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Discussion Starter #1
Hello. I'm installing front and rear cameras. While I have the dash apart, I figured I would install a phone charger with two lines that come up through my tray area on top of the dash.

My question is about tapping into the DC power for the windows. Its on acc, but when I turn the key off the multi meter reads .49V. Is this normal? Will this slowley drain my batt?

I get a solid 12V with the key on.

Thanks
 

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Discussion Starter #3
Why are you tapping into the windows? Just grab the switched ign off the back of the Cig lighter (with a proper fuse)
I'm running two seat heaters for the rear seats off the cigar lighter circuit, and I put a dual 2.1 amp (4.2 amps total) USB charging head where the cigar lighter used to be. I figure that circuit is loaded enough. Plus the windows are a lot closer to the dash. I've already completed this wiring. I was just wondering if anyone knew why it would read anything but 0 with the key off.
 

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Yeah, I wouldn't run seat heaters direct off the power plug there, it's not really meant to handle that kind of draw for prolonged periods of time but YMMV

As for the power, I believe that you are seeing that because there is no load with a DVOM, if you used something with a slight load it would read 0 but as this vehicle is highly computerized, it's prob best to check a wiring diagram to see.

However, another option (and an easy test) is that you can easily reach the wires coming off the keyswitch harness, I THINK the switched ign is pink/white (but don't quote me) measure that one and see what you get with key off..if its also .49 then you are prob fine (stray voltages don't kill batteries, something draining it will)
 

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I wouldn't run seat heaters of the cig lighter plug, run a dedicated 12v switched from the fuse box. Tap into the cig lighter plug to power your USB chargers.
 

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Discussion Starter #7
Why shouldnt I use this circuit?

What we are calling a "cigarette lighter" in reality is a 12V DC power outlet with a 20A fuse. It's meant to supply DC power. Together these seats draw <10A on high. I've been using this for two years without a single issue, both seats running on high often for prolonged periods of time while charging an ipad off the same circuit.
Running a dedicated line has some undesirable side effects; most notably direct access to my battery. If a switch gets bumped or forgotten, the battery gets drained. The 12V DC power outlet is an ACC item, so I get protection.

Thanks for the idea on testing. I'm pretty sure you're correct about the wire color. I'll have to check when I get back home from a trip.
 

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Running a dedicated line has some undesirable side effects; most notably direct access to my battery. If a switch gets bumped or forgotten, the battery gets drained. The 12V DC power outlet is an ACC item, so I get protection.
Run a line from the battery with a 20 or 30a fuse within 6 inches of the battery, then run it into the cabin and into a 20/30a SPDT relay, use the cig plug or acc wire off the keyswitch harness to trigger the relay and it is now switched and won't kill the battery :)

Yes the vehicle has a 20a fuse on the accessory plug, but just because it has that fuse does not mean it is rated to run consistently at that amperage, that is the rating it is designed to blow at. IIRC the wiring in the car is 18 gauge on the acc plug and I would imagine the traces on the TIPM aren't even that big, which is not good for 10a consistent, yes it is working now and likely will for a while but eventually it may not (Heat cycles etc) at best you would start blowing fuses, at worst you damage the TIPM

Not telling you what to do, it's your vehicle man :) Just telling you what I have seen over doing electrical work on cars throughout my years :)
 

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Discussion Starter #9
Just telling you what I have seen over doing electrical work on cars throughout my years :)
Thanks for the above post, your insights, and experience! You inspired me to do MATH! :D

Bench tests on the heaters I'm using reveal a draw of 2 amps on low, 4 amps on high (times two units). That's a potential draw of 8 amps total, with both seats on high.

The USB port I replaced the 12V DC socket with has a potential draw of 4.2 amps total, with both ports in use. (I hardly use it now that I have two dedicated charging cables in my dash tray from the window power circuit.):awesome:

The total potential draw for this configuration is 12.2A/146.6W.

Here's the MFG limitation from the owners manual:

"Do not exceed the maximum power of 160 Watts
(13 Amps) at 12 Volts. If the 160 Watt (13 Amp)
power rating is exceeded the fuse protecting the
system will need to be replaced."


Math is hard, but it can be awesome.:D Even drawing the full potential off this circuit leaves me 0.8A below the MFG limitation, so I'm satisfied that this configuration is appropriate.

Again I appreciate your contribution to the thread. I'm hoping this information can be useful for someone in the future.
 

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Thanks for the above post, your insights, and experience! You inspired me to do MATH! :D


The total potential draw for this configuration is 12.2A/146.6W.


Math is hard, but it can be awesome.:D Even drawing the full potential off this circuit leaves me 0.8A below the MFG limitation, so I'm satisfied that this configuration is appropriate.

Again I appreciate your contribution to the thread. I'm hoping this information can be useful for someone in the future.

:iamhappy: Glad I could help (And I'm kind of enjoying this thread :) ), but ya may want to go back and check a few other things..

1) The wiring behind the Accessory Socket (As a former smoker who quit 12 years ago I have a hard time not calling it a cig lighter LOL) I believe is between 16 and 18 gauge wire (One of these years I'll pull my dash apart again and check), that size wire is rated for a max amperage in power transmission mode of 2.3 - 3.7 amps

American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies and wire breaking strength

Now those wires CAN handle MUCH higher in chassis wiring mode, but that is for SHORT distances (If I recall correctly it's defined as having a resistance in the milliohm range, very short distances) so that does not apply here.


Now you say that your max draw is +/- 12Amps, now I will freely admit that MATH is not my strong point (Counting beyond 21 takes some thought :lmao: but last I checked even at the high side of 3.7, that's still give or take 8.3 amps more then the wiring can hold in real life... Sure it may be ok for now, but are those wires heating up when you use it causing minor damage you cannot see (yet), and worse is it harming your TIPM.

Now granted, you say you are drawing 12.2A/146.6W Those numbers actually tell me that you did your calculations assuming a 12v power supply from the battery (P=V*I) and it is true that no vehicle electrical system sits exactly at 12v all the time, when the engine is running it can be up over 14v (Alternator charging current etc) so unless there is a voltage regulator on that ACC socket (Possible, but I do not know ) at around 14V you are talking closer to 10.5 amps (Assuming the wattage is constant) which is better, but still more then that size wiring was meant to handle...

In reality tho, I doubt those seats are putting out that much wattage which is why it's probably been working ok for you (for now) and hey it's your ride so your rules apply :) but if it were me I'd be running a min of 10 gauge wire from the b+ to power my accessories :)

:awesome: (Again, enjoying this thread and I too hope it's useful)
 
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