alternator on Cummonsics 8.3 monoco Exec

[terboggs]

How do i check to see if the alternator is bad on this bad boy

[timaz996]

Put your coach on fast idle 800 rpm + Then check the voltage at you chassis battery. Should be min of 13.5 if your battery is charges, more if not.

[Tdkkart]

 Put a volt meter across the battery, measure the voltage. Start the engine, wait a couple minutes, check the voltage again, if the voltage is going up above the first measurement, the alternator is likely OK. Turn on items like the headlights and the heater fan while increasing the engine speed to 1500rpm, the voltage should remain fairly constant.

[terboggs]

i cannot start it, i get a click

[Tdkkart]

8 minutes ago, terboggs said:

i cannot start it, i get a click

 Well then, you'll need to start with batteries, or their connections first. Get it started, then check to see if the alternator is keeping up.

[terboggs]

how do  i bypass the alternator to start with just the battery

[Tom Cherry]

2 hours ago, terboggs said:

how do  i bypass the alternator to start with just the battery

Options…so read carefully….

If you are on 50 Amp, or even 30 A service or use your Genny.  Turn off BOTH disconnect battery switches.  Hookup a jumper cable between the positives of the house and chassis. Then turn back on disconnects.  This will prevent any surges.  Now turn on shore or crank the Genny. Let that “sit” for awhile….   Maybe an hour.  That will partially charge the chassis.  Leave the jumper in place.  Start the engine.  Let it run for maybe 15 minutes.   Remove the jumper. You can shut down genny or disconnect shore….obviously engine still running.

Put a VOM on the chassis.  Since you probably only partially charged the batteries, the alternator should be charging.  I agree with anything above say 13.5.  It might be closer to 14…or a smidge over.  The normal “sitting ready to start” chassis battery should be, if pretty “good” around 12.6/7.  

OK….ASSUME you have a mid to upper 13 or so.  You can let it run another 10 minutes.  Shut it down.  Turn on headlights for 5 minutes or so.  That “knocks off” the flash charge that your alternator put on.  Measure the voltage again.  If it is close to 12.5-.7, then your chassis is close to being recharged.  Probably good batteries.

Then….restart using ONLY CHASSIS.  THAT will put a good load (pulling 1200 A to start).  Now the chassis needs to be recharged….if all is well with your alternator and voltage regulator, the alternator should be pumping a lot of current.  The engine needs to run 5 - 10 minutes….then again measure the chassis batteries.  That will be the “normal when driving” charging voltage.  

There is a lot of “debate” about…OMG…if isn’t at least 1X.X VDC, you have a problem….followed by “hand wringing”.  In reality sometimes, due to temperature, age, load (like AC is on), etc…you might drift below 13.5.  But, in reality also, even the low 13.0’s might be OK.  So, my “crystal ball” says that you see or measure at least 13.5.  

performance is the real test.  Like driving for several hours…So, when you get ready for a trip.  Measure the batteries prior to cranking.  Then let it run for 10 minutes….then voltage should be pretty high, Then drive it on a trip.  Then measure it when you get to the CG..Obviously leaving the engine running.  That is gonna be the “fully charged” battery voltage for your rig with the current batteries.  If so…then higher is better, but as long as the rig starts and such….then…whatever it is…it is.

Final “lesson”.  If the ambient temp is above 90…and 95 would be better.  Shut down, after your long haul, the engine.  Wait maybe 8 - 10 minutes.  The engine is gonna get hot, naturally….you cut off the coolant.  Turn the key normally.  If you didn’t get that “OMG SILENCE…IT AIN’T GONNA START” pause….your Chassis batteries are fine.  If you got the pause, but then it started, budget for new chassis in the next year.  Again, this is the poor man’s hot soak load test.  If the ambient is under say 90 or in the mid 80’s,   and there was the dead silence….think about new in the near future 

 

[Guest Ray Davis]

18 hours ago, terboggs said:

  i cannot start it, i get a click        how do  i bypass the alternator to start with just the battery

Forget the alternator for now & find out why it won't start.

More info is needed.

When it clicks do the headlights dim?

Has the coach been running recently or has it been sitting?  The batteries will go down sitting unless it's plugged in.

Has it been starting ok or is this an ongoing problem?

I like to have a battery charger on board for such occasions.   I would try charging the batteries.

