Alternator does not Fully Charge the Batteries

[hellosailor]

Something to bear in mind is that automobile electrical systems are designed as systems. While they may be set to 14.4v, the battery size, the alternator amperage, and the entire system load are designed integrally.

In 1980 the battery voltage might have been 14.4 (or 13.8 on riceburners) with a 55A rated alternator, 60-70A for a better car with air conditioning and options. Today? 150A is standard on many cars. Still the same nominal 14.4v volts, but the alternator has tripled in capacity, and one can rashly assume part of that is because there are more loads sucking up ore of that power, not just the "14.4 at the battery" being considered.

On boats with pretty much every system being an accidental kludge job...your knottage may vary?

[mitiempo]

Originally Posted by hellosailor

Something to bear in mind is that automobile electrical systems are designed as systems. While they may be set to 14.4v, the battery size, the alternator amperage, and the entire system load are designed integrally.

In 1980 the battery voltage might have been 14.4 (or 13.8 on riceburners) with a 55A rated alternator, 60-70A for a better car with air conditioning and options. Today? 150A is standard on many cars. Still the same nominal 14.4v volts, but the alternator has tripled in capacity, and one can rashly assume part of that is because there are more loads sucking up ore of that power, not just the "14.4 at the battery" being considered.

On boats with pretty much every system being an accidental kludge job...your knottage may vary?

While automobiles are designed as systems the 14.4 alt is still used, whether a bare bones vehicle or a fully optioned one. As far as alt size, it really makes no difference to the battery, which is the determining factor. As long a alt voltage is constant the battery determines current until the alt's maximum output is reached, rarely if ever on a car but common on boats.

[Fuss]

Originally Posted by mitiempo

I am not justifying not buying and fitting an external regulator - as stated they have many benefits and are essential with a large bank of Agm batteries for alternator lifespan.

But I will stick to my statement that millions of cars run at 14.4 volts alt output or close to it all the time, without adverse effect.

Measured mine yesterday - 14.43 at the battery cold and 14.21 at the battery when hot - with fan and light loads on.

True, around 14.4 is what modern cars run at, measured at the battery, they don't measure 13.8 after load and voltage drop.

However, the only alternator on sailing boats should be industrial. An industrial alternator will run very hot for years with no damage. 90+% capacity for two+ hours. They are designed for this.

Some external regulators enable you to downrate your car alternator, but this is compensating for having the wrong alternator fitted. We need all the amps we can get don't we?

If your car based alternator is not causing you any problems after 5 years, then its probably because you are undercharging your batteries.

[sailinglegend]

Originally Posted by mitiempo

....But I will stick to my statement that millions of cars run at 14.4 volts alt output or close to it all the time, without adverse effect.

Measured mine yesterday - 14.43 at the battery cold and 14.21 at the battery when hot - with fan and light loads on.

This proves my point that they don't run at 14.4 volts when they get hot.

Originally Posted by mitiempo

.....As long a alt voltage is constant the battery determines current until the alt's maximum output is reached, rarely if ever on a car but common on boats.

If a sustained high voltage is maintained for too long then it can lead to overcharging. It is not too much current that causes overcharging - yes the battery is self-limiting and will take only the current it needs - but too much voltage "when the battery is fully charged". This leads to excessive gassing because the energy from the high voltage has to go somewhere - it can't put any more amps in the battery so it makes more gas. Battery gassing is affected by the ambient temperature, so at 25ºC they gas at 14.34v but at 40ºC they gas at 14.0v. This is why batteries need temperature compensated charging voltages with a sensor on the batteries, not on the alternator. Just one of the features of a proper external regulator.

Gassing is needed for batteries to mix the electrolyte, but not excessive gassing. The voltage must be reduced below the gassing voltage when the battery is fully charged. This is very important for sealed "maintenance free" batteries where lost water cannot be replaced.

[FlyingCloud1937]

One thing to take note of.

Every new/rebuilt alternator comes with a written warning. Stating if the battery is less than 70% SOC. Before installing the alternator, re-charge the battery with a bench charger.

