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Modification at vacuum cleaner power supply

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Hello,

Someone Electro: get an MOSFET that can suply more curnet.If its high enugh it will be just warm whithout an heatsink.

the IRF3205 can suply 110A at 55V and its in an TO-220(This is like most power transistors and voltage regulator) Over here you can get it for $2.


I have checked the price here and is around 8€, a little bit more expensive than in your country. Anyway if you think with this one would not be necessary heatsink sounds good...

Someone Electro: All you need then is an simple 555 timer to drive it

Why? With the tests with the IRFP350A I only drove it with 2 resistors to get the 10V at Vds.

Oznog: Still, off the shelf, I'd say this project can easily run 30-40euro or more, and the results will be less than "satisfactory" due to the size and heat generated. It will also run down your battery pretty fast! That's why I suggest getting a 12v vacuum which is quite common.

I take it you want a learning experience here. First thing to learn is nobody will ever design a linear regulator like this, it's impractical. When we have to step down voltages like this we use a DC/DC converter- a switching reg- which will do the job cleanly. Cool, efficient, and cheaper than huge FETs and heatsinks. It would be difficult for us to communicate how to do this to you because it doesn't sound like you're ready for advanced circuits like this.


At the moment I didn´t pay any euro in all my tests, I found this IRFP350A on an used board I had from a broken gym running machine and I worked on my job workbench where I have all the material for working, power supplies, soldering station, oscilloscope...
I also checked the prices for this 12V vacuum and I won´t buy one, not necessary. The battery I will use is the car´s one when the car is running at idle so it took the power from the alternator so no problems to discharge the battery.
I don´t care about people do themselves, I had an idea and I´m trying to find the best and cheap way to do it, if it´s finally not possible to do due to the price and it has no sense then no problem, at least I know I tried it and I learnt a lot of things. In my job I´m the only electronic technician and although my studies were for designing electronic circuits (1 year private school for general electronic knowledge + 2 years official school for electronic technician), I don´t have a lot of options to design. I try to learn new things every day because sometimes my job don´t give me that knowledge or I have to take it myself, I don´t have job mates to discuss here about pure electronic, all my mates are pure mechanic guys. I always then have to test or think myself only using my electronic knowledge or asking in forums as I´m doing to get new ideas...
I know there are a lot of more professional ways to do this project I asked for but it´s only like a hobby in this case exactly so I don´t want to use a SMPSU or DC/DC or whatever has no sense in this case.
I think I´m prepared to analyse circuits, design, repair... because I already did it, may be not so as you or not so as I would like, but why not?

Sebi: When You thinking about independent box, i think my idea a with car-bulb better. Try with 120W bulb (or two 60W parallel) Johnson motor is very strong and bullet-proof: my hand-drill specified for 12V 6A and i use this device about 20 years with self-built thyristor RPM controller from 24V. When the 3mm diameter drill go through a metal plate, the current over 20A! ...and work fine. I know, this is a barbarism, but i purchased two spare motors and no needed.

Thank you, if I can I will test also that option, but if I put this bulb in serial in theory the bulb will take the 12V and then I only will have 2,4V available at the motor, isn´t it? That wouldn´t be enough voltage at the Johnson motor where I have to put at least 3,7V.

Will B: I dont think that motor could possibly draw 7A ..
0.7 is more like it..
that motor is only about an inch in dia.!!


You are wrong, it runs 7A, and more if I put more voltage at its pins. This DC motors are very powerful, believe me!!!

Thanks for all your answers.
 
2PAC Mafia said:
Thank you, if I can I will test also that option, but if I put this bulb in serial in theory the bulb will take the 12V and then I only will have 2,4V available at the motor, isn´t it? That wouldn´t be enough voltage at the Johnson motor where I have to put at least 3,7V.

Don't dismiss it until you've tried it!, a cold bulb has a far lower resistance than a lit bulb - by careful bulb selection you may well find one that works pretty well. It could be a cheap easy solution for what you want.

Bear in mind, a bulb ISN'T a zener diode (or even an LED) it doesn't drop a specific amount of voltage.
 
Hello Nigel,

I have test a car bulb of 21W giving 10V and it consumps 1,6A, that means 16W. What about the possibility of connecting 4 bulbs of 21W in parallel (64W) regulating the voltage at them to 10V with the MOSFET also in parallel (Vds) which then doesn´t need heatsink because the power to dissipate would be around 10W.
That would be very cheap and depends on the box where I install everything it could be used also as a car light, with a switch on the MOSFET circuit that doesn´t regulate the voltage when you want to use the box only as a light (switch off regulator).
 
You're still thinking of bulbs as resistors!, and they are VERY different, when cold they are a much lower resistance than when hot, so your calculations are pretty well irrelevent.

Try placing a headlamp bulb in series with the motor, power it up and see what voltage you get on the motor. Most headlamp bulbs have different sized dip and mainbeam, you might find one better than the other.
 
I have an simalar Jonson motor also from an vacum cleaner.It runs on 6V and can consume 7A wen driving a big load.Its rated at 11 000 rpm and thats fast.

