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PostPosted: Feb 6th, '12, 14:18 
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Seriously, this cant be healthy.
Seriously, this cant be healthy.
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I bought a little $10, 2 watt, 12 volt air pump that plugged into some kid safe low power fishtank thing. Got it home, cut the plug off and connected to my 12 volt battery, then read the packet and found it's AC.

Who makes 12 volt AC products?

Anyway... does anyone know if I can make a 12 volt DC to 12 volt AC converter that doesn't waste too much power, with just sticks and coconuts or something? (Gilligan's island professor could do it I'm sure)

Is there a name for a circuit like this I can search for? Like a rectifier circuit is the other way.

All the inverter circuits I see change the voltage as well.

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PostPosted: Feb 6th, '12, 14:51 
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Seriously, this cant be healthy.
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I opened it up in the hope that there might be a rectifier inside that I could just bypass, but there's nothing in it.

Just the diaphragm, lever, magnet, and a coil.

Which means the frequency of vibration is set by whatever the AC is doing it's thing at.

But that probably means it isnt important.

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PostPosted: Feb 6th, '12, 15:20 
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I will talk to an engineer tomorrow at work, he likes tasks like this, but they always involve a hot glue gun....

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PostPosted: Feb 6th, '12, 16:06 
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BullwinkleII wrote:
Got it home, cut the plug off and connected to my 12 volt battery, then read the packet and found it's AC.



Just couldnt help yourself could you.... :)

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PostPosted: Feb 6th, '12, 17:03 
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Yep you can make one.
You can do it mechanically by connecting a 12v dc motor to a 12v dc alternator

Otherwise build an inverter

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Its easy to make an AC squarewave if thats ok... not sure if your pump would like it that much.
Anyway you just need a H-Bridge and drive it from your picaxe.
Google "H-Bridge" Building one right now actually...

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PostPosted: Feb 6th, '12, 17:14 
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You can filter the square wave by making a low pass or maybe even better a resonant filter (at 50Hz)

You said you wanted to learn electronics BW, making this would teach you a lot about electronics and power. :D

PS: I believe it is certainly within your capabilities too..if my opinion is of any worth :wink:

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PostPosted: Feb 6th, '12, 18:53 
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One thing i should have bought when i first started playing with power electronics is a bottle of magic smoke. It would have saved me heaps of money being able to put the smoke back in rather than replacing the blown MOSFET's all the time. Also i would recommend safety glasses after i nearly lost an eye.

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PostPosted: Feb 6th, '12, 20:40 
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rsevs3 wrote:
One thing i should have bought when i first started playing with power electronics is a bottle of magic smoke. It would have saved me heaps of money being able to put the smoke back in rather than replacing the blown MOSFET's all the time. Also i would recommend safety glasses after i nearly lost an eye.

You blew a MOSFET?
Kudos :)

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PostPosted: Feb 6th, '12, 20:59 
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Not just A MOSFET Dui.... and when you say blew, it didnt just stop working, it blew half of the plastic casing off! Good times...

I actually started a graveyard with all the components i blew up with that project.

Actually BW has seen a photo of one of the final prototypes before we ran out of time and had to give it up. We were so close too.

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PostPosted: Feb 6th, '12, 23:26 
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PostPosted: Feb 7th, '12, 03:36 
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SuperVeg wrote:
Its easy to make an AC squarewave if thats ok... not sure if your pump would like it that much.
Anyway you just need a H-Bridge and drive it from your picaxe.
Google "H-Bridge" Building one right now actually...


H-Bridge. thanks

And I take it the square wave is because it's always either on or off (in it's AC-ness) like a city scape, rather than gradually building up and then down like a mountain range?

IF that's the case, and I do definitely realise I'm getting ahead of myself here, but wouldn't it use less power if the peaks were controlled so they were shorter, and with a gap in between? If all I have to do is attract the magnet 60 times a second, it shouldn't matter if the pulse is only for a zillionth of a second.

In fact I dont think I need AC. The diaphragm acts as a spring, so I should be able to return the position using it's springy-ness. I think they are just using the AC-ness as the thing to do the timing. So if I add a $2 chip that pulses for pointX of a second on, then stays off for pointY of a second, then that should be all I need. I presume the other side of the AC is repelling the magnet away. In fact it looks like the repelling bit is doing most of the work, as the diaphragm seems to be pulling the magnet back over the coil.

My hello world project was a flashing LED, the next was a transistor that did the same with a motor, so I think that's all I need.

Does this make sense?

Is there an issue with the coil overheating or becoming a magnet or anything if I only run it one way ie DC pulses?


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PostPosted: Feb 7th, '12, 03:53 
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DuiNui wrote:
rsevs3 wrote:
One thing i should have bought when i first started playing with power electronics is a bottle of magic smoke. It would have saved me heaps of money being able to put the smoke back in rather than replacing the blown MOSFET's all the time. Also i would recommend safety glasses after i nearly lost an eye.

You blew a MOSFET?
Kudos :)


I blew up an electric frying pan and actually put a hole in my eardrum.

And that's according to my doctor, and not just some dream I had :)

All I did was plug it in.

So forget eye protection, I recommend wearing full riot gear every time you get out of bed :)

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PostPosted: Feb 7th, '12, 04:08 
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If you could even get the motor to rotate i think you would be struggling for torque. I would be surprised if you could get it to turn at all though, and you would need to know to location of the rotor in relation to the magnets to know when to have the pulse. You would also have to line the motor up to get it started.

Maybe if the motor was spinning and you knew the location of the rotor and magnets you might be able to keep it spinning with DC pulses. :dontknow:

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PostPosted: Feb 7th, '12, 04:26 
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Sorry that was unclear.

I meant I could use the same code and circuit as I did to make the 12 volt motor pulse like the LED. I could use that same code to send a 12 volt pulse to the air pump.

ie I had the ADC output from the PICAXE going to a transistor connected to a 12 volt supply. The ADC output can be set to pulse at whatever rate for whatever period (the words duty cycle spring to mind but I cant really remember which aspect that describes)

But now I'm thinking that I can just use two of those circuits to make 12 volt AC if I need to.

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