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Topic: 24v on 12v system how? (Read 823 times) previous topic - next topic

24v on 12v system how?

Noticed voltage was keep dropping, next found out engine batteries were not getting charged. When tested with engine running at center "A" bolt position of the isolater 24v. Replaced the alternator with another rebuild one and again 24v ..... how? Took The isolater out of the path and all good at 13.6v
So both alternators are good. Problem is the isolater. I will get a new one tomorrow. I just don't understand the 24v. If the regulator in the alternator is not getting a response then it pushes out the max it can all the way up to 24v? Anyone had this experience?
Thank you,
Al

Do anyone know a good place to order a 200 amp Alternator?
Former 2003 GV U295 (6230) (2015 - 2025)
Former 94 GV U225 (2013-2016)

Re: 24v on 12v system how?

Reply #1 –
Got my non-DUVAC alternator at NAPA, but had to modify it to connect the sense line to the isolator. Are your alternators the DUVAC type?
1997 U270 34FT Build 5140 Cummins 8.3 Allison 3060R
Solar 1920Watts, 14KWH lithium. Orion BMS.

Re: 24v on 12v system how?

Reply #2 –
Try Quality Power on the net,should have any amperage you want.
96 U270 BUILD 4810
85 380SL
Drummonds TN.

Re: 24v on 12v system how?

Reply #3 –
If the sense terminal of the alternator reads very low, the alternator will continue to raise the voltage to try to meet the correct voltage as it sees at the sense terminal.

No idea how high it can go.
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: 24v on 12v system how?

Reply #4 –
May only be a wire or connection problem with the sensor wire
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: 24v on 12v system how?

Reply #5 –
EASY TEST:  What is voltage at the sense terminal of the alternator.  I would do this with the engine at 1000 RPM or so (BE CAREFUL OF MOVING PARTS!). Probably safest from driver's side of bed with bed up-- that way you are clear of moving parts and have easy access to the back of the alternator.  You could also use small jumper wires (careful so you don't short them to any metal).

If different than at the chassis battery DETERMINE WHY AND FIX IT.

Only when the sense terminal reads chassis battery should you even look at the alternator.

And, yes, if you have an IGN terminal, it should also read chassis battery voltage with the ignition on.
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: 24v on 12v system how?

Reply #6 –
I had that problem, over 24 volts at the center post of the isolater. It was shot so wasn't getting enough voltage at the sense terminal
so the alternator put out max voltage. Replaced the isolater and back to normal
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: 24v on 12v system how?

Reply #7 –
I see that there is another chat for the same subject : Varying Charging Voltage
Former 2003 GV U295 (6230) (2015 - 2025)
Former 94 GV U225 (2013-2016)

Re: 24v on 12v system how?

Reply #8 –
Al,

Post your results to my test (two posts above).  Then we have some facts to work from.
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: 24v on 12v system how?

Reply #9 –
Quote from: wolfe10 –
EASY TEST:  What is voltage at the sense terminal of the alternator.  I would do this with the engine at 1000 RPM or so (BE CAREFUL OF MOVING PARTS!). Probably safest from driver's side of bed with bed up-- that way you are clear of moving parts and have easy access to the back of the alternator.  You could also use small jumper wires (careful so you don't short them to any metal).

If different than at the chassis battery DETERMINE WHY AND FIX IT.

Only when the sense terminal reads chassis battery should you even look at the alternator.

And, yes, if you have an IGN terminal, it should also read chassis battery voltage with the ignition on.
I am not by my FT right this moment but passing information to my friend who is trying to take care this for me. I may ask a question that has a obvious answer sorry.
i read on the other discussion here that there is a known issue that the FT by design wired the Alternator voltage sense wire on to some location that is not ideal and advised that there should be a direct cable with a 1 amp fuse to engine battery positive terminal from the alternator. In fact  Alton at FT had done this for my previous 94FT when they had installed a new Alternator ( i just did not recall this last night :-(  )    Now on my 2003 I do not know (as of this writing) where the Alternator volt sensing wire is connected to get its volt reading to be able to regulate correctly.  I wonder in addition to that i should add another one directly connecting to the engine battery ... anyway first thing first, replace the isolater (as OldGuy).
So there are 2 small gauge wires from the Alternator, one is IGN and the other must be the Volt sensing wire.
Former 2003 GV U295 (6230) (2015 - 2025)
Former 94 GV U225 (2013-2016)

Re: 24v on 12v system how?

Reply #10 –
Al,

There are quite a number of acceptable places for the sense wire (with inline fuse).  Basically, any large-gauge wire directly connected to the chassis battery.  Yes, this ASSUMES that connection are clean and tight.  But, that is pretty easy to verify.  Check voltage that the chassis battery and then at any other location that you are considering, such as the isolator (but if in OE position behind the driver's wheel, a TERRIBLE location IMO), the battery boost solenoid, etc.  And certainly directly to the battery is just fine.  But, I have even seen where they were on a chassis battery terminal, but the terminal to battery was in bad shape, so reading did NOT reflect actual battery voltage.

In most cases, just making sure the connections are clean and tight takes care of it.  And, yes, I am a firm believer in moving all the electricals behind the drivers wheel "indoors".  On our 1993 U240, there was room in the "electrical area" at the foot of the bed.  Did not even have to cut any wires.  On others high and on the forward wall of the engine compartment is a lot cleaner/dryer location.

On the last coach I inspected absolutely everything on that panel behind the driver's wheel was rusted/corroded and every single component and many of the wire terminals needed to be replaced.  And, yes, voltage on the Javelina monitor was 17+.  Poster child for "don't even start trouble shooting until everything is clean, tight and components functioning.

Starting by automatically condemning the alternator can be both expensive and frustrating! That does not mean that alternators don't fail.  But make sure they are properly wired and receiving the correct "signal" before condemning them.
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: 24v on 12v system how?

Reply #11 –
Thank you Brett.
"high and on the forward wall of the engine compartment is a lot cleaner/dryer location" This is how it is on my current 03. Just a bit dusty ( I need to blow & clean) but other than that i did not think the area is too dirty or in bad shape.
I had the original alternator rebuild shortly after purchased & had hopped it was not the problem & it is not. Last night we just wasted a bit of time performing some unnecessary troubleshooting steps, such as replacing the alternator with the spare rebuild one.

In the mean time James (FT Tech Support) responded. He said that on my 03 the alternator sensing wire should be connected to Isoletor (I will check and verify myself too) We know the Isoletor is bad and replacing it today.  I will know more sometime tonight.

Former 2003 GV U295 (6230) (2015 - 2025)
Former 94 GV U225 (2013-2016)

Re: 24v on 12v system how?

Reply #12 –
Again, the location of the "battery end" of the sense wire is NOT critical, as long as it is a good clean connection and reads chassis battery voltage accurately.

Lots of good locations on that front wall of the engine room.
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: 24v on 12v system how?

Reply #13 –
Installed a new 200 amp battery Isolator, problem solved.
Thank you all for your help,
AL
Former 2003 GV U295 (6230) (2015 - 2025)
Former 94 GV U225 (2013-2016)