Questions about using 2 alternators on 1 battery bank

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I was reading threw the postings here & saw something about using 2 alternators. I didn't see if this was even posible. Does anyone know FOR SURE if it can be done & what if anything extra is needed to do this. Are internal or external regulators better if I do use two? or one for that matter. What are the downsides to using 2? I would think the regulator from 1 reads the output of the other & shuts down the voltage out. Or they fight w/ each other & both burn up.
 
Depends on size of battery bank, alternator size, and load load from equipment when the engine is running.
All the Sealine twin engine boat upto 1990/1, ran both alternator in parallel for charging the three battery banks. When they went onto two banks and no split charging, the one alternator was having trouble charging domestic battery and supplying boat current demand.
What is your sepc ?.

Brian
 
Don't know what your situation is but here is ours if it helps:
Ex-hire boat, one Thorneycroft engine, two alternators, master switch on the (linked together) negatives, one alternator dedicated to engine battery which only starts the engine,, one dedicated to the twin battery bank for lights etc.

The positive sides are NOT linked together in any way, only the negative side via the master isolation switch. As the boat is 40 yrs old ish it seems to have been a working system and BSS haven't picked it up either. One thing about the master switch on the negative side is there is only one switch, on previous boats switching was on the positive and meant separate switches so this is more simple.
 
There is nothing wrong with using two alternators, many engine manufacturers provide "second alternator kits" eg Volvo, Yanmar. However, if using an external regulator you MUST use one regulator designed for two alternators. I am not sure what would happen if you used no external regulator ie just the alternators own internal regulator but as that is such an inefficient approach for battery management it is not realy worth considering if you are trying to upgrade matters. An alternative approach is to feed two externally unregulated alternators into an XSplit device. This is intended to feed two battery banks in an efficient manner but would probably do the job for you. The only snag with the company that makes XSplit is that their kit is not very customer friendly and you might well get yourself into a technical nightmare which even they find very difficult to solve. It happened to me!

All the above is my own, very inexpert opinion and should be considered with suitable caution.

Good luck
 
Thornycroft fit twin alternators as standard on all their new engines. One is dedicated to the engine battery and the other does the domestic battery(s). They DO NOT charge the same battery. You CANNOT charge a battery from two alternators..all sorts of sensing problems.

Contact Advercbm for some REAL professional advice and low cost solutions that REALLY do work...ten years our system has worked.

www.adverc.co.uk

Cheers
 
Seems you should take your own advice!

[ QUOTE ]
You CANNOT charge a battery from two alternators..all sorts of sensing problems.

Contact Advercbm for some REAL professional advice and low cost solutions that REALLY do work...ten years our system has worked.

www.adverc.co.uk

[/ QUOTE ]If you look here on the Adverc website, you'll see a diagram showing how twin alternators can charge the same battery bank,using one Adverc regulator to control both alternators.
 
Re: Seems you should take your own advice!

I use an Adverc controlled 120amp alternator to charge 3 batteries through blocking diodes.
Plus an internally regulated alternator charging two of the above batteries at the same time.
 
Re: WOW, that\'s response.

I posted this in the middel of the night & hours later there are 7 replies, thanks all. Here are more details then.
1- 675 amp hours (house bank)
2- all is on one 12v bank
3- I want 2, 100amp- 135amp alternators charging or able to put power out.

I sail and enjoy cruising on my boat. I would like to have the alternators put out enough to rund my inverter and my A/C (about 100 amps off the 12v side, 12 amps on 120v) I'd rather have 2 alternator incase I'm somewhere and 1 dies, I'd still have one to live on until I get somewhere I could get the 2nd. I'd just go w/o A/C till then.
 
Re: WOW, that\'s response.

Provided that the neutrals are bonded two alternators will charge one battery bank with no problems. All that will happen is that, unless the alternator regulators are exactly the same (1), as the batteries get near to full charge one alternator will shut down earlier than the other as it senses a voltage above its cut off point.

