# The proper way and reason to use a relay with remote turn on wire for multiple amps



## BlueSQ (Mar 22, 2007)

I'm making a thread about this topic after doing a ton of research in a lot of different threads. The information wasn't conflicting as much as it just left me with more questions. I thought I had this thing down, I bought the bosch style relay, had everything ready to go.

Then I read this: "I'm not a fan of the bosch style relays for this application. The coil on some will pull upwards of 200ma which may be more than several amps combined. Some amps will require only 1ma to turn on while others may require 50ma or more. First thing I would do is get out your dmm and see how much current is being used without a relay before you decide if you really need one or not. If you insist on using a relay I'd try to find a smaller one that has a lower current requirement for the coil or if you insist on using a bosch style relay I'd use the circuit about halfway down this page to lower the required current for the coil."

(From here: http://www.diymobileaudio.com/forum...7-remote-wire-distribution-relay-help-me.html )

There was also this: "If you use a relay, place a 1n4002 (for example) diode in series with the remote out from HU to avoid possible damage to headunit."

and

"...Using a flyback suppression diode between the positive and negative legs of the coil, along with a blocking diode in series with the head unit turn-on Power Wire (line on the diode facing towards the relay) is a common practice. In fact, most of the 28vdc relays we use on aircraft have a suppression diode already built in, and we still add a blocking diode on the positive leg of the coil if the Power to the relay coil is being supplied by a sensitive unit and not by a direct power bus. I'd actually advise doing both as well, diodes are inexpensive, and it will provide another level of protection for your head unit"

(From here: http://www.diymobileaudio.com/forum...cussion/162813-using-relay-turn-two-amps.html )

That lead me to research the diode mentioned in that post as well as the low current coil requirement. Turns out that's kind of a lesser known but highly recommended method of wiring this up.

So from the general advice of "use a bosch style relay" that's thrown around I found two major caveats in using a remote wire relay:

1) *A relay coil can draw more current than multiple amps / dsps*

AND

2) A* diode is mandatory*

Good luck trying to find any product that fits both of those bills. Even the pre-made amp relay kit from SMD doesn't have the diode and doesn't specify relay coil current draw. I saw this: Install Bay ERS-126 (ers126) 3 Wire Relay Socket With Diode but it is only a 3 wire relay and not designed for the remote turn on application.

That's a lot to consider for what I thought was simple. Given that info, I have to decide if I even need the relay. That was an entirely separate set of research. It's my understanding that you *ONLY need a turn on remote wire relay if you have voltage drop at the furthest accessory in the chain.* So if I check voltage at the remote terminal on the furthest accessory in the setup and it's anything less than 11.8-12v I need one because in that case the current draw is proving too great for the headunit.

My set up consists of two amps, a dsp and satellite radio receiver. I have one splice at the head unit to power the satellite receiver, the other run of that splice goes to the trunk where the two amps and dsp are. I didn't daisy chain it in the back, rather I spliced it and sent it out 3 ways from there. Once I finish wiring it up under the hood I'll be able to check the voltage but I just wanted to confirm the above info with the forum.


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## bugsplat (Nov 7, 2014)

Hmmm very interesting... i'm going to have to test mine. I'm honestly not sure what I have. Grabbed the first relay I saw at the autoparts store. Figure they all would act the same. 

One benefit to a relay that was not mentioned to me was getting your smaller devices on the same Pos line as your amps. You can use your cars remote line to trigger the relay and in turn power your small devices. This allows me to hook up all devices off the same distro block. I use the relay to segregate the cars engine-noise laced accessory line from my gear as much as possible. My bluetooth receiver had a horrible whine before I used a relay. Don't know whats going on with my cars electrical system but the factory accessory line is very noisy.


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## Bayboy (Dec 29, 2010)

Doesn't having a DSP negate the use of a relay especially since you're only powering up two amps after that? Mine goes from deck remote out to dsp. Then dsp remote out to amps. Skipping the dsp's remote can increase turn on/off noise as well it would seem.


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## bugsplat (Nov 7, 2014)

My Minidsp C-DSP has a delayed remote. Has a 1.5-2sec delay to the amps I think. Works well. I may have gone overboard and added the DSP to the relay and the amp get turned on by the DSP.


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## BlueSQ (Mar 22, 2007)

Bayboy said:


> Doesn't having a DSP negate the use of a relay especially since you're only powering up two amps after that? Mine goes from deck remote out to dsp. Then dsp remote out to amps. Skipping the dsp's remote can increase turn on/off noise as well it would seem.


Yes, if your DSP has a remote out.

Unless I'm missing something, a Mosconi 4 to 6 does not have that when using low level pre out inputs.

However yes, if you have a product with a remote out like a Phoenix Gold DD5 then this is not an issue for you - you would not need a relay.


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## Lanson (Jan 9, 2007)

Shoot, that's something to think about! I have used a relay often but never added diodes.

I'm using a solid-state relay at the moment, which seems good. I think NVX makes it.


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## claydo (Oct 1, 2012)

I have never used a relay, and haven't had any trouble......maybe I'm just lucky, but my pioneer head unit has been remote activating three amps for several years with no issues......


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## seafish (Aug 1, 2012)

IN short the reason to use a proper diode is to prevent high voltage spikes from damaging equipment while the relay coil energizes and de-energizes. 

