# Using a relay to control remote turn on.



## DonutHands (Jan 27, 2006)

i was suggested to use a relay as a possible fix for my amps turning off while in use.

i will be using the remote turn on to control 3-4 amps and a crossover.

so other than a relay purchased at radioshack, is there anything designed specifically for car audio applications?


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## coffee_junkee (Jul 13, 2006)

A Bosch or similar relay can be had at Autozone or NAPA for cheap. Rat Shack has them too. Wire her up like this:

85-Ground
86-Remote turn on from your deck
87-Fused lead from your distro block or other suitable constant +12v
30-Out to all your amps/processors

That shoud get you fixed up bud!!

Kris


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## DaveRulz (Jun 22, 2006)

I have found this helpful in the past

http://www.partsexpress.com/resources/relays.html


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## jeffrey (Jan 3, 2007)

Yep! And you can use 87a for things that require absence of power to activate.


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## DonutHands (Jan 27, 2006)

specs from the amps im using

4 Channel Amplifier4 x 75 watts into 2 ohms, 4 x 50 watts into 4 ohms, 2 x 150 watts bridged mono into 4 ohms, 0.1% THD from 20 to 20kHz. 85 dB signal-to-noise ratio. 20 Hz - 20 kHz frequency response. Number of channels: 2/3/4/5/6. 150 mV - 4V input sensitivity, 10 k ohms input impedance

is that 150mV voltage used by the remote turn on? if so, isnt that kind of high?


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## azngotskills (Feb 24, 2006)

no thats from your HU via RCAs iirc


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## DaveRulz (Jun 22, 2006)

no, that 150mv is not the amp turn on voltage. That's the bottom end of the input sensitivity. 

Remote turn on runs off of 12 volts. Run the remote wire from your head unit to 86 on the relay. Run a separate fused constant power wire to 87. Ground 85. Connect the remote turn ons for the amps to 30.

This will turn your amps on with your head unit.


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## chad (Jun 30, 2005)

Put a Diode in parallel with the coil of the relay to snub back EMF, it's not REALLY needed for mechanical type closures but for semiconductor based turn on circuits like in a stereo it can mean life or death of the circuit.

Chad


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## DonutHands (Jan 27, 2006)

chad, i dont really know what you are saying.

put a diode? in parallel? with the coil of the relay.

so i connect somthing to the remote turn on wire before it reaches the relay?


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## solacedagony (May 18, 2006)

So I guess the diode would go between 85 and 86?


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## chad (Jun 30, 2005)

In parallel with the coil of the relay The banded side of the Diode should be on the lug with the remote lead, the un-banded side on the side with ground. Use a 1N4001 or better. An 01 will be quite fine for this app though. Just solder it right to the lugs or incorporate it into the plug if using one. Many Bosch style plugs already have the Diode built in 

When a relay disengages it can/will produce an EMF pulse sometimes in the order of tens of times the working voltage, sometimes more, transistor based turn on devices don't care for this too much. This is why you will also see diodes across A/C clutches, etc. ALL relays MUST have them in the electronic world for longevity of the driving circuitry. 

Don't believe me? Put your fingers across the batery in your car, don't feel squat eh? Now have someone clack the starter and see how fast you get off of that battery  Back EMF rearing it's ugly head. This is why they say to unplug your cell phone charger before starting your car. Reverse polarity diodes in amps and accessories do more than protect from reverse polarity 

Chad


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## BodegaBay (Dec 16, 2005)

If you did a search, you would have found this DIYMA thread in July 2006 that answer your exact questions.


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## DonutHands (Jan 27, 2006)

does the amp rating matter much? 1A or 30A?

also, how do i determine what size fuse i should be using?


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## chad (Jun 30, 2005)

For the diode? Nope, it is for the coil, the amp rating is the rating for the contacts.

For this app the higher the amp rating is not necessarily better. Higher rated relays usually have a higher pull force which equates to more energy needed to pull the contacts down. If you are having problems such as you are now you need as low of current draw on the turn on circuit as possible! The pull force is higher for a faster disconnect to prevent arcing of the contacts under load if they are just creeping away.

Again the remote turn on current required is peanuts for modern gear, unless you are using older relay controlled devices, and I mean OLDER then I don't see why the headunit can't turn the stuff on and keep it on  But I've been baffled before!

The link that Bogeda Bay just provided has a tutorial from BCAE SP? that is very good for you to read right now. It will explain ALL of your questions, but we are always willing to help too!

Chad


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## SteveLPfreak (Sep 26, 2005)

chad said:


> Put a Diode in parallel with the coil of the relay to snub back EMF, it's not REALLY needed for mechanical type closures but for semiconductor based turn on circuits like in a stereo it can mean life or death of the circuit.
> 
> Chad



As usual, Chad's correct. Just get this relay from Navone and be done with it.

http://www.autosound2000.com/filters.html


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## DaveRulz (Jun 22, 2006)

Yup, I learned something. I'm going to have to put a diode on my amp turn on relay.


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## khail19 (Oct 27, 2006)

SteveLPfreak said:


> As usual, Chad's correct. Just get this relay from Navone and be done with it.
> 
> http://www.autosound2000.com/filters.html


The only one I see on that page is the N-52R Isolating Relay, second from the bottom of the page. I'm assuming that's the right one?


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## DonutHands (Jan 27, 2006)

well my gear is new, so this relay may not be my fix at all. 

but i might as well try it out with this relay because i can pick it up local

http://www.radioshack.com/product/i...w=relay&numProdsPerPage=100&parentPage=search

and a 7.5 amp fuse before the amps


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## SteveLPfreak (Sep 26, 2005)

khail19 said:


> The only one I see on that page is the N-52R Isolating Relay, second from the bottom of the page. I'm assuming that's the right one?



Exactly. The N-52R works great, takes care of back EMF, and has a high input impedance.


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## chad (Jun 30, 2005)

internecine said:


> well my gear is new, so this relay may not be my fix at all.
> 
> but i might as well try it out with this relay because i can pick it up local
> 
> ...


That and the diode will solve the romote turn on voltage drop (with a fuse (1A) on the relay INPUT side of the new turn-on source)

If that don't work your problems are greater :blush: 

Lose the 7.5 before the amps. If it does not turn on with 1A then something is very wrong unles you are running something H-U-G-E! 

Chad


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## DonutHands (Jan 27, 2006)

relay, diode if it dosent have one, and 1A fuse on the remote


thanks chad, reading it on forum posts and bcae1.com are one thing, but additionally having people help with specific questions is a big help

thanks


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## chad (Jun 30, 2005)

Need a 1A between B+ and the relay contacts (the new turn-on source), a 1A on the remote won't hurt but is not there normally.

7.5A is WAY too much, if you are consuming (popping) 1A as a remote turn on source there are problems somewhere.

Chad


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## DonutHands (Jan 27, 2006)

the 7.5A was from the relay calculator on bcae1.com but that was suggested to go between the relay and the devices being switched on.


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## ws6 beat (Jul 14, 2005)

what if you dont use the head units remote turn on instead you use ignition with a switch does that still require a diode.


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## chad (Jun 30, 2005)

Well...... maybe not..... but YES!!!! why risk it? A diode costs a few pennies. Granted the electrical system SHOULD absorb an EMF Pulse of a little relay but IMHO it's not worth it, I mean your starter does not have one, but again, what's a few pennies?

Chad


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