12v power budget for inverters - max draw of adapter ports

[dwangoAC]

Greetings,

TL;DR: What is the maximum power draw of both 12v power ports simultaneously?

I need a *lot* of power for 14+ hours and I need to work out a sane power budget given the amount of equipment I need to power during that time. During a May 4th event I'm calling Desert Tesla Charity Drive viewers will be able to freeze or melt us as they Crowd Control our heated seats and set the temp of my Tesla Model X 100D during a 14+ hour desert livestream at TAS.Bot benefiting National Alliance on Mental Illness. Our (dis)comfort is free to watch and can be enhanced by charitable meddling. (And yes, I'll be doing this entirely on autopilot; it's a great opportunity to share what driving a Tesla can be like.)

Here are the things I need to power in total:

- A laptop running Linux to stream from that could draw as much as 110 watts (I've measured it; I'm looking at using a different laptop to hold that down to 65 watts but I'm uncertain if it is possible)
- A second laptop to control features of the stream that will draw as much as 85 watts
- A Behringer XR18 sound board at 21 watts
- A GoPro camera at up to 4 watts
- A phone for mobile tethering at up to 5 watts
- A second phone for backup tethering and audio streaming at up to 5 watts
- A microphone pack at up to 3 watts
- A weBoost Drive 4G-X OTR mobile signal booster at probably up to 10 watts

Adding that all up, we're at a continuous draw for 14 hours at 243 watts. Based on what I've found so far the two cigarette lighter style aux power adapter ports are rated at 12v 11a but still up to 150 watts somehow because creative math. What I haven't been able to determine for certain for the Model X 100D is if that rating is for each port or if that is the total limit for both 12v power ports combined. We can offload some things to USB (powering the GoPro and the two phones as well as the USB drive I use for the Tesla dashcam / Sentry features) but the two laptops, the WeBoos, and the sound board all need to run off of AC. I have a 300A and a 450A inverter but it's an unfortunate amount of DC > AC > DC loss.

One possible help is the "spare 12v power circuit" described in ModelXSparePower.pdf that appears like it might be on its own fuse but I can't tell for certain from that document if it's a dedicated fuse or not. Finally, there are the max battery drain concerns mentioned in the thread on How to Achieve Optimal Sound Without Overloading 12V Battery which might apply here as well, although because this is a one time 14 hour trip I'm a bit less concerned.

So, my primary ask ultimately comes down to how the fuses are laid out. I've found conflicting information (or information specific to the Model S), so please feel free to point me at Model X 100D specific documentation. Thanks in advance for any help you can provide, and join us on May 4th, it's free to watch at TAS.Bot all day. Thanks!

 

[arnis]

You have to tap into 12V system not from cigarette lighter ports. They are not made for that load.
One of the ways is to tap into 12V battery, or right after current sensor to be more precise.
Get good thick cables, protect them with 30A fuse right at the beginning of positive cable (no more than few inches) and have a quick connector on them for easy access further away, like... in the frunk.
Thick wires must be bolted to appropriate surfaces - no clips are allowed and definitely I do not recommend cutting OEM wires.

 

[dwangoAC]

You have to tap into 12V system not from cigarette lighter ports. They are not made for that load.

You're definitely not wrong, although if I can confirm that the cigarette lighter aux 12v power ports and the spare 12v connector are on separate fuses it may be enough if I spread out the load such that nothing exceeds 100w.

One of the ways is to tap into 12V battery, or right after current sensor to be more precise.
Get good thick cables, protect them with 30A fuse right at the beginning of positive cable (no more than few inches) and have a quick connector on them for easy access further away, like... in the frunk.
Thick wires must be bolted to appropriate surfaces - no clips are allowed and definitely I do not recommend cutting OEM wires.

So about that - I have a 450 watt inverter that on its own could satisfy all of our needs. I could easily secure it in the frunk with a good 30A fuse within a few inches of the connection point but that means my AC ports start in the frunk. Is there a way to get a standard extension cable from the frunk area into the car cabin? When you say "No clips are allowed" what do you mean by that?

Thanks for the help so far!

 

[arnis]

There is a risk of backfeeding electricity through your shunt from one source to anouther. For example,
if one of your sources is from spare 12V connector and second is from cigarette lighter port, if vehicle
deenergizes one, your connection will keep that circuit live through cig. port. I would not recommend connecting two sources.

Clips - I mean connectors that use springs to hold on. Like jumper cables/alligator clips.
Some inverters come with those clip -those are not reliable connectors.

Therefore you need to route thickl 12V line from frunk into the cabin. There are some rubber grommets through the firewall, you need
to use those.

If your inverter is 450W then maybe you should use 35A fuse just to be sure you wont blow the fuse.
But keep away from low quality fuses like these:
100pcs 2a-35a Mini Blade Fuse Assortment Set Auto Car Truck Motorcycle Fuses Kit for sale online | eBay
They are hardly real fuses. They are all fakes and will not actually blow at the rating they are made for.
Get some spares from old vehicles or buy from reliable source from known brand.

