Low charge current from alternator, what am I missing?

[GILow]

So, today I finally needed to charge the batteries from the engine. This is the first time I’ve had to do this since installing this engine.

Batteries are a bank of 6 Trojan T105’s, wired in series/parallel to provide 675 AH @ 12 volts.

Alternator is a 75 amp, factory fitted model from Beta, about a year old. No smart regulator or anything, totally standard factory setup.

State of charge on the house bank was 70%, according to my battery monitor, which feels about right, based on the lack of solar and the hard work they’ve been doing the last few days. Battery voltage was 12.4V with a few minor loads running, such as AIS, gas alarms, etc. (Nothing all that significant.)

So, I started the engine and, after a minute, switched on the shunt to connect the house bank to the engine bank.

And I got 45 amps of charge. Nothing more. No change from increasing engine revs either, I got that from 1000 rpm, right through to 2200.

Battery bank voltage climbed quickly to 13.6 and stayed there while charging.

I checked for voltage drop across the charge cables and got just 0.15 volts loss. Alternator was not particularly warm.

So, is this the alternator saying 13.6 volts is heaps? Or should it have gone higher and harder? I thought 14.2 was the current “standard”?

Am I going to need to retrofit a smart regulator to get the full potential of this alternator?

Over to the charge enthusiasts.

Matt

[OzeLouie]

Matt, batteries and charging them is outside my area but have pickup from others that batteries have a charge limit of 'xx' amp/hrs per hour and that's all you can poke into them regardless of how many A/h is presented.
Louie

[sailorboy1]

Have no idea what voltage the alternator should do. Does seem you should get more than 45 charge amps plus whatever normal loads you had on, so maybe 60 amps total, out of a 75 alternator. But since increasing the rpms had no effect it sounds that is all it can do.

[GILow]

Originally Posted by OzeLouie

Matt, batteries and charging them is outside my area but have pickup from others that batteries have a charge limit of 'xx' amp/hrs per hour and that's all you can poke into them regardless of how many A/h is presented.
Louie

Yes, I looked into this a while back. Based on the experience of others with a similar setup, for this particular bank 100 amps should be no problem at all, at least not until they are nearly full. Maybe even more at this state of charge.

P.S. there is no such thing as amps/hrs. Just amps. I'm telling you this now so StuM doesn't come along and tick you off at length.

[GILow]

Originally Posted by sailorboy1

Have no idea what voltage the alternator should do. Does seem you should get more than 45 charge amps plus whatever normal loads you had on, so maybe 60 amps total, out of a 75 alternator. But since increasing the rpms had no effect it sounds that is all it can do.

Yeah, it's a worry. There were practically no loads at the time so 45 was all the alternator was delivering.

If it should deliver more, well, it is under warranty. But before I poke Beta with a big stick I figured I should check with the brains-trust to see if I've missed something.

[Wotname]

Matt, can you provide the make and model of the alternator that Beta fitted - might be a sticker on the alternator?

[rslifkin]

45 amps very well might be all the batteries can accept at 13.6 volts. With an internally regulated alternator, there's a trade off. You can either crank up the voltage for faster charging, or you can keep it closer to a float voltage to avoid cooking the batteries when motoring for hours with them already full.



My internal regulated alternators do push a bit more voltage than yours, however. Fully warmed up in hot summer weather, I usually see around 13.9 volts. Colder weather or right after a cold start will be higher. For what it's worth, if I fire up the engines (1x 55A Mando alternator on each) and bring them to a 1200 rpm high idle to warm up a little, I usually see around 45 amps into the batteries with the bilge blowers still running (closer to 60 amps if I shut them off). So I'm getting about 30 amps per alternator, plus whatever the engines are using. But 1200 rpm for me is also not enough to quite hit full output, I think.


Was anything using power at the time you observed this? If you're using, say, 15 amps, then the alternator is putting out 60, but the batteries are only getting 45.

[smac999]

Was the 45a measured at the alternator. Or what you are seeing at the battery monitor? If you are seeing +45 at battery monitor you need to add the engine bank charging abd also the house loads. So you might be 55a+ at alt.

45-55 is probably all you are going to get from a 75a internal reg alt. Add a balmar external reg for better charging.

