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Discussion Starter #1 (Edited)
Things We Know and Things We Would Like to Know About the Smart ED Battery

Pack = 17.6 Kwhr (marketing description)

Cells = 98 40Ahr LiNiMnCoO2 derivitive - Nominal voltage 3.6v (not confirmed)
Computed Pack Voltage (98 x 3.6) = 352.8
Computed Pack Capacity (98 x 3.6 x 40ahr) =14.112 kWhr.

Something is already wrong with these numbers because the pack capacity doesn't compute using the above numbers. Even using a voltage of 4.2 per cell only calculates to a 16.46 kWhr capacity.
Does anyone have a couple of sources that tell us how many cells are in the car?



Thanks to emcconnell we have the following document that talks about the cells in our car:
http://old.life-needs-power.de/2009/23-04-2009_13-00_LNP-Li-Tec presentation_life_needs_power_TS_29_03_09_2a.pdf

Or at least that is the current assumption. I will look for a more definitive source.
 

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According to the Assurance Plus documentation, the program notes a "guaranteed battery capacity of 41.6 Ah, up to 10 years". Considering the literature elsewhere guarantees 80% charge/range, that would indicate to me the pack is higher Ah. (41.6/0.8 = 52Ah Very even number that...) Not a surprise, give we have the highest charge/density in a commercial car right now (yes, even better than Tesla, by their own admission).

At 98 cells, assuming 3.6v standard, that would make it 18.345 kWhr. We could have closer to 50Ah cells, making it 98 * 3.6 * 50 = 17.64kAh. Dead on the money number wise. That would also put a nominal draw of about 16.1A per cell to get the 57kW max for the engine, which is about typical of such cells (16.5A). If we have 52Ah cells at 3.6v though, that would make it 94 cells.

My bet is that smart again went "green" and is using LiFePO4 cells, which uses much more common elements (Iron/Phosphorus vs Nickle/Manganese) and has a nominal voltage of 3.45v. Magically, 52 * 3.45 * 98= 17.58. That would also explain the density difference, as LiNiMnCoO2 is ~147mAh/g, where LiFePO4 is closer to 170mAH/g.

I'm still looking for that reference to the number of cells in the pack, but I know I saw it on a reliable site as 98 cells (probably smart pre-launch literature). I'll keep looking for it, and ask around a bit, and let you know what I find out. But for sure, we're looking at cells near or better than 50Ah for the smart, just on the warranty info alone.
 

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You want answers? I got answers

These come from an extremely reliable source.

These are the questions I asked

1) What kind of rpm’s does the engine turn at max speed?
2) How many batteries are actually in the battery pack?
3) Do we really use the battery as stated on the SOC gauge (0% to 100%), which would be bad for Li-on batteries, or is the gauge calibrated true 20-80% range shows on the gauge as 0% to 100% ?
In other words, when the SOC gauge shows 100% charge, is that a true 100% of actual capacity, or is it really less, to maintain long battery life?
4) What is the final drive gear ratio?
5) Is it possible to disable the “creep” function (car moves when driver takes foot off of gas)?
6) Is the “pa-pa-pa-pa-pa” noise that is experienced in the first few feet of driving after starting the car up a self-check of the ABS system or something different?
7) How much does running the A/C (or heat) affect range and battery capacity?
8) Are our batteries Lithium-Ion, or LiFePO4 batteries?

And these are the answers that I got back. Enjoy.

Response:

1)11,800 RPM
2)93 individual cells
3)The SOC displayed on the gauges is not the actual SOC in the battery management system. What is displayed is a “customer friendly” version that is more acceptable and expected by the customer. The battery management system will protect the battery from deep discharge or overcharge so there can be no damage to the battery from regular driving and charging the complete SOC window.
4)9.922:1
5)Not possible that I am aware of, but I will check. The creep was a request to add from our market based feedback from the Generation 2 which did not have this feature.
7)The exact impact on range from the a/c or heat is not something we can provide. Range is a factor of many inputs like ambient temp, driver style and consumer loading. The PTC heater and a/c compressor do not have a fixed load. They change depending on demand. So they can consume as little as 2kW or as much as 4 kW peak power . I can’t share internal documents on this, but I did attach a customer sharable table that Germany created. It is in km and not miles. Preconditioning has a big impact on range, since you can eliminate the initial high load to heat/cool the interior on first start.
8)Lithium-ion

The answer to question #6 was
Answer to #6
The audible noise and felt pulsation is coming from the ESP/ ABS hydraulic pump. At approx. 10 miles (ten feet?) it goes through a self test/ priming cycle. This happens one time after the start up. It can be felt mainly in your left foot, because the ESP/ABS hydraulic pump is mounted right in that area.
This is normal on all ED’s and gas powered SMART’s. On gas cars it is less noticeable as the engine noise almost overshadows it.




