broosth
Posts: 20
Joined: Sun Aug 19, 2018 4:32 am

Cost of charging?

Mon Oct 01, 2018 10:30 pm

One of my friends has a Bolt; another a plug-in hybrid Clarity. Both have been told that a lever 2 charger costs less to use than a level 1 charger. My engineering intuition tells me that a kilowatt-hour delivered to the car costs the same at 120 v or 240 v. Am I missing something or are my friends badly informed? This issue is separate from that of lower power costs at certain times of day.

WetEV
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Location: Near Seattle

Re: Cost of charging?

Mon Oct 01, 2018 10:43 pm

broosth wrote:One of my friends has a Bolt; another a plug-in hybrid Clarity. Both have been told that a lever 2 charger costs less to use than a level 1 charger. My engineering intuition tells me that a kilowatt-hour delivered to the car costs the same at 120 v or 240 v. Am I missing something or are my friends badly informed? This issue is separate from that of lower power costs at certain times of day.


Efficiency is higher at higher charge rates.
#49 on the LEAF 100 mile club.
Most everything around here is wet during the rainy season. And the rainy season is long.
2012 Leaf SL Red
2014 Leaf SL Red
Can't sit in a Bolt seat, hoping for better soon.
Or perhaps a Buick version? Buick Electra 225???

SparkE
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Location: SF Bay Area

Re: Cost of charging?

Mon Oct 01, 2018 10:44 pm

A 240V EVSE (the "charger", which converts AC to DC current, is in the car) is generally slightly more efficient than a 120V EVSE.

Suppose it is 10% more efficient to use 240V (which is over-stating it). In order to make up the approx $500 for the EVSE (i.e., break even), a person would have to suck up $5000 worth of electrons at 120V. At $0.20 a kWh (I'm just making that up) that is 25000 kWh (enough to drive over 100,000 miles in a Bolt). At $0.10/kWh : 50,000 kWh.

Don't sweat it.

broosth
Posts: 20
Joined: Sun Aug 19, 2018 4:32 am

Re: Cost of charging?

Mon Oct 01, 2018 11:40 pm

Thanks. I am not sure why it would be more efficient, but I have not seen any technical discussion of the process. I see lots of explanations of charging rates, but nothing about the AC/DC converter process nor the issues of cell charge balance. As a person with an EE degree (albeit 48 years out of date) i'd like to see more detail.

BarfOMatic
Posts: 59
Joined: Sat Feb 25, 2017 8:03 am
Location: Santa Clara, CA

Re: Cost of charging?

Mon Oct 01, 2018 11:48 pm

start reading through the last few years of posts - the topic(s) has/have been covered before.

Edit: Oh, and since this is NOT AT ALL specific to the Bolt, can this thread be moved out of the Bolt-specific part of the forum? Pretty please?

WetEV
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Location: Near Seattle

Re: Cost of charging?

Tue Oct 02, 2018 1:13 am

broosth wrote:Thanks. I am not sure why it would be more efficient, but I have not seen any technical discussion of the process.


This isn't a graph of the Bolt's charger, which is just a high power DC to DC converter with an adjustable output voltage and current limits, but is of a more common part with much lower power output.

Image

Do you really want to dive into DC to DC converter design? I've designed some low power ones, but not a 7kW one...
#49 on the LEAF 100 mile club.
Most everything around here is wet during the rainy season. And the rainy season is long.
2012 Leaf SL Red
2014 Leaf SL Red
Can't sit in a Bolt seat, hoping for better soon.
Or perhaps a Buick version? Buick Electra 225???

SparkE
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Joined: Sun Sep 11, 2016 5:53 am
Location: SF Bay Area

Re: Cost of charging?

Tue Oct 02, 2018 3:37 am

Moving to "off-topic" area ...

And WetEV - did you mean AC-to-DC converter?

SparkE
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Location: SF Bay Area

Re: Cost of charging?

Tue Oct 02, 2018 3:49 am

An article :

Understanding AC/DC power supply efficiency : https://www.xppower.com/Portals/0/pdfs/ ... C_0810.pdf

WetEV
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Posts: 386
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Location: Near Seattle

Re: Cost of charging?

Tue Oct 02, 2018 4:52 am

SparkE wrote:And WetEV - did you mean AC-to-DC converter?


Done in two steps for every system I've looked at.

Rectified and filtered to DC with some ripple, then put into a DC to DC converter.

Amusing. A Youtube teardown of a power supply, including a "cat move a little bit. Go go go."

https://www.youtube.com/watch?v=B19rB_FR5Mk
#49 on the LEAF 100 mile club.
Most everything around here is wet during the rainy season. And the rainy season is long.
2012 Leaf SL Red
2014 Leaf SL Red
Can't sit in a Bolt seat, hoping for better soon.
Or perhaps a Buick version? Buick Electra 225???

theothertom
Posts: 38
Joined: Wed Sep 19, 2018 4:13 pm

Re: Cost of charging?

Tue Oct 02, 2018 2:21 pm

broosth wrote:One of my friends has a Bolt; another a plug-in hybrid Clarity. Both have been told that a lever 2 charger costs less to use than a level 1 charger. My engineering intuition tells me that a kilowatt-hour delivered to the car costs the same at 120 v or 240 v. Am I missing something or are my friends badly informed? This issue is separate from that of lower power costs at certain times of day.

Heat looses due to resistance tend to be higher with lower voltages. So 240V is more efficient than 120.

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