1990 GV Alt sensor rely, Where?

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1990 GV Alt sensor rely, Where?

September 20, 2022, 02:11:29 pm

Situation: We are here in Bakersfield at Cummins Rv Center. Alternator just replaced before we left. When key is turned on 12 volt exciter wire energized. As soon as engine starts blows exciter fuse. Believe it could be a relay. I have all the wiring diagrams except the one labeling the relays. Whole lot of relays to pull and test each one. Call in to Foretravel looking for diagram. Any body out there might know which relay it might be and where it's at?

Thanks in advance

Re: 1990 GV Alt sensor rely, Where?

Reply #1 – September 20, 2022, 03:26:48 pm

Steve,

What kind/model alternator was fitted as replacement? Identical to the one it replaced? Are you sure the "excite" wire is connected to proper post on alternator?

If the alternator tried to send full charging current backwards down the excite wire that would surely blow a fuse.

I can't help with the source for your excite wire. My OEM B-2037 and B-2126 12V diagrams do not show a excite wire - they only show a sense wire connected directly (no fuse) to start battery post on isolator.

Re: 1990 GV Alt sensor rely, Where?

Reply #2 – September 21, 2022, 12:26:53 am

Chuck: Sucess!!! Chad Tech support from Foretravel saved the day. Relay is mounted on the Isolator board inside the back door bay just ahead of the resonator. Chad said drawing of the circuit not perfect, but I found it. Problem was me! I hooked up the exciter wire to the regulator terminal when it should have gone to positive lug on the alternator. Problem solved and we are on our way again. Going to sleep better tonight.
Thanks to all for your help.

Re: 1990 GV Alt sensor rely, Where?

Reply #3 – September 21, 2022, 12:38:15 am

We have liftoff! Mistakenly hooked up excite wire to regulator lug, not positive terminal. Chad at Foretravel tech support guided me thru the process as well as Jared at Buchanon Electric, Oakland CA. Jared said on the core I turned in that only 2 lugs had been used and to NOT connect excite wire to Regulator terminal and to hook it up to positive terminal. He said the way Foretravel fused the circuit saved me from burning up the $750 alternator. Another reason to love our coach. We are on our way. Durango or bust.

Re: 1990 GV Alt sensor rely, Where?

Reply #4 – September 21, 2022, 08:27:05 am

Quote from: steve31 – September 21, 2022, 12:26:53 am

I hooked up the exciter wire to the regulator terminal when it should have gone to positive lug on the alternator.

OK, so your excite wire is now connected to the B+ (large positive) terminal on the alternator? That is...unusual...

Typically on externally excited alternators there is, to facilitate the excite wire connection, a separate (small) terminal which is labeled "I" or "IGN". See example photo below.

Apparently I'm not clear on how your alternator is wired, but as long as it is working correctly, that's all that matters.

Hope the rest of your trip goes smoothly!

Re: 1990 GV Alt sensor rely, Where?

Reply #5 – September 21, 2022, 01:20:03 pm

Quote from: Chuck & Jeannie – September 21, 2022, 08:27:05 am

OK, so your excite wire is now connected to the B+ (large positive) terminal on the alternator? That is...unusual...

Apparently I'm not clear on how your alternator is wired, but as long as it is working correctly, that's all that matters.

Hope the rest of your trip goes smoothly!

American English at work. So now we just sit back and wait. If he's back because his chassis battery went dead, then he connected the excite (I, or IGN) directly to the battery. If the battery doesn't go flat then he's connected the sense wire directly to the battery. Or the OP may have connected the I or IGN wire to a switched B+ terminal, and all will be well.
Art

Re: 1990 GV Alt sensor rely, Where?

Reply #6 – September 21, 2022, 07:24:19 pm

Quote from: Old Toolmaker – September 21, 2022, 01:20:03 pm

If the battery doesn't go flat then he's connected the sense wire directly to the battery.

So far we have mostly been talking about the excite wire being possibly misconnected. BUT, if the OP's alternator does require a sense wire, then connecting it to the POS (+) post on the chassis battery would be just fine.

Re: 1990 GV Alt sensor rely, Where?

Reply #7 – September 21, 2022, 10:39:15 pm

Attached is the picture of the way I had it hooked up incorrectly that I sent to the folks at Buchanon Electric. They still had the core I turned in and had not rebuilt it yet. They informed me that I had only used 2 lugs, positive and negative as the 3rd lug ( regulator ) was unused and dirty. This alternator is an exact duplicate of the old one. Right down to the mounting arrangement. Brand is Prestolite. My fault for not taking picture on removal of the old unit. The ring terminal on the end of the exite wire was sized for the positive lug, larger than the ring terminal on the negative wire which would not fit on the positive terminal. Testament to engineers at foretravel who wired it up. My fault all the way.

Re: 1990 GV Alt sensor rely, Where?

Reply #8 – September 21, 2022, 11:25:31 pm

Quote from: steve31 – September 21, 2022, 10:39:15 pm

They informed me that I had only used 2 lugs, positive and negative as the 3rd lug ( regulator ) was unused and dirty.
This alternator is an exact duplicate of the old one. Right down to the mounting arrangement. Brand is Prestolite.
The ring terminal on the end of the excite wire was sized for the positive lug...

