Enginer PHEV automatic over/under voltage protection

I've started talking to a robotics guy I know from the local EV club about how we can use the balancer's warning to trigger some sort of pack disconnect. IMO this is pretty simple thing to do and can be done without cutting anything, and very minimal rewiring. I'm just not an electronics guru, so I need help to put it all together.

My current thought is to use a simple VOX circuit (microphone activated switch) that is triggered by the buzzer on the balancers. The VOX circuit will feed a signal to a programmable micro controller (the arduino is what I'm familiar with and its cheap). The micro controller will then control a relay to disconnect the pack from both the charger and dc to dc converter. This allows protection from both over and under voltage.

Once the pack is disconnected, we need to reconnet it somehow. But, with the arduino, we can do pretty much anything with it. We could wait an hour then reconnect the pack, hoping that the balancers have pulled the high cell back down and continue to top off the pack. As soon as the buzzers go off again, it would disconnect for another hour. Another alternative is that we could wait for a manual signal from the user to connect the pack again. This signal could be from another switch added up in the dash area, or even from turning the phev system of and back on (this would require tapping into the phev switch). At that point, the pack would be reconnected and ready to go.

The setup would cost less than $50.

The drawbacks of course are you are stuck with the balancer's set voltage points. Personally, I'd like to adjust them a little bit. However, this is a quick fix and I'm hoping Enginer eventually comes up with something on their own.

Thoughts?

 

True, that is a possible problem. You might have to hit a reset switch to get the pack to reconnect. Or, the sensitivity of course could be adjusted with the circuit posted. Another alternative is with the arduino you could even program it to ignore other noise and have the mic only listen for the beep. I think this is probably overkill. I think if you have noises as loud as those buzzers going off in the case, you have other problems.

 

I ordered the VOX circuit this morning. The current plan is to just deal with charging. This seems to be the area where we are having most of the problems due to charging unattended and not being able to hear the balancer buzzers going off.

I am thinking that I will make an additional box that goes between the charger and the wall. Inside the box is the VOX circuit, arduino, a wall wart (for 12V power), and a solid state relay. There will be leads going to the inside of the phev box to the microphone. Since we aren't charging on the go, sound won't be an issue. When the balancers go off, it cuts power to the charger. Pretty simple. Once the charger is unplugged, the arduino powers down and it operates as normal.

I'll keep this thread updated as I build it.

 

Well, I may or may not complete this project if Jack comes out with the new balancer that controls the dc to dc and charger.

In any case, there would be no way to differentiate between false and true alarms with this setup. However, if you start up the charger and the alarm goes off again, it simply shuts it down again. So, no worries there.

BTW, how do you qualify a false alarm?

 

Interesting. I could program the arduino to watch for situations such as these. Say, the alarm must beep 5 times before it cuts power to the charger.

 

Unfortunately, once you get the alarm signal you have to have some logic behind what to do with it. Do you want it to disconnect the charger until you hit a button? Do you want it to turn off for 30 minutes? If you just hook it up directly, it will turn off the charger until the alarm stops sounding, then it will turn the charger on again. This is why I am using the arduino. Once I get this circuit setup, it would probably work just fine with your cell monitor's alarm. You just would hook it up where my vox circuit would normally connect to.

There are simpler ways of doing this with specialized chips. I just don't know how to do that. Plus, the arduino isn't expensive and you can do a lot more with it if you want.

 

I started and mostly finished the coding for the arduino during lunch today. I added a lot of comments (everything after the //) so hopefully someone other than me can understand how it is operating.

If it is complete gibberish I can type out how it is working.



/*
PHEV Automatic Charger Disconnect
This program monitors a signal from an alarm. Upon
getting a verified signal that the alarm is going off,
the Arduino disconnects power via a relay.
*/

const int AlarmPin = 1; // pin to monitor alarm signal
const int RelayPin = 2; // pin to signal the relay
int AlarmPinStatus = 0; // relays AlarmPin status
boolean RelayPinStatus = true; // RelayPin on/off
boolean AlarmCheck = false; // makes sure alarm goes off before counters can increment again
int AlarmCounter = 0; // counts alarms to verify true/false alarm
unsigned long LastAlarmTime; // time since the last beep
unsigned long ChargerOffTime; // time since the charger was turned off


void setup() {
pinMode(AlarmPin, INPUT);
pinMode(RelayPin, OUTPUT);
digitalWrite(RelayPin, HIGH); // turn relay on
}

void loop() {

AlarmPinStatus = digitalRead(AlarmPin); // read AlarmPin status

if (AlarmPinStatus == HIGH && AlarmCheck == false) { // check for alarm & alarm check
++AlarmCounter; // increment alarm counter
LastAlarmTime = millis(); // set last beep timer
AlarmCheck = true; // prevent AlarmCounter increment until alarm turns off
}
if (AlarmPinStatus == LOW) { // verify alarm is off before counters can increment again
AlarmCheck = false;
}
if (millis() - LastAlarmTime > 20000) { // if it has been more than 20 seconds since the last beep
LastAlarmTime = 0; // reset last beep timer
}
if (AlarmCounter = 15) { // if alarm has gone off 15 times within 20 seconds
AlarmCounter = 0; // reset AlarmCounter
digitalWrite(RelayPin, LOW); // turn charger off
RelayPinStatus = false;
ChargerOffTime = millis(); // set charger off time
}
if (millis() - ChargerOffTime > 3600000 && RelayPinStatus == false) { // wait 60 minutes with charger off
digitalWrite(RelayPin, HIGH); // turn charger back on
RelayPinStatus = true;
}
}


Wow, thats really messy and hard to read on a forum...

In any case, that part is pretty much done.

 

Well, timing is going well. I received the VOX circuit tonight. The kit is pretty small, so I went ahead and soldered it up tonight.

Kit and contents.





The assembled kit. I must say, the kit is pretty straight forward, but there are no step by step instructions. So, you really have to be careful about getting things in the right place (only had to move one item I had soldered down), and getting polarity right and things like that.





Its getting late for me (wake up at 4am for work blah), so I'll do some testing later this week. I'll get some video and adjust it or something.

I'll be going to the local EV build this weekend. At that point I'll be picking up a solid state relay from a member of the group.

 

Thanks for the kind words Brad.

I've also been thinking about how to automatically disconnect the dc to dc converter and I think I have it figured out. The idea is to tap into the ethernet line that goes up to the switch up front. This can be done with connectors so install is very easy and no wire cutting is necessary. The switch up front sends a 12v ready signal to the dc to dc converter. I will use that 12V to power the arduino and another relay. The relay will disconnect 12V power after the arduino thus keeping power to the arduino, but cutting it to the dc to dc converter. This will also prevent the arduino from drawing 12V power while the car is off. Thusly, if you turn the PHEV switch up front off, the arduino will power down. When you turn it back on, it will restart the program canceling the 60 minute timer currently built in to the program.

Thoughts?