Gerula

Does anyone know the exact specs for this resistor? Mine is crispy beyond recognition.


Thanks in advance.

YHR

Find out out why it got crispy before you change it.

BlackCat_2

R22 on RX18 -
Red - 2
Red - 2
Gold - 0,1

22*0,1=2,2 Omh,

This resistance limits the current through the transistors and motors

Gerula

Are you sure it's not red-violet-gold, like it's neighbour R18? (2.7ohm)

BlackCat_2

You know - on my card RX -18 This resistance is the same and there are two red and two gold stripes.
But it is not critical 2.2 or 2.7. Power Dissipation resistance is more critical. So - 2 - 3 Ohm - this is normal

Gerula

So it would be a good idea to put there a higher wattage resistor? In order to better protect the power transistor Q5?

BlackCat_2

At first glance - you're right.
But maybe - not really.
These resistors as fuses are current. If the current (the total power consumption) rises more - resistors burn. Motors - will not have time to burn . But transistors - will still burn in any case,

With higher wattage resistor - Motors - will burn too

Gerula

So basically it would be the other way around: putting a lower wattage resistor will protect both the power transistor and the motors, right? But it would probably burn more often.

BlackCat_2

None. This is not a good idea. As you said - these resistors will burn even more from working currents.
But in excess these currents - all the same transistors will burn first

Gerula

And now the big question: what's the wattage of the stock R22? I checked today at a local alectronic shop, and found some that are of the same body lenght but slightly thinner, and others that are much larger (1.5x long, 1.5 thick)

BlackCat_2

Unfortunately now I have forgotten the table size and wattage resistors. And I can not exactly answer your question.
Ask the store resistor of the same size.
In no case - no more.
If you will be given approximately two times less - take 4 pieces of double the value of resistance. And connect the two pieces in parallel.

Or for first - try - the same body lenght but slightly thinner

Gerula

Thanks a lot, I'll give it a try.

YHR

Replace it with the same resistor. Higher wattage won't hurt, and in this case might be beneficial. I higher wattage resistor still offers the design resistance needed in the circuit. It can handle more current flow though.