 

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Nice, so they are very likely 52Ah packs then. (52 * 3.6 * 94 = 17.5968K, or 17.6 for marketing).

On #3, the real question isn't really about damage though. The question is how much cushion is built in. I'd assume at least 5%, since that's pretty standard in the industry for phones and laptops. But they may have gone beyond that a bit. I really doubt they're holding back more than 10% on either side. I'm also betting the SOC meter isn't exactly linear either, based on my own observations.

Nice to have some solid answers though.
 

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I was surprised at the almost 12,000 rpm rate and the 1:1 final drive ratio
Well OK, 9.922:1 final drive, not much difference.
 

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#3 gives me less range anxiety as I'd already, by necessity, decided that charging to 100% is ok since there weren't any red flags in the manual suggesting that charging to 100% should be avoided if possible. The charge before 20% red flag in the manual was giving me some concern as my 50-60 degree weather usage gets me down to 30-40% for my daily commute (without hypermiling).

Knowing that the "range" estimate on the dash is intended to be a safe usage level from the perspective of the battery, gives me some additional comfort, knowing that it isn't so bad if I need to occasionally drop to the less than 5% level.

today's driving temp low was just below 50F and I used 65% SOC. Tomorrow is dropping into the 30's so I'll have a new data point for myself tomorrow.
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LOL, you are correct, I was thinking it was .9922:1
10 revs of the motor to make the wheels turn once.

that is going to take a few minutes to get my head around, as geared transmissions usually have a final drive of 1:1 or lower (in the case of overdrive). But our motor turns 4 times the RPM's of an "average" engine which hits 2800rpm's or so at 75mph, so that would make sense.
 

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LOL, you are correct, I was thinking it was .9922:1
10 revs of the motor to make the wheels turn once.

that is going to take a few minutes to get my head around, as geared transmissions usually have a final drive of 1:1 or lower (in the case of overdrive). But our motor turns 4 times the RPM's of an "average" engine which hits 2800rpm's or so at 75mph, so that would make sense.
Final drive numbers would include differential gearing which is anywhere from 2 to 1 and higher...:wink:
 

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Now I'm really going to have to unravel my brain from my spinal cord...

Gonna take me awhile to digest this...

"Normal" ICE diffs have specs like 355 or 411 (you can tell I was a Ford truck guy), which means that the driveshaft has to spin 3.55 times to make the wheels spin once.

You think our diff is the 10:1 itself, or it gets reduced before entering the differential? My impression was that there was an output shaft from the motor that goes right to the diff, but I haven't looked to see if there is a gear reduction before it gets there.

Judging by the size of the differential case, I would think that the 10:1 was in the differential itself.
 

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I don't know how the total reduction is achieved in the EV's but imagine there is at least 2 reductions or at least 3 gears...:confused:
 

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Discussion Starter #12
According to the Assurance Plus documentation, the program notes a "guaranteed battery capacity of 41.6 Ah, up to 10 years". Considering the literature elsewhere guarantees 80% charge/range, that would indicate to me the pack is higher Ah. (41.6/0.8 = 52Ah Very even number that...) Not a surprise, give we have the highest charge/density in a commercial car right now (yes, even better than Tesla, by their own admission).
..................
I checked out that link and that was for the gen 2 pack built by Tesla and compared to the Tesla Roadster. All I know at this moment is that the battery in our car is built by LiTec. I have found nothing that clearly states how many cells and what capacity cells. I am tempted to find a way to to measure pack voltage and that would give us one data point to which we could make some other calculations.
It is odd that they are guaranteeing the pack in Ahrs and everything else is stated in kWhrs. Without additional information I don't know for sure if that is indeed a 20% degradation or less as suggested in the LiTec PDF that emcconnell shared with us.
Still so much to know.
 

