What Wall Charger to Buy???

[ajdelange]

Well of course I'd like to think I have the scientist's perspective; my colleagues always said I did even though I was supposed to be an engineer. But give me an opportunity to play games with the English language and I'll do it!

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[HaulingAss]

Furthermore the I did not mention "charging overhead". I mentioned "phantom drain" which is not charging overhead at all but in fact keep-alive overhead for the vehicle. Phantom drain is an ongoing thing. It happens when it happens (for example if you turn on the radio while sitting parked (i.e. vehicle in "P") or if TeslaFi asks for vehicle state in the middle of the night.

I consider the phantom drain that occurs while charging to be charging overhead when the only thing preventing the car from going to sleep is that it is being charged. This is not a difficult concept to grasp. And 120 volt charging prevents the car from going to sleep for many more hours than faster charging would. That means it has a lot more charging overhead. The winter I used 120 volt charging my car almost *never* went to sleep because it was either charging or I was using it.

 

[HaulingAss]

I'm afraid your reasoning is, once again, a bit off base here. When charged at a very slow rate the current going to the battery is small. Heat dissipated in the battery is proportional to the battery internal impedance and to the square of the charging current. Thus you will never have lower charging loss than when using the 120V adapter. And the loss has nothing to do with temperature difference. If charging current is I charging loss is I^2R where R is the real part of the battery impedance. Grossly simplifying if the thermal impedance of the battery to ambient remains constant over some range the teperature rise across the battery will remain about the same.

It appears you are unaware that Tesla uses active heat management of the battery when charging in cooler weather. Therefore the loss in efficiency when charging at 120 volts is not due to the charging itself, but the active thermal management of the battery. When computing which method of charging has higher losses it is necessary to take *all* losses associated with charging at that rate into effect. Since 120 volt charging is so slow, and builds so little heat naturally, much more supplemental heat is required.

Neither does a parked car which is not charging. The increase in phantom drain from a charging car is the software overhead required to supervise the charge and communicate the results to the app and monitoring programs, if any. Common sense says this is a very small additional burden,.

Wrong. A parked car that is not charging *does* go to sleep when it's not being polled by an app. But it will never go to sleep when the battery is actively charging. That wastes a lot of electricity right there (without even considering active thermal management).

 

[ajdelange]

I consider the phantom drain that occurs while charging to be charging overhead when the only thing preventing the car from going to sleep is that it is being charged.

So if I am in the car charging from a 120V outlet and turn on the radio and the heater those loads become part of charging overhead?

This is not a difficult concept to grasp.

I'm having a little trouble with it but let's go with it for now. You would further assert that this higher "charging overhead" would result in a higher electric bill relative to what would happen if I turned on the radio and heater when connected to a 48A HPWC?

And 120 volt charging prevents the car from going to sleep for many more hours than faster charging would. That means it has a lot more charging overhead.

The flaw I see in this logic is that you are assigning loads which have nothing to do with charging (radio, heater) even though they have nothing to do with charging. The additional load that really has to do with charging is the extra computing load that collecting the volts and amps data from the charger imposes. Your electric bill will go up by the cost of that minimal extra consumption - not by the cost of other phantom loads which just happened to be on when you were charging.

Even if you could somehow shift my entire phantom drain onto the charger's budget that would not result in an appreciably higher cost to charge.

Is this your choice for the ONE "error" of mine we are going to discuss as adults?

 

[ajdelange]

When computing which method of charging has higher losses it is necessary to take *all* losses associated with charging at that rate into effect. Since 120 volt charging is so slow, and builds so little heat naturally, much more supplemental heat is required.

The amount of energy required to raise the temperature of a mass from T1 -> T2 is the difference between those temperatures (in K) multiplied by the thermal mass of the object whether it be from a high power or low power source. Whichever it is the same amount is required of the charger as either it comes from the charger or from the battery which battery must be replaced by the charger to charge to the same level (fast charging). So yes, it appears that it takes more energy to charge to a given level if the car is cold but no, it does not matter (appreciably) whether you are charging from a fast or slow source. There is an underlying assumption here the questioning of which could allow a rebuttal to this point. Do you see it?

Wrong.

Well actually the statement is correct but rather than getting into when a car sleeps or doesn't I thought I'd look at the UMC specs to see if the 120 volt mode requires "a lot of electricity" relative to the 32 Amp mode to add a mile of charge. Based on this at 120V you would require 25% more electricity. Is that "a lot"?

 

[Crissa]

It’s an easy recommendation. Nobody is going to buy one and regret waking up with 80% SOC every morning.

Sure. I would agree to that. It also is a great addition to a home.

But there are two others in this thread saying it's a must for most.

And that I object to.

-Crissa

 

[ldjessee]

The biggest cost savings for me was insulating the roof of my garage and when I replaced the garage door, I replaced it with an insulated and sealing one.

