Alternator does not Fully Charge the Batteries

[hellosailor]

tuomas-
In a conventional (automobile) charging system with the regulator integral to the alternator, you will find one charging wire coming out of the alternator, and then a separate wire harness usually with three wires in it, plugged into the alternator as well. Two of those wires are for ignition switch sensing and exciting and the third is a dedicated voltage sense wire that goes to the battery.
This is called a "3-wire" system and the advantage is that it accurately senses when the engine is on or off (ignition sensing), it always consistently excites the alternator based on that, and it accurately reads the battery voltage via the dedicated sense wire. The problem for boats is that if the sense wire is disconnected while the engine is running, the alternator will immediately go to full output and can burn out in 30 seconds. When boaters switch battery banks, if there is no provision to switch the sense wire, either it is disconnected or connected to the wrong battery, creating a charging problem. Switching it properly costs money. ("Echo chargers" and other automatic switches are still fairly new, and of course still cost extra money, but they also solve this problem.)

The alternative, which is simpler, cheaper, faster to build, is to just tie the voltage sense wire to the charging output lead, usually joined at the starter in a "Y" before the charging output also goes to the distribution panel. This is called a "1-wire" system and because it is simple, is sometimes used on off-road vehicles as well. The problem is, a 1-wire system never accurately senses battery voltage, it is reading it's own output not the battery, so it never charges the battery(s) as well.

And because the 1-wire system does not have the extra dedicated wire to tell it the engine has been turned on, and the dedicated wire to excite it when the engine is on, a 1-wire system typically will not charge until it sees higher engine rpm's and generates enough internal magnetic excitement to get itself started. Typically you need to "blip" the engine to a speed well above idle in order to get it to start charging, but that will depend on how well the alternator itself is magnetized.

Advantages to both systems. One is cheap and simple but crude. The other, more complex and (slightly) expensive but more sophisticated.

But if you have a 3-wire and it is not energizing properly, that would indicate something is wrong. Or unique to that external regulator.

[tuomas]

Hellosailor, thanks for the comprehensive clarification. I think Sterling is none of these.

My problem was the voltage needed to the alternator output B+, too. I did not touch the wirings to D+ i.e. th rotor is still excited through the ignition switch and light bulb. For some reason this alternator type needs voltage also to the stator windings to fire up. But this works now via Sterling's own system.

[tuomas]

Here are some initil results:

During weekend I used the 210 ah consumer battery bank to some 75% level and started the engine to see what happens. At some 1/3 rpm I saw 42 amps going to the battery. Most likely some 50-60 amps with full rpm. Unfortunately we had good winds and had to sail, could not test this thoroughly

I also have a feeling that the sulphation of the batteries has become a little better as the volts do not drop as badly as before. Still may have to buy new batteries.

Anyway, pretty pleased at the moment.

[Stu Jackson]

I may have mentioned this earlier in this discussion, but I've been away a few days, sailing, Google: 12v alternator handbook

[tuomas]

Some conclusions after a 5 week holiday sail and new leasure battery bank of 270 Ah: Sterling is a very good peace of equipment. Steady 44 amps running into the battery, so leaving in the morning + coming in in the evening adds about 40-50 Ah into the batteries, which is about the amount we seem to use. During longer engine operations, bulk charging fills the battery completely.

The only drawback is that whether the alternator fired or not must be checked after each start. The firing voltage delivered from Sterling based on the signal from the solenoid may be too short.

[mitiempo]

Originally Posted by tuomas

During longer engine operations, bulk charging fills the battery completely.

Wrong. Any lead acid battery - flooded, gel, or agm - requires a long time to charge completely as the battery's resistance increases. The last 15% or so takes many hours. There is no magical way around this.

[tuomas]

Well, according to my battery monitor it's not wrong. With a long engine operation I meant several hours.

