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Can I replace the 1N5395 diode in this diagram with a FR157 diode? Basically I need to lower the heat of my hair dryer and I think the 1N5395 diode in this diagram does exactly this but I have only a FR157 and also I read it's better to use 4 amps or even 6 amps diode like the BY500-400! Care to elaborate? Thanks!

enter image description here

http://www.seekic.com/circuit_diagram/Electrical_Equipment_Circuit/POKO_TD_169C_Hair_dryer_circuit_diagram.html

Edit: So in my dryer I have this heating element (220V, 150W): enter image description here

Wouldn't a FR157 or a RL205 work to cut the power in half thus reducing the temps?

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No your plan is not going to do what you want. First of all the FR157 has a max reverse voltage of only 50V which is not sufficient for this use. Secondly, and more important, the existing circuit uses the diode at a half-wave rectifier. This cuts the power into the hair dryer in half when you switch it to "low". So the only two options are 100% power and 50% power. Putting a different diode in place of the 1N5395 will get you back to the same place you started.

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  • \$\begingroup\$ Sorry, but I am noob. What's the difference between FR and 1N? The max reverse voltage? I googled both and both are "Fast rectified diodes"? Also, can I replace it with a RL205 Diode? It has 600V max reverse voltage and 2 amps? Thanks! \$\endgroup\$ – Gigamegs Jun 16 at 11:53
  • \$\begingroup\$ @Gigamegs I'm not clear why you want to replace the diode at all. \$\endgroup\$ – jwh20 Jun 16 at 13:12
  • \$\begingroup\$ @jwh20 It's broken. Wouldn't the RL205 work? Thanks! \$\endgroup\$ – Gigamegs Jun 16 at 13:16
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    \$\begingroup\$ Yes, it looks like an RL205 is a suitable replacement for a 1N5395 in this application. It has a 2.0A avg. forward current rating and a 600V reverse voltage rating. \$\endgroup\$ – jwh20 Jun 16 at 13:30
  • \$\begingroup\$ Repair is a better reason to ask the question just about any 1n diode with the ability to handle line voltage at the same current or more would work the data sheet for the 5395 shows 280v rms max and 1.5a for your application you just need to exceed these values with the new part, note if the heating element is shorting it will immediately blow the new diode. For a repair Yes an rl205 would work it is 2 amp 420v rms . \$\endgroup\$ – Ed Beal Jun 16 at 13:32
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I was posting as a comment on diy but it moved here and i don’t have the rep to upvote or comment here so left as an answer.

Do you understand How diodes work?

You will see no real difference max rms voltage on both is well above line (280/700)voltage they both breakdown around .6 v in one direction and block in the other the fr157 has a higher breakdown spec but that is irrelevant they both will do the same thing. In this circuit as jwh20 mentioned in his answer the data sheet I looked at showed the 157 as700 but as I said it is irrelevant both diodes will do the same thing.

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  • \$\begingroup\$ Good question. I read about it here: elprocus.com/…. Basically it cuts the AC in half? I also read it's technically forbidden for heavy applicance, because it has somewhat negative effects on the power grid! But's so cheap and thus so popular. Thanks! \$\endgroup\$ – Gigamegs Jun 16 at 13:40
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    \$\begingroup\$ Yes a diode is a 50% reduction. many dimmers in the past were SCR’s silicon controlled rectifiers they do the same but also can vary the turn on point in the half wave the longer the delay the dimmer the lamp. Wave shaping electronics diodes, SCR’s and triacs all create harmonics and in heavy loads AFCI protective devices may trip as some can not tell the difference in an arc and the noise created by the electronic wave shaping. Most consumer electronics use these devices in the power supplies. \$\endgroup\$ – Ed Beal Jun 16 at 14:16
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No you can't. FR157 is only good for 1A, your hair dryer almost certainly uses much more current than that.

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