Mysterious Mercathode System

[Dave M.]

I checked the diagram for a 2002 240 DA. It looks like this. It still has the Mercathode system hooked in parallel to the bilge pumps and stereo memory. These are directly off battery 1 as before, although I did not include the battery switch in this image.



This is the way mine is wired, with a fuse instead of a breaker for the Mercathode system.

 

[Dave M.]

for the mercathode to work the battery must be in the "Both" position. The way Sea Ray installs the mercathode if the battery is in the 1 or 2 position the system does not work, only in the both...the right way to install would have been wire it right into the harness.

I think this explanation is physically impossible (well, almost). The Feeder, or output, of the selector switch can draw the electricity it needs whenever it is connected to either battery, as long as the battery is charged. There is no circuitry that adds additional capability when the switch is in 'Both'.

The only way I can see that it could possibly work as you describe is if it is wired as the diagrams show, and your #1 battery is disconnected. In that case, there would be no power from Battery 1 to power the Mercathode system or the bilge pumps except when battery 2 was connected to support battery 1. This happens only in the 'Both' position.

Back to you. Is there another possible explanation? If what I say above is true, then you could not start your engine on Bat 1. :huh:

 

[Dave S]

trust me, keep leaving it off and you will be able to tell when you inspect your zincs...my boat was burning through them the year I bought it....chewed them to bits in 2 months...spent a week looking through the boat and the Merc Mercathode manuals...and viola!

Can you clarify this comment for me? Shouldn't the Zincs deteriorate if the Mercathode is working properly or were they just deteriorating too quickly? And during this initial period of ownership, was your battery switch on or off? I guess that's what seems a bit confusing to me. Also, would you get severe corrosion of the zincs if the galvanic isolator wasn't installed or working properly?

I would also like to know where I might find the Mercathode installation instructions. Where did you get yours? I may just resort to removing the DC panel to look at the wiring itself. I will be testing mine this AM with my multi-meter and will look for this drop in voltage that you mention.

 

[MLauman]

for the mercathode to work the battery must be in the "Both" position. The way Sea Ray installs the mercathode if the battery is in the 1 or 2 position the system does not work, only in the both...the right way to install would have been wire it right into the harness.

I think this explanation is physically impossible (well, almost). The Feeder, or output, of the selector switch can draw the electricity it needs whenever it is connected to either battery, as long as the battery is charged. There is no circuitry that adds additional capability when the switch is in 'Both'.

I was thinking the same thing. The only thing you get with another battery is more current - hardly necessary in this case. The only time that scenario might be useful would be in the case of a dead #1 (assuming the mercathode is wired to #1).

In addition, it is widely considered bad practice to continuously leave your battery switch in the BOTH position for reasons unrelated to the mercathode. I cannot imagine Sea Ray or any builder encouraging that, let alone requiring it.

 

[Dave S]

Just returned from a quick trip to them Marina. It was 29 outside..............brrrrrrrrrrrrrrr.....but sunny. :grin:

For all you 260DA guys, I have another tale to tell later about the shortcut Sea Ray took on wiring the refrigerator and the cabin and cockpit AC outlets to the same breaker. :smt009 All I can say is I am getting a good education. :grin:

Now back to the Mercathode Sytstem. Maybe those who understand electrical matters better than me can tell me if there is any significance to what I found when I checked things with my meter. First of all I found the Mercathode is powered all the time no matter what position the battery switch is in. I should also mention that my battery charger was operational when I took these readings. All readings were taken from the purple wire on the Mercathode Block since this is the hot wire. I found a bare metal ground too so all readings should be accurate. All readings were taken in the order shown here:

BOTH.........13.85 volts and steady

Battery 1..............12.70 volts initially and then slowly dropping

Battery 2...........13.17 volts and steady

OFF............13.19 volts with up and down fluctuations

Maybe some of you can draw some conclusions from the voltage flucuations. But it sure appears to me that with the switch off the battery charger is doing it's job (thus both the up and down fluctuations) and the Mercathode is active as well.

 

[Dave M.]

I was thinking the same thing. The only thing you get with another battery is more current - hardly necessary in this case. The only time that scenario might be useful would be in the case of a dead #1 (assuming the mercathode is wired to #1).

