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Old 10-20-2020, 10:43 AM   #1
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06 HR Battery Isolator Problems

My solenoid (Big Boy Battery Isolator Relay P/N 77-90006-120) is good, Coil has a constant 12vdc going to it, However the ground which excites the coil is not active.I am wanting to know the source of the ground that paths from the solenoid back to the PC board, The PC bord does have a small push switch for testing the solenoid which tells me the selenid is good. Unit located on the back of the coach engine compartment right side. Reference: 2006 PBQ45 Monaco Holiday Rambler Navigator 45-foot Detroit diesel Pusher
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Old 10-20-2020, 12:34 PM   #2
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Jamie, that must be one nice coach! The Detroit Series 60 option is one of the best and there are lots of folks searching for one.

The Intellitec Big Boy isolator relay should not have a constant 12v going to it. Voltage is purposely cut back to reduce heat. I think it's actually pulsed.

I assume the real issue is your chassis battery is not charging when plugged into shore power?
Have you removed the Big Boy and checked the internal contacts?
I have looked at several and they all had carbon buildup on the copper contacts.
Attached are the Big Boy rebuild instructions courtesy of Mike Canter.
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File Type: pdf Big Boy Relay rebuild instructions.pdf (566.1 KB, 6 views)
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Old 10-20-2020, 12:45 PM   #3
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Need a few more symptoms. Why are you diagnosing this? That is for example, your coach batteries are not charging from the alternator, or your engine batteries are not charging from shoreline or generator.

Even if the solenoid is clicking when you push the button mentioned that does not mean the solenoid is working properly. The contacts are known to fail and can often be cleaned.

Welcome to the Forum: I would actually suggest you start a new post This is a very old post you are tagging into and some folks may pass it by.

A new post will let people read the issue from the beginning versus following someone that has already solved their issue.

The system you are working on is often called a "Bird" system. Bi-directional-relay-delay.

I will find a link to some information that and post. https://1drv.ms/u/s!Aqrv2TUdbV6xjz9U...NHG_U?e=Dfwtuu
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Old 10-21-2020, 06:25 AM   #4
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The quick and easy test for the Big Boy isolator, it to do a "voltage drop test" across the large terminals (with contracts closed/power flowing). A voltage drop of more than 0.2VDC indicates bad contacts.
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Old 10-21-2020, 07:28 AM   #5
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The difficulty with a voltage drop test across the solenoid is if the batteries are close to being full there will be too little to cause a voltage drop. It is indeed a valid test but one should fully understand how to do it.

Turn the inverter on and run the microwave or convection oven using it to but a heavy load on the house batteries. Run this for 20 minutes or so. Boil lots of water if needed or just pre-heat a convection over. Measure the voltage on each large post. Start the engine and watch the voltage on each side of the solenoid. At some point the solenoid should kick in so don't jump back with a startled reaction and hurt yourself.

The voltage on each side should be the same if the solenoid is working properly. The solenoid is just a simple nail across a fuse. If the ends of the nails have arced over the years they will not carry as much and cause the drop.
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Old 10-21-2020, 10:41 AM   #6
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Thank you for this document, The issue I am having is the ground from the PC Board 6 is not energizing the coil low side (X2) of the Big Boy Relay.The coil hi side (X1) does have a constant 12vdc on it. On the PCB6 I have a small switch that I can press to energize the Big Boy Relay, If I use a clip clip lead from the coach chassis ground to the Big Boy Coil I can get the relay to engage and stat engage thus letting the coach's alternator charge both the engine and house battery bank.
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Old 10-22-2020, 09:01 AM   #7
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Good morning

I am attaching two items. One is the drawing from Monaco that is the schematic for the circuit board in your rear run box that controls the Big Boy. If you are able to read schematics, that might be really helpful for you. The other is a picture of the face of my hand-held oscilloscope while connected across the control terminals of our Big Boy. You can see what the energizing waveform from Board #6 looks like.

If your Big Boy device is very warm to the touch, the control system is working. I believe that when you are connected to shore power or your have your Onan running the Big Boy should be energized, and should remain energized. It doesn't energize immediately, but after maybe half a minute, it should energize and stay energized to keep both the chassis and the coach batteries charged. It may or may not be energized when just the engine is running. The engine alternator should NOT be considered to be a battery charger. That can put a pretty high demand on the alternator for an extended period, and that is not the sort of load it is intended to serve. If you start your day's run and the chassis battery is low, I believe that board #6 will keep the Big Boy de-energized until the chassis battery reaches sufficient charge before bringing the coach battery into the picture, thus limiting the demand on the engine alternator.

The control from board #6 is not as simple as a relay just closing a couple of contacts to energize the Big Boy. It checks for proper voltages to be present on each of the two batteries and it requires the proper charging source voltage to be present. Time is also a factor. When charging voltage first becomes available, it waits a time for voltages to stabilize before tying the batteries together.

Here are two things that I believe to be true. First, I believe that when you are connected to shore power, or your Onan is running, your Big Boy should be energized and after a while, should become quite warm. (You should also be able to take a long screwdriver or mechanic's stethoscope applied to the "can" of the Big Boy and hear a humming sound from it.). Second, you should not read more than a small fraction of a volt with your voltmeter applied with one probe on the left main power lug and the other on the right main power lug on the bottom of the Big Boy. If a significant voltage is present across those two lugs AND the Big Boy is energized, your contacts need to be serviced. If either of those conditions are not true, we need to talk further.

I have struggled in the past with fully documenting the control philosophy of the Big Boy and board #6. I know that MANY have had issues with the contacts becoming contaminated over time resulting in improper performance from the Big Boy. I have NEVER heard of anyone actually having a problem with board #6. I'm sure it can fail, and probably has in some instances, but I think it is unlikely that your problem is related to board #6.

Check back. We want to know what you learn. Cheers, and stay well!!
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