Ask an Electrical Engineer

CHeil402 · Mar 10, 2021

Like several people on this forum, this will be my first EV. I’ve always wanted an EV since the very first Tesla came out a while back but was a die-hard manual transmission fan and never saw a vehicle that really made it worth the tradeoff… but I finally think the MME is that car. However, it’s not my first experience with electric vehicles. My day job when I’m not on these forums is a passenger train professionally licensed electrical engineer and you’d be surprised how much they have in common (just at a larger scale). As I’ve posted before even a diesel train is really just a diesel generator powering an electric motor.

Anyway… I’ve been following this forum for a while and really have had a connection to this wonderful group of people. There’s been a lot of technical questions about the car in general and on powering it. So I’m starting this thread to “give back” to the wonderful group of people here working through issues (@ChasingCoral) and providing insight (@hybrid2bev) while I eagerly await mine.

I wanted to essentially start an ask-me-anything-type of post specific to electrical engineering. I’m not saying that there isn’t already a plethora of great information on here, and I will do my best to link to existing discussions where I can and give credit where credit is due, but I wanted to open a discussion for any type of related question. There are no dumb questions. What’s a volt? What’s the difference between a kW and kWh? What’s a heat pump? Why is there a high voltage and low voltage battery on my car? What’s a GFCI? Etc.

I don’t posit to know everything, so I will take my time in answering questions and doing research where I can. I will try to separate my opinion from fact and would be happy to have others voice their opinions as I’m sure there are plenty of people on here smarter than myself… science should be humble and accept new evidence when presented with it. I know a lot of this information is widely available on the internet, but sometimes you don’t know what to ask, there is conflicting information, or answers are too technical. Although I’m an engineer I was raised by a bartender dad and waitress mom, so I like to think I’m a better communicator than the stereotypical engineer and I will try to make the answers as clear as possible, but also link to more detailed sources where applicable for those interested. I’ve known and worked with plenty of brilliant people that just couldn’t communicate effectively.

Sorry for the long post and if it falls into the void of the forum, so be it, but I’ll keep an eye out for posts now or in the future! I hope, if nothing else, to inspire thought.

CHeil402 · Mar 10, 2021

Marciaf · Mar 10, 2021

CHeil402 said:
Like several people on this forum, this will be my first EV. I’ve always wanted an EV since the very first Tesla came out a while back but was a die-hard manual transmission fan and never saw a vehicle that really made it worth the tradeoff… but I finally think the MME is that car. However, it’s not my first experience with electric vehicles. My day job when I’m not on these forums is a passenger train professionally licensed electrical engineer and you’d be surprised how much they have in common (just at a larger scale). As I’ve posted before even a diesel train is really just a diesel generator powering an electric motor.

Anyway… I’ve been following this forum for a while and really have had a connection to this wonderful group of people. There’s been a lot of technical questions about the car in general and on powering it. So I’m starting this thread to “give back” to the wonderful group of people here working through issues (@ChasingCoral) and providing insight (@hybrid2bev) while I eagerly await mine.

I wanted to essentially start an ask-me-anything-type of post specific to electrical engineering. I’m not saying that there isn’t already a plethora of great information on here, and I will do my best to link to existing discussions where I can and give credit where credit is due, but I wanted to open a discussion for any type of related question. There are no dumb questions. What’s a volt? What’s the difference between a kW and kWh? What’s a heat pump? Why is there a high voltage and low voltage battery on my car? What’s a GFCI? Etc.

I don’t posit to know everything, so I will take my time in answering questions and doing research where I can. I will try to separate my opinion from fact and would be happy to have others voice their opinions as I’m sure there are plenty of people on here smarter than myself… science should be humble and accept new evidence when presented with it. I know a lot of this information is widely available on the internet, but sometimes you don’t know what to ask, there is conflicting information, or answers are too technical. Although I’m an engineer I was raised by a bartender dad and waitress mom, so I like to think I’m a better communicator than the stereotypical engineer and I will try to make the answers as clear as possible, but also link to more detailed sources where applicable for those interested. I’ve known and worked with plenty of brilliant people that just couldn’t communicate effectively.

Sorry for the long post and if it falls into the void of the forum, so be it, but I’ll keep an eye out for posts now or in the future! I hope, if nothing else, to inspire thought.

Marciaf · Mar 10, 2021

Just picked mine up this weekend and yes the charging gives me a bit of anxiety. Lol
I sell real estate Soo I NEVER know what my days are like.
As I'm learning, if I buy a conversion adapter I feel I might have a little sense of security as the network builds out. Allowing me to charge at ALL charging stations even Tesla ( with exception of super charging). Is this correct?
Not really understand the difference between CHadMo and CCS.
Dumb it down for me lol
Marcia.

sockmeister · Mar 10, 2021

Can batteries on an EV maintain their maximum discharge rate / power output for extended lengths of time (like, at a track)? How much will power output decrease with state of charge?
(Fellow stickshift fan here! Bring back the Mustang Lithium!)

