Using 2 alternators to charge a house bank

[Thumbs Up]

I have two alternators charging one house bank on my catamaran. I am glad to see that Balmar makes a solution for this, when I was studying the potential problems I never came upon this solution. With my budget the best solution for me was to do nothing, and they work fine. They are both 60 amp single wire, internal regulator automotive type alternators which you can buy at Napa for $60.00. At that price I can afford to keep spares. So far I have had no problems. When the batteries are low, both are definitely charging. When the charge starts to taper off I have no idea which one charges more but it doesn't really matter, if one breaks, I already have a spare. With the price of one high output marine alternator and regulating setup, I could buy a lot of spares and since my battery bank always gets topped off by my solar regulator anyway, I don't need any kind of smart regulators on the alternators. For me, a lot of times the simplest and cheapest solutions are the best and if your budget is limited enough are your only solutions anyway. Another good reason to carry a spare alternator is that if a bearing in the alternator fails, you won't be able to run that engine because the belt also drives the coolant circulation pump. With a high quality marine alternator, you will be less likely to need the spare, but if you do need it you won't have it because it cost too much to begin with.

[Andina Marie]

We have thousands of customers who for the last 20 years have connected multiple alternators together on the same battery (bank) every time they run. If there was any problem we would have heard something by now.

Regulators don't get "confused", all they see is a battery voltage and adjust their output to correspond. If the voltage on the battery is higher due to another charging source the regulator doesn't "know" or even care where that charge is coming from, it adjusts its mode to correspond to what the battery needs.

It is true that no two regulators will have exactly the same theshold mode switching levels and one will switch before the other so for a short period of time one will be doing more work than the other but the total time to charge will be extended only a few minutes at the most. You can purcase all sorts of control systems to save 3 minutes charging if you like gadgets but it is not necessary.

[Journeyman]

Agreed, in the case of two voltage regulators and two alternators even if you set radically different Absorption setpoints, say 14.0V and 14.5V the higher set point alternator would simply continue to source current until its setpoint was reached. The other alternator would have shut down at the lower value and being putting out nothing.

[hellosailor]

"We have thousands of customers who for the last 20 years have connected multiple alternators together on the same battery (bank) every time they run. If there was any problem we would have heard something by now."

That's kinda like saying, if 3/4 of all the cars on the highway were running with dangerously underinflated tires, we'd have heard something about it. Oh, wait, we did. The Ford Explorer/Firestone rollover problem.

Meanwhile 3/4 of all the cars on the road STILL have dangerously underinflated tires, but Ford has made the Explorer less, ah, singular at demonstrating it. The problem still remains.

That a lot of folks are bolting up two alternators and not complaining, just means they are getting what they expect. it does not mean they are getting efficient charging, or optimum charging, in any way, does it?

Given a big enough, hungry enough battery bank, the battery will draw down both alternators until it is getting full, and only then would the alternators be left to figure it out. If they were to turn each other on and off intermittently, the charging might take an extra half hour, and who would know? Certainly not the average owner.

Sometimes, you want to enquire about the man behind the curtain. Other times, not.

[cal40john]

I can't see any reason why there would be reduced efficiency. If you're saying that adding a 3 stage regulator that can handle two alternators will improve charging time then that's a different argument.

John

Originally Posted by hellosailor

full, and only then would the alternators be left to figure it out. If they were to turn each other on and off intermittently, the charging might take an extra half hour, and who would know? Certainly not the average owner.

Sometimes, you want to enquire about the man behind the curtain. Other times, not.

[Journeyman]

HelloSailor,

I don't see any scenario under which they would "turn each other off".

They have no knowledge of each other. They simply track the voltage of the house bank.

As regards efficiency during Bulk they are both full field. So no inefficiency there.

Once at Absorption the fact that only one might be doing the heavy lifting is of little consequence since the required current to maintain Absorption ramps down quickly.

Unless I am missing something.

[goboatingnow]

Originally Posted by hellosailor

.......

