Discussion
It seems many people struggle with the correct units for EV battery capacity.
I've seen kw, kW, Kw, KW/H, kW/h, etc. being used.
There is no such thing as kW per hour and kW itself is written incorrectly much of the time anyway.
The correct expression is of course kWh, i.e. kW multiplied by hours, power multiplied by time, which measures energy.
I guess understanding the difference between power and energy is not for everyone.
Why therefore did manufacturers use kWh when there is seemingly a much more fool-proof unit for energy, i.e. MJ (megajoules)?
This would also see a scale of say 0-1000 to be used which allows easy differentiation between battery sizes.
For reference, 1 kWh is 3.6 MJ, so a 100 kWh battery would be 360 MJ.
Am I overthinking this?
I've seen kw, kW, Kw, KW/H, kW/h, etc. being used.
There is no such thing as kW per hour and kW itself is written incorrectly much of the time anyway.
The correct expression is of course kWh, i.e. kW multiplied by hours, power multiplied by time, which measures energy.
I guess understanding the difference between power and energy is not for everyone.
Why therefore did manufacturers use kWh when there is seemingly a much more fool-proof unit for energy, i.e. MJ (megajoules)?
This would also see a scale of say 0-1000 to be used which allows easy differentiation between battery sizes.
For reference, 1 kWh is 3.6 MJ, so a 100 kWh battery would be 360 MJ.
Am I overthinking this?
motco said:
robbieduncan said:
People should be familiar with kWh: that's what their domestic electricity is charged in
Exactly that.I guess I was also harking back to the time of cubic inches....427, etc.
Megajoules also rolls off the tongue much easier than kWh, definitely easier for the punters to use IMO.
I think it was a missed opportunity.
Edited by GT119 on Tuesday 17th December 17:45
There's the familiarity and the fact charger outlets are rated in kW, 7kW, 22kW etc. That makes estimating how many hours it will take for a charge a bit easier.
ie, 40kWh battery, 22kW charger, easy to estimate 2 and a bit hours. (40/22)+reality
144MJ battery, 22kW charger... errrrr... 22kJ/s=0.022MJ/s... 144/0.022... =6545seconds... /60/60 to get 1.8hrs... then add a bit. Not so easy to do in your head!
ie, 40kWh battery, 22kW charger, easy to estimate 2 and a bit hours. (40/22)+reality
144MJ battery, 22kW charger... errrrr... 22kJ/s=0.022MJ/s... 144/0.022... =6545seconds... /60/60 to get 1.8hrs... then add a bit. Not so easy to do in your head!
motco said:
In the time honoured PH tradition I'll post this example of megajewels...
I think that's sort of where I'm coming from.The word megajoule just sounds so much sexier than killowatt-hours, and given that EV's have somewhat of an image problem for your average alpha male petrolhead, as witnessed on here, I think 'megajoules' could have helped with that.
I'm guessing that kWh was probably used because it can be easily be equated to the charging time for a given battery size at a given rate.
For example, in simplistic terms, assuming 100% efficiency (which obviously is not what happens in the real world), a 100kWh battery charging at 10kW would take 10 hours to fully charge. Using MJ would make that a less direct equation.
For example, in simplistic terms, assuming 100% efficiency (which obviously is not what happens in the real world), a 100kWh battery charging at 10kW would take 10 hours to fully charge. Using MJ would make that a less direct equation.
GT119 said:
It seems many people struggle with the correct units for EV battery capacity.
I've seen kw, kW, Kw, KW/H, kW/h, etc. being used.
There is no such thing as kW per hour and kW itself is written incorrectly much of the time anyway.
The correct expression is of course kWh, i.e. kW multiplied by hours, power multiplied by time, which measures energy.
I guess understanding the difference between power and energy is not for everyone.
Why therefore did manufacturers use kWh when there is seemingly a much more fool-proof unit for energy, i.e. MJ (megajoules)?
This would also see a scale of say 0-1000 to be used which allows easy differentiation between battery sizes.