Water and soda stored in the garage would freeze during the winter before, now it does not.

Now, the garage door R rating is still lower than the walls and the roof, but still better than it was.
I have a Leaf, so temperature when charging is always on my mind.

If you are building, I would add either a sub panel or a dedicated circuit for the loads in the garage.
But, I have survived going on 5 years (August this year will be 5) with nothing better than 120v EVSE at home.

So, I think many people on this thread are right and many people are wrong, but mostly they are wrong when saying other people are wrong.

A person's average use and a nation of people's average use have a good chance of not being the same.

My commute (was 7 miles one way) has gone almost completely away, even though my new job is technically further away. Working remote has changed lots of driving patterns. I expect as many jobs (not all, not most, just many) remain remote (because it costs the company less money and they can be done remote), I think we will see the average commute distance actually come down in the next year or two. This is complete speculation on my part, if it was not obvious.

I have a plan that when I get the Cybertruck and if my mileage changes dramatically (ie, more than 20 miles a week to get groceries, etc), then I will repurpose a now unused circuit breaker in my panel to have an electrician pull a plug to the garage and plugin a 240v EVSE. Why not just hardware it in? Same reason my stove, frig, washer, dryer, and microwave are not wired in.

 

[Crissa]

Why not just hardware it in? Same reason my stove, frig, washer, dryer, and microwave are not wired in.

Technically an EVSE is just a fancy outlet, tho.

-Crissa

 

[ajdelange]

There is so much wrong here I don't have the time to fix it now. Let it be sufficient to let newbies know that all of the above information should not be relied upon.

I know your time is valuable but we don't want all this wrong information staying out there so again I ask you to pick just ONE thing that is incorrect and see if we can't correct it. We'll work them off one at a time.

 

[ajdelange]

I think it is less efficient, I’m just not sold on the magnitude here.

Would love to see some more solid numbers on this with someone measuring the actual wattage consumed.

I would hardly call it "solid" but the specifications for the UMC indicate the number of miles added per hour of charging and the current drawn from each of the UMC configurations. These numbers suggest that the 120V configuration would require 25% more power.

It's relatively easy to measure the power drawn by the UMC. What is very difficult to get at is the power delivered to the battery. TeslaFi claims to do that, however. I confess that I have never used my UMC before so take this with a grain of salt. In a charge Wednesday at an average of 24.8A using HPWC TeslaFi tells me it took 1.08 kWh to load each kWh (92.5% eff). In a charge yesterday afternoon at an average of 12A from the UMC at 120V it tells me I used 1.42 kW for each kWh loaded (70.4% eff.). That's a difference of 0.34 kWh/kWh. If I charge 30 kWh/day (enough for 100 mi) that would mean an extra 10.2 kWh (costing me an extra $1.30/da were I buying the electricity from the local utility at the average 13¢/kWh). Is that an inordinately large difference? Up to the reader to decide.

One thing I will say is that the HPWC is orders of magnitude easier to use than fiddling with the UMC. You just grab the nozzle whenever you come home. OTOH my neighbor uses his UMC which he just dangles over the fence and is, I suppose, equally accessible.

 

[RMK!]

Thank you all for reminding me why I hate having "discussions" with engineers (real or imagined) ...

 

[Ogre]

Thank you all for reminding me why I hate having "discussions" with engineers (real or imagined) ...

I have a lot of friends who are engineers.

And a few acquaintances who are blowhards.

Conversation with the engineers is never a problem.

 

[SwampNut]

I have a lot of friends who are engineers.

And a few acquaintances who are blowhards.

Conversation with the engineers is never a problem.

+1

I can have an engineer friend here for a weekend and never run out of chatter and things to do around the shop. I made the mistake of inviting an acquaintance who wrote walls of text like we've seen here from the "I self identify as an engineer" and it was terrible. I've stopped reading any of it.

 

[HaulingAss]

I have a lot of friends who are engineers.

And a few acquaintances who are blowhards.

Conversation with the engineers is never a problem.

I can see that being true. But you have a relatively small and far from random sample size.

 

[HaulingAss]

Sure. I would agree to that. It also is a great addition to a home.

But there are two others in this thread saying it's a must for most.

And that I object to.

-Crissa

Who are the two people in this thread claiming a Wall Connector is a "must" for most people?

I certainly think most people would best served over the long-term if they have better than the bare minimum 120 volts and they should shoot for a minimum of 240 volts and 30 amps but if that's just not realistic for the situation (whether it be excessive time or money due to site specifics or some other valid reason) then certainly do what it takes to get by with less.

The practical bottom line is no one wants to spend the additional time and money to visit a Supercharger simply because their home charging solution didn't have enough power to keep up with heavier than average consumption for a short spell. It reducess the functionality and convenience and capabilities of a car or truck probably costing between $40K and $80K to not have enough power to keep up with two or three days of consumption that might be heavier than the normal or average usage for that person.

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