How many amps can you get from the 12V system for emergency situations?

[marcmerlin]

which fuse are you referring to? The DC-DC converter is supposed to output 200A (not sure if that's continuous) and definitely does not have a 50A fuse, I've drawn 120A from it already. I'm talking about a model 3.
I'm not sure which car you're talking about and where the nose cone connector goes to, but if it's the 12V battery, forget it, don't do that.

 

[Bernard_S]

There's a lot of stuff powered by 12V. I think power steering, seat heaters, window defrosters, the computers, displays, lighting, etc...

I agree, but all of that stuff is low power apart from the power steering pump, but even that would only be about 50 amps max. Are we sure it really is capable of 200A ? That's a big expensive DC/DC converter for no good (apparent) reason.

 

[marcmerlin]

That's what I've read, and I've gotten 120A from it in a test, so I'm willing to believe it'll do around 200A

 

[n2mb_racing]

I've resigned myself to the limitations of the much easier setup of using the terminals behind the nose cone. I'm worried about blowing the 50A fuse though, as I don't fancy having to replace it myself. So here is my question:

If I connect a 100A short automotive cable to the positive terminal, and connect that to a mega size 40A fuse and then the fuse to the positive terminal of my inverter, I should be safe, right? If I overdraw, my local fuse will blow and the 50A Tesla fuse near the 12V battery stays good?

If you have a model 3, you can go right to the battery posts. They are right under the plastic covers under the hood at the top. I think the nose cone and fuse is on the model S.

 

[marcmerlin]

If you have a model 3, you can go right to the battery posts. They are right under the plastic covers under the hood at the top. I think the nose cone and fuse is on the model S.

OMG, no you cannot. Please read the thread, this has already been answered.

 

[n2mb_racing]

OMG, no you cannot. Please read the thread, this has already been answered.

Sorry, I meant if you only want to use 6A or less. Of course, for that much you could probably just use the 12V power outlet...

 

[unkel]

which fuse are you referring to? The DC-DC converter is supposed to output 200A (not sure if that's continuous) and definitely does not have a 50A fuse, I've drawn 120A from it already. I'm talking about a model 3.
I'm not sure which car you're talking about and where the nose cone connector goes to, but if it's the 12V battery, forget it, don't do that.

2014 Model S with the positive and negative terminals behind the nose cone. The positive terminal is connected to the 12V battery via a 50A fuse. Here is Will Prowse blowing that fuse on his car at 4:54 (while pulling 90A, watch for about 60 seconds)

So if I connect an inverter to the positive terminal via a 40A fuse, I should be fine? Obviously my load will be limited to 500W at most

 

[marcmerlin]

Sorry, I meant if you only want to use 6A or less. Of course, for that much you could probably just use the 12V power outlet...

I'm not sure you can even pull 6A full time from the model 3 battery, I didn't measure carefully, but I believe the battery recharging system isn't even meant to provide that much power.
You'll get more power (10A+) from the cigarette lighter adapter.

Unkel, ok, model S, sure. It's totally different. My thread is in the model 3 section, if you're talking about model S, you need to be specific that you're talking about a different car

 

[n2mb_racing]

I'm not sure you can even pull 6A full time from the model 3 battery, I didn't measure carefully, but I believe the battery recharging system isn't even meant to provide that much power.
You'll get more power (10A+) from the cigarette lighter adapter.

Unkel, ok, model S, sure. It's totally different. My thread is in the model 3 section, if you're talking about model S, you need to be specific that you're talking about a different car

Good point. Is the 12V power outlet on all the time? Or does it shut down?

 

[marcmerlin]

It shuts down at the same time than the 200A DC-DC system, so you have to keep the car awake with sentry mode or camper mode or something like htat.

 

[unkel]

Unkel, ok, model S, sure. It's totally different. My thread is in the model 3 section, if you're talking about model S, you need to be specific that you're talking about a different car

My bad. In my enthusiasm, I didn't realise I was posting in a Model 3 thread!

