What is draining my 260 Battery?

[thunderbird1]

I have two batteries on my boat. With the selector switch set to number 2 (my house battery), the number 1 battery continues to discharge. Over a weekend, number 1 might drop from 12.6v down to 12.2v. On some weekends we have observed the number 2 house battery (the one selected) discharge less than the suspect number 1. Odd huh?

Here is where the mystery gets more challenging. When the battery selector is set to off, both batteries remain charged. This rules out items which bypass the battery selector switch such as the bilge pump. Moreover, the battery is probably not defective because it does not discharge when the selector is set to off.

Any idea what might be draining my battery?

 

[Dave S]

My understanding is both batteries should be taking a charge from the onboard charger regardless of where your power switch is set as long as you remain plugged into shore power. It's probably normal to see a bit of a drop in voltage once shore power is disconnected and nothing is charging the batteries. Are you getting the readings off Smart Craft?

 

[thunderbird1]

Are you getting the readings off Smart Craft?

Yes, Smart Craft. Is there anything directly connected to battery #1 (bypassing the selector switch), other than the battery charger, bilge pump, and windlass? Any suggestions about how best to diagnose the problem?

 

[Dave S]

All of my manuals are at the boat but I believe the owners manual has a complete wiring diagram. I would take a quick look at that to see what is directly wired to the batteries that doesn't go thru the breaker panel (such as sump pumps or the outdrive trim switch). I will try to remember to montor my batteries as well over the next few weeks so maybe I can give you a comparison on my readings as well. You might also want to use battery #1 as your "house battery" for awhile rather than the number 2 battery and compare readings that way.

 

[Dave M.]

From your other post it looks like you may have already guessed what your problem is. I downloaded the boat manual and looked at the wiring diagram. Things wired to battery 1 are:

Mercathode
Bilge pump
Emergency bilge pump
Sump pump
Stereo memory
Battery charger 1

The link that Wesley sent suggests the Mercathode may be your problem.

This thread belongs in the electrical section.

 

[thunderbird1]

Thank you Dave S and Dave M. Once the darn cold wind stops blowing here, I'll dig deeper into the Mercathode system, assuming it may be the source of my discharge. I still don't understand why the battery stops discharging when the selector switch is set to off. It is possible, I suppose, that my Mercathode system is installed incorrectly (that it runs only when the battery selector switch is on).

 

[Dave M.]

Thunderbird1,

Sorry, I forgot to compare my answer to your original description of the symptoms. It does not explain them. Here are three possible scenarios:

1. You are wrong about the symptoms.

2. There is some other thing going on here that is the cause, and you have not yet recognized it exists.

3. You are right about the symptoms and have listed them all. If so, then in indicates to me that the Mercathode system is the problem. It is doing its job trying to protect your Bravo III. It has a sensor in the water that tells it how much current it needs to put out to do its job.

When you have the battery selector in posiition 2, then you apply power to some stuff in the boat, at least switches, and maybe a fridge or something. Now you have DC current flowing in the boat. The Mercathode sensor rightly or wrongly senses that the Mercathode system is not putting out nearly enough current to effectively do it job, and ups the current it dumps into the water.

You have not mentioned where you are on these weekends when you observe this happen. Are you tied up, or on the hook somewhere? Are there other boats nearby?

Dave

 

[never monday]

Is it posible the battery switch is wired backwards? I'm just always looking for the obvious.

 

[thunderbird1]

You have not mentioned where you are on these weekends when you observe this happen. Are you tied up, or on the hook somewhere? Are there other boats nearby?

Dave

Dave: On one occasion tied up with no other boats present. On another, tied up with lots of boats present. The reason I discovered the issue is my battery charger was broken for 2 weekends, so we watched our battery discharge carefully (and conserved like crazy). Thank you so much (never monday and Dave S too) for helping me diagnose the problem. I'm not enough of an electrician to confirm whether the switch is wired backwards, but I'll ask my dealer to check it for me.

 

[Dave M.]

I am not any sort of authority on the Mercathode system, I only know what I have been reading on the internet.

When you were tied up with the broken battery charger, were you connected to shore power? If so, then your boat is one of many in an interconnected system. Depending on any other boats in the system, your Mercathode system may have to work hard to protect against the harm the other boats are trying to inflict on your boat. Same for any stray current that might be trying to flow in the shore power ground system.

I think it is valid to expect that the Mercathode current drain on your battery may be much more when connected to shore power than when not connected, especially with other boats also connected.

I don't see why this would relate to whether you were using the other battery or not, if shore power is the culprit. Maybe it is coincidence. I also don't see how a realistic wiring error would produce these results.