1996 Beaver Alternator with DUVAC problem

[Jana Nagy]

I am posting for my husband Mark:

Approximately a month ago, our leece-neville alternator with a DUVAC signal input went out.  Simultaneously, our tach and our engine compartment fan quit working.  Then after we replaced alternator the tach started working and the engine compartment fan started working however, the engine compartment fan would not shut off and the tach would only work if the running lights were on.  So i proceeded to find what controlled the engine fan. (originally, the engine compartment fan would run for 30 minutes after shutdown which told me that it had to be an off-delay timer relay.)
I was able to find the off delay relay controlling the electric engine compartment fan. It is initiated by the output of the alternator charging terminal that goes directly to the center post of the isolator.  The current problem is that there is always 12v at this output even when the engine is turned off which also drains the battery over time. I have determined that this voltage is bleeding through the alternator from the duvac sensing wire.  So I thought this new Alternator was defective and put on another new alternator and got the same results.  So I am thinking these newer alternators from this manufacturer are wired differently than the original ones.  OR - there is another relay somewhere that is in the DUVAC wire circuit that interrupts its continuous connection?
Can anyone verify one or the other.  Maybe look on your motorhome and determine if you have continuous 12v at the charging port of the alternator and continuous 12v at the DUVAC port of the alternator with engine off.)

(My second issue is the tach - when the engine it first started, the tach works fine.  After about one to two minutes it quits working. But if I turn on the running lights, the tach works.  Thoughts?)

We have a 1996 Beaver, model 38’ emerald marquis with a cat 3176B engine.

[Steve Huber Co-Admin]

Jana,
You may have the wires switched. One of the wires to the back of the alternator (Terminal B) will have battery voltage on it at all times. Verify it is not hooked to terminal A. Duvac wiring is shown in the 1990s wiring diagrams in Coach Assist.
Steve

[Jana Nagy]

Hi Steve,
Wish it was that simple.  I have pictures of the original connections and the alternator is well marked with Ignition (yellow wire 14 Ga) and DUVAC (red 12 Ga.) which are in the same orientation as the old alternator.
Mark (Jana's husband)

PS: For some reason they can't figure out how to approve my forum application and recommended using a different sign on. So, I used my wife's (Jana) info to apply and that one worked.

[Steve Huber Co-Admin]

Asked  Roy to look into registration problem.
Do you know which terminal has constant 12v other than terminal If so you could add a relay triggered by ignition power to interrupt the 12V when the coach is shut down.
There are a number of members here who have replaced their LN alternators so hopefully one will respond.
Steve

[Jana Nagy]

I already bought the relays & designed the fix, but I was hoping something I missed came up before I jump in. I am going to hold off for a few days before I add the relays.  Hopefully a response on the tach will come in as well.  I am hoping the tach issue may just be a poor ground because when I do turn the lights on, all the gauges drop a few digits, ie oil pressure, voltage, & air pressure. And the common connection being the ground.
Thanks,

Mark Nagy

[Eric Maclean]

Mark
This thread may help
Eric

http://beaveramb.org/forum/index.php/topic,11541.msg77511.html#msg77511

[Jana Nagy]

Hello Eric,

Thank you for the link. However, I already read that link and it didn’t solve my situation so unless something else comes up I will probably install my relays as explained earlier. Once I finish that I’ll post how I solved it.

Mark

[Eric Maclean]

Mark
Your tach problem is likely loose connection at the gauge itself ( most likely the ground) for that one or may all the dash
The connection stud nuts have a bad habit of working loose creating this sort of troubles.

The link in the previous post will show the terminal position on the back of the alternator
You should have two smaller 14 awg wires one is the igntion feed which should only be hot with the ignition switch turned on the other should be hot all the time this is the sense wire this is used because the alternator output is connected to two battery banks through a battery isolator which are in effect a pair of diodes , these diodes create a volt drop which would not allow the voltage regulator to accurately control the battery charge voltage.
To cure this issue the alternator has a sense terminal this terminal is used in a system to monitor the charge voltage of the primary battery bank in this case the chassis batteries. The battery isolator may have a smaller terminal that this sence wire can hook to or the sense wire can go directly to the chassis battery positive terminal.

[Eric Maclean]

Mark
The delay module will have a constant 12 volt feed and an ignition control wire I think you may have have the ignition control feed connected to a constant feed ( sense terminal) instead of a switched ignition feed.

However if the problem is that the module has failed it may not shut off at all.

These timers have been used for years for furnace fan delay shut offs they are essentially an electronic relay which a timer built in

This link is to a delay module
https://www.automationdirect.com/adc/shopping/catalog/relays_-z-_timers/timer_relays/t2s-fd-33-125d

Do you have a picture of the back of the alternator and the wiring as it is connected?

[Mark Nagy]

I installed a relay between the DUVAC from the battery to the Alternator and signal the relay from the ignition at the alternator.  This solved turning off the engine compartment fan through the 30 minute off delay relay.  I plan on adding one more tweak. This will be replacing the fan off delay timer relay with a programmable combination on & off delay timer relay so I can delay the start of the compartment fan until after the engine is started and still have the off delay after the engine is shut down. 
My tach issue happened to be my fault.  A month ago, I was under the dash (can't remember why HaHa), but while there I noticed a wire that appeared to come off of a terminal, so I plugged it back in. Then later on I had the Tach not working unless I turned on the lights. So the other day I was fiddling with the ground wires and the wires on the tach.  Then I remembered I had previously connected one that I thought came off of the tach.  After removing it the tach works fine.
So all is now good and the alternator is performing as advertised.
Again, I appreciate all your assistance.

PS: I attached a picture of the back of the alternator.  The yellow wire is the ignition wire.  The Ignition wire sticker on the alternator fell off, but the DUVAC sticker is still there on the right side terminal.