Correct "Big Boy" operation

[bpperk51]

Just replaced the Big Boy again. Last time was 18 month ago. My question is, Should the Big Boy stay latched when on shore power and all batteries are at full charge? The Monaco manual indicates that it activates or latches when the engine is running. So, if that is correct, why is my Big Boy latched or activated when on shore power? If my set up is correct then the only time it is not activated is when the shore power is not connected and the engine is off. Is that correct or do I have some other failure? Thanks in advance or your indulgence.

[twinboat]

That's exactly how many Bi-Directional isolation systems work.

[vito.a]

The Intellitec Big Boy isolator relay can be frustrating. I've cleaned the contacts on ours twice and just recently replaced it with a new one. I plan to rebuild the original and keep it as a spare. A friend bought his coach new in 2006 and his Big Boy only lasted 6 months.
I think part of the issue is the "coating" Intellitec uses on the contacts tends to burn and form carbon. It would be much better if they had used lower resistance metal contacts, but silver or platinum would have been very expensive.

From page 413 of your owners manual:

The Isolator Relay provides a simple means of isolating the two battery

systems, house and chassis, and connecting the batteries together when the engine

is running.

A momentary dash-mounted switch is added to provide a "BOOST" for the

engine batteries from the domestic batteries.

When using the battery boost switch, the relay may have to deliver the full

starting current to the engine batteries. The relay contacts must close and provide

low resistance without the harmful effects of arcing. To be sure relays can perform

under harsh conditions, the contacts are protected with a unique antioxidant

coating. The relay is of heavy construction and can easily deliver the needed

current. In a battery charging situation, both batteries will charge at equal voltage.

77-90006-120

Nominal Actuation Voltage ----------------------12 Volts DC

Actuation Current-----------------------------------5.6 Amps

Continuous Duty ---------------------------------No

Minimum Actuation Voltage ----------------------9 Volts DC

Maximum Continuous Carry Current---------200 Amps

Maximum Short Term Current (30 Sec) ----1200 Amps

As I understand it works at least three ways. It closes when you depress the boost rocker switch, it closes when on shore or generator power and the house batteries reach a preset voltage and then it charges the chassis batteries, and it closes when the chassis batteries reach a preset voltage to charge the house batteries from the engine alternator.

There is a circuit in the rear run box that reduces the voltage after it closes so it runs cooler, but mine still gets quite hot.

Also, you can download a soft copy of your owners manual. It's great for doing quick searches.
Monaco owners manuals:
https://www.monacocoach.com/rv-owners-manuals

[CountryB]

Here's more of what Vito and twinboat said - straight from the Bird's mouth:

[bpperk51]

Thanks, That is exactly what I have read in my manual, (One came with the unit and I downloaded one 2 years ago. But, it seems that there must have been a better way to isolate the batteries. I am familiar with how this is done in our fire engines and ambulances at the voluntary fire dept. where I have been a member for 40 some years. In those vehicles we have a solid state unit and no need to separate the power but instead want to be sure that both sets of batteries receive a full and equal charge from either the alternator when the engine is running or on the shore line.
In the motor home the situation is quite different. It seems that the "Big Boy" is activated at all times except when the engine is off and there is no shore power. I just think this should have been different or was the controller for the Big Boy defective. Thanks for confirming this for me.

[153stars]

People on here convinced me to drop my diode isolator for blue sea brand charge relay.
I'm not sure of your exact mod necessary if you can use the switch controlled version to replace big boy or just go automatic. But they boast a lifetime warranty. On mine it can replace isolator and boost in one part.
But I might make it redundant with boost solinoid.
I'm a newbie to owning RV have helped people with campers and RVs in my camp club for 30 years. I do have have 25yrs in plant experience elect.systems . From PLCs to 4160v switch gear. Above that voltage I don't service.

[bpperk51]

I notice on my ScanD that my voltage never gets above 13.2 volts and sometimes is at 12.9 volts. Could my alternator be the reason that my Big Boy is always on. That it never gets the battery systems above that. Some alternators are putting out 14.5 volts so as to completely get batteries to be at full charge. I haven't read the voltage at the alternator, but I am thinking I might need to do that. I also read in the manual, under the heading alternator, that it is adjustable. Just how is that accomplished?

