Plug to Motor Energy Losses and Efficiency

[Scottydog]

I did some searching to find if this was covered, but only found small snippets here and there.

It was something that I always thought was insignificant until I started testing out my own build and was pretty amazed at the difference between the energy used by the scooter via the Cycle Analyst and the energy used to charge the batteries back up to full charge via a Kill-a-Watt plug mounted device.

When I tested my scooter I managed to use 2.265 kWh on the CA, but it took 2.99 kWh to charge back up. Basically 24% of the energy seems to have been lost by the time the motor sees it. I found this link this quote matches exactly what I found. "For me, based on my Cycle Analyst and Kill-a-watt, 1 Wh delivered to the motor requires about 1.3-1.4 Wh pulled out of the wall"

https://endless-sphere.com/forums/viewtopic.php?f=2&t=63840


It made me think of questions relating to this.

What are the variables on this? Charger efficiency, controller efficiency, temperature, battery type, state of charge, charging rate, discharge rate, copper losses?

I am using a Zivan charger, GBS cells and Kelly KEB controller.


1 Charging and discharging rate. If I charge at say 5 amps vs 12 amps is it likely that the higher amps can create more losses than 5 amps? Conversely if I discharge at 2C vs 1C on the low C rated GBS cells does this incur losses? Basically is keeping in with the correct C rating of a cell important for efficiency? (I gather heat production in unsuitable cell is an indication of poor energy conversion.... to a point?)

2 Chemistry - The GBS cells are apparently high internal resistance cells. Does this resistance create more losses than low IR cells? Also as the IR increases through age does this lower efficiency?

3 Temperature - Does the lower temp increase IR and thus reduce efficiency? (this is my understanding that it does?)

4 Charging range - Would charging up to say 70% - 80% be more efficient than, the final 20%? Does charging the final 20% incur an efficiency penalty?


..... I am sure there are many other points, but these were some that I was pondering on.

In this link I also saw a point about losses from plug to motor.

http://www.greencarreports.com/news/1090685_life-with-tesla-model-s-one-year-and-15000-miles-later

 

[major]

I did some searching to find if this was covered, but only found small snippets here and there.

It was something that I always thought was insignificant until I started testing out my own build and was pretty amazed at the difference between the energy used by the scooter via the Cycle Analyst and the energy used to charge the batteries back up to full charge via a Kill-a-Watt plug mounted device.

When I tested my scooter I managed to use 2.265 kWh on the CA, but it took 2.99 kWh to charge back up. Basically 24% of the energy seems to have been lost by the time the motor sees it. I found this link this quote matches exactly what I found. "For me, based on my Cycle Analyst and Kill-a-watt, 1 Wh delivered to the motor requires about 1.3-1.4 Wh pulled out of the wall"

https://endless-sphere.com/forums/viewtopic.php?f=2&t=63840


It made me think of questions relating to this.

What are the variables on this? Charger efficiency, controller efficiency, temperature, battery type, state of charge, charging rate, discharge rate, copper losses?

I am using a Zivan charger, GBS cells and Kelly KEB controller.


1 Charging and discharging rate. If I charge at say 5 amps vs 12 amps is it likely that the higher amps can create more losses than 5 amps? Conversely if I discharge at 2C vs 1C on the low C rated GBS cells does this incur losses? Basically is keeping in with the correct C rating of a cell important for efficiency? (I gather heat production in unsuitable cell is an indication of poor energy conversion.... to a point?)

2 Chemistry - The GBS cells are apparently high internal resistance cells. Does this resistance create more losses than low IR cells? Also as the IR increases through age does this lower efficiency?

3 Temperature - Does the lower temp increase IR and thus reduce efficiency? (this is my understanding that it does?)

4 Charging range - Would charging up to say 70% - 80% be more efficient than, the final 20%? Does charging the final 20% incur an efficiency penalty?


..... I am sure there are many other points, but these were some that I was pondering on.

In this link I also saw a point about losses from plug to motor.

http://www.greencarreports.com/news/1090685_life-with-tesla-model-s-one-year-and-15000-miles-later

Hi Scotty,

My opinions:

1) Yes, higher currents (higher charge and discharge rates) cause more I²R losses, so less efficient.

2) Yes, higher cell internal resistance means higher losses. Again, I²R. Both charge and discharge. So lower efficiency.

3) Yes, colder batteries have higher R and therefore higher I²R, so lower efficiency.

4) Lithium has nearly (very, very nearly) 100% coulombic efficiency. So I don't think charge at the top 20% is less efficient than from 60-80%. However, if your system balances at or near the full SOC, then some energy may be dissipated in the BMS.

I also recommend instrument calibration before spending a lot of time and/or money chasing down a percent or two. I have and like the Kill-a-watt meter, but for $25, I question absolute accuracy. For comparisons, it's great. And the CA which I used was pretty high quality, but with the external shunt, a calibration check there won't hurt.

major

 

[Scottydog]

Hi Scotty,

My opinions:

1) Yes, higher currents (higher charge and discharge rates) cause more I²R losses, so less efficient.

