Ask an Electrical Engineer

[Scarpia]

Haha, good catch... what can I say, I'm an EE. Thanks and fixed.

Ha, I work with a bunch of EE's, I totally get it. I love you guys.
Monitoring this thread will unfortunately consume a lot of my free time now.

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[UW2]

Why does my screen heat up on long trips?

 

[CHeil402]

Why does my screen heat up on long trips?

A seemingly simple question with a whole field of engineering behind it. The short answer is inefficiencies. To further explain, it's because short of an electric heater whose sole purpose is to make heat, no electronic device is 100% efficient (short of a superconductor). All electronic devices have losses at some scale, and that inefficiency is lost to "waste heat" or "Joule heating". Some devices are worse than others. For example a screen should ideally convert all of its electricity into light, but it can be as bad as only using 10 - 30% of that for light generation that you see. The rest of the electricity has to go somewhere, and what isn't used is consumed by internal resistance as heat. An electric heater is just literally burning electricity.

So on the MME screen, the power electronics generate heat (a converter can be about 95% efficient), the PCB traces and wires generate heat as they have internal resistance, and the screen panel itself also wastes electricity as heat. This is a normal thing, so engineers have to design to accommodate it. While heat does destroy electronics, higher heat does so much more rapidly. All electronics have maximum design temperatures that their life is designed towards so products need to be designed simply to keep the heat below that level. Things like heat sinks, heat fins, heat pipes, and fans are designed to move this waste heat out of the electronics that generate the heat and dispose of it into the air. Some materials are better at transferring heat and some are better at insulating heat and it is subject to the ambient temperature as well. When the car is cold inside, it will be better at absorbing that waste heat. Also direct sunlight will drop that ability to shed heat.

So in summary, the electronics generate heat because they aren't perfectly efficient. That heat has to be designed for by disposing of it somewhere and appropriately rating the materials to withstand typical operating temperatures. As long as you're using the screen, more heat is constantly added to it. So long as it can properly dispose of this heat, there's nothing to worry about.

 

[UW2]

A seemingly simple question with a whole field of engineering behind it. The short answer is inefficiencies. To further explain, it's because short of an electric heater whose sole purpose is to make heat, no electronic device is 100% efficient (short of a superconductor). All electronic devices have losses at some scale, and that inefficiency is lost to "waste heat" or "Joule heating". Some devices are worse than others. For example a screen should ideally convert all of its electricity into light, but it can be as bad as only using 10 - 30% of that for light generation that you see. The rest of the electricity has to go somewhere, and what isn't used is consumed by internal resistance as heat. An electric heater is just literally burning electricity.

So on the MME screen, the power electronics generate heat (a converter can be about 95% efficient), the PCB traces and wires generate heat as they have internal resistance, and the screen panel itself also wastes electricity as heat. This is a normal thing, so engineers have to design to accommodate it. While heat does destroy electronics, higher heat does so much more rapidly. All electronics have maximum design temperatures that their life is designed towards so products need to be designed simply to keep the heat below that level. Things like heat sinks, heat fins, heat pipes, and fans are designed to move this waste heat out of the electronics that generate the heat and dispose of it into the air. Some materials are better at transferring heat and some are better at insulating heat and it is subject to the ambient temperature as well. When the car is cold inside, it will be better at absorbing that waste heat. Also direct sunlight will drop that ability to shed heat.

So in summary, the electronics generate heat because they aren't perfectly efficient. That heat has to be designed for by disposing of it somewhere and appropriately rating the materials to withstand typical operating temperatures. As long as you're using the screen, more heat is constantly added to it. So long as it can properly dispose of this heat, there's nothing to worry about.

Maybe the cooling is not ideal, it does get hot.

 

[UW2]

How to keep the rats away? Tell me no soy was used on the wires please.

 

[highland58]

I have a charge point on a 60amp circuit, so it delivers 48amp to the car. Chargepoint reports that my car pulls a constant 11kw while charging.

Now that I have my car, I have the same setup and it says 11.14kw average rate on the last charge. I set it to stop at 90% and I will see what it says tomorrow.

 

[CHeil402]

Maybe the cooling is not ideal, it does get hot.

I don't know the exact design specifications of the MME screen, but assuming the temperature levels out at some point (doesn't continue to get hot) and it stays below 90 deg F I would think this to be normal. If you have an IR thermometer you could take a measurement.

 

[CHeil402]

How to keep the rats away? Tell me no soy was used on the wires please.

Get a cat? I don't believe soy wires were used like they were in Toyota...

https://www.macheforum.com/site/threads/psa-watch-for-vermin-rats-mice-squirrels.3853

Or get an ultrasonic rodent repellent for your garage/driveway.

 

[Maquis]

Thanks for starting this thread. My background is also EE by education, but in the late 90s, I switched careers to the "dark side" (I.T.). So it's been over 20 years since I have practiced engineering. I have kept up to date on power distribution and electrical codes and have tried to offer some expertise in these areas. Of course, these newfangled lithium batteries weren't really a thing back then, so I'll leave that to those with proper experience.

Also, living in a rural area, I've dealt with rodents munching on wires. In my experience, the ultrasonic repellents either don't work at all, or will only provide some relief when first installed. Eventually, the critters get used to it, maybe? They definitely don't like the smell of mothballs, but noone want their MME smelling like grandma's closet! I put mothballs in farm macinery that sits idle over the winter and they definitely work.

