# Sendyne



## onegreenev (May 18, 2012)

I have lots to learn. Anyone want to help?


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## onegreenev (May 18, 2012)

Yup, just diving in head first into the frying pan.


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## onegreenev (May 18, 2012)

Did my initial setup and basically I need to do a setup with some A123 cells and charge them and discharge them and see what the results are with this device and to measure temp during the entire charge and discharge cycle. Do it again and again to check accuracy. I'd like to do split voltage divider among two cells. If one is off from the other I'd like to know during the charge discharge cycling. Not sure if I can do a voltage divider yet. I think I can only check voltage at this point. I will do logging and posting results. This may make a great monitor for my pack. A safe BMS of sorts.


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## winzeracer (Apr 3, 2012)

onegreenev said:


> Did my initial setup and basically I need to do a setup with some A123 cells and charge them and discharge them and see what the results are with this device and to measure temp during the entire charge and discharge cycle. Do it again and again to check accuracy. I'd like to do split voltage divider among two cells. If one is off from the other I'd like to know during the charge discharge cycling. Not sure if I can do a voltage divider yet. I think I can only check voltage at this point. I will do logging and posting results. This may make a great monitor for my pack. A safe BMS of sorts.


Looks like a great little unit. So they are only for evaluation? Any idea what they cost?


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## onegreenev (May 18, 2012)

The evaluation is quite usable but mor designed for proof of concept. $300 for the evaluation kit. Going to be connecting it up for testing.


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## Ivansgarage (Sep 3, 2011)

Would there be a way to, like hooking it up to a gas gauge or meter.??



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## onegreenev (May 18, 2012)

Ivansgarage said:


> Would there be a way to, like hooking it up to a gas gauge or meter.??
> -------


I don't think it wii run a fuel gauge. Fuel gauges are not so accurate so not likely any thing else would make it better. Check and see how accurate it is with a gallon of gas in the tank.


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## PStechPaul (May 1, 2012)

That's a very impressive unit with fantastic specs, but I hope they are true and not fantasy. 

I have designed, and currently manufacture, a current measuring device called the Ortmaster, and it can measure full scale currents from 50A to 10,000 amps AC or DC (true RMS). The low range can display current as low as 0.01A, but the basic precision is 10 bits (actually 9+sign), so it can only resolve 50/512 or about 100mA. This is with a 1000A 100mV shunt (also 100 uOhms, as used in the Sendyne), but it is for intermittent duty, so I can overdrive it by 10x for up to 100 mSec.

DC measurement is easier because you don't need to preserve the waveform and you can use active, passive, and digital filtering to read the average DC current. However, I think you can get a false reading by smoothing the waveform if it has high harmonic content like PWM. So it may be suitable for measuring battery current but perhaps not so much for motor current.

The specifications claim a resolution of 3 mA out of FS value of 513 A. This is 5.8 PPM which suggests an 18 bit ADC which resolves 3.8 PPM. Actually, if the input is both plus and minus, that is really another bit. But there is also a claim of uniform resolution of 61 uA, which is 50 times more sensitive, which requires another 6 bits. There are 24 bit ADCs, so this may be possible, but it also means reading a voltage to within 6.1 nanovolts. 

Without serious lab instruments, proving or disproving these claims is impossible, so I question what the required accuracy and resolution needs to be. Overall accuracy, I think would not need to be any better than 1%, especially if it is guaranteed to be the same for charging and discharging. It does not matter if you read 50% SOC or 51% SOC as long as it is consistent. If you need to detect very small currents to totalize amps in and amps out for coulomb counting, then a higher resolution might be needed. I suppose the 3 mA is reasonable, which corresponds to 100Ah over a 3.8 year period, but I question the need for, or ability to measure, current as low as 61 uA, especially in a noisy and temperature variable automotive environment.

My point is that it should be possible to accomplish much the same function for quite a bit less. A proper 1000A shunt such as I use is only about $35 and should be subject to much less temperature variation than a small PCB shunt as pictured. Remember that 500 amps into 100 uOhms is 25W, and what I see looks good for only maybe 5W at best. A good $5 instrumentation amplifier can boost the 50-100mV to about 2-4 volts for the ADC, and with 12 bits you can read to 122 mA. You can use an isolation amplifier or you can convert to digital and use less expensive isolation components.

