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ML-ACR to replace Big Boy or Diode Isolator/Lambert/Battery Boost Relay


pwhittle
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I had previously posted this as a reply in another thread, but I have referred people to it and wanted to have an easier way for them to locate it. I have also made some updates to the original post here.

I cleaned my Big Boy once, and when it needed it a second time, I replaced it (and the BIRD circuitry) with a Blue Sea ML-ACR. A much better solution that costs less than a Big Boy Relay. 

The ML-ACR is a simple device that does one thing: connects or disconnects the house and chassis batteries. It has automatic voltage sensing so that if either bank is being charged and the other is not, then it will connect the two banks of batteries.

The features I like about it are

- Will charge both sets of batteries from the alternator or output from the inverter/charger
- Auto mode as well as manual off and manual combine override via the remote switch or on the relay itself
- LED status indicator on the remote switch that replaces the Battery Boost switch in the dash/side panel
- Takes no current to hold it in either position, so does not run hot
- Sealed from the elements
- Senses charging on either bank of batteries to combine in Auto mode
- Has high current ratings
- Continuous Rating 500A
- Intermittent Rating 700A (5 Mins)
- Cranking Rating 1450A (30 seconds)
- Lifetime warranty

I had previously replaced the diode based isolator and battery boost relay with the ML-ACR on our 1994 Signature and it has operated without issue since 2014.

I have helped Vanwill replace the same setup on his 2000 Dynasty and another friend on his 2002 Signature.

In those cases the ML-ACR replaces the isolator, the Battery Boost Relay, and the Lambert style or Trik-l-Amp or Trik-l-Start solution to keep both sets of batteries charged.

For our coach the ML-ACR replaces the Big Boy relay and renders the circuitry that drives the Big Boy unnecessary. I left the circuitry in place and just taped up the outputs that would go to the Big Boy.

Mechanically the ML-ACR is a similar size to the Big Boy relay and we used 1/8”x3/4” copper bar to connect the ML-ACR to the existing wiring.

We also ran a pair of wires from the RRB to the dash for the remote switch. We could have run one wire and reused the existing wire from the Batt Boost switch.

The remote switch also needs fused power and ground which we picked up from the FRB.

Notes:

- It is possible to build relays or some other logic  to drive one of the Isolation inputs on the ML-ACR to disconnect the batteries when you have two charging sources such as when the generator is powering the Inverter/charger and the engine alternator is providing charge as well. I chose not to do that, and just use the switch on the dash to disconnect the two battery banks to let the alternator charge the chassis batteries and the inverter/charger to charge the house batteries
- If you have different type of batteries, say house AGM and chassis lead acid, you should consider not leaving both banks connected all the time when you are on shore power where the Inverter/charger is configured for the AGM batteries as that could overcharge the chassis lead acid batteries and damage them. This may have contributed to the death of our original chassis house batteries, but they were in the coach when we bought it, so they may have just lived out their useful lives. When I replaced them, I installed Duracell AGM's to get close to the Lifeline AGM House batteries in charging voltages. You can always connect the banks the day before you are ready to travel or if you see the charge is down on the chassis batteries.
- This is not a suitable solution when the house batteries are Lithium. Lithium batteries require a different charging profile than AGM or Lead Acid so you would preferably install a DC-DC converter to keep both sides charged when there is a single charging source instead of connecting both banks


Manufacturer link: ML-ACR Automatic Charging Relay with Manual Control - 12V DC 500A - Blue Sea Systems

Amazon link: Amazon.com : Blue Sea Systems ML-ACR 12V DC 500A Automatic Charging Relay with Manual Control, Beige : Boating Battery Switches : Sports & Outdoors

Paul

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21 minutes ago, pwhittle said:

I had previously posted this as a reply in another thread, but I have referred people to it and wanted to have an easier way for them to locate it. I have also made some updates to the original post here.

I cleaned my Big Boy once, and when it needed it a second time, I replaced it (and the BIRD circuitry) with a Blue Sea ML-ACR. A much better solution that costs less than a Big Boy Relay. 

The ML-ACR is a simple device that does one thing: connects or disconnects the house and chassis batteries. It has automatic voltage sensing so that if either bank is being charged and the other is not, then it will connect the two banks of batteries.

