[MoonUnit]

Hi all,


I am using the Netgain ACX1 controller, and am in the process of configuring it.


It has a Battery Protection function, which allows you to specify over- and under-voltage levels at which it will shut down charge/discharge, and cut-back levels at which it reduces charge/discharge.


I understand that, in normal operating temperature conditions (say 15deg C, for example), charge/discharge is not really affected by temp, and thus this battery protection method will be fine for regen braking and traction discharge.


However, when it's cold (say 5 deg or lower) I understand that regen may need to be limited to prevent damage to cells.



When it's cold, I understand the pack resistance increases. So if regen braking is trying to charge the pack, and the resistance is high enough, it will push up the pack voltage and hopefully this ACX1 Battery Protection function will stop the regen and protect the pack.


Is the above correct, or will the voltage not rise enough to trigger the over voltage protection when cold, leading to possible damage of the cells from regen current at cold temps?


Much obliged.



[Netgain SME ACX1 Contoller, Hyper 9 Motor, 5 Tesla modules, Orion BMS2]

 

[john61ct]

I don't know, but

Ambient temps are not the issue, but the cell temperature, actually internal but can't measure that so use the skin temp.

The regular charging is just as much an issue, not just regen.

I would just make sure the cells are nice and warm while in use.

Some heat is internally generated at high current rates, but you don't want to rely on that.

 

[MoonUnit]

I don't know, but

Ambient temps are not the issue, but the cell temperature, actually internal but can't measure that so use the skin temp.

Hi John,


this is the crux of the issue. I was going to heat the modules, but I had been dissuaded from doing so as is just one more thing to fail. Thus I was going to rely on the Orion BMS2 to limit the charge rate depending on measured temp. The Orion can communicate this to my charger via CAN, but the Netgain controller is not currently able to limit charging from regen via CAN. All it can do is use the over/under voltage protection.



Hence my question - whether the over/under protection is a useful proxy for temp and implied regen charge rate. I fear not ...

 

[john61ct]

I agree likely not.

Can you just switch regen off when temps go too low?

How do you handle regular charging when everything's all frozen up?

 

[MoonUnit]

Can you just switch regen off when temps go too low?

Yes, I could. It would be better if it were done automatically, in case driver forgets to switch the profile depending on the temp.

How do you handle regular charging when everything's all frozen up?

The BMS won't permit charging if the temp is below a set level, and communicates this to the charger via CANbus. So in the absence of a heating mechanism, one waits until it is warmer ...

 

[john61ct]

Wow, so not your primary transport then 8-D

Yes of course I meant automatically.

If regen can get up to high C-rates, I'd set it to only work in T-shirt weather.

 

[OR-Carl]

Hey Moonunit, I am working on a similar setup, so a lot of your questions are things I have been thinking about too. I am thinking that I am going to try and implement a heated coolant loop of some sort. If there was a reservoir with a normal hot water heater element in it, it could probably use pack voltage to quickly bring the temperature up high enough that regen/charging would not cause damage to the cells. It really shouldnt take that much power to raise a few gallons of coolant up to 40-50 degrees F.



I was thinking that if you had a system like that, you could use a temperature controlled relay driver to set the regen profile by monitoring the coolant tank temperature. That way you could drive off with the regen disabled by default, and once the system was up to temp it would automatically switch on one of the other profiles. The relay board could also act as a thermostat for the heating element.



I look forward to seeing what you come up with for your system!

 

[MoonUnit]

Hey Moonunit, I am working on a similar setup, so a lot of your questions are things I have been thinking about too. I am thinking that I am going to try and implement a heated coolant loop of some sort. If there was a reservoir with a normal hot water heater element in it, it could probably use pack voltage to quickly bring the temperature up high enough that regen/charging would not cause damage to the cells. It really shouldnt take that much power to raise a few gallons of coolant up to 40-50 degrees F.

I was thinking that if you had a system like that, you could use a temperature controlled relay driver to set the regen profile by monitoring the coolant tank temperature. That way you could drive off with the regen disabled by default, and once the system was up to temp it would automatically switch on one of the other profiles. The relay board could also act as a thermostat for the heating element.

I'm using the Orion BMS2, and am re-using the thermistors inside the Tesla modules. The Orion can turn on/off heating and cooling (via relays) and I did originally plan to do this. The Orion can set the regen rate via CAN and also via an analogue voltage level between 0 and 5V depending on SoC and pack temp.



I think what I'll end up doing is using that analogue level to interrupt the brake input to the controller. It can be set to only regen on brake pressure, so if it doesn't see it, it can't happen. However, this is a poor solution, IMHO, because it's either on or off, with no graduation. Alternatively, as you suggest, it could be used to select a non-regen profile.


It's disappointing that the ACX1 does not recognise charge limiting via CAN.

 

[electric_jeep]

Hi MoonUnit, besides this regen issue, how has you ACX1 controller been with the Orion BMS? Are you using the Orion2?

 

[MoonUnit]

Hi MoonUnit, besides this regen issue, how has you ACX1 controller been with the Orion BMS? Are you using the Orion2?

I am using the Orion2, but as yet I have not got the controller in the car, so I can't comment on its primary function right now. It has very little interaction with the Orion, given its inability to communicate via CAN.

 

[Immo1282]

How do you handle regular charging when everything's all frozen up?

Don't really see it as a huge problem - Plug in after you stop rather than before you leave for your next journey. Most Li batteries are quite happy discharging when cold, so if you come back from a drive and the batteries have warmed up through use, then plug it in. Would have to figure out how to prevent regen when cold though.

 

[john61ct]

And of course "cold" has wildly varying meanings between say Anchorage and Virginia.