Adjustable Automotive Alternator Voltage Regulator

12 volts / 6.8 amperes = 1.76 ohms

Neither Bosch or Mitsubishi ever made an alternator even industrial grade that has this low of resistance in the bobbin. You can measure across the two brushes, engine off, with an ohm meter. But sometimes transient carbon glazing between brush and rotor fouls this up.

I used to wind Delco Industrial 35 and 30 SI 12-volt alternators to 1.70 ohms (full bobbin ampere turns) and wind stators triple Delta to get 145 amps for school buses. Those alternators had Transpo 911-04 regulators bolted to the flat plate on the rear of the alternator. The 04 was self-excited from the stator residual magnetism. No ignition switch wire. Those alternators went from 75-90 amps cold rating to 145, and from 0 amperes at 1,600 rotor RPM to 40+ amperes.

One way to determine what Chinese resistor philosophy is being used is to overload/fail a 50 watt versus a 100 watt wire wound unit. Tungsten maintains a very flat resistance until it melts. But these resistors are most probably nichrome.

The 100-watt resistor price was so cheap I bought three.

MEXICOWANDERER wrote:
These alternators have a 3.0 ohm rotor coil. At 14.5 volts = 4.83 amperes or 70 watts. You can come to your own conclusion about component life-span.

Is the only difference between a 50 watt and hundred watt 10 ohm resistor the Extra Surface area in which to dissipate the heat?



If so hopefully I mitigated that with the added heatsink on the 50 watt resistor.

Can't remember for sure, but believe I have seen 6.8 amps of field current on my field wire from transpo540HD when the battery was super depleted with my DC clamp meter.

May I add that I simply am not comfortable with voltage levels exceeding 14.7. Blizzard weather helps to cool components but even down here I see 14.4 - 14.6 @ 75F ambient. And I am switching to a group 29 AGM. When travel in excruciatingly hot weather I am going to dial battery voltage back to 12.85. The battery will be under-hood. Short runs around the village - 14.5 volts.

A 100-watt resistor is going to run less hot than a 50 watt. These alternators have a 3.0 ohm rotor coil. At 14.5 volts = 4.83 amperes or 70 watts. You can come to your own conclusion about component life-span.

It's about time I email Marles, and request the Megawatt .002 cent pot get replaced with a vertical multi-turn pot. They do make 3-turn 500 ohm pots and they would be cost effective.

I had that VR bookmarked long ago, but gave up when I realized the engine computer would fire up the check engine light and goto default A/F mixture and spark timing, killing MPGs

Thankfully someone else figured out how to trick the engine computer, and I paid some 30$ for what is a 3 dollar resistor. The 10 OHM stamp was filed off.



I thought the 10 OHM resistor was for tricking the ECM into thinking it was still attached to an externally regulated alternator. What I do know is If the ECM's VR would choose 13.7 and I've chosen 14.8v, 30 seconds later the CEL does come on. The light will go out next engine startup, but the code is stored and it defaults to preprogrammed AF mixture and spark timing and MPG suffers. Solution is to reset ECM and then, 14.7v max.

I have put my clampmeter over the 10OHM resistor leads at different voltages with a near fully charged battery, but did not record the data, but it did change as I spun the potentiometer.

My 50 watt resistor does get hot, so I thermal epoxied another heatsink to it. I wonder if the VR in the ECM is getting as hot when bypassed.

I really love being able to nearly instantly achieve absorption voltage, when the RPMS are there, or spin the dial up and watch the amps increase with my digital hall effect ammeter whose sensor os now on a + battery cable, previously on the alternator output(+).

It is a crime when a depleted battery in desparate need of maximum recharge when driving, is only allowed 13.7v, like some some of sick battery torture.

Also the 14.9v My ECM always sought on cold startup for a few minutes is a bit ridiculous. My ECm would occasionaly decide to hit this voltage well after driving for a bit and when the battery was already fully charged and hot too, when 13.7v was more appropriate. I wonder how the ECM chooses its voltage. My engine actually sucks some underhood airflow through the ECM.

A few weeks back, My battery was accepting 29 amps at 14.7v when I parked and kept idling. I slowly lowered voltage to 13.6v, and about 30 seconds later amps settled at 9.2 amps. ~66% more amperage delivered into my ~ 75% charged AGM battery at 14.7 compared to 13.6v.

I've also lowered voltage when a damp cold drive belt was squealing when accellerating when feeding a very depleted battery 70+ amps.

My Transpo540HD has an additional heatsink added to its underside, and later I added a 60MM fan to that, I hope it proves durable. it has been in operation for 14 months or so.

I am assuming if it fails I could hook up the enginne comuter ECM in an emergency, but another Transpo540HD would be an easier fix. Guess I should carry a backup, and modify it for the remote potentiometer so it would be plug and play.

The VR modification is pretty much my favorite electrical modification, but the Meanwell rsp-500-15 with the remote 10 turn pot, extra heatsinking and venitaltion, will seek any voltage between 13.12 and 19.23 with 40 available amps and has been in regular use since 9/14.

Both made possible by the OP