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Hi Guys,

Sorry if this post is a little long - I figured that if I gave as much info as possible - then some one may be able to help me.

The car I own does not have any options available for swapping out the Head Unit - no facia kit available for aftermarket stereo etc.

The stock headunit is a touch screen LCD and becausethe car originally came with an option of an OEM DVD player kit - I was able to use the composite video inputs to install an Apple TV in the car (Hidden neatly behind the dash). Some of you may be aware - but if you remove the 110/240v power supply from the latest gen Apple TV - it actually runs on 12v power and works perfectly in a car. It has Netflix, Spotify, Apple Music etc etc and can be controlled safety via Siri commands while driving.

Car car is too modern to have a traditional “Accessory wire” on the stock headunit (as the head unit is turned on/off via CAnBUS / GMLAN via the cars ECU).

to power the Apple TV (along with a HDMI-composite video converter, a HDMIaudio -Optical audio exactor) - I ran a dedicated 12v power wire directly from the battery , fused it, and installed a standard 12v relay which is triggered by the power circuit for my power Windows (as the power Windows follows the same turn on/turn off procedure as the car stereo - it turns on when I unlock the car, and stays on for a certain amount of time after I remove the key, and switches off when I open the car door to get out if I have removed the key).

I’m also using this dedicated circuit as the remote turn on signal for my amplifier, subwoofer and Audison DSP, which have their constant power as seperate fused direct feeds from the battery.

The system works flawlessly except for one thing....

If I’ve been using the system with the engine turned off and then go to start the car - everything powers off for a few seconds while the car is cranking.

I understand that this is normal and it’s not an issue for most of the devices as they turn back on immediately - but the Apple TV takes a while to start back up and then I have to go back into whichever music app I was using and search for the song I was half way through...

I’d like to be able to prevent the Apple TV from losing power while the engine is starting.

my understanding is that the car is cutting off the 12v power window circuit while the engine is cranking - which then turns off my relay and cuts power to the Apple TV.

my first thought was to replace the relay with a time delay one. I noticed that I can buy a relay which features a trim pot for setting an amount of time that the relay stays on for after it loses voltage on the trigger input. Seemed like a great idea until I saw that these relays cost hundreds of dollars.

While searching on Google for a solution I came across threads on this forum where people suggested connecting a capacitor and diode to the relay to cause voltage to be supplied to the coil of the relay for 5 seconds after the power is shut off. This seemed to be a great and cheap solution - so I went out and grabbed a 16v 2200uf capacitor and a diode (based on what others had used as a suitable capacitor for supplying enough current to a 12v relay to keep it triggered for 5 seconds or so.

this did not work for me (and I’m 100% sure that I wired it up correctly ).

I’m feeling that even with the relay open - the car battery is dropping too much voltage to keep the Apple TV alive while the engine is cranking over.

I’d love some advice on a better solution , and wondering if anyone would recommend maybe using a bigger capacitor to try and keep the Apple TV itself powered on for five seconds or so after the relay cuts power to it.

I’m just not sure if this is a practice idea or what type of a capacitor I’ll need to keep the Apple TV alive for 5 seconds or so. Any help would be greatly appreciated.

I don’t know what calculations are needed to be done but I’m willing to experiment a bit if someone could point me to a good starting point.

a Google search revealed that the Apple TV draws 1.083 amps of current and runs at 12v

does anyone know what spec of capacitor I might need to provide that much current for about 5 seconds without the voltage dropping too low??

many thanks

- Tim
 

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1A means that 2200uF is too low.

Even a 1F capacitor will have the right side of the equation be 1Ax5-seconds (inside the integral.).. it may be less than 5 seconds, as the interruption may have the player restart??

I suspect that you probably need at least 1/4-F if it is only a second, but likely more like 1F... as 1A is a bit of current to sustain.
 

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Discussion Starter #3
1A means that 2200uF is too low.

Even a 1F capacitor will have the right side of the equation be 1Ax5-seconds (inside the integral.).. it may be less than 5 seconds, as the interruption may have the player restart??

