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Making the stereo work with the key in the off position...

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wrybread
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Making the stereo work with the key in the off position...

Post by wrybread » Thu May 23, 2019 12:51 am

I like to set up my car stereo so I can use it even with the car off, and ideally so the cigarette lighter socket can deliver power too, so I can leave my phone charging. I usually just hook up a switch between the constant 12v+ and the switched 12v+ in the stereo harness, but I did that just now with my SC-816 and blew two fuses...

Can anyone think of a reason for that, other than user error?

I verified the wires with my multimeter and all looked good. No power to the switched line until I turned the key. Other line had power always.

And this diagram agrees with my wire choices:

https://www.tehnomagazin.com/Auto-radio ... nector.htm

Connecting one of the green/brown wires (constant 12v+) to yellow/purple (switched 12v+). In this diagram that's wire 1 and 3.
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wiring.jpg
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BEJinFbk
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Re: Making the stereo work with the key in the off position...

Post by BEJinFbk » Thu May 23, 2019 8:12 am

Instead of an SPST switch, use an SPDT.

Connect the common contact to the radio
ign and the batt and harness ign to the two
switched contacts of the switch.

That way, the ign lead from the harness is
disconnected from power when you flip to
batt and there’s no backfeed up the harness.


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Re: Making the stereo work with the key in the off position...

Post by wizechatmgr » Sat May 25, 2019 2:01 am

Or install a diode and it will just always have power and never backfeed =)


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Re: Making the stereo work with the key in the off position...

Post by wrybread » Sat May 25, 2019 10:34 am

That's a good idea. Any recommendation on which diode by chance?



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Re: Making the stereo work with the key in the off position...

Post by wizechatmgr » Sat May 25, 2019 6:05 pm

My thought is one of these on each power line (aka V1,V2) going towards the radio should do it... They are basically one way valves for electricity.

pardon the garbage schematic no guarantee I have the cathode anode correct, it's just here for purposes of clarity
radio.png
radio.png (6.26 KiB) Viewed 134 times
https://www.amazon.com/RUITASA-Schottky ... 4253919969


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Re: Making the stereo work with the key in the off position...

Post by abscate » Sun May 26, 2019 1:44 am

The diode needs to be rated for the expected power draw if about 10 watts for the charger, plus 50% margin


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Re: Making the stereo work with the key in the off position...

Post by wizechatmgr » Sun May 26, 2019 3:09 am

abscate wrote:
Sun May 26, 2019 1:44 am
The diode needs to be rated for the expected power draw if about 10 watts for the charger, plus 50% margin
Absolutely...
These are rated for 10 amps each. Worst case scenario he uses two or three in parallel for each voltage source.


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Re: Making the stereo work with the key in the off position...

Post by wrybread » Sun May 26, 2019 12:10 pm

Great ideas, will try next week.

I still don't get why bridging two circuits would cause a short or a power draw. I was working by headlamp after a long day so maybe I did something stupid. My plan is to insert two 5a fuses and connect the two lines with a multimeter set on current measurement to see if I see the same power draw.

If it blows that again, plan diode.



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