Using 100 amp mopar alternator to charge batteries out of a vehicle

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Art McConnell

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I'm using a 100 amp alternator to charge the batteries in a solar panel system that powers my mobile home. I am off-grid, and this is my only source of power in my home. The alternator is run by a 7.5 HP small engine. The alternator/engine setup is for cloudy days. The wiring for the system is all homemade-no car harness involved. I have two questions: I'm using the old Mopar style voltage regulator with the two prong connector. Can I use the regulator designed for the 60-65 amp alternator, or does the 100 amper require a different regulator? Also, does my wiring harness not being balanced have an effect on output? My output used to taper off around 14.5 volts, which was fine. But now its over 15 volts, which is too high for my system. Is there a way to control this, or is my regulator bad, or is it due to an unbalanced wiring harness?
 
You may want to upgrade to the newer electronic regulator and see if it changes. The older ones were adjustable inside and getting harder to find or try the solid state version of the old style regulator. What do you mean by an "unbalanced system"? The car systems would develop the same issues your having which was either the alternator or regulator. How old is your alternator? if you take it to a parts store most can test it for you.
 
Sedanman said:
You may want to upgrade to the newer electronic regulator and see if it changes. The older ones were adjustable inside and getting harder to find or try the solid state version of the old style regulator. What do you mean by an "unbalanced system"? The car systems would develop the same issues your having which was either the alternator or regulator. How old is your alternator? if you take it to a parts store most can test it for you.
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I am using the flat style electronic regulator. Can I assume that style regulator serves all amperages? I bought the alternator at NAPA about 10 years ago.
 
Ah ok,that is the new style. I would take the Alternator in and have it tested. If that's not it replace the regulator. The system is pretty basic and if either isn't the issue you may have a wiring issue but the 2 steps above usually fixes the problems in cars.
 
Sedanman said:
You may want to upgrade to the newer electronic regulator and see if it changes. The older ones were adjustable inside and getting harder to find or try the solid state version of the old style regulator. What do you mean by an "unbalanced system"? The car systems would develop the same issues your having which was either the alternator or regulator. How old is your alternator? if you take it to a parts store most can test it for you.
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As for an unbalanced system, I have wondered if the resistance in the wiring harness in the car might be carefully balanced to control the output. Surely the resistance between the voltage sensing point and regulator input would influence the output, would it not?
 
I would talk to RustyRatRod or crackedback on that one. I'm not much of a wiring guy. The factory wiring wasn't the greatest since the charging went into the dash and worked it's way back to the battery to charge it. It put a lot of strain on the wiring which eventually caused failures ending in fried wiring.
 
chrysler_external_voltage_regulator_wiring.jpg

A regulator and alternator are wired as above. After your 7.5 HP engine is started, a switch is used to connect the two --> connections at top. The battery (+), is connected to the output post of alternator. The battery (-), is connected to alternator body and regulator body.

The regulator "I" terminal senses the battery voltage when switch is closed, and terminal "F" goes low to energize field if voltage is too low, and increased alternator output. If you measure "I", to ground with voltmeter when running, and voltage is around 14V, the regulator is good. If the battery voltage is higher than that, then measure the voltage between the battery (+) and the "I" terminal. If wiring is good, there may be less than 0.1V, if more than that, you have poor wiring, or bad connection in switch or terminals. The other place to measure voltage is battery (-) to regulator case, that should be near zero, if not, that may also result in high battery voltage, because the regulator is fooled by the ground voltage loss.
 
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Back when Mopar had a 100 amp optional alternator, there was a voltage regulator (p/n 3755850) specifically for 100 amp alts. Now that you can no longer get these regulators from a dealer and everything is one size fits all ching chang crap, how well something works is just a gamble. Unless it's a cop car restoration, I replace these alternators with a later model.
You didn't say which alternator you are using. Since this is a home power unit and not a car, why not just go with a later model alt such as a Delco Remy CS-144. The junkyards are full of them and they are cheap much more powerful and reliable and if it dies just go get another one.
 
I use and adjustable solid state voltage regulator that a fellow makes for old motorcycles with excited field alternators on my valiant. It is only the small alternator though. I always had around 14.9v which I though was too high even warmed up and that's with good grounds and the 12v sense wire right from the battery through a relay. This one I set a 14.2 and I'm a happy camper. I just had to change the field wiring as the stock one controls the - to one of the brushes and the new one controls the +

I bought it from Oregonmotorcycleparts .com and it fits an Xs650 Yamaha.
might be worth firing him an email to see if it will work on a bigger alternator.
 
KitCarlson said:
View attachment 1714994990
A regulator and alternator are wired as above. After your 7.5 HP engine is started, a switch is used to connect the two --> connections at top. The battery (+), is connected to the output post of alternator. The battery (-), is connected to alternator body and regulator body.

