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Topic: engine alternator? (Read 933 times) previous topic - next topic

engine alternator?

Guys, we exercised our 99 u320 today...I normally have the boost swith on, but noticed low voltage when i turned it off today, less than 12 volts...started generator, and with boost sw on had 13 volts plus, boost off , less than 12.....Back in drive way, house batteries show 13.2, starting batteries show 12.7, they will start the coach, but after starting with the boost off they draw down to about 12.4, which makes me think they are being drawn down running what ever gets power with the ignition key on...looks like the alternator is not putting out...where do  go from here,  Mot is closed today..any ideas?  thanks....no significant voltage at the alternator, running or not or at the isolator....
Dave  and Wendy
99 U320, 05 Mini Cooper

Re: engine alternator?

Reply #1 –
Dave,

Could be the alternator, regulator or battery isolator.

I would start checking voltage at the battery isolator (since it is easy to access with the bed up) with engine off and then running at each lug.

Brett
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: engine alternator?

Reply #2 –
just checked key on not running no significant voltage...where should I be measuring it, there are three terminals...
Dave  and Wendy
99 U320, 05 Mini Cooper

Re: engine alternator?

Reply #3 –
any info on how to check isolator vs alt, vs regulator?
Dave  and Wendy
99 U320, 05 Mini Cooper

Re: engine alternator?

Reply #4 –
Turn on the engine. Check the voltage at the isolator. It should be about 14 volts.  You can also check the back of the alternator on the voltage out stud.
Could be an exciter wire too make sure you have all of them connected too.
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: engine alternator?

Reply #5 –
I have four wires on the back of the alternator, 2 large, 2 small...do I measure across the 2 large, if so I am getting no voltage running, or not running...
Dave  and Wendy
99 U320, 05 Mini Cooper

Re: engine alternator?

Reply #6 –
you will only have voltage when the alternator is putting out voltage when the engine is running.  First check and see whether you have any at the isolator with the engine running. If not then you need to see if you have any at the output stud.  Look with a mirror and you will see it.  It is kind of a pain to reach and watch your probe wires.  If you are not getting any voltage at the alternator then you should probably pull it and have it rebuilt.  I had mine done 4 months ago and I have an 01.
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: engine alternator?

Reply #7 –
Actually, the outer large lugs each go to a battery bank (one to chassis and one to house battery bank).  So, with engine off you should have a voltage reading from them to ground-- the same as what it reads at the batteries.  If different, check connections.

Then, with engine running, voltage at the center terminal should be in the high 14.s and low 14.s at the outer lugs.

Please post actual voltages, not "no significant voltage".  That will help us to help you.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: engine alternator?

Reply #8 –
Brett, I talked with him on the phone. He was not getting any voltage from the stud.  Well he said some fluctuating millie volts. IT is an original alternator so it is probably needing to be replaced.
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: engine alternator?

Reply #9 –
thanks to all of you, isolator shows 12.7, and 13.2 , but zero at centerstud with engine runninng, exciter shows 12 volt with key on ..I have pulled the alternator and will try to get it rebuilt on Monday, and will post results.....Thanks once again for the support.....
Dave  and Wendy
99 U320, 05 Mini Cooper

Re: engine alternator?

Reply #10 –
Quote from: dstrat1 –
thanks to all of you, isolator shows 12.7, and 13.2 , but zero at centerstud with engine runninng, exciter shows 12 volt with key on ..I have pulled the alternator and will try to get it rebuilt on Monday, and will post results.....Thanks once again for the support.....

Have them test the alternator first before you pay to have it rebuilt. Also the alternator probably has a built-on voltage regulator that can be bought for much less money than an alternator rebuild.

On the other hand rebuilding the unit might be a good idea given the age.

Wish mine were easy to get off... I'm going to hire a young guy to take mine off and have it checked and (probably) rebuilt. Same set of issues.

Good luck!

Craig
1993 U225 36' Unihome GV with PACBRAKE exhaust retarder, Banks Stinger and Solar Panels.
Toad: 1999 Jeep Wrangler 2-door soft-top.

"No one has ever had to evacuate a city because the solar panels broke."

Re: engine alternator?

Reply #11 –
took it to pearland alternator, 204 later got it back, works fine...some how, now the road relay 4 has a locked page, the summary page that usually displays, oil preess, boost , temp etc,, that shows, no info, but other pages prove, info is being sent from the ecm..puzzling......
Dave  and Wendy
99 U320, 05 Mini Cooper

Re: engine alternator?

Reply #12 –
You probably disconnected the battery when you had the alternator serviced. Try pulling the ground off the battery for a couple of hours and then reconnecting it.
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: engine alternator?

Reply #13 –
yes , i did disconnect the grounds from the starting batteries....now the road relay shows normal info, , but on the engine monitor main page, just question marks, if you page down, the same info is displayed on other pages, so it has a data link, but the one page is frozen......
Dave  and Wendy
99 U320, 05 Mini Cooper

Re: engine alternator?

Reply #14 –
just redisconnected the starting battery grounds, and now all is normal with the road relay 4........thanks for all input
Dave  and Wendy
99 U320, 05 Mini Cooper

Re: engine alternator?

Reply #15 –
FWIW,
90% or more of all DC electric issues are caused by poor grounds / bonding, cleaning ground cables, checking torque is a good thing if you feel comfy doing it.  I had to add additinal 2/0 ground cables to my batteries to frame to resolve an issue I had.
Having a good VOM and knowing how to use it is a wonderful tool.
Cheers
Dave M
 

Re: engine alternator?

Reply #16 –
I agree with Dave M.  I've made it a habit to clean and apply a thin coat of dielectric grease to all these DC electrical connections including the battery terminals.  The dielectric grease will prevent corrosion from forming which is the #1 culprit for bad grounds in DC circuits (especially if anywhere under the coach or engine compartment.  I know my start batteries, battery isolator, relays/solenoids get the brunt of these road elements and spray from the rear tires).

Have any elect not had any chassis electrical issues since...
Peter & Beth Martin
No Forrest? What have you done?
MC# 15890 until Dec 2016; FMCA #F329677
Cincinnati, OH