Given a big enough, hungry enough battery bank, the battery will draw down both alternators until it is getting full, and only then would the alternators be left to figure it out. If they were to turn each other on and off intermittently, the charging might take an extra half hour, and who would know? Certainly not the average owner.

Sometimes, you want to enquire about the man behind the curtain. Other times, not.

Hello sailor, you've had several posts explaining why it's quite practical to parallel alternators. There is no electrical issue. Please explain how they " turn each other on and off intermittently "

Why do people, persist in inventing problems. In bulk mode both alternators charge in absorption mode generally the battery current is less then any one of the alternators, so one of them will finish the battery, the other will effectively idle. If the bank absorption current was bigger then one of the alternators capacity, both alternators would contribute to finishing the battery as well. Please it's just simple electrical circuit theory. To suggest that two alternators would take longer to charge then one simply flies in the face of such theory.

What "centre fielders" and other dual controllers do, is balance the two regulation points and ensure that the load is shared evenly between the alternators. It doesn't in reality contribute much anything to improving charging time.

Dave

[hellosailor]

Well, guys, the engineers who are being currently paid and employed in the business fo charging systems, all seem to say "There may be conflicts". I'm just trying to understand this. Lots of folks here say no, there couldn't possibly be any problem--but then again, everyone in the business seems to think there COULD be a problem.

Considering the variety of electronics out there? Since I don't have a dual-alternator system and a lab full of equipment to test it, I can only take all the opinions as just that: Opinions, best guesses, no real measurements and observations to really show what is happening.

"They simply track the voltage of the house bank." Not quite accurate. They track the voltage at the battery terminals--but that voltage may be coming from the batteries, and from other charging sources. And that's assuming a dedicated voltage sense lead going to the battery terminals, too. Perhaps for "just" dual alternators this assumption works, but once you mix in external regulators tripping timeouts, and other power sources...the larger picture looks less certain, doesn't it?

[goboatingnow]

Firstly any decent EE is a " professional ". Any simple DC circuit analysis shows how a set of imperfect voltage sources interact. Manufacturers technical guys ( ie support you mean, ) rarely know anything really , often the real design people are contract design houses , this is what mastervolt does for lots of product . You almost never get to talk to these Gods.

Timers , trips etc are all irrelevant , the regulation processes ate the same at a DC circuit level.

The alternators can be connected. The effect of non matched regulation is that one alternator will do the absorption mode, but who cares.

Maybe there's a book needed here ( boats electrical system modelling for beginners ) if you model the circuit am alternator regulator seems it is already connected to several other voltage and current sources anyway. ( back emf, load dumping, inductive stores etc) it simply doesnt see a simple battery.

How many people have started their engines with a shore charger still connected , many I suspect , does this "blow" an alternator . No of course not. Any designer of such regulators must account for other voltage sources in the system. ( transient or permanent )


Dave

[RUSTYNAIL]

I'm new to this forum, and I am enjoying the feedback from this string of replies to the original request about dual alternators. I come from a different background working with lots of small commercial fishing boats that their lives depend on their battery systems, and worked their alternators and battery systems hard every day 50 miles offshore. Fuel prices have tripled, so shutting their engine down early is a new necessity. By getting the fishermen to install amp meters and digital volt meters, we solved a lot of battery charging problems. They quickly learned when to shut down their engines after the alternator current settled down, and they learned to quit buying regular lead acid 8D batteries, and go to smaller AGM or gel cells for their electric reel battery banks because they have a lower internal resistance and will take more current input with a regular 75 amp alternator. The bigger alternators were hard on single pulley belts. Simplicity and dependability is a must way offshore.

[hellosailor]

Dave, no offense to anyone here, but an EE is usually just a B.S.EE., a batchelor of science in electrical engineering. In some states you require a state "professional license" to practice that skill, and that makes you one kind of "professional". But you can still have the BSEE credential without a professional license, and be an amateur, which means that you are in it for the love of the field, as opposed to a professional, in the larger meaning of one who gets PAID for those same skills.