Polymon · Mar 10, 2021

MME will be my first EV.
I know Tesla owners who only charge to 80% unless they're going on a long trip. Should I treat my MME the same?
Is there danger in shortening battery life if I run them down below 5%? Or has Ford built in a big enough buffer for this not to matter?

CHeil402 · Mar 10, 2021

Marciaf said:
Just picked mine up this weekend and yes the charging gives me a bit of anxiety. Lol
I sell real estate Soo I NEVER know what my days are like.
As I'm learning, if I buy a conversion adapter I feel I might have a little sense of security as the network builds out. Allowing me to charge at ALL charging stations even Tesla ( with exception of super charging). Is this correct?
Not really understand the difference between CHadMo and CCS.
Dumb it down for me lol
Marcia.

Great question and you take the honor of first!

When any new technology starts out there isn't a "standard" way of doing it yet. Think of the charge port like a USB port, it's a way to share power and data between your car and a power source. Much like with Apple using Lightning connectors and others using USB (Micro-B, C, etc.), Tesla was somewhat of a pioneer in the EV space and decided to just come up with their own standard (the Tesla connector). Once other manufactures got involved, they decided to make an open standard realizing that having each car manufacturer with a different plug was ridiculous (like back in the day when each phone manufacturer need it's own charge plug). The main standard that evolved in the US was the SAE J1772 connector which came out around late 2009. Meanwhile, around the same time, Japan decided to use the CHAdeMO connector. So we started out with 3 main standards: Tesla, SAE J1772, and CHAdeMO. This is a "standards war" where CHAdeMO essesntially lost and will be phased out eventually, but is still around for legacy support for the time being. Only time will tell about the Tesla plug however. For example, in Europe, the EU forced Tesla to switch to CCS.

While this worked for a while with smaller battery cars and low charge rates, SAE J1772 was unfortunately limited in it's maximum power delivery capabilities as it used smaller diameter cables/pins. So it was extended to include the CCS plug (which is what's behind the little flap on the MME charge port).

When you charge your car you can do so at one of three general "levels" per the SAE definition...

Level 1 chargers use 120 volts alternating current (VAC) which is what you get from a standard US outlet. The downside to this is typical outlets are limited to 15 or 20 amps (the rate the power flows) and you need to de-rate them by 20% for safety. Power is defined as volts x current, or in this case 120 V * (15 A * 80%) = 1,440 W (or 1.44 kW). While this can certainly charge your car, it has a big battery (88 kWh for the extended MME), so it would take 88 kWh / 1.44 kW = 61.1 hours to charge in ideal conditions (longer as it's not a perfectly efficient process).

Level 2 chargers use 240 VAC which has standard US outlets that can support up to 50 A (a NEMA 14-50 outlet) that was previously used for things like electric ovens. Now you can deliver up to 240 V * (50 A * 80%) = 9.6 kW which can deliver over 600% the charge rate! For the MME, both L1 and L2 use the J1772 connector (or the top half of that plug not under the flap).

Both L1 and L2 chargers are AC but batteries are DC or direct current, so an onboard AC to DC converter (in the car) changes the power to charge the battery, but is limited in its capability as well. That's where Level 3 comes in where it takes that conversion off the vehicle and puts the equipment on the wayside to provide DC power at up to 350 kW, but that higher power needs the bigger CCS pins in the MME.

Sorry for all the background info there, but it's good to get on the same page. To answer your original question, the MME can charge from an L1 or L2 J1772 connector at your house or at a public charger only because that's all that physically fits in it. You can get an adpater to swtich from a Tesla plug to a J1772 plug for L1 and L2 destination chargers only (not for an L3 Tesla supercharger): http://www.umc-j1772.com/index.php?route=product/product&product_id=50 and if you travel all over the place it might be beneficial to get one since some hotels that were early EV caterers are more likely to have Tesla destination chargers as they were the first widely supported EV. Although, the Ford Mobile Charger can certainly come with you and plug into any outlet you can find (either 120 V or 240 V NEMA 14-50).

If you're at a public fast charger you're limited to CCS. You can't use a Tesla Supercharger, but I wouldn't worry about finding one that only supported CHAdeMO as it would likely be the other way around if they only had one.

Good luck and happy travels.

CHeil402 · Mar 10, 2021

sockmeister said:
Can batteries on an EV maintain their maximum discharge rate / power output for extended lengths of time (like, at a track)? How much will power output decrease with state of charge?
(Fellow stickshift fan here! Bring back the Mustang Lithium!)

