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Discussion Starter · #1 ·
I wanted to let the group know we now have a group of guys here who can diagnose the N82/2 BMS where "Workshop Failure" is incurred as a result of battery total depletion stateside. No shipping off to parts unknown. We repaired my Smart's BMS this past week, cleared the offending codes and diagnosed hardware failure. As far as I am aware, my BMS is ready to install. What I don't yet know is whether any other failures occurred, as we've seen sometimes with the current sensor, etc. I'll hopefully install the reassembled HV battery and test this coming week or so. Regardless, it might make sense to contract with us to repair your BMS if it fails, as a quicker, and quite possibly less expensive option.

Bill Kichman
cell 717 507 1611
Lebanon, PA
 

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Discussion Starter · #3 ·
Aha, you wanted an update. I reinstalled the BMS, it's perfectly fine, but found my current sensor like others', was toast. Got an immediate current sensor error, and a couple other expected ones due to the contactor opening. So I just received a good used sensor from another member here, and will install it all back in, in the next few days. No worries on the BMS itself, it's definitely fixed. And others are working on cloning the MB-only current sensor that's tailored just for MB's use, and not available for sale. So things are really looking up for this problem overall.
 

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How to test CS? Schematic?

I work around the CS avoiding ever including it in any charging hookup circuit. Allegedly it dies accidentally, mysteriously unlike other electronic devices. Not to mention the emotional reactions that the lowly CS engenders here in this forum. I say it is time to assemble a complete data sheet and best practices compendium on this bad boy.
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The real strange thing about the current sensor is just the missing collection on information spread all over the web and forums.
Several spend time and came tomsimilar ideas to overcome the issues.
It is really funny to read again and again on the different approaches by newbies.

On the other side i understand also the owners of the necessary knowledge, spend real big effort on solving the issue with the sensor to realise a working replacement.
So just this effort is something to refinance by offering the replacements in a price range of 400 to 500 $ or €.

You could compare the current sensor with a 12V powered router. If you connect him to a overvoltage by mistake or misfunction of the power supply, the power input will burn and no more function is there.
Also no more function on the controller inside or data lines.

Easy methode for a first check is to measure the resistance of the pins against the busbar. Here you can measure at least the leak current of the protection function.
If this is not the case the connection to the current sensor controller die is broken.
By the way the controller inside the current sensor is build on 2-3 chip in package design on a pcb which is again transfer molded with a epoxy including glas fibers.

Better way is to connect it to a LIN master and test the communication.
The requested current value is submitted on LIN Bus PID 0x34.

Other similar looking EBS2 current sensor produced Bosch for other brands and cars response on other PIDs or in another format.
So they are not compatible.

Big challenge of current sensors is the wide bandwidth needed to measure small leakage currents but also the high currents beyond 200A must not cause a measurement error.

The EBS2 from Bosch is also a measurement system and not a stupid open or closed loop current sensor. Even this small device holds more calculation power than installed in the Apollo spaceship:)

Never the less uring Smart design phase they needed even to optimise the internal algorithms for best performance on system level.
 

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So in normal driving you might measure 100A on moderate acceleration? I'm curious how the 55kw Bosch motor will behave with a 72v battery pack delivering a max of 100A. That would be 7kw or some 10hp which could do useful work in another application. This assumes the Bosch would perform in linear fashion. Just winging it here :)
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You mixed something there are 3 stacks each with 31 cells in series. Means 93S with about 3,4V to 4,2 and the peak current is really beyond 200A. The fuse inside trigger official on 225A.

So there are even more than 70kW peak by battery.
 

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So you haven't driven around a level residential neighborhood at 20 mph max keeping the power meter (the gauge on the right) under 7 kw? I believe I have many times, but my car is not here just now so I can't check it out. So given a 72v pack and a 72v controller (400A rated for BLDC or PMDC motors) I figure the 55kw Bosch will perform ok at this low power level just as it does every day in the SmartED. But if limited to 72v will it perform ok compared to 360v?

15 to 20 kw motors are hard to come by so I figure I might as well see how this spare Bosch performs. Sorry for the off-topic sidetrack but this project looks good for this summer.
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I don't think you could get it to draw 100 amps at 72 volts.

