Confused by My Alternator to battery Charger

[churchward]

OK I am going to risk it and bring up an electrical topic.

 

On board I have a Sterling battery to Alternator charger that controls(?) (It’s one of the big square units not the PDAR thingy) and splits the output of my single alternator to the two battery banks. Intrigued by one of Gibbos technical guidance and discussion pages on his Smartgauge site about alternator controllers and modern alternators I thought I would take some readings on what he voltage was at the alternator and what difference the sterling unit made to the voltage going to the battery.

 

The results were somewhat as expected except in one small way. I shall explain. The cycle on start-up is that the Sterling unit for the first couple of mins just sends the alternator output to the starter battery (no voltage boost) to quickly help it recover from starting the engine. I measured the alternator output at this point, as this should be the voltage as generated by it. The output was 14.58V, quite high I thought. The unit then acts as a charge splitter and diverts alternator output to both sets of battery banks (I think) then finally gets to it's "bulk" charge phase when it should be boosting the voltage to 14.8V or so. This it seems to do measured at the output from the Sterling unit to the domestic battery bank (not the starter).

 

Now getting to the odd bit the alternator output voltage seems to drop at this point to 14.38V. Why would it do this and is it the Sterling unit effecting this or just something in the Alternator?

 

Anyhow I can see why Gibbo claims that alternator controllers don't do much these days with Alternators already pushing out a high voltage themselves.

 

If or when the Sterling unit goes the way of the pear I shall I think add the Smartbank advanced unit to my Smartgauge (when Father Christmas delivers it!) and relay, as I am not sure the Alternator to Battery charger is of any real benefit.

[Scotty]

As I understand it:

The Sterling unit is putting a load on the alternator forcing the voltage down, then in theory the alternator will 'fight back' and put out a higher current.

The Charger then uses this extra current to boost the output voltage given to the batteries.

[churchward]

As I understand it:

The Sterling unit is putting a load on the alternator forcing the voltage down, then in theory the alternator will 'fight back' and put out a higher current.

The Charger then uses this extra current to boost the output voltage given to the batteries.

True, but as measured at the alternator the opposite seems to be happening i.e. the voltage is higher (not by much) before it starts adding in it's "artificial load"

[Gibbo]

OK I am going to risk it and bring up an electrical topic.

 

On board I have a Sterling battery to Alternator charger that controls(?) (It’s one of the big square units not the PDAR thingy) and splits the output of my single alternator to the two battery banks. Intrigued by one of Gibbos technical guidance and discussion pages on his Smartgauge site about alternator controllers and modern alternators I thought I would take some readings on what he voltage was at the alternator and what difference the sterling unit made to the voltage going to the battery.

 

The results were somewhat as expected except in one small way. I shall explain. The cycle on start-up is that the Sterling unit for the first couple of mins just sends the alternator output to the starter battery (no voltage boost) to quickly help it recover from starting the engine. I measured the alternator output at this point, as this should be the voltage as generated by it. The output was 14.58V, quite high I thought. The unit then acts as a charge splitter and diverts alternator output to both sets of battery banks (I think) then finally gets to it's "bulk" charge phase when it should be boosting the voltage to 14.8V or so. This it seems to do measured at the output from the Sterling unit to the domestic battery bank (not the starter).

 

Now getting to the odd bit the alternator output voltage seems to drop at this point to 14.38V. Why would it do this and is it the Sterling unit effecting this or just something in the Alternator?

 

Anyhow I can see why Gibbo claims that alternator controllers don't do much these days with Alternators already pushing out a high voltage themselves.

 

If or when the Sterling unit goes the way of the pear I shall I think add the Smartbank advanced unit to my Smartgauge (when Father Christmas delivers it!) and relay, as I am not sure the Alternator to Battery charger is of any real benefit.

 

That's operating correctly. It's doing what it is supposed to do.

 

If you run your batteries down much further (so that the Sterling is forced into a proper bulk charge - at present you're only seeing the acceptance stage) then run the same tests you will see the voltage at the alternator (when the Sterling is split charging) drop much lower. What it does is load up the alternator until the alternator voltage drops down to 13.5 volts, it then transforms this voltage back up to the required acceptance voltage (14.8 in your case).

 

At present this isn't happening because the domesticas aren't flat enough and it can get the voltage right up without having to load the alternator voltage down.

 

Gibbo

 

True, but as measured at the alternator the opposite seems to be happening i.e. the voltage is higher (not by much) before it starts adding in it's "artificial load"

 

But your post says 14.58 dropping to 14.38?

 

Gibbo

[churchward]

That's operating correctly. It's doing what it is supposed to do.

 

If you run your batteries down much further (so that the Sterling is forced into a proper bulk charge - at present you're only seeing the acceptance stage) then run the same tests you will see the voltage at the alternator (when the Sterling is split charging) drop much lower. What it does is load up the alternator until the alternator voltage drops down to 13.5 volts, it then transforms this voltage back up to the required acceptance voltage (14.8 in your case).

 

At present this isn't happening because the domesticas aren't flat enough and it can get the voltage right up without having to load the alternator voltage down.

 

Gibbo

 

 

 

But your post says 14.58 dropping to 14.38?

 

Gibbo

 

Ta, yes I did say that and I was right I just confused myself in my second post!

[towbarman]

As I understand it:

The Sterling unit is putting a load on the alternator forcing the voltage down, then in theory the alternator will 'fight back' and put out a higher current.

The Charger then uses this extra current to boost the output voltage given to the batteries.

YOUR RIGHT NO NEED FOR STERLING JUST PUT SENSING WIRE FROM ALTERNATOR TO A LOW VOLTAGE POINT IN ELECTRICS IE 12V THEN THIS TRICKS ALTERNATOR TO THINK BATT IS FLAT FULL CHARGE AHEAD TO MAX AMPS OF ALTERNATER NOW DOES SAME AS STERLING WITHOUT STERLING /PS FIT 30AMP SELF SWIT CHING SPLIT CHARGE RELAY AS USED IN MODERN TOWBARS TODAY Y HAVE A STERLING?

[Gibbo]

YOUR RIGHT NO NEED FOR STERLING JUST PUT SENSING WIRE FROM ALTERNATOR TO A LOW VOLTAGE POINT IN ELECTRICS IE 12V THEN THIS TRICKS ALTERNATOR TO THINK BATT IS FLAT FULL CHARGE AHEAD TO MAX AMPS OF ALTERNATER NOW DOES SAME AS STERLING WITHOUT STERLING /PS FIT 30AMP SELF SWIT CHING SPLIT CHARGE RELAY AS USED IN MODERN TOWBARS TODAY Y HAVE A STERLING?

 

I repeat my comment in the other thread.

 

Gibbo

[ditchcrawler]

I repeat my comment in the other thread.

 

Gibbo

He may be new and shout, but his advice is a bit like looking for a gas leak with a candle

[chris w]

YOUR RIGHT NO NEED FOR STERLING JUST PUT SENSING WIRE FROM ALTERNATOR TO A LOW VOLTAGE POINT IN ELECTRICS IE 12V THEN THIS TRICKS ALTERNATOR TO THINK BATT IS FLAT FULL CHARGE AHEAD TO MAX AMPS OF ALTERNATER NOW DOES SAME AS STERLING WITHOUT STERLING /PS FIT 30AMP SELF SWIT CHING SPLIT CHARGE RELAY AS USED IN MODERN TOWBARS TODAY Y HAVE A STERLING?

Well 99% of the alternators used on boats won't have a "sensing wire" terminal on the alternator. So what are you going to do now?