[CountryB]

14 volts is normal but 13.5-ish "at the gauge" is okay too. Note that alternator voltage is measured at the alternator output terminal. Your Scan Gauge is measuring voltage at the ECM. So there is some voltage drop in the cabling and connections, and due to cable resistance. Your Scan Gauge reading is probably a few tenths off from the actual alternator output.

I would check the output at the Alternator. What make/model is your alternator?
Most modern alternators do not have an adjustable regulator - you just replace it when it fails.

When you say "On" I assume that to mean the contacts are closed. In that case the Big Boy should not be On if the voltage is below 13.3 (although that is an approximate voltage) - since your not reaching 13.3 the Big Boy should remain in open position.

But in actuality the Big Boy may consider 13.2 enough voltage to close. When it closes it is charging both House and Chassis batteries.

Could be that the internal solenoid is sticking and keeping the contacts closed (Big Boy On). You could remove the small control wires on the BB and then see if there is continuity across the large contacts. If there is, the Big Boy is sticking closed.

[twinboat]

Once the BIRD closes the BIg Boy at 13.4 volts, it will stay closed at lower voltages. Its possable that the voltage reached the close threshold right after startup, with out you noticing it.

Its explained here if you can read it.

[CountryB]

@Twinboat, your description uses 13.1 volts as the closing threshold and the description I have says 13.3 V - so who knows what the actual closing voltage is (somewhere between 13.0 and 13.4 depending on year BB made and if you allow for manufacturing tolerances).

[bpperk51]

This is from my manual. I think it is time to test this Leece Neville alternator. I will do that and get back to you folks later. I appreciate the help. I will get o the bottom of this!

Specifications:
• The integral rectifier system utilizes 12: 50 Amp diodes mounted in multiple aluminum heat sinks for efficient heat dissipation during high-output operation.
• Aluminum housings
• Bi-directional fan
• Front bearing: 305 cartridge type
• Enclosed brush system
• Operation Ambient Temperature Range (-40º to 200º F)
• Negative Ground Configuration
• Regulator Adjustment Range 13.6 to 15.4 Volts
• Batteries may start to gas at 14.3 Volts • Max. Operating RPM 8000

AlternatorTesting:
• Check all wiring for burnt or loose electrical connections. Repair as needed.
• Check all grounds and electrical connections to confirm they are clean and tight. a. Alternator ground to chassis frame. b. Motor block ground to chassis frame. c. Chassis battery ground to chassis frame. d. Alternator positive output to isolator center terminal.
• Inspect the alternator for damage. A broken fan blade can damage an alternator or throw it out of balance.
• Check belt, pulley and fan for wear. Replace as needed.
• Do not disconnect the battery, or battery wire, from the alternator with the engine running as this can damage the alternator or regulator.
• The pulley for the alternator should be torqued to 80 foot pounds.
• Chassis battery voltage with the engine OFF should range from 12.2 to 12.7 Volt DC.
• Chassis battery voltage with the engine at idle should range 13.5 to 14.2 Volts DC.
• The output of the alternator range is 13.6 to 15.4 Volts DC. Connect a volt meter to the (B+) terminal of the alternator and chassis ground. Idle the engine up to 1200 RPM.
• Connect a clamp-on amp-meter, if available, to the positive battery cable to verify the battery state/rate of charge. NOTE: The alternator is not a battery charger. It is designed to maintain proper electrical system voltage. A battery with a low state of charge, or a dead battery, may overheat and damage the alternator.

[YC1]

Great information from the Gurus and spot on.

Welcome to the forum.

[bruceisla]

I'm confused .... are we still talking about being on Shore Power and the Big Boy is constantly picked (as stated in beginning of thread)? If so, why are we talking about the alternator?

[vito.a]

Brad is thinking his alternator output is low therefore overworking the Big Boy relay and that is why it's short lived.

My theory: I've had several of these relays apart and there is a lot of black burned carbon in them. I think there is a large batch of Big Boy relays out there with a deficient coating on the contacts. This coating burns and forms carbon that prevents the copper contacts from closing properly and this creates more heat and burning.

The contacts are a copper washer and a copper stud with a rectangular head that acts as a contact.
It would be great if we could purchase a rebuild kit. The parts are similar to an early Chevy starter solenoid,

Attached are the Big Boy relay rebuild instructions courtesy of Mike Canter.