The features I like about it are

- Will charge both sets of batteries from the alternator or output from the inverter/charger
- Auto mode as well as manual off and manual combine override via the remote switch or on the relay itself
- LED status indicator on the remote switch that replaces the Battery Boost switch in the dash/side panel
- Takes no current to hold it in either position, so does not run hot
- Sealed from the elements
- Senses charging on either bank of batteries to combine in Auto mode
- Has high current ratings
- Continuous Rating 500A
- Intermittent Rating 700A (5 Mins)
- Cranking Rating 1450A (30 seconds)
- Lifetime warranty

I had previously replaced the diode based isolator and battery boost relay with the ML-ACR on our 1994 Signature and it has operated without issue since 2014.

I have helped Vanwill replace the same setup on his 2000 Dynasty and another friend on his 2002 Signature.

In those cases the ML-ACR replaces the isolator, the Battery Boost Relay, and the Lambert style or Trik-l-Amp or Trik-l-Start solution to keep both sets of batteries charged.

For our coach the ML-ACR replaces the Big Boy relay and renders the circuitry that drives the Big Boy unnecessary. I left the circuitry in place and just taped up the outputs that would go to the Big Boy.

Mechanically the ML-ACR is a similar size to the Big Boy relay and we used 1/8”x3/4” copper bar to connect the ML-ACR to the existing wiring.

We also ran a pair of wires from the RRB to the dash for the remote switch. We could have run one wire and reused the existing wire from the Batt Boost switch.

The remote switch also needs fused power and ground which we picked up from the FRB.

Notes:

- It is possible to build relays or some other logic  to drive one of the Isolation inputs on the ML-ACR to disconnect the batteries when you have two charging sources such as when the generator is powering the Inverter/charger and the engine alternator is providing charge as well. I chose not to do that, and just use the switch on the dash to disconnect the two battery banks to let the alternator charge the chassis batteries and the inverter/charger to charge the house batteries
- If you have different type of batteries, say house AGM and chassis lead acid, you should consider not leaving both banks connected all the time when you are on shore power where the Inverter/charger is configured for the AGM batteries as that could overcharge the chassis lead acid batteries and damage them. This may have contributed to the death of our original chassis house batteries, but they were in the coach when we bought it, so they may have just lived out their useful lives. When I replaced them, I installed Duracell AGM's to get close to the Lifeline AGM House batteries in charging voltages. You can always connect the banks the day before you are ready to travel or if you see the charge is down on the chassis batteries.
- This is not a suitable solution when the house batteries are Lithium. Lithium batteries require a different charging profile than AGM or Lead Acid so you would preferably install a DC-DC converter to keep both sides charged when there is a single charging source instead of connecting both banks


Manufacturer link: ML-ACR Automatic Charging Relay with Manual Control - 12V DC 500A - Blue Sea Systems

Amazon link: Amazon.com : Blue Sea Systems ML-ACR 12V DC 500A Automatic Charging Relay with Manual Control, Beige : Boating Battery Switches : Sports & Outdoors

Paul

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B385F5DE-F9EF-416E-B8F2-8255719E4286.jpeg

6EED8874-B955-4424-A226-573E1F93AF78.jpeg

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I replaced my BIG BOY with a COLE HERSEE part# 48530 Smart Battery isolator 200A.  .

I have the Blue Sea ACR on my boat, but I chose the Cole Hersee for my MH  because it was the exact same physical dimensions and terminal locations as the BIG BOY that it replaces and it was also cheaper than the Blue.  The COLE HERSEE has the same operational features as the Blue Sea ACR.

It also shares the same disadvantage that one has to make sure not to having your inverter/charger in the charging mode when you have the chassis engine running.  

 

Jim

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  • 5 weeks later...
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On 1/11/2021 at 7:03 PM, Jim Byrd said:

It also shares the same disadvantage that one has to make sure not to having your inverter/charger in the charging mode when you have the chassis engine running.  

 

I have been having a few issues with my alternator, replaced it and the new one lasted less than 2000 miles.  It was replaced under warranty, but the alternator guy said he felt there might be something wrong with my coach that caused the failure.  I told him the original alternator was good for 160,000 miles before it quit, and didn't think there was anything wrong with my coach.  I saw your comment and wondered about it, I have always run the generator anytime it is hot to run my AC's and have never turned the charger off.  I have never had a problem until now, but I am not sure I even have a problem and wonder if it is as simple as the new alternator was bad??  Can you elaborate on your comment please?  Thank you.

