Power Control Relay

[AndySpill]

The Power Control Relay (PCR), as I understand it, is a normally closed relay that is present and runs on circuit 42 for Wrangler JLs that have dual AGM batteries by factory design.

To rephrase this, the Etorque, with its 48V battery doesn't have an Aux battery, Fuse 42, or a PCR, and a jumper is built into high amp connection points N1 and N2 in the Power Distribution Center (PCR): i.e. the vehicle's intelligent fuse box.

Anyway, given the PCR's normally closed status, this means that at all times it (the PCR) isn't energized, the two batteries of the dual AGM battery JLs are connected in parallel, which as we've learned can cause a good battery to have its useful life reduced simply because the other battery died. We've heard stories of a bad Aux battery, more than a main one, taking both batteries "out," and how if one battery dies, replacing both is indicated.

..and the PCR it is only energized during ESS events and an instant at cold crank to test the Aux battery to separate the batteries.

Given this, why would it not have been a better design for this relay to have been open when the dual AGM battery JL is parked and no alternator is running to feed both batteries with power? Might this design allow more time for a bad battery to take out a good one in that the batteries would only be connected in parallel when an alternator is feeding them both?

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[YBABRAT]

2 reasons longevity for relay and adding power on cold weather starts.

The system works but compromised by small capacity limiting the charge characteristics of a larger battery. Jeep should have used two batteries of same capacity or made room for a H8 battery size to rid the dual battery setup. I made room for mine easily, so I know it can be done and save on manufacturing costs.

 

[AndySpill]

2 reasons longevity for relay and adding power on cold weather starts.

Thanks for that.

I did think of that: the idea, on your first point, that a relay which is set, be it normally closed as is the case here, or normally open, to that state in which it requires no electrical current, for most of its time, is the more reliable of the two, but there's bistable (i.e. latching) relays too, which remain in the setting (on or off) that the introduction of electrical current to them put them in, even after that electrical current to the relay is withdrawn.

As for cold weather starts and the idea that both batteries in the dual AGM battery JLs provide current for the cold crank, there's nothing, I'd think, preventing the main battery from providing the miniscule electrical current (milliamps) to close a circuit in a relay, to link up the Aux battery to the main in parallel prior to the cold crank. With a bistable relay, this would even be just firmware programming I'd think.

 

[YBABRAT]

Thanks for that.

I did think of that: the idea, on your first point, that a relay which is set, be it normally closed as is the case here, or normally open, to that state in which it requires no electrical current, for most of its time, is the more reliable of the two, but there's bistable (i.e. latching) relays too, which remain in the setting (on or off) that the introduction of electrical current to them put them in, even after that electrical current to the relay is withdrawn.

As for cold weather starts and the idea that both batteries in the dual AGM battery JLs provide current for the cold crank, there's nothing, I'd think, preventing the main battery from providing the miniscule electrical current (milliamps) to close a circuit in a relay, to link up the Aux battery to the main in parallel prior to the cold crank. With a bistable relay, this would even be just firmware programming I'd think.

Whether or not it is bistable. Not having to apply a latch state to start engine, is a feature, when set during parallel mode with engine running, and with ignition off. Which is 90% of the time. So when ignition is off there no need to apply latch. This keeps wear and tear at a minimum. The only time it latches off is when ESS is activated, then latches back on after start to stay that way until the next ess event.

IMO a standard normally closed relay would be a simpler choice as it would only need an ess trigger to open. Once the trigger is inactive, it would close on its own.

The oem main battery can run ess by its self, but when in extreme circumstances with power draw the aux battery boosts the capacity for starting without effecting electronics.

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