Delaying a USB powered device with a relay

Thread Starter

john2k

Joined Nov 14, 2019
146
I have a 12V USB hub for the car that powers up when ACC is on along with a android tablet. One of the USB devices I have connected is a USB sound card. However, I need to delay the start-up time off this sound card. I've plugged it into a spare usb extension and then cut the +5v red cable and currently wired it to a toggle switch so I can manually delay the start-up of the USB sound-card which is doing the job for now. But I need to automate this and i'm wondering is there a way to use a 12v relay with some sort of start-up delay so have this automatically turns on after power is on for 10 seconds or so?

Thanks
 

MisterBill2

Joined Jan 23, 2018
8,808
Probably that module world work, but the pain is that it would need to be mounted and insulated to avoid short circuiting since it is just a module intended to be installed in some sort of enclosure. Anotheer possible option would be if your vehicle has an "ACC-2" circuit that is already delayed. That was used on at least some models of cars a few years back. I think that it was for heated seats and such. That would be the cheap and easy way if your vehicle has it.
 

Tonyr1084

Joined Sep 24, 2015
6,000
I had gauges with customizable color schemes. One of those gauges would always default to factory original when I started the truck. Power would come on and the gauge would remember the color setting, but then when I started the truck power would be interrupted briefly, then come back but the gauge would default to factory. So I built this circuit which delayed the powering of the gauge for four seconds. By then the truck was running, so no problems with my color. The gauges had a memory which was always powered, so they would remember the color. For whatever reason it didn't like the temporary interruption. This circuit solved that problem. However, using a 12 volt relay will likely change the timing. Adjusting R1 to a higher value would solve that problem as well.
1606664045720.png
 

Tonyr1084

Joined Sep 24, 2015
6,000
You can modify the relay to control the 5V power or you can use it to control the 12V source. But if you control the 5V then you'll need a DPDT relay so the relay can switch the 12V power on to itself. Otherwise, if only controlling the 5V you'll need to remove D1. K1 should either have a built in diode or you can add one externally to prevent the back EMF. That protects Q1.
 

MisterBill2

Joined Jan 23, 2018
8,808
I would not ever want the music coming on automaticly every time I start the engine. Worse yet would be a radio coming on with some mouth blabbing away as soon as I started. I had to move the radio power connection directly to the battery to get my wife to switch it off when she parked the car.
If the sound comes up immediately you would never hear the sound of something wrong with the engine.
 

sghioto

Joined Dec 31, 2017
2,363
Since you already have access to the 5 volt line through the switch I would use a 5 volt relay circuit. Delay time appx 10 sec. with the component values listed.
EEE Delayed Relay turn on.png
 

Thread Starter

john2k

Joined Nov 14, 2019
146
So I ended up buying one of the following pictured item. Seems to work great. Just need to get a narrow small project box for it. One thing I've noticed is just running this module without anything going through the common or the NO the module becomes a little warm. It's not hot just warm. Is it normal for these modules to generate heat and warm up? I'm assuming putting a common for the switching isn't going to really add to the heat is it because essentially it's just energising the relay that's letting common and NO pins connect?

 

MisterBill2

Joined Jan 23, 2018
8,808
Relay coils do warm up after a while. One the motion of the contacts stops, all of the pwer eventually becomes heat. Not a lot of heat, but some heat.
 
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