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If the two battery banks are joined together while the alternator and the inverter/charger are both charging, the alternator and the inverter/charger are fighting against each other. It is better to disconnect the banks and let the alternator charge the chassis batteries and the inverter/charger charge the house batteries.

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2 hours ago, willbo777 said:

I have been having a few issues with my alternator, replaced it and the new one lasted less than 2000 miles.  It was replaced under warranty, but the alternator guy said he felt there might be something wrong with my coach that caused the failure.  I told him the original alternator was good for 160,000 miles before it quit, and didn't think there was anything wrong with my coach.  I saw your comment and wondered about it, I have always run the generator anytime it is hot to run my AC's and have never turned the charger off.  I have never had a problem until now, but I am not sure I even have a problem and wonder if it is as simple as the new alternator was bad??  Can you elaborate on your comment please?  Thank you.

One our coach (04 Holiday Rambler Endeavor) the alternator trouble WARNING light will come on.  When you have both charging devices (chassis alternator and coach inverter/charger in the charge mode) connected to a common battery the voltage regulator of the two charging circuits are not designed for this configuration.  

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I just don't realize why in all my years and miles, I never had any problem or indication.

12 hours ago, pwhittle said:

If the two battery banks are joined together while the alternator and the inverter/charger are both charging, the alternator and the inverter/charger are fighting against each other. It is better to disconnect the banks and let the alternator charge the chassis batteries and the inverter/charger charge the house batteries.

I can see this, but with my Big Boy system, I don't believe I can force the batteries apart?  I guess I will try to turn off the charger in the future, I am still puzzled why this all worked fine for years and years.

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3 hours ago, willbo777 said:

I just don't realize why in all my years and miles, I never had any problem or indication.

I can see this, but with my Big Boy system, I don't believe I can force the batteries apart?  I guess I will try to turn off the charger in the future, I am still puzzled why this all worked fine for years and years.

My coach came with the BIG BOY but it would only combine the coach and chassis battery banks when you manually presses the switch on the dash.  The coach batteries didn't get any charging when driving down the road unless you had you generator running to supply power to the inverter/charger.

I never had the problem until I replaces the BIG BOY with an ACR,

Jim

 

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35 minutes ago, Jim Byrd said:

My coach came with the BIG BOY but it would only combine the coach and chassis battery banks when you manually presses the switch on the dash.  The coach batteries didn't get any charging when driving down the road unless you had you generator running to supply power to the inverter/charger.

I never had the problem until I replaces the BIG BOY with an ACR,

Jim

 

Jim,

The previous owner must have changed the charging system on your 04 Endeavor.  I have a 99.9% confidence that it didn't have an Intellitec Big Boy interconnect relay when it came out of the factory.  Monaco was using Trombetta interconnect relays on the Scepter, Camelot and below on the food chain in the 2000- 2007 Era.  The Navigator, Dynasty, Sig and Exe used the Intellitec Big Boy relay in those years and after.  

On my 05 Endeavor there is a relay in the front run bay under the driver's window that disables the interconnect relay when the generator is running. This prevented the interconnect of the batteries when the generator was running.  I don't know when Monaco started or stopped installing this relay.  It isn't inside the distribution panel box and appears to be an "after thought".  

It also came from the factory with an Intellitec interconnect relay delay (IRD) and not a bidirectional interconnect relay delay (BIRD).  I installed a BIRD (removed from my 2000 Endeavor) and put another relay in the bypass circuit so the interconnect is disabled only when both the generator and engine are running.  I did this because the OEM system didn't charge the chassis batteries from the generator.  I wanted my chassis batteries to be charged while dry camping with only generator power. Again, as I said before this bypass relay is not installed on all coaches.   

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  • 9 months later...

I realize this is an old post but I've been very interested in all of the various dual battery system configurations and I ran across this. As I get older I find it's not a good idea to be dogmatic about anything because sometimes I'm wrong. So hopefully this is helpful or else I will learn something.

My motorhome came with an IRD so it only charged in one direction. I have since modified that so it charges both ways. The way mine was designed if both the engine and generator were running the two battery systems would stay connected together and having done that many times I had no trouble. So when I made my modification I made no provision for disconnecting them in those circumstances.  

The way voltage regulators on both converter/chargers and alternators work is the same. As battery voltage increases they begin to decrease their amperage to maintain a constant voltage. If they are both trying to charge then whichever one is set for a higher voltage will do the lions share of the work and the other one will start cutting back. They don't actually fight each other.

I hope this is helpful.

Tom

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