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relay for electric fan


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Ikessky 
Member - Posts: 13
Member spacespace
Joined: January 25, 2005
Location: United States
Posted: April 26, 2011 at 12:50 PM / IP Logged  

I'm hoping the gurus here can help me with a little question I have about installing an electric fan in my truck.  This is the diagram I will be using:  https://img.photobucket.com/albums/v697/ikessky/schematic.gif

This is the relay that is supposed to be used in the diagram:  https://img.photobucket.com/albums/v697/ikessky/relay_0332002156_relay_drawing.gif
Here is a relay that I can get for free:  https://img.photobucket.com/albums/v697/ikessky/relay_0332002150_relay_drawing.gif

I see that the difference in relays is that the 156 has an internal diode.  What am I at risk of if I use the 150 relay instead?  From what I can tell, I could risk back-feeding a voltage spike into my fan controller if I don't have the diode.

oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: April 26, 2011 at 5:39 PM / IP Logged  
You are "at risk", but fairy small.
But you can easily add an external diode - typically a 1N400x type (1N4004, 1N4007). Cost about 5c to 20c each - though I suggest by several - even a pack of 10 or 100 (100 for $5).
They come in handy when (a) you lose or wreck the first "one & only" you bought with $15 P&P or petrol, & (2) whenever you want to parallel or interconnect different signals to control a relay or lamp etc, or suppress other spikes etc.
The diode "line" end should go towards the +ve end of the coil (ie, #86), other end to -ve end (ie, #85).
syl20rochon 
Copper - Posts: 298
Copper spacespace
Joined: October 16, 2009
Location: Ontario, Canada
Posted: April 26, 2011 at 6:09 PM / IP Logged  
Make sure the your relay is rated at 75amps and yes use external diodes to avoid spikes.
Sylvain Rochon
MECP security specialist
Tech support for remote starters
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Ikessky 
Member - Posts: 13
Member spacespace
Joined: January 25, 2005
Location: United States
Posted: April 26, 2011 at 8:34 PM / IP Logged  
I'm sure that I can find some diodes at work that I can use also. The relay I will use is a 75a, it just doesn't have the internal diodes like the one in the original diagram. I'm already putting a 1N5406 diode (600V, 3.0A) on the fan itself. Would one of those work on the relay also or is that too big? I see the ones you recommended are only 1.0A.
When I wire in the diode, does it matter how I do it or just that it connects from the wires on #85 and #86 (like an "A" or a "H" if you will)? Obviously which end goes where matters, as you stated before.
syl20rochon 
Copper - Posts: 298
Copper spacespace
Joined: October 16, 2009
Location: Ontario, Canada
Posted: April 26, 2011 at 8:49 PM / IP Logged  
A diode is like a fuse, the coil of a relay draws around 150mA so I would recommend a 1amp diode. Also, make sure that you install it in it's proper polarity. The grey lines is called a cathode and should be on the positive side.
relay for electric fan -- posted image.
Sylvain Rochon
MECP security specialist
Tech support for remote starters
26 Years of experience counts
I'm here to help.
Ikessky 
Member - Posts: 13
Member spacespace
Joined: January 25, 2005
Location: United States
Posted: April 26, 2011 at 9:47 PM / IP Logged  
That answers my questions perfectly! I greatly appreciate all the help guys! This truly is a low buck project. I bought the controller on ebay for less than $20, the relay and diodes are free, and the fan will run me around $60 or less!
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: April 27, 2011 at 2:52 AM / IP Logged  
With thanks to syl20rochon - at last! - my style of diagram.
And I'll probably use that in the future (assuming that is ok) though I might add a + & - to show the major point that the Kathode (line) end goes towards +ve. [Otherwise the diode is forward biased hence effectively a short between + & - and hence blowing the control circuit or fuse or the diode!]    
IMO it's a great diagram. It even "aligns" the main contacts to show that 87a is "normally" connected (hence its NC label/designation where Normally means as if it's on the shelf - ie, de-energised - as opposed to whatever its normal operating position might be...
