Mains battery charger - beneteau

[davidej]

We have bought a second-hand Beneteau 361 with twin batteries, which has three isolator switches, one on each positive lead and one on the joint negative lead.

While investigating a voltage drop at a new chart plotter that we have installed, we decided to clean up all the battery terminal joints (with all the isolator switches OFF). We found that, when one of the batteries had been completely re-connected and the positive terminal of the other connected, there was a full 12.6V between the negative lead and the battery terminal. Using an ammeter we found a current drain of around 20-30 mA. The plot thickened when we found that the main busbar showed voltage, when the reconnected battery was switched off, but the switch for the non-connected battery was on.

Further investigation showed that the mains battery charger causes this. It has two positive leads and a joint negative one, each connected to the live side of the three isolator switches. When it was disconnected, these strange symptoms disappeared. I assume it is giving a connection between the positive sides of the two batteries even when they are switched off, thus allowing current to drain from one battery to the other.

Is this normal or do we need to do something about it? If so, what?

If the apparently separate batteries are effectively linked through the charger, it makes nonsense of any sort of battery discipline, trying to keep one with enough charge to start the motor.

Any comments or suggestions would be welcome.

 

[VicS]

Normally as far as I am aware battery chagers with two or more outputs have the outputs independent of each other. It may be an unsuitable charger or be faulty As you say it makes a nonsense off all your battery discipline if your diagnosis is correct.

What type is it maybe someone will know a bit about it.

 

[davidej]

It is Factory fitted so should be suitable.

Will check the make next time I am aboard.

 

[VicS]

Reading through your post again I realise that the voltages you have observed may be creating unnecessary alarm if they were measured with a high impedance meter such as a digital one. They will give readings even when there are very high resistances which will limit current flow to next to nothing.

Exactly how, where and under what conditions did you get this 20 -30 mA reading.

If all that is ever going to flow between the two battery circuits is of this order it may not be significant or anything to worry about.

 

[davidej]

You are quite right - I used a (cheap) digital meter.

When I touched the lead to the terminal it gave a little spark so I put the meter on the 5 Amp range (where you have to put the test lead into a different socket). It read )0.02/0.03 amp. I tried the 200mA range and didn't get anthing.

Does this tell you boffins anything?

Why would all the circuit breaker lights on the main switch panel light up with only the isolaters for the disconnected battery on if there is no leakage of current from the other battery?

Thanks for your help

 

[andy01842]

The problem with a DVM is it has a very high resistance on its input i.e. it takes only a very small current to drive it. Therefore a small capacitor across the input or output of a electronic device (input of chartplotter or output of battery charger) can give 12.6volts but at minimal amps for micro seconds, this can lead to very misleading readings. A light bulb can be a better choice than a DVM in some instances.

 

[Skylark]

Hi David,

I have the same boat. Do you have the owners manual containing the wiring diagram? PM me if you need a copy. The two +ve isolation switches are interconnected. Either "on" will take power from both batteries.

David

 

[davidej]

HI david 361

I do have the manual onboard.

from memory - it shows the two positive isolaters connected on the boat side but not the battery sides. this should mean that if one was off, no current could be drawn from that battery. However the mains charger is connected to the battery side of the isolaters and thus could be a path for current between the two batteries when the switches are off.

I am still no nearer understanding what is going on.

Cheers!

 

[KREW2]

Is it a sterling battery charger?
I don't know if this is applicable to your problem as I know very very little about electrics, but here goes. Last year I added another battery to my bank of two. The third was a designated starting battery all linked through a 1 / 2 / both switch and, connected to a 20 amp sterling charger. I was suprised to see that when I disconnected battery no1 and had the switch turned to position no1 The meter still showed a small amount of voltage at the control panel, however when I disconnected the charger there was none. I phoned sterling and they told me this was correct, and not to worry about it.