# Need help to calculate a couple of resistors

Discussion in 'General Electronics Chat' started by tavo91, Jul 13, 2016.

1. ### tavo91 Thread Starter New Member

Jul 11, 2016
15
1
Hi, I need some help to calculate the value of some resistors for a problem that I am trying to make.
I have a signal of 0 to 5 V(That part is not important I am not taking that in consideration in my circuit drawing) and I need to connect a fan of 120 VAC and 1200 walts(So I need a 10 A in the circuit ) so I already have the circuit but I am missing the values of the resistors so if somebody can help me explain how to calculate this values it will be really appreciate.
PD: If you guys think that my components can be better please let me know(MOC 3010 and BT137 )

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2. ### Papabravo Expert

Feb 24, 2006
10,338
1,850
To start with you need an estimate, from the datasheet for the MOC3010, of the forward voltage drop of the diode on the input side of the MOC3010. You also need to estimate the current you want to flow in the input diode of the MOC3010, in order for it to turn on the output TRIAC. That will allow the determination of R1.

3. ### DickCappels Moderator

Aug 21, 2008
2,746
665
It can become complicated and I don't have a good model to share, but the answer is presented in figures 9 and 10 of the pdf file at the URL below.
http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=moc3010&fileType=pdf

Now that you know how to drive the thing, expect it to be very noisy. I have tried this with 240 VAC 50 Hz and the fan buzzes loudly. Switching to a variable transformer made work smoothly and as quiet as ever -maybe more quiet since it was turning slower. Others have had similar experiences with fans and light dimmer type circuit.

4. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,497
511
I just looked at ti datasheet from 2009 for MOC3010.

It does not have any explanation about Rin. In their test circuit, Figure 1, they have input signal that is 5 volt pulses. If I remember fight, you also going to use 5 volt pulses for input. I would guess that you don't need Rin resistor because you are using input signal that the part was designed to receive.

Just in case, look at ti website for application notes for this part. Application notes often have a lot of practical info and howto that do not make into datasheet.

5. ### #12 Expert

Nov 30, 2010
16,655
7,294
The emitting LED is rated for 60 ma. From 5V, that needs (5 - 3)/0.06 =33 ohms
but I wouldn't run any LED at its maximum. Try 68 ohms

The thing R2 does is delay the start of the big triac. Try 180 ohms.

6. ### tavo91 Thread Starter New Member

Jul 11, 2016
15
1
But if i use the one in figure 9 or figure 10 it will be a current of 10 A?

7. ### tavo91 Thread Starter New Member

Jul 11, 2016
15
1
Also do you guys know any good program that can simulated this i only have Proteus but i am really bad with proteus.

8. ### benta Member

Dec 7, 2015
101
24
The MOC3010 needs minimum 15 mA through the LED to trigger in all cases. With a maximum LED forward voltage of 1.5 V, you have:
(5 - 1.5 V) / 0.015 A = 233 ohms. Choose 220 ohms as standard value.

For R2, the datasheet suggests 180 ohms, which looks right to me.

Benta.

9. ### #12 Expert

Nov 30, 2010
16,655
7,294
Thanks for helping me with the LED current. My usual datasheet site is down.

10. ### tavo91 Thread Starter New Member

Jul 11, 2016
15
1
Perfect! And another question can i skip the capacitor or not?

11. ### tavo91 Thread Starter New Member

Jul 11, 2016
15
1
Hey guys I already put the circuit together but I am getting a current of only 3.57 A any advice so it can be 10 A? I put the 180 and 220 Ohms on the resistors

12. ### DickCappels Moderator

Aug 21, 2008
2,746
665
Never heard of a triac being less than all the way on or all the way off more longer than a couple of microseconds. If you see 3.57 amps then that is what the load will take with the applied voltage (waveform being taken into account).

When talking about a phase controlled waveforms, the term "Amps" does not contain much information. True RMS, Average, Average represented as RMS...?