Yes, you are correct. A dead battery 1, if it draws no current from the good battery 2, will act the same as no battery.

Can't we assume that the Mercathode system will always be wired to battery 1, and therefore you should always use battery 2 for your house battery? I have never seen any exception to this in the Sea Ray documentation for a single engine boat.

In addition, it is widely considered bad practice to continuously leave your battery switch in the BOTH position for reasons unrelated to the mercathode. I cannot imagine Sea Ray or any builder encouraging that, let alone requiring it.

It might be a good idea to list the reasons why. I am sure I don't know them all. Maybe the result can be sort of a mutual understanding that will help us all. When I bought my boat, the Captain who took me out to show me how to operate it was honest and admitted he really did not understand the electrical system. I have been working to understand it ever since, especially since the manual contains no wiring diagrams.

 

[MLauman]

It might be a good idea to list the reasons why.

As I understand it (there might be others)...

• Leaving the switch set to 1 or 2 ensures that you have a good 'get home' battery. With the switch set at BOTH you can run both batteries down at the same time and not have enough juice to crank.
  
• Modern multi-bank chargers have seperate leads for each bank (battery in this case) and can sense the charging needs of each one and adjust accordingly. This capability is lost when the switch is set to BOTH as both leads become logically combined. Why would Sea Ray install multi-bank chargers if they intended the switch to remain set at BOTH?
  
• With the switch set at BOTH, a low charge battery will attempt to draw down the higher charge one to its level. This problem is worsened when one of your batteries starts developing bad cells (as all do eventually).
  
• Not really an issue, but why even install a 1-2-BOTH switch if you're going to leave it in BOTH all the time? You could just parallel the batteries and use a simple On-Off switch - cheaper and simpler.
  

These assume a typical small single engine cruiser with 2 batteries with typical factory rigging.

I guess a better question in my mind is 'why switch to BOTH?'. The only thing I can think of is to crank the engine when neither battery can do it alone. Or maybe if you have 2 low batteries and want to charge them with the alternator - assuming you don't have an isolator.

 

[Dave M.]

I should also mention that my battery charger was operational when I took these readings. All readings were taken from the purple wire on the Mercathode Block since this is the hot wire. I found a bare metal ground too so all readings should be accurate. All readings were taken in the order shown here:

BOTH.........13.85 volts and steady

Battery 1..............12.70 volts initially and then slowly dropping

Battery 2...........13.17 volts and steady

OFF............13.19 volts with up and down fluctuations

Maybe some of you can draw some conclusions from the voltage flucuations. But it sure appears to me that with the switch off the battery charger is doing it's job (thus both the up and down fluctuations) and the Mercathode is active as well.

I think in the BOTH condition, you have the situation like MLauman describes, where the both chargers are trying to logically decide what to do, but both are driving the same load. Thus one should expect them to be unable to make good decisions. Here I think the float voltage is too high. So I think you should not leave the switch in BOTH when you are away from your boat.

When you went to Battery 1, you may have had some additional load on the battery from the selector switch. It depends on whether you had any DC items turned on or not. If so, when you went to Battery 2, then you removed this load, and the battery 1 voltage went back up a bit.

Then going to off, as far as the Mercathode system is concerned, should be no different than being in the Battery 2 position, as Battery 1 has no house load in either position, and is being charged by itself in either position. I think what you see here is very reasonable.

 

[Dave M.]

It might be a good idea to list the reasons why.

As I understand it (there might be others)...

• Leaving the switch set to 1 or 2 ensures that you have a good 'get home' battery. With the switch set at BOTH you can run both batteries down at the same time and not have enough juice to crank.
  
• Modern multi-bank chargers have seperate leads for each bank (battery in this case) and can sense the charging needs of each one and adjust accordingly. This capability is lost when the switch is set to BOTH as both leads become logically combined. Why would Sea Ray install multi-bank chargers if they intended the switch to remain set at BOTH?
  
• With the switch set at BOTH, a low charge battery will attempt to draw down the higher charge one to its level. This problem is worsened when one of your batteries starts developing bad cells (as all do eventually).
  
• Not really an issue, but why even install a 1-2-BOTH switch if you're going to leave it in BOTH all the time? You could just parallel the batteries and use a simple On-Off switch - cheaper and simpler.
  