An bulb cod work nicely.The low cold resistance wod give the motor more power at start so it will get to its top rpm faster.
 
williB said:
I dont think that motor could possibly draw 7A ..
0.7 is more like it..
that motor is only about an inch in dia.!!
Little motors like that for model airplanes and cars are rated for hundreds of Watts. 30A or more is common. just think how well one would perform as a generator. It would be difficult to turn because it is very efficient with its very powerful magnets and close spacing to the coils.
There is a range of quality in motors for models. The cheap but still pretty good motors have brushes and sleeve bearings. Better ones are brushless and have ball-bearings.
I have a cheap little one with its own gearbox (nylon gears) attached. It draws 10A at 8.4V efficiently, or much more current (too much) with more load. I am afraid of the extremely high current if it is stalled by something.
 
Hello,

I put this information for everybody who was interested about this project, every idea was useful to know different possible ways to carry on it, so thanks.

I checked the possibility of the bulbs connected in parallel using some car bulbs but as I didn´t have the material to do it and I had to buy it to put them inside the box properly finally I took another way.

I removed the IRFP350A, two potentiometers of 10K and PCB sockets from different damaged boards, the fan and heatsink I took from a computer damaged motherboard. I had some small free boards so I designed and made the PCB.
I put everything inside a PVC usual electrical box which I also found in my workshop.
I modified the connections inside the vacuum cleaner to switch on and off now my installed input plug signal (L, N, G plug) removing also the 3 batteries from inside the vacuum cleaner.
I made the cables modifying some of them I also had in my workshop and with those plugs is no possible to reverse the polarity (only one position).
So finally there are two cables, one can connect the box to the vacuum cleaner and the other the box to the 12Vdc car plug.

The fan was connected directly on my PCB using the direct car Vdc and the MOSFET can be regulated with the two potentiometers. I did some measurements and finally regulated the potis to have the values as follows:

Vdc car´s output when is running and nothing connected at plug: 14,4 V
Vdc car´s output when is running and vacuum cleaner is on: 11,8 V
Temperature at chip case: 40 / 60ºC
Temperature at heatsink: 60 / 90ºC
Vdc interface box output for vacuum (Johnson motor): 5,2 V
Idc vacuum cleaner consumption: around 9A

I should say I know that´s too much work and money if you don´t have none of them but as I said I didn´t spend any money and I had free time to do it, also the experience of solving the different problems to design that was useful for me.

You can see some photos from the interface box open.

Thanks.
 

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2PAC Mafia said:
Vdc car´s output when is running and nothing connected at plug: 14,4 V
Vdc car´s output when is running and vacuum cleaner is on: 11,8 V
What is in the wiring of your car to cause the 2.6V drop, which burns 23.4W? Maybe the alternator doesn't have much output at idle.

Temperature at chip case: 40 / 60ºC
Temperature at heatsink: 60 / 90ºC
The chip case is hotter than its heatsink, isn't it?
Its power dissipation is (11.8-5.2) x 9A= 59.4W. The Mosfet's thermal resistance from its crystal to its case is 0.64 degrees C/W, then its crystal temp is (59.4 x 0.64)+90= 128 degrees C. Pretty darn hot.

Vdc interface box output for vacuum (Johnson motor): 5,2 V
Idc vacuum cleaner consumption: around 9A
That's 46.8W for the little motor. It must be cooling itself.

You can see some photos from the interface box open.
It looks great, you did a fine job. But the Mosfet might fail soon with such a high internal temp.
 
Hello Audioguru,

I hope you and your family are fine, here now is getting a little bit colder but until now the weather was very good...

What is in the wiring of your car to cause the 2.6V drop, which burns 23.4W? Maybe the alternator doesn't have much output at idle.

I´m not sure but even with my desk power supply 0-30V / 10A there is a drop of 5,3V and I get at the input only 9V, strange is that you can see at the digital display 12,5V but as you see they are not real.
I guess the car´s output from the alternator is limitted to supply that 11,8 voltage in case of big current as this case... but I´m not really sure about the cause of this drops.

[/quote]
The chip case is hotter than its heatsink, isn't it?
Its power dissipation is (11.8-5.2) x 9A= 59.4W. The Mosfet's thermal resistance from its crystal to its case is 0.64 degrees C/W, then its crystal temp is (59.4 x 0.64)+90= 128 degrees C. Pretty darn hot.

I measured with a laser termometer and I read those values, the chip case is always colder than the heatsink (dissipation plate cooler). The maximum value I read was nearly 90ºC and was on the top of the dissipation plate. I put some conductive thermal paste between the chip and the dissipation plate. This 128 degrees C you mean, are they internally at the chip?

That's 46.8W for the little motor. It must be cooling itself.

Yes, with the batteries originally the motor received nearly 4Vdc and the consumption was around 7A but somewhere I read these motors are usually to work on a range of 3 to 6Vdc. With this voltage I increased the rpm so I also improved the vacuum behavieur, I think it will support well those 46.8W.

It looks great, you did a fine job. But the Mosfet might fail soon with such a high internal temp.

Thanks, I also tried to install a small 12Vdc motor from a CD player with a propeller from another broken CPU fan added but it was not possible because it vibrated too much and was difficult to fix and hold it on a good place. I also wanted to achieve a good temperature for the chip but those values I wrote are the ones I have.
We will see, if the Mosfet fails I´ll tell you...

Thanks.
 
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