Would you do me a big favour and look at about 60s of the YT clip and confirm that I should be ok by adding a 40A fuse in a connection to an inverter from the positive pole behind the nose cone? As in my fuse will blow before the Tesla 50A fuse would get a chance to blow?

 

[marcmerlin]

You should be fine as long as you have a fast blow fuse and the car is a slow blow fuse (which is likely true).

 

[unkel]

You should be fine as long as you have a fast blow fuse and the car is a slow blow fuse (which is likely true).

Forgive my ignorance, but I had never heard about fast or slow blowing fuses. Just one of these 40A mega fuses will do?

https://www.amazon.com/Littelfuse-0...?keywords=40A+mega+fuse&qid=1585664037&sr=8-3

Given that the Tesla fuse didn't blow until Will Prowse put about 90A through it, it must be a near certainty that this fuse will blow well before then?

 

[Sertis]

Did anyone note the proper bolt size and thread to connect to the terminals without unscrewing the original bolt on the DC/DC terminals?

 

[cali8484]

They require 13mm wrench socket so likely M8 bolts. Not sure of the thread pitch. Typical for M8 is 1.5mm.

 

[glebvk]

Hi

Let's talk about voltage drop for 100A (1300W) use:
0.7V was lost in total:

Given that the car outputs 13.5 to 14V, this drop is not big enough to matter since the inverter works all the way down to 10V or so.

That 0.7V seems to translate to a 5% loss just between a battery and inverter.

Had you tried running the system for some time at considerable load?
What's the ballpark of overall efficiency?
Would there be any warnings from the car after a battery discharges considerably?

 

[marcmerlin]

That 0.7V seems to translate to a 5% loss just between a battery and inverter.

Had you tried running the system for some time at considerable load?
What's the ballpark of overall efficiency?
Would there be any warnings from the car after a battery discharges considerably?

To answer your questions:
1) I imrproved the wiring to reduce the voltage drop
2) yes, there is a loss of efficiency
3) no, I didn't calculate it end to end, nor do I care This is not a design for long term use, but emergency use
4) I ran my fridge and a 100W light bulb for multiple hours to test, saw no problems. This was nowhere close to the 200A/12V limit though, maybe 33% at most.

While this was fun and interesting to build, I'm not going to spend a lot of effort refining this, this is really for emergency use, and I've already spent more time on it that I will probably ever get out of it, so I'm trying not to make this worse

 

[marcmerlin]

Forgive my ignorance, but I had never heard about fast or slow blowing fuses. Just one of these 40A mega fuses will do?

https://www.amazon.com/Littelfuse-0...?keywords=40A+mega+fuse&qid=1585664037&sr=8-3

Given that the Tesla fuse didn't blow until Will Prowse put about 90A through it, it must be a near certainty that this fuse will blow well before then?

The tesla DC-DC does not have a fuse that blows, it's a self resetable circuit. I'm not sure how many times it will self reset, but I'm assuming a fair amount. Putting a fuse in front is fine, as long as you have a stack. Given that the system is rated for 200A, you can put 4 of those fuses in parallel (160A).
But remember that there will be an influx of current when you plug the inverter in, that will go beyond 200A, blow your fuses and reset the car's DC-DC unless you put a big resistor to slow down the inverter capacitor charge.

 

[glebvk]

Thanks, for the update

4) I ran my fridge and a 100W light bulb for multiple hours to test, saw no problems. This was nowhere close to the 200A/12V limit though, maybe 33% at most.

There's a surge in the current when the fridge compressor runs and especially starts, and it does put peak current to the test.

But when averaged over several hours, modern fridge consumes under 30W (A+ energy label stands for 273kWh per year).

 

[n2mb_racing]

But when averaged over several hours, modern fridge consumes under 30W (A+ energy label stands for 273kWh per year).

Mine consumes 100W average. Yikes. It's 19 years old.