Service battery being drained whilst switched off

[ste7ve]

I have a Nimbus motorboat with a bank of 3 x 80Ah service batteries.
I replaced them last week and also also installed a Victron app on my phone which displays the battery condition, via bluetooth from the Victron battery monitor. This makes it easy to see the current and voltage when going around the boat.
At anchor yesterday (first time on this boat), I found that even with the main service battery switch on OFF I had a continuous current drain of 17 to 20 amp, with corresponding drop in voltage. This may partly explain why I had to replace the old batteries, apart from them never having been topped up, and why the shorepower charger always seemed to be on.

There are clearly things which are wired not through the main battery switch, eg. feeds to two auto bilge pumps, maybe also the radio. I could not find anything running at all that would be taking this level of power, which was up to 250 watts. Something should be getting hot because of this rogue current flow...!

Has anyone some thoughts on what may be causing this situation?

The only thing I wondered is if the Mastervolt charger could somehow have a fault causing the current loss, because clearly it is connected to the battery bank.
I also have a Mastervolt Battery Mate, which controls the charging from the alternator across my 3 battery banks, engine, service and heavy gear (thruster & windlass).

 

[Poey50]

I thought I was going to read about some small hidden vampire loads! I've no idea as to cause but I hope you have disconnected the negative cable to the house bank until all is sorted. As you say that is a lot of power going rogue.

 

[Toodle-oo!]

Turn off the heater!
I'd be tracing each and every cable that comes off the batteries.
I'd also look at how your three banks are connected - maybe the load is attached to one of them and for some reason your service bank is supporting that bank.
New boat teething problems! Can the previous owner assist?

 

[vyv_cox]

20 amps sounds like a very bad short. Have you wired the battery+ to the anodes? At that current something will be getting hot.

 

[Boater Sam]

Disconnect every + feed off the batteries. Connect back one at a time till you find which one.

How are you measuring the amps loss? Clamp ammeter?

Other causes, alternator duff even though it will charge [ should isolat with the switch but some don't ] or one duff battery in the bank.

 

[peteK]

Are you sure you read the meter correctly and its not milliamps.

 

[VicS]

20 amps sounds like a very bad short. Have you wired the battery+ to the anodes? At that current something will be getting hot.

If its going out via the anodes they will soon be gone

 

[greeny]

I have a Nimbus motorboat with a bank of 3 x 80Ah service batteries.
I replaced them last week and also also installed a Victron app on my phone which displays the battery condition, via bluetooth from the Victron battery monitor. This makes it easy to see the current and voltage when going around the boat.
At anchor yesterday (first time on this boat), I found that even with the main service battery switch on OFF I had a continuous current drain of 17 to 20 amp, with corresponding drop in voltage. This may partly explain why I had to replace the old batteries, apart from them never having been topped up, and why the shorepower charger always seemed to be on.

There are clearly things which are wired not through the main battery switch, eg. feeds to two auto bilge pumps, maybe also the radio. I could not find anything running at all that would be taking this level of power, which was up to 250 watts. Something should be getting hot because of this rogue current flow...!

Has anyone some thoughts on what may be causing this situation?

The only thing I wondered is if the Mastervolt charger could somehow have a fault causing the current loss, because clearly it is connected to the battery bank.
I also have a Mastervolt Battery Mate, which controls the charging from the alternator across my 3 battery banks, engine, service and heavy gear (thruster & windlass).

We don't know what gear you've got onboard or the wiring configuration so any attempts to advise you would only be guesses. As has been said earlier, check it's not milliamps (more in keeping with radio etc). Do you have an inverter by any chance that has been left on and is running something at 240 volts. Fridge, ac unit, heaters? Need to start disconnecting at the battery to find the culprit if it really is 20 amps.

 

[ste7ve]

Thanks for ideas so far
Just to answer some of the questions:
- I have the voltage and ampage shown continously on my phone with a time graph as well. It's an excellent Victron facility
- I have done no wiring changes to the boat at all other than swap out the old batteries with identical new ones.
- I have individual isolator switches for all 3 battery banks. With them all off and no charging going on the current drain is still there and it takes the voltage down to around 12.6V

 

[Boater Sam]

If all 3 battery banks are isolated, which bank is going down?
If you are using the Victron to show you, the batteries cannot be isolated!!!! You cannot be doing both!!!
If you really have isolated by disconnecting ALL the batteries, with a volt meter which battery is duff and pulling the rest down?

