A solution to charging Li-ion in winter freezing weather: Testing an outdoor temperature-controlled charging system.

[SamRich]

I commute daily on my ebike in Western NY and...

and I don't want to charge by batteries indoors this winter.

I have an unheated, detached garage where I store my ebikes and I have been wanting to build an insulated, heated, fireproof-ish, charging solution that I can use in that garage.

Sort of like a reverse refrigerator with a charger inside.

So here's what I built and plan to test in the upcoming months:

I picked up an old school galvanized garbage can at Home Despot:

Some pink insulation:

a roll of metal sheeting and a heating blanket:

I placed a layer of insulation at the bottom of the can.
Placed a metal plate on top of that and rolled the blanket around the metal sheeting and placed that on the metal plate.
I then insulated the remaining gap and made an insulation bag cover to put on top but under the lid.

And voila! An insulated, heated, fireproof-ish, charging station:

I also wanted to insure that the battery doesn't charge below freezing, in case the heating blanket fails or can't keep up with the cold, and that the heater doesn't overheat the battery on warmer days.

So I used an Arduino that I had laying around and hooked it up to a DHT11 temperature sensor and a relay board to control the heater and charger separately based on temp.

The logic goes as folllows:
If Temp <3C/35F: Turn off charger and turn on heater.
If 3C/35F<Temp <15C/65F: Turn on charger and turn on heater.
If 15C/65F<Temp <45C/110F: Turn on charger and turn off heater.
If Temp> 45C/110F: Turn off charger and turn off heater.

Also added an I2C 2x16 diplay for info.

Here's the actual code:

#include <LiquidCrystal_I2C.h>
#include <dht.h>
int tim = 500; //the value of delay time
LiquidCrystal_I2C lcd(0x27, 16, 2);
int Charger_PIN = 11;
int Heater_PIN = 12;
int PWR_PIN = 13;
int Freeze_temp = 3;
int OP_temp = 15;
int MAX_temp = 45;
dht DHT;
#define DHT11_PIN 2
void setup() {
  Serial.begin(9600);
  Serial.println("DHTxx test!");
  lcd.init(); //initialize the lcd
  lcd.backlight(); //open the backlight
  pinMode(Charger_PIN, OUTPUT);
  pinMode(Heater_PIN, OUTPUT);
  pinMode(PWR_PIN, OUTPUT);
  digitalWrite(PWR_PIN, HIGH);
  digitalWrite(Heater_PIN, LOW);
  digitalWrite(Charger_PIN, LOW);
}

void loop()
{

  // Wait a few seconds between measurements.
  int chk = DHT.read11(DHT11_PIN);
  lcd.setCursor(0, 0);
  lcd.print("Temp: ");
  lcd.print(DHT.temperature);
  lcd.print((char)223);
  lcd.print("C");

  if (DHT.temperature >= MAX_temp)
  {
    lcd.setCursor(0, 1);
    lcd.print("Chgr:OFF");
    lcd.print(" Heat:OFF");
    digitalWrite(Charger_PIN, HIGH);
    digitalWrite(Heater_PIN, HIGH);
  }
  if (DHT.temperature >= OP_temp & DHT.temperature < MAX_temp )
  {
    lcd.setCursor(0, 1);
    lcd.print("Chgr:ON");
    lcd.print(" Heat:OFF");
    digitalWrite(Charger_PIN, LOW);
    digitalWrite(Heater_PIN, HIGH);
  }
  if (DHT.temperature <= OP_temp & DHT.temperature >= Freeze_temp )
  {
    lcd.setCursor(0, 1);
    lcd.print("Chgr:ON");
    lcd.print(" Heat:ON ");
    digitalWrite(Charger_PIN, LOW);
    digitalWrite(Heater_PIN, LOW);
  }
    if (DHT.temperature < Freeze_temp)
  {
    lcd.setCursor(0, 1);
    lcd.print("Chgr:OFF");1
    lcd.print(" Heat:ON");
    digitalWrite(Charger_PIN, HIGH);
    digitalWrite(Heater_PIN, LOW);
  }
  delay(1000);

Note the ambiguous ONF setting (a bug)

Here it is in the garage with the DHT11 sensor in the garbage can..ahem, I mean, in the temperature-controlled charging system:

For remote monitoring, I placed one of my Notion sensors that is part of my wireless home monitoring system, at the bottom of the can.

I can use the puck to monitor temperature, sound (detect smoke alarms), water and motion (for doors and windows) and send alerts to my phone. https://getnotion.com/

I tested the heater yesterday in 10C/50F weather and it performed well.

But might need to add another 60W heating blanket in February when it hits -20C/5F.

Here's a screenshot of the Notion app showing the internal temp of the unit rising after I turned the system on:

So tell me what could go wrong?

 

[Punx0r]

Good idea :thumb:

I'd be surprised if you need an extra heating blanket if it's used indoors (garage/workshop) as the volume is pretty small and well insulated. If it doesn't hold temperature.

 

[LuboN]

If the battery is frozen, it will take some time to warm up to its core. Because You don´t have temperature sensor inside the battery, the easiest way to sort this out is to delay the charging after the temperature inside the chamber reaches "warm enough". The delay should be longer if the initial temperature was lower and vice versa.

 

[SamRich]

If the battery is frozen, it will take some time to warm up to its core. Because You don´t have temperature sensor inside the battery, the easiest way to sort this out is to delay the charging after the temperature inside the chamber reaches "warm enough". The delay should be longer if the initial temperature was lower and vice versa.

That's a very good point although I don't plan to ever leave it in below freezing temperature. I could have another probe inside to double check in case it was left in a freezing environment for too long.

 

[SamRich]

Just wanted to follow-up after using it for a few months. I has been working great with outdoor temps nearing 10F (-15C).

It's stays pretty solid at 9- 11C (50F). Drops a bit when really cold. Here's the internal temp of the last month.

And here's the temp of in my detached garage:

 

[grindz145]

This is awesome Sam. I want to come over and check this out

I think about this alot myself. I actually have a prototype heater that I'm building for a battery with a controller and a TCO. Ideally bikes would perform this function all on their own. Cooling is actually a much harder problem to solve. Luckily, we don't have much of that issue

Luckily I'm able to bring my bike into my office. Ideally it's a little warmer than 0C too. As long as it's less than like 1C it should be fine though.

I worry about people who aren't even aware of this. Many ebike BMSs really lack the appropriate thermal controls necessary to avoid separator bridging at low-temperature fast charging.

 

[SamRich]

This is awesome Sam. I want to come over and check this out

PM me on FB and we'll set something up!

I worry about people who aren't even aware of this. Many ebike BMSs really lack the appropriate thermal controls necessary to avoid separator bridging at low-temperature fast charging.

To address this issue and the one brought up above. I have a pretty smart BMS that has temp sensors that can turn on and off charging and discharing - totally worth it and it's BT connected to my phone!

 

[grindz145]

Excellent! You're ahead of most BMSs.