Of course, this is a complete solution for $300, and probably considerably less for just the components in some quantity, so it may be worth the cost.


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## onegreenev (May 18, 2012)

Well measuring AH and coulomb counting this way may be moot. There is a group working with magnetics to determine SOC for your pack and so far it has proven quite accurate even when cold or hot. Even when the battery is old or new. 

http://www.cadex.com/_content/New_Advances_in_Lithium_Ion_Battery_Fuel_Gauging_Final.pdf


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## PStechPaul (May 1, 2012)

That's an interesting article. It compares several methods of determining both SOC and SOH, and the much touted Coulomb counting is not necessarily as accurate as often claimed. I think there is a large region from about 20% to 90% SOC where voltage variation is too small to be conclusive, and keeping track of current (or power) in and out may be best. But at the extremes of SOC the voltage change may be enough to recalibrate the calculation, especially for determining SOH, which diminishes over time and number of cycles. 

Since a 100 Ah cell may start out as 105 Ah capacity and then deteriorate to, say, 80 Ah after several years or a couple thousand cycles, and each charge and discharge operation may have a diminishing effect on capacity (but perhaps not symmetrically), there may be a shifting effect with Coulomb counting that might only be determined and corrected when the cell reaches close to its limits. So, unless the magnetic measurement system becomes available and is proven, the best method may be an occasional "calibration" involving a full charge/discharge cycle to determine SOH, and then monitoring the energy transfer over time should be accurate enough for perhaps 100 cycles or several months. So it does seem that extreme accuracy and low current sensitivity are not necessary.


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## tomofreno (Mar 3, 2009)

onegreenev said:


> Well measuring AH and coulomb counting this way may be moot. There is a group working with magnetics to determine SOC for your pack and so far it has proven quite accurate even when cold or hot. Even when the battery is old or new.
> 
> http://www.cadex.com/_content/New_Advances_in_Lithium_Ion_Battery_Fuel_Gauging_Final.pdf


 Thanks for the link. From the article:


> It is with good reason that I chose a lithium ironphosphate battery to highlight the efficacy of our magnetic sensor. As illustrated in Figure 5 and described above, these batteries are notoriously difficult to monitor - other techniques that attempt to gauge the amount of energy remaining in these batteries are ineffective. Indeed, the inability to precisely monitor lithium iron phosphate batteries have limited their station in the marketplace.


 Huh? I've had no significant problem with my Coulomb counting TBS gauge over the last 4 years and 28k miles on my LiFePO4 cells. Sure it may drift a couple Ah (180Ah cells) over a few partial charge cycles, but it automatically re-zeros at the end of every full charge, or I can easily manually reset it. The numbers for Ah used on trips I regularly do are spot on, e.g. always 72 - 74 Ah used to the top of Mt. Rose summit. No more variation than I would expect due to the slightly varying driving conditions trip to trip. 

Looks like an interesting possible approach, but it is not clear to me that it is inherently more accurate than Coulomb counting. For example, how do you account for the effects of current due to free charge in the material when attempting to infer changes in the bound charge current density by measuring changes in the magnetic field?


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## PStechPaul (May 1, 2012)

This discussion has led me to question what effect temperature has on the capacity of lithium cells (or other chemistries). I found an interesting article which offers a mathematical model of a lithium cell and some experimental verification:
http://www.mathworks.com/tagteam/71...Lithium Battery Model with Thermal Effect.pdf

It seems that there is a significant temperature effect which shows a decrease in internal resistance as well as a large increase of effective capacitance, but a very small increase in voltage. So it may be that a cell which is charged at a higher temperature may attain a SOC which has more energy than one charged at the same current and time at lower temperature. The voltage component seems to be only 1% or so, but the resistive component changes as much as 30% from 5C to 40C, and the capacitance may double or triple (but this may not reflect the capacity).

