Blue Sea ML-ACR wiring question

jmn

Member
I have a few questions about the Blue Sea ML-ACR that I was hoping I could get some input on. I've searched the forum and haven't been able to find specific answers, so I thought I'd start a new thread.

A little background: I have the ML-ACR with manual control (the yellow knob on top of the unit) and the SPDT red switch. I installed this about 5 years ago when I did my initial build out, and it worked just fine up until last summer. I would basically always have the yellow knob in the ON (or remote) position since its mounted under the driver seat and not super easily accessible while driving. I'd always keep the red switch in the OFF position and switch it to ON only after the engine was started if I needed bulk charging while driving (I mostly rely on solar for charging my house batteries, but occasionally need a boost if I'm not getting enough sun or don't have access to shore power).

Now when I turn the red switch to ON, the ACR won't combine the batteries. The LEDs on the switch will do a double blink, pause, then repeat, which according to Blue Sea troubleshooting means "Manual override - check ACR for switch states OR ACR mechanical failure." The ACR appears to still work, because when I push the yellow knob down it will combine the batteries, it just won't combine them via the switch. I've double checked the wiring for the switch and everything appears normal.

I also checked the voltage at the starter battery, the house battery, and both sides of the ACR and everything seems okay. Voltage at house battery and house battery side of ACR were both 13.5V. Voltage at starter battery and starter battery side of ACR were both 12.3V with engine off, and 14V with engine running.

My first question is if anyone else has experienced this, or might have an idea of what's going on? I haven't contacted Blue Sea yet, but plan to.

My other question is in regards to the connection between the negative terminals of the starter and house batteries, or rather if such a connection is necessary. While looking at the wiring diagram while trouble shooting this, I notice that Blue Sea has the negative terminals of the house battery and starter battery go to a bus bar along with the black wire from the wire harness from the ACR, and the bus bar is grounded to the chassis. In my setup, the negative terminal from my house battery runs through a shunt which is connected to a bus bar that is grounded to the chassis. The black wire from the ACR wire harness is grounded to the chassis at a different point, but both are OEM grounding bolts. The starter battery is obviously also grounded to the chassis, but otherwise not connected to my house batteries negative terminal in any way. Is there a need to having a direct connection between the negative terminals of both the starter and house batteries?

Anyways, thanks for any input.

Jacob
 

Kevin.Hutch

2011 Mercedes 313 906
I have a few questions about the Blue Sea ML-ACR that I was hoping I could get some input on. I've searched the forum and haven't been able to find specific answers, so I thought I'd start a new thread.

A little background: I have the ML-ACR with manual control (the yellow knob on top of the unit) and the SPDT red switch. I installed this about 5 years ago when I did my initial build out, and it worked just fine up until last summer. I would basically always have the yellow knob in the ON (or remote) position since its mounted under the driver seat and not super easily accessible while driving. I'd always keep the red switch in the OFF position and switch it to ON only after the engine was started if I needed bulk charging while driving (I mostly rely on solar for charging my house batteries, but occasionally need a boost if I'm not getting enough sun or don't have access to shore power).

Now when I turn the red switch to ON, the ACR won't combine the batteries. The LEDs on the switch will do a double blink, pause, then repeat, which according to Blue Sea troubleshooting means "Manual override - check ACR for switch states OR ACR mechanical failure." The ACR appears to still work, because when I push the yellow knob down it will combine the batteries, it just won't combine them via the switch. I've double checked the wiring for the switch and everything appears normal.

I also checked the voltage at the starter battery, the house battery, and both sides of the ACR and everything seems okay. Voltage at house battery and house battery side of ACR were both 13.5V. Voltage at starter battery and starter battery side of ACR were both 12.3V with engine off, and 14V with engine running.

My first question is if anyone else has experienced this, or might have an idea of what's going on? I haven't contacted Blue Sea yet, but plan to.

My other question is in regards to the connection between the negative terminals of the starter and house batteries, or rather if such a connection is necessary. While looking at the wiring diagram while trouble shooting this, I notice that Blue Sea has the negative terminals of the house battery and starter battery go to a bus bar along with the black wire from the wire harness from the ACR, and the bus bar is grounded to the chassis. In my setup, the negative terminal from my house battery runs through a shunt which is connected to a bus bar that is grounded to the chassis. The black wire from the ACR wire harness is grounded to the chassis at a different point, but both are OEM grounding bolts. The starter battery is obviously also grounded to the chassis, but otherwise not connected to my house batteries negative terminal in any way. Is there a need to having a direct connection between the negative terminals of both the starter and house batteries?

