Check my alternator / battery logic here

[jac]

Motoring to Portland and notice a smell from the engine start battery and excessive heat. Domestic battery is fine - alternator feeds both batteries via a VSR. On examination battery is slightly deformed so has been replaced but for obvious reasons I’m keen to determine the cause and prevent it.

Multimeter shows 17.5v at the battery with the engine at 2000 rpm so my initial guess is that the alternator regulator is not working. Would anyone disagre.

secondly - likely damage to the new battery from a short period of overcharging - say 30 minutes max although probably less. Will obviously visually check it for deformity and ensure is topped up.

 

[Boater Sam]

You will wreck another battery. Replace/overhaul the alternator.

 

[pmagowan]

IIRC some battery chargers go to as much as 18v for desulphation of the battery but I am not sure of the profile but I would assume you won't 'wreck another battery' instantly. You might make it bubble a bit. Defo need to get things sorted so that a more regular voltage is applied. Get your nose a prize!

 

[VicS]

Motoring to Portland and notice a smell from the engine start battery and excessive heat. Domestic battery is fine - alternator feeds both batteries via a VSR. On examination battery is slightly deformed so has been replaced but for obvious reasons I’m keen to determine the cause and prevent it.

Multimeter shows 17.5v at the battery with the engine at 2000 rpm so my initial guess is that the alternator regulator is not working. Would anyone disagre.

secondly - likely damage to the new battery from a short period of overcharging - say 30 minutes max although probably less. Will obviously visually check it for deformity and ensure is topped up.

Something definitely wrong. You are likely to damage the new battery and the domestic battery at that sort of voltage.

Check for a disconnected battery sense wire especially if you have any fancy advanced regulator fitted ( eg a bit of Sterling's gear ) otherwise get the alternator checked/repaired.
.

 

[Alex_Blackwood]

IIRC some battery chargers go to as much as 18v for desulphation of the battery but I am not sure of the profile but I would assume you won't 'wreck another battery' instantly. You might make it bubble a bit. Defo need to get things sorted so that a more regular voltage is applied. Get your nose a prize!

That is battery chargers, not an alternator. Sounds like duff regulator. I would have alternator checked out ASAP.

 

[jac]

Something definitely wrong. You are likely to damage the new battery and the domestic battery at that sort of voltage.

Check for a disconnected battery sense wire especially if you have any fancy advanced regulator fitted ( eg a bit of Sterling's gear ) otherwise get the alternator checked/repaired.
.

No sensing wire that I can see and certainly no advanced regulator (on the list for the winter, budget dependent of course!) but would have assumed that 17.5 volts would be way over what a working standard alternator would output even if sensing a very low battery.

I’m inclined towards just buying a new alternator- boat is new to us so of unknown maintenance provenance so repairing an alternator that may then have other issues to save a few quid seems risky.

 

[PaulRainbow]

No sensing wire that I can see and certainly no advanced regulator (on the list for the winter, budget dependent of course!) but would have assumed that 17.5 volts would be way over what a working standard alternator would output even if sensing a very low battery.

I’m inclined towards just buying a new alternator- boat is new to us so of unknown maintenance provenance so repairing an alternator that may then have other issues to save a few quid seems risky.

I agree, just get a new alternator.

 

[pmagowan]

That is battery chargers, not an alternator. Sounds like duff regulator. I would have alternator checked out ASAP.

Yes, my point is that it will not cause a battery to self destruct in short order but not going to be good for any prolonged time. The OP wanted to know if the 30 mins would have wrecked a battery. I agree that there is something duff about the alternator/regulator, there is not much else in that system other than wire. If I was debugging I would check all connections and if good remove the alternator and either replace or repair or both so there is a spare.

 

[jac]

Yes, my point is that it will not cause a battery to self destruct in short order but not going to be good for any prolonged time. The OP wanted to know if the 30 mins would have wrecked a battery. I agree that there is something duff about the alternator/regulator, there is not much else in that system other than wire. If I was debugging I would check all connections and if good remove the alternator and either replace or repair or both so there is a spare.

Only other component that I know it has ( and I should stress that I have not gone through tracing every wire to see for any divergence from the original wiring diagram) is the VSR. Can’t see how a VSR would impact overcharging though.

we do have shore power charger but was not on shore power when tested. Also have solar but tested before dawn so no impact and now in bright sunlight battery is showing 13.05 so I’m discounting that.

was chatting the local sea start engineer as their boat is here and we’re members. His view is also alternator so will look to source and replace.

 

[Refueler]

Alternator to local shop and get it checked out first - BEFORE buying new alternator ....

It may be a simple fix ... or a replace the unit fix .... but before spending that hard earned cash - worth it to find out that it is alternator and not something else.

 

[VicS]

No sensing wire that I can see and certainly no advanced regulator (on the list for the winter, budget dependent of course!) but would have assumed that 17.5 volts would be way over what a working standard alternator would output even if sensing a very low battery.

I’m inclined towards just buying a new alternator- boat is new to us so of unknown maintenance provenance so repairing an alternator that may then have other issues to save a few quid seems risky.

Only other component that I know it has ( and I should stress that I have not gone through tracing every wire to see for any divergence from the original wiring diagram) is the VSR. Can’t see how a VSR would impact overcharging though.

we do have shore power charger but was not on shore power when tested. Also have solar but tested before dawn so no impact and now in bright sunlight battery is showing 13.05 so I’m discounting that.

was chatting the local sea start engineer as their boat is here and we’re members. His view is also alternator so will look to source and replace.

The point about checking for a disconnected sensing wire is that if the alternator / fancy regulator is battery sensing it will go to max output volts if the sensing is disconnected trying to get the volts up on the sensing. All the while it sees zero on the sensing it thinks its not outputting enough volts

Getting the alternator checked and repaired by an auto-electrician should be cheaper than buying a replacement. Some alternators are relatively easy to fix DIY. Some are not.
(at different times I replaced the brushes, the regulator , the rectifier and the slip rings on a Lucas ACR )

The VSR wont cause the trouble.