 

[ewoodrick]

I think that I'd suggest not running from the Tesla battery. The Model S has, from what I've seen, a little issue with 12V batteries and I suspect the 12V charging system. What you are really asking is that can the charging system source 243 watts @12V = 20A for 14+ hours. And while it is at it, not run the 12V battery dead and disable the whole car. That's a total of 280Ah or 3kWh, a significant amount of power.

I'd suggest moving maybe a small generator to handle the load, but if you are moving the entire time, you probably need to get some 12V batteries SLA, or LFP and swap them in and out as you charge the car.

I do these operations on a semi-regular basis with Amateur Radio and you are really asking for issues to attempt to pull that amount of power from the car. 10-30 minutes wouldn't be an issue, but 14+ hours is doomed for bad results that you wouldn't want everyone to watch.

 

[arnis]

Tesla's DC-DC converter can easily generate half a kilowatt of 12V power for days. Though it is important to keep the vehicle on.
Same applies to regular vehicles.

 

[dwangoAC]

So I'm heading down the path of attempting to reduce my power budget by as much as possible. I've managed to make some headway on switching to a 65 watt main laptop and an older 85 watt secondary laptop (each with their own streams on separate networks).

Regarding shunting power, I wouldn't be joining two 12v sources at any point. I'm grouping power consumption into the following:

Rear 12v power port - barrel connector splitter 1 (direct connect at 12v):
- 12v cell signal booster, 10 watts
Rear 12v power port, barrel connector splitter 2 (150 watt max inverter):
- Sound board, 21 watts
- Microphone pack, 3 watts

Front 12v power port (300 watt max inverter):
- Power supply for laptop 1, 65 watts

Spare 12v power port (450 watt max inverter):
- Power supply for laptop 2, 85 watts

Rear USB port 1: GoPro, 4 watts
Rear USB port 2: Mobile phone for streaming audio and backup stream, 5 watts
Front USB port 1: Mobile phone main stream tether, 5 watts
Front USB port 2: USB thumbdrive for Sentry mode / dashcam, 1 watt

So, our subtotals are 34 watts on the rear 12v port, 65 watts on the front 12v port, 85 watts on the spare 12v port, and 15 watts across all USB ports for a total max draw of 199 watts. We'll gain some by not actually drawing the max wattage from the laptops but lose some from inverter inefficiencies.

So, 200 watts continuous but spread across the entire system. My hope is that this is enough but please advise if this is dangerous over the course of 14 hours. I'm not willing to use a generator, although I could use deep cycle batteries mounted on a hitch hauler. I'm trying to avoid that. Thanks for the continued feedback and points of view!

 

[arnis]

It's cumbersome to have so much wiring coming from all directions.
If you want something better than than, you have to bring it from the frunk.

200W is totally safe. But vehicle must be on. You can switch off climate control.
If vehicle is off some ports switch off, but AFAIK one stays on. You can discharge
12V battery fully if you keep something non-controlled plugged in there.
Some inverters switch off before they drain source completely.

 

[dwangoAC]

It's cumbersome to have so much wiring coming from all directions.
If you want something better than than, you have to bring it from the frunk.

In some ways, having things spread out reduces wiring troubles - the back 12v serves the sound board and the signal booster which are in the back, laptops in the middle and one in the front right, phones in the center. I don't think having a single entry point for power is going to make cabling any less of a problem than it's already going to be.

200W is totally safe. But vehicle must be on. You can switch off climate control.

We'll never have the vehicle off throughout the 14 hour stream. We'll either be charging or driving. Worst case, we stop for a quick bathroom break for 5 minutes and even then the car won't shut all the way down as we'll probably leave climate on (for all the good it will do us if people crank the heat up, but I digress).

I'm very happy with the signal booster that was sponsored by Wilson Electronics - we mounted it to a bike rack and it turned out well:
http:// https://ic.pics.livejournal.com/ac/9096/1403631/1403631_original.jpg

The full album is here:

Photostream

More updates as we do more testing. Thanks for the help all, and follow along at TAS.Bot on May 4th.

 

[dwangoAC]

I'm considering tapping to the 12v lead at the fuse box instead of the spare 12v to get a more reliable connection point. This would allow the 450 watt inverter to shoulder the bulk of the burden, and I have decent 12v cables with coupling locations, designed for solar panel installations. However, I'm currently searching the best way to pass this through the firewall of a model X and the only thread that came up when I looked for rubber grommet firewall was, uh, this one. I'll keep searching but in the meantime if someone has any diagrams or documentation on the location of this please let me know. Thanks!

