Best lithium setup for Navitas 600/5kw?

[fstop]

Originally Posted by Sergio

The actual question if You want to ask them is:




If You can post their answer or any comments they have it would be nice to understand the capabilities of the Navitas AC Controller.

I see from other threads that Navitas is adding a lot more configuration parameters to deal with different lithium battery packs and BMS limitations.

There will be a drop down box to choose which type of battery (a number of specific ones, including RoyPow, will be choices) on a dealer app update early next week. This I'm told from a conversation about something else a few days ago with one of their techs.

One thing to note from this conversation is that they've found the RoyPow batteries aren't happy with high current regen levels, and can trip the BMS. I didn't ask about other batteries, but these are the kinds of parameters they were having to research etc... before offering options in the app.

He was interested to hear that I've never had my BMS trip, even when hard testing my mechanically actuated braking regen control. It's in another thread, but basically allows regen to be at a base level under normal driving, but with more than a pre-set amount of brake pedal travel, begins to increase off-throttle regen proportionally to continued brake pedal travel. This results in additional braking power (additive and in tandem with the mechanical brakes) and a (IMO) better braking "feel", while at the same time greatly reducing required physical brake pedal pressure.

When testing this mechanism out, the regen is cranked up significantly during hard stops, yet I never had a BMS reaction from it. By design it doesn't change regen much if at all during "normal" gentle stopping.

I'm thinking that there could be some variability in the BMS parameters of these packs depending on production date, and that only makes things that much harder for Navitas as far as knowing specific parameters for all the different battery options out there. I'm sure this must be one of many reasons it has taken a while to get this into the app.

[Sergio]

The BMS tripping during Regen is directly related to how much "head-room" you have available between the charging voltage and the cell "HV cutoff".

I did my first "Pedal Brake Regen" interface with the Alltrax XCT three years ago and it worked really well with the Lead Acid batteries as I could pump as much as 140 amps during "brake".

When I converted to Lithium at the end of last year I changed the electronics to take advantage of improvements I made these past years and due to the fact that at the most I can now pump about 60 amps of Regen current.

The Alltrax XCT does a nice job of automatically reducing the Regen current to keep the voltage below Your maximum voltage setting for the Controller.

I charge my cells to 4.05v and the HV cutoff is at 4.18v so I don't have much room between full charge and the "Top".

However 60 amps is about as much as I need to stop the cart going down hill, I have my system set to gradually raise the Regen current as I place my foot on the brake pedal so I don't have to press the pedal to the point of engaging the mechanical brakes unless I want more braking power.

[fstop]

Originally Posted by Sergio

The BMS tripping during Regen is directly related to how much "head-room" you have available between the charging voltage and the cell "HV cutoff".

I did my first "Pedal Brake Regen" interface with the Alltrax XCT three years ago and it worked really well with the Lead Acid batteries as I could pump as much as 140 amps during "brake".

When I converted to Lithium at the end of last year I changed the electronics to take advantage of improvements I made these past years and due to the fact that at the most I can now pump about 60 amps of Regen current.

The Alltrax XCT does a nice job of automatically reducing the Regen current to keep the voltage below Your maximum voltage setting for the Controller.

I charge my cells to 4.05v and the HV cutoff is at 4.18v so I don't have much room between full charge and the "Top".

However 60 amps is about as much as I need to stop the cart going down hill, I have my system set to gradually raise the Regen current as I place my foot on the brake pedal so I don't have to press the pedal to the point of engaging the mechanical brakes unless I want more braking power.

Sounds like you have your brakes nicely tuned for driveability. Navitas told me there is a way to get an analog input into the controller so that I can streamline my approach, though I imagine it will drive almost identically (but maybe be a little easier to adjust initially).

So I mentioned to them that the system voltage on my cart changed hardly at all during braking, and his response was that the voltage wouldn't increase much but the current was what was tripping the BMS units in some of the RoyPows. Apparently some of them don't want much more than 25 or 30 amps (I think those were the numbers - not positve) on the charge side from what he said.

So I'm not sure if all that is accurate, but that's what he told me, and I think why he was surprised I hadn't triggered the BMS during some of the heavy regen tests. I'll say I've never seen the voltage (I have a display in my dash) ever go above charging voltage during any regen. When I say charging voltage I mean the voltage of the pack 30 min or so after I remove charging. The RoyPow charger has a trickle or float type stage at the end (which they say is fine, but I know you and others have said isn't good, so I have a smart switch and HA program that cuts off the charger when it goes into this mode) and the voltage on the dash meter during this is about 2.5v higher than the pack voltage after it settles for a bit.