 

[ste7ve]

If all 3 battery banks are isolated, which bank is going down?
If you are using the Victron to show you, the batteries cannot be isolated!!!! You cannot be doing both!!!
If you really have isolated by disconnecting ALL the batteries, with a volt meter which battery is duff and pulling the rest down?

It's the service batteries as originally explained.
The battery monitor is always on and only draws 1mA. The addition of the bluetooth dongle plugged into it is also very low.
The shunt for the monitor is wired in as standard on the negative side of the battery bank.
There are no duff batteries, all the others are fine.

 

[vyv_cox]

A little rule of thumb when investigating machinery faults is to first check that the instrumentation is giving the correct information. My experience is that if something is drawing 20 amps from a battery the voltage would be a lot lower than 12.6. My suspicions lie with the app or sensors.

 

[ste7ve]

20 amps sounds like a very bad short. Have you wired the battery+ to the anodes? At that current something will be getting hot.

Vyv
I haven't changed any of the battery wiring, just replaced with identical batteries.
Are you suggesting that if I disconnected the main, earthed anode it might be a good place to start?

 

[Boater Sam]

Sorry but you cannot have all the batteries disconnected if the Victron is still working.
Disconnect EVERYTHING on all battery positives and test with a voltmeter.
Reconnect one thing at a time, check the current each one draws as you connect. That way you will find out where the power is going.
#How do you know all the batteries are OK if they are not all disconnected so that you can check the voltage of each individual battery?#

Whats this main earthed anode you are talking about? You have a landline connected? You have a GRP hull with earth cables to external anodes?

 

[ste7ve]

Sorry but you cannot have all the batteries disconnected if the Victron is still working.
Disconnect EVERYTHING on all battery positives and test with a voltmeter.
Reconnect one thing at a time, check the current each one draws as you connect. That way you will find out where the power is going.
#How do you know all the batteries are OK if they are not all disconnected so that you can check the voltage of each individual battery?#

Whats this main earthed anode you are talking about? You have a landline connected? You have a GRP hull with earth cables to external anodes?

OK understand what you are saying, it could be a duff brand new battery.
Can only measure current via the monitor but that should be OK.
Sorry wrong wording about anode. It has a black wire on it which I assume is connected to the main negative point for all the batteries.

 

[pvb]

#How do you know all the batteries are OK if they are not all disconnected so that you can check the voltage of each individual battery?#

You seem to be assuming that there's one faulty battery which is affecting the others. However, this wouldn't result in any current flow through the monitor's shunt. The batteries have a common negative.

 

[pvb]

OK understand what you are saying, it could be a duff brand new battery.

That wouldn't cause a current to flow through the shunt.

 

[Boater Sam]

OK understand what you are saying, it could be a duff brand new battery.
Can only measure current via the monitor but that should be OK.
Sorry wrong wording about anode. It has a black wire on it which I assume is connected to the main negative point for all the batteries.

You seem to be assuming that there's one faulty battery which is affecting the others. However, this wouldn't result in any current flow through the monitor's shunt. The batteries have a common negative.

As has been said, without a multimeter to compare readings how do you know that the Victron is not giving you false information? With 20 Amps flowing you should have smoke, flames, stink and panic!

I know that the shunt is in the main neg, I was trying to get the OP to disconnect everything, he seems to have a lot of battery circuits with 3 master switches.
Its good training too for fault finding on batteries to check individual battery resting voltages.

 

[Rocksteadee]

Are you sure you read the meter correctly and its not milliamps.

20ma would be about right for radio memory

 

[JumbleDuck]

A little rule of thumb when investigating machinery faults is to first check that the instrumentation is giving the correct information. My experience is that if something is drawing 20 amps from a battery the voltage would be a lot lower than 12.6.

I agree. Switching on a couple of LED lights and the GPS is enough to pull my house bank (120Ah) down to 12.6V. 20A going out would have it MUCH lower.