Question about % and kWh for charging

[minjaep]

I recently used a DC charger using the free EA balance. I charged 83% in total from 17% to 100%, and FordPass told me I have used 80kWh of the balance. I turned off the vehicle while charging.

Quick math tells me (given the usable battery of mine is 91kWh) 83% of 91kWh is 75.5kWh. Where did 4.5kWh go? Does it mean that this amount was wasted while charging, but EA still charge me about this portion? It is indeed a lot, which is about 5%. Or, if 83% was actually 80kWh, does it mean the percentage does not increase linearly with respect to the actual kWh?

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[alexgorod]

Did the charging cable get warm? That's your lost KWh...

 

[SpaceEVDriver]

Also, using DC fast charging to charge from 90% to 100% is where most of your heat waste happened. Stop at ~85% and you'll get more of what you pay for.

 

[minjaep]

Did the charging cable get warm? That's your lost KWh...

I didn't know that I should pay for the electricity to heat the cable lol... Also, if 4.5kWh was lost while charging 75.5kWh, it means the loss is 6%. Is it normal for fast charging? I heard some wireless charging has an efficiency of 95%.

 

[minjaep]

Also, using DC fast charging to charge from 90% to 100% is where most of your heat waste happened. Stop at ~85% and you'll get more of what you pay for.

After reading https://www.caranddriver.com/features/a36062942/evs-explained-charging-losses/ I found above 90% is normal for DC charging. Actually its efficiency is much better than AC charging which is just 65-85%. Interesting fact.

I might need to test later, but if this is correct, charging up to 80% might not give 99% of efficiency, say.

 

[Cm12]

After reading https://www.caranddriver.com/features/a36062942/evs-explained-charging-losses/ I found above 90% is normal for DC charging. Actually its efficiency is much better than AC charging which is just 65-85%. Interesting fact.

I might need to test later, but if this is correct, charging up to 80% might not give 99% of efficiency, say.

99% efficiency would be pretty stellar but I don’t see a scenario where that happens. The more your battery is charged, the harder it is to continue to charge it. Simply put, the chemical process of charging a battery at 10% is more efficient than one at 50%. And at 50%, it’s more efficient than 80%. More efficiency means less loss of energy. The science underlying all this is far too long to explain in a forum post, but there are some YouTube vids that do a good job of illustrating how EV charging works. Most of us never really think about loss until we have a very large battery (such as the MME or a backup generator), so it’s kind of a shock to the system at first.

 

[Logal727]

Wait till you hear about how much gas is wasted not moving an ICE vehicle

 

[JohnnyForensic]

After reading https://www.caranddriver.com/features/a36062942/evs-explained-charging-losses/ I found above 90% is normal for DC charging. Actually its efficiency is much better than AC charging which is just 65-85%. Interesting fact.

I might need to test later, but if this is correct, charging up to 80% might not give 99% of efficiency, say.

Regardless, in the end, there is very little you can do to mitigate this. As mentioned before, you only want to charge to 80% on DCFC chargers. That should give you enough juice to make it to your destination or to the next charger on your route anyway. Above that, the time to charge increases dramatically for the 80-100% range (though it’s better if you have the charging curve update which I don’t, but it’s still not going to help tremendously).

Losing 5% is going to be pretty normal for this kind of thing. Even so, you’re still paying a lot less than you would for gas, so…?‍

 

[minjaep]

99% efficiency would be pretty stellar but I don’t see a scenario where that happens. The more your battery is charged, the harder it is to continue to charge it. Simply put, the chemical process of charging a battery at 10% is more efficient than one at 50%. And at 50%, it’s more efficient than 80%. More efficiency means less loss of energy. The science underlying all this is far too long to explain in a forum post, but there are some YouTube vids that do a good job of illustrating how EV charging works. Most of us never really think about loss until we have a very large battery (such as the MME or a backup generator), so it’s kind of a shock to the system at first.

That is different science than I learned. I don’t think it is harder to charge from 80-90 vs 70-80 for chemical reason. The charging efficiency should be almost flat until very last step like above 95 and Mach-E already have a lot of buffer. So my guess is that I won’t lose much by charging to 100. The efficiency is just low because I think Mach-E uses a huge current which produces more heat.

 

[hawkeye3point1]

Where did 4.5kWh go?

Most of it went to raising the battery temp.. Every time I use a L3 charger, the car runs the coolant heater to get the battery to 80-90 deg., it is necessary to max out charging speed. That heater draws 5 kw.

 

[Cm12]

That is different science than I learned. I don’t think it is harder to charge from 80-90 vs 70-80 for chemical reason. The charging efficiency should be almost flat until very last step like above 95 and Mach-E already have a lot of buffer. So my guess is that I won’t lose much by charging to 100. The efficiency is just low because I think Mach-E uses a huge current which produces more heat.

Yes, heat is an issue, but you have to be careful to not conflate things here. If your assumption were true, then reducing the amperage (less energy, aka heat) would result in 100% efficiency.

 

[minjaep]

Yes, heat is an issue, but you have to be careful to not conflate things here. If your assumption were true, then reducing the amperage (less energy, aka heat) would result in 100% efficiency.

I don't think your comment is relevant as I asked what is the most dominant factor of energy loss in the usual DC charging. Of course, in a low-current setting, there should be other factors dominating the effect of efficiency; that I have zero interest in.

 

[Cm12]

I don't think your comment is relevant as I asked what is the most dominant factor of energy loss in the usual DC charging. Of course, in a low-current setting, there should be other factors dominating the effect of efficiency; that I have zero interest in.

My apologies for wasting your time. You seem to have all this figured out without anyone’s help, so I’m not sure why you even asked the question on an internet forum.

 

[1969Camaro]

99% efficiency would be pretty stellar but I don’t see a scenario where that happens. The more your battery is charged, the harder it is to continue to charge it. Simply put, the chemical process of charging a battery at 10% is more efficient than one at 50%. And at 50%, it’s more efficient than 80%. More efficiency means less loss of energy. The science underlying all this is far too long to explain in a forum post, but there are some YouTube vids that do a good job of illustrating how EV charging works. Most of us never really think about loss until we have a very large battery (such as the MME or a backup generator), so it’s kind of a shock to the system at first.

Nice pun "Shock to the system"

 

[minjaep]

My apologies for wasting your time. You seem to have all this figured out without anyone’s help, so I’m not sure why you even asked the question on an internet forum.

I asked the question mainly because I was not sure whether I pay for the electricity that the charger uses or that my car has received. And This was answered by the first comment that I pay for the energy loss.

The following question was just where this energy loss came from. And I agreed that heat is the main factor after researching. Out of the topic, someone mentioned the level of the battery is another main factor. That I disagree.

Hmm... I didn't say your comment wasted my time. Appreciate any input.

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