bits salvaged from old PC PSUs.

It can't be because that airpump is also an AC 'vibrator' pump (and indeed there is an indentical model without the output control) They're called Optima (and Maxima) and were sold by Rolf C Hagen aquarium products. However they're 'arm' type as opposed to the better, quieter but more expensive 'armature suspended between two diapragms' type.

It was seeing this rather simple circuitry, the only difference between the two models, that got me going down this path originally.

Sorry nothing comes to mind and I've pondered on this for a few days now. The only thing I could think of was perhaps a water pump and venturi set up going into a separating tank to get your pressurised air? Not very elegant but then again not my field.

Cheers,

That's interesting but way beyond my skills to design / build. All I need is to find a supplier. ;)

I just searched and the cheapest was US$90 delivered. It's a shame there isn't something smaller and cheaper - the one I found does 1 to 400Hz and is rated at 400w. I only need perhaps 5 to 50Hz and maybe 50w (my pump is rated

Yeah, thanks but I wasn't asking advice on aquarum air pumps.

I have a couple decades in the aquarium industry under my belt, half of that as a consultant on large private and public aquatic systems. I have maybe 20 airpumps of varying sizes and the little 'domestic models' are noisy and unreliable in the longer term. I've always belived in, wherever possible using kit that's way over-rated for the requirement and then using it at a lower duty cycle so that it lasts a long time.

That said this is looking to be too problematic, requiring far more of my limited time than I'd hoped so I might go through my collection of smaller pumps and find the least-noisy one that will supply the ~5l/min that I need and hope that it lasts. It's a shame to mothball this really quiet and efficient 30l/min unit though. I was hoping to be able to leave it in place and just ramp up the output again if required.

I'm sure that I'll find another use for the 'power controller' that I bought hoping it would do the job. It wasn't hugely expensive, I just ate lightly for a few days and saved enough money to pay for it.

Cheers,

I haven't quite been able to get all this out of my head, and as a result I've come up with a few things to add regarding this method of power control (always sending complete mains cycles to the load):

Most notable would be that, while looking through one of my electronics books, I stumbled across the real name for this form of power control. It's called "Burst Fire", as it generally describes a method whereby busts of mains cycles are provided to the load over a period determined by the quantity of power reduction required. It is most commonly used to control large electric heating elements, where the Phase Control method may cause excessive noise on the mains supply.

There are Burst Fire power control ICs available, two that I have found are below:

The first pages of those datasheets show circuits to perform the required task.

There are Burst Fire power controllers available as pre-built modules, but I couldn't find any cheap Chinese ones during my breif searching (they may be listed under another name, or even included amongst listings with Phase Control types). These are the two cheapest models at RS:

United Automation, ZVS-16DV, Thyristor Power Controller Assembly, 3.7kW, 16A, 58 x 55 x 36mm

- $99.06 AU ($108.97 NZ):

United Automation, PR1-DIN-2.5KW, Thyristor Power Controller Assembly, 2.5kW, 11A, 94 x 75 x 83mm

- $99.30 AU ($109.23 NZ)

Both about the same price at around $100, and both far over spec'ed for your application (though all such controllers are likely to be, due to the technology and their intended application as heater controllers).

As a final note, here are my other circuit ideas (they will likely exceed your design ability, but I feel like putting them on the record):

Use a 4527 BCD Rate Multiplier IC clocked from a mains Zero-Crossing Detector circuit, and with it's output buffered and used to control a TRIAC switching the mains waveform. This allows the number of mains cycles sent to the load over a time period of ten cycles to be varied from 0-9 using a rotary switch with BCD outputs. The main advantage of this circuit would be that I wouldn't have to buy anything if I built it myself. :)

Use a CA3059 TRIAC Control IC and a 555 timer configured as an oscillator with a frequency variable using a potentiometer, or multi-pole switch. The 555 output enables the CA3059 to turn on the TRIAC at the next mains crossing point after it goes high, and to turn the TRIAC off at the crossing-point after it goes low. In this way, it works like one of the dedicated Burst-Fire ICs above, sending "bursts" of mains to the load. Actually... I could avoid buying anything for this too, if I replaced the CA3059 with some discrete circuitry to provide the same functions. Probably no more complicated than the previous option.

Thanks Kev, interesting stuff. I've put the project on the back burner for now (and the SCR unit in a 'box of bits').

Cheers.