DIY Electric Car Forums banner
1 - 14 of 14 Posts

·
Registered
Joined
·
9 Posts
Discussion Starter · #1 ·
..i dont understand, when i go to a store, the label as 12V/60Ah, then i know the battery will hold 60h if im draining 1A/h at 12V..

But when looking at high voltage batteries, they are usally labeled with kwh.... now why is that?

example, 64kwh battery, measuring 400Vdc gives 160Ah.

If my usage is lower 50%, cause i change motor, that will give me 320Ah...and I could the same batterypack is now rated 128kwh..( i guess the same goes for amps) But why kwh?
 

·
Registered
Joined
·
801 Posts
Because 12v Lead-Acid batteries are standardized. When somebody tells you 400v Lithium-Ion, you actually don't know much about it from that alone - chemistry, number of cells in series or in parallel...
 

·
Registered
Joined
·
210 Posts
nominal voltage is used to calculate kWh of a battery 355.2v for 96s the voltage can be higher or lower depending on the nominal voltage of the cells used. bu that is beside the point
lets say you do have a 160Ah battery @400volts if you change the voltage of battery to 200 volts you now have a 320 Ah battery @ 200v 320x200= 64000 Wh same as 160x400v=64000Wh
later floyd
 

·
Registered
Joined
·
8 Posts
I dont understand why you are asking this question, do you not know the relationship between volts, amps and watts. If you have two then you know the third because of Watt's Law.

If my usage is lower 50%, cause i change motor, that will give me 320Ah...and I could the same batterypack is now rated 128kwh..( i guess the same goes for amps) But why kwh?
This question is not clear what you are asking and what are you reducing 50%. Are you reducing the battery pack to half its size and making it 200 Volts? or something else

It might be more clear if you understand the base units;
amp or a watt is a rate
amp-hr (Ah) or a watt-hr (wh) is a capacity

Watt's Law works the same if you are using power in watts or the capacity in watt-hrs as long as you are using the corresponding amps or amp-hrs
watt = volts * amps
watt-hr = volts * amp-hr

So if you are using a 50% less voltage because of the lower nameplate voltage on the new motor then it would make sense that the capacity is reduced by using half of the pack
 

·
Registered
Joined
·
210 Posts
If my usage is lower 50%, cause i change motor, that will give me 320Ah...and I could the same batterypack is now rated 128kwh..( i guess the same goes for amps) But why kwh?
Appears to me they doubled the ah so there by reduced the voltage so the same size battery is just 48s2p vs 96s1p. they multipied the 320Ah by 400v instead of 200v. Easy enough mistake to make.
later floyd
 

·
Registered
Joined
·
7,965 Posts
amp/hr (Ah) or a watt/hr (wh) is a capacity
Not "amp/hr" or "watt/hr" (which would be the nonsensical amps per hour or watts per hour), but "amp-hr" and "watt-hr", correctly given as "Ah" and "Wh" (well, you had "wh", but at least you didn't have a nonsensical "/" there ;)).

Amp-hours is charge capacity; watt-hours is energy capacity... but yes, they are capacities rather than rates.
 

·
Registered
Joined
·
8 Posts
Not "amp/hr" or "watt/hr" (which would be the nonsensical amps per hour or watts per hour), but "amp-hr" and "watt-hr", correctly given as "Ah" and "Wh" (well, you had "wh", but at least you didn't have a nonsensical "/" there ;)).

Amp-hours is charge capacity; watt-hours is energy capacity... but yes, they are capacities rather than rates.
Oops, good catch, I fixed the original post
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #9 ·
Because 12v Lead-Acid batteries are standardized. When somebody tells you 400v Lithium-Ion, you actually don't know much about it from that alone - chemistry, number of cells in series or in parallel...
yeah, its like saying only 12V acid batteries at the store...

I dont understand why you are asking this question, do you not know the relationship between volts, amps and watts. If you have two then you know the third because of Watt's Law.
ok, my feeling tells me that using kwh is just advertising when not telling the nominal voltage of the highvoltage-battery. As cricketo mentioned "Because 12v Lead-Acid batteries are standardized. "... but example when i looking at high voltage batteries system as in a electric cars the advertising, it usually goes like "I got this badass kwh battery package for you to buy... but i cant tell you the nominal voltage of the battery"

Is it 12VDC/64kwh or 380VDC/64kwh battery in the car? heck i dunno but it would be much easier if they labeled the voltage and kwh at the batterypack..
 

·
Registered
Joined
·
801 Posts
yeah, its like saying only 12V acid batteries at the store...


ok, my feeling tells me that using kwh is just advertising when not telling the nominal voltage of the highvoltage-battery. As cricketo mentioned "Because 12v Lead-Acid batteries are standardized. "... but example when i looking at high voltage batteries system as in a electric cars the advertising, it usually goes like "I got this badass kwh battery package for you to buy... but i cant tell you the nominal voltage of the battery"

Is it 12VDC/64kwh or 380VDC/64kwh battery in the car? heck i dunno but it would be much easier if they labeled the voltage and kwh at the batterypack..
The application is different, and kWh gives you a better idea of the capability. So specifically an average electric car will require a certain number of Wh to travel 1km of distance. Say 200Wh per 1km. It doesn't matter at what exact voltage it's done, it will still be roughly the same amount of energy whether say battery is 350V, 400V or 450V. So then how do you compare a car that has a 350V battery to a 450V ? The capacity in kWh helps there, providing a single number.
 

·
Registered
Joined
·
3,035 Posts
yeah, its like saying only 12V acid batteries at the store...


ok, my feeling tells me that using kwh is just advertising...
Science and feelings don't mix - you'd fit in well in America 😂

When you multiply power (Watts) by time (seconds) you get Joules, which is the direct measure of ENERGY.

When you muliply current (Amps) by time (seconds) you get Coulombs, which is electrical CHARGE (not battery charge)

Using hours vs seconds gets a bastardized, non SI unit, but it remains ENERGY and electrical CHARGE, respectively, where a kWh is 3,600,000 Joules of energy and Ah is 3,600 Coulombs of electrical charge.

Physics, not feelings.
 

·
Registered
Joined
·
801 Posts
Science and feelings don't mix - you'd fit in well in America 😂

When you multiply power (kW) by time (seconds) you get Joules, which is the direct measure of ENERGY.

When you muliply current (Amps) by time (seconds) you get Coulombs, which is electrical CHARGE (not battery charge)

Using hours vs seconds gets a bastardized, non SI unit, but it remains ENERGY and electrical CHARGE, where a kEh is 3600 Joules of energy and Ah is 3600 Coulombs of electrical charge.

Physics, not feelings.
Elon once commented on the topic [of measurements] that measuring thrust in newtons when building an orbital booster is stupid :D
 

·
Registered
Joined
·
3,035 Posts
Yes, I'm sure he's disappointed it hasn't been changed to Elons of thrust already

Edit: I wast bored at a traffic light and didn't have time to proofread....had a bunch of typos that you managed to capture, lol
 
1 - 14 of 14 Posts
Top