problem with 555

is that what all the problem could be ? should I take any other precautions ?

Thunderchild said:

is that what all the problem could be ? should I take any other precautions ?

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No, I think that it's not the problems cause.

The main problem is the 555 supply. By the datasheet the maximum is 18V, but the datasheet is an advertising sheet too, so always use the half of the specs. If it is 18V, always use under 18/2 = 9V.

The capacitor in the mosfet gate, it's not needed.

Take a look at this drawing.

I have a PWM circuit driving an 8A motor with an IRF540 Mosfet from an 8.4V supply. It works fine and it doesn't have a diode across the motor, just a 0.1uF ceramic disc capacitor.
The Mosfet has a built-in 100V zener diode across it that protects it.
My circuit would be more efficient with a diode across the motor as a "free-wheeling" diode.

hm I wanted to keep this simple does it have to be so complicated. where can I get info on controlling mosfets I am a bit new on these ones. as you said the 555 is not too hardy so just a 20 volt spike could kill it, it gets very hot like it were connected round the wrong way so perhapps it is getting reverse fed but a inductive spike - well here goes will let you know in a few minutes

oops what a mess me and you were poosting simutainiously. well IT WORKS
put the clamping diode on the motor and a diode on the supply of the 555 and it really rolls 100 % control from nuting to max. but the motor is huming does this mean I need to increase the frequrnzy ?

Good, you fixed it.
Your 555's frequency is only about 144Hz. Decrease the capacitor at pins 2 and 6 to 0.01uF for a whining sound at 1400Hz and it won't hum. Try 0.001uF and it will whistle at a very high audible frequency and maybe the motor will run slower due to its inductance.

hm it is humming like a mains transformer but loader I will lay hands on some smaller caps tomorow, silence is esential here it is to be used in a room at night and I don't want to be kept awake or wake the house up.

ok so i used a 0.01 uF condenser and now it is a higher pitched wistle or could it be a higher hum do I increase or decrease the frequenzy, how can I calculate the frequenzy for this circuit ?. the motor is 12 V 7 A is there a specific frequenzy that works best on different powered motors ? This has to be SILENT not a bloody door bell.
thanks

Decrease the value of the capacitor until the frequency is so high that you can't hear it, and the Mosfet gets too hot because it isn't switching fast enough, and the motor runs slowly due to its inductance reducing its pulsed current.

right now well 3 0.01 uF condensers in series should give 0.0033 uF and this still makes a screaching noise am I stuck with it ? I tried a 0.1 uF condenser on the motor but that did little I suppose because this is mechanical not electrical hum then I put a 220 uF electrolitic which cause more spaking (more current I presume) when I attached the clip to the batttery and the condenser got hot what happened ? it also made the drop off speed higher so I had less control over the speed as it would sudenly stop at a higher speed than before without a condenser in paralel I can run this 7 A motor (with the mechanical load of the fan) at as little as 100 mA and at just 250 mA it is making a comfortable draft but an unreasonable wistling must fix that perhaps go hifher in frequenzy.

ok making the pot around 25 K with 0.0033 uF it is almost silent, will go a little higher, the mos is ok but the clamping diode on the motor is heating up especially at low speeds what can I do ?

You can't put an electrolytic capacitor across the motor! It might explode!
The Mosfet will try to charge the capacitor with an extremely high unlimited current, then the motor will run from the charge in the capacitor at an extremely high current while the Mosfet rests, over and over at the frequency of the oscillator. Of course the capacitor will get hot from all that current. You are lucky that the electrolytic cap and Mosfet didn't blow up.

For the oscillator, I calculated that 0.1uF makes 144Hz and 0.01uF makes 1440Hz. then your three caps in series makes only 4320Hz. Many people can hear frequencies that are nearly 5 times higher (20kHz). I am an old geezer and could hear even higher frequencies when I was a teenager because ultrasonic burglar alarms were too loud, but now I can't hear above about 14kHz.

The oscillator is up to about 17280Hz.
Now it needs a Schottkey diode that is much faster than an ordinary silicon junction diode.

ah not anything to do with like possible 20 or more volts going across a diode that has a voltage drop of 0.5 volts ?,
yea I see your point with the capacitor I was hoping it would yes bost the motor just enough to not keep going totaly off as I think it is the rotor that is flipping back and forth as it jolts forwards or backwards when it goe on and off hence the hum. so bassically if i understand cotrectly it will always do this, I though that over a certain frequenzy it would not have time to hum/return so would stop whining but from what you say and I have experimented it seems basically I have to get it out of range on my ears, so if i increase the frequenzy is there a risk the clamping diode will become ineffficient, i also have a diode in series with the positive of the 555 perhaps it is this that is now really protecting it.

IC555 tester

IC555 tester for test from free Electronics Circuit on web

https://www.guidecircuit.com/Circuit%20Measurement%20&%20Test%20555%20tester.htm



Source :https://www.guidecircuit.com/index.htm

To cure the problem do the following:

1. Connect the battery directly to the motor with thick wire.
2. Connect with thick wire a diode from the drain of the mosfet to the batery/motor connection (this is most important). The diode should preferably by fast type and rated at motor current and take care the direction of the diode.
3. Connect the battery ground directly to the mosfet source pin with thick wire.
4. Coonect a 2,000uF capacitor from mosfet source pin to battery/motor connection with thick wire.

(the above points take care of the heavy current section).

5. Power the 555 circuit also from the battery/motor connection but with a 10 ohm resistor in seroius. Or else use a separate wire and connect to the battery + terminal. Here you can use thin wire.
6. Connect the ground (pin 1) of the 555 directly to the mosfet source pin (you can use this wire).
7. Put a 10uF capacitor from pin 8 directly to pin 1 of the 555.
8. You can reduce the gate resistor of the mosfet to something like 100 ohms to reduce the switching time.

I am using a circuit like this and it works perfectly. The 555 can handle 18v so 12v should not be a problem. It is better to use gate voltages at 12v as the mosfet will turn on better and heat up much less.

If the mosfet you are using is suspicious use a new one.
Hope you are successful.

hm well the diode on the motor can unsoldered and it did not burn anyrthing out probably because I put a diode in series with the 555 (phew lucky I had that second thought saved me another € 1.1 on another 555) well it did not burn the ic out but the motor did slow down, now I presume that this is because the reverse curent spike is trying to drive the motor in the other direction right ? but i had a thought: If i disconected that diode that is getting hot so some curent is going into it and getting wasted in heat whay not remove it altogether as my purpose is also to be as energy efficient as possible or will this require the sme amount of current extra to keep it going at the same speed ?like the power is lost anyhow ?

I also had another crazy thought: say I had two scotky diodes and rechanelled the reversed spike back into the power supply say putting a 12>14 volt zener diode accross the power to protect from the highest peaks of current ? I nkow this sounds crazy but I am talking of being as efficient as possible and anything getting hot is a waste of power.

can I remove the gate resistor completely ? as fastest switching of the mosfet is preferable as we are at quite a high speed now

say guide thats a pretty craped up site you found it is more adverts and non existing links thatn a real site and there are not any explanations for the diagrams not to mention the "exelent" quality of english I think some dude is out to make some money on adbverts and waste our time unless that is a site started like 10 minutes ago, you can't even contact them

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