thomasow' SAR and regulating charge current w/ SoC

[john61ct]

From a source I trust, not talking about LFP specifically, but I believe most lithium chemistries are similar in this regard.

>> The amount of current you can push into a battery without damaging it is related to its state of charge (SOC); large for low SOC and decreasing as SOC increases.

>> For example, the Tesla supercharger uses three steps - a high CC at low SOC, lower CC in the upper part of the SOC range, and then CV at the terminal voltage. "Optimal" would probably be a continuous tapering of current as a function of SOC.

_____
Note this is not talking about **current acceptance** dropping due to the chemistry's resistance. In this domain, **chargers** routinely adjust current rates dynamically during a single cycle as part of their regulation profile. A opposed to only holding voltage to a setpoint, as our mainstream marine sources do.

It is very common in EV fast charging use cases to hit 3-5C rates. Of course longevity suffers as a result, but by dropping the C rate as SoC climbs, that "damage" is ameliorated to some extent.

I believe varying from 1C down to .5 or .3C between say 20% and 80-85% SoC could be an acceptable compromise when reducing ICE-charging runtimes is important to the owner.

Much like cycling down to 30% rather than 50% when reducing weight is critical with a big lead bank.

[rgleason]

Recent, Al's response to some of my questions.

Rick,

Hello. Will be looking for Newhaul, and anyone else who happens to make it over. I understand we are largely looking to be there from opening day through Saturday, maybe Sunday. Then the next weekend.

I THINK there are the questions you posted and wanted to ask, see my comments here:



1. Will it support the field currents required for a 200a alternator? How many amps field current? (Balmar ARS is limited to 8 amps I think.)
à The WS500 regulator’s default wiring harness is protected by a 15A fuse. There is the potential to support up to 30A with a custom cable if truly needed. The regulator its self is able to support much higher, it is really the connector which is the limit.


2. Will we be able to charge LifePo4 with Constant Current (user adjustable) and stop when voltage reaches a user set limit (13.88v for example)?
à Yes, refer to the VSR Users Guide (for now, until we get a revised WS500 Users Guide finished) for the details of the CPE. (Charge Profile Entery) and will see there is a lot of flexibility in defining how the regulator behaves. Because of the additional capability in the WS500 CPU, we have expanded that some – please stay tuned for when we get the updated guides posted.


3. Will we be able too then drop down to a lower CC charge rate and set another voltage limit? At which point all charging stops?
à Again, Yes.

4. Can we cut the field current with a NO/NC signal from a BMS?
à You can disable to regulator in several ways via a hardware signal, all depending on your goals. The ENABLE line can be de-powered, turning off the regulator. If CPE #8 is selected the Feature-in wire may be used to force the regulator into ‘Float’ mode (and of course, you can set Float to do what every you want – including turning off the regulator). And as a safety stop you could place a NC relay into the ALT+ line, we recommend that vs. the Field line as it leaves the flyback diodes intact.

5. Can we control a disconnect relay to disconnect the charge bus? With appropriate user settings?
à No, not from the WS500 regulator. This is really the preview of a BMS. Prime concern is: The WS500 regulator does not have the ability to see cell level details like a proper BMS dies.


As to sharing a WS200 shunt, I am not sure. Looking at the photos it seems a rather integrated unit and I am not sure if there are any attachment screws to allow access. If there are, the default 500A/50mV calibration on the WS500 could early be adjusted if needed.

And yes, the WS500 is indeed a continued and improved Gen-4 regulator. We are using a more capability CPU to allow better processing, but also provide additional room to enable new (and future) features (I was at 96% code space utilization on the VSR Gen 3). Over the past year I have integrated my learning’s (both hardware and software) from the work of Michael Frost. The MISRA coding standard has been applied and the code is mostly compliant (some issues still with a few supporting libs) to bring additional reliability to the project, that combined with increased robustness of the hardware and literally 1,000 of hours of in-house testing.

Hope this has answered your questions.

-al-

[john61ct]

good stuff