The 13v is normal with a big bank that is depleated It’s in bulk. The voltage will climb as it charges.


If you have an inverter plug a heater in or hair dryer etc So you are pulling -150a from bank and try alt again. Now it’s probably charging 12.5-13v and you will see max alternator amps. And you’re know if the 45a amps is from a low absorb voltage of 13.6 And the alt was limiting itself or if that is simply the max bulk amps.

[Stu Jackson]

Matt,


1. You were at 70% SOC, that's a pretty full battery bank. This "charge limit" someone mentioned is called battery acceptance. As banks get fuller, they can accept less current, at whatever the charging voltage is.

2. You mentioned the voltage. Had you measured the voltage ever before when using the alternator? Do you know what the regulator is set for? As banks begin to charge the voltage rises from the charge source(s) until the the pre-set limit or target is reached, at which time the current will begin to drop. I'm sure you know this, it's battery charging 101.

That said, many of us have noted that the battery acceptance of a nominal 400 ah bank is around 50 to at most 75A at 50% SOC. The lower the voltage the less A will be "pushed". It appears that your regulator is set to 13.6V which is a tad lower than most of us have experienced with internal regulators. Maine Sail has commented on this many times.

With a 70% SOC one would expect less than 50 A anyway.

The only suspicious item is that the current didn't change when you revved the engine. Hmmm... I'll continue to think this one over.

[sailorboy1]

My last sets of 440ah T105 house would accept way more than 45 at 70% soc. At that soc they would accept at least 100 amps.

I seriously doubt this is a battery acceptance issue.

[Nord Sal]

Belt tension?

[Cadence]

Originally Posted by GILow

So, today I finally needed to charge the batteries from the engine. This is the first time I’ve had to do this since installing this engine.

Batteries are a bank of 6 Trojan T105’s, wired in series/parallel to provide 675 AH @ 12 volts.

Alternator is a 75 amp, factory fitted model from Beta, about a year old. No smart regulator or anything, totally standard factory setup.

State of charge on the house bank was 70%, according to my battery monitor, which feels about right, based on the lack of solar and the hard work they’ve been doing the last few days. Battery voltage was 12.4V with a few minor loads running, such as AIS, gas alarms, etc. (Nothing all that significant.)

So, I started the engine and, after a minute, switched on the shunt to connect the house bank to the engine bank.

And I got 45 amps of charge. Nothing more. No change from increasing engine revs either, I got that from 1000 rpm, right through to 2200.

Battery bank voltage climbed quickly to 13.6 and stayed there while charging.

I checked for voltage drop across the charge cables and got just 0.15 volts loss. Alternator was not particularly warm.

So, is this the alternator saying 13.6 volts is heaps? Or should it have gone higher and harder? I thought 14.2 was the current “standard”?

Am I going to need to retrofit a smart regulator to get the full potential of this alternator?

Over to the charge enthusiasts.

Matt

To be honest I didn't read your post closely. It sounds to me that you have lost a diode in the alternator and are only getting half wave recification

[Stu Jackson]

Originally Posted by sailorboy1

My last sets of 440ah T105 house would accept way more than 45 at 70% soc. At that soc they would accept at least 100 amps.

I seriously doubt this is a battery acceptance issue.

Internal or external regulation? Voltage setpoint?


Seem to be important figures to include, if you would, please. Thx.

[Cheechako]

With 100 - 125 amp alternators and external regulator I rarely got over 15 mins of hard charging to a bank. 100 amp alt may put out 80-85 amps for 15 mins or less before backing off.
With an internal reg and unknown alternator you really don't know what it's supposed to put out I suppose. But only 45 amps from a 75 amp sounds probable.

Resting voltage on a charged marine battery seems to be about 12.45 IME.

The other possibility is that you ordered a 75 amp alternator option and it never got installed before the engine was shipped? You may want to check that...

[Cheechako]

Originally Posted by GILow

Yeah, it's a worry. There were practically no loads at the time so 45 was all the alternator was delivering.

If it should deliver more, well, it is under warranty. But before I poke Beta with a big stick I figured I should check with the brains-trust to see if I've missed something.

Try testing it with a heavy load going, it will likely jump up.