I suspect that you probably need at least 1/4-F if it is only a second, but likely more like 1F... as 1A is a bit of current to sustain.
thanks for the reply. It actually turned out that about 5F would be required to keep the Apple TV alive for 5 seconds. Which is a pretty extreme bank of capacitors needed. So I’ve scrapped that idea and built a mini backup battery/UPS setup to power the Apple TV during the interruption.

which is working

I’m now just having trouble keeping my 12v relay alive. Seems that 6600uf isn’t enough to keep a 12v relay energised for 5 seconds...
 

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Discussion Starter #5
Depends what you mean. If you are asking if I want the power to the Apple TV wired to the ignition circuit - i do not
 

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Depends what you mean. If you are asking if I want the power to the Apple TV wired to the ignition circuit - i do not
I didn’t mean that no... 🤷🏽‍♂️ All the stuff you wrote above and you figured I would suggest using an ignition feed? Way to insult someone’s intelligence...
 

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Hi Guys,

Sorry if this post is a little long - I figured that if I gave as much info as possible - then some one may be able to help me.

The car I own does not have any options available for swapping out the Head Unit - no facia kit available for aftermarket stereo etc.

The stock headunit is a touch screen LCD and becausethe car originally came with an option of an OEM DVD player kit - I was able to use the composite video inputs to install an Apple TV in the car (Hidden neatly behind the dash). Some of you may be aware - but if you remove the 110/240v power supply from the latest gen Apple TV - it actually runs on 12v power and works perfectly in a car. It has Netflix, Spotify, Apple Music etc etc and can be controlled safety via Siri commands while driving.

Car car is too modern to have a traditional “Accessory wire” on the stock headunit (as the head unit is turned on/off via CAnBUS / GMLAN via the cars ECU).

to power the Apple TV (along with a HDMI-composite video converter, a HDMIaudio -Optical audio exactor) - I ran a dedicated 12v power wire directly from the battery , fused it, and installed a standard 12v relay which is triggered by the power circuit for my power Windows (as the power Windows follows the same turn on/turn off procedure as the car stereo - it turns on when I unlock the car, and stays on for a certain amount of time after I remove the key, and switches off when I open the car door to get out if I have removed the key).

I’m also using this dedicated circuit as the remote turn on signal for my amplifier, subwoofer and Audison DSP, which have their constant power as seperate fused direct feeds from the battery.

The system works flawlessly except for one thing....

If I’ve been using the system with the engine turned off and then go to start the car - everything powers off for a few seconds while the car is cranking.

I understand that this is normal and it’s not an issue for most of the devices as they turn back on immediately - but the Apple TV takes a while to start back up and then I have to go back into whichever music app I was using and search for the song I was half way through...

I’d like to be able to prevent the Apple TV from losing power while the engine is starting.

my understanding is that the car is cutting off the 12v power window circuit while the engine is cranking - which then turns off my relay and cuts power to the Apple TV.

my first thought was to replace the relay with a time delay one. I noticed that I can buy a relay which features a trim pot for setting an amount of time that the relay stays on for after it loses voltage on the trigger input. Seemed like a great idea until I saw that these relays cost hundreds of dollars.

While searching on Google for a solution I came across threads on this forum where people suggested connecting a capacitor and diode to the relay to cause voltage to be supplied to the coil of the relay for 5 seconds after the power is shut off. This seemed to be a great and cheap solution - so I went out and grabbed a 16v 2200uf capacitor and a diode (based on what others had used as a suitable capacitor for supplying enough current to a 12v relay to keep it triggered for 5 seconds or so.

this did not work for me (and I’m 100% sure that I wired it up correctly ).

I’m feeling that even with the relay open - the car battery is dropping too much voltage to keep the Apple TV alive while the engine is cranking over.

I’d love some advice on a better solution , and wondering if anyone would recommend maybe using a bigger capacitor to try and keep the Apple TV itself powered on for five seconds or so after the relay cuts power to it.

I’m just not sure if this is a practice idea or what type of a capacitor I’ll need to keep the Apple TV alive for 5 seconds or so. Any help would be greatly appreciated.

