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Old 10-25-2021, 01:46 PM   #1
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Get me some alternator voltage under the bed

At some point I thought that when the engine was running I would read a higher voltage on the cable / post stubbed out under the bed. Now I do not see this and wonder if it's a blow fuse or if I just remember incorrectly.

Whether it was or not, I NEED it under the bed with the cable coming in from that house battery.

Maybe I have it backwards and the converter just sends higher voltage back to the house batt for when the engine is off.

Can someone have a look at these schematics and speak from experience and help me shore up how to get the alternator voltage under the bed with the existing wiring?

Finally - please know that this house battery is going away permanently. The two black cables tied to the POSITIVE post that supplies the alt voltage will be free for me to steak.

I want to use the existing cables to get this voltage under the bed and not have to run new cabling.

Thanks in advance for your SME and speculations. See attachments.





.
Attached Files
File Type: pdf 12V Chassis.pdf (448.1 KB, 49 views)
File Type: pdf 0080075_-_1-7_012116.pdf (241.1 KB, 41 views)
File Type: pdf 0053593_G_1-2_101315.pdf (75.3 KB, 29 views)
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Old 10-25-2021, 02:24 PM   #2
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See page 6 of the troubleshooting doc "House Battery Charging From Vehicle's Alternator". The relay under the hood sends the charge voltage to the house battery which in turn connects it to the 12 volt circuitry.
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Voltmeter.JPG  
Attached Files
File Type: pdf RV Electrical Troubleshooting (ver 2).pdf (2.01 MB, 24 views)
File Type: pdf Quick Multimeter Instructions (ver 1).pdf (376.3 KB, 10 views)
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Old 10-25-2021, 02:42 PM   #3
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That didn't anywhere nearly answer my question. "IS THERE ALREADY a cable going from the house battery to the bed area near to the converter", that's pretty much a yes or no answer.


The cables are in loom and strapped down, difficult to trace. On the 3 4G cables coming in under the bed in the same loom and with some other 12v wires, none of the white, black or red shows me alternator voltage back there while the engine is running.




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Old 10-25-2021, 02:50 PM   #4
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Nice wiring diagrams. Keep a copy in the MH, and don't loose the electronic copies


With the engine running, what voltage are you reading at the relay under the hood, and at the bed? Can you take any amp readings? If so, take a reading at both locations.

It seems normal for the wire AWG to be to undersized. I see on your diagram Jayco says they are using 4 AWG wire. It would be nice to know what type of wire they use, as they are not all equivalent.

This wire calculator maybe helpful: I entered 30 amps, 13.8 Volts, and a 50 foot wire length (remember the wire does not run straight from point A to point B, so I took a guess on the length. Per the calculator you should have a 2 AWG wire, to keep you voltage drop under 3%.

https://www.wirebarn.com/Wire-Calculator-_ep_41.html

This link (Chart) will let you know how many amps a particular wire gauge can handle over a certain distance. Just remember DC and AC are not the same thing. DC needs much larger conductors.

http://assets.bluesea.com/files/reso...on_chartlg.jpg
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Old 10-25-2021, 03:13 PM   #5
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You said the house battery was “going away”. How are you going to regulate the output of the alternator? It has a built in regulator but that is controlled by battery voltage. The old alternators did not have one built in. They were separate.
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Old 10-25-2021, 03:25 PM   #6
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I don't need wire size calculators, I need 14v at the bed. I know how to use a meter and stated that the 14v wasn't there, just 12.8 and that might be from my OTHER TWO BATTERIES that aren't part of this equation.

There are 3 of the 4g wires on the main house positive, the alternator voltage two are crimped together.

How am I going to regulate the alt . . . . I'm not. I'm stealing that voltage and using it else wise under load.

All SLA house batts are going away. The gen starter motor swill run off the new engine 850CCA battery.

No more side track questions please, answer if you can figure out the alt voltage path to the bed or not. THX.


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Old 10-25-2021, 03:47 PM   #7
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Lol.....

Love the attitude, yer the kinda guy we love to help
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Old 10-25-2021, 04:20 PM   #8
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Jagiven is correct in his approach, but there is NO difference in the voltage at the dmark if engine is running or not, this isn't about voltage drop. It's about the absence of alt voltage and how the hells can I get it back there is it isn't really going there to begin with.




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Old 10-25-2021, 06:23 PM   #9
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Quote:
Originally Posted by Captain Morgan View Post
That didn't anywhere nearly answer my question. "IS THERE ALREADY a cable going from the house battery to the bed area near to the converter", that's pretty much a yes or no answer. Some simpleton guide to using a VM wasn't warranted.

.
Your first post DIDN'T mention voltage measurements so I assumed that you did not know how to use a voltmeter. MANY people asking electrical questions have never used one so I created a quick training guide which I included.

If your rig has a converter, which you stated that it does, there HAS to be a cable between it and the battery otherwise it would not be able to charge the battery. Don't need a wiring diagram to know this.

