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Solution for amateur radio operators? Impossible to use magmount antennas in a Tesla

VerityZooms

Member
Apr 19, 2016
131
108
Chicago, IL
The DC-DC converter is always running when the car is "on", so no risk of it "kicking in and generating more noise" the converter cycles on and off as needed when the car is "off". While it's hard to know what the total free capacity of the DC-DC converter is, I'd hazard a guess that it's probably over 1000w (though it may vary a bit if using all 5 seat heaters and the rear defrost!)

Honestly, I can't imagine a scenario in amateur radio that I would worry about capacity in this vehicle. And better than any ICE, you have 85kWh of capacity on-tap without starting the engine!

As for capacity to fuse for, etc, that will be based on your gear similarly to any other vehicle or even stationary installation.

This car has more 12V capacity than many standard vehicles, so unless you're running an HF amplifier pushing out a kW or more, I simply wouldn't worry about it.

Well, amplifier is precisely where I'm wondering about it: I'm doing the power-system installation now; but on advice from friends, I'm trying to “amplifier-proof” the setup ahead-of-time. (Avoid re-wiring the entire car, basically, if I ever do decide to install an amp.)

Regarding the draw of smaller items — my understanding is that there's a power-management system in series with the 12V battery, somewhere; and I'm additionally curious how it will react to adding a bunch of parallel loads? (I'm a noob, does that even make sense?)
 

green1

Active Member
Mar 25, 2014
4,548
1,495
Calgary, Alberta, Canada
Well, amplifier is precisely where I'm wondering about it: I'm doing the power-system installation now; but on advice from friends, I'm trying to “amplifier-proof” the setup ahead-of-time. (Avoid re-wiring the entire car, basically, if I ever do decide to install an amp.)

Regarding the draw of smaller items — my understanding is that there's a power-management system in series with the 12V battery, somewhere; and I'm additionally curious how it will react to adding a bunch of parallel loads? (I'm a noob, does that even make sense?)
I'm not entirely sure that it does make sense... You'll connect directly to the battery. Not to somewhere else. Make sure it's fused appropriately, and that the wire is rated for the current you plan to use.
If you truly want to run kW levels of RF output, I'm not sure any car is really the place to do that from.
 
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VerityZooms

Member
Apr 19, 2016
131
108
Chicago, IL
I'm not entirely sure that it does make sense... You'll connect directly to the battery. Not to somewhere else. Make sure it's fused appropriately, and that the wire is rated for the current you plan to use.
If you truly want to run kW levels of RF output, I'm not sure any car is really the place to do that from.

Well, again, I'm relatively new; but much of what I have learned, I've picked up from KØBG's site — particularly, to bind the transceiver's power at the chassis, not directly to the battery's terminals. (Not to mention that the Model X's battery-terminals are effectively unreachable — best you can do without disassembling half of the front-end of the car, is the opposite end of the battery's connection — distribution block and chassis for positive and negative, respectively.)

That's where my IC-7100 is currently tied in; and where I'll be tying up my new distribution block here in the next couple weeks, unless you've information to the contrary? :p
 

Ingineer

Electrical Engineer
Aug 8, 2012
1,507
3,712
DO NOT connect anything to the negative terminal of the battery. This will affect the current sensor there and skew the readings which could result in unexpected problems with the AGM charge algorithm.

The positive terminal is fair game, but just be sure to use a fuse as close as possible to the terminal.

You should ground the transceiver to the chassis as close as you can to reduce the ground loop impedance.
 

green1

Active Member
Mar 25, 2014
4,548
1,495
Calgary, Alberta, Canada
DO NOT connect anything to the negative terminal of the battery. This will affect the current sensor there and skew the readings which could result in unexpected problems with the AGM charge algorithm.

The positive terminal is fair game, but just be sure to use a fuse as close as possible to the terminal.

You should ground the transceiver to the chassis as close as you can to reduce the ground loop impedance.
Are you sure about this? I've never met a vehicle where you couldn't attach directly to the negative terminal on the battery, and when dealing with large draws I highly recommend AGAINST attaching anywhere else. All my aftermarket power needs are connected to the 2 battery terminals.
I am also having a lot of trouble from an electronics stand point coming up with any possible mechanism whereby it would be a problem.
 

rabar10

Model 3 >> Focus Electric
Moderator
Dec 3, 2010
1,455
189
Indianapolis, IN
Are you sure about this? I've never met a vehicle where you couldn't attach directly to the negative terminal on the battery, and when dealing with large draws I highly recommend AGAINST attaching anywhere else. All my aftermarket power needs are connected to the 2 battery terminals.
I am also having a lot of trouble from an electronics stand point coming up with any possible mechanism whereby it would be a problem.
Interpreting Ingineer's comment -- sounds like the current sensor for the 12V is on the negative side i.e. between the battery and chassis connection. If you connect directly to the negative post, the load will bypass that current sensor.
 

green1

Active Member
Mar 25, 2014
4,548
1,495
Calgary, Alberta, Canada
Interpreting Ingineer's comment -- sounds like the current sensor for the 12V is on the negative side i.e. between the battery and chassis connection. If you connect directly to the negative post, the load will bypass that current sensor.
I'm failing to see how that's a problem. In fact, it seems more likely to be a problem if i connect without bypassing the sensor as the car may not be very happy with large unexplained current draws.
 