The original power control is not likely to vary voltage but will control "on time" so the motor will always get full battery voltage with PWM time control to reduce overall power.
 

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Do you know if the Bosch 55kw motor, or the very early Tesla-produced SmartEV motor, are permanent magnet or induction motors? It might not matter in every case but it would be good to know. Other than that what might be significant is the overall inductance of the particular motor which might render it unusable in a vastly different voltage range ie 72v vs 360v. Indeed the Smart inverter/controller is PWM and not voltage controlling so I will need to closely match motor to controller. Thanks.
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I don't think you could get it to draw 100 amps at 72 volts.

The original power control is not likely to vary voltage but will control "on time" so the motor will always get full battery voltage with PWM time control to reduce overall power.
My understanding is that PWM works exactly as if voltage is being varied. i.e. at 50% duty cycle, the motor "sees" half the battery pack voltage.

Recall that torque is governed by the current the motor draws and motor speed is governed by voltage - the top speed of the motor under any given load being the voltage needed to move enough current through the motor against the induced "back emf (voltage) plus enough current left over to produce the torque needed to propel the car at the desired speed. At 72 volts, the motor will run, but the top speed will be very low and the torque will be low at all but almost standstill speed.
 

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Do you know if the Bosch 55kw motor, or the very early Tesla-produced SmartEV motor, are permanent magnet or induction motors? It might not matter in every case but it would be good to know. Other than that what might be significant is the overall inductance of the particular motor which might render it unusable in a vastly different voltage range ie 72v vs 360v. Indeed the Smart inverter/controller is PWM and not voltage controlling so I will need to closely match motor to controller. Thanks.
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I believe that the 451 EDs use a permanent magnet motor and the 453's use an induction motor - or is it the other way around?
 

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Only if you are talking averages. With PWM the motor makes full power for a short time.

It is kind of like putting an elastic band on the front of your smart car and pulling it, the car would not move. If you applied that pull power to something that stored it then hit the car with a lump of the power every twenty minutes then the car would move very slowly. << That is not a good analogy really but it is early. :)
 

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OK, been thinking. Let's try this way:

Attach one elastic band to your car and stretch it two inches. The car will stay where it is.
Attach a thousand elastic bands to your car and stretch them two inches for half a second. The car will move.
Wait 500 seconds and do it again, the car will move again.

Same average power into the system but the latter will move the car, the former will not.

It is exactly the same as knocking a nail into wood with a hammer. Average power is very small but PWM allows you to get the nail in. You can spread the power over time as much as you want, the nail will not go in.
 

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Ok maybe more concret:
Jeb referenced to a 451 ED2 document -> PSM means permanent synchrous motor
451 ED3 uses the discussed Bosch PSM.
453 ED4/EQ uses a field magnetised synchronous motor or FSM. The permanent magnets of the rotor is there replaced against a coil based system powered over a brush system. Please don't mixed it up with a IPM.
 

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453 ED4/EQ uses a field magnetised synchronous motor or FSM. The permanent magnets of the rotor
is there replaced against a coil based system powered over a brush system. [Jmk2020]
No, not brushes.!! That would be sooo retrograde, even for Daimler :)

Tesla uses two types of motors: 1. induction, where the 'coils' are actually copper rods running lengthwise inside the rotor and : 2. Permanent magnet, where rare-earth magnets are imbedded inside the rotor. Some cars have one type in front and the other in the rear. Induction offers more power and pm is more efficient so pm is usually in front where it does most of the work while cruising. And 'rare earth' elements are not necessarily scarce btw.

Nice to know Smart has pm, thanks JB.
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PWM varies the duty cycle of the pulsating DC voltage with the peak voltage showing full Vsource. But if you read using an average reading voltmeter you very well might get a lower reading. The truth of this to be documented when I setup some stuff here, fwiw.
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As the motor for the Smart 453 is based on Renault technology YES brushes but not for main current like DC-motors but for the field of the FSM. The are service free over lifetime but on indroduction dirt caused some issues :) And PWM is used to generate the current, so voltage is just follow and the DC-link voltage needn't be the Peak to peak.

Search for FSM oder SSM and you will understand.
Even the new BMW iX uses this technology:

 

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These are not brushes as in brushes/commutator but rather brushes/slipring. These just might 'last forever' but I'm sure Elon would never do this.!!
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