I think these are all valid reasons. One more reason that I can think of is that if you don't start your engine with a single battery, alternating between them at times, you won't find out when one of them degrades to the point it can no longer start the engine. You would want to know that.

These assume a typical small single engine cruiser with 2 batteries with typical factory rigging.

Gotcha! This was just a tiny trap, now you have to explain what you think 'typical factory rigging' is. Or you don't, if you don't want. I confess I thought I knew. I thought it was just like my boat with the alternator feeding both batteries all the time through a isolator (diode pair). I am really curious if your boat is like this, or how many are.

When I started looking at the schematics to figure out some questions people had, it became apparent that Sea Ray does not include the isolator. Instead, the alternator output is fed to the Feeder, or output terminal of the Selector switch. Therefore it will only charge the battery that is selected. The sense line of the alternator also goes to the selector switch output.

When I read months ago peoples warnings about not switching the switch when the engine was running because it could destroy the alternator, I could not understand the reasoning behind that. Now that I see that new boats feed the alternator output, and sense through, the selector switch and not an isolator, I understand the warning. I still think that logically you should be able to switch between 1, BOTH, and 2 under power, as the switch should have "make before break" contacts. But if they get a bit burned and stop working that way, then switching could be an issue, as you could 'open circuit' the alternator output and sense line.

I guess a better question in my mind is 'why switch to BOTH?'. The only thing I can think of is to crank the engine when neither battery can do it alone. Or maybe if you have 2 low batteries and want to charge them with the alternator - assuming you don't have an isolator.

Since new boats won't charge both batteries unless the switch is in BOTH, I think there might be many times when you want it in both. Why would not not want to top off both batteries when under way?

And if you are going to verify each battery can start the boat, then you will be starting it in either 1 or 2. But then if you want both batteries charged, are you going to just switch it to BOTH, or are you going to turn off the engine, move the switch, and start again?

I don't have the answer. I do have the isolator, so the question does not pertain to me. I suspect the isolator was added to mine by the dealer in Portland when new, at the same time the 4 house batteries and inverter were installed. If it was normally included in the mid-90's boats, that would be good to know.

 

[MLauman]

One more reason that I can think of is that if you don't start your engine with a single battery, alternating between them at times, you won't find out when one of them degrades to the point it can no longer start the engine. You would want to know that.

Yes, I should have listed that because that's how I run - 2 identical multi-purpose batteries that I alternate between on each outing.

now you have to explain what you think 'typical factory rigging' is.

That was intended as a disclaimer - you want a disclaimer on the disclaimer? I was just referring to the simple '2 battery thru a switch' scenario with a 2-bank charger.

Since new boats won't charge both batteries unless the switch is in BOTH, I think there might be many times when you want it in both. Why would not not want to top off both batteries when under way?

It's not limited to new boats - mine has no isolator. I know when I leave the slip that I have 2 fully charged batteries, so there's really nothing to top off. I have my designated 'working' battery for that day which is the only one I'm concerned about charging. The other one is just a 'hot spare' which under normal circumstances won't see any use.

And in the unlikely event that I do have 2 low batteries, I would probably prefer to let the alternator charge one at a time anyway (see bullet 3 above).

 

[Dave M.]

All that stuff above!

A very good explanation and "SOP". Thank you! :thumbsup:


I don't have two identical batteries, and do have an isolator, so never really understood what the proper procedure was for a conventionally wired boat.

 

[thunderbird1]

Pulled my boat for 100-servicing today and guess what? Even with the standard Mercathode system plus sacrificial anodes (including the prop nut anode), I have a small amount of pitting at the bottom of my skeg where I dragged it through some sand earlier in the season. All is well (dealer will sand and paint the skeg), but I'm definitely having the beefed-up Mercathode system installed.

In my case, the prop nut anode is taking the biggest hit, while the anodes on trim tabs (further away from the stainless steel prop) exhibit almost no corrosion.

 

[asimpkinsjr]

Dave S., spent some time with my dealer today and also looking through the merc schematics...and the merc corrosion manual.

some ground work...