[Sergio]

If Your pack voltage does not go UP during Regen then something is definitively limiting the current (perhaps the BMS) after all it does go UP when You plug your charger at a much lesser current.

Your charger is not on trickle mode, it is on "Constant Voltage", mine does the same thing and I let it run for a few hours after the charge ends (automation control) as it works with the shunts to allow any low voltage cell to go up in voltage as any higher cells may be discharged by the shunts.

[fstop]

Originally Posted by Sergio

If Your pack voltage does not go UP during Regen then something is definitively limiting the current (perhaps the BMS) after all it does go UP when You plug your charger at a much lesser current.

Your charger is not on trickle mode, it is on "Constant Voltage", mine does the same thing and I let it run for a few hours after the charge ends (automation control) as it works with the shunts to allow any low voltage cell to go up in voltage as any higher cells may be discharged by the shunts.

So that's good to know - you'd recommend letting it stay in this condition then for a while.

I'll adjust automation accordingly.

Thanks!

[Sampras1977]

Originally Posted by NCPW

Yes, when talking about DC carts but this discussion is about 3 phase AC systems.

No. As I wrote this is first hand from Navitas in reference to the AC system this thread is about (and I am using).

[ecpchris]

Came across another option from a local dealer who sells Evolution golf carts. They have a lithium setup, $3k otd for 110ah version with Club Car bracket, charger and hardware. 5 year warranty. 400a peak discharge. Thoughts on how it will work with the Navitas?

Product Number L48110
FUNCTIONAL SPECIFICATIONS
Norminal Voltage 51.2V
Cell Chemistry LiFePO4
Cell type Prismatic
Cell norminal Voltage 3.2V
Ampere-hour Capacity 110Ah
Watthour Capacity 5.28kwh
Charge Efficiency >98%
Impedance
Cycles @ 80% DOD >3500
MECHANICAL SPECIFICATIONS
Dimmensions (L'' x W'' x H'') (inch) 23＂x 13＂x 9＂
Weight (Kg/lbs) 49.9kg/109.7 Ibs
Case Meterial Aluminum Alloy
Terminal M8 X 1.25 - 20
Inpress Protection Marking IP56
DISCHARGE SPECIFICATIONS
Continous Discharge Current ≤110A
Peak Discharge Current 400A - 15 msec
Protection Recover Automatic (30 sec)
Low Voltage Disconnect 41.6V
Self Discharge per Month @ 25℃ <5%
CHARGER SPECIFICATIONS
Continous Charge Current ≤70A
Max Charge Voltage 58.4V
Over-Voltage Recover Automatic (≤54.4V )

[ecpchris]

Originally Posted by fstop

There will be a drop down box to choose which type of battery (a number of specific ones, including RoyPow, will be choices) on a dealer app update early next week. This I'm told from a conversation about something else a few days ago with one of their techs.

One thing to note from this conversation is that they've found the RoyPow batteries aren't happy with high current regen levels, and can trip the BMS. I didn't ask about other batteries, but these are the kinds of parameters they were having to research etc... before offering options in the app.

He was interested to hear that I've never had my BMS trip, even when hard testing my mechanically actuated braking regen control. It's in another thread, but basically allows regen to be at a base level under normal driving, but with more than a pre-set amount of brake pedal travel, begins to increase off-throttle regen proportionally to continued brake pedal travel. This results in additional braking power (additive and in tandem with the mechanical brakes) and a (IMO) better braking "feel", while at the same time greatly reducing required physical brake pedal pressure.

When testing this mechanism out, the regen is cranked up significantly during hard stops, yet I never had a BMS reaction from it. By design it doesn't change regen much if at all during "normal" gentle stopping.

I'm thinking that there could be some variability in the BMS parameters of these packs depending on production date, and that only makes things that much harder for Navitas as far as knowing specific parameters for all the different battery options out there. I'm sure this must be one of many reasons it has taken a while to get this into the app.

Navitas just released this update a few minutes ago. Pretty slick - it has settings for 72v now as well as drop box for batteries, among other settings.

[Left Coast Kiteboarding]

Originally Posted by ecpchris

Navitas just released this update a few minutes ago. Pretty slick - it has settings for 72v now as well as drop box for batteries, among other settings.

I downloaded it about an hour ago. Gonna go out at lunch and play with it. Really hoping is tuned better for Li packs.

[fstop]

Originally Posted by ecpchris

Navitas just released this update a few minutes ago. Pretty slick - it has settings for 72v now as well as drop box for batteries, among other settings.

System voltage of 72v (or anything up to the max - you've been able to type in the number and not just select 36 / 48 / 72) has been around since my first experience with this controller almost a year ago.

The battery specifics however are new to the dealer app.