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Old 17-11-2017, 07:34   #1
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Battery charging systems used with twin diesel engines.

First I should explain I have been a monohull owner and part time cruiser for the last 45 years. Thinking of purchasing a cruising catamaran in the 40 to 45 ft range in a couple of years so I have a lot to learn.

Very attractive to me is the redundancy provided by twin powerplant installations. I was wondering what are popular arrangements for 12VDC and 120VAC generation in this situation.

On a boat with single propulsion plant the addition of a generator gives us redundant means of charging batteries. For a twin engine boat, I would think a separate generator could be avoided, along with its weight and expense, if high output alternators controlled by smart DC voltage regulators were mounted on both propulsion engines. Of course all AC power would always be provided by a high output invertor. And we still would want a powerful AC driven smart battery charger for use at the dock.

`otice I used the word smart to describe the regulation of the high output alternators. I have a Balmar programmable regulator on my boat which was the best one I could find back in 1999 and it still works exactly as designed, but it does not use current shunts so it can only use a time and voltage setting to dtermine the charging cycle. I hope there are more modern 12V regulators that will use both voltage and current readings at the batteries to determine the charging cycle.

So any real world experiences long these lines are greatly appreciated.
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Old 17-11-2017, 09:33   #2
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Re: Battery charging systems used with twin diesel engines.

Do you foresee AirCon, or other heavy continuous AC loads, on this boat?

If so, that would be one reason for a genset on a twin engine boat. For example, I sometimes captain charter boats where the guests expect AirCon at anchor...so a genset is a must.

If not, then a genset is certainly not necessary. Short duration heavy AC loads, like a microwave, can handled by a big inverter.

My config, which has served me well:

Twin engines, each with their own alternator (65A) and smart regulator (NextStep). I run two regulators for redundancy. The regulators control solenoids for automatic paralleling of house + start batts for charging. House bank is currently 2x8D AGMs. Separate start batt for each engine.

375W of solar w BlueSky 3000i controller keeps up with demand in good sun. At anchor, I only run engines about an hour a week to top up.

Many twin engine cruising boats have a generally similar set up.
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Old 17-11-2017, 09:49   #3
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Re: Battery charging systems used with twin diesel engines.

Will you have a dive compressor? It needs a generator.
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Old 17-11-2017, 10:43   #4
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Re: Battery charging systems used with twin diesel engines.

On the wonderful redundancy of twin engines, I would point out something the commercial aircraft designers have to say. Two engines actually creates FOUR times the number of expectable failures. (2x2) It doesn't just double the number of failures, it squares them.

So while it does give you a limp-home mode...a normal auxiliary sailboat does carry the auxiliary diesel engine, and that IS the backup powerplant.

Twin engines? Like trying to housebreak two puppies at once. They'll find ways to gang up on you.
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Old 17-11-2017, 11:50   #5
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Re: Battery charging systems used with twin diesel engines.

Quote:
Originally Posted by waterman46 View Post
>>>>>>>>>>>>>>>>
I hope there are more modern 12V regulators that will use both voltage and current readings at the batteries to determine the charging cycle.

>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>
You might want to read the manual for the Balmar MC-614, their latest, at Balmar | Marine Charging Systems | Battery Monitors | Multi-Stage Voltage Regulators | High Power Alternators | Serpentine Pulley Conversions.

I am unaware of any regulator(s) that will do that.

You can "manage" the voltage and the times, but none will measure current.
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Old 17-11-2017, 12:15   #6
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Re: Battery charging systems used with twin diesel engines.

Although I've never heard of it on a boat, it is becoming common to use "Charge Management Systems" on cars, where there is indeed a "coulomb counter" on the battery (ground usually) and the charging system does change the alternator output based on the battery condition, the overall *current* flow, and other information.

So surely, one of the same evil engineers could design one of those for a boat.

But that's more than just a "regulator" and alternator. The only thing you can really control on an alternator is the feedback, which will change the output voltage. The output current is pretty much fixed by the alternator's speed. There is an old kludge to vary the effective current by pulsing the alternator output (the 70's Delcotrons pulsed from 10-100,000 times per second) but again that's a kludge, or a question of semantics.

All the fancy computer electronics is just great, in theory. And maybe it even provides better battery charging. Till it fails, or the program gets corrupt, and then there's no way to diagnose or fix the clever little thing.
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Old 17-11-2017, 20:38   #7
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Re: Battery charging systems used with twin diesel engines.

I had a 43 foot cat with twin diesels. Each diesel had two alternators. The larger of the two alternators produced 250 A throw Belmar regulator. The total ran into an vine hundred amp hour battery bank. The back and had a 3000 W inverter. Although it would run all of together with some power management set up running air-conditioner all night without the engines running. It also ran a washer dryer combination, water maker and your usual range of electrical accessories. Quite reliable AC power and sufficient DC power for all of our needs. Cost less top rate that a good size gender weighed less and took up less space. In five years I put 5000 hours on the two engines and had to rebuild up completely. Itís still cost less.
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Old 17-11-2017, 21:38   #8
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Re: Battery charging systems used with twin diesel engines.

