Regen current and max charge current for lithium batteries

[InvalidUsername]

The max charge rate for my lithium batteries is 50A. My controller allows me to set the max regen current. From my observations, this setting is obviously not current going to the battery; it's negative armature current.

When I monitor armature current during regen with the 1314 software those values are well above what is registering on my dash-mounted shunt meter. The difference seems to be proportional based on armature PWM. In other words, if the software shows armature current at 100A and armature PWM at 3%, the shunt meter shows something like 3A.

It's really hard to drive and watch the computer and the shunt meter while things are changing quickly, so I'm not really sure about the exact percentages. But it seems like if I want to limit charging current to 50A I need to determine what a normal PWM is during regen and multiply that with max armature current to get the maximum regen current the system will produce. Which if the 3% PWM is correct and the max armature current is 275A, then I will never have to worry about exceeding 50A during regen because 0.03 * 275 = 8.25, which is in line with the shunt meter currents I've been seeing during regen.

Anyone care to comment?

[Pat911]

I would have assumed that regenerative current was the current going into the battery, but it looks like you’ve proven that it isn’t. Well with Curtis at least.

[InvalidUsername]

The reason I started looking at this is because when I set max regen current to 50A regen basically went away.

Here's a data log of a test I did. Negative values for armature current is when regen occurs. Sorry for the crappy formatting. Armature current * (armature PWM/100) = values that I was seeing on my shunt meter (for example, the first regen value -60 * PWM value of .30 = 18A). I suspect actual regen current is the sum of armature current times armature PWM plus field current times field PWM. The faster the speed and the quicker the pedal is fully released causes increases in armature amps and armature PWM, so conceivably the regen current going to the battery could exceed 50A. For example an armature PWM of 50% at 110A would be 55A of actual regen current.

So I guess it requires finding a balance to get the right max regen setting. I think I'll set mine at 100A because regen works at that setting and I don't think actual regen current will rise above 50A the way I drive.


Armature Current Armature PWM Field Current Field PWM
97 11 3.6 21
33 25 3.6 19
40 29 3.4 18
-60 30 4.4 19
-57 30 4.2 20
-60 29 4.4 19
-60 30 4.6 18
-57 27 4.6 20
-53 27 4.6 20
-53 26 4.4 20
-50 25 4.2 19
-60 40 3.8 17
-67 42 4.4 20
-60 32 4.6 20
-60 32 5 20
-60 30 4.6 21
-53 28 5 20
-50 27 4.4 20
-50 22 4.2 19
-47 21 4.2 20
-43 20 4.2 18
80 47 3.8 28
77 51 4.2 26

[TheCartBoy]

The tuning parameter you have available, regen current limit, this is looking at the armature current only?

[InvalidUsername]

Originally Posted by TheCartBoy

The tuning parameter you have available, regen current limit, this is looking at the armature current only?

This seems tp suggest that it's armature current only. It also sounds like it's current going to the battery, but that's not possible. Probably just more crappy Curtis documentation that often confuses more than it helps.

Regen C/L
50 – 275 A 
Defines the maximum current the controller will supply to the motor during regen braking operation. During regen braking, this parameter controls the regen current from the motor’s armature into the battery.

[Volt_Ampere]

For regen to be effective, the current has to go to the battery. It's true that armature current and battery current differ but at least with my Alltrax, they don't differ by an order of magnitude.

[TheCartBoy]

Invalid, you got me curious about this. I tried this on a 1515 clubcar.

With 1314 you can record data to a text file then plot it in excel.

I added these:
Signed Battery Current
Arm Current
Armature PWM

Then added my own column for Calculated Battery Current, based on your equation (Arm Current * Armature PWM / 100), it somewhat follows the Signed Battery Current, but not exactly.

I didn't have a hill steep enough to see armature regen currents above 80 amps. And the minimum set point for the regen C/L on this is 100 amps. I was hoping to see the effects of weaker regen based on that parameter setting and prove your theory that the current limit is on the armature current only.

Maybe you can try the experiment yourself, does the 1266A have "Signed Battery Current" in the monitor?

[InvalidUsername]

Originally Posted by TheCartBoy

Maybe you can try the experiment yourself, does the 1266A have "Signed Battery Current" in the monitor?

No, I've been wishing it had B+- current. Then it could be precisely determined. I put an amp clamp on the B- cable and got values similar to my shunt meter: 3-25A

[InvalidUsername]

Originally Posted by TheCartBoy

Then added my own column for Calculated Battery Current, based on your equation (Arm Current * Armature PWM / 100), it somewhat follows the Signed Battery Current, but not exactly.

Field current * Field PWM probably has to be added in

[TheCartBoy]

Originally Posted by InvalidUsername

Field current * Field PWM probably has to be added in

You were right. Now the calculated and monitored follow each other.