The way a guest switch works and we verified with a continuity tester today... when the switch moves its actuating on the feeder...not the poles marked as 1 or 2, thus when the switch is in 1 2, is disconnected, when in 2, 1 is disconnected, when in both both are connected...and when in off...the feeder to both poles is shut.

That being said...the only way the mercathode is always hot is if its actually connected to the feeder wire going into the guest switch rather than the 1 pole or 2 pole... but this would conflict with the wiring diagram SR ships in the manual..

They explained that its not uncommon to see SR accidentally wire to the feeder but usually in systems where there are more than 2 batteries.

The gradual voltage drop Im seeing and some others may see could actually be caused by a large blue capacitor on fridge that they indicate has been seen on boats to back-charge the system even when the power is shut off as it discharges partially powering parts of the boat...lights and such.

My dealer says Merc specifically calls for the mercathode to run directly to the battery, however its done...but they also indicate they spoke to SR and there was a reason SR was not doing this as merc recommended and it may have something to do with the ABYC or NMMA certification of the boats according to the service mgr at my dealer.

One place to look and Im going to do it soon as the yard puts the door in the shrink on my boat is to take the cover off the guest switch and see how wired...which would explain why Im seeing what im seeing and what you are as well....I suspect you will find your mercathode somehow wired to the feeder...it would also explain why the schematics show an in-line fuse between the mercathode and the power source which does not make much sense if it ran through one of the 2 breaker panels as does everything else on batt 1 and 2.

 

[asimpkinsjr]

for the mercathode to work the battery must be in the "Both" position. The way Sea Ray installs the mercathode if the battery is in the 1 or 2 position the system does not work, only in the both...the right way to install would have been wire it right into the harness.

I think this explanation is physically impossible (well, almost). The Feeder, or output, of the selector switch can draw the electricity it needs whenever it is connected to either battery, as long as the battery is charged. There is no circuitry that adds additional capability when the switch is in 'Both'.

The only way I can see that it could possibly work as you describe is if it is wired as the diagrams show, and your #1 battery is disconnected. In that case, there would be no power from Battery 1 to power the Mercathode system or the bilge pumps except when battery 2 was connected to support battery 1. This happens only in the 'Both' position.

Back to you. Is there another possible explanation? If what I say above is true, then you could not start your engine on Bat 1. :huh:

In poring over the wiring diagrams and working with the service mger to play with a guest switch one other scenario would explain my problem...if the feeder and either batt1 or batt2 got reversed when the guest switch was put in....and thats what Ill be checking once the door gets put in the shrink wrap but that is usually only seen when a boat is a model with more than 2 batteries according to the dealer.

 

[asimpkinsjr]

trust me, keep leaving it off and you will be able to tell when you inspect your zincs...my boat was burning through them the year I bought it....chewed them to bits in 2 months...spent a week looking through the boat and the Merc Mercathode manuals...and viola!

Can you clarify this comment for me? Shouldn't the Zincs deteriorate if the Mercathode is working properly or were they just deteriorating too quickly? And during this initial period of ownership, was your battery switch on or off? I guess that's what seems a bit confusing to me. Also, would you get severe corrosion of the zincs if the galvanic isolator wasn't installed or working properly?

I would also like to know where I might find the Mercathode installation instructions. Where did you get yours? I may just resort to removing the DC panel to look at the wiring itself. I will be testing mine this AM with my multi-meter and will look for this drop in voltage that you mention.

I burned through a set of zincs in 2 months....there where only 2 months left in the season the first yr I bought the boat and by the time the boat was pulled 2 months after it came off the truck the zincs fell off while it was sitting in the travellift...that was the first clue so over the winter I had them look at it and they pored over the boat with a continuity and volt tester and what they found led them to believe that my mercathode was only working when the guest switch was in the both position but when turned off which is standard practice and recommended when u r not on the boat...the mercathode was disengaged leaving the zincs as the only protection....u will see in my other post the drop is likely because the mercathode is no longer getting power but the drop looks gradual because of a backcharge coming from the fridge capacitor...or thats the info that came up today

 

[Dave M.]

Dave S., spent some time with my dealer today and also looking through the merc schematics...and the merc corrosion manual.

some ground work...

