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2021 Refresh: Model S (and X?) Changes to 12v System

Phlier

Bluebird
Jun 12, 2019
2,143
3,968
Utah
Buried in one of the Model S sticky threads, there was a post by a guy wondering why his Escort radar detector was throwing "High Voltage" warnings on his new 2021 Refresh Model S.

The short version of this story is that the Refresh cars have a fairly significant change to the 12v (let's call it the Low Voltage (LV) system from here out) system.

The refresh Model S (and I'm assuming this to be the case for the X, too, although I have been too lazy to verify it yet) DOES NOT have a 12v lead acid battery. Instead, it has a lithium battery, but as of right now, I'm not sure of the exact chemistry.

Check out this video at the timestamp:

He states that the pack is 1p/4s. What this means is that there are four cells wired in series. The nominal voltage for a lithium cell is 3.7 to 4.1 (and occasionally 4.2) volts. This means that when the battery pack is powering the low voltage system, the potential voltage for the LV system is between 14.8v and 16.4 volts. There is the potential of the high end being 16.8 volts if the cells used in the pack are capable of 4.2v at max charge.

In the post I mentioned about the guy having "High Voltage" warnings going off on his Escort, he mentioned that this only happened after the car was shut down, ie, the LV battery pack is powering the LV system, and since the LV battery pack was charged, it was doing so at 16.4-16.8 volts. Yet he didn't get this warning when the DC/DC convertor was powering the LV system, which I'm assuming means that when the DC/DC convertor is powering the LV system, it does so at 14.2 volts, which is what it always has been in Tesla cars up til now.

Also note that in the Owner's Manual for the Refresh S, it states that AC inverters plugged into the LV system must be capable of supporting an input voltage of 16 volts.

So the purpose(s) of this thread...

  • Please be aware of the changes to the voltage of the LV system in refresh cars
  • There is no lead acid 12v battery in refresh cars
  • Things plugged into the LV system must be able to take up to 16v

And also, please feel free to fill in any missing information, as well as correcting anything I've gotten wrong. Any additional information you can add is greatly appreciated.

Let's get the gaps in our knowledge filled in here so that people don't end up frying LV accessories.
 
Last edited:

strider

Active Member
Oct 20, 2010
3,649
1,038
NE Oklahoma
Thanks for sharing! I have a Plaid X on order so this will apply to me. There are no refresh Xs in the wild yet so will have to wait until deliveries start to confirm. It will be interesting to see what the lifespan of this battery is.
 

Ostrichsak

Active Member
Sep 6, 2018
3,702
4,285
Colorado, USA
Hmm... while I understand the negatives to aftermarket items not designed to withstand higher voltage (most are engineered and built to handle just under 15v as it's customary for car's low volt system to hit just about 14.2v under acceleration/higher RPMs) this overall could be a REALLY good thing for the low voltage electronics installed in the car from the factory.

It's been said for quite a number of years that 24v low-volt systems would allow for smaller wire harnesses and all sorts of positives. Getting an industry to change what has been around forever across all manufacturers... good luck with that.

Now think about all of the low volt items powered by the low volt battery in a tesla that would be affected in a positive way. As was mentioned already, windows can be programmed roll up/down faster. One of my biggest complaints with the windshield wipers (even though the auto-sensing feature on older cars is basically broken) is that the highest speed is medium on most other cars in the industry. Now they can be faster w/o any other adjustments to current hardware assuming the motors are capable of being reliable at that voltage. Sometimes when a motor runs slower due to less voltage it can experience more resistance and require more power to complete the task.

Another sore point is the LED headlight output. Now that there's more power going in there's a really good chance they give off more light. There's also a solid chance that some accessories will last longer as, in many cases, under-voltage to motors and such can be more problematic than over-volting the same item by the same amount. Not always but... sometimes.

Especially if said items are all engineered for 16v. Imagine cell phone chargers that are manufactured with 16v in mind rather than ~12v and how much faster they could charge your phone. This would be especially good for wireless charging that is inherently inefficient. Faster laptop chargers... lots of upside here.

I'm rarely one to defend Tesla's actions as most seem nonsensical but, for once, I'm going to sit back a bit and watch to see how this unfolds. This could be the nudge that the auto industry has needed for decades.

p.s. Admittedly I haven't yet taken the time to watch the video so maybe this is addressed.
 
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4SUPER9

MSLR #RN11510 6/7/21
Jun 6, 2013
3,084
2,919
California
Thank you very much for this information. Now, does anyone have a solution? My installed radar is expensive and I would not like to fry it. Is there such this is a step-down by 1-2V?
 

Phlier

Bluebird
Jun 12, 2019
2,143
3,968
Utah
Thank you very much for this information. Now, does anyone have a solution? My installed radar is expensive and I would not like to fry it. Is there such this is a step-down by 1-2V?
I have seen a buck convertor that plugs into a 12v vehicle accessory plug, and will take >12v and reduce it to 12v, but of course.... I can't find it right now.

When I finally do track the thing down, I'll post a link to it here.

The other option is to hard wire a buck convertor in upstream of the 12v accessory plug, but it would be a lot more fiddly than a plug-n-pray option, of course.

