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Old 09-28-2022, 03:41 PM   #1
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2005 Monaco Exec Chasis battery dead

My 2005 Monaco Executive is plugged into shore power yet the chassis batteries discharge. I thought that these would be charged while plugged into 120V. Am I missing something ? New unit to me so I am just learning. Any insight would be appreciated.
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Old 09-28-2022, 04:11 PM   #2
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Do the house batteries charge when the engine is running ?

Can you use the Boost switch to get the engine started from the house batteries ?

If no to both questions, you have a bad isolation solenoid. In many coach's, that also handles keeping the chassis batteries charged.
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Old 09-28-2022, 04:22 PM   #3
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More than likely your Intellitec Big Boy isolation solenoid needs cleaning or replacing.
They are notorious for carbon buildup on the two contacts. It's in the rear electrical bay to the right of the engine.
(The picture is sideways)
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Old 09-28-2022, 09:35 PM   #4
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I installed the Echo Xantrex charger, easy install and keeps house batteries charged.
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File Type: pdf Echo-charge-OwnerGuide(445-0204-01-01).pdf (618.4 KB, 13 views)
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Old 09-28-2022, 09:38 PM   #5
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Forgot to say Welcome to the forum.
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Old 09-30-2022, 03:33 PM   #6
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I agree that it is probably the Battery Isolator Relay (BigBoy).

But, some other things to check; are you sure that the manual battery disconnect switch is to the ON position (switch should be a lever type switch in the battery compartment)?

Although, I believe my Dynasty will still charge with the manual disconnect switch OFF.

Are the batteries actually discharging (measured less than 12v?) or are you just not getting 12v power to the MH?

I had no 12v power due to a bad "salesman switch" solenoid (in the engine compartment).

Bad batteries are also a possibility - sometimes you can get a "surface" charge that makes the battery look good, but they will not power anything for more than a few minutes.

Good luck - Jim
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Old 10-04-2022, 03:52 PM   #7
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Thanks for the great responses. A new Big Boy is on the way from Amazon.
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Old 10-09-2022, 07:59 PM   #8
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Holy overpriced old technology. What does that thing do (other than a cool name) do that a VSR does not ?
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Old 10-10-2022, 05:35 AM   #9
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Here is some good info on maintaining the Big Boy,

https://www.irv2.com/forums/attachme...0&d=1529291844
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Old 10-11-2022, 08:39 AM   #10
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Thanks for the detailed instructions, especially safety info.
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Old 10-11-2022, 04:37 PM   #11
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We have a 2006 Monaco Diplomat. Our house batteries do NOT charge the chassis batteries even when plugged in. According to some we've met along the way, there are some Monacos, even if the Big Boy is working, that will not charge the chassis batteries. We have solved this by using something called a Trik-l- charger that will take care of that. Once it is hooked up you don't have to do anything else.
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Old 10-11-2022, 05:27 PM   #12
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Welcome to the forum.

The system that keeps you house (also called coach) and chassis (also called starter) batteries charged is a bit complex and you need to learn about it to make it work for you. Note that there is NO single document that describes this in your manuals. This post is probably the only place you will ever see it described completely - it may be a good idea to print it and put it with your manuals. Go ahead and ask me why I know so much about it!

The first point is that there are TWO sources of charging power for the two isolated 12v systems. The 240 v side (called shore power but includes generator and solar power sources) provides power to the house 12v system including the house batteries. You will have a Magnum inverter and probably a display that shows bulk/absorb/float charging states and related voltages (bulk highest, float lowest). This system has a temperature input that may be connected to a sensor attached to your batteries. This can fail and cause a high temperature signal to the inverter which will prevent the inverter from sending more than float voltage to the house batteries. This can prevent your starter batteries from charging when on shore power (if you read further you will see why this is the case). I said it may be connected, mine is disconnected (feel free to speculate why).

This system does NOT charge your chassis batteries directly. The chassis batteries are charged by the alternator driven by the engine (as is your car battery). This system does NOT charge the house batteries directly.

