Frunk Auxiliary Power Tap / Power Feed Specs (48V and 400W)

[JBee]

The steering (front and rear) systems have independent harnesses by themselves.

I'm not worried about the cable harnesses, rather power supply. They also have two redundant 48V supplies on top of the 48V battery.

But I still wouldn't want to risk connecting a large consumer on the 48V battery and risk loosing one redundancy for an accessory. Not hard to add a battery, and then not gave to deal with a warranty claim.

Besides, I like steering more.

Sponsored

 

[scottf200]

There is the 400w switched tap. There is also shown two bolts next to the 48v battery which directly tap said battery. I mean, nobody said anything about that being where winch accessory gets its power, but that is 100% where wrench accessory gets its power.

I see. Well, aren't those just standard 'jump' posts that are on all cars? I've used them on my TMX as well.

Tesla model Y with lead acid or lithium battery manual section here: https://service.tesla.com/docs/Publ...UID-BDCCB025-63E2-4F5F-9D59-34177FBDFF6C.html

 

[CyberGus]

There is the 400w switched tap. There is also shown two bolts next to the 48v battery which directly tap said battery. I mean, nobody said anything about that being where winch accessory gets its power, but that is 100% where wrench accessory gets its power.

I would not be confidant enough to say "100%" this is all true.

I can believe those are the jumper posts, but this image does not show exactly where the hot goes (the ground post looks bonded to the frame). There was an interview (Munro?) where one of the engineers said something about being able to jump with 48v or with 12v, so maybe that hot wire goes to a controller that detects the voltage...?

It's also not clear whether the 48v accessories draw from the small battery, from a DC/DC converter on the main pack, or both.

If that hot post ties directly into the battery and/or 48v bus, then it's awfully careless to leave it uncapped.

 

[Timelord]

You can't jump a cybertruck with 48v. If your 48v bus is dead flat, your 800v bus is flat. Or worse problems are going on. If you ever have to jump 48v bus to get enough smarts working to communicate NACS charging, you probably should not be charging the destroyed battery pack in first place.

Obviously I'll read the specs when they are made available, and I will design accordingly. I remain entirely confident that is the winch capable power tap location.

 

[JBee]

I would not be confidant enough to say "100%" this is all true.

I can believe those are the jumper posts, but this image does not show exactly where the hot goes (the ground post looks bonded to the frame). There was an interview (Munro?) where one of the engineers said something about being able to jump with 48v or with 12v, so maybe that hot wire goes to a controller that detects the voltage...?

It's also not clear whether the 48v accessories draw from the small battery, from a DC/DC converter on the main pack, or both.

If that hot post ties directly into the battery and/or 48v bus, then it's awfully careless to leave it uncapped.

There are three 48V supplies, but we don't know which is connected to what.

There's two DC converters and one 48V battery. I'm assuming one of the DC converters is charging the 48V battery and it doesn't have its own charger circuit as well.

I'm also thinking all the 48V loads are supplied directly from one of the two DC converters and that the 48V battery is just a reserve. It wouldn't make sense to charge cycle the 48V battery which would degrade it and cause more electrical losses. Same like with an alternator on a ICE.

 

[Timelord]

Also, I get the intuition that leaving the 48v bolt uncapped feels very wrong, but that is a reasonable low voltage install. Modern cars have plenty more DC lug exposure than that.

 

[JBee]

You can't jump a cybertruck with 48v. If your 48v bus is dead flat, your 800v bus is flat. Or worse problems are going on. If you ever have to jump 48v bus to get enough smarts working to communicate NACS charging, you probably should not be charging the destroyed battery pack in first place.

Obviously I'll read the specs when they are made available, and I will design accordingly. I remain entirely confident that is the winch capable power tap location.

In the Monroe video they did say you can jump at 48V and 12V.

I'd be very cautious connecting to the battery as I mentioned before, because if the SbW setup. Its not just a short to be worried about, it's also brownouts, noise etc.

 

[JBee]

Also, I get the intuition that leaving the 48v bolt uncapped feels very wrong, but that is a reasonable low voltage install. Modern cars have plenty more DC lug exposure than that.

