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Why anti grind/starter cut relays drain batteries.


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howie ll 
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Posted: August 16, 2011 at 5:37 AM / IP Logged  
X 2 with Oldie, does that make me Howie 8? The point is
85 = Neg side of coil,
86 = POS side of coil
Above two are by international convention, in fact it doesn't matter or5 even better remove it from the relay and place in line on the alarm's GWA, neg when armed with the diode band towards the alarm.
30 input and 87 output.
Again in real life doesn't matter but with a 5 pin, 87a is connected at rest to 30; on activation 87a is connected to 30.
oldspark 
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Posted: August 16, 2011 at 6:16 AM / IP Logged  
ImAnIdiot Due Diligence #2 for 20110816:
As corrected:
howie ll wrote:
Again in real life doesn't matter but with a 5 pin, 87a is connected at rest to 30; on activation 87 is connected to 30.
IE - 87 to 30 is closed when activated, not 87a.
Otherwise correct, a relay coil doesn't care about the 85 & 86 polarity (+ or -), it is only when adding a spike-suppression diode that it is important. Get the diode wrong, and it will burn out (since it's a short from +12V to - or gnd) which may damage the controlling circuit (alarm) due to over-current etc, but shouldn't have detrimental effects on the relay; the diode can be replaced. So too any burnt skin or maybe any damaged eye injured during the diode burn-out. In case of fire etc, consult your insurance policy, but the supply of a relay-diode in contravention of the normal conventions should rule out any "Act of God" insurance clauses. (But check too for "Act of Idiots (other than yourself)" clauses.)
howie ll 
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Posted: August 16, 2011 at 6:34 AM / IP Logged  
Oops Why anti grind/starter cut relays drain batteries. - Page 2 -- posted image.
tenchu 
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Posted: March 03, 2013 at 2:36 AM / IP Logged  
howie ll wrote:
X 2 with Oldie, does that make me Howie 8? The point is
85 = Neg side of coil,
86 = POS side of coil
Above two are by international convention, in fact it doesn't matter or5 even better remove it from the relay and place in line on the alarm's GWA, neg when armed with the diode band towards the alarm.
30 input and 87 output.
Again in real life doesn't matter but with a 5 pin, 87a is connected at rest to 30; on activation 87a is connected to 30.
Thank you for this post... I will have to fix my relay in the morning. After reading your explanation, I would assume that this incorrect wiring would also prevent from the relay actually cutting off the starter?
howie ll 
Pot Metal - Posts: 16,466
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Posted: March 03, 2013 at 3:16 AM / IP Logged  
Yes.
Correct circuit. but if using a pre-supplied relay holder, always check if there's a diode present then look for the diode band. That's the POS side of the coil.
tenchu 
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Posted: March 03, 2013 at 11:23 AM / IP Logged  
There is a diode, should I replace with a regular relay?
howie ll 
Pot Metal - Posts: 16,466
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Posted: March 03, 2013 at 11:26 AM / IP Logged  
No, just make sure that the side your band points to is where your ignition + supply goes.
Frankly if you have to ask this question you shouldn't be attempting this install.
oldspark 
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Posted: March 03, 2013 at 5:16 PM / IP Logged  
Though in fairness, I reckon many competent wirers & DIYers can have problems with diodes.
But IMO, once the correlation between the diode symbol & its body-line are understood, then any application should be easy.
VIZ:
- (conventional) current flows from +ve to -ve,
- current only flows in the direction of the diode symbol's arrow;
- the arrow points into the perpendicular line which is at the same end as the line on the diode's body.
Also the ---|<-- symbol is like a "K", hence the line end is the Kathode = cathode, ergo the other and must be its anode. (That's in case readers strike those references.)
The only complication in this case (where used as a snubber or spike-protector across relay coils) is that the diode's -ve end (for normal current flow) goes to the +ve of the coil.
Though it may not be obvious that that is to short circuit the spike when the relay coil's -ve end (85) is more +ve than its 86 end, it should be obvious that if connected the other way (Kathode or line or "-ve" end to relay coil -ve & anode/+ve to 86), then that diode will conduct when 86 is +ve, and hence blow itself else the fuse or circuit driver since the diode conducts the current from 86 (+12V) to 85 (-ve or GND).
All the above is easy to see on a diagram with + & -/GND with a coil and the diode circuit symbol (with its arrow) and comparing the 2 diode connection possibilities.
(This should not be text only tutorial.)
automatedsales 
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Posted: August 28, 2013 at 10:59 AM / IP Logged  
informative post, I suddenly missed doing project
Automated Sales
overworked 
Copper - Posts: 133
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Posted: September 07, 2013 at 5:57 PM / IP Logged  
I often recommend to people using a pull up resistor instead of diode, this way they can wire the coil any direction they want.
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