I don’t know what calculations are needed to be done but I’m willing to experiment a bit if someone could point me to a good starting point.

a Google search revealed that the Apple TV draws 1.083 amps of current and runs at 12v

does anyone know what spec of capacitor I might need to provide that much current for about 5 seconds without the voltage dropping too low??

many thanks

- Tim
Did you actually measure 1A current draw on the Apple TV? Seems kind of high.

Ge0
 

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The Apple TV can probably work fine down to 8-10V, and probably the cranking is only 1-2 seconds of low current...
And that works out to 1/2F.
Which is a lot more than original 2.2mF
 

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The Apple TV can probably work fine down to 8-10V, and probably the cranking is only 1-2 seconds of low current...
And that works out to 1/2F.
Which is a lot more than original 2.2mF
I'm still questioning if that little box actually draws 1A. That's dissipating 12W which is difficult for a little plastic box.

Ge0
 

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I'm still questioning if that little box actually draws 1A. That's dissipating 12W which is difficult for a little plastic box.

Ge0
NFI... I just used the OP's number and comouted the integral by chin rubbing.

Seems like it should be clipping with only 12W?
 

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NFI... I just used the OP's number and comouted the integral by chin rubbing.

Seems like it should be clipping with only 12W?
Clipping? No LOL!!!. Just power dissipation. A lot of heat would be generated. A sealed little plastic box with no fan has no where to expel hot air.

Ge0
 

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Clipping? No LOL!!!. Just power dissipation. A lot of heat would be generated. A sealed little plastic box with no fan has no where to expel hot air.

Ge0
The humour was not great, but those other posts about needing lots of watts for a 100W tweeter was the intended reference point.

Some watts will probably go out of the unit somewhere. But I agree, it seemed like 1A was a lot.
 

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The humour was not great, but those other posts about needing lots of watts for a 100W tweeter was the intended reference point.
Oh Sh!t. Admittedly I was a lttle dull there. I didn't catch your reference :)

Ge0
 
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Here is what I am thinking...
280827
 

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Keep diode. Use smallest rechargeable battery or an ultracapacitor to power TV

Other option is a larger ultracapacitor parallel to the car battery, or a 2nd car battery. Either should prevent excessive voltage drop and the tv powering down.

Have you tried a new car battery?

Examples(I make no recommendations since I source cap's and build my own):

One of my favorites:
 

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Raspberry pi as a control board. $39 bucks and can do way more than you'll ever need.
 

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Keep diode. Use smallest rechargeable battery or an ultracapacitor to power TV

Other option is a larger ultracapacitor parallel to the car battery, or a 2nd car battery. Either should prevent excessive voltage drop and the tv powering down.

Have you tried a new car battery?

Examples(I make no recommendations since I source cap's and build my own):

One of my favorites:
The capacitor on the battery only works if the ignition switch is not cutting the accessory power when the starter is engaged. So whether it is 58F or 600F would not work... how that switch works should be checked pretty early on.
 

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Here is my 5 minute childish drawing:
280857


The questions is how big to size the capacitor based on how much current the Apple TV is really pulling during use.

Ge0
 

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Here is my 5 minute childish drawing:
View attachment 280857

The questions is how big to size the capacitor based on how much current the Apple TV is really pulling during use.

Ge0
My teenager suggestion would be adding a 1-ohm/20W power resistor (or a 12V light bulb) either before or after the diode, in order to prevent the in rush current from blowing the fuse...
 

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My teenager suggestion would be adding a 1-ohm/20W power resistor (or a 12V light bulb) either before or after the diode, in order to prevent the in rush current from blowing the fuse...
Haven't you ever hooked up power to a brand new beefy power amplifier? There is a quick zap when you connect the positive battery terminal as the power supply primary caps charge up. But, that's about it. The ESR on big bulk electrolytic's is high enough to minimize inrush. But then I'm only thinking about roughly 20,000uF of capacitance. That would charge well before the fuse heats up enough to blow.

On the other hand, if you want to add a 1F monster cap then yes, your teenage intuition to add a in-line resistance would be a great idea until the cap fully charges :).

I still want to see how much current an Apple TV is really pulling. Not just what is printed on a wall wart or power brick.

Ge0
 
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