In between the two is your cross over charging system. It has two very different ways of connecting the two isolated systems. The first is the Boost switch on your dash. It is connected to a small relay in the run box in your engine compartment (a metal fuse box for the 12 v systems). The boost switch will send a high voltage signal to your Big Boy, which should then close and it will connect the two 12 v systems. This switch should NEVER be held closed for more than 30 seconds or the solenoid inside the Big Boy will burn out and you will have a junk Big Boy. The Boost switch is only intended to let power from the house batteries reach the starter circuit to start the engine in the even that you have let the starter batteries discharge.

The second way the circuits can be connected is when the Intellitec BIRD circuit (in the rear run box) detects a charging voltage on EITHER of the 12 volt systems (it is connected to both). A charging voltage means a voltage of 13.3 volts or higher. If the charging voltage is detected on the chassis side there is a 2 1/2 minute delay before it sends a signal to the Big Boy to close, this is done to let the engine come up to a steady idle when starting before a load is added to the alternator. It will open the relay if it detects a voltage of 12 or lower for more than one minute to allow power to be preserved for engine operations.

On the house side it will also delay for 2 1/2 minutes after detecting a charging voltage, but it will open relay if it detects a voltage lower than 12.8 volts (I assume this is because the inverter is more sensitive to minimum voltage).

In either case, it will send a new signal to close the Big Boy 2 1/2 minutes after it again sees 13.3 volts on either side.

For trouble shooting and possible problems there are several things to consider. The most expensive will require a new Big Boy or BIRD circuit, but I have had several problems and never had to replace more than a small relay in the wiring between the Boost switch, BIRD, and Big Boy that is used to combine the boost and BIRD signals into a single input to the Big Boy (cost about $10).

You can tell you have a bad relay if the Boost switch doesn't send a signal to the Big Boy. I'm avoiding saying 12 volts because what it actually sends is what ever voltage is available from the the system. This is worth noting because it requires at least 10.5 volts to close the Big Boy.

The Big Boy can fail in a way that it just requires cleaning to fix, if this is the case you will be able to hear it clunk after it gets the signal (some one can press the Boost switch which is instant or you can use the 2 1/2 minute delay to plug into shore power and wait. Note that sometimes the solar panel can trick you because the BIRD is constantly seeing a charging voltage - best to pull the fuse on the solar connection when testing the charging systems.

If it clunks and you don't see zero volts across the Big Boy terminals it is probably dirty. If it doesn't clunk you can feed 12 v to the input lead and if it clunks, your problem is up stream. If it doesn't clunk when given 12 volts directly it is probably a victim of someone holding the Boost switch down and frying the little solenoid that closes the Big Boy (an internal part that from what I can tell is not reparable).

Last little thing to watch out for. If you have read this far you deserve a medal, but there is an undocumented feature of the BIRD system that I learned from their support people. When the BIRD system first activates the Big Boy it sends a high voltage signal to it just as the Boost switch does, but in order to avoid burning out the solenoid after about 15 seconds it starts sending a modulated signal that keeps it open but doesn't send a steady current to it. On a voltage meter this will look like it is getting around 1 1/2 volts. This is not documented anywhere and was a real puzzler for me trying to sort out what was wrong with mine. It will make you think you have a bad BIRD circuit when it is actually doing what it is supposed to.

Good luck with your coach. And if you don't already own one, buy a good multimeter.
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Old 10-11-2022, 05:31 PM   #13
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Quote:
Originally Posted by rschley View Post
Thanks for the great responses. A new Big Boy is on the way from Amazon.
As per my short manual, it may not be your Big Boy, or it may be the Big Boy just needs cleaning. It takes about 30 minutes to clean as per the document already posted. As you have found out, the Big Boy is spendy.
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Old 10-11-2022, 06:58 PM   #14
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Quote:
Originally Posted by rschley View Post
My 2005 Monaco Executive is plugged into shore power yet the chassis batteries discharge. I thought that these would be charged while plugged into 120V. Am I missing something ? New unit to me so I am just learning. Any insight would be appreciated.
Shore power only charges the house batteries. You can add a second charger for the chassis batteries (that's what I've done...) to resolve this.

There is no provision to charge chassis batteries on a Monaco coach in that era.
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