Electrical charging shenanigans

[Dawnrazor]

Evening everyone,
I was wondering if someone could help shed some light on a recurring electrical problem i’ve got with my Elan 384.

When the engine (Volvo D2-40) is fired-up, a battery warning alarm icon lights up along with the audible alarm, which has recently been diagnosed as an overcharging alarm. This usually occurs within a few moments of starting the engine, but on occasions can take 10minutes or so to sound.

This originally started to happen in February this year when she went back in the water. I put it down to the batteries being as old as the boat (2009) and it having been a particularly cold winter that had finally killed them off, as it had generally been sluggish to turn-over and always seemed to spend an age charging the batteries when on shore power.

I replaced the batteries with a 3x Varta LFS95 batteries (1 x engine starting + 2 x domestic) which were a bit more potent than the 3 x 65ah “Topla” batteries fitted by Elan. The alarm still sounded however, and a local marine engineer said it was most likely the alternator at fault. So, that was replaced as well recently.

.........the overcharging alarm however still sounds.

The 2x battery banks are charged via a Mastervolt diode which is connected to the alternator. I think the Mastervolt diode is the ‘BI 1202-S’ model. I don’t have the manual for it unfortunately and it was fitted at the factory. The charging system is original factory-fit, apart from the batteries and the alternator which have all been replaced very recently.

From checking the charge at the diode when the alarm is sounding, it appears the engine battery is being charged at 15.4-16.5v whereas the domestic bank is charged at 14.4v constantly. Is the diode likely to be at fault? It’s distributing current when the engine is running and at rest when no charging is taking place all the batteries are registering 12.4-12.6v.

Before the alarm sounds, both banks are being charged at 14.4-14.6v.

I would really welcome your thoughts on this one as it’s driving me nuts. I’m not particularly electrically-minded unfortunately, so please be kind!

 

[pvb]

When the engine (Volvo D2-40) is fired-up, a battery warning alarm icon lights up along with the audible alarm, which has recently been diagnosed as an overcharging alarm. This usually occurs within a few moments of starting the engine, but on occasions can take 10minutes or so to sound.

It's been wrongly diagnosed - that alarm warns you that there's no charging.

The 2x battery banks are charged via a Mastervolt diode which is connected to the alternator. I think the Mastervolt diode is the ‘BI 1202-S’ model. I don’t have the manual for it unfortunately and it was fitted at the factory. The charging system is original factory-fit, apart from the batteries and the alternator which have all been replaced very recently.

You can download the manual from the Mastervolt website.

From checking the charge at the diode when the alarm is sounding, it appears the engine battery is being charged at 15.4-16.5v whereas the domestic bank is charged at 14.4v constantly. Is the diode likely to be at fault? It’s distributing current when the engine is running and at rest when no charging is taking place all the batteries are registering 12.4-12.6v.

The high charging voltage would suggest that the sense wire is faulty, although that wouldn't explain why the charge voltage to the domestic bank is normal. I'd suggest you ask a decent marine electrician to sort it out.

 

[earlybird]

The diode will typically drop 0.6 - 0.8 v when a useful charging current is passing. This can be measured as a voltage between the diode input terminal, connected to the alternator, and either of the two output terminals. If the reading is very different on one side, the diode may be faulty, although I can't suggest why 16.5 v. Have you got some type of alternator booster to compensate for the diode drop? 14.4v. is good however.
If the starting battery really is seeing such a high voltage for significant periods then it could well suffer damage, though the resting voltage seems fairly OK, even a bit low.
As suggested, you need it investigated.

 

[Dawnrazor]

The diode will typically drop 0.6 - 0.8 v when a useful charging current is passing. This can be measured as a voltage between the diode input terminal, connected to the alternator, and either of the two output terminals. If the reading is very different on one side, the diode may be faulty, although I can't suggest why 16.5 v. Have you got some type of alternator booster to compensate for the diode drop? 14.4v. is good however.
If the starting battery really is seeing such a high voltage for significant periods then it could well suffer damage, though the resting voltage seems fairly OK, even a bit low.
As suggested, you need it investigated.

There isn't an alternator booster fitted, it's just the standard Penta alternator.

Charging voltages to both banks are similar to start with, and then the engine battery bank goes up in voltage considerably, at which point the alarm goes off.

I'll have to take a look at the sensor cable. I'm also tempted to swap some batteries around to see if there is any noticeable difference, although the alarm went off with the original components, and is still doing the same with new batteries and alternator. I'm leaning towards either damaged wiring or a faulty diode.