 

[waterskier_1]

I agree with Ray, don't worry about the alternator until you can get it started.  I would use my toad to jump start, just like you would any other vehicle.  If your batteries are below 11.0 volts or so, the built in inverter/charger will have disconnected itself, and starting the generator will not help.  The proper thing is to use an external battery charge to charge the batteries. If they hold a charge, then load test them.  If they are all good, then start troubleshooting the alternator and any other charging problems.

  -Rick N.

[terboggs]

21 hours ago, Ray Davis said:

Forget the alternator for now & find out why it won't start.

More info is needed.

When it clicks do the headlights dim?

Has the coach been running recently or has it been sitting?  The batteries will go down sitting unless it's plugged in.

Has it been starting ok or is this an ongoing problem?

I like to have a battery charger on board for such occasions.   I would try charging the batteries.

 

it has been off and on starting for two month, most if the time id put a jump on the top two batteres instead of the bottom four.  To get it home we had charger on it for a few hours and it did not start, and then suddenly did, i drove it home ,parked and one hour latter did not start. That is why i am wondering alternator. 

[Tom Cherry]

5 minutes ago, terboggs said:

it has been off and on starting for two month, most if the time id put a jump on the top two batteres instead of the bottom four.  To get it home we had charger on it for a few hours and it did not start, and then suddenly did, i drove it home ,parked and one hour latter did not start. That is why i am wondering alternator. 

OK...now, this is HOW a BOSCH alternator works...and I had the SAME issue.  BUT, you probably have the Leece Nevill.  Get the PN or Model off the Alternator and call them.  IF the (or maybe one) Diode is back in that style alternator, it will bleed or drain the current off.  I could NOT keep a boat battery charged for more than 3 weeks.  I was told by several sources and an electric shop (starters and alternators) that you have to eliminate ALL the "parasitic" loads...which was easy on my boat...disconnect the radio as the "presets" memory was the only circuit that was ON, with the key off.

SO, then you test the drain. You have to put an ammeter, INLINE...not clip on, with the positive to the alternator.  A normal alternator will maybe be below 20 milliamps or so...or lower.  YES, there is always a drain..., at least on my boat...  BUT, I measured 180 milliamps.  OPPS.  So, I had it rebuilt.  I TOLD the shop (same one that told me how to test).  Put it back on....OPPS...still bad.  Took the rig in.  They tested.  The head tech, a rather domineering and knowledgeable person...who knew immediately WHICH Purple wire to pull and test, then proceeded to tell one tech that he messed up.

He apparently did not listen or did not test or did NOT replace the diodes.  They kept it overnight....fixed it.  NARY A PROBLEM.  So, if your batteries are draining that quick....then, there is obviously a parasitic load.

NOW....what you have NOT talked about is the condition of the Starting Batteries.  If they are really old....or one of them just DIED...all the charging and such will NOT make any difference.  The quick way.  Charge them for maybe an hour.  Then pull the jumpers.  Test with a VOM the batteries.  IF you get anything less than say 11.5 VDC...like a 10 number, you have a SHORTED cell in one of them.  That shorted cell will, in parallel or even hooked up right, NO CHARGE..and if in parallel, will steal the amps and the other one...supposedly good, will not charge well.  

SO, Pull the Jumpers.  Test them.  You MIGHT then want to take to a battery distributor....I like Interstate...as their distributors have the PROPER testing equipment.  The auto shops or NAPA or whatever have the cheap testers....(under $100) and the distributors have the REAL testers ($500) and the real testers are better.  You SHOULD, individually, charge each battery overnight....obviously disconnected....and then take them both in....

Otherwise....from what you say....it looks like you have bad batteries....even with a bad alternator, I can NOT imagine a parasitic load through the diodes...  

BUT, if you are curious.  Remove the Jumpers.  Charge each one for several hours....look at the amps on the charger.  THEN let them SIT for a day or so.  Install the Jumpers.  It should crank.  That means that SOMETHING is draining them and you as left alone...they do not discharge.

Have to isolate....and then figure out what to do.  No sense throwing money at an alternator that might be good.  

[Tdkkart]

39 minutes ago, terboggs said:

it has been off and on starting for two month, most if the time id put a jump on the top two batteres instead of the bottom four.  To get it home we had charger on it for a few hours and it did not start, and then suddenly did, i drove it home ,parked and one hour latter did not start. That is why i am wondering alternator. 

At this point, I doubt that neither your batteries or your alternator are bad, sound more to me like a bad connection somewhere in the chain.