Today, I "fixed" the alternator

[roaringgirl]

There were a number of problems related to this particular application, where there's a battery isolator between the alternator output and the 2 separate battery banks:
1. The charge sense wire was attached directly to the output of the alternator. I have moved it to the house-battery post of the battery isolator.
2. Because the alt is behind the batt separator, the internal reg can't know the voltage of the batt, hence it needs to be externally regulated. I rewired the internals to bypass the internal reg, so the external reg can actually decide on the field voltage.
3. Inside the alternator there was a feedback loop (by design) so that once running, the reg took input from the alternator itself, so again, when behind a batt isolator, the alternator was not responding to the batt voltage, only its own output voltage. I removed this internal loop.

It is now giving 14.3V (as requested by the reg) and providing at least 40A (i don't have any more load I can give it right now, but it may provide more).


These are 3 reasons why this installation has never and could never have worked properly. It wasn't me so I can safely say that whoever installed it was a muppet.

 

[Wing Mark]

Do you have a fuse between the alternator and the batteries?
Do you have a spare alternator ready to fit?

 

[roaringgirl]

Do you have a fuse between the alternator and the batteries?
Do you have a spare alternator ready to fit?

Yes there is a fuse.

There is a separate alternator for the engine start, and we have 1kW of solar, a wind turbine and a hydro-generator; but no spare alternator!

 

[chubby]

Do you have a fuse between the alternator and the batteries?
Do you have a spare alternator ready to fit?

How many do keep a spare alternator on board for coastal cruising in European waters?

 

[Wing Mark]

How many do keep a spare alternator on board for coastal cruising in European waters?

A lot more than interfere with the internal current limiting of the alternator would be my guess?

 

[PaulRainbow]

Do you have a fuse between the alternator and the batteries?
Do you have a spare alternator ready to fit?

How many boats have fused alternators ?

How many people carry spare alternators ?

 

[PaulRainbow]

There were a number of problems related to this particular application, where there's a battery isolator between the alternator output and the 2 separate battery banks:
1. The charge sense wire was attached directly to the output of the alternator. I have moved it to the house-battery post of the battery isolator.
2. Because the alt is behind the batt separator, the internal reg can't know the voltage of the batt, hence it needs to be externally regulated. I rewired the internals to bypass the internal reg, so the external reg can actually decide on the field voltage.
3. Inside the alternator there was a feedback loop (by design) so that once running, the reg took input from the alternator itself, so again, when behind a batt isolator, the alternator was not responding to the batt voltage, only its own output voltage. I removed this internal loop.

It is now giving 14.3V (as requested by the reg) and providing at least 40A (i don't have any more load I can give it right now, but it may provide more).


These are 3 reasons why this installation has never and could never have worked properly. It wasn't me so I can safely say that whoever installed it was a muppet.

Your description seems a little confusing. Are you saying that you previously had an internal regulator, but now have an external one ? Or are you referring to the sense wire ?

 

[roaringgirl]

Your description seems a little confusing. Are you saying that you previously had an internal regulator, but now have an external one ? Or are you referring to the sense wire ?

The alternator was previously internally regulated, it also had an external regulator. I rewired the internals to skip the internal regulator and to remove the feedback loop that took the field current directly from the alternator output. The external regulator had a sense wire which was hooked up to the alternator output, this doesn't work when the alternator is separated from the battery banks by an isolating diode pack, so I moved the sense wire as well - it is now sensing voltage at the house battery.

 

[PaulRainbow]

The alternator was previously internally regulated, it also had an external regulator. I rewired the internals to skip the internal regulator and to remove the feedback loop that took the field current directly from the alternator output. The external regulator had a sense wire which was hooked up to the alternator output, this doesn't work when the alternator is separated from the battery banks by an isolating diode pack, so I moved the sense wire as well - it is now sensing voltage at the house battery.

Gotcha. It's quite common for the alternator to be machine sensed, even when a diode is fitted. It does work, in as much as it senses the alternator output, but, as you say, it doesn't work properly because it does not take into account and voltage drop through the diode. Whoever fitted the external regulator and wired it to the alternator was indeed a muppet

 

[dslittle]

How many do keep a spare alternator on board for coastal cruising in European waters?

We do (and a spare starter motor…)

 

[halcyon]

Gotcha. It's quite common for the alternator to be machine sensed, even when a diode is fitted. It does work, in as much as it senses the alternator output, but, as you say, it doesn't work properly because it does not take into account and voltage drop through the diode. Whoever fitted the external regulator and wired it to the alternator was indeed a muppet

What make/type is the external reg ? some drop down in voltage by reverting to the internal alt reg, OP does not have one now.

Brian

 

[PaulRainbow]

What make/type is the external reg ? some drop down in voltage by reverting to the internal alt reg, OP does not have one now.

Brian

No idea, not my boat.

 

[halcyon]

No idea, not my boat.

No but a point that should have been raised, also reading the service battery volts for alt reg can result in high voltage to engine battery via a blocking diode, all need checking.

Brian

 

[PaulRainbow]

No but a point that should have been raised, also reading the service battery volts for alt reg can result in high voltage to engine battery via a blocking diode, all need checking.

Brian

If the batteries are being charged from an alternator via a diode or fet based split charge device, you have two choices, you sense the voltage of engine battery, or the voltage of the domestic bank. If you base the charging on the engine battery, which is likely fully charged (or thereabouts) you'll be applying a relatively low voltage to the domestic bank, which will take much longer to charge and almost certainly will never get fully charged. If you sense the domestic bank voltage the batteries will be charged at a higher voltage and will charge much faster.

Sure, the engine battery will be sitting at a higher voltage than it needs to be at, but if it's charged it won't take any current, so no big deal IMO. It's no difference to the many boats that have mains chargers that use the same charge regime for all batteries (that's most chargers), no different to all of the boats using solar power with a VSR and no difference to all of the boats that charge from the alternator with a VSR.

Basically it's just about everyone who doesn't have totally different charging systems for multiple banks or those that have devices such as B2B chargers etc. Holding the engine battery at absorption voltages is, in most cases, not an issue. If the domestic bank needs a higher charging voltage than the engine battery can tolerate, that would be a different story.

But, you know all of this Brian.