The regulator "I" terminal senses the battery voltage when switch is closed, and terminal "F" goes low to energize field if voltage is too low, and increased alternator output. If you measure "I", to ground with voltmeter when running, and voltage is around 14V, the regulator is good. If the battery voltage is higher than that, then measure the voltage between the battery (+) and the "I" terminal. If wiring is good, there may be less than 0.1V, if more than that, you have poor wiring, or bad connection in switch or terminals. The other place to measure voltage is battery (-) to regulator case, that should be near zero, if not, that may also result in high battery voltage, because the regulator is fooled by the ground voltage loss.
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Are the field windings polarized in this alternator, or can the field leads be reversed without causing malfunction?
 
Vreg senses and attempts to control dV between its I input and its case (see post 7 drawing). The case thus needs a good connection to BATT-. Also insure that I is the same voltage as BATT+ (within 0.1 V). The voltage setpoint is fixed in Vreg. Most of my Mopar cars run ~14.3 V when the alternator is working, indeed even my M-B cars run the same (GM/Motorola style alternator).

I think the newer electronic Vreg's continuously change the alternator field current to adjust the voltage output, whereas the older relay type just turned the field on and off. Either will keep the battery charged, but continuous control avoids switching glitches, which other electronic devices appreciate.
 
BillGrissom said:
I think the newer electronic Vreg's continuously change the alternator field current to adjust the voltage output, whereas the older relay type just turned the field on and off.
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Observations with a voltmeter may lead you to this conclusion, but a scope will show that solid-state regulators also control the field by "on"-"off" but at a faster rate. Electronic regulators use "on"-"off" control to reduce transistor losses, improve efficiency, reliability and transient load response. Even the first (1971) Mopar electronic regulators work that way. The mechanical regulators work in a similar fashion, but the switching speed is much slower due to the mechanical inertial of relay, and delay related to collapsing field in relay coil. A comparator that drives a transistor, is orders of magnitude faster. The faster switching speed improves regulation and greatly reduces undesirable noise transients.

While the transistor turns "on"-"off", on a repeating basis, the coil current is fairly smooth, holding the value necessary to regulate the alternator output. The field is an electro-magnet, with significant inductance, so field current is stored, and freewheels in the "off", then "on" results is a nearly linear charge ramp, until the desired alternator output voltage is reached. The switching interval matches with the need for varying load, losses and alternator RPM. View with a scope, will reveal a very small saw-tooth riding onto of the field signal. Observation of the field driver transistor base or gate will reveal the digital control signal.

The term SMPS, is "switched mode power supply", it is the most common voltage and current, means of regulation today.
 
Here is a picture of the box (with part number) of the adjustable regulator I bought off of eBay. I think I paid $20.00. I bought it from Roadrunner Electronics.
IMG_20160619_201000209-640x480.jpg
 
An adjustable regulator still works in the same "on" - "off" mode, however the voltage setpoint is adjustable. The voltage setpoint is always analog, the comparator determines when output is above or below setpoint, plus or minus a small voltage, about 0.1V, that serves as hysteresis. The hysteresis is a small window, where switching stops because voltage is in acceptable range.

A temperature thermostat is an "on"-"off" controller. It works the same way as a voltage regulator. If the room is cooler than the setting, then the furnace is "on", when the temperature increases, and reaches setpoint the furnace turns "off". The amount of time the furnace runs, depends on size of house, conditions outside, thermal losses, furnace size. The action of a voltage regulator is much faster...

When a transistor is "on" the losses are low, when "off" the current flow is zero. There are losses in the transition, but minimal, if the transistor, fits the application. The value of the hysteresis, impacts the switching interval. If the hysteresis is too small, then the transistor would operate in the active mode, similar to adjustable rheostat, that is horribly inefficient, as power is wasted as heat, and is dissipated by transistor. It is similar to furnace is always on, opening doors and windows to regulate heat. The heat loss is a huge drop in efficiency.
 
Interesting that the electronic Vreg's switch on & off at a fast rate. That is common in modern electronics for controlling DC loads. One method is termed PWM - Pulse Width Modulated. But those require digital timing, which the Mopar Vreg probably doesn't have. I expect the switching results as the output voltage crosses the transistor's trigger threshold.
 
PWM is a duty-cycle at a fixed base frequency. The alternator regulator is hysteretic, so is not locked to base frequency. As stated before, it is comparator, with hysteresis.

A regulator with a voltage input may require gain, to insure the transistor is in saturation. Modern day circuits use MOSFET or IGBT transistor with logic level gates with comparator, to directly drive transistor.
 
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