[nugeo]

We had a similar issue where house batteries, 300amp hrs was taking forever to charge off the alternator. We now have an external Balmar MC-614 connected to the Electromaax 80amp alternator. Whilst still a relatively new installation the difference seems to be quite remarkable. The charge rate on the boats ammeter sits much higher than it used to and for much longer. It has bulk, absorption and float functionality which I'm told keeps the batteries in much better shape. I can't argue the science behind it, all I can say is from personal experience the external regulator dramatically decreases the time it takes to fully charge the house batteries - result, my fridge now keeps the beer colder for much longer which was the motivation to install the external alternator regulator.

For interest, Sterling Power also have an external regulator with a good reputation, it was a toss up between the Balmar and the Sterling but we went Balmar in the end.

If anything the fridge works a bit too well now !

[colemj]

Originally Posted by nugeo

For interest, Sterling Power also have an external regulator with a good reputation, it was a toss up between the Balmar and the Sterling but we went Balmar in the end.

We have both. The Sterling works as advertised and costs half of the Balmar. It can be used with an OEM alternator and with N-type alternators. The Balmar costs double, but has more functionality like belt manager and programmable timings and voltages. It can only be used with P-type alternators and cannot be used with OEM alternators without modifications to them.

Mark

[nugeo]

Originally Posted by colemj

We have both. The Sterling works as advertised and costs half of the Balmar. It can be used with an OEM alternator and with N-type alternators. The Balmar costs double, but has more functionality like belt manager and programmable timings and voltages. It can only be used with P-type alternators and cannot be used with OEM alternators without modifications to them.

Mark

Yes agree, the Sterling works with any alternator as long as you either have the field control wire or are willing to install the field control wire yourself. Install is similar and Sterling is a lot cheaper. We went Balmar for two reasons, Electromaax have paired up with Balmar so support from Electromaax was available (which we used) and 2nd I like the additional functionality - we use the belt load manager as we are on single V-Belt. Actually I have a Sterling PDAR unit sitting in my cupboard from my previous boat, I may have to eBay it at some point.

[Cheechako]

Originally Posted by mitiempo

Wrong. Any lead acid battery - flooded, gel, or agm - requires a long time to charge completely as the battery's resistance increases. The last 15% or so takes many hours. There is no magical way around this.

Not sure I get this... you say "wrong" and then go on to say pretty much what he said: "longer engine operation" just sayin'.... Not uncommon to motor for 8 hours cruising, during which time you pretty much are as full as you are going to get.

[mitiempo]

Depends how much longer. If motoring 8 hours - pretty much all day - they will be close to fully charged most likely. The last 15% or so of charge will take that long and there is not much anyone can do about that. That is where solar comes in.

[tuomas]

Sorry mixed up the terms: meant absorption charge but said bulk. Anyway, on calm days with motoring of 3-4 hours I get full batteries.

Someone had installed a push button to fire the alternator if it does not fire upon engine start. I think I will do that, too. Any other ideas?

[ullar]

Originally Posted by tuomas

Someone had installed a push button to fire the alternator if it does not fire upon engine start. I think I will do that, too. Any other ideas?

Did that this spring. Works a treat.

[sailinglegend]

Originally Posted by tuomas

Anyway, on calm days with motoring of 3-4 hours I get full batteries.....

You have to be clear on what "Full Batteries" really means!

A little green light that says "FULL" or a Battery monitor that says "100%" may not mean that batteries are really fully charged. A charging current down to 0.5% of the battery capacity at an Absorption voltage (not Float) of about 14.4 volts means the batteries ARE 100% full.

The problem is that all regulators are designed to "charge" batteries and not "overcharge" them, so they may tell you the batteries are "Full" when they are only at a 90% State of Charge. They do this because they do not know exactly how much current has actually gone into the battery and how much has gone to the boat loads. At a much lower float voltage they will take a very long time to charge that extra 10%.

See Maine Sail's site for discussion on this "Charging Gotcha" and Premature Efloatulation, and on why Battery Monitors cannot maintain any level of accuracy as the batteries age and the battery parameters change.

If batteries don't get back to 100% once a month they will build up hard Lead Sulfate crystals which will reduce their capacity and their service life. If they can be Equalised at a voltage of about 15.5v for several hours this may remove the crystals and restore their capacity. This is not possible on most types of sealed batteries.