Lazy alternator 1990 dodge b350

Question

I have a 1990 dodge class b islander rv.

I have rewired it myself to include far heavier wiring than was originally installed. It is basically #2awg wire direct bolted to alternator pos stud, then to 100A fuse then to continuous duty solenoid, then to batteries. Negative is the same size cable bolted to frame of vehicle.

My problem is my alternator likes to sit back and relax at about 13.5 volts all the time. Idling rpm is worse and can barely hold 13 volts especially when in gear and warm. 120A Alternator is only a year or 2 old.

Not ok with me when I'm trying to charge my 2 golf cart batts and run a 16.7A dometic absorption fridge on DC mode.

I've measure only about .1 to .2 volts drop between front and back (ie starting battery 13.5 v, golf cars at 13.4 or so). This is under light to medium charging current to batteries (batteries probably at 75% soc or so, as well as powering the fridge.) And to add, with fridge off and 100% soc batteries, voltage is almost the same, nowhere near 14v

Seems to me my wiring is more than adequate but the voltage regulator keeps voltage too low for powerful charging, especially at low rpm. As far as I can tell the regulator is working as designed and is integrated into the computer of the vehicle, not an external module. Also research seems to show that chrysler designed the charging voltage to be temperature compensated, ie drop voltage when ambient is warmer.

I've measured 14v on a cold startup in the winter, but even then the voltage tapers off slowly as the engine warms, and I don't camp in the winter so its not of much use.

And so...

I wonder if this kit will give me exactly what I need? The key being that this regulator is set by default at 14.5v, and also features an adjustment screw on the back to change voltage if necessary.

Seems like a fairly inexpensive and easy solution.

What do the knowledgeable DC and alternator folks think?

Thanks

http://store.alternatorparts.com/hd-external-voltage-regulator-conversion-field-replacement-kit.aspx

landyacht318 · Answer

I have an 89 b250.The voltage range on mine was 13.7 to 14.9v, and it would choose either with no regards to logic.Idle speed output on mine is fairly pathetic at elss than 50 amps total when hot.I bypassed the ECM's VR and added an adjustable external VR with a dashboard mounted potentiometer to choose any target voltage between 13.2 and 15.3.Detais available here:http://forums.woodalls.com/index.cfm/fuseaction/thread/tid/28630366/srt/pa/pging/1/page/1But hot idle speed maximum output is not impressive.  Not the fault of the VR but lack of rpm.

jamesjudaspries · Answer

Thanks for sharing your project. however, I think I need a more automatic, bolt on solution with less fabrication. But I must admit, Manually changing the voltage is appealing.

what kind of voltage would you see if the pot was set to max power at idle?

landyacht318 · Answer

With a full battery and minimum loads like no blower motor or headlamps, 15.3.
Depleted battery blower motor on high( 18 amps) and headlamps (~15 amps) I'd be lucky if it would raise above 13.

The alternator can only make so much juice, even fully fielded. Idle speed on mine is 550 rpms. It just cant make very much at that rpm.

My VR mod was because 13.7v when the battery was still depleted is way too low, and 14.9v when it is full is way too high.

Generally I set it to 14.4 and only lower it when I know battery is full.

scottg · Answer

If the regulator is still on the fire wall in that year then I would replace it. The lower voltage is a classic failure mode and regs are cheap.
1993 trucks started having it built into the ECM - which was stupid. (You can even see the dimples on the fire wall where the assemblers were to attach it using self tapping screws.)

landyacht318 · Answer

Dodge vans started putting the VR in the engine computer in 1988 for the 318 and 89 for the 360 engine.

Voltage seen will be influenced by electrical load on the system and what the ECM's VR allows.

Running the absorption fridge on DC, along with blower motor on high, at idle, is simply more than the alternator can make even fully fielded.

When my alternator was failing, with what mex said was a shorted stator, it was able to produce less and less, requiring more rpm to maintain voltages above 13.0v.

Failure of the VR in the ECM either requires a new ECM, or for one to bypass it and wire up an external VR.

The 10 ohm 50 watt resistor needs to go in between former field wire terminal connector to alternator to keep check engine light off.

https://alternatorparts.com/external-voltage-regulator-high-output-alternator-kit.html

I basically used the above link, but instead of using the Mopar VR, I used the Transpo540HD for a Ford, which had the internal potentiometer to adjust voltage. I just modified the VR to accept wires for a remotely mounted VR.

This superior Modification was possible for me due to Mex's knowledge and helpful nature.

Now if the alternator can not raise battery voltage to above 13.7v ever, even at higher rpms then I would say the Alternator or VR is failed/failing, but at idle when maxed out and the voltage can't be held above 13.7v, that is to be expected simply because of lack of RPM.

If the loads are higher than what the Alternator can produce, voltage is going to fall no matter what the VR is asking for.

I also have a K type thermocouple epoxied to the additionsl heatsink epoxied to my transpo VR. At Idle with a big load the VR temperature also climbs as the field current maxes out trying to maintain the voltage I have chosen. More RPM has VR temperatures decline again, and My VR is inside my Van, not in engine compartment and engine heat or underhood airflow are not influencing variables.

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Lazy alternator 1990 dodge b350

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