This is because the auto alt is designed as a power supply for on-board systems, not a battery charger.

Plain and simple.

Delco Remy, advise to size the alternator to 50% larger then the total loads of the system. This is lights, fans motors and such.

They don't say anything about battery size, until you get into the starter motor section

Lloyd

[mitiempo]

Originally Posted by Fuss

True, around 14.4 is what modern cars run at, measured at the battery, they don't measure 13.8 after load and voltage drop.

However, the only alternator on sailing boats should be industrial. An industrial alternator will run very hot for years with no damage. 90+% capacity for two+ hours. They are designed for this.

Some external regulators enable you to downrate your car alternator, but this is compensating for having the wrong alternator fitted. We need all the amps we can get don't we?

If your car based alternator is not causing you any problems after 5 years, then its probably because you are undercharging your batteries.

How many marine engines - Beta, Yanmar, Volvo, etc - come with an "industrial" alternator?

The ability to downrate the alt is an important option for anyone with a decent size bank of Agm batteries, or a large bank of flooded batteries for that matter. Agm batteries have an acceptance of C or greater. A 100 amp alt de-rated to 70% will outlast a 70 amp alt running at max by a large margin. If the flooded bank is large enough it can also cause the alt to run at max output for a long time. Agm batteries are responsible for the demise of many alternators. Confirm this at any good marine alt shop. Too many buy Agm batteries and leave the rest of the charging system the same as it was with flooded batteries, often enlarging the bank at the same time, then wonder why the alt gave up. The addition of an external 3 stage regulator, de-rated for longer alt life, with temp sensors for both alt and batteries both extends the alternator's lifespan and that of the batteries.

[sailinglegend]

Originally Posted by mitiempo

How many marine engines - Beta, Yanmar, Volvo, etc - come with an "industrial" alternator?....

Probably none!!!! They come with a small cheap internally regulated auto alternator, unless you or the dealer specify and fit a proper alternator with an external regulator when the boat is first ordered.

What we are saying is/should be "best practice" on a cruising boat, but it comes at a huge price, but it will make your batteries last longer and charge quicker and make your cruising experience a much better one.

[mitiempo]

Originally Posted by sailinglegend

Probably none!!!! They come with a small cheap internally regulated auto alternator, unless you or the dealer specify and fit a proper alternator with an external regulator when the boat is first ordered.

What we are saying is/should be "best practice" on a cruising boat, but it comes at a huge price, but it will make your batteries last longer and charge quicker and make your cruising experience a much better one.

I agree on a boat with more than one battery for house and one for start. The Hitachi alts on Yanmars for example lower the output voltage by enough when warm so that external reg or not they can take a long time to charge a serious bank to full.

[tuomas]

Hi all, here is some updating:

Checked the alternator: measured the diode bridge - ok, checked the carbon collectors - ok. I did notice oxidized connections and that the cables from alternator to batteries is only some 2.5 mm2. Don't have the equipment to check the regulator.

Original theory was good theory but not the right one.

Here's the next theory: old, a little loose belt (deflection >20 mm, supposed to be ten) + oxidized connections + a little narrow cable + alternator max only 14.2 V according to the plate = loss of some tenths that the alternator sees but cannot compensate because it's operating near max output.

In addition, a hoarding fridge (that is now reinsulated) for a couple of years with this loading problem seems to have resulted in early sulphatization of the batteries (output gets down from 12.4 to 12.0 volts even with 1.5 amps..)

Will have to wait until spring to do further testing.

[donradcliffe]

I went back and read the OP, and I have another theory.

The boat has a "Surepower 702" battery isloator, which is diode based, and will drop the voltage from the alternator about 0.6 volts.

Quoting from the Surepower manual:

"NOTE: Be sure that the alternator has remote sense capability. Most single-wire Delco alternators do not have this provision. The voltage regulator must sense battery voltage. The sense line should be connected to the main battery terminal of the Isolator. Call the Sure Power customer-service department if a particular application arises which is not covered."

