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Old 05-24-2020, 05:20 PM   #1
FAKKY
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When to use a relay

Outside of the obvious (30A draw etc) ........ when should you use a relay ?

I am planning on putting both of the devices on my truck. I have spared fused circuits from my EZ harness. Debating on plugging straight into them or adding relays. Both products below recommended relays.

~7.5A fused
https://www.amazon.com/Audio-Systems.../dp/B00IBI50NK

https://preview.tinyurl.com/y7v839y5
~ 3A tested with multimeter


So this got me thinking - I know the basics of relays and how to wire them ...... but why use them for those mid level draw accessories ..... 5A-10A. Cant these be protected adequated with correct gauge wire and fuse ? I mean there are plenty of 5-15A circuits on these wiring harnesses ?

I know would need to measure length of wire an guage to ensure could carry load ...... but outside of that ?
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Old 05-24-2020, 06:15 PM   #2
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Re: When to use a relay

I think some people end up using relays because the decorative switch they want to use for the device will not handle the current, although the wires going to the switch and device may be able to.
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Old 05-24-2020, 07:28 PM   #3
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Re: When to use a relay

I set mine up for big amp draws, and ign. hot stuff. So I know it's turning off when key is off.
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Old 05-25-2020, 09:47 AM   #4
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Re: When to use a relay

I guess what I dont get is why for example would a 7.5A max draw radio recommend a relay ....

when for example a cigarette lighter which draw 10-15 amps .... sits on just a fused circuit..... no relay.

The decorative switch thing makes a little sense ...... but most switches should handle 10A.

http://www.bosch-classic.com/en/inte...300300x_1.html

https://www.elecdirect.com/cole-hers...xoCiK8QAvD_BwE

etc
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Old 05-25-2020, 11:27 AM   #5
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Re: When to use a relay

That stereo looks interesting to me. I think you have a good idea putting that in your truck. Have you hooked it up enough to hear if the speakers sound good and have decided where to mount them? Let's see a picture of where in the instructions it is suggesting a relay, perhaps how they word it will give a clue about the reason they suggest one.
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Old 05-25-2020, 11:29 AM   #6
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Re: When to use a relay

It could be a general recommendation to avoid overloading the standard wiring harness. Older vehicles often don't have a lot of extra power capacity designed into the harness. By using a relay that pulls power direct off the battery or a high power junction, you lessen the chances of exceeding the max rating of the OEM harness.
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Old 05-25-2020, 11:46 AM   #7
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Re: When to use a relay

Quote:
Originally Posted by dmjlambert View Post
That stereo looks interesting to me. I think you have a good idea putting that in your truck. Have you hooked it up enough to hear if the speakers sound good and have decided where to mount them? Let's see a picture of where in the instructions it is suggesting a relay, perhaps how they word it will give a clue about the reason they suggest one.
Pretty basic instructions Going to hook it up now - will reply by this evening when finished with truck work as to how it sounds.





Quote:
Originally Posted by Dead Parrot View Post
It could be a general recommendation to avoid overloading the standard wiring harness. Older vehicles often don't have a lot of extra power capacity designed into the harness. By using a relay that pulls power direct off the battery or a high power junction, you lessen the chances of exceeding the max rating of the OEM harness.
Honestly - thats the best reason I came up with too. Seperate out the draw from the main harness. But then I got to thinking - well if I am not using a cigarette lighter ..... and another 10% of the circuits ..... and the radio already has a dedicated 20A circuit ...... then .... shouldnt need a relay

Which led me here.
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Old 05-25-2020, 12:38 PM   #8
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Re: When to use a relay

It's interesting the diagram shows a relay but the written instructions just say hook it up to a switched source. I think the instructions are poorly written or poorly cobbled together. Here is my theory: Somebody at some point may have drawn that diagram for a customer who was asking them how to incorporate a time delay relay so the radio continues to work for 30 minutes after shutting off the motorcycle. You can buy time delay relays like that, even adjustable ones. So the diagram probably was accidentally included in the instructions, without explanation.
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Old 05-25-2020, 12:43 PM   #9
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Re: When to use a relay

Interesting ^^^

Well curiosity got the better of me so I amped it out ...... and its generally 0.5 to 1A at full volume. There is a spike on "boot" for around 0.1 second to 3A.

Think Im fine

The sound - is awesome for what it is ....... 2 small speaks tied to an amplifier. $70.
Like my dad says - good enough for the girls we run with.

Ill post a video later.
Only downsides I can see are .....

1) Large connection "beep" on startup - annoying - wonder if that can be fixed or not.
2) No controls - only volume. Everything done through phone or AUX input. But thats fine as generally these days all I do is run stuff through my phone anyway - reason for buying.
3) In high bass scenarios --- it starts to lose it a little ... not bad enough that your like yuck ... bt that you might back it off 20%.

Good value and importantly goes with truck and my style of playing music.
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Old 05-25-2020, 01:49 PM   #10
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Re: When to use a relay

I would be interested in seeing/hearing a video. The start up beep sounds like it would be annoying. Is that when the bluetooth device connects, or when the unit gets power? If it is when it gets power I suppose you could add a 5 second on power on delay relay and use it to connect the speakers after the beep occurs. The things you have to do when you get a Boss instead of a Bose... :-)
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Old 05-25-2020, 06:48 PM   #11
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Re: When to use a relay

https://www.youtube.com/watch?v=xFPlMd6oOnM
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Old 05-25-2020, 07:06 PM   #12
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Re: When to use a relay

Turn your PC sound up

Definately loud enough ..... wife asked me to turn it down standing at door .....
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Old 05-25-2020, 09:24 PM   #13
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Re: When to use a relay

Yes, sounds pretty good from here.
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