 

[CHeil402]

Thanks for starting this thread. My background is also EE by education, but in the late 90s, I switched careers to the "dark side" (I.T.). So it's been over 20 years since I have practiced engineering. I have kept up to date on power distribution and electrical codes and have tried to offer some expertise in these areas. Of course, these newfangled lithium batteries weren't really a thing back then, so I'll leave that to those with proper experience.

Also, living in a rural area, I've dealt with rodents munching on wires. In my experience, the ultrasonic repellents either don't work at all, or will only provide some relief when first installed. Eventually, the critters get used to it, maybe? They definitely don't like the smell of mothballs, but noone want their MME smelling like grandma's closet! I put mothballs in farm macinery that sits idle over the winter and they definitely work.

I've seen some of your posts about electrical questions and they looked good. Certainly why I said I'm not the do-all-end-all authority by any means!

We had a mouse get in my house once and my wife freaked and made me call an exterminator. When they came they walked around but said honestly there isn't much you can do to keep them fully out if they want to come in and that having cats was the best repellent there was. They caught the mouse that did get in.

 

[cassmoney0523]

I have seen more than one online write up claiming Tesla is better vs MME while citing the heat pump. Do you think having a heat pump would have made the vehicle better in a significant way? In other words, are we missing out on something big without it?

thanks, additionally... your thread and time/attention to it is greatly appreciated

 

[EVguy]

NEMA 14-50 or 6-50 plug/socket preference?

I currently have an old Nissan home charger that is on a 40 amp circuit that has a NEMA 6-50 plug attached. I know that I can use this old charger to charge my upcoming MME but I am concerned about its age (8yrs). I also know that I can purchase another home charger that uses a 6-50 plug, but I cannot use the Ford MME provided charger/cord to plug directly into the wall socket as I believe the MME charger uses a 14-50 plug. I assume manufacturers are using this type plug for many folks who may already have existing 240 circuits in their garages for dryers, etc.

1) What is the purpose of the neutral wire used with the 14-50 plug/socket when used to charge EV at 240 watts? It is certainly not needed if the vehicle can also use a 6-50 plug that has no neutral wire.

2) Would the Ford provided cable/charger (or any other home charger) work if plugged into a 14-50 socket that has no neutral wire attached to the wall socket? If it did and was not a code violation, I could just change the wall socket in the garage when I upgrade my home charger to use a NEMA 14-50 plug, which would also allow me to use the included Ford MME charger. That way I would not need to run a new neutral wire.

Thanks for your time with this subject matter.

 

[breeves002]

I have a charge point on a 60amp circuit, so it delivers 48amp to the car. Chargepoint reports that my car pulls a constant 11kw while charging.

It seems to be a current limit not total power. 48A AC is the limit. If you have some nice high voltage you could see as high as 12kW in a perfect world coming into the charger.

 

[breeves002]

1) What is the purpose of the neutral wire used with the 14-50 plug/socket when used to charge EV at 240 watts? It is certainly not needed if the vehicle can also use a 6-50 plug that has no neutral wire.

2) Would the Ford provided cable/charger (or any other home charger) work if plugged into a 14-50 socket that has no neutral wire attached to the wall socket? If it did and was not a code violation, I could just change the wall socket in the garage when I upgrade my home charger to use a NEMA 14-50 plug, which would also allow me to use the included Ford MME charger. That way I would not need to run a new neutral wire.

Thanks for your time with this subject matter.

Not trying to thread hijack but I was reading and I'll answer this one.

Either plug is fine one just has a neutral for if you need 120v.

1. No purpose. It is not needed. I tried this for fun with the MME included charger. I disconnected the neutral from my 14-50 plug and the charger worked properly. It is only used in applications where you need 120v as well as 240v - for instance, clothes dryer. The light bulb will be 120v most likely.

2. As answered in point 1, YES it will work. It is a code violation to not have a neutral run to a 14-50 socket. You can purchase NEMA 6-50 to 14-50 adapter cables though and use your currently installed outlet to charge with the included MME charger if you'd like to. However I think the Nissan EVSE if it still works you could just continue to use.

 

[breeves002]

I have seen more than one online write up claiming Tesla is better vs MME while citing the heat pump. Do you think having a heat pump would have made the vehicle better in a significant way? In other words, are we missing out on something big without it?

thanks, additionally... your thread and time/attention to it is greatly appreciated

Man I'm on a roll so hopefully OP doesn't get mad at me.

The new Teslas with the heat pump will be more efficient. A heat pump is literally reverse air conditioning. It is way more efficient than resistive heat because you don't heat everything up - fluid, tubing, etc. The way it works is fairly simple, it just changes the direction of flow of refrigerant which swaps the jobs of the condenser and evaporator.

Heat pumps do have their limitations - like needing defrost cycles when it gets cold to melt the ice off of the condenser, and they really don't work well in a car when it starts to get fairly cold (not sure what temp but likely still above freezing). They really help save energy when its 40-60º and you just need a little bit of warm air. Down at 20º it isn't going to help much as the resistive heater will likely have to run to generate enough heat to keep the cabin warm - especially at night.

Lets be real though - is the lack of a heat pump a deal breaker? All of the 2019 Tesla lineup doesn't have heat pumps. Sure you're going to use more energy in cooler weather but for 99% of people it doesn't matter.

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