Proximity to a vehicle part being ground is the problem. You weld things with those voltages.

Not so much worried about electrocution at those voltages, but care should still be taken.

 

[Timelord]

Random note: Cybertruck is using 20a circuits/outlets.

In the Monroe video they did say you can jump at 48V and 12V.

I'd be very cautious connecting to the battery as I mentioned before, because if the SbW setup. Its not just a short to be worried about, it's also brownouts, noise etc.

You look up the power allowance on the terminals, design for accessory to be under it, and put a fuse inline. Steer by wire changes nothing. 12v bus is critical to modern vehicle operation for at least a couple decades. Not rocket surgery here. Read the manufacturer rating and off you go.

 

[Timelord]

Proximity to a vehicle part being ground is the problem. You weld things with those voltages.

Not so much worried about electrocution at those voltages, but care should still be taken.

I gotcha. Personally, I would probably give mine a quick wrap of electrical tape, but check out all the ground points and how close they are to your car battery positive terminal. Include the metal hood.

Not at all disagreeing that you really, really don't want to short it, but it looks a reasonable install. Not the best, but reasonable.

 

[JBee]

Random note: Cybertruck is using 20a circuits/outlets.



You look up the power allowance on the terminals, design for accessory to be under it, and put a fuse inline. Steer by wire changes nothing. 12v bus is critical to modern vehicle operation for at least a couple decades. Not rocket surgery here. Read the manufacturer rating and off you go.

I'm not saying it's rocket science.

But saying that SbW is "not new" is simply incorrect.

Until there's some miles on it, there is no data to validate your assumptions on a wheeled vehicle with millions of untrained, un-qualified users doing mods.

The airline industry trains and qualifies for maintenance, and operation in case of failure, and "engineers" every accessory attached.

Somewhere inbetween is where a prudent person would call for caution.

Ideally, Tesla will provide clarity on how to connect what with casual disbandon.
Then have at it.

 

[Timelord]

Ideally, Tesla will provide clarity on how to connect what with casual disbandon.
Then have at it.

Of course. God I wish the technical data would be released already. I know I can at least afford that much of the truck. ?

 

[scottf200]

I'm also thinking all the 48V loads are supplied directly from one of the two DC converters and that the 48V battery is just a reserve. It wouldn't make sense to charge cycle the 48V battery which would degrade it and cause more electrical losses. Same like with an alternator on a ICE.

I'm afraid it is very different than an alternator in the sense that the DC-to-DC can be triggered whenever they deem it necessary. I'm guessing you don't own a Tesla? It is well known that the Tesla cars monitor the 12v level and kick in the DC-to-DC to top it off. Lot of forum info on this on TMC as people put in always on Dashcams or fridges or whatever (running off low voltage battery when car is off / contacts open). I have a 12v fridge in my TMX as an example that I leave on 24x7 while road tripping. I have a battery monitor [URL] that is very very low amperage and takes a sample every minute or so. You can connect your phone and see graphs of the DC-to-DC kicking in over 24 hr periods or over a couple-week timeframe. HTH

 

[CyberGus]

I'm afraid it is very different than an alternator in the sense that the DC-to-DC can be triggered whenever they deem it necessary. I'm guessing you don't own a Tesla? It is well known that the Tesla cars monitor the 12v level and kick in the DC-to-DC to top it off. Lot of forum info on this on TMC as people put in always on Dashcams or fridges or whatever (running off low voltage battery when car is off / contacts open). I have a 12v fridge in my TMX as an example that I leave on 24x7 while road tripping. I have a battery monitor [URL] that is very very low amperage and takes a sample every minute or so. You can connect your phone and see graphs of the DC-to-DC kicking in over 24 hr periods or over a couple-week timeframe. HTH

The low-voltage battery is to power the system when the vehicle is sleeping (i.e., the main pack contactors are open). If you're using accessories, then the vehicle is most certainly awake, with the main pack engaged and DC/DC available.

Sponsored