Steve,

Do you have a model number for the alternator?

The reason I ask is because I can find many online references to Prestolite alternators. Some of them look similar to the one in your photo, but with one glaring exception. All of the externally excited models have a dedicated terminal post for the excite wire connection. The alternator in your photo does not have this post, which leads me to conclude that it is not a externally excited model. See photo below of typical externally excited Prestolite models.

You have 3 wires connected to your alternator - the big positive and negative cables, and the smaller "mystery" wire. I would really like to see where the other end of the smaller 3rd wire is connected. I suspect this wire is not functioning as a excite wire, but has some other purpose. I am at a loss to figure out what that purpose would be.

Any wire connected to the large B+ terminal on the alternator will see full charging current when engine is running. I am surprised that 3rd wire has not gotten hot enough to melt the insulation...unless the other end of the wire is not connected to chassis ground. That's why I wonder where it is connected.

Re: 1990 GV Alt sensor rely, Where?

Reply #9 – September 22, 2022, 10:33:26 am

Quote from: Chuck & Jeannie – September 21, 2022, 11:25:31 pm

Any wire connected to the large B+ terminal on the alternator will see full charging current when engine is running. I am surprised that 3rd wire has not gotten hot enough to melt the insulation...unless the other end of the wire is not making a constant ground connection. That's why I wonder where it is connected.

My 1991 GV I believe had similar alternator wiring to Steve's 1990 GV. The excite wire has a diode in series right before the connection to the alternator B+ post - see schematic and pic. This allows a self-excited alternator to work with an isolator. Foretravel did this for a few years until switching over to the externally excited LN alternator. This diode excite technique also works with a Delco alternator which I put in my coach. The diode blocks reverse current that Chuck mentions that would overload the excite wire.

Re: 1990 GV Alt sensor rely, Where?

Reply #10 – September 22, 2022, 10:38:15 am

OK - that solves the mystery!

Thanx Peter for that info! Very interesting. First time I have heard of that setup. So in that case there is a excite wire but no sense wire... I can see why FOT moved on to a more efficient charging solution.

Re: 1990 GV Alt sensor rely, Where?

Reply #11 – September 22, 2022, 10:43:11 am

Correct. When I upgraded to the Delco 40si alternator I added a sense wire. That's the small red wire in the picture.

Re: 1990 GV Alt sensor rely, Where?

Reply #12 – September 22, 2022, 10:51:53 am

Also, this is how the isolators work that have an excite post for use with a Delco alternator. They have a diode in series with the excite post connected to the isolator's alternator B+ post.

Re: 1990 GV Alt sensor rely, Where?

Reply #13 – September 23, 2022, 11:40:40 pm

Yes, I have the model number. Will lift up the bed when Lori gets out of it LOL. Will post tomorrow.

Re: 1990 GV Alt sensor rely, Where?

Reply #14 – September 24, 2022, 11:27:56 pm

Here is the number plate. This is the original alternator on build.

Re: 1990 GV Alt sensor rely, Where?

Reply #15 – September 25, 2022, 11:03:39 am

Steve,

Have been on a road trip. Here is the schematic from our Foretravel Media: https://www.foreforums.com/index.php?action=media;sa=album;in=194;nw;start=35 You can see both alternator wires on the isolator with the last terminal on the right going to the excite position on the alternator.

See attachment with wire codes below.

This whole panel is in a terrible location and gets a lot of road spray and is frequently very rusty. Several members including Brett moved it up into the front compartment under the bed where it stays dry.

Good idea to take the most important schematics to the print shop for their largest blowup. Thanks again to Bill Chaplin for starting me down this road.

Pierce

Re: 1990 GV Alt sensor rely, Where?

Reply #16 – September 25, 2022, 12:30:18 pm

Quote from: Pierce & Gaylie Stewart – September 25, 2022, 11:03:39 am

You can see both alternator wires on the isolator with the last terminal on the right going to the excite position on the alternator.

Pierce,

My original B-2126 wiring schematic showed the same notation as yours. I think the wire 59 RD labeled ALT EXCITER is incorrectly named. If it is a excite wire then it should be connected to a "hot with ignition switch ON" source. Instead, it is connected to a "always hot" source. I changed the label on my diagram to show it being a ALT SENSE wire.

If, on your coach, you have a EXCITE wire and it is connected as shown in your diagram, then it is incorrectly connected. If it is connected to some other source, then you might want to correct your diagram.

Re: 1990 GV Alt sensor rely, Where?

Reply #17 – September 25, 2022, 01:53:04 pm

Quote from: Chuck & Jeannie – September 25, 2022, 12:30:18 pm

Pierce,
My original B-2126 wiring schematic showed the same notation as yours. I think the wire 59 RD labeled ALT EXCITER is incorrectly named. If it is a excite wire then it should be connected to a "hot with ignition switch ON" source. Instead, it is connected to a "always hot" source. I changed the label on my diagram to show it being a ALT SENSE wire.
If, on your coach, you have a EXCITE wire and it is connected as shown in your diagram, then it is incorrectly connected. If it is connected to some other source, then you might want to correct your diagram.