I'll try to keep the answer here higher level as there are PhD level papers regarding batteries alone (and beyond my level of expertise). And to some extent, this is unique to the battery characteristics between battery suppliers... with that out of the way, in general:

Any battery can provide any power level output but is limited primarily by heat. Heat is what kills electronics, but especially batteries. In an ideal world, batteries provide power and cables deliver that power to a load which uses that power... but in the real world (much less exciting), batteries have an internal resistance (as do cables). The power consumed by this internal resistance is turned into heat in what's known as "Joule heating". Current is the rate of power delivery, so higher power demands more current (assuming the voltage is constant). Power = Current ^2 * Resistance, so the power consumed by the internal resistance increases with the square of current, so the stronger the draw you start increasing this loss exponentially.

So a battery doesn't care if it's delivering it's maximum rated power (or C-rate) for one second or one hour, but what it does care about is how much heat is generated as bad things happen when batteries get into thermal runaway (just ask Samsung on the Note 7). So as long as you have a properly designed thermal management system you can burn rubber to your heart's content! That's where manufacturers are unique and I can't give a super specific answer to the MME here... but that's why force cooled battery EV's can drive harder than naturally air cooled ones, like the old Nissan Leaf's.

To answer the second part of your question, a lithium battery is good at delivering close to full power until close to full discharge and I believe just as how Ford blocks off the full battery capacity, I would find it unlikely that the dashboard charge indicator of 0% is actually 0% of the pack capacity. So drive it low as long as you can get home at the end!

CHeil402 · Mar 10, 2021

Polymon said:
MME will be my first EV.
I know Tesla owners who only charge to 80% unless they're going on a long trip. Should I treat my MME the same?
Is there danger in shortening battery life if I run them down below 5%? Or has Ford built in a big enough buffer for this not to matter?

There has been a lot of discussion on this topic and there are differing opinions, so I will try to stick to general facts here as best I can.

Lithium batteries don't like full discharges and don't like full charges for extended periods of time. The lithium ions that do the work have to move between the positive terminal (anode) and the negative terminal (cathode) to provide power. When in either fully depleted or fully charged, the anode or cathode is under more pressure which can cause the formation of dendrites (like little metal stalactites that puncture the internals of the battery).

The MME extended battery capacity is 98.7 kWh, but is software capped by Ford at 88 kWh (or around 89% of total pack capacity). This is a rather large reserve as Ford (at least for now) is "playing it safe" with battery degradation. Tesla on the other hand is taking a "riskier" approach and exposing more of the total pack capacity to the end user and trusting that they won't charge more than they need to on a regular basis (as evidenced by the car UI listing the max charge separately for a trip vs day-to-day and encouraging the latter). The Model Y for example has a 75 kWh battery capacity and exposes 72.5 kWh (or around 97% of total pack capacity).

Lithium batteries prefer to stay between 20 - 80% of their capacity to extend their life. Ford recommends setting a maximum state of charge (SOC) of 90% for daily use... and as previously explained, 90% of the user meter (88 kWh * 90% = 79.2 kWh) is actually 80% of total battery capacity (79.2 kWh / 98.7 kWh = 80%).

Because Tesla exposes more of the total pack capacity than Ford, the end user has to set the preferred charge range lower than the MME to get the equivalent pack SOC.

As far as the low end, I don't know what Ford or Tesla use as the reserve, but I find it unlikely that 0% on the range-o-meter is actually 0 kWh in the pack for the same reasons.

Long story short, for daily trips, the battery in the MME will prefer to stay charged daily to 90% compared to letting it fully drain before plugging it in.

breeves002 · Mar 10, 2021

CHeil402 said:
To answer the second part of your question, a lithium battery is good at delivering close to full power until close to full discharge and I believe just as how Ford blocks off the full battery capacity, I would find it unlikely that the dashboard charge indicator of 0% is actually 0% of the pack capacity. So drive it low as long as you can get home at the end!

As an EE myself (just doing microelectronics and board design), I wanted to add my two cents to this piece of your answer. I have a ton of experience with lithium ion and metal batteries in my field of work though on a way smaller scale than car battery packs. The largest pack we've ever used is 295Wh. Smallest is less than 1Wh. Wh, not kWh!

Voltage drop.

For starters, battery cells have a minimum voltage. When you draw current from a battery the voltage drops. This is due to resistance and is the same thing that happens on standard electrical wires. The higher the current the higher the voltage drop. Therefore, when you "floor" your MME an incredible amount of current will be flowing from the battery to the motor. The larger the battery the more "spread out" the current will be as there are more battery cells so you'll have less of a voltage drop. The lower the SoC of the battery pack, the lower the overall pack voltage. All but some extremely expensive lithium metal batteries have voltages that adjust based on SoC. At a lower SoC you're at a lower voltage and therefore when you want 1000A of current from the battery, it may be difficult for it to deliver that without hitting a safe minimum voltage of the HVB pack.

