Best way to avoid frying batteries when motoring (Volvo D2-40) for days

[svlamorocha]

Hello everyone,

Here is the setup:

- Catamaran with two Volvo D2-40 HP engines with the standard 115A alternator with "builtin charging sensor" (whatever that marketing BSesque wording means)

- House bank comprised of four 6V Trojans (2 series x 2 parallel) for a total capacity of about 780Ah @12V

- Battery combiner that links house and engine banks when the alternator is charging

Thsi boat will go on a long passage that might take days of motoring at a time. I tried to find out in all the Volvo docs if the stock voltage regulator on these Volvos has any mechanism to reduce voltage/current once the batteries are fully charged, to no avail.

Does anyone have any insight as to how much should someone worry about damaging the batteries when motoring for a few days with this setup?

Does anyone know how does the stock regulator in the Volvo D2-40 work?

Thanks in advance.

C

[sailorboy1]

you need to know how the alternator is regulated, if it is a multi-stage unit that reduces the voltage to a float of 13.2-13.5 or so there isn't going to be a problem

If not and the voltage stays higher you need to plan on checking the water more often

[svlamorocha]

Originally Posted by Don L

you need to know how the alternator is regulated, if it is a multi-stage unit that reduces the voltage to a float of 13.2-13.5 or so there isn't going to be a problem

If not and the voltage stays higher you need to plan on checking the water more often

I just got a word from Volvo and they confirmed it has two stages only... .. this means 14.3V at the battery terminals forever until the batteries run out of water! I guess we will be careful..

Cheers

C

[sailinglegend]

Originally Posted by svlamorocha

... .. this means 14.3V at the battery terminals forever until the batteries run out of water! I guess we will be careful.....

This is a good example why alternators should have external regulators. You can easily put a switch in the wire that powers the internal regulator and turn it off. This feed comes from the ignition switch. Turning off the ignition will also stop the alternator charging, but you will lose all the instruments.

A standard automotive alternator with its internal regulator is designed for charging a start battery that never gets highly discharged. This alternator regulator combination will not properly charge a deep cycle house bank, the battery capacity and life will be severely reduced. Marine alternators will be much more expensive and can be controlled by an external multi-stage regulator. They also may have a “Hot Rated” output that will give a more realistic idea of their true performance when under heavy load.

A good regulator will also delay the charge current for about a minute at start up until the engine oil is well distributed. A 100 amp alternator draws 4 HP which is a heavy load on an engine when starting with a weak battery.

It is often too easy for the alternator to get too hot when motoring. A good external regulator will also accept sensors to measure both the alternator and the battery temperatures and control the charge rate. An alternator could be providing 15 amps to the boat systems, another 25 amps to say a watermaker or an inverter, and then a heavily discharged bank may be demanding 50 or 60 amps. In this situation the batteries may not get charged and the alternator will burn out from continually trying to deliver its maximum output if not protected by a temperature sensor. Battery temperature will also rise with a heavy charge current so the charge voltage must be reduced as the temperature rises. At 25ºC batteries start to gas at 14.4v, at 40ºC they gas at 14v so the external regulator will reduce the charging voltage automatically to compensate for this. If batteries are fitted in an engine compartment it is very easy for them to get too hot and lose water. This is fatal for sealed batteries.

A good regulator should have setting for different battery types, but it should also be programmable to match the alternator and battery bank sizes. Balmar's regulators allow many parameters to be changed, for example they may set the Boost voltage to 14.38, hold that for a while and then reduce it below the gassing voltage to 14.18, for the duration of the absorption stage. They can be programmed to stay longer in the absorption stage without dropping down to float too early.

[hellosailor]

C-
A built in charging sensor isn't marketing BS, it is simply normal integral alternator design. Every decent alternator (with internal regulator, car style) has a battery voltage sense lead, and it adjusts outut current according to battery voltage. It may be putting out 14.3-14.4 volts at all times, but it is designed to sense the battery voltage level and to throttle back the current.
As one leading manufacturer said to me, a car alternator is NOT designed to charge deep cycle batteries. It is designed to not overcharge SLI batteries during long trips. It may only take 15 minutes to recharge a car battery (or boat starting battery) but a car may run for 1-8 hours after that, and the alternator is designed to not overcharge during those long runs. Same thing for trucks that typically go 8-12 hours on the highway.

Unless you have more numbers, like the charging voltages spec'd for your battery and the details of how your alternator throttles back, you can't assume it will do any harm. And if you have wet lead batteries and this is an unusually long trip for you, just bring along some distilled water to top them up and don't worry about it, unless you want to invest time and money fast installing an external regulator, which is always better for deep cycle batteries but can be a waste for a one-shot trip.

Just one man's opinion.

[Andina Marie]

Batteries start to lose water above 14.2 volts (+/-) so at 14.3 the loss should be minimal. Trucks that run (nearly) 24/7 are typically sitting around 14.2 and don't have unusual water loss problems.

[laika]

What about AGM batts? Does it take more juice for them to start gassing?

[goboatingnow]

Originally Posted by sailinglegend

This is a good example why alternators should have external regulators. You can easily put a switch in the wire that powers the internal regulator and turn it off. This feed comes from the ignition switch. Turning off the ignition will also stop the alternator charging, but you will lose all the instruments.

A standard automotive alternator with its internal regulator is designed for charging a start battery that never gets highly discharged. This alternator regulator combination will not properly charge a deep cycle house bank, the battery capacity and life will be severely reduced. Marine alternators will be much more expensive and can be controlled by an external multi-stage regulator. They also may have a “Hot Rated” output that will give a more realistic idea of their true performance when under heavy load.

Modern car alternators are merely the power source for the cars extensive electronics subsystems. Charging the battery is an entirely secondary operation. Alternators are regulated to provide a constant DC power source in a car.

The electrical systems in a modern car are not battery powered in effect.

Dave

[bill good]

What I would do is fit a 70 amp diode from each of the alternators which would reduce the battery voltage by .6 to.7 of a Volt. You may have to put a smaller diode in the reverse across this diode to give exciting voltage. 13.8V will keep the batteries charged. You can get auto water dispensing systems for those batteries. (Just finished a timer to cut off the alternator my starting batteries which might help as it can be set up for mins to hrs) Now running LIFEPO4 no more lead!!

Regards Bill

[svlamorocha]

Many thanks to everyone!!!

[Cotemar]

I have a Catamaran with two Volvo D1-30 HP engines with the standard 115A alternator also.

I do not have a battery combiner to connect the house to the starting battery.

I have and emergency switch which I leave on so I charge and use both house and starter batteries as one.

We only use one engine when cruising anywhere as that is all I need to get to hull speed.
The boat came from France to Newport USA motor sailing for 38 days on one engine at a time.

Your boat and engines can handle very long runs without frying you batteries, so no worries