ISIS Power - use alternator to power engine compartment Powercell ?

[Turbo67camaro]

I have a 3 Powercell ISIS Power system. One in the trunk, one in the cabin, one in the engine compartment. The battery is in the trunk. I'm planning on a 3 wire, remote voltage sensing alternator system, which will likely be a 140amp via the Vintage Air Frontrunner system.

I'm thinking there may some benefit to applying some of the Madelectrical.com wiring tips to my ISIS install. In particular, using the alternator output to power the engine compartment Powercell with the benefit being less total voltage loss across the entire system, by shortening the distance that some of the amps flow. In a standard ISIS install, with a trunk mounted battery and a front engine, the full power output from the alternator would travel all the way back to the trunk incurring significant voltage loss, and then amps to power the front Powercell would have to flow from the trunk to the engine compartment, again incurring significant voltage loss. I'm thinking the below may be more efficient. If anyone has any good or bad comments on what I'm thinking I'd love to hear them, since I'm no wiring expert by any means. I think there could be some risk in doing this in that the front Powercell may be supplied with voltage closer to 14 instead of 12, and I don't know if the Powercell can handle the extra voltage. I think my routing of the remote voltage sensing wire all the way back to the trunk may be overkill as well, and perhaps routing it only to the engine compartment junction block would be more reasonable. Use of a 1 ga alternator to battery charge wire may be warranted in this case as well since ISIS recommends a charge wire that can handle the full alternator output (140 amps in my case) in a 3 wire alternator scenario.

92820

[Turbo67camaro]

I talked to Mike at ISIS today about this design and he thought there weren't any issues with it overall. The Powercell has internal controls to shut off power output at ~18 or 19 volts, so having access to higher voltage from the alternator in the 14 volt range at the junction should not be a problem. He thought a 4 gauge high temp charge cable with a 150 amp fuse close to the remote solenoid in the trunk would be sufficient, although I may go with a 2 gauge wire just to be sure. I think the 2 gauge wire has the potential to charge the battery a little too fast if the battery charge is low. Perhaps the newer batteries can handle a fast charge better than the old ones, in which case a fast charge may be a good thing, but I think on old school batteries a fast charge had a negative impact on their lifespan.

He also thought that the remote voltage sensor wire passes such little current, that there would be little voltage loss over the long distance between the alternator and trunk, so a smaller gauge wire could be used for that. I've seen some recommendations for the sense wire ranging from 14 gauge to 10 gauge, so I need to dig more to figure that decision out. I've not been able to find documentation on how much current is likely to flow in the sense wire to calculate the voltage drop (i.e. E = I x R - where E is the voltage drop, I is the current in amps, and R is the resistance in ohms).

[Turbo67camaro]

DelcoRemy information on remote voltage sensing:

http://www.delcoremy.com/Documents/Flyers/Delco-Remy-Remote-Sense-Flyer.aspx (http://www.delcoremy.com/Documents/Flyers/Delco-Remy-Remote-Sense-Flyer.aspx)

"If installing an alternator with Remote Sense capabilities in a vehicle that does
not have a Remote Sense line, connect a fused (5 Amp) insulated wire from
the Alternator Remote Sense terminal to the positive (+) battery terminal or the
common distribution point such as the starter solenoid battery (+) terminal.
Use a #16 gauge red insulated wire, preferably with a 1/4” ID Convoluted
Polyethylene Conduit. Also install a standard inline fuse holder with a protective
cap. Use a low voltage (5 Amp) automotive standard blade style fuse."

Their recommendations are not likely expecting a sense wire going all the way to the trunk. No luck yet on confirming about how many amps flow through a remote sense wire to see if it makes sense in a trunk mounted battery scenario to use 14 gauge or larger sense wire. If the amps are small enough it won't much difference either way.