Re: 555 PWM circuit

I am not sure about the motor ratings.

I tested it and I have this values:
12V
No load: 1,5 A
Normal use (conected to a gearbox and to a wheel and moving 80kg in a
flat path): 10A

I saw the 30A peak while trying to climb a small step.

So what do you think is the best idea? Use a more powerfull
transistor? Connect 2 BUZ11 in parallel? And what do you think about
the new design that "Phil allison" posted some posts above:

http://www.cpemma.co.uk/555pwm.html

Thanks.



On 18 nov, 22:48, Nobody <nob...@xxxxxxxxxxx> wrote:
On Sun, 18 Nov 2007 11:12:07 -0800, Vicente wrote:
I will try with that capacitor, but, do you know what is for? and can
I use a "non-polraity" capacitor?

It's for supply decoupling, i.e. preventing the switching current from
causing noise on the supply lines.

It doesn't need to be polarised, but polarised electrolytics are normally
cheaper than the alternatives at large sizes (i.e. >1uF).

On the other hand, what do you think about using 2 parallel BUZ11 (30
A peak burnt out one)? How do I have to connect them?

You can connect FETs in parallel. Just connect all pins of the same type
together (i.e. connect both gates to the 555, both drains to the motor,
both sources to ground).

But you need to look into why you're burning out a FET rated at 33A while
driving a motor which you say is only supposed to draw 10A.

If the motor is rated at 10A at no load, it could draw a lot more while
spinning up. You should really think about adding current limiting.

More generally, don't expect to be able to take a circuit designed for a
couple of amps and just scale the components up to handle ten times that.
At lower currents, some things can just be ignored, while they may need to
be dealt with at significantly higher currents.

.

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