Ingineer

Electrical Engineer
Aug 8, 2012
1,507
3,712
The negative terminal contains a device called the IBS (Intelligent Battery Sensor). This communicates via LIN to the gateway which controls the 3-stage charge algorithm for the 12V AGM battery. If you create load directly on the battery, this can cause disruption to the algorithm that can result in overcharge in the absorption phase and boil the electrolyte out of the AGM battery and thus drastically shorten it's life.

Also, attaching a RF transciever to this can introduce interference to the LIN bus, which I've seen cause the IBS go MIA at which point the gateway will end 12v support, your car will die within an hour, and you will be stuck on the side of the road.

The reason for grounding any RF equipment as close to the body as possible is to avoid any RF return into sensitive areas, the IBS being one! This is also prudent to avoid running a long ground lead which could unintentionally radiate negative common-more RF interference and could disrupt even more systems in the car.

If you want to do take that chance, by all means please do so, but I have a lot of experience with these cars and RF systems as well, so ignore good advice at your peril.
 

Ingineer

Electrical Engineer
Aug 8, 2012
1,507
3,712
Also, The DC-DC converter can easily handle a 50A excess load with no problems. The IBS is used to prevent discharge of the 12V battery as it attempts to null the current during the float phase after completion of the charge. You are best to connect the aux loads to the main fuse box (with the large fuses) instead of the battery. The body is aluminum, but it conducts well as it's large and as long as you use prudent termination methods for the negative terminal as close to the load as possible, and include a common mode choke on the power wires (if not built in), you should not have any issues. Use ox-gard or a similar grease at the AL/CU interface to prevent possible corrosion.
 
Well, again, I'm relatively new; but much of what I have learned, I've picked up from KØBG's site — particularly, to bind the transceiver's power at the chassis, not directly to the battery's terminals. (Not to mention that the Model X's battery-terminals are effectively unreachable — best you can do without disassembling half of the front-end of the car, is the opposite end of the battery's connection — distribution block and chassis for positive and negative, respectively.)

That's where my IC-7100 is currently tied in; and where I'll be tying up my new distribution block here in the next couple weeks, unless you've information to the contrary? :p

Take everything on K0rg's site with a grain of salt. He's got a bit of an agenda against hybrids/EVs and a lot of what he talks about flat out isn't true.

For instance you can run a 1/2 wave without needing to ground to the chassy for UHF/VHF. I run up to 50W without even being directly connected to the battery with little RFI issues.
 

VerityZooms

Member
Apr 19, 2016
131
108
Chicago, IL
The negative terminal contains a device called the IBS (Intelligent Battery Sensor). This communicates via LIN to the gateway which controls the 3-stage charge algorithm for the 12V AGM battery. If you create load directly on the battery, this can cause disruption to the algorithm that can result in overcharge in the absorption phase and boil the electrolyte out of the AGM battery and thus drastically shorten it's life.

Also, attaching a RF transciever to this can introduce interference to the LIN bus, which I've seen cause the IBS go MIA at which point the gateway will end 12v support, your car will die within an hour, and you will be stuck on the side of the road.

The reason for grounding any RF equipment as close to the body as possible is to avoid any RF return into sensitive areas, the IBS being one! This is also prudent to avoid running a long ground lead which could unintentionally radiate negative common-more RF interference and could disrupt even more systems in the car.

If you want to do take that chance, by all means please do so, but I have a lot of experience with these cars and RF systems as well, so ignore good advice at your peril.

Also, The DC-DC converter can easily handle a 50A excess load with no problems. The IBS is used to prevent discharge of the 12V battery as it attempts to null the current during the float phase after completion of the charge. You are best to connect the aux loads to the main fuse box (with the large fuses) instead of the battery. The body is aluminum, but it conducts well as it's large and as long as you use prudent termination methods for the negative terminal as close to the load as possible, and include a common mode choke on the power wires (if not built in), you should not have any issues. Use ox-gard or a similar grease at the AL/CU interface to prevent possible corrosion.

Okay, wow, this is a high density of useful information.

Can you elaborate on some of the following (where on earth did you source all this? Ex-Tesla?), if you have that information available?

