58 MPG by 2032

[Grumpycat]

kWh is independent of voltage. Amp-hours requires knowledge of the voltage to determine kWh. Amp-hours times voltage equals Watt-hours. Amp times volts equals Watts. I know, in this day and age math is hard, and racist.

And in support of @WinterDeere the CCA rating is hyped by starter battery vendors as a valid means of comparing starter batteries to the point consumers think they know everything about buying batteries and are smart with CCA. It is meaningful for comparing starter batteries but says almost nothing about capacity. Lithium “upgrade” starter batteries have astronomical CCA ratings but about 1/4 the amp-hours. So CCA doesn’t translate outside the starter battery realm, and then only to lead-acid batteries.

These same smart consumers ”know” batteries only last 3-5 years and therefore believe the same will be true for EV traction batteries. Sadly Nissan worked hard to make that come true with the LEAF.

 

[WinterDeere]

Amp-hours becomes important on a starter battery when you (a) have a vehicle that doesn't want to start, or (b) a vehicle that sees frequent starts (eg. UPS trucks). If you've ever sat cranking a stubborn car on a cold morning until the battery eventually goes dead, you've had a chance to display CCA and amp-hours, all in the same sitting!

 

[nickfank]

How do you figure out example a car battery has 800 cold
cranking amps = how many KWH how to figure this??
How long would a lithium 100 ah battery last drawing 15 amps?
My wife had the 6400 btu unit cooled her 17x12 room an the
8400 cools the kitchen. dining room and we keep the
temp at 75 F because the temps are close to 100+ here
no need to cool where we are not! I an usually outside with
no a/c working in the heat as I don't like going from 100+ to
75 degrees F when your soaking wet from sweating!

willy

Several good responses to this, but I'll add a little detail...

volts times amps = watts, so the 12V, 800CCA battery can briefly supply 9.6 kW. No telling how long it can do that though, unless they tell you the Ah rating as well.

If your battery (lithium, or any other chemistry) is rated for 100Ah, it will last 6-2/3 hours drawing 15 Amps. (100/15)



Watts tells you how much power you have right now, and watt-hours tells you how long you can maintain that power before your battery is dead or your fuel tank is empty.

A watt and a BTU/hr is a unit equivalent to horsepower. (1HP = 746 watts = 9,000 BTU/hr)

Watt-hours and BTUs are equivalent to gallons of fuel. (1 gallon of diesel = 38 kWh = 138,700 BTU)

Putting this into practice:

If I have a 35HP tractor, that tells me how hard the tractor can pull, but not for how long. If I also know I've got 3 gallons of fuel in the tank, now I know I can pull at the full 35HP for one hour before I run out of fuel.

We can do the same thing with watts:

If I have an electric tractor with a 50 volt battery that can supply 500 Amps, then by multiplying 50 times 500, I know it can pull with a force of 25kW (33HP). If I add the information that the battery can supply 1000 Ah, now I know the battery will need to be recharged after 2 hours working at full power.

Since BTU tends to be used for air conditioners, I can't come up with a good tractor version, but that 6,400 BTU air conditioner includes a hidden time component that the marketing folks left out. In air conditioning jargon, 6,400 BTU means that the air conditioner is removing 6,400 BTUs of heat from the room every hour. That means that if you turned on a 530 watt heater in the same room, or burned .05 gallons of diesel fuel each hour, it would exactly balance the air conditioner and the temp wouldn't change.

 

[Grumpycat]

Amp-hours becomes important on a starter battery when you (a) have a vehicle that doesn't want to start, or (b) a vehicle that sees frequent starts (eg. UPS trucks). If you've ever sat cranking a stubborn car on a cold morning until the battery eventually goes dead, you've had a chance to display CCA and amp-hours, all in the same sitting!

LiFePO4 "upgrade" batteries are popular in the motorcycle market for being lighter than AGM. They suffer at 50°F, and while they have spectacular lead-equivalent-CCA ratings, as you say, when the engine doesn't start quickly the battery quickly depletes for lack of total Wh.

