BQ40Z50-R2: BQ40Z50-R2

Hello Jason,

This gauge uses our impedance track algorithm to measure and predict battery capacity. Here is a document explaining the process, and here is another one. One of the things that is nice about this method is that it has no issue tracking damage/degradation from partial cycles/temperature/any cause. That is because the battery's impedance value shows these changes and we can know by measuring. We also have a parameter called SOH (state-of-health) that can be read from the gauge that tells you the degradation of the cells. Let me know if you have any more specific/follow-up questions.

thanks,

Alex Mazany

Hello Jason,

I accepted your friend request and saw your message. Lets continue this conversation there or in email.

thanks,

Alex Mazany 

Hello Jason,

I'm not quite sure what you are referring to. There is no alarm for SOH on this part; you will need a host controller to read the SOH value and determine from there. We do have alarms for remaining capacity as the battery is being used if that is what you mean. If you have a microcontroller, you could read the SOH and when that reaches 70% then you would be at roughly 70% of the initial design capacity.

thanks,

Alex M.

Hello Jason,

1) The closest thing to what you are describing would be the design capacity register which is just the number from the battery's datasheet. There are some other tools, such as the Qmax which is measured and updated over the operation. There is also a register that tells how many times Qmax has been updated. It sounds like for what you are doing, you wouldn't necessarily need the max Qmax over the lifetime information. The minimum capacity to guarantee a certain time of operation would be based on the current capacity, which you could read from the updated Qmax. I don't see why it would depend on the initial capacity.

2) The impedance is used by the gauge to implement a variety of features. You would not gain much information by reading the impedance directly, but rather from the various registers calculated using the impedance. For example, FCC is essentially Qmax, but using system information and impedance to account for voltage drops to give a more accurate estimate of how much energy can be extracted from the battery under load. 

thanks,

Alex M.

Hello Jason,

Say you need at least 700mah to run for 4 hours, I think it makes more sense to read the Qmax/FCC to see if it is >700mah, rather than try to calculate based on SOH and the initial capacity. I mentioned that you can track Qmax and how many times it has been updated, but I don't think that extra information would be very useful. So I think the latter method (just checking if Qmax/FCC is okay) makes more sense.

FCC is the calculated using Qmax, impedance, and load conditions. I find this image helpful:

The battery may have 1000mah, but under load, the voltage will drop according to the impedance. This will cause the battery to hit the terminate voltage sooner, and you won't get all of the energy out of the battery. The TRM has an explanation in section 6.1. You can program the gauge with the load you expect to use in your application, and it can use that to simulate a discharge and find the expected FCC.

thanks,

Alex M.

Hello Jason,

There are quite a few options for the load, including user-inputted values. Unfortunately, really complex load profiles can't be modeled well using this. The better you can model the load, the more accurate the gauge's FCC and REMCAP predictions will be. But an approximation will still give you decent accuracy depending on how close it is. Quite a few of these are measured by the gauge, so something like "Avg I Last Run" would adjust on each individual device on the field without any extra math on the host's part. 

thanks,

Alex M.

Hello Jason,

I'm a little uncertain about what you mean by FCC analysis algorithm. If you mean just acquiring an FCC, the gauge calculates that itself based on the load mode configuration you set. If you mean reading the FCC in order to do some calculation on the host, you would have to be more specific about what that calculation is. The built-in PF protections and alerts can offer protection for a large range of failure conditions. As for the the other questions:

1) By two algorithms are you referring to CEDV vs. Impedance track? Or are you talking about constant current vs. constant power mode? Assuming you are talking about the load modes, it is based on the load you expect to see in your application. For example, if the battery is supplying a buck converter, you may see battery current increase as its voltage decreases. However, this is a constant power load which would be well modeled by load mode 1. This gauge uses impedance track, so it isn't possible to use CEDV with it. 

2) By the predictive maintenance initiative, do you mean setting up an alert for when the capacity degrades below a certain threshold? There is a built-in PF alert for this, so it would not take much work to use that. Setting up the host to read that alert and forward the message to the user/maintainer of the equipment would be more effort. But that depends on system-level implementation that I do not know. This is why I have a hard time assigning a time for implementing a feature; I don't know the rest of the system/host that plays a big role in the implementation. 

3) Again, I'm not sure what you mean by this. In terms of tasks to set up the gauge, you do need to identify the CHEMID and run a learning cycle on the battery to generate a golden image for the gauge. We have materials about this, and it does take some effort. This only needs to be done once though, and all of the gauges can be loaded with the golden image to configure them for your application. 

thanks,

Alex M.

Hello Jason,

From my understanding of your questions, you're looking to disable the pack once you pass a certain degradation level. You have to ensure a certain amount of runtime for the system. Let me know if your question is different.

As Alex mentioned, we do offer some features like the Capacity Degradation PF that will disable the pack if the Qmax drops too low. We also report the RunTimeToEmpty, but this will fluctuate with the discharge rate.

It would be difficult to guarantee a minimum runtime without knowing all the conditions (discharge rates, temperature, etc) of the battery since batteries are very non-linear.

Sincerely,

Wyatt Kelle