GEN 4 Disconnecting the Battery Sensor

While venturing out into the cold this morning to charge the battery on my Gen 4, it occurred to me that if I unplug the wires to the battery sensor in the earth lead that it might disable the stupid BMS and it would make the alternator charge properly.

It cuts the charge right back within a couple of minutes, so unless I drive 4 hours a day it is never going to charge the battery by itself- I actually bought a new battery when the last one went completely flat and didn't seem to accept a charge from the car when I jump started it (D'oh- I forgot about the stupid BMS!)


Or is there a wire on the alternator that can be disconnected to remove BMS control and make it revert to voltage sensing? (The alternator is a bit harder to get at than the battery sensor though.

The only worry is that it will somehow cause the ECU to throw a wobbly and put it into limp mode or something.

Is there a description in the manual of how the BMS works and is wired?

 

I have had mine disconnected from the battery for the last six months. No dash warning lights or anything. It certainly keeps your battery charged a lot better. 
Beforehand my tracker was always sending me a notification to say it going into sleep mode due to vehicle battery being low. That  used to happen within 5 minutes of parking up, after an hour's driving.

I think the BMS just charges the battery enough to start the engine next time and doesn't want to keep anything in reserve.

Soeley wrote:

I have had mine disconnected from the battery for the last six months. No dash warning lights or anything. It certainly keeps your battery charged a lot better. 
Beforehand my tracker was always sending me a notification to say it going into sleep mode due to vehicle battery being low. That  used to happen within 5 minutes of parking up, after an hour's driving.

I think the BMS just charges the battery enough to start the engine next time and doesn't want to keep anything in reserve.


 

What do you mean "disconnected from the battery"?

Have you just removed the false negative terminal clamp with the electronics and milliohm shunt and joined a new clamp onto the remaining earth lead, leaving the sensor dangling with it's cables connected, so it thinks that the battery voltage and current are zero? (I think- unless there is an earth in that bunch of cables rather than off the shunt)

Or have you just unplugged the connector off the sensor, leaving the milliohm shunt in series with the lead, but the sensor unable to report anything?  This is what I propose- as it is simplest and  I don't have any JIS clamps.


I've seen posts about always charging though the milliohm shunt, by connecting the charger to a chassis earth so the BMS knows the battery has been topped up, but I just take no notice, as even if the BMS did know I'd been topping up the battery (which I seriously doubt, but wouldn't put it past the systems to be on all the time flattening the battery), it would cut the charge back even more!

Yes, I think the BMS just puts back what it thinks came out on starting, then cuts back to a small trickle charge, it assumes that there was no self-discharge or parasitic draw.
I know the idea is to reduce emissions by 0.00001g per mile (every little helps!) but it just doesn't charge the battery properly below the 1200 miles a month expected use case.

The Other Car is even worse, the parasitic draw is huge, and it takes about 8 hours a week on the optimate to keep it from shutting down the locking and interweb connectivity)

I disconnected the connector to the shunt, capped off the shunt with a blanking cap and wrapped the lead connector in self amalgamating tape.

So at a quick glance it looks as it should at the battery earth post.

Brilliant!
I'll get that done then.

I still have to charge The Other Car weekly though, it gets even less use and the parasitic draw is immense running perimeter detection interweb connectivity, listening for the key etc.

I expect it will also disable the extra charge when the steering is turned and the air con is running, but there will be no need if it runs constant voltage, the alternator will just max out when you turn the wheel and drop back as the voltage recovers like they did for fifty odd years before BMS was invented.

BMS is just another "solution" looking for a "problem" IMHO.