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Okay, after a number of months of manually disconnecting my battery between trips, I am keen on having this completed. The electrical system has a full-time parasitic draw of .3 amps, which is enough to kill a battery in a short while if left for more than a day at a time. I checked the presence of a faulty diode in the alternator by disconnecting the two positive leads and the draw remained. This project is not only a work around for a short circuit at large but also of use in the case of connecting an auxiliary battery, not to mention coincidental anti-theft utility. I am not sure how kill switches are usually wired, but here is an updated wiring schematic:
The jumper from the negative side of the relay coil to the chassis has the effect of keeping the relay coil energized after releasing the momentary as the negative terminal of the battery connects to the chassis through the main circuit of the relay. This way one need only turn the ignition to ACC then tap the switch to connect the starter battery, then when parked the relay is broken as soon as the ignition removes power from the ACC lead to the relay coil terminal. My remaining problem is the switched 'ACC' 12V lead I am using is pulled from the stereo harness, which actually loses power as the ignition is turned from ACC to ON along with the blower fan and whatever else to conserve energy for the starter.
Pictured is the setup in progress. I tested the current draw of the starter motor with a clamp meter and found a value of roughly 230A. Pictured is a continuous relay with a max rating of 300A. The wiring of the auxiliary battery was hastily added to the diagram and actually needs another switch/relay between the chassis and its negative terminal, which means I also cannot use the chassis for the negative house circuitry.
I am fairly certain that probing around will turn up a switched 12V circuit that does not lose power when the starter is engaged, though it could be difficult so thought I would ask if anyone knows a good place to tap a solid switched 12V. Maybe behind the ignition itself?
I've mounted a few electrical items in that location...the rubber bumper will channel water onto the solenoid in heavy rain. I've been adding standoffs to my devices so they clear the drip zone.
I guess going back to the earlier part of the thread, can you make up a some test cable lengths to try homing in on which leg of the circuit tree is having the parasitic draw? There are just a set number of circuits and paths to ground in that wiring harness. I know someone mentioned pulling fuses to start eliminating possibilities and working methodically through the wiring diagram checking current draws. Some things are energized when the ignition is off, but most should not be. I think I would attack the problem from that end and see if I could puzzle out where that current is going and let that be my guide to find what needs to be replaced or re-insulated. Somewhere in there is a bad component or a bad spot in a wire. Find it and you're home free.
Besides I would need to set up an isolator relay anyway for an auxiliary battery and why not bypass the problem in the process. It's not like there would be any downside to the battery being disconnected when parked, save the clocks being reset. As mentioned in the original post, I tried pulling all the fuses behind the kick panel on the drivers side and the drain remained. I haven't done the same with the fuse/relay box under the hood, but I figure the draw could be somewhere between the battery and the various fuses, and at that notion I had started thinking of a work around.
The setup has been tested with everything in place except a dedicated 12V instead of the stereo's ACC since it shuts off when starting. Therefore I just need to find the most accessible place to splice into 12V switched by the ignition that remains live. If this is not possible, a rocker switch can be in place of the momentary switch with the jumper from the chassis to the negative coil removed and dedicated 12v instead of ACC to the positive coil.
Try IG2 that's ignition key switched on when in start position. You'll probably need to bridge these two together (ig1 & ig2) with a diode array so you're not back feeding voltage to the one that's off. Then you can look at smoothing it if needed for the brief bit where it switchs from one to the other.
Unless you're gonna throw a super capacitor on it to handle cranking time.
really not sure about tapping both ig1 and ig2 concurrently, but I noticed the relay coil draws about .65 amps and the truck usually starts in 2 seconds .. seems like a modest capacity would work but not sure how to spec one. I have a couple lying around most likely for lower voltages that I might try; still I would like to think there is a circuit somewhere that has power in both the ACC and and START position.
really not sure about tapping both ig1 and ig2 concurrently, but I noticed the relay coil draws about .65 amps and the truck usually starts in 2 seconds .. seems like a modest capacity would work but not sure how to spec one. I have a couple lying around most likely for lower voltages that I might try; still I would like to think there is a circuit somewhere that has power in both the ACC and and START position.
650ma is your current demand from a 12.6v source, the nearest resistor size 4.7 ohms and it's going to dissipate 2watts.
Now you plug that into an RC time calculator, assuming your relay stays latched at 9.6 volts and it gives a 2 farad capacitor.. About the size of a 1liter bottle and you don't want that under the hood where it's gonna see high temp changes.
I tested the current draw of the starter motor with a clamp meter and found a value of roughly 230A.
how do you have that plywood attached to the inside of the passenger side fenderwell?
I hope you used a good calibrated clamp meter...i get they are used since they can get a higher amp reading than using a DMM. We can't even use a clamp meter where are work..
11-23-2020, 10:41 PM