You could also get a dual ended 12v accessory plug harness and wire a buck convertor inline on that harness.
 
Last edited:

Snowstorm

Active Member
Dec 8, 2016
1,568
1,505
Ontario Canada
16V LV system seems problematic. There are very few accessories that will take 16V. Inverters are either 12V (10-15) or 24V (20-30). Most things designed for 12V will handle up to maybe 14.5V, but not 16V. What is Tesla thinking?

Did someone actually measured the output from the cigarate lighter?
 

4SUPER9

MSLR #RN11510 6/7/21
Jun 6, 2013
3,084
2,919
California
Would this buck converter work? Per the description: "DC 24V to DC 12V down converter: input voltage: DC 24V(15-40V Wide Range Input); Output voltage: 12V; No-load current: 10-15mA; Output current: 2A max; Output power: 24W max"
 

KevinY

Member
May 27, 2017
156
101
Hawaii
I for one love the fact that this car has a higher voltage. Higher voltage = lower amps. System operating at up to 16V will reduce equipment amperage draw by about 10%. This could the the difference in running a 16awg over a 14awg wire.
Personally I think you have very little to worry about plugging in your electronics.
 

KevinY

Member
May 27, 2017
156
101
Hawaii
16V LV system seems problematic. There are very few accessories that will take 16V. Inverters are either 12V (10-15) or 24V (20-30). Most things designed for 12V will handle up to maybe 14.5V, but not 16V. What is Tesla thinking?

Did someone actually measured the output from the cigarate lighter?
20210926_084225.jpg
 

Phlier

Bluebird
Jun 12, 2019
2,143
3,968
Utah
I would assume that your car is asleep when you're taking this measurement, as you're within the Li-on battery voltage range.

If it's not too much trouble, would you mind taking this same reading when the car is powered up, so that the DC/DC convertor is powering the LV system?

I think (but I'm not positive, hence the need to measure it) that when the DC/DC convertor is powering the system, that it still does so at 14.2 volts, as all Teslas have done in the past.

If your car is in fact awake in this picture, it means that they have increased the LV system voltage that the DC/DC convertor supplies, which is a bit unexpected.
 

Phlier

Bluebird
Jun 12, 2019
2,143
3,968
Utah
Would this buck converter work? Per the description: "DC 24V to DC 12V down converter: input voltage: DC 24V(15-40V Wide Range Input); Output voltage: 12V; No-load current: 10-15mA; Output current: 2A max; Output power: 24W max"
The link you supplied takes me to a list of results, not an individual product, but judging by the specs you listed, it should work. The only way to really know is to roll the dice and give it a shot. :)
 

scottf200

Active Member
Feb 3, 2013
4,290
4,247
Chicagoland ModelX S603
I'd consider putting this 12v monitor on the battery. only draws 1mA

Amazon:

Thread on it showing some output:
 

Phlier

Bluebird
Jun 12, 2019
2,143
3,968
Utah
Oops. Let me try again: Buck converter
It might work. It depends on if the DC/DC convertor powers the LVS at a voltage of less than 15 volts, as that is the minimum input voltage for that buck convertor. Keep in mind that we don't know what voltage the DC/DC convertor powers the refresh cars at yet. If it's still 14.2v (as it always has been), then that one won't work due to its minimum voltage requirement of 15v.
 
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KevinY

Member
May 27, 2017
156
101
Hawaii
I would assume that your car is asleep when you're taking this measurement, as you're within the Li-on battery voltage range.

If it's not too much trouble, would you mind taking this same reading when the car is powered up, so that the DC/DC convertor is powering the LV system?

I think (but I'm not positive, hence the need to measure it) that when the DC/DC convertor is powering the system, that it still does so at 14.2 volts, as all Teslas have done in the past.

If your car is in fact awake in this picture, it means that they have increased the LV system voltage that the DC/DC convertor supplies, which is a bit unexpected.
20210926_160036.jpg

While in drive. Don't be scared just do it.
 
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Snowstorm

Active Member
Dec 8, 2016
1,568
1,505
Ontario Canada
So the “12v” system on the new Tesla is actually 15.5V? This means it would be nearly impossible to find a DC to AC inverter that would work as they usually cut off at 15V.
 

4SUPER9

MSLR #RN11510 6/7/21
Jun 6, 2013
3,084
2,919
California
It might work. It depends on if the DC/DC convertor powers the LVS at a voltage of less than 15 volts, as that is the minimum input voltage for that buck convertor. Keep in mind that we don't know what voltage the DC/DC convertor powers the refresh cars at yet. If it's still 14.2v (as it always has been), then that one won't work due to its minimum voltage requirement of 15v.
I understand. Perhaps I am looking for something different, and I am not sure if such an animal exists. What I envision is a converter that lowers the voltage by “x” , regardless of input. So, if I had such a device that lowers everything by 1, or 1.5, or maybe as much as 2, then I know my electronics will be safe. Well, as long as the voltage stays above a certain amount to keep my device operational. In other words, if our cars spit out 14-16, and we lower that across the board to 13-15, we should be better off.
 

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