2) Yes, higher cell internal resistance means higher losses. Again, I²R. Both charge and discharge. So lower efficiency.

3) Yes, colder batteries have higher R and therefore higher I²R, so lower efficiency.

4) Lithium has nearly (very, very nearly) 100% coulombic efficiency. So I don't think charge at the top 20% is less efficient than from 60-80%. However, if your system balances at or near the full SOC, then some energy may be dissipated in the BMS.

I also recommend instrument calibration before spending a lot of time and/or money chasing down a percent or two. I have and like the Kill-a-watt meter, but for $25, I question absolute accuracy. For comparisons, it's great. And the CA which I used was pretty high quality, but with the external shunt, a calibration check there won't hurt.

major

Major cheers for your thoughts, I feel quite satisfied by them. I like the way you used I²R which reminds me how I should think about it! I find it interesting as it's not something that I see any conversation about regarding choosing cells and operating for greatest efficiency. Most cell conversations are about power or capacity.

For my setup I'm not worried so much, but will be interesting to keep a log and then compare to when I get new cells. (Thinking of Enerdel modules)

At the moment I have the Zivan set below the 3.55V that triggers the BMS boards. I'll leave it that way until I get a Battery Satiator which I want to mount onboard. I'll use it to do occasional full charges, but most of the time leave it at 80%ish.

The GBS cells I have were second hand (3 year old) but free! The total capacity is rated at 3.64 kWh, so the 2.265 kWh I am seeing is much lower. Could be my slight under charging and early low voltage cutoff, but probably mostly the age and sitting under a bike cover baking in the summer sun! (plus two hurricane knock overs back to back in a week!)

I got 37km / 23 miles so is fine for now, but would be awesome to get 40 - 45 miles with new Enerdel or equivalent!

 

[Punx0r]

IIRC you should be seeing better than 90% charge efficiency (i.e. 1 kWh taken from pack, <1.1 kWh to recharge it) unless you're charging at too high a rate for your battery and making some serious heat.

I think Major has a good point about potential inaccuracy of your measuring devices.

 

[spinningmagnets]

The battery and motor are both using the same volts, the charger must convert 120-ish AC into the DC voltage of your pack. It is "possible" to have a charger that uses very high efficiency components, but...because house electricity is so relatively cheap, there is no pressure on vendors to upgrade their chargers, and they are sold by lowest price.

 

[dogman dan]

IMO, what you are measuring, is how much you heat the charger, and how much you heat the cells themselves.

Also included would be any heating of the wires and plugs, but I doubt that those are much worth worrying about at 100-250w flowing through those wires. But the charger gets so hot it needs a fan to cool it, the cells will warm as well, but not all that much at the low rate you charge at.

I was losing about 25% when doing an overnight, balancing charge. Much of that loss from just having the charger plugged in, green light. Much better number if I charged, then unplugged immediately.

 

[Scottydog]

Dogman

Makes sense the loss in heat. It's interesting though as the charger never gets warm by much.

I did get the numbers from comparing my 150cc 4T scooter to the electric bike. They are similar in weight and I babied the gas scooter to match the driving to the same as the less powerful electric. This is what I got:



Electric scoot is $3.60 per 100km ($0.45 per kWh)
Gas scoot is $6.07 per 100km ($1.961 per l)

Electric scoot 7.995 kWh per 100km
Gas scoot 3.093 l per 100km (91mpg)

I used 0.773kg or CO2 per kWh for our diesel powered energy grid on island
2.4kg CO2 per l of gasoline

643kg for electric per year CO2
772kg for gas per year CO2

Assuming 200km per week (looks to be my norm)

Electric scoot per year $374
Gas Scoot per year $631


In 5 years $1283 saved, but not even half the cost of the battery. I played with improved charging efficiency, not much in it. Maybe regen would help also, something I don't have with my current Kelly KEB.

 

[dogman dan]

Pretty hard to make any gains over the cheapest to operate motor vehicle on earth, the sub 250cc motorcycle or scooter.

I'd be very happy if people just swapped their 4 door one ton pickups for scooters. But on the bright side, your choices are a huge improvement over even very efficient cars with just one person inside.

 

[Scottydog]

Dogman so right about the swapping thing, especially where I live being super scooter friendly! So I get that many guy prefer their wives to drive a car, though for me girls that ride scooters move up a notch for me! But so many of my guy buddies drive a car daily to work when they could ride a bike or even own a bike and still drive the car!

When I go to work it's nuts being stuck in traffic seeing 10 cars in a row with single person occupancy! When I decided to make the electric scooter was during one very still morning I was getting sick from the fumes which were not dispersing!

But I did revise my numbers as I figured the true energy cost on my bill would be much lower than the reference number I used to use a few years back.

 

[Scottydog]

I also edited the spreadsheet calculations with numbers based on suggested percentage improvements with lower ir cells and using regen. I not sure the assumptions are 100% accurate but I used 20% gain for regen and reduced losses from 24% to 15%.