CA V3 & Grinfineon 25A controller -> LoVGain kicking in ?

Hi all,

I had my first ride today with my freshly set up CA V3 plus Grinfineon 25 Amps controller plus MAC Hub Motor in the rear.

I am running a 10s5p battery made from Samsung 29E 18650 cells. So I set up the CA accordingly:

• Li-Ion cell chemistry

• 14.5 Ah battery capacity

• 10 cell count

• 30V Low voltage cutoff

Ok, this looks reasonable to me based on the cell specs and my experiences with my battery packs with Kuteng controllers. I was riding my MTB with PAS sensor enabled and mostly around 80-240 Watts "base" power level with a PAS ratio of 4 Watts per RPM but this just as a side note.

On my way back home I had used up something like 8 or 9 Ah of my battery and the voltage shown was around 33-34 Volts. So for my everything looked fine and dandy. With my other bike featuring a 15 Amps Kuteng controller I would still ride a battery in such state at lower power levels (e.g. 150 Watts) until it reaches a voltage level around 30 to 31 Volts. Never had issues with this.

The CA showed an empty battery in the SOC icon on the left side of the screen. Suddenly power from the motor stopped although the battery still had enough voltage (34V > 30V low voltage cut off). I lowered the low voltage cut off to 28V just out of curiosity and had power from the motor again but just to be without support a few minutes later. Now I found a parameter called "LoVGain" in the Battery configuration section. For me this was set to 800 by default. Funny enough the original CA guide from Grin doesn't say anything on this parameter but the in-official guide states that this parameter is connected to some sort for power reduction to protect the battery from further dragging down too much. Also it seems that under higher load (I guess I was possible running a bit to high support level of 150 to 200 Watts) possibly LVC situations might arise where the trottle output from the CA is completely reduced to zero (see page 31 of unofficial CA V3 user guide).

So my questions:
Could it be possible that LVC "kicked" in and simply reduced power output from the controller to zero watts because the battery did not provide enough current ?

The user guide states that one can choose Batt->VltCutoff versus Batt->LovGain. Is this only possible via external CA V3 software running on a PC ? (sorry if this is obvious. I am still exploring the CA abilities :wink: )

I do not think that my batteries have real issues. I just have stressed them a bit with higher loads (> 600 Watts) compared to their usual usage together with Kuteng controllers (more like 4-500 Watts).

Thanks in advance,
Holger

HolgiB said:

Could it be possible that LVC "kicked" in and simply reduced power output from the controller to zero watts because the battery did not provide enough current ?

Click to expand...

The CA won't limit anything because of insufficient current being provided...but it can, if configured to do so, limit because of insufficient *voltage*.

When the current draw on a battery (not how much it provides, but how much the system is attempting to pull from it) exceeds what it is capable of at that moment based on it's State of Charge (SoC) and internal resistance (Ri), the voltage drops (sag).

The user guide states that one can choose Batt->VltCutoff versus Batt->LovGain. Is this only possible via external CA V3 software running on a PC ? (sorry if this is obvious. I am still exploring the CA abilities :wink: )

Click to expand...

I don't knwo the answer to that one, but AFAICR there are a few settings that aren't in the onscreen menus, that are in the PC software. I have never explored that one, though.

I just have stressed them a bit with higher loads (> 600 Watts) compared to their usual usage together with Kuteng controllers (more like 4-500 Watts).

Click to expand...

Well, that's up to 50% higher load than they previously saw. That is very significantly higher load, which causes significantly more voltage sag, and heats the battery more, stresses them more, etc.

Whether that is enough to cause the problems you see, I don't know, but it is possible.

Thanks for your reply !

amberwolf said:

The CA won't limit anything because of insufficient current being provided...but it can, if configured to do so, limit because of insufficient *voltage*.

Click to expand...

This would be also my understanding based on my experiences with KT controllers. They also will not cut off the motor unless the voltage drops below the lower limit configured for the battery.

amberwolf said:

When the current draw on a battery (not how much it provides, but how much the system is attempting to pull from it) exceeds what it is capable of at that moment based on it's State of Charge (SoC) and internal resistance (Ri), the voltage drops (sag).

Click to expand...

I am not shure how much "real time" the voltage display of the CA is but with my Kuteng LCD3/8 displays the voltage values dropped when I used higher current support levels which is normal since the voltage drop over the Ri increases.

I didn't notice any big drop in voltage on my way back home yesterday when power cut off and the battery voltage (34 Volts) was still way ahead of the configured low voltage limit of the CA (30 Volts). I also verified that the voltage of the battery when I got home just to be shure that the CA didn't show any bogus values.

What seems somewhat logical to me:
The CA acts as PID controller with the voltage drop over the shunt inside the controller. Thus adjustments for a choosen power level always have a certain delay. So showing "real" realtime voltage would possibly not be really helpfull since there will be pretty shure some wobble in the voltage. Thus I suspect the CA only shows some smooted / delayed voltage value for the battery rather than what you would see when connecting a multimeter to your battery.

Unfortunatly I wasn't aware of the CA diagnostic screen yesterday where a big "V" seems to indicate if low voltage cut-off kicked in. If this was the case then still the question remains: Why did it cut-off when the battery voltage was above the lower voltage limit ?

amberwolf said:

I don't knwo the answer to that one, but AFAICR there are a few settings that aren't in the onscreen menus, that are in the PC software. I have never explored that one, though.

Click to expand...

Hm, I guess by setting the lower voltage level to zero it will eliminate this LoVGain stuff in the PID algorithm of the CA.

amberwolf said:

Well, that's up to 50% higher load than they previously saw. That is very significantly higher load, which causes significantly more voltage sag, and heats the battery more, stresses them more, etc.
Whether that is enough to cause the problems you see, I don't know, but it is possible.

Click to expand...

Also true, but I ramped up power only a the beginning of my tour to test out the increase of motor temperatures from my MAC under heavy load when going up the hill.

What is quite different between a CA / Grinfineon combo and a Kuteng controller though it the current drawn from the battery for a choosen "support level". For a Kuteng controller in torque simulation any support level only sets a certain maximum current level. Thus the power (Watts) you get from a battery will drop with decreasing voltage. Not really much but at least something like 25% (10S battery 42V -> 30V).

The CA on the other hand provides a certain wattage per support level which means that the current drawn from the battery with increase with decreasing voltage. This is nice on one hand since you get constant support no matter how low your voltage is but on the other hand puts more stress to your battery which already has declining power the more it discharges.

What seems to match so far though is the SOC diagramm since the Cell volts per charge diagramm (page 15 official CA guide) defines something below 3.5 Volts as "empty battery".

Have a nice weekend !