urgent - high volt readings when running

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patsdad

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Mar 28, 2006
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I'm leaving on a long trip in 3 days, and trying to work the bugs out of my 1983 ( Chevy 350 ) Class C.  I'm seeing normal reading on the battery state gauge and the dash volt meter with the engine off - 13V on both. When running, both meters show just over 15 V, the edge of the red zone on both.  Also, I have occasional alternator belt squeal on the roadl, and the belt is tight and new(ish).  So, the alternator seems to be working very hard for some reason. I have the coach battery switch off ( coach battery shouldn't be affecting, if I understand the function of that switch.)  Also, meters and belt squeal behave the same with that switch in the 'dual' position.  I have the charger on the engine battery, and it's drawing about 2.5 amp, 3 with some accesories running.  So, that battery seems normal to me.

Do I have a bad regulator ?  And, if you think that's the culprit, is it going to be built in to the alternator on an '83 Chevy 350 ? 

I appreciate any insights.  I've got a few days to de-bug, and then this puppie's on the road . . .

Update - I topped off the engine battery with my garage charger until it was reading just 1 amp draw, and vehicle still indicates 15+ volts when running.
Local auto parts stocks 78 amp alternators for this engine - I can't find anything in the paperwork with the MH that indicates what amperage the stock unit is.  I also came across the warning not to start the genny with the battery switch in 'dual'  due to possible alt damage. . . wondering if this is what happened.  The voltmeter was high on the test drive before I bought, but I figured it was just a low battery from sitting. . . . .
 

Chet18013

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Full time in RV. Home is where we are parked
Before you panic to much, get a GOOD multimeter and measure the voltage with it right at the battery terminals, with the engine running and the dash volt meter showing the high reading.. The dash meters are not very acurate. Chances are that your vehicle has a pretty good current draw when running.

If you indeed do have that high a voltage at the battery, check the vehicle and see what is turned on that you can turn off to reduce the load. Make sure the inverter, heater and AC, lights, etc.,  switches are off. If the multimeter shows  14.5 V or less, I would not be to concerned. If it's higher, you need to have the alternater checked by a garage that can check the current (AMPS) that the system is drawing.

See:

http://www.batterystuff.com/tutorial_chargers.html

Chet18013
 

Gary RV_Wizard

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Automotive voltage regulators run fairly high, often around 14.4 DCV.  15+ is too high, though, if it stays that way very long (say, more than 30-45 minutes). It should not go that high at all if both batteries are fully charged.  As Chet says, do not rely on the dashboard meter for accurate readings. If you suspect a problem, use a "real" voltmeter to verify what is happening.

Your battery disconnect switch in the coach may not disable the charge circuit from the engne alternator - most likely it just disconnects the loads from the battery.

A bad cell in either battery can cause a high charge rate, even though the unloaded voltage reads OK. ["OK" is a minimum of 12.6 VDC and it really should read about 13.0-13.6 if it has been charging recently.]  To be sure a battery is good, it needs to be tested under load. Most auto parts stores will load test a battery for free - you might even be able to drive in and borrow the tester to use in their lot or one of their guys may come out and test it for you.  You can also check a floded cell battery with an inexpensive hygrometer - that's a pretty reliable way to detect a bad cell. You suck up some battery "water" into the hygrometer and the indicator says something like Good-Fair-Poor. Anything less than "Good" on a fully charged battery means replacement time.
 

patsdad

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Mar 28, 2006
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25
thank you very much for the replies !  I swapped out alternators ( which includes the voltage regulator ) , and still have the same readings on both of the MH meters  ( the alt bearing had a slight grind in it anyway, so that wasn't a waste of time ).  I disconnected the coach battery, and it had no effect.  Both batteries act OK on a charger - draw 2 or 3 amps for a few minutes, then settle down to 1-2.  My cheapo multimeter isn't precise enough for this, so I need to get down to my buddies with the good one.  And, it sounds like I need to get both batteries checked under load.

I really appreciate the help.  If both batteries check out OK, and an accurate meter still shows higher than 14.5, and batteries are charged, what would you recommend ?
 

Karl

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Do you have flooded cell batteries - the kind where you can add water? If so, remove the caps and while the engine is running, observe the liquid in them. There should be SLIGHT bubbling, and it should be the same for all cells. If one is bubbling significantly more than the others, this would indicate a bad cell or one on the verge of going bad. Get a decent hydrometer from any auto supply store., and check the s.g. of the cells. They should all read nearly the same, and this will indicate the state of charge too. Finally, place a known load on the batteries of, say, 10 amperes (or 20), and measure the s.g. of each cell at regular intervals, like every 30 minutes. There are charts which will show the state of charge based on those readings, and depending on the 20 hour ampere hour rating of your batteries, it will tell you  if you've got a battery going bad. The hydrometer itself may come with the necessary charts, or you can download them from almost any major battery mfg's site.   
 

patsdad

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Mar 28, 2006
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thanks again for all the help.  Apparently, both the dash gauge and the overhead battery state gauge read a little high - a high-quality multimeter reads 12.9 V at rest, and 14.4 when running - around what the voltage regulator should be running at, according to my pro mechanic friend.  He also suggested I pull fuses, one by one, with it running, and look for a change  -  that would indicate if one of the circuits was causing the regulator to sense a load and step up.  No change from pulling any of the fuses.

So, it looks like a case of paranoia, brought on by gauges reading slightly high.    I appreciate the help.  Nice to know I can reach some knowlegeable people when I need to . . . .    hope I get a chance to return the favor some time . . . .

Chris
 

John From Detroit

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patsdad said:
So, it looks like a case of paranoia, brought on by gauges reading slightly high.    I appreciate the help.  Nice to know I can reach some knowlegeable people when I need to . . . .    hope I get a chance to return the favor some time . . .

Don't worry,  Soon you will be answering questions :)

Dash meters are normally approximate at best.  Always use a calibrted meter if you can.  Of course I spend way too much on meters some days (and a dollar on others) and happen to know how to calibrate them but not, always, how to adjust them
 

John From Detroit

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Karl said:
How do you calibrate a meter? Inquiring minds want to know.

How do you calibrate a meter, Depends on the meter.  For volt meters you use a known voltage source (Lab standard is best however expensive and involved) A fresh standard carbon zinc dry cell is 2.0 volts if I recall correctly (It has been long enough I'd need to re-read the manual)

Easiest way is to hook up in parrallel with a lab standard for voltage, current in serries  Resistance is not normally critical enough to matter (I'm mostly interested in zero or infinity when doing MH work)
 
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