Anyways, thanks for any input.

Jacob
Not being familiar with the Blue-Sea ACR I must speculate.

Firstly it appears that the yellow button is a mechanical operation of the isolator not electrical so it could be as simple as the earth connection for the ACR that has become disconnected or the electronics of the ACR has failed.

Secondly many specify the same ground point be used simply to remove any question that there is a poor connection at or between the ground points used. Many bodies are rubber shock absorber mounted on the chassis leading to some interesting grounding connections. In theory, they should all be at exactly the same potential and this could be measured if there is any doubt. Conversely, a temporary connection of the ground points with a length of wire could disprove this as the problem.
 

autostaretx

Erratic Member
Since you have a shunt you do NOT want to run a new wire from the starter battery negative to the house battery negative.

Doing so would bypass the shunt, and any numbers it was telling you would be useless.

As you said, it worked for years ... so in essence it's correctly wired now.
BUT 5 years is a long time, so it wouldn't hurt to "refresh" all of the connections throughout the system
(who knows? one of the battery post clamps may have loosened over time...)

"refresh" means open them up, clean them off, reassemble.

--dick
 

Kevin.Hutch

2011 Mercedes 313 906
Since you have a shunt you do NOT want to run a new wire from the starter battery negative to the house battery negative.
--dick
If the start battery negative was connected to the load side of the house battery shunt, as the existing earth would be, this would not affect the shunt readings as all current going into and out of the house battery would still pass through it. There should be only one connection between the shunt and the battery no matter what.

The chassis would only be a parallel path negative return to the shunt for any load connected to the chassis, as it would be now.
 

SSTraveler

2014 LTV Unity Murphy Bed
Make sure you have yellow switch on Remote and that the remote SPDT is wired correctly. I added my wiring diagram, I used to replace my Isolator Solenoid and Isolator Relay Delay under the passenger seat of my 2014 Leisure Unity Motorhome, in case it can be of use. If everything thing is proper then it sounds like you have a bad SPDT switch. I'm not sure if the Blue Sea warranty covers lifetime of the switch but I would call them to get a switch replacement. I would remove the switch and check its operation with a voltmeter.
 

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Midwestdrifter

Engineer In Residence
Its possible the units internal coil has failed. I would contact BS support, they are typically helpful. Have someone flip the switch to combine while you watch the relay. Does it click or make any noise? If not, it may be an internal failure.
 

jmn

Member
I will call tech support today and see what they say.

As far as the switch, it is definitely wired correctly, it worked just fine for over 4 years. It still received power because the LED lights turn on, just won't engage ACR. I'll check it with a voltmeter later as well and update.

I'm thinking I'll try running a ground wire from the negative terminal on the start battery to a common ground with my house battery (on the LOAD side) to see if that makes any difference. This might seem like a silly question, but does the wire size for this matter? I have 2awg running from both batteries to the ACR. The only reason I wouldn't want to use that big of a wire is because I'm nearly out of room in the channel that runs from the start battery into the driver's seat pedestal.

Thanks for all the input

Jacob
 

jmn

Member
Midwest-

The relay makes no noise when I flip the switch. I can manually engage it with the yellow button on top of the ACR, and it does combine the batteries this way, but the switch does nothing except blink the LEDs.
 

wankel7

Active member
Make sure you have yellow switch on Remote and that the remote SPDT is wired correctly. I added my wiring diagram, I used to replace my Isolator Solenoid and Isolator Relay Delay under the passenger seat of my 2014 Leisure Unity Motorhome, in case it can be of use. If everything thing is proper then it sounds like you have a bad SPDT switch. I'm not sure if the Blue Sea warranty covers lifetime of the switch but I would call them to get a switch replacement. I would remove the switch and check its operation with a voltmeter.
Shouldn't there be fuses between the start battery and the ACR and the ACR and the house batteries?
 

