Best Way to Measure 12v Battery Current Drain for BCM Power Trick?

[Artric]

I've found that if I grid charge the car with power to the BCM (currently by leaving the key in the ON position with all accessories powered off), the car will count the charge, as long as it is started AFTER the BCM is powered up.

This was discovered using Peter's BCM gauge. It will read all the way up to 100%, then immediately give a positive recal on start of the ICE (which appears to verify that it is impossible in my car to recal without the ICE running). In fact, of the car goes into Auto Stop, or FAS is used, the positive recal will stop counting upward on the gauge, even though the BCM will reset to 80% immediately instead of also climbing like the gauge (if not already reading high from powering the BCM).

At this stage, I'm curious tobmeasure the drain on the 12v battery. Is there any way to do so without purchasing an expensive clamp style gauge? I have a battery tender that runs at 600ma, and I wonder if that is enough to compensate. I also have a unit that charges at 2-10A, but I doubt it is very efficient.

Ultimately, I plan to power the BCM and Peter's gaige by pulling power from my RS-25-12 within the grid charger. Does anyone know how many watts it would take to power that circuit?

My piggyback charger (boosts from 350 to 1400mah charge rate) has an RS-25-12 that is currently doing nothing, so if it is just on the brink of having enough power for it, I have a backup in place.

Any info on this? What's the best way for me to find the current drained and the current needed for the BCM?

[retepsnikrep]

Artric I think this was answered in one of my posts in the grid charger thread some weeks ago. Around 500ma was the answer I think? It also described how to power the bcm without powering up the car using a couple of diodes. I would think your 600ma unit will just about cover it.

[Artric]

Perfect! I'd seen talk about it, but never a definitive answer. Was it in your BCM Gauge thread? I'd like to hear about the setup with the diodes, etc.

Thanks!

[RobertSmalls]

It was in Mike's grid charger thread, iirc. Contains the word "diode" for sure.

[Cobb]

My VOM will measure up to 10 amps. You would just need to disconnect the negative from the battery and put the VOM in the loop in the amp measuring mode and leads in the correct connectors. Of course if you have a fluke, its all automatic.