And it shows that the switch arm goes to the NO Normally Open #87 contact when the coil is energised thereby pulling the arm in towards the coil.
Those conventions seem to be common and what I endeavor to do in circuit diagrams, though for layout reasons that may not always be followed (ie, Reader: always beware!). But I always show relays in their de-energised state (ie, "Normal") EXCEPT when explaining how a circuit works whereby I might show it in its energised/closed position to clarify power flow...
The actual relay-coil ends are really irrelevant but #86 is the more +ve by convention - that convention being for relays with inbuilt diodes. (Cathode is always #86.)
I don't use inbuilt-diode relays hence I don't worry about the convention in practice... I prefer external diodes so that I can easily replace them, and also "swap" ends if that better suits my layout.
But I stick to #86 +ve & #85 -ve in diagrams IF I include those labels. (That has only happened since joining this forum!) My diagrams are circuit or schematic diagrams for easier operational understanding by readers, and they can use their relay of choice. (EG - I tend to use Jap JIDECO and others that do not have those DIN labels. Whereas this (and most) forums/sources tend to use Hella/Bosch types, AND show physical diagrams to assist wiring installation etc.)
Ikessky - the 1N5406 is fine. Yes it's big, but a (power) diode is a power diode - usually only its current capability is the critical factor.
And for spike suppression - usually a voltage of or above 200V, but 400V (IN4004) is the commonly available lowest voltage power diode. [And a bit of extra margin; 12V coil spikes are often ~100V and sometimes around 200V, hence 400V or higher is chosen. FYI - that's the breakdown voltage aka PIV of the diode which means (eg) above +400V at the Kathode end overcomes the diode's reverse blocking voltage capability (aka breakdown voltage), hence letting through current, and possibly or probably damaging the diode. PIV is Peak Inverse Voltage.]
The 1N5406 600V/3A diode exceeds the usually recommended 400V/1A diode. It will handle an extra 200V and 2A - not that current should be an issue (1A is enough), though it does imply more electrical ruggedness. (You can quench a 600V 3A spike, so the expected <200V <1A is no problem. But other things apply too - like construction - eg, because its bigger it may have more flexing/vibration (probably irrelevant); or maybe different internals that aren't as physically strong.)
But use the 1N5406 etc. It's free, or cheap, or available.
And yes, I have blabbed again, but hopefully provided more understanding (else shown my misunderstanding!!), and enabled you to remedy problems more easily - eg, in the very unlikely event that the bigger & better 1N5406 seems to continually break...   
Geez - that was almost Diodes-101 and Diodes-102! (Or Diodes-201?)
Professor Rambles over & out. (Over & Out for this reply only...)
PS FYI - I write Kathode to match the diode's circuit symbol and the band/line on the diode itself. The arrow-head in the K shows the direction of current flow, the upright | in K and line/band on the diode being the "brick wall" end that blocks current should it try to come in that way. When looking at a real diode, picture the K and IMO you easily remember which way current flows.)
Ikessky 
Member - Posts: 13
Member spacespace
Joined: January 25, 2005
Location: United States
Posted: April 27, 2011 at 6:50 AM / IP Logged  
Many thanks to all of you!  This thread has really helped me understand how a diode works and the importance of them.
Ikessky 
Member - Posts: 13
Member spacespace
Joined: January 25, 2005
Location: United States
Posted: April 27, 2011 at 9:17 AM / IP Logged  

One more question.  What size fuse should I use coming from the battery?  The diagram shows using a fuseable link, but I like the idea of a fuse instead.

syl20rochon 
Copper - Posts: 298
Copper spacespace
Joined: October 16, 2009
Location: Ontario, Canada
Posted: April 27, 2011 at 9:26 AM / IP Logged  
It all depends on the rating of your fan, it's normally written on it.
Sylvain Rochon
MECP security specialist
Tech support for remote starters
26 Years of experience counts
I'm here to help.
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