Alternator not charging? (1990 Pace Arrow)

[holemania]

hello all,

we have a 1990 pace arrow with chevy 454.

driving back from holiday campout, noticed engine missing/backfiring...then, blinkers quit working...then, engine just died & wouldn't start.

i don't think i have the emergency battery switch, so i disconnected main battery cable and attached it to the coach battery. ( i have one chassis battery and one coach battery...side-by-side).

well, rv started up fine and we got the rest of the way home.? i removed the chassis battery and purchased another commercial starting battery @ 950 cranking amps....cleaned all terminals and installed it.

it cranks the rv fine now, but when i measure with my multimeter at battery terminals, it doesn't seem to be charging....it's down to 12.39v now...started at 12.54v.

also, with engine running, if i disconnect the chassis battery, the engine dies (i've always thought this is a quick & dirty way to check the alternator on a car, but not sure if this holds true on an rv).

i suspect the alternator or something else in the charging circuit is faulty, but am not sure how to isolate this.? does anyone have feedback or advice on how to further check this out?? or should i just take it into a garage and have it troubleshot?

if i'm pretty sure it's the alternator, i could probably change it if i can figure out how to get to it...under the removable cover in the coach or from underneath the chassis...seems like it's right in the middle and hard to get to...

thanks for any help!!

dave

 

[John From Detroit]

Well,,,, Just off hand I would say you have done a good job of describing bad alternator syndrom

Question, does this ride have a serpentine belt (one belt that snakes, serpent style around everything) or traditional fan belts?  Might just be a belt, check them first.

It can also be a fusible link, so meter the alternator output terminal before you break out the wrenches

As to where to find it... you are on your own

(There are other possiblities too, and without the service manual for your motor home I am way more likely to put my foot in my mouth than help you beyond the above)

 

[holemania]

john,

thanks for reply....i'm in michigan area too...tri-city area...

yes, it does have a serpentine belt that seems to have good tension on it.? as far as i can tell, there is only two electrical connections on the alternator...(1) the large red cable that then attaches to a small can assembly under a shroud...this can assembly has 2 large connections (one on each side) 2 small connection points in the center of the can (not sure if this can assy. is a regulator or isolator)? ?(2) a small 4-pin plug on the side of the alternator that only has one wire connected in the plug.

from the "small can assembly" my large red wire branches out to the starter, etc....still haven't been able to trace exactly everywhere the 12v positive goes from the chassis battery...it goes thru the central electrical panel and branches out...so, i'm not sure yet the actual charging path from the alternator to the chassis battery.

i presume it is not a fool-proof test to disconnect the chassis battery while the engine is running...when i did, the engine quit...

also, i did meter the alternator output and it's very close to what i measure at the battery terminals (with the red wire connected)...

dave

 

[Karl]

Dave,
It's almost surely a bad alternator or voltage regulator. Some alternators have the v.r. built into them; not seperately mounted. That 'can' might be the emergency start cut-over solenoid, and cannot be ruled out as the problem. Maybe you just haven't found the emergency pushbutton, or maybe you don't have one.

i presume it is not a fool-proof test to disconnect the chassis battery while the engine is running...when i did, the engine quit...

Not only is it not a foolproof method, it can fry your electronics! If the alternator is good and voltage regulator is doing its' job, disconnecting the battery can cause the voltage to rise to very high levels. Not good. Without the battery, the voltage regulator has no battery voltage to sense, so it puts out more and more voltage to compensate. The battery also acts like a capacitor to smooth out the pulsating dc produced by the alternator/rectifiers. Some electronics don't respond kindly to pulsating d.c. either.

 

[holemania]

karl,

thanks for your response...

i've taken off all negative & positive connections and wire-brushed them clean...no resolution there, either.

i disconnected the large, red wire from the alternator and, with the engine running, only measured about .025vdc.  i would expect to see 12-13vdc at the output of the alternator with no load.

i'm reluctant to go out & buy an alternator unless there's some kind of return policy, so i guess i'll take 'er in and spend a few big bucks to get this thing resolved.

i'm surprised that my chassis battery isn't charging with shore power or the generator running...only the coach battery charges with shore power.  i guess the only way to charge the chassis battery without switching cables is from the alternator.

does anyone know if it's safe/ok to jumper the red posts together (of coach & chassis battery) while connected to shore power to charge up my chassis battery?

please advise if you have any feedback & thanks!

dave

 

[Karl]

does anyone know if it's safe/ok to jumper the red posts together (of coach & chassis battery) while connected to shore power to charge up my chassis battery?

it's o.k. to do that as long as there is no hydrogen gas present from a bubbling battery. A spark could cause an explosion. Connect the jumper from the good battery first as it's more likely to be producing gas, then connect the other end to the dead one. That will minimize the chance of a spark causing problems. Shut off the charger first, 'cause that will cause bubbling.

 

[John From Detroit]

Some coaches have a multiple charger system so that either engine or shore power will keep all the batteries charged, (Mine does) in fact it turns out my coach has something of a "Battery charge equalization system" (Like the crossfire system for the rear tires) in that the batteries parrallel so long as they both have sufficent voltage, when the voltage on either battery drops, the other system isolates so as to protect itself,

Or so the technician told me, and it makes sense from observed things that happened.

Prior to owning my MH I'd never heard of such a system for batteries.

If you have no measurable output from the alternator, then either the alternator is bad, the voltage regulator is bad or... you have a bad wire somewhere.

I do not know how to test the alternator beyond what you have done as my car has a built in voltage/current regulator in the alternator.  I do know there is a way to test it, and any service center can do it.

 

[Gary RV_Wizard]

You should be showing something like 14.3 volts from the alternator (typical charging voltage for an automotive system).  But a failed alternator is usually a diode failure, which shows as adequate voltage but no aurrent (amperes) flowing.

In any case, your symptoms are classis alternator. Pull it out and take it to an auto parts store for testing.