Wh/mile, range difference when using/switching to Li from lead

ElectriCar said:

Just curious what changes you noticed in your conversion for those of you who have made the jump to lithium. My 91 S10 truck averages about 480wh/mile now. The current weight is 4147 lbs. 1500lbs of that is battery.

I figured if I switched to one string of 130ah 3.4V Calb batteries I would lose about 1100lbs of batteries, cable and steel rack. That's 25% of the current truck weight!

My lead pack is 33.4kw. The new pack would be 19.9kw after bumping to 153V from 144. The higher voltage should also lower my required amps for a given speed/load thus lowering the peukert losses somewhat further extending max range.

So I'm really excited about the new wh/mile and range possiblilties with the switch. Any real world experiences you folks can share with us lead heads???

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I can't help you with this too much yet...as I havn't received my Li yet. I do recall reading some posts about this though...do some searching and perhaps you will find it.

Couple of comments though... I would recommend going with 180Ah cells minimum on your truck. Your pack will last much longer and you won't worry about stressing it. This is the smallest I would recommend for a small pick up truck.
Nominal voltage is generally accepted as being 3.2 on this chemistry..not 3.4 I think. You really should calculate your pack and nominal on this number as this is where the majority of the discharge will be at (for low current draw). Based on your number of 153 and 3.4 I assume you are considering 45 cells. This would give you a nominal pack voltage of 144, not 153 and about 18.7 KWh.
Peukerts plays very little role in LiFePo... but it's true that your current will go down with higher voltage... not sure that it will in this case though.
Good luck! I'm excited to go Li also! 65 Calb 180Ah cells coming...

Edit... Rickard talks about a rule of thumb using .11 x vehicle weight for calculating efficiency in WH/mile. Assuming your truck is 4000lbs with lead, that's 440 wh/mile. If you dropped 1000 lbs and had a weight of 3000, your efficiency should go to around 330 wh/mile. This may not be exact...but an indicator for you. Charge efficiency of Li is better also which helps....

I wouldn't trust Rickard's rule of thumb too much. He based his .11 number on two cars that have typical aerodynamics of passenger style (coupe, sedan) vehicles and his own driving style. This will largely be affected by the speed of use and aerodynamics of the vehicle as well. A truck will be worse than this, especially at speeds around 50MPH and above. Either way, I personally aim to have 30% of my charge available for the longest trip that I plan on running with the car in case a detour happens or weather or wind is bad and causes loss of range, and also because staying above 30% state of charge should extend the life of the batteries.

I'm personally probably going to have quite a bit extra compared to my actual commute if I can fit it in because if I had a 100 mile range in a small car, I'd be able to go pretty much anywhere that isn't an out of state road trip from where I live in the Twin Cities with that range which would allow me to utilize an electric car in pretty much every situation. Your needs will vary from mine though. If I went cheap 60 miles would cover my real-world range needs as my work commute is 30 miles and longer trips are typically within 30 miles from home, I'd probably have a range of absolute max 80 miles to empty to acheive that. ..that's just my situation though.

DIYguy said:

It's just a rule of thumb... but I would say that it's not too bad. I actually have a pickup truck, and the numbers work out pretty well. How do you know that he only based it on his two vehicles? I don't recall him saying that... he does kind of rattle on though...lol

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Well two or three. He bases everything on his personal experience and if anyone tells him otherwise he throws a fit. Basing a range calculation entirely on weight and not on other dynamics such as vehicle speed, driving style, and aerodynamics is foolish. He doesn't mention any of this even though he's has Brian and Tracy(I think) drive his cars with very different results in wh/mile. If driven at a constant speed on the highway at 60MPH, weight has less to do with maintaining that speed because weight has a bigger role in acceleration, braking, and hill climbing. In those cases aerodynamics plays a bigger role. In stop and go driving in slower environments like what Rickard puts his cars through, it seems that weight wins out. I drove a trip going 630.5 miles and got 73MPG on a gasoline car going 70MPH average on mostly flat interstate carrying camping equipment that caused my car to be very near, if not over its weight limit. Aerodynamics play a bigger role in that type of driving. Of course that is a gasoline vehicle but with an electric vehicle the idea is the same, if traveling at high speeds for highway commutes the speed will kill your range with a vehicle that isn't aerodynamic more than weight ever could.

I'm just saying, he is leaving too much out by just tossing out a number and going 'here you go, use this'.

DIYguy said:

Edit; GM S10EV rated at 450 wh/mile city and 410 wh/mile hyway. Ranger EV was 362 wh/m @ 60mph, 242 @ 45mph and 315 combined. Some of those numbers sound rather "ambitious" though.lol...

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What does that mean??? Anyway, the GM's number is comparable to my truck.

His formula though fits nicely with what I've guestimated and so I think it probably is a good "ROT". Surely he based it on several vechicles, more than two I would hope.

The more I think about this the more I'm confident it will be close to his number of 335, loosly calculated from the weight loss I'll experience. I was thinking it may be around 325-350, perhaps as low as 300 if I'm overlooking something.

My thinking is that if I lose 1000lbs, that's 25%. 75% of the current average wh/mile will bring it right down there to about 360wh/mile. Using less amperage due to reduced weight will reduce losses due to resistance too, further reducing your wh/mile usage. I'll explain.

