Controller - minimum voltage?

[MCJEFE]

Ok guy's bear with me here... I know that I am asking a vague question but what's the minimum voltage that different controllers will operate at before shutting down? I think that I've read 44v for some.

I may be opening pandora box and I myself have been a big supporter for using LV disconnect to protect the pack. What I'm wondering is if is reasonable to use built in minimum operating voltage of the controller protect against over discharging?

The only incidences of over discharging damage that I am finding is due to improper storage, not due to running the batteries dead from driving... Here's my thinking, if the various carts controllers have a minimum operating voltage for example of 44v will shutdown the the lowest cell voltage would be 3.14v which still a reasonable distance from the 2.5v minimum.

Of course this assumes that the pack is properly balanced as the controller is only concerned with total pack voltage.

Who knows what the minimum voltage is for different types of controllers?

Thoughts?


Sent from my SM-G960U using Tapatalk

[Sergio]

I wrote about this subject a while ago for Alltrax XCT controllers and how to use the Low voltage setting for both limiting the current and providing a sort of "limp mode".

The Alltrax XCT will both limit the overall discharge current in order to keep the pack above the low setting and will also limit the Regen current to keep the pack voltage below the High voltage limit.

I think most OEM controllers have a very low setting, around 40v or so since they are not interested in protecting batteries, but just being operational.

[fstop]

Originally Posted by MCJEFE

Ok guy's bear with me here... I know that I am asking a vague question but what's the minimum voltage that different controllers will operate at before shutting down? I think that I've read 44v for some.

I may be opening pandora box and I myself have been a big supporter for using LV disconnect to protect the pack. What I'm wondering is if is reasonable to use built in minimum operating voltage of the controller protect against over discharging?

The only incidences of over discharging damage that I am finding is due to improper storage, not due to running the batteries dead from driving... Here's my thinking, if the various carts controllers have a minimum operating voltage for example of 44v will shutdown the the lowest cell voltage would be 3.14v which still a reasonable distance from the 2.5v minimum.

Of course this assumes that the pack is properly balanced as the controller is only concerned with total pack voltage.

Who knows what the minimum voltage is for different types of controllers?

Thoughts?


Sent from my SM-G960U using Tapatalk

I know the Navitas I'm using has a LV mode that limits current at around 40v, but the set point isn't changeable. As mentioned above it's mainly to protect the controller itself I think.

I've been in contact with them on a few niggles I've had with the controller's manners, and they've implemented changes in beta FW. I'm on a 3rd beta firmware now and recently they've added a parameter to limit current for some of the drop-in lithium options out there (Allied mainly, I'm guessing), and that parameter can be input to whatever figure (up to 600a).

I think they'd possibly consider adding LV protection parameters as well if they are convinced of the value (and there is sufficient programming capability and memory in the controller) of it and it could be done effectively.

I know my eBike has this functionality in the controller and is user-programmable, and like the low voltage mode in the Navitas, performance begins to get very sluggish and slow when it hits the threshold you set.

[Sergio]

An adjustable High Voltage setting is also important for folks that use Regenerative brake.

Ideally You need both battery current limit and battery voltage limits to get the best performance out of the controller.

[fstop]

So I had an email exchange with one of the (very capable) Navitas engineers on another point, and mentioned the value of having programmable LV behavior in the controller FW.

Me:
On another note, some discussion on a technical golf cart enthusiasts' forum has involved utilizing simpler BMS systems in lithium pack builds, and the benefit that having programmable low voltage behavior in the controller itself (vs the BMS) would provide.
I know you and I briefly discussed via phone the TAC2's LV behavior (I"m guessing set where it is primarily to protect the controller itself), and I'd think allowing another user definable (higher) LV setting that would react similarly would be something possibly worth considering as your FW builds increasingly allow for flexibility with regards to lithium packs. Even with a competent BMS that provides ample cell protection, it would be very useful to have a definable point where it was obvious to the average driver (especially those that didn't build or install the pack) that the battery was low and it was time to think about charging or stopping. Some of the SOC monitoring solutions out there for lithium at the moment aren't the best, and with the TAC2's wide range of acceptable voltage, flexibility in defining a LV point at which current limiting begins could be a huge plus I think.

Navitas:
...We are going to be adding more parameters to the controllers to account for the lithium batteries that are now available...

I think they're up on what improvements could be programmed into their hardware, and they've been very responsive as far as my experience goes. Everybody on the forum generally says the same of the Alltrax folks, so hopefully we'll see some useful options in coming FW revisions for both types of controllers.