BCAE has the best info and explanations on the use of relays and diodes. Skip to the section on "quenching diodes" or read the whole dam thing cuz its so good--

Relays


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## Bayboy (Dec 29, 2010)

BlueSQ said:


> Unless I'm missing something, a Mosconi 4 to 6 does not have that when using low level pre out inputs.



Yikes...... never thought they would make something like that. Seems a bit odd since you only have 6 outputs (1-2 amps max).


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## BlueSQ (Mar 22, 2007)

Bayboy said:


> Yikes...... never thought they would make something like that. Seems a bit odd since you only have 6 outputs (1-2 amps max).


If you use high level RCA inputs, that acts in itself as a turn on signal for the processor. Then you can use the remote terminal as an output to amps and such.

If you are using low level signal RCA inputs (like I am) then you have to use a remote wire to turn it on.

This is specific to my application, but the idea is the same. I have the remote wire spliced out because I'm hesitating on using a relay. As far as I can tell, the specific diode resistance and the exact mA required to open the relay hasn't been determined for 12 volt car audio and/or isn't listed on most products out there making it difficult to choose out of the thousands of bosch style relays. Why add a relay if it takes more power to open it than it does to power all accessories combined - plus the point in which is opens and closes (like seafish mentioned) seems to be an additional cause of issues if a diode isn't applied - and again, even if it were applied, what specific resistance should it be?


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## Bayboy (Dec 29, 2010)

Yeah.... just seems crazy they would make that DSP like that. Not like it would be meant to turn on enough amps to be trouble. Can't blame you in this case.... I would have done the same especially running no more than one (5 channel) or two amps for the whole setup. A relay seems a bit too much for such a case.


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## Mike Warren (Oct 26, 2016)

BlueSQ said:


> Then I read this: "I'm not a fan of the bosch style relays for this application. The coil on some will pull upwards of 200ma which may be more than several amps combined.


It's almost always fine to drive 2 or 3 amps from a single remote output, but if you need more drive current, use a solid state relay.

The installers where I work use these for this sort of thing:

*ASV3222 Programmable Switch*

It can be programmed with a turn-on delay to prevent turn-on pops. (unfortunately, nothing can help with turn-off pops.)


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## GEM592 (Jun 19, 2015)

My 80 PRS has turned on five old school Orion amps (plus the 3 preamps, two crossovers, and one bridging module they power) without any relays with no problems whatsoever for several years now.


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## Sine Swept (Sep 3, 2010)

Here's another trick. Dust off your multi meter and set the dial to DC amps. Remove the remote wire from your amp. With the leads of the meter jump + Battery to the now empty Remote terminal. Your amp will turn on and the current draw will be displayed on your meter. I have read of some headunits being only capable of a 300 mA draw. I have also read of some amps out there that use a fair amount of current to turn on, not that I have found one in testing. There are also ways of using a transistor to make a solid state relay, ie the same concept as a relay without any moving parts and no collapsing coils!


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## Mike Warren (Oct 26, 2016)

Sine Swept said:


> I have read of some headunits being only capable of a 300 mA draw. I have also read of some amps out there that use a fair amount of current to turn on, not that I have found one in testing.


Neither have I, and I've been in the car audio industry for over 30 years.




> There are also ways of using a transistor to make a solid state relay, ie the same concept as a relay without any moving parts and no collapsing coils!


This is a circuit for that. With the BD139 it can supply up to about 700mA.


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## syc0path (Jan 23, 2013)

BlueSQ said:


> It's my understanding that you *ONLY need a turn on remote wire relay if you have voltage drop at the furthest accessory in the chain.*


That's not necessarily true. There will be some variability in the voltage required to turn on various devices. I had 2 amps in a car, and if I turned it up a little bit w/ the car turned off, the mid amp would cut out while the sub amp would continue to play. I checked the voltage at the at the battery terminals and remote terminals of both amps, and both amps were getting the same voltages. Basically, the mid amp required a slightly higher turn-on voltage than the sub amp. 

I thought about adding a relay, but then (as mentioned in this post) I realized that a Bosch-style relay would draw more power than both amps and the processor combined. So I upgraded my grounds to increase overall voltage, and that fixed the issue.


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## masnow (Jul 7, 2017)

I think this question may be elementary for some but what, if any, effective difference is there between splicing the rem wire from 1 to 4 lines versus daisy chaining from one amp/processor to the next?


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## JH1973 (Apr 21, 2017)

Bayboy said:


> Doesn't having a DSP negate the use of a relay especially since you're only powering up two amps after that? Mine goes from deck remote out to dsp. Then dsp remote out to amps. Skipping the dsp's remote can increase turn on/off noise as well it would seem.


Agree and glad you posted.My remote goes from HU to DSP and from DSP remote out to first amp then from that amp to last amp.I've had 0 issues with pops turning on or off.


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## schmiddr2 (Aug 10, 2009)

masnow said:


> I think this question may be elementary for some but what, if any, effective difference is there between splicing the rem wire from 1 to 4 lines versus daisy chaining from one amp/processor to the next?


Parallel vs series. Not going to make a difference for a remote wire. Just depends on the layout of the amps which one is easier. If the voltage drops in series then it will it parallel as well.


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## sheldoncreamer (8 mo ago)

I think the whole relay thing is because people started adding led lights to the amp rack. you obviously don't need a relay if your going from mobridge to DSP to amp 1 then amp 2.


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