When you say the alternator has a 'standard' controller, does this mean it has an internal regulator (without remote sense capability)?? If so, this is your problem. The solution would be to either install an external regulator or replace the isolator with a combiner (which doesn't have a voltage drop).

[hellosailor]

"from alternator to batteries is only some 2.5 mm2."
A standard US automotive alternator/regulator uses a #10 AWG wire for the charging output, and that's 2.59mm^2 in size. While that is inefficient, it is standard practice. It is probably not your problem but could be replaced with something better (thicker) in any case.

" Don't have the equipment to check the regulator. "
You don't have a simple multimeter? All you need to check a regulator with, is a simple DC voltmeter with a 20VDC scale. The most basic and useful electrical tool on a boat. And a set of alligator clips, so you can attach the leads and leave them attached without tying up your hands.

"Here's the next theory: ..."
All valid points. And given that an alternator should never exceed 14.4 volts in normal use, the fact that you're seeing 14.2 with some issues, indicates the first step is to address those issues.
Belt deflection is a reasonable way to measure tension, but if you look around you can find belt tension gauges, sometimes very expensive sometimes quite reasonable. You hook them over the belt and read the tension the same way that you would read a small scale, much easier than messing around with rulers.

"early sulphatization of the batteries "
That can explain a lot of things. You can take a battery out for load testing, or run a load test yourself, to confirm that.

[westwinds]

With your wiring for alternator at maximum output, you will get a .6 volt drop for ten feet of 10 gauge wire.

Here are other options for the "Surepower 702" battery isolator:

Battery Isolators and Automatic Charging Relays Compared
Battery Isolators and Automatic Charging Relays - Blue Sea Systems
Blue Sea Automatic Charging Relay
m-Series Automatic Charging Relay - 12/24V DC 65A - Blue Sea Systems

Battery switches are another option, but you have to think about what you are doing. If you forget to switch to house battery, you can run down both batteries if the engine is not running.
Blue Sea Systems HD Battery Switch, get the one with field disconnect to prevent alternator destruction when switching while engine is running. Needs external field wire used on external alternators.
Blue Sea HD Battery Switch 4 Selector
Perko Standard Battery Selector Switch With Make Before Break Design, that protects running alternator while switching batteries, but will blow alternator diodes when switched to off if engine is running. Use where there is no field wire from alternator.
Blue Sea Systems E-Series Dual Circuit Plus Battery Switch
Blue Sea Systems E-Series Dual Circuit Plus Battery Switch, E-Series battery switches allow users to switch between battery banks without power interruption. Will blow alternator diodes if switched to off while engine is running. They are ideal for marine and RV applications because they are ignition protected, and made from non-corrosive marine grade metals.
Perko Standard Battery Selector Switch

[tuomas]

I tried to find the voltage drop of 702 in the internet but did not find it. If it is really 0.6 volts then the case is clear: despite the remote sensing (that I do have and is correctly installed) voltage at the battery terminal is just too low since the regulator is saturated. With this drop 14.1 volts at the battery terminals (that I measured during charging) is 14.7 volts commanded voltage in the alternator terminals - a figure that the alternator cannot produce. Even if the drop were 0.3 volts, 14.4 volts at battery terminals would require commanding 14.7 in the alternator side.

In my understanding there is an important lesson to learn in here: Remote sensing by itself is not enough UNLESS the alternator can produce 14.4. volts + anticipated drop = 15.0 volts!

Hellosailor: sure I have a multimeter. Volvo's service manual tells I need their special tool to measure the regulator. How do I measure the regulator with multimeter?

[tuomas]

I mean offline measuring, the alternator is on my desk now.

[westwinds]

Originally Posted by tuomas

I mean offline measuring, the alternator is on my desk now.

Take the alternator to an auto parts store, one that has an alternator testing machine, and see what the voltage is. The 702 has fins on it so you know it gets hot. That implies a voltage drop because volts times amps means watts. So 42 amps times .6 volts is like the heat from a 25 watt light bulb.