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Discussion Starter #1
I took some measurements of battery current to get a better feel for how the Power meter on the dash works. I know power != current, but it's easier to measure with a clamp-on meter. I started with a fully-charged battery and it was cold at 0C. It's a bit odd:
0 to 50% is linear and almost exactly 1:1 with current: 25% = 25A, 50%=50A
Above 50% it quickly gets non-linear: 75% = 130A, 100% = 200A


There is a small problem here: 200A out of a 390V battery is 78kW, a bit too much. The extra could be inverter and battery impedance losses, but it sounds like a lot for that. Maybe the cold increases the battery impedance, that could explain the range loss in the winter.


On the recuperation side, the scale is linear, with 10A per segment. 40A to saturate the gauge, but then you can get more recuperation, up to 65A, but the gauge doesn't move any further.


The worst part: I'm seriously disappointed about my beloved recuperation paddles: Turns out you can't get maximum recuperation just by switching to D+. This only get up to 50A. I had to tap the brake to get 65A. Well, for most times they are fine, just keeping in mind that it's OK to tap the brake if D+ isn't braking fast enough.


9A charging from a Level 2. That seems about right.


Now, battery current it easy to measure with a clamp-on hall effect probe. It would be nice to get voltage, too. The power meter is reading power, after all, not current. That could explain some of the mystery. Anyone know how to get access to the terminals?
 

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There are so many warning stickers slapped under the car in various places, plus tons of warnings in the Service Manual about the HV system, that I would be remiss if I recommened that you mess with it.

9A charging from a Level 2 charger is not right at all.
Level 2 Chargers are 240v and should pull 16 to 30A, depending on who makes them and what model.

Are you talking about the 8A setting on the factory charger???
 

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Wish the yellow warning stickers under the bottom below the doors were black so you couldn't see them :icon_biggrin:
 

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Discussion Starter #4
There are so many warning stickers slapped under the car in various places, plus tons of warnings in the Service Manual about the HV system, that I would be remiss if I recommened that you mess with it.

9A charging from a Level 2 charger is not right at all.
Level 2 Chargers are 240v and should pull 16 to 30A, depending on who makes them and what model.

Are you talking about the 8A setting on the factory charger???
Don't worry, I'm careful.

No, it's 9A into the battery. 9A * 390V = 3.5kW. It was taking 16A @ 234V = 3.7kW from the wall, leaving 200W for charger losses and running the coolant pump.

The smart will pull no more than 16A from the 240V AC side, no matter what EVSE you have.
 

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I took some measurements of battery current to get a better feel for how the Power meter on the dash works. I know power != current, but it's easier to measure with a clamp-on meter. I started with a fully-charged battery and it was cold at 0C. It's a bit odd:
0 to 50% is linear and almost exactly 1:1 with current: 25% = 25A, 50%=50A
Above 50% it quickly gets non-linear: 75% = 130A, 100% = 200A...
It's great to see that someone actually needed to know this enough to do it. I wasn't sure about how to get the display on the dash since I don't have a remote hall-effect sensor for my multimeter.

Granted we are working with macro power and electricity which doesn't need an excuse to use your body to complete the circuit. I have a healthy respect for high voltage / current sources.

It would be awesome if M-B had included an advanced owners kit with the ED, but I'm sure I can get most of the data from the OBD2 port. Or at least I hope I can.
 

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I am not completely clear on what it is you are after but I have some random thoughts.

Are you measuring power or current? I assume you are using a non-contact current probe. That only gives a partial picture because power consumption is equal to amperage multiplied by voltage.

Battery voltage is not constant but is constantly changing with use and goes down with state of charge, which is a more useful indicator anyway.

Battery efficiency decreases with a decrease in temperature and this decrease is not necessarily linear.

You keep using the word recuperation. Do you mean regeneration?

Unless you have specific training in electric or hybrid vehicles or are a high-voltage qualified electrician I strongly suggest you stay away from the battery terminals. There is a reason dealer techs who are electric or hybrid qualified need to have specific training and tools before they are allowed to work on them.

If you want detailed information about what is happening the best and safest way is to obtain a scan tool that will give you detailed information on the vehicle in question. I do not know anything about what data is available on a smart electric but as an example on a Toyota Prius there are pages of detailed data down to the level of specific battery cell voltage and state of charge in the battery pack. A much better way to go.

Be safe, not toast.
 

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It would be nice to log this data and plot it along side vehicle trip data, including speed, acceleration, braking, etc in real time. I think I'll talk to the Fleetcarma guys and see if they can pull this data from the OBD2.
 

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9A charging from a Level 2 charger is not right at all.
Actually, that sounds reasonable. Considering the changer is 3.3k, the max current draw for a 240V charger would be 13A. In that regard 9A sounds reasonable if the battery is over ~70% charged, or in C&D charge mode.
 

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From my measurements, I see no indication that amperage drops significantly when above 70% SOC. My data shows that for the duration of the charge from 72% to 100% that the average amperage draw was 14.2 amps @ 248v or 3.5kW - that's with 8 - 9% charger loss, which is also consistent with my data.
 

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I agree with Mr Hanna on this, draw should be in the 13.5+A range on a 240v charger.
The SOC is fairly linear, which would mesh with other threads hinting that 100% SOC might only be 80% of true battery capacity. That allows for the charger to have a nice even charge throughout the linear portion of the Li-on battery's charge/discharge curve.

The internal battery management system just doesn't let you go into the peak voltage or low voltage spikes in the curve; it keeps you in the middle 80%

This has been verified by the people at Daimler-Benz, they just won't verify exactly what the percentage is. We are all guessing at that number.
 

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Discussion Starter #12
Hi Marc,

just curious: how do you measure charger loss?

It's easy to measure AC power in, but I haven't found a way to measure DC power out. I can get current with a clamp-on probe, but no access to voltage.

Do you have access to the BCM? I guess puncturing the insulation on the battery leads is an option, but a scary one.

I agree that AC power in doesn't drop off until the battery is very nearly full. But I have seen it drop a little when above 95% SoC.
 

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Indirectly, yes. The data logger I have installed reads this via the OBD2 port. I'm trying to get Fleetcarma to report more data.
 

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Check out Fleetcarma.com
I got into a study at the University of Waterloo, so I get the data logger and web portal access for free.

My charge details from last night
Charger energy (kWh): 16.89
Charger Loss (kWh): 1.35
Start SOC (%): 9.1
End SOC (%): 98.5
 

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That's what I thought. Fleetcarma seems willing to work with me regarding the output data to the web interface, so hopefully I'll have even better data in the future.
 
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