Alternator output Voltage a bit high

[Ceirwan]

Just fitted a new engine start battery today, after wiring it in I fired up the engine (1gm10) on the domestic bank and then switched to the new engine start battery.
The engine sounded like it took a bit of a load on which I thought odd as the battery was new and fully charged.

A quick check from the trusty multimeter showed the charging voltage at around 15.04 volts which seems rather high to me, the alternator is the standard 35AH one that came with engine.
Any thoughts, likely causes? (The regulator is still the standard one thats built in. )
From what I remember it should be more like 14.4-6

 

[VicS]

Just fitted a new engine start battery today, after wiring it in I fired up the engine (1gm10) on the domestic bank and then switched to the new engine start battery.
The engine sounded like it took a bit of a load on which I thought odd as the battery was new and fully charged.

A quick check from the trusty multimeter showed the charging voltage at around 15.04 volts which seems rather high to me, the alternator is the standard 35AH one that came with engine.
Any thoughts, likely causes? (The regulator is still the standard one thats built in. )
From what I remember it should be more like 14.4-6

I think I would take the alternator in to an auto-electrician for checking.

 

[morgandlm]

I think I would take the alternator in to an auto-electrician for checking.

A good idea but before that perhaps also check the charging voltage when on the domestic battery and check that you have not done something odd with the wiring (you mentioned "wiring in", not simply connecting.

Morgan

 

[Ceirwan]

Voltage is at around 15.04 on both, when selected together and on just the domestic or start when selected individually.
I'm in the process of completely re-wiring, but right now all thats connected are the batteries, engine and the 1-2-both switch. Theres not a huge amount to get wrong with that wiring!

 

[charles_reed]

Voltage is at around 15.04 on both, when selected together and on just the domestic or start when selected individually.
I'm in the process of completely re-wiring, but right now all thats connected are the batteries, engine and the 1-2-both switch. Theres not a huge amount to get wrong with that wiring!

Definitely into the auto-electrician's for a check, if the reading is correct. That old Hitachi 35 amp, on its own regulator charges at about 13.5v.

Very new, replacement alternators appear to start off @ about 15v and within seconds drop to 14 with heavily discharged batteries and 13.5v with well charged batteries.

Only other possibility is that your voltmeter, because of a failing internal 9v battery, is over-reading. Probably the most sensible thing to do is check that first

 

[lw395]

Voltage is at around 15.04 on both, when selected together and on just the domestic or start when selected individually.
I'm in the process of completely re-wiring, but right now all thats connected are the batteries, engine and the 1-2-both switch. Theres not a huge amount to get wrong with that wiring!

If the batteries are both fully charged then the current will be very low.
Alternators don't always regulate well down to no current.
If it's a cheap meter it my be reading the peaks of the spikes.
Put at least a 1 amp load on it and see what you get.

 

[Stemar]

Only other possibility is that your voltmeter, because of a failing internal 9v battery, is over-reading. Probably the most sensible thing to do is check that first

This would be the first thing I'd check.

What's the reading on a rested, charged battery? I'd expect about 12.7 v. If it's more, turn the radio on for a few minutes, turn it off and try again. If it's still reading high it's the voltmeter at fault.

 

[Ceirwan]

This would be the first thing I'd check.

What's the reading on a rested, charged battery? I'd expect about 12.7 v. If it's more, turn the radio on for a few minutes, turn it off and try again. If it's still reading high it's the voltmeter at fault.

I'll go with the check of the multimeter before I start unbolting stuff. I'd expect the alternator to be OK, the engine is pretty new hasn't seen much use and throughout winter the boat is dehumidified and heated.
I've also got a bat charger that can check voltage so I can do a comparison.

 

[Ceirwan]

Thanks to all help. Defective multimeter adding a cheeky 0.7v. Charging exactly 14.4v