I believe that sterling make a unit that does this job of combining alternators to charge one bank allthough if I was doing it I would just run them in parrallel.

I often run the genset / battery charger at the same time as the engine when cruising to cut down on recharge times.

(1) physical impossibility due to component tollerances.

Julian
 
Re: two alternators

We are running two alternators one is a 270 amp used to charge the house bank [840 aHr 12v] which is regulated using a smart external regulator and current limited to 220 amps. The second is a 135 amp alternator also externally regulated to charge the start battery. The only reason for the large second alternator is in case I have a fatal failure in the primary charging system, I can still charge the house bank.

I would think you are far better off getting a large primary alternator for you 640ahr bank [rule of thumb is 25% or about 160 amp] and have a smaller second alternator charging you start bank which can be switched in if needed. Externally regulate both so you get real 3 stage charging.
 
[ QUOTE ]
You CANNOT charge a battery from two alternators..all sorts of sensing problems.


[/ QUOTE ]

In the 80's we supplied over a 1000 sets of switch gear that included charging three battery banks from two engines. This used a split charge sytem with two relays, so effectively charging one bank with two alternators. To date we have never had a problem reported with boats, or with the stand-a lone sytems sold since.
Assuming you have alternators with a good regulation volt, say 14.4 volt, the lower set alternator will basically shut down, doubtfull if both will be identical. The lower set one will pulse on and off for a time, but that is only what it does in normal use when it regulates. By the time you get up the that regulation level, it is probable that you only need one alternator.
Start simple, if you have a problem with the two alternators hunting or similar, or very high service loading, you can allways spend more money on a differant regulator to control both.


Brian
 
Every catamaran owner is probably charging a single battery bank with two alternators (albeit from different engines). The important point is to get a suitable regulator, and I would support the posts above suggesting you contact ADVERC.

fair winds
 
Some replies

The replies that tell me how 2 alternators can charge 2 or more banks isn't the question & doesn't help. This is ONE bank and will only be one bank.

I did look into the adverc and they DO have a device that will combine the 2 alternators to go to one bank for $600.00. Expensive but does work.

To the person that said just get 1 high output alternator. I know that too, rather than spend 4,5,6 hundred dollars on 1 alternator and put all eggs in 1 basket, I'd rather buy 2- 100 to 125 amp alts. for $100-150 each, save money & have a ready supply of replacement alts. as I go cruising.

To the catamaran comment, I will look into these owners. If they don't have or don't need a $600 unit to do this, it may be an avenue I can take.
 
Re: Some replies

I refer to my post above.
There are no problems using 2 alternators on one bank. all that will happen is when the bank gets near to full charge one alternator will shut down before the other but you wont need it by then.
If the alternators are "new" ie under a couple of years old you wont need an extrenal controller either as they will charge at 14.2.
If you want to get more out of an older alternator and are using standard wet cell batteries have a look here.

http://www.smartgauge.co.uk/alt_mod.html


Julian
 
ok

so you have 2 alt's., internal regulators, a commpn ground, bot positives go to one bank and thats it?

All works well? No problems, no extra devieces?

If so that's great
 
Re: ok

Parglena's right. It will work fine. When the battery is very low both alternators will push out their maximum current but with fairly large batteries as yours, that's not an issue. However, if you are cruising and trying to make up your overnight usage during the day when the engine is running, a 'smart charger' such as an Adverc or Sterling will reduce the time you need to run your engine. But the simple answer to your question is that it is fine to put the two together.
 
Re: ok

[ QUOTE ]
so you have 2 alt's., internal regulators, a commpn ground, bot positives go to one bank and thats it?

All works well? No problems, no extra devieces?

If so that's great

[/ QUOTE ]

Yes it will, Its not what I run at present but have done in the past.

Julian
 
Re: ok

Many thanks to all. I'll get 2 like kind alternators and try this. If I don't blow something up, I'll try to let everyone know what happened.
 
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