LiFePO4 can't rate CCA at the temperatures lead-acid batteries are tested. So they do a Cranking Amps at a warm temperature and misguidedly quote that number and footnote in the fine print how lithium CCA is different.

 

[WinterDeere]

I believe they probably use Ah over Wh for most batteries because it is more a true measure if the stored chemical charge. Voltage will drop as battery depletes, making watt-hours a less consistent metric, for that application.

 

[Williy]

Thank's to y'all for the information.
I was thinking of getting a Jetta tdi but in 2015 no more vw diesels
for the USA too much garbage you have to put on machines.
However the Jetta with the gas engine is getting over 40 mpg
and I think its smaller so will make it easy t;o squeeze into a
parking spot. We are in the last days and IMHO fuel prices at
going to esculate

willy

 

[etpm]

Our power spiked from 11c/kwh to 17c/kwh, I didn't even realize it. I installed new equipment to cut power, and factored the cost of the equipment would pay for itself in about 15 months. The bill didn't go down the next month by any measurable amount so I went to verify that the usage recorded was lower. I have my own instruments for monitoring consumption as well. The reading was ~2500kwh, vs the forecasted 3500kwh on the old equipment. However that massive increase in costs just killed any savings I would have seen.

I will be pushing my solar array install up to as soon as possible to try and further offset the increased costs. It's really not a selling point for EV's when it's going to cost me more to run them. Once I have a big enough array in place I'll be ordering batteries and disconnecting entirely.

Which types of battery chemistries are you considering? Even though where I live in western WA gets much less usable solar than other places in western WA I am still considering solar. And I would like batteries to obviate a generator when the power goes out. I don't think, for me, that 100% solar would be economical at this time.
Thanks,
Eric

 

[bnold]

LiFePO4 "upgrade" batteries are popular in the motorcycle market for being lighter than AGM. They suffer at 50°F, and while they have spectacular lead-equivalent-CCA ratings, as you say, when the engine doesn't start quickly the battery quickly depletes for lack of total Wh.

LiFePO4 can't rate CCA at the temperatures lead-acid batteries are tested. So they do a Cranking Amps at a warm temperature and misguidedly quote that number and footnote in the fine print how lithium CCA is different.

Thing is absolutely amazing in my KTM.
Thing feels like a feather and is tiny.

 

[Grumpycat]

I believe they probably use Ah over Wh for most batteries because it is more a true measure if the stored chemical charge. Voltage will drop as battery depletes, making watt-hours a less consistent metric, for that application.

Wh is the true measure of the battery's capacity. It is a number one can use to compare batteries irrespective of voltage.

Short circuit amps (as with CCA) will taper off as voltage declines as battery discharges.

For many batteries the Ah rating is measured as a continuous amperage for 20 hours. Requires trial and error to determine. IIRC a 1 hour test is used for automotive starter batteries.

Wh is much the same but the area under the curve is integrated. Again "in a set time", and again one has to guess by trial and error how many amps to draw.

Many do not realize how hard it is to produce a S.O.C. meter for a battery, State Of Charge, to know how much is remaining. Can not just measure voltage and temperature. Am amazed at how well Tesla has calibrated the "fuel gauge" on my Model S.

 

[WinterDeere]

Wh is the true measure of the battery's capacity. It is a number one can use to compare batteries irrespective of voltage.

I'm not sure this is true, or at least I'm not used to seeing "Wh" ratings printed on battery casings, those I've checked have been nearly always expressed in "Ah". Again, I believe this has to do with battery chemistry and physics, as it's a stored charge (Coulombs) which translates to consistency in amps (Coulombs/second), and no consistency in watts under condition of diminishing voltage. I'm not a battery expert, and I hated all three terms of Chemistry I was forced to take, it would be good if we could hear on this from someone who actually designs batteries.

Wh is much the same but the area under the curve is integrated. Again "in a set time", and again one has to guess by trial and error how many amps to draw.

Again, EE here... you don't need to explain what watt-hours are, this is kindergarden stuff. If you want to get into skin effect and variation in effective conductivity due to surface roughness at higher frequencies, or moding of various conductor arrangements due to physical geometry and inhomogeneous dielectrics between them, I'm your man.