charging system mc8

[artglass]

 My mc 8bhas a 2-3 volts variaiton in the voltage when running on a mc8 enough to make the  dash fan, ac fan  surge  the battery voltage when running has 27.5 to 31.00 volts,the voltage regulator has the following voltage starting  at the top screw mounted in the bus top one has none, mid one has 25-26 volts, bottom one has 27 to 27.5 volts any one have any expierence are we looking at the regulator or the alternator? any help would be much apprecated , thanks in advance
    Kevin

[Sojourner]

My mc 8bhas a 2-3 volts variaiton in the voltage when running on a mc8 enough to make the  dash fan, ac fan  surge  the battery voltage when running has 27.5 to 31.00 volts,the voltage regulator has the following voltage starting  at the top screw mounted in the bus top one has none, mid one has 25-26 volts, bottom one has 27 to 27.5 volts any one have any expierence are we looking at the regulator or the alternator? any help would be much apprecated , thanks in advance
    Kevin

Kevin....I am having problem to be clear what your quoting "the voltage regulator has the following voltage starting  at the top screw mounted in the bus top one has none, mid one has 25-26 volts, bottom one has 27 to 27.5 volts".....could you explain with little more detail? A couple photos would even be more better still to eliminated extra confusing and quicker straight answers.

We can help solve the problem.

Sojourn for Christ, Gerald

[artglass]

the top screw on is the negative  terminal , the mid screw is the field terminal, the bottom one is the positive terminal as  so the book reads , not sure how to determine if the problem is the regulator or the alternator.
   Kevin

[buswarrior]

Surging power in these big alternators usually indicates imminent darkness.

If it is failing, you will not get much more warning.

My guess is the alternator.

The regulator's job is to get the alternator to output a set voltage. Shortly after starting the bus, the batteries will be low and charging back up, and having things turned on will make the regulator excite the field more strongly, to keep the system at the set voltage. The voltage readings at the three regulator posts alone don't tell us enough.

If alternator output is fluctuating, the effect is the same as microphone feedback, the regulator will start responding by raising and lowering the voltage as the alternator struggles with its generating problems... it becomes difficult to identify which is the cause.

Failure of these delco regulators is rare, they are tough, if relatively dumb, by modern regulator standards.

happy coaching!
buswarrior

[artglass]

    I am in penescola ran 450 miles today and is still doing the same thing voltage also jumps around on the outpost post on the alternator the same as on the batteries any one have any instructions on diagonosing this problem or is ther some one on the west side of florida that any one would recommend on checking this out i willl be going to naples the first of the week . Not using the bus ac , is still putting out about the same voltage.Any help would  be appreciated
   Kevin

[Sammy]

Kevin, you must first confirm that both batterys are fully charged and all cable connections including ground studs are secure and clean.

[artglass]

     checked the grounds ,got them cleaned up , doing the same thing ,called mci they had me run 24 volts to the regulator  positive side  , solved the problem, so it is either the  field relay or the circuit breaker , any one in the sarasota area know where you can get a 24 volts 15 amp circuit breaker, without ordering thru mci? any help would be greatly appreciated.
     Thanks ahead of time  Kevin

[JackConrad]

    I keep circuit breakers on hand at my shop.  I have never seen them marked 12 or 24 volt, just the amps (10, 15, 20, 30, etc.)  I think you can go to any auto parts hose and purchase a 15 amp circuit breaker. Now, if you want one to fit on the MCI bus bar, that will probably have to come from MCI.  I have never seen that type any place else.  Jack
PS: I am near Arcadia, there is also a busnut just north of Arcadia.

[Sojourner]

Sorry for not getting back soon until now.
About voltage at each regulator tab.
Top is ground to engine/alternator ground
Mid is field…it should never be higher than 12 volts and range is from 6 to 12 volts…it depend of the battery state of charge….the higher voltage mean greater charging rates.
Bottom is battery voltage.

If your batteries are old and one of any cell could be weak, it will cause the charging to fluctuating up & down. If batteries is good…then move on the next step.
If all alternator & battery’s wire connection are good. Equips with proper size wire or OEM size with no wire frayed at the connection terminals are good. All connection each stud and tab are cool but if it warmer than wire…you have poor connection. IR gun will help tell about the condition of the connection. However, at the Bat+ at the alternator will be warm from the unit but it higher than the alternator’s housing, need to inspect & clean with power off. All others should test cool to barely warm. If all wires and connection are very good, then click onto this  MCI "Not Generating" Troubleshooting Guide

Keep us posted.

FWIW

Sojourn for Christ, Gerald