Chuck,

Quite right. I just went out to our coach and the Foretravel schematic is incorrect so will change it and try and figure out where the excite wire comes from. Tone generator should find the source.

The PO of our coach replaced the 4 lug isolator with a 3 lug isolator but wired it incorrectly so the house and engine batteries were connected together. I didn't realize it for a couple of months until both banks went flat at my son's wedding.

Thanks for the tip!

Pierce

Re: 1990 GV Alt sensor rely, Where?

Reply #18 – September 25, 2022, 03:32:08 pm

Quote from: steve31 – September 24, 2022, 11:27:56 pm

Here is the number plate. This is the original alternator on build.

Steve,

The alternator in your photo is a Prestolite Electric model 8LHC2010Z. I found a previous Forum discussion about this alternator, in case you are interested.

Prestolite alternator-no output???

This alternator is now obsolete, so info is hard to come by. In spite of that, I was able to find two online references. One is the page linked below, and the other is a catalog page reproduced as a .jpg image below.

Prestolite Electric - Corporate Home » 8LHC2010Z

It is clear from the catalog page that this alternator is self-excited. It should turn itself on without requiring any type of external EXCITE wire connection.

Note that this alternator has no provision for a remote SENSE wire. If it is used with a Foretravel standard issue diode based battery isolator, it may not supply proper charging voltage to the chassis (start) batteries.

I would recommend checking the charging voltage (engine running) at the B+ terminal on the alternator, at the alternator post on the isolator, and at the chassis battery post on the isolator.
For proper charging you would like to see around 14.2 volts at the isolator chassis battery post.

Re: 1990 GV Alt sensor rely, Where?

Reply #19 – September 25, 2022, 08:13:57 pm

Quote from: Chuck & Jeannie – September 25, 2022, 03:32:08 pm

It is clear from the catalog page that this alternator is self-excited. It should turn itself on without requiring any type of external EXCITE wire connection.

This is correct only when the alternator has a continuous battery voltage present on the alternator B+ post. However with an isolator you need to provide the necessary voltage on the alternator B+ post to turn on the self-excited LN alternator (and a Delco alternator). The diode excite method discussed earlier in this thread is used for this purpose.

Re: 1990 GV Alt sensor rely, Where?

Reply #20 – September 25, 2022, 09:12:01 pm

Of course yer right Peter - I keep forgetting about needing the "turn-on" voltage with the diode isolator.

How about the lack of remote sense? How did FOT get around that problem when using this type of alternator?

Re: 1990 GV Alt sensor rely, Where?

Reply #21 – September 25, 2022, 10:40:24 pm

Quote from: Chuck & Jeannie – September 25, 2022, 09:12:01 pm

How about the lack of remote sense? How did FOT get around that problem when using this type of alternator?

I'm not the expert on LN alternators as I have never actually worked with one - but they have adjustable regulators (I think?), so Foretravel likely adjusted the voltage to compensate for the approx 0.7 V diode isolator voltage drop. So to have 14.2 V at the battery as previously recommended you would want to adjust the alternator to approx 14.9 V.

Later alternators with the sense feature automatically adjust to provide proper battery charge voltage with any type of isolator or load condition. Advantages of the sense feature are a much faster recovery when batteries are significantly discharged, and improved alternator output at idle.

Edit: the LN brochure above in fact does say the regulator is externally adjustable.

Re: 1990 GV Alt sensor rely, Where?

Reply #22 – September 26, 2022, 12:36:04 am

Currently I am charging at 12.9 voltage according to the info from the previous owners after market gauges he installed. Yes I know that is low however according to the folks I got the alternator from this can be adjusted. I can live with this until we get back and they replace the diode I smoked when I hooked it up incorrectly. The circuit created by Foretravel with the fuse saved the alternator. The folks that rebuilt it says that this alternator is self excited, When ignition switch turned on 12 volt is presented to the alternator to the positive alternator lug. Upon startup and alternator begins turning charging commences. Since system is currently working not going to screw around too much until I am home. Still have plan B if I have to with generator, solar panels and boost switch. Agree that Isolator and related relay needs to be housed in a weather resistant environment and trust me it's on the list to address. In the meantime, I am getting charge by the alternator and still have plan B. I can make this work until I get home.

Re: 1990 GV Alt sensor rely, Where?

Reply #23 – September 26, 2022, 07:28:28 am

Quote from: steve31 – September 26, 2022, 12:36:04 am

Currently I am charging at 12.9 voltage according to the info from the previous owners after market gauges he installed. Yes I know that is low however according to the folks I got the alternator from this can be adjusted. I can live with this until we get back and they replace the diode I smoked when I hooked it up incorrectly.

What is the resting voltage on your chassis battery? This would be after 3 hours of no charging.
That 12.9V reading could mean that all 160A are in use and the alternator output voltage is being rolled back to protect the alternator from damage. Voltage reading only have meaning when the battery is already full of electrons.

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