I deeply cycle a group27 Northstar AGM
in my Vehicle with an upgraded charge circuit. The alternator is a Chrysler 50/120 externally regulated model. The problem is the voltage regulator
is internal to engine computer, and it decides either 14.9v, or 13.7v is fine and dandy, with apparently no regard to logic or reason. 13.7v when the battery
is still depleted is infuriating, 14.9v held when I know the battery
is full is frustrating. Sometimes it would choose 14.1v, just to irritate me.
If one tries to bypass the ECM's regulator
, one gets an illuminated check engine light. Can't pass a California
smog test with an illuminated CEL.
I found one outfit claiming to have a 'trick the ECM' device that will keep the CEL off. I bought it and it is a simple 50 watt 10 OHM resistor. It works, but does get very hot. I thermal epoxied a larger finned heat sink to it.
For an external voltage regulator, I picked up a Transpo F540HD originally designed for a Ford for 25$. It has a 2K ohm potentiometer inside it for adjusting voltage.
I bought a 2K ohm Bourns 10 turn potentiometer with counting dial, Depotted and removed the mini voltage pot in the 540HD, soldered wires to its legs. I mounted the Pot on the dashboard next to my digital voltmeters.
I grounded one field terminal on the alternator to its own casing, and ran a 12 awg wire to the F terminal of the 540HD VR. I soldered a ring terminal to the casing of the VR and ran 10AWG to the casing of the alternator. I found a dedicated wire under my dashboard live only with the engine running and ran this to the S terminal. The A terminal, always on, should go right to battery(+), but I cheated and put it on the (+) output stud on alternator. I also put a K type thermocouple in with this new wire harness and thermal epoxied the probe to the alternator casing. The 4th VR terminal, the I terminal is for the Idiot light. I did not use this terminal.
Now I can choose any voltage between 12.8v and 15v from the driver's seat.
The Transpo 540HD gets warm. I added another finned heatsink to its backside.
There is some voltage sag at hot idle, upto 0.3v. My gas engine idles at 525 rpm
when hot, so this was expected.
The dial indicator on the bourns potentiometer is not super repeatable, depending on the state of charge of the battery. One full turn equates to about 0.3v difference.
Idle speeds give it the most issues. At Idle, I can compensate for the sagging voltage by twisting the pot upward, but then of course at higher rpms when moving, it overshoots the voltage. So mostly I don't bother as with this TPPL AGM
there is not too much difference in Amp flow at 14.1v vs 14.4v, and redlights only last so long.
I do crank it way down to 13.0v on some cold starts with a depleted battery and let the engine oil
warm up some before cranking it upto 14.5v and allowing 60+ amps to flow.
The check engine light stays off unless I crank voltage above 14.7v. But it goes out on the next restart. The battery is not inside engine compartment or subjected to its heat.
The temp sensor on my alternator has proven interesting. With ~50 amps total output is registered 119F while moving 25 to 40MPH. Then, when parked and idling making 32 amps total, temp shot upto 139f.
Parked, hot idling and maxed out with lights Blower motor
and everything else on making around 45 to 50 amps, within 30 seconds temp had risen to 160F.
The combination of a moving vehicle, and higher rpms on the alternator nearly instantly have the temperature drop, and idling at a redlight has the temperature increase rapidly when the battery is depleted, and more slowly but still by 10 to 15F when the battery only needs 15 to 20 amps to be held at 14.5v.
As expected, but actual data confirming my suspicions was nice.
The 10 ohm 50 watt 'trick the ECM' resistor visible in background
I ran the twisted leads for the remote
potentiometer through a ferrite and anti chafe sleeve, and used 'amazing goop' as stress relief.
I've only measured a 6.2 amp field current
maximum, at this point.
I can return the original ECM's voltage regulator to duty quite easily in the event of failure. Or just acquire a backup Transpo F 540HD for 25$.
I am very happy with the modification. The only issue is the 0.3v voltage sag at hot idle speeds, and this 'might' be mitigated somewhat if I were to actually hook the VR's A terminal to the battery instead of the ALT(+) stud.
Of course it is a manual system too. Nothing Automatic here, but my personal preference is manual voltage control on all my charging
This inexpensive transpo voltage regulator could be good to have onboard as a backup in the event of a failure at sea.