The way a guest switch works and we verified with a continuity tester today... when the switch moves its actuating on the feeder...not the poles marked as 1 or 2, thus when the switch is in 1, 2 is disconnected, when in 2, 1 is disconnected, when in both both are connected...and when in off...the feeder to both poles is shut.

This is just another way of saying that in position 1, the feeder draws power from pole 1, in position 2, it draws power from pole 2, and in both it draws power from both AND connects pole 1 to pole 2. And in OFF, none of them are connected. However, pole 1 is always hot from battery 1, and pole 2 is always hot from battery 2 (at least if connected and the batteries are charged).

That being said...the only way the mercathode is always hot is if its actually connected to the feeder wire going into the guest switch rather than the 1 pole or 2 pole... but this would conflict with the wiring diagram SR ships in the manual..

The only way it can be always hot, regardless of switch position, is to wire it to either pole 1 or pole 2, as they are always hot if the corresponding battery is good. And I don't agree with your terminology. I would say that the 'feeder' wire "comes out" of the guest switch, not "goes in". Normally current is drawn out of the feeder terminal to supply the loads. The only time current goes into the feeder terminal is when the boat is running, and the alternator is charging up the selected battery. When on shore power, the converter charges each battery individually through the breaker panel.

One place to look and I'm going to do it soon as the yard puts the door in the shrink on my boat is to take the cover off the guest switch and see how wired...which would explain why Im seeing what im seeing and what you are as well....

IMHO it is not necessary to take it apart, unless yours is broken. You have already described above how it works.

I suspect you will find your mercathode somehow wired to the feeder...it would also explain why the schematics show an in-line fuse between the mercathode and the power source which does not make much sense if it ran through one of the 2 breaker panels as does everything else on batt 1 and 2.

I know mine is not wired to the feeder. I have traced the wires 'hand over hand'. The reason that mine has a fuse, even though it is fed from the breaker panel, is that it does not have a breaker position of its own in the breaker panel even though it is connected to the common source wire in the panel. It uses a fuse instead. In the newer boats, it gets a breaker, not a fuse. I think something else there also gets a fuse, I don't remember if I have identified what it is yet.

I have pictures, but I am sort of 'in between' computer systems at the moment. I am running a new version of SUSE linux, 10.2, that I have been installing and setting up today. I don't have all my apps installed yet to make nice pictures to post.

 

[asimpkinsjr]

Dave M,

If you put a continuity tester on pole 1 when the switch is in the 2 or off position you get nothing and likewise the same experiment yields the same results if you put the tester on pole 2 with the switch in the 2 or off position...that being said and agreed how can you have a powered mercathode controller even when the switch is in the off position, or the 2 position consdiering its wired to the 1 position in the schematics?

 

[Dave M.]

Dave M,

If you put a continuity tester on pole 1 when the switch is in the 2 or off position you get nothing and likewise the same experiment yields the same results if you put the tester on pole 2 with the switch in the 2 or off position...that being said and agreed how can you have a powered mercathode controller even when the switch is in the off position, or the 2 position consdiering its wired to the 1 position in the schematics?

I am beginning to wonder if we are talking about the same thing here. So I want to use only Sea Ray terminology, and their wiring diagrams as I posted on the second page of this link. If you go look at those, you can click on them and bring them up full size.

I don't know about the continuity tester you are using, or how you are using it. So I don't necessarily agree with your assessment of the results of using it, I couldn't interpret them without knowing more. But I do agree with what you said earlier about how the Guest switch works. But how the Guest switch works, and what position it is in, is normally also irrelevant to the question at hand if you have the normal Sea Ray wiring.

If you go back and look at the wiring diagram, you will see that battery 1 is solidly wired to the terminal called Bat 1 on the guest switch. So the Bat 1 terminal will always be powered 'hot' by battery 1, if battery 1 is a good, charged battery.

Now, for a moment, forget what happens inside the Guest switch. The Bat 1 terminal is connected directly to battery 1. Now you find a wire from this same Bat 1 terminal; it runs to the circuit breaker panel. It uses the Bat 1 terminal only as a physical wiring connection point, so this wire to the breaker panel is also always hot if battery 1 is good.

At the breaker panel, this wire that is always hot from Battery 1 provides power to the Mercathode system, the two bilge pumps, and stereo memory if present. Also the sump pump if present. So they are always hot, regardless of the position of the Guest switch.