For reference, 1 kWh is 3.6 MJ, so a 100 kWh battery would be 360 MJ.
Am I overthinking this?
Many struggle with the use of capitalisation of engineering units to which is sloppy and disrespectful to the engineers which gave the units their name.I've seen kw, kW, Kw, KW/H, kW/h, etc. being used.
There is no such thing as kW per hour and kW itself is written incorrectly much of the time anyway.
The correct expression is of course kWh, i.e. kW multiplied by hours, power multiplied by time, which measures energy.
I guess understanding the difference between power and energy is not for everyone.
Why therefore did manufacturers use kWh when there is seemingly a much more fool-proof unit for energy, i.e. MJ (megajoules)?
This would also see a scale of say 0-1000 to be used which allows easy differentiation between battery sizes.
For reference, 1 kWh is 3.6 MJ, so a 100 kWh battery would be 360 MJ.
Am I overthinking this?
Sadly I see this with my work to, a general dumbing down.
It’s all part of the “spelling and punctuation aren’t important” trend I suspect. Engineers are by disposition pedants, because we have to be, but for non-engineers, it really doesn’t seem to be important, and trying to educate folk often isn’t well received no matter how well intentioned or politely done.
I can see a move to MJ being popular though, ‘cos,like,it’s megga,innit.
I can see a move to MJ being popular though, ‘cos,like,it’s megga,innit.
Evanivitch said:
... lets not get started on manufacturers that quote Ah batteries!
AA NiMh rechargeable cells are usually quoted in mAh which is fine as long as every maker follows, but manufacturers of nickel/zinc (NiZ) rechargeables use mWh simply because, I suspect, the terminal voltage of these cells is 1.8v and the mWh figure is artificially inflated numerically. In fact they have less energy than a mid-quality NiMh cell.GT119 said:
I think that's sort of where I'm coming from.
The word megajoule just sounds so much sexier than killowatt-hours, and given that EV's have somewhat of an image problem for your average alpha male petrolhead, as witnessed on here, I think 'megajoules' could have helped with that.
You were doing so well with your pomposity until you spelt kilowatt incorrectly. The word megajoule just sounds so much sexier than killowatt-hours, and given that EV's have somewhat of an image problem for your average alpha male petrolhead, as witnessed on here, I think 'megajoules' could have helped with that.
By the way, it’s EVs not EV’s.........
Chris-S said:
It’s all part of the “spelling and punctuation aren’t important” trend I suspect. Engineers are by disposition pedants, because we have to be, but for non-engineers, it really doesn’t seem to be important, and trying to educate folk often isn’t well received no matter how well intentioned or politely done.
I can see a move to MJ being popular though, ‘cos,like,it’s megga,innit.
Mj, pfft. Real men use Gj,innit.I can see a move to MJ being popular though, ‘cos,like,it’s megga,innit.
REALIST123 said:
GT119 said:
I think that's sort of where I'm coming from.
The word megajoule just sounds so much sexier than killowatt-hours, and given that EV's have somewhat of an image problem for your average alpha male petrolhead, as witnessed on here, I think 'megajoules' could have helped with that.
You were doing so well with your pomposity until you spelt kilowatt incorrectly. The word megajoule just sounds so much sexier than killowatt-hours, and given that EV's have somewhat of an image problem for your average alpha male petrolhead, as witnessed on here, I think 'megajoules' could have helped with that.
By the way, it’s EVs not EV’s.........
Chris-S said:
It’s all part of the “spelling and punctuation aren’t important” trend I suspect. Engineers are by disposition pedants, because we have to be, but for non-engineers, it really doesn’t seem to be important, and trying to educate folk often isn’t well received no matter how well intentioned or politely done.
I can see a move to MJ being popular though, ‘cos,like,it’s megga,innit.
A scene from The Fast & Furious 23:I can see a move to MJ being popular though, ‘cos,like,it’s megga,innit.
What you got under the hood?
This baby's packing 700 em-jays...
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