 

[dwangoAC]

Well, the closest I found was this thread: Routing Cables Through the Firewall

That could work for small gauge, it's not "through" the firewall so much as around it though because it loops outside the car. I tried it and got a thin 12v designed wire through designed for solar panels but I saw drops when exceeding 65 watts of power. I don't think I can get a proper 120v power cable of suitable gauge through there without damaging something. I was able to do a test run with a 450 watt inverter connected to the center console 12v power port and I got my laptop down to 50 watts but the downside is the other laptop really likes to climb over 85 watts so I have concerns about that one.

Any information on said grommet on a 2017 era Model X would be helpful. In the meantime, here's the cheesy promotional spot my team made for the event:

 

[dwangoAC]

So I picked up a screwdown connector with a fuse holder and it looks good:

And here's how the wire is snaked around the firewall:

Unfortunately, this didn't quite work out - if the laptop battery was charging at the same time the laptop was open it was drawing over 100 watts on the initial resume from suspend and that caused the inverter to shut down. (Also, the original holder only had a 7.5 amp fuse which blew almost instantly; I replaced it with a 30 amp fuse based on the gauge of the wire but clearly the gauge is insufficient). What I observed on my power meter is my inverter would go from producing nice 130 volt power to dropping below 110, and the fan on the inverter noticeably dropped in speed (even the kill-a-watt screen dimmed out).

I may try putting the inverter in the frunk (heat concerns?) but then I have to find a flat power cable to run between the frunk and the inside... If this route doesn't work I'm back to trying to source all of my power from inside the cabin. Any additional advice is welcome.

 

[arnis]

Almost well done.
Wire appears to be slightly too thin for 20A draw.
Also negative lead appears to be resting on painted/primed surface.
You need bare metal or paint-penetrating washer for better results.
Sand clean area under that negative lug connector. Torque it up well so it will not slide even if you push it hard (turning around screw).
I would keep inverter indoors, close to firewall for shorter low voltage wiring.
If you have multimeter measure voltage difference under heavy inverter load near the source (should be 13V, depending on vehicle DC-DC converter mode) and at inverter input terminals.
If it is like 1V or more, you should get thicker wires.
If it is tiny, then likely inverter is poop. Ideally inverter should be at 50-80% load out of nominal maximum (not boost power).

Where did you get that 30A fuse?

 

[dwangoAC]

I came to the same conclusion that the wire was too thin, so today (prior to reading your message) I replaced it with 12 gauge wire and built my own wiring harness with a new 30a fuse holder and ran it into the car so the inverter can rest under the passenger seat which reduced the cable length as well. No more problems with draw. Expected draw is 200 watts normal, 250 watts max against a 450 watt inverter.

I'll know more after the live "dress rehearsal" with all of the equipment in the car tonight.

 

[dwangoAC]

OK, the full rehearsal went flawlessly. We were able to get the overall load of all devices combined on the inverter down to roughly 100 watts, with other peripherals only adding about an additional 20 watts max. This is far lower than my worst-case scenario planning. The max I pushed the inverter to was a bit shy of 200 watts but it held up fine there too. We'll have to see how it holds up over 14 hours but I have higher confidence this will work now than I've had before.

The final question I need to solve is where in the car the mobile data antenna is located so I can place the signal booster near it, but that's a problem for another day and another thread. Thanks again for the support and I hope to catch you on Saturday May 4th at Desert Tesla Charity Drive May 4th 2019 by Team TASBot if you're inclined. Thanks!

 

[arnis]

Are you sure boosting signal without tapping into OEM cellular module has real effect?
I'm not sure it technically actually works.

 

[dwangoAC]

The science behind signal boosting works, if you do it right. First, here's a picture:

The external antenna is above the car with a clear view of the horizon in all directions, and is powered. The internal antenna is a small omnidirecitonal antenna with a range of about a meter. If you get the two too close together you'll end up with oscillation, but otherwise it will provide a better signal by pushing more power and from a better vantage point than the phone. The question is where the internal car antenna is located and if it would benefit from having the internal signal booster antenna nearby, but that's an entirely separate topic.

 

[dwangoAC]

Post mortem: The event was a success, raising $1.5k during the (largely unpublicized) drive. We're still working on making a highlight video.

I encountered some ground loop issues I encountered when powering the GoPro off the USB port on the car but having the HDMI go into a laptop that also had an analog audio signal from the sound board which resulted in a wonderful buzzing noise. I resolved it by powering it off the inverter as well. Total average wattage stayed around 200 watts and we ran everything from the single 450 watt max inverter as a result of the other inverter I had failing.

The signal booster worked wonders. It can't invent signal out of thin air when there isn't one but it certainly helped us to stay connected in sections I thought for certain we would drop. We had some losses during mountain passes as expected but overall I was very pleased with the performance.

Some of the most interesting things that happened were related to autopilot handling, especially around how TheAxeMan (the other person going with me) reacted to learning how to keep it happy. The disengagements were educational and I hope we can highlight those on the video we are still editing, but I digress. Thanks to everyone here who contributed information!