Short answer: At lower states of charge you may be current limited due to voltage drop of the HVB. So you may notice a loss in power.

RobbH · Mar 10, 2021

For the Tesla Tap and other adapters; what is the amp rating we should buy? If I understand it correctly we are limited by the onboard charger's rating but I can't seem to find that...

Thnaks!

JamieGeek · Mar 10, 2021

RobbH said:
For the Tesla Tap and other adapters; what is the amp rating we should buy? If I understand it correctly we are limited by the onboard charger's rating but I can't seem to find that...

Thnaks!

Onboard charger is limited to 10.5kW. Its on my window sticker:

Ford Mustang Mach-E Ask an Electrical Engineer 1615397361576

RobbH · Mar 10, 2021

JamieGeek said:
Onboard charger is limited to 10.5kW. Its on my window sticker:

That indirectly helps so if I understand TeslaTap's page correctly:

40 amp Tap - will do 10kw max for 3 hours and 8kw continuous. Not the full capacity of the onboard charger but close.
50 amp Tap - will do 12.5 kw continuous
80amp Tap - will do 20kw

So to go back to my original post which Tap should we get 40 or 50? Is there an issue with using the 50amp tap or will the onboard changer only draw what it can handle?

CHeil402 · Mar 10, 2021

RobbH said:
That indirectly helps so if I understand TeslaTap's page correctly:

40 amp Tap - will do 10kw max for 3 hours and 8kw continuous. Not the full capacity of the onboard charger but close.
50 amp Tap - will do 12.5 kw continuous
80amp Tap - will do 20kw

So to go back to my original post which Tap should we get 40 or 50? Is there an issue with using the 50amp tap or will the onboard changer only draw what it can handle?

There have been several threads discussing the Tesla Tap and it's a product that I'm not personally familiar with.

https://www.macheforum.com/site/threads/jdapter-and-teslatap-charging-adapters.2136/
https://www.macheforum.com/site/threads/tesla-tap-mini.2744/

That being said, first I think it's important to understand what an EVSE is and isn't. I've posted about this before myself, but to summarize, the EVSE's only job is to safely provide power to your car. It doesn't do any AC/DC converting, etc. The EVSE has a maximum current rating that it can deliver and it will advertise this value to the connected car. The car also has a maximum current that it can accept. The car is the one in control of charging and will essentially ask how much power it can draw from the EVSE and will ask for the maximum between what it can accept and what the EVSE can provide.

As far as I know, the Tesla Tap is a relatively passive device (I could be wrong as I'm not familiar with it). Assuming it is, all it does is act as a physical adapter and EVSE protocol converter between a Tesla wall charger and the onboard J1772 logic controller of the MME, the key takeaway from that is that the EVSE has a maximum power rating based on the conductor sizing and it cannot tell the car (who is in control of the charging) what it's rated for.

If you connect it to an EVSE that's rated for 40 A and your car can accept 50 A, then you'll be fine with a 40 A rated Tesla Tap... however, if you connected it to a 50 A EVSE and the car can accept 50 A, that's bad as you'll over tax the Tesla Tap.

So assuming you're not going to know what EVSE rating you're connecting to, you should size it for the car's maximum current draw. Based on the window sticker provided by @JamieGeek for a 10.5 kW onboard charger, the most it will draw will be (10.5 kW / 240 V = 43.75 A). Therefore, if I were to buy one for any scenario (and because the MME to my knowledge doesn't allow you to limit the charge current through Sync 4A) I would go with the 50 A or larger.

If you know for a fact that you're connecting it to an EVSE that is limited to 40 A, then you'll be fine... but if you want a tool for unknown situations, I would get 50 A or greater.

PS- Never connect the Tesla Tap to a Tesla Supercharger! Only to a destination charger that works at L1 or L2.

UPDATE: To clarify a little bit, there is no harm in oversizing the Tesla Tap (other than cost) as the value (e.g.: 40 A, 50 A, 80 A, etc.) is just what the maximum current the conductors in the adapter can handle.

FPLiptak · Mar 10, 2021

JamieGeek said:
Onboard charger is limited to 10.5kW. Its on my window sticker:

Strange,

Mine looks like this:

Ford Mustang Mach-E Ask an Electrical Engineer 1615400157843

No mention of 10.5 KW OnBoard Charger or Up to 150KW DC Chrg Capabl

???

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CHeil402

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