SSTraveler

2014 LTV Unity Murphy Bed
I will call tech support today and see what they say.

As far as the switch, it is definitely wired correctly, it worked just fine for over 4 years. It still received power because the LED lights turn on, just won't engage ACR. I'll check it with a voltmeter later as well and update.

I'm thinking I'll try running a ground wire from the negative terminal on the start battery to a common ground with my house battery (on the LOAD side) to see if that makes any difference. This might seem like a silly question, but does the wire size for this matter? I have 2awg running from both batteries to the ACR. The only reason I wouldn't want to use that big of a wire is because I'm nearly out of room in the channel that runs from the start battery into the driver's seat pedestal.

Thanks for all the input

Jacob
16awg for ground wire should be adequate.
 

Zundfolge

Always learning...
Dunno if you've ruled this out yet but I'd also suspect the switch itself too. Test voltage at the switch output where it contacts the ACR? Could be a bad connection not providing sufficient voltage internally. From what I'm reading it seems like that's the only place you haven't tested voltage.

Also/and have you tried just providing straight 12v juice from a jumper wire to the ACR?
 

jmn

Member
There are fuses between both batteries and the ACR, these aren't the problem.

I checked the switch, and when engaged it is sending power to the ACR, 14V at the red wire that goes to the ACR, so switch doesn't seem to be the problem.

I spoke with tech support, they initially thought maybe it went into some sort of manual override mode (the explanation of why it went into this mode wasn't very clear). To reset it, they had me start the engine, turn the switch to AUTO with the yellow knob in the REMOTE position, and wait 10 minutes. When nothing happened, they determined based on everything else that the solenoid coil must have failed, so they're sending me a new unit to replace this one. He said these things typically last 20 years, but it's not out of the question that a coil here and there could wear out prematurely. Anyways, kind of reassuring it wasn't anything I did wrong (at least it doesn't appear to be the case).

One thing I came to realize while thinking about the connection between negative terminals that I'm sure others are aware of but that I hadn't thought of: if you add a ground from the start battery negative terminal to another ground point, whether or not its a shared ground point with the house battery, you will be bypassing the quick disconnect thing that's next to the gas pedal. So anytime you need to disconnect the start battery, you'd have to either disconnect both of these ground points or access the main battery compartment and disconnect the main terminal connection. Certainly something that can be worked around, but you'd want to make sure anyone servicing your rig knows about this.

Thanks for all the responses!
 

john61ct

Active member
Wow that's a first never heard of one of those failing, been bulletproof on hundreds of builds thousands of owner forum posts.

Just goes to show nothing is perfect
 

Midwestdrifter

Engineer In Residence
Was the replacement free of charge? If so that's good support. I have been beating on mine for 5 years. Still has very low contact resistance.
 

Kevin.Hutch

2011 Mercedes 313 906
One thing I came to realize while thinking about the connection between negative terminals that I'm sure others are aware of but that I hadn't thought of: if you add a ground from the start battery negative terminal to another ground point, whether or not its a shared ground point with the house battery, you will be bypassing the quick disconnect thing that's next to the gas pedal. So anytime you need to disconnect the start battery, you'd have to either disconnect both of these ground points or access the main battery compartment and disconnect the main terminal connection. Certainly something that can be worked around, but you'd want to make sure anyone servicing your rig knows about this.
That isolator is between the start battery and the chassis ground to isolate the start battery, regardless of how you connect multiple chassis grounds to isolate both batteries you either need a common chassis connection or two isolation points. Battery terminals are usually used for this but in the NCV3 Sprinter, the battery is not easily accessed so they add an external isolation point.

This is why when providing a circuit it is important not to leave things out, especially isolators.

BTW if the yellow button still works it must be mechanical in operation, not electrical.
 

john61ct

Active member
ML is magnetic latch, so only consumes significant power in transition

While static, in either the isolating or combining state, super low, I assume just the V sensing.

And of course House and Starter circuits usually have a common "ground" to chassis (also for return in some cases)
 

Kevin.Hutch

2011 Mercedes 313 906
I guess, John you are confirming the yellow button is a mechanical not electrical activation or lockout.

I would have to disagree with you that house and starter batteries share a common ground point.

In my experience the house battery is grounded to the chassis close to where it is mounted, whilst the start battery has a dedicated ground/isolation point that could be easily bypassed by connecting the two negative terminals.
 

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