As a matter of fact, if your boat is wired like the diagram shows, you could take a hammer and start smashing the Guest switch into little tiny pieces :smt021 that you throw overboard (go ahead and do that now). As long as you are careful to preserve the Bat 1 terminal and the wire to the battery 1, plus the wire to the circuit breaker panel that connect to it, your Mercathode system will still work.

:smt018 Wait, there is a problem. When the say "Gentlemen, start your engines", you won't be able to. :smt100 Maybe you should just pretend you smash it to bits as a 'thought experiment'. Your ignition power does come through the switch and needs it to be intact to run the boat.

 

[asimpkinsjr]

Dave M,

If you put a continuity tester on pole 1 when the switch is in the 2 or off position you get nothing and likewise the same experiment yields the same results if you put the tester on pole 2 with the switch in the 2 or off position...that being said and agreed how can you have a powered mercathode controller even when the switch is in the off position, or the 2 position consdiering its wired to the 1 position in the schematics?

I am beginning to wonder if we are talking about the same thing here. So I want to use only Sea Ray terminology, and their wiring diagrams as I posted on the second page of this link. If you go look at those, you can click on them and bring them up full size.

I don't know about the continuity tester you are using, or how you are using it. So I don't necessarily agree with your assessment of the results of using it, I couldn't interpret them without knowing more. But I do agree with what you said earlier about how the Guest switch works. But how the Guest switch works, and what position it is in, is normally also irrelevant to the question at hand if you have the normal Sea Ray wiring.

If you go back and look at the wiring diagram, you will see that battery 1 is solidly wired to the terminal called Bat 1 on the guest switch. So the Bat 1 terminal will always be powered 'hot' by battery 1, if battery 1 is a good, charged battery.

Now, for a moment, forget what happens inside the Guest switch. The Bat 1 terminal is connected directly to battery 1. Now you find a wire from this same Bat 1 terminal; it runs to the circuit breaker panel. It uses the Bat 1 terminal only as a physical wiring connection point, so this wire to the breaker panel is also always hot if battery 1 is good.

At the breaker panel, this wire that is always hot from Battery 1 provides power to the Mercathode system, the two bilge pumps, and stereo memory if present. Also the sump pump if present. So they are always hot, regardless of the position of the Guest switch.

As a matter of fact, if your boat is wired like the diagram shows, you could take a hammer and start smashing the Guest switch into little tiny pieces :smt021 that you throw overboard (go ahead and do that now). As long as you are careful to preserve the Bat 1 terminal and the wire to the battery 1, plus the wire to the circuit breaker panel that connect to it, your Mercathode system will still work.

:smt018 Wait, there is a problem. When the say "Gentlemen, start your engines", you won't be able to. :smt100 Maybe you should just pretend you smash it to bits as a 'thought experiment'. Your ignition power does come through the switch and needs it to be intact to run the boat.

Dave M.,

On my boat the current situation is that the mercathode only seems powered when the guest switch is in the both position (evidenced by testing the dealer did on the controller), something that we now are thinking could be a result of a miswire at the guest switch ...what Im questioning is how on Dave. S's boat is getting power to the mercathode when the guest switch is in the off or 2 position based upon the wiring diagrams from the owners manual which an excerpt of which you have posted. Im not sure if you are explaining that it makes sense to you based upon SRs diagrams or not...

 

[MLauman]

On my boat the current situation is that the mercathode only seems powered when the guest switch is in the both position (evidenced by testing the dealer did on the controller), something that we now are thinking could be a result of a miswire at the guest switch

There is no way to wire (or miswire) the switch to produce that result. The only plausible explanation for this condition would be a (highly) defective switch - could the knob be out of sync?

what Im questioning is how on Dave. S's boat is getting power to the mercathode when the guest switch is in the off or 2 position based upon the wiring diagrams from the owners manual which an excerpt of which you have posted. Im not sure if you are explaining that it makes sense to you based upon SRs diagrams or not...

Dave S's results are exactly as they should be per the diagrams and my boat is the same way. The effect of connecting the mercathode wire to the batt1 terminal on the switch is exactly the same as connecting the mercathode directly to the #1 battery. It makes no difference which position the switch is in.