Hi, OP here and thanks for the posts. I won't have air con at anchor or an electric dive compressor so dont have to consider huge loads. And yes, all an alternator regulator can control is actually the current in the field windings, but that control can or could take into account any number of external measurements including charge current into the battery bank


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I had a 43 foot cat with twin diesels. Each diesel had two alternators. The larger of the two alternators produced 250 A throw Belmar regulator. The total ran into an vine hundred amp hour battery bank. The back and had a 3000 W inverter. Although it would run all of together with some power management set up running air-conditioner all night without the engines running. It also ran a washer dryer combination, water maker and your usual range of electrical accessories. Quite reliable AC power and sufficient DC power for all of our needs. Cost less top rate that a good size gender weighed less and took up less space. In five years I put 5000 hours on the two engines and had to rebuild up completely. It’s still cost less.
Fantastic system there and it's pretty much what I am hoping to do so thanks very much for that input. A careful reading of your post also reveals an amusing reference to the cost of a certain body part, a typo I am sure!!

As for the battery charging issue, we can compare existing DC alternator controls to the charging sequence available in most any good AC driven charger, and this is my main concern. I have a 20 year old Heart 2000 invertor-charger which runs from 120VAC, usually supplied by the A.C. generator at anchor

In bulk charging phase it puts put 100A until the voltage reaches the programmed value, I think from memory its about 14.4V, depend on battery type and temperature. Then switches to Absorption mode which maintains the 14.5V *while monitoring battery charge current* until current drops to the programmed value, which my faulty memory recalls to be about 4% of rated AH battery bank capacity (expressed in amps). At that point the batteries are considered to be fully carged and voltage drops to 13.7 or so for float mode
The exact numbers are not important, but very important is that this charge cycle needs to know the charging current at the battery to know when to drop out of acceptance mode
This requires current shunts at the battery so that other 12V equipment that is in use will not affect the.charge current measurement.

From the responses so far I don't see such smart regulation of alternators to be available. What I do on my boat if I am charging batteries while motoring, I set the programmable acceptance mode time of the Balmar regulator to 30 minutes. If the battery AH meter then shows I need more charging then I momentarily turn off the ignition switch. When turned on again it resets the Balmar regulator to give me another 30 minutes at absorption voltage charging.
Not a very convenient solution.
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Old 19-11-2017, 09:22   #9
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Re: Battery charging systems used with twin diesel engines.

Take that Heart charger with you if you can...they are bullet proof! Ive got one aboard thats about 20 years old and never missed a beat (now on its second boat). And their electronics are big and clunky enough they can actually be repaired. Not fancy, but they work.

By contrast my Xantrex Truecharge2, lots of fancy features, but lightweight and built in China, just crapped out after being run all of 6 times for about an hour each time over a 1 year period...over priced junk.
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Old 19-11-2017, 09:34   #10
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Re: Battery charging systems used with twin diesel engines.

Also, while smart alternator controllers are generally quite reliable, they do fail. My trusty old Next Step, ~12 years old, finally died a few years ago...in a remote location of course. I built a manual charge controller out of spare electrical parts to limp along until I could replace. Now, I run two Next Step 2s...just in case.

If you plan on remote cruising, its good to have a back up. I prefer active (in use) redundancy where possible, stuff stowed unused in the Tropics on a boat often does not fare well.

I think an alternator(s) with selectable internal/external regulation would be a good option.
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Old 19-11-2017, 16:46   #11
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Re: Battery charging systems used with twin diesel engines.

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Originally Posted by belizesailor View Post
Take that Heart charger with you if you can...they are bullet proof! Ive got one aboard thats about 20 years old and never missed a beat
I saw what you did there!
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Old 19-11-2017, 16:57   #12
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Re: Battery charging systems used with twin diesel engines.

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I saw what you did there!
Ha, fortunately my 57 yo one has never failed me either!
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Old 19-11-2017, 17:51   #13
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Re: Battery charging systems used with twin diesel engines.

Relevant recent thread WHAT IS A GOOD GENERATOR ??

Go to MC-614 for adjustability, future-proof for maybe LiFePO4.
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Old 21-11-2017, 08:07   #14
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Re: Battery charging systems used with twin diesel engines.

In my last boat I had a simple yet effective setup.

Both engines run on one starter engine, so both alternators can feed their full output into one shared battery. To me a starter battery is a consumable so I don't care much if its not perfectly charged (just like in a car).

A battery-to-battery / B2B charger takes energy from the starter battery and charges the service battery bank with configurable bulk, absorption and float voltages compensated for temperature and voltage drops on the wires.

The more energy the charger takes from the starter battery the harder the alternators work to provide this energy, no need to change the regulators.
The b2b charger makes sure the starter battery is recharged before it starts to charge the house battery, and it never takes the alternators voltage lower than float voltage of the starter battery.


B2B chargers are available from several companies. Smaller ones are sold as charge boosters for RVs Sterling technolgies has marine versions up to 120A.

I used a 45A booster from Votronic as I had only a 300Ah battery bank.
Easy to setup (2 thick charging wires and two small voltage sensing wires to each battery, plus mounting the temp sensor at the battery).
This setup worked like a charm for 2 years.


But: we had plenty of solar so we never had to recharge using the engine. Of course charging happened automatically when motoring but it was never required.


Current boat came with some sort of charge coupler box (two alternators in, two batteries out). Works OK but of course only with flat alternator voltage, and uncompensated voltage drops so batteries will never be full.
Not good, but more than adequate for our needs. Again plenty of solar for our needs and batteries are typically full by noon.
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Old 21-11-2017, 12:14   #15
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Re: Battery charging systems used with twin diesel engines.

> Sterling technolgies has marine versions up to 120A

Charles has told me a 180A version is being released RSN
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