Lithium has less internal resistance so you have two factors that reduce losses versus lead.
1. Lower IR means for a given current consumption, voltage drop in the pack is reduced. From what I've read, this is significant vs LA packs. What that does is provide more power to the motor and further reduces amp draw, in addition to what it dropped directly due to weight savings. Currently my pack voltage drops about 20% on acceleration.
2. Now that more voltage is available to the motor, less current will be needed through the pack/motor leads. This is because Power = Voltage x Amps. This reduced current will reduce voltage drop further because of resistance in the wires & connections which again leaves more voltage at the motor. How much savings one will get from this part depends on what size wire was used to tie the pack together and how many amps is pulled through them. Larger wire has less resistance = less voltage consumed = more available at the motor.

Now if the savings due to voltage drop is reduced from 20% to say 5%, you're saving 15%. That's like increasing your pack voltage 15% which will translate to savings on your power consumption because voltage drop is wasted power. That's why your pack warms when charging/discharging.

Still I don't know how to actually calculate the savings, only deduce some things but basically those things are the only ones I can see that will be affected.

So in my case, I'll lose 25% or more on weight and 10-15% on voltage drop I suppose. Will my wh/mile drop 35-40%? That's what I'd like to know from other people's experiences. 35% would put me at 312wh/mile. Not bad and seems reasonably close to what I've read...

PatricioIN said:

I've done a lot of guessing on this subject based on my own personal EV and estimates of others from EValbum. My zx2 EV with lead weighed 3200lbs and averaged 275 wh/m. I figure if I do the exact same conversion with lithium (45 130Ah cells) it would weigh only ~2700lbs. That gives me a comparable 229 wh/m. I simple take my new weight x 275 / old weight for wh/m.

This may not be very scientific, but it seems to gel quite well with other's observed wh/m ratings on EValbum, using lithium cells. Really, it's all just a shot in the dark anyway until you're actually done with your EV and can calculate what you're actually averaging. Hopefully a very close shot in the dark, but a guess nonetheless!

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When you get it on the road you'll see it will be less than 229 due to the differences I just attempted to explain above. 229 would only take into account the change in weight. Lithium has a much lower internal resistance than lead.

At this moment I'm getting ready to take some notes on this. My lead powered truck is in the garage and I'm waiting for the temp to stabilize on the battery after driving it home. I'm going to record that temp then charge the pack, then record the temp again while noting the kw supplied. Then I'm going to try and half way come up with a number that approximates the kw consumed to heat the pack to the degree that it did. Water weighs 8lbs/gal. I'm going to assume that 1500lbs of battery behaves like 1500 lbs of water!

1Kwh = 3414 btu of heat. It takes 1btu to increase the temp of 1lb of water 1 degree. So I'm going to try and "Gestimate" some number of kw consumed due to the internal resistance. That would be a gestimate of the kwh wasted in charging the battery at about 30A. MUCH less than the amount wasted in discharging the pack at 50-250A. Are you totally confused now???

Ok after measuring temps, time and Kw of my lead pack while charging, here's the info. I left the truck plugged in after the pack was charged because we had a pet emergency so the final wh/mile estimated below to actually drive the truck will be a little high. At that point it overcharges the pack to desulfate the batteries, using a lot of extra energy in the process.

At start the PakTrakr stated temp was 63F, garage temp was 44 and the face of several batteries averaged about 46.

After charging for about two hours, the meter indicated I had used 5.71 kwh to recharge AND partially desulfate the pack. That was 660wh/mile, more than I normally use with the cabin heat, about 60 based on my records.

The PakTrakr indicated a 4F rise in temp to 67F. The plastic battery tops however had risen 6 degrees F to 52F! Lets split the difference and say the 1500lb pack temperature increased 5 degrees F. For 1500lbs of water to increase 5 degrees F would require 7500 btu.

7500btu's divided by 3414 yields 2.19kw. Taken from 7.13kw total input to the charger = 4.94kw to recharge the battery after 10.8 miles of driving. That comes out to 457kw/mile with the heater on while coming home today (and overcharging a little)!

2000 watts of heater and 350 watts of blower for 20 minutes = 783 watts to heat the cab. Spread over 10.8miles = 72 watts/mile. Deduct that from 457 leaves 385 watts/mile to drive the truck. If you deduct 60 from the 385 for the overcharging, it leaves 325wh/mile. Based on my normal average of about 480wh/mile, that's a reduction of 20%. And the best thing about this is that this 20% loss is only while charging at 30A. It is more than 20% when discharging due to a much higher discharge current for a total of over 40% loss due to internal resistance!

That sounds a bit high so I'm going to monitor this temp/kw thing a few more times to get better data by unplugging the charger upon full charge.

SO, going to lithium will eliminate a good bit, though not all of this wasted power in my lead pack.

DIYguy said:

... Rickard talks about a rule of thumb using .11 x vehicle weight for calculating efficiency in WH/mile.....

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I can validate Rickard’s rule of thumb for my 3500 lb Lithium DC conversion. As of my last charge, my overall average AC energy consumption over the past 5383 miles has been 384.4 Wh/mi: 2069.1 kWh / 5383 mi = 383.4 Wh/mi.
And 383.4 / 3500 lbs = 0.1098

The majority of my driving is low speed urban city traffic where vehicle aerodynamics are not much of a consideration.

All AC energy measurements were taken by my trunk mounted revenue-grade Itron Sentinel meter with a 0.2% accuracy class. My odometer isn’t quite as accurate with a 1.2% error when compared to GPS. This results in a total energy consumption accuracy of somewhere around 98.6%.