  • Just out of curiosity, what do you mean by ‘three-stage charge algorithm’ and ‘float phase?’
  • Besides “drawing more than my Tesla thinks I'm drawing”, what do you mean by ‘disruption to the algorithm?’ Or is that the only concern?
  • Can you elaborate on “grounding any RF equipment as close to the body as possible?” Do you mean … using the shortest wire possible between the negative terminal of an RF-manipulating device, and the chassis of the vehicle; or do you mean connecting the negative wire as closely to the battery's attachment to the chassis (i.e. reducing the return-path overall), or …
  • I'm new to these things, but how would the negative DC lead be carrying common-mode? I thought that was an ‘improperly-grounded-feedline’ thing. #noob — I've mostly been following KØBG's instructions; but it only mentions choking on the feedline — “The last place to install them is inside the vehicle.”
  • Are you talking 50A @ 100% duty-cycle? Will it handle higher amperage at a reduced duty-cycle? (I'm installing a high-power hifi in addition to possibly an amplified HF RF amp. Yeah. Although, of course, there's no situation where they'd all be drawing their full current simultaneously — since it's illegal to transmit audio over the HAM bands, the hifi will necessarily be silent when I'm transmitting :p)
  • “connect the aux loads to the main fuse box (with the large fuses)” — I'm currently attached at the point where the battery's positive lead attaches to the distribution box (see photos when I was figuring this out the hard way in my other thread); but not across any particular fuse/terminal in that block. (The positive lead is fused along its length.) Do you have photos of what you mean?
  • Thanks for the ox-gard tip; somebody (at Firestik, actually — yeah, there's a CB radio in the mix, to boot) mentioned the AL/CU galvanic corrosion, but didn't give me any ideas what to do about it.

(You've been so helpful, don't feel bad if you don't want to dive into responding to my mess! <3)
 

KD7UFS

New Member
Feb 21, 2017
1
1
Moriarty, NM
Two comments. A mag mount on steel can be a quarter wave whip. The other 1/2 of the antenna is the car body (ground plane). Most through the glass antennas are usually a center driven dipole, top 1/2 is one side of the dipole, the bottom 1/2 is the other. There are two common ways to do this. One is the lower 1/2 is hollow, and the feed point is actually in the middle. The other way is you feed the bottom, and there is a phasing coil in the middle. Either way, the antenna is twice as long as the 1/4 wave whip.

Regarding connecting to the negative battery terminal, don't. As pointed out before, there is a current sensor in the negative lead. The problem is not just the current drawn by your radio. Most ham radios have the negative lead connected to the chassis. Not only your radio current but all the 12V current drawn by your vehicle (or charging current) now has an alternate path any time your radio or the shield of our coax touches your cars metal. With some radios the hang up button on your mike is grounded also. This can be a lot of current, think headlights and resistance heater. Since the current sensor has internal resistance, this can result in a lot of current going through your radios negative lead. Not being fused, it might even melt (think fire).
 
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berkeley_ecar

S 90D (fully loaded) delivered 18 Mar 2017
Jul 21, 2014
256
214
Berkeley, CA
Drilling holes is a bit scary :p

It would be interesting to know which if any areas of the car are some steel alloy as opposed to largely aluminum.[...] :)
I believe the actual bumper part of the frame in front is also steel. Easiest to see if you visit a store and examine the stripped down frame with battery and motors that is generally on display...
 
I have used a Diamond K412S lip mount on the rear hatch of 2016 Tesla Model S. The mount comes with a very thin coax and BNC connector that is easy to run through to the front driver's seat. I mainly operate a Kenwood TH-D72A running APRS (144.390 MHz) at 5 watts in the Los Angeles area with a Comet SBB-5 dual band antenna. I had started out with a Comet B-10 antenna, then a Comet SBB-2 antenna, but both antennas were not enough radiator in the air to get an APRS signal out. Since SBB-5 is taller, tends to scrape along the roof of some parking structures which I was trying to avoid with B-10 and SBB-2. APRS performance (i.e. being received and transponded by the local/mobile APRS nodes) with this antanna installation on Model S is about 60% to 70% compared to a mag mount antenna on the center rooftop (a kind of reflector) of Lexus. The lease on the Model S is up end of August 2019, and next lease will be Model X. I hope the same lip mount antenna installation can work on the rear hatch of Model X, will post the outcome.
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Hi TGA - The rubber padding between the mount and the car, and the metal strip between the set screws on the underside of the lip do come with the Diamond K412S mount. I needed to sand off some paint on the underside so an electrical contact can be made with the hatchback. I had called Diamond about getting shorter set screws because the original set screws were still too 'tall' to fit in the channel when the hatchback closes. Diamond was very obliging ([email protected]) to send a set of shorter set screws. The rubber padding seems to protect the paint quite well as I had removed and re-installed the mount to slide it a little lower down along the hatchback edge as the SBB-5 was a little too tall for some parking structures. The coax connector is actually SMA (not BNC ! ). The mag mount comparison antenna (on Lexus rooftop) is Diamond MR77sma. I hope this helps!

73's Harold Yuan - WB6DOC
 
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Just found this thread and I have a few questions. I pulled my FT7900R out of my IC before I got my 2019 S. After reading comments here and on a few other threads, I want to be sure of a few things before I dive into putting in the S. I want to put the antenna on the trunk lid. I have the same diamond mount and cable mentioned in a previous post, and I know it won't interfere with the opening and closing. I also will put the main unit in the trunk, so I want to get power from there. Per some posts from Ingineer, I think I should be OK to tap into the 30AMP 12v circuit to the hatch motor, correct? I initially was going to put it in the frunk and tap off the 12 v battery, but that doesn't seem like a good idea because of the current sensor. Lastly, I wonder if anyone knows the best route to get the control wires from the trunk to the cubby in the center console as the control head fits perfectly in there.
Thanks to all for any advice.

73, Steve N2QLQ
 

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