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Discussion Starter #13
I don't know how the total reduction is achieved in the EV's but imagine there is at least 2 reductions or at least 3 gears...:confused:
I don't know gears like you do, but everything I have read in the conversion community says that less gears mean better efficiency. We know that there is a differential and that means at least a ring gear and the axel gears. I think the axels are on the same plane as the electric motor shaft. Does that mean there is no pinion gear? Is it possible to have a 9.9 to 1 reduction from a gear on the motor to the ring gear? I may not be describing the ring gear correctly but if you look at the case it looks to be large in diameter with the center aligned with the axels. Does the fact that at top end the motor is going 11.5K rpm have any bearing on the design?
 

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I don't know gears like you do, but everything I have read in the conversion community says that less gears mean better efficiency. We know that there is a differential and that means at least a ring gear and the axel gears. I think the axels are on the same plane as the electric motor shaft. Does that mean there is no pinion gear? Is it possible to have a 9.9 to 1 reduction from a gear on the motor to the ring gear? I may not be describing the ring gear correctly but if you look at the case it looks to be large in diameter with the center aligned with the axels. Does the fact that at top end the motor is going 11.5K rpm have any bearing on the design?
In cars with transverse engine and transmission combos all driving force shafts are parallel to each other... So, there is no hypoid style ring & pinion gear like found in a conventional rear axle... The spider gears inside the differential carrier have no bearing on gear reduction, they allow free turning of the vehicle. The carrier will have a helical cut gear ( rather large) mated to a smaller helical cut gear... These 2 gears would be your final drive ratio...
As an example to get a 10 to 1 reduction with only those 2 gears the motor would have a 2" diameter gear and the carrier gear would be 20" in diameter..
That would be crazy right??? My guess, they have put at least another gear in the mix to achieve the proper reduction and keep the gears minimal in size and produce enough dimensional offset to get the cv shaft to clear the electric motor housing..
 

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The ideal method is a direct reduction - i.e. gear on motor shaft direct to gear on final drive. As Ampster said, extra gears reduce efficiency. In machinery, direct drive is always the most desirable, but in an automotive application the motor is under load straight from a stop (unlike machinery), therefore you would have some serious difficulty getting into motion - I can see this as the only reason why they would not go direct drive (there are some very efficient low rpm electric motors out there) - otherwise they would have to have used a capacitor to get the car into motion, or just draw an excess amount of amperage, and I think that would have thrown the efficiency out the window.

Mind you, having said all that, the motor gear would have to be 1/10 the size of the final drive gear to achieve that, which assuming the motor gear is no less than 2" in diameter, would require a final drive gear of 20", which clearly is not the case.

So yes, I agree with Barney O, probably three gears. It could easily be achieved in the space provided and would provide the least amount of efficiency loss.

Edit - yeah, what he said ^^^
 

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Discussion Starter #16
Based on the size of the transmission/differential (about 10") there is probably a third gear in there. I have tried to find a picture but nothing yet.

These three phase AC motors have a lot of torque so I am sure they are direct drive. In my VW conversion (also 3phase AC)I left the clutch in the drivetrain but never use it. I run around town in second gear and never shift or use the clutch. I tried starting in 3rd gear a few times but the starting torque spun my clutch, and that was with a 2500 lb Kennedy pressure plate. After that have left it in second gear.
 

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The smart is not direct drive... According to TroopLewis in post #3 the electric motor is reduced in rpm by a 9.92 gear reduction...That explains the super high rpm of the electric motor that turns 11'800 rpm...This super low gear reduction will keep the amp draw from going off the chart under acceleration and keep the motor R's up in sweet spot...Direct drive would be like having the axle shafts connected directly to electric motor and no gear reduction... Don't think this motor and battery pack could handle that...
There also has to be a parking pawl mechanism in the gearbox somewhere...
Would be nice to see pics of the gearbox internals but imagine MB would rather not give up proprietary info like that..:wink:
 

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Discussion Starter #18
Thanks for the clarification. I was using the term incorrectly. I thought an earlier poster was implying that it had a clutch so I went through that long explanation about not needing the clutch.
 

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Thanks for the clarification. I was using the term incorrectly. I thought an earlier poster was implying that it had a clutch so I went through that long explanation about not needing the clutch.
It may have a torque limiter device which is similar to a clutch used for dampening and overload purposes...:confused:
 

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OK, tech guys, I have a bit more info for you.
There is no output shaft on the motor, it sits on and is geared directly to the differential.

Only two gears, one on the motor and one in the differential.
 
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