The ESR is probably easily accounted for as a measure of charging and discharging efficiency and may be modeled as simple wattage based on current and temperature. But the actual capacity seems to be more complex. I have read that lithium cells should not be charged when cold, or at least the charge current should be limited until self-heating or external heat raises the temperature. But I also wonder if the energy of the heat itself figures into the amount of energy stored in the cell? 

So, suppose you charge a cell with a certain number of Ah at, say, 5C, until the voltage starts rising to indicate full SOC. And suppose that it is a 100 Ah cell but it only takes 80 Ah before showing full. If that cell were then heated to 40C, and then discharged, would it still supply 80 Ah or would it supply 100? And if the cell that had been charged at 5C were heated to 40C, and then charged, would it accept the additional 20 Ah or would it still show 100% SOC according to the voltage profile?

If the temperature itself adds to the energy available, then it might not be considered wasted or a loss, and it would be essentially a thermoelectric effect that could boost efficiency of the system by using otherwise wasted heat from the motor and controller to heat the cells.


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## onegreenev (May 18, 2012)

I charged a cell at below freezing and kept the charger on until it was well below zero like 20 or so below. At that point all functions just stop. I took the cell to more than -56 degrees below zero. May have been even colder but I was unable to measure below -56 degrees. I then checked the voltage and it showed 3.33 volts but when I connected a load it only showed millivolts. Even if you wanted you could not extract any thing. I calculated 14aH into the cell before it would no longer accept a charge. Once warmed I got 14ah out. 

Pete


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## ellen.gooch (Feb 19, 2014)

@PSTechPaul, sorry that I just saw this post now. I asked engineering to respond to it. We're happy to answer any questions.

"_That's a very impressive unit with fantastic specs, but I hope they are true and not fantasy. _"

Indeed, all of the published specifications have been measured and re-measured, and re-measured, and re-measured --- with hundreds of tests in the Thermal Chamber (thousands of test hours, as these test are very slow), using precision purpose-built equipment. The datasheets are available on line; the one for the module contains measured data information. You can see it here: http://sendyne.com/Products/SFP100 Current Measurement Module.html (second icon down on the left).

"_I have designed, and currently manufacture, a current measuring device called the Ortmaster, and it can measure full scale currents from 50A to 10,000 amps AC or DC (true RMS). The low range can display current as low as 0.01A, but the basic precision is 10 bits (actually 9+sign), so it can only resolve 50/512 or about 100mA. This is with a 1000A 100mV shunt (also 100 uOhms, as used in the Sendyne), but it is for intermittent duty, so I can overdrive it by 10x for up to 100 mSec._

_DC measurement is easier because you don't need to preserve the waveform and you can use active, passive, and digital filtering to read the average DC current. However, I think you can get a false reading by smoothing the waveform if it has high harmonic content like PWM. So it may be suitable for measuring battery current but perhaps not so much for motor current._"

Well, the definition of a DC level of a waveform over a specific period of time is the integral of that waveform over that specific time period. With filters, if they are linear enough and do not have "peaking" (resonances) at some frequencies (i.e. the good old passive RC filters), the outcome is the same -- if the filter's time constant is long enough.

"_The specifications claim a resolution of 3 mA out of FS value of 513 A. This is 5.8 PPM which suggests an 18 bit ADC which resolves 3.8 PPM. Actually, if the input is both plus and minus, that is really another bit. But there is also a claim of uniform resolution of 61 uA, which is 50 times more sensitive, which requires another 6 bits. There are 24 bit ADCs, so this may be possible, but it also means reading a voltage to within 6.1 nanovolts._"

Actually, this is a little incorrect. The IC has a 24-bit A/D (with sign, so the quantization is to the +/- 2^23 levels), the resolution of the current measurements is about 61 microAmps (about 4.5 nanovolts resolution on the shunt's voltage). The 3 mA you refer to -- is the guaranteed maximum offset current (zero current error); this is for the whole operating temperature range of -40 °C to +125 °C. The reason this is possible is that for the same wide temperature range of -40 °C to +125 °C the IC is guaranteed to have no more than +/- 150 nanovolts (yes, NANOvolts, 0.15 µV) of input voltage offset, while it is coupled to the shunt. Again, the datasheet provides the actual measured data, over the complete temperature range, in a chart form.
That very low offset was the primary requirement when the IC was first envisioned; it allows Coulomb measurements that are accurate for a long interval (since even low DC errors accumulate in long-time charge measurements).