The 12 volt circuit in these things will connect the battery to the fuse panel and converter, which is often near the fuse panel. I doubt they would run a separate cable from the converter to the battery and one from the fuse panel to the battery. So, you can pretty much guarantee there is a cable between the battery and your converter under the bed (which is where it is in my Greyhawk).

The reason I stated to check the relay under the hood is because that is what controls the charging voltage going to the battery/converter/fuse panel. If that relay is not working you WILL NOT measure a charging voltage at you converter/battery/fuse panel. The first step is to verify that the charge voltage is being sent to the battery through the troubleshooting steps in my guide.

Before tracing wires, verify the relay is working!
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Old 10-25-2021, 06:30 PM   #10
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I have a 2018. What voltage do you have at the house battery with engine running? What voltage do you have at the distribution panel with engine running? What voltage at engine starting battery with engine running?
Someting to consider depending what you want to run off the alternator. As the battery reaches a state of charge, the electromotive force becomes strong enough to oppose the current flow from the alternator, the amperage output from the alternator will drop to close to zero, while the voltage will remain at 13.5 to 14.5
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Old 10-28-2021, 10:09 PM   #11
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Originally Posted by Captain Morgan View Post
Yup, this forum takes the long way around to getting to the heart of things.
Well, I'll bite my tongue.

With the engine running, I was getting 14.7 at the bay relay. I don't recall the value, but it was noticeably less at my house battery mid-coach.

Rather than measuring voltage - what about a continuity test? If you want to trace a cable, trace the cable using one of the handful of ways cables get traced.

You have a wonderful day and I do hope you get the answer you need.

Oh, I have no recollection of anyone posting on this topic before. I think I'd remember because I've been interested in relocating the house batteries to the back,
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Old 10-29-2021, 06:59 AM   #12
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"IS THERE ALREADY a cable going from the house battery to the bed area near to the converter"

To keep my answer succinct,

Yes,

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Old 10-29-2021, 07:34 AM   #13
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I added batteries and moved the ones I had. They’re on the driver side in the bay behind the generator. For now I ran 2awg to the existing location and everything is working well. It’s not the permanent solution though. I’m hoping to add a Victron multiplus and clean up all the wires. There are other good manufacturers that make good combo charger/inverters. These things allow you to run all of your 120 plugs from your batteries unless shore power is present. I think you install them right behind the current transfer switch for gen/120. On all of these you can turn off the inverter side to save juice and just run the 12V system. It will simplify my wiring but I’ll need somebody to build a schematic for me. I know enough to be dangerous and as the great philosopher Clint Eastwood said, “A man’s got to know his limitations.”
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Old 10-29-2021, 09:51 PM   #14
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Quote:
Originally Posted by craigav View Post
"IS THERE ALREADY a cable going from the house battery to the bed area near to the converter"

To keep my answer succinct,

Yes,

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You sir, are a wise man!
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Old 10-30-2021, 11:22 AM   #15
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If You want dedicated voltage from your alternator, just run you some wires from your engine battery to were ever you want to be able to have this voltage. And remember ATTITUDE IS EVERYTHING…..Good Luck….
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Old 11-03-2021, 02:40 PM   #16
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Great documents, THANKs... WELL WRITTEN
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Old 11-03-2021, 02:44 PM   #17
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If You want dedicated voltage from your alternator, just run you some wires from your engine battery to were ever you want to be able to have this voltage. And remember ATTITUDE IS EVERYTHING…..Good Luck….
There is most likely already alternator voltage available nearby in the coach, (near) wherever your coach battery is, and if not currently working when Engine=ON, then most likely problem is a bad internal contacts on a CHARGE SOLENOID OR BATTERY MANAGER RELAY. Had to change my 22yo CHARGE SOLENOID myself, earlier this year,= would CLUNK, but not connect. LUCK
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Old 11-07-2021, 09:00 AM   #18
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Quote:
Originally Posted by Captain Morgan View Post
At some point I thought that when the engine was running I would read a higher voltage on the cable / post stubbed out under the bed. Now I do not see this and wonder if it's a blow fuse or if I just remember incorrectly.

Whether it was or not, I NEED it under the bed with the cable coming in from that house battery.

Maybe I have it backwards and the converter just sends higher voltage back to the house batt for when the engine is off.

Can someone have a look at these schematics and speak from experience and help me shore up how to get the alternator voltage under the bed with the existing wiring?

Finally - please know that this house battery is going away permanently. The two black cables tied to the POSITIVE post that supplies the alt voltage will be free for me to steak.

I want to use the existing cables to get this voltage under the bed and not have to run new cabling.

Thanks in advance for your SME and speculations. See attachments.
.

Take a look at the attached Harness Drawing. (It's for my 2016 Greyhawk MV)
If you can decipher their routing designations, it looks like there is a 4 gauge circuit running from the chassis battery back to the insolator stud/power center. It shows circuit junctions at the house battery and battery disconnect solenoid, but it may be continuous.


.
Attached Thumbnails
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