DC Power Engineering Alternator Current Draw

[Ladybridgeport]

When I receive my three alternators from dcengineering, they supplied a 3/-40 amp relay for each alternator. I connected an O-scope to see what the current draw is since I was taking the power from my rear battery to switch on the relay. One thing I noticed when trying to determine the fuse rating for the alternator turn on is that the current draw for the alternator turn on is in the milliamps. Keep in mind there are 3 hot wires and 1 ground. The ground is through the alternator case and is grounded to wherever the alt is mounted. The 1st hot wire is the output to your battery. The 2nd hot wire turns on the alternator which measures in milliamp current draw. The third hot wire powers the alternator which also draw milliamps in current. Why would they supply such a large relay for the alternator if it's max current draw is not even close to 1 amp?

Edited February 3, 2012 by Ladybridgeport

[Guest DC Power Kyle]

We provide those relays because they're extremely reliable and they have negative spike suppression for the regulator. Plus, it's never a bad thing to have overhead.

[Ladybridgeport]

We provide those relays because they're extremely reliable and they have negative spike suppression for the regulator. Plus, it's never a bad thing to have overhead.

Normally when I go to start my car. I turn on ignition and my volt meter is around 13.4 volts. when running, it's at 15.1 volts

Sometimes when I start my car, the dash volt meter reads 10 volts. when I metered the batteries and alternators, I got a reading of 17.3 volts. then my batteries sizzle, which is hydrogen gas being released from being overcharged. My headlights were dim and all my vehicle accessories were running off 10 volts, every wire connected to my alternators or batteries showed 17.3 volts. I turned my car off & started back up 5 times and problem repeated. this usually only happens in the morning or after vehicle has been sitting awhile. The alternators had a weird smell, not burning more popcorn like.

For my 3 alternators, the 1st is in the OEM location with OEM harness metrapack plug. The second and third alternators turn on with the 40/60 relays supplied by DC power inc the 40/60 amp relays. I used custom metrapack connectors and terminals to make custom length harnesses. The wiring for the relays is as follows: Vehicle Accessory 2 switches on 30/40 amp 12vdc automotive relay that allows power from the battery to a power distribution block which turns on the two DC power inc supplied relays, in turn switch on the alternators (alternator plug wire 1). A separate positive feed for each alternator is fed through the other wire via fused from the batteries (alternator plug wire 2). I kept the wiring the same as the instructions suggested except the relays are under the dash instead of next to the alternators to prevent being exposed to the elements since the car is driven in the winter. Prior to making this change, I called Stan and he recommended 12 AWG power wire which I used.

The problem is intermittent. Alterations to vehicle power system. Removed front battery. Added 9 batteries in the trunk with steel welded battery tray bolts to buts that were welded to body. Battery 1 is separated by a 500 amp isolator relay when engine is off and in crank position. Battery 1 is connected to other 8 batteries in ignition position. 1/0 power and separate 1/0 ground wire run from the battery busbar to the vehicle starter., piggyback from starter with 100 amp fuse to vehicle wiring harness fuse distribution with another 100 amp fuse. (OEM had power wire from alternator to starter piggy backed to battery, then to vehicle wiring harness.) 4/0 AWG power with 400 amp fuse and separate 4/0 AWG ground cable are run from each alternator to the battery busbar fused 400 amps at busbar as well. The following pic is the adapter to extend the OEM alternator harness since I had to make an H bracket for it to fit right. The second pic is the custom harness for the 2nd and 3rd alt. The 3rd pic is the 1st alt with OEM wiring (OEM harness with the extension adapter I made from pic 1). On 2nd and 3rd alternator, the first wire on the plug (at the end of harness) is constant positive and the 2nd wire (3rd position on harness) is hot when vehicle accessory 2 is hot. the last pic is my wiring layout for my accessories. I do not have any stereo equipment installed yet so there is not heavy draw other than the vehicle accessories.