"_Without serious lab instruments, proving or disproving these claims is impossible, so I question what the required accuracy and resolution needs to be. Overall accuracy, I think would not need to be any better than 1%, especially if it is guaranteed to be the same for charging and discharging. It does not matter if you read 50% SOC or 51% SOC as long as it is consistent. If you need to detect very small currents to totalize amps in and amps out for coulomb counting, then a higher resolution might be needed. I suppose the 3 mA is reasonable, which corresponds to 100Ah over a 3.8 year period, but I question the need for, or ability to measure, current as low as 61 uA, especially in a noisy and temperature variable automotive environment._"

We use a custom-built better than 10 ppm shunt (operated at specific room temperature and thermally corrected by the built-in sensor) and 7.5 digits 25 ppm voltmeter for our calibrations (the other equipment is basically referenced and calibrated by these two units, or use ratiometric methods). This gives us a very comfortable TUR (Test Uncertainty Ratio) for calibrating 0.05 % (500 ppm) units.

The extremely small current resolution of 61 µA helps in reducing rounding errors in calculations, as this product is partially analog and partially digital signal processor; besides, deep averaging of the noisy signals can recover usable data. For example, at 1 Hz data report rate, the unit has 1.5 mA rms (Max) noise (specs); at 0.01 Hz -- that value gets reduced by 10 times (square root of 100) to only 150 µA rms. Depending on application, one may or may not need such a high resolution -- but it is always better to have it than not 

"_My point is that it should be possible to accomplish much the same function for quite a bit less. A proper 1000A shunt such as I use is only about $35 and should be subject to much less temperature variation than a small PCB shunt as pictured. Remember that 500 amps into 100 uOhms is 25W, and what I see looks good for only maybe 5W at best. A good $5 instrumentation amplifier can boost the 50-100mV to about 2-4 volts for the ADC, and with 12 bits you can read to 122 mA. You can use an isolation amplifier or you can convert to digital and use less expensive isolation components._"

The SFP100EVB can ship without a shunt, allowing users to connect to any external shunt they like; current ranges scale appropriately with the capabilities of the shunt. 

For $35 you may get, perhaps, a 1 % or a 0.5 % shunt -- and this is for operations typically between 0 °C and 60 °C; shunts with better accuracy can only operate at ONE specific temperature. On the other hand, the SFP100EVB is specified for better than +/- 0.4 % over the full -40 °C to +125 °C temperature range, this is not theoretical but measured and verified.

The shunt selected for this assembly is simply the lowest-resistance off-the-shelf commercially available unit, it is quite small in size; that's why on the SFP100EVB it is only characterized for 100 A continuous operations (at room temperature), 200 A for 1/2 hour, and that 513 A mentioned above (the maximum unclipped current sensed) -- is only for 10 seconds. While the shunt's manufacturer specs it for 36 W, we never allow that much heat to be dissipated for any length of time; local temperature of the shunt (sensed by the circuit, quite precisely) is never allowed to be higher than +125 °C. Irreversible resistance changes may occur in the shunt, if it is allowed to heat up past approximately 140 to 160 °C.


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## Tesseract (Sep 27, 2008)

That was a helluva reply, ellen.gooch. I think I'll have to take a second look at you guys as a result.


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## ellen.gooch (Feb 19, 2014)

We aim to please, Tesseract -- or at least to provide reliable data


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## PStechPaul (May 1, 2012)

Yes, very impressive. It sounds as if you really know what you are talking about, and that helps build confidence in your products. I don't need anything like this at this time, but it's good to know it's available. Thanks for the detailed reply, and good luck!


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## onegreenev (May 18, 2012)

I'll be doing some work with mine here soon. Not a large piece but impressive. I want some good accuracy.


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