Is the 12V socket in the trunk of my SUV reliable for battery hookup?

[boromir]

Took me a while to realize the new-ish SUV we got has a 12V socket in the back and I could plug the batteries there instead of fiddling with the fuse box. Anyone do it that way? Is this usable and safe? Looking at getting one or two batteries since we park in parking deck, ~400ft from apartment, and we don't drive the car but 3x a week

 

[gamesfrager]

As long as that 12v socket is switched. If it keeps providing power even when the car is shutoff after a while; then you run the risk of killing your car's battery.
There is no harm from connecting a battery pack to a 12v socket. I had that setup for over 2 years until I had the time to wire into the fuse box.

 

[boromir]

As long as that 12v socket is switched. If it keeps providing power even when the car is shutoff after a while; then you run the risk of killing your car's battery.
There is no harm from connecting a battery pack to a 12v socket. I had that setup for over 2 years until I had the time to wire into the fuse box.

nice. It is switched, it turns on/off with the car. Did you have to roll your own plug or did it come in the pacakge? I keep seeing wiring toolkits but they don't seem to contain a "wall" plug

 

[gamesfrager]

nice. It is switched it turns out. Did you have to roll your own plug or did it come in the pacakge? I keep seeing wiring toolkits but they don't seem to contain a "wall" plug

Oh, so your 12v socket is a household type of plug! Interesting. I guess you need to get something like this https://www.amazon.ca/gp/B07RMH3R8P and then a wall socket plug to connect it to. I couldn't easily find a simple adapter.

 

[boromir]

Oh, so your 12v socket is a household type of plug! Interesting. I guess you need to get something like this https://www.amazon.ca/gp/B07RMH3R8P and then a wall socket plug to connect it to. I couldn't easily find a simple adapter.

thank you for that suggestion. Actually it turns out the cargo area has a 12V/180W socket, another one under the front dash, and the back seats have an 3-pin AC 115V/150W household plug ('22 SantaFe Calligraphy). I might actually be able to hide the cable decent enough without messing with the fuse box and hide everything in the storage bins

 

[EricSan]

Just be careful with how much current you pull from the utility outlet. I would not attempt to pull more than about 70-80w (no more than half of its rated capacity) from that type of port. Although fused with a 15A fuse, those utility ports are often wired with pretty thin wire that is really not meant to carry that much juice for an extended period of time. I melted a utility port plug-in adapter by charging a parking battery at 8A. I don't know if it wiggled loose or not, but the tip melted due to excess heat. The fuse was still intact. This could have caused a fire...

I would DEFINITELY not pull large current (more than 4-5A) from a fuse box. Most new cars have "smart" fuse boxes that monitor current draw and will behave in unpredictable ways if the current draw exceeds (unknown to you) expectations.

If you are charging a battery pack, I recommend going straight to the battery and using a time delay relay as shown below:

Shopping List:
40A 10s Time delay relay: https://www.amazon.com/gp/B0744HSF8P
12g Heavy duty relay harness with coil diode: https://www.amazon.com/gp/B078T8CMF6
8g Heavy duty Maxi fuse holder for battery connection: https://www.amazon.com/gp/B0B6R8J932
Alternate: 10g Heavy duty fuse holder for battery connection: https://www.amazon.com/gp/B08BWRSPY1
11g heat resistant wire with XT60 terminal: https://www.amazon.com/gp/B0CX56S7QF
Add-a-fuse for relay coil:https://www.amazon.com/gp/B0D3XHHFDX
Ratcheting crimping tool: https://www.amazon.com/gp/B07WMB61J5 or this one: https://www.amazon.com/gp/B08F3JKDD3

The time delay relay lets the car's electrical system settle down after starting the engine and gives some time for the alternator to actually start providing voltage to the battery. The 12g relay harness is necessary to handle the current flow (thinner wires will overheat). Same goes for the 8g fuse holder that connects to the battery terminal - the 12g ones that I've used heat up with anything more than 8A of current flow. The metal that holds the fuse itself is too thin and generates heat, which is unacceptable to me. The 11g heat resistant wire is the best I've found that comes with an extra heat shield (up to 400F) and a sturdy XT60 connector already installed. It is more expensive than others, but worth the additional cost. This wire should fit through the spare chase way in the rubber grommet that separates the engine compartment from the interior for most cars. There are no special requirements for the add-a-fuse, this is a low current connections whose only purpose is to power the relay coil, which is likely to be less than 150mA at 12v. Connections between the relay harness, the wire that connects to the battery and the wire that connects to your parking battery should all be soldered well to avoid cold solder joints and fitted with heat shrink insulation (electrical tape unravels with heat and time). The best solution is to wrap the solder joint in tape, then apply heat shrink to keep it from unraveling. The wires that connect to the positive battery terminal and the chassis ground point should use high-quality ring terminals that are crimped well with a good quality, ratcheting crimping tool.

 

[gamesfrager]

In all honesty, I too didn't want to fiddle with the fuses in my car. But after trying it, it's really not that scary anymore. It makes for a much cleaner setup and you get to know your car better too not to mention you will keep those ports available 🙂
Just make sure you reads the fuse pamphlet and try to avoid tapping into critical fuses.
Use a good quality fuse tap and proper fuse value. That's it.

 

[EricSan]

In all honesty, I too didn't want to fiddle with the fuses in my car. But after trying it, it's really not that scary anymore. It makes for a much cleaner setup and you get to know your car better too not to mention you will keep those ports available 🙂

Nope, not that scary at all 😉 but it's not the place for a high current draw. If you hard wire the camera itself into the fuse box so it runs while the engine is on, that's not a problem at all - the current draw is minimal. It also makes for a nice and clean installation and prevents tripping on wires.

If you are charging a parking battery from the car, the safest way is shown in my diagram above.

 

[boromir]

Just be careful with how much current you pull from the utility outlet. I would not attempt to pull more than about 70-80w from that type of port. Although fused with a 15A fuse, those utility ports are often wired with pretty thin wire that is really not meant to carry that much juice for an extended period of time. I melted a utility port plug-in adapter by charging a parking battery at 8A. I don't know if it wiggled loose or not, but the tip melted due to excess heat. The fuse was still intact. This could have caused a fire...

View attachment 77612

I would DEFINITELY not pull large current (more than 4-5A) from a fuse box. Most new cars have "smart" fuse boxes that monitor current draw and will behave in unpredictable ways if the current draw exceeds (unknown to you) expectations.

If you are charging a battery pack, I recommend going straight to the battery and using a time delay relay as shown below:

Shopping List:
40A 10s Time delay relay: https://www.amazon.com/gp/B0744HSF8P
12g Heavy duty relay harness: https://www.amazon.com/gp/B078T8CMF6
8g Heavy duty fuse holder for battery connection: https://www.amazon.com/gp/B0B6R8J932
11g heat resistant wire with XT60 terminal: https://www.amazon.com/gp/B0CX56S7QF
Add-a-fuse for relay coil:https://www.amazon.com/gp/B0D3XHHFDX
View attachment 77613

Thank you for that Eric. I was just perusing your posts yesterday 🙂

I can't remember if the Santa Fe has the battery in the front or in the back under the cargo mats, if it's under the car it would be rather easy to hook up that way since I too do not want to mess with the fuse box. Especially after my transmission died last month at 20K miles, and Hyundai corporate made it clear if they think it was my fault they won't cover it. Guess that's the price you pay for "10 yrs 100K miles warranty" 🙄