When I say professional, I mean the folks getting currently PAID to practice those skills. Not retired, not indulging in some other specific area, but folks being currently paid to exercise those specific skills in this area of electrical engineering.

No, I haven't been talking to salesmen, some of the folks I spoke to included the head of engineering at one of the largest players in the US market. He doesn't get paid to answer the phone, but sometimes you get lucky and a call gets passed along to someone like that.

Are these guys qualified? One can hope so. Are they overcautious? Quite possibly. Would it be rational to simply throw out everything they said as utter nonsense?

"Homey don't think so."

Which is why I look for public discussion and actual experience with some of the setups. And I don't dismiss your opinion any more or less than theirs.

[Andina Marie]

I think I'm qualified. I have a degree in Electrical Engineering. I've been designing electrical equipment for over 50 years. I've run the engineering dekpartments of 3 large companies with over 250 empolyees. I designed a microprossor controlled multi bank charging regulator/monitor. I was a guest lecturer at Western University. I currently have my own business manufacturing and selling Combiners since 1993 that parallel twin engine starting batteries thousands of times every day. All our products have unconditional warranty, it there was a problem I would have heard by now.

[btrayfors]

Originally Posted by Andina

I think I'm qualified. I have a degree in Electrical Engineering. I've been designing electrical equipment for over 50 years. I've run the engineering dekpartments of 3 large companies with over 250 empolyees. I designed a microprossor controlled multi bank charging regulator/monitor. I was a guest lecturer at Western University. I currently have my own business manufacturing and selling Combiners since 1993 that parallel twin engine starting batteries thousands of times every day. All our products have unconditional warranty, it there was a problem I would have heard by now.

Andina,

No question you're "qualified" :-)

But, I think you are responding to a different question than the one posed re: the effect of two (or more) charging sources tussling with one another.

In fact, on your own website you have a very good description of what happens in that situation, which clearly points out that once past the bulk stage it is indeed likely that one charging source will "conflict" with another, meaning will cause the second one to reach it's next set point prematurely:

Quote
Q What happens if two alternators end up charging the same banks?


A Let's dispel the myths of multiple battery charging sources.
All a battery charger sees on the 12 volt circuit is a voltage.
It has no "knowledge" of what else is on there, charging or discharging.
It just responds to the voltage it sees at any one time.

1. If it is a dumb regulator or charger and the battery voltage it sees is less than its built in threshold, it charges at full strength governed by the difference between its internal voltage/source impedance and the actual battery voltage. When the voltage rises to the threshold, it stops charging. This process my cycle on and off at different speeds depending on loads, etc.

2. If it is a smart alternator or charger, then the above scenario is complicated by having multiple threshold voltages at which it changes from full charge to topping-off charge to maintenance charge, to off, however the underlying principle is the same. There may also be timers and temperature inputs that modify the thresholds.

So what happens when there is more than one charging source is all those regulators that see a voltage less than the (next) threshold, charge the battery as though the other charging sources weren't there. They don't "know" anything else is charging. During the bulk charge, when the battery voltage is below all the thresholds, all the sources will be putting out the maximum they can. As each charging source reaches a threshold it changes its charging rate accordingly. Since no two regulators will have exactly the same threshold(s) this means that some of the paralleled regulators will tend to cut down or shut down before others and leave the job of finishing the charge to them but by that stage the current requirements are within the capacity of the one(s) that continue(s) to remain on line. Unquote

Bold is mine.

I'd just add a qualifier to that last statement, i.e., "often within the capacity of the one(s) that continue". With AGMs and gels, and other low-internal resistance batteries, and unless the capacities of the charging sources are known, it may well be the case that some potentially useful charging capacity is foregone. Unless there's an electrical traffic cop (e.g., the Balmar Centerfielder)!

Bill

[goboatingnow]

When I say professional, I mean the folks getting currently PAID to practice those skills. Not retired, not indulging in some other specific area, but folks being currently paid to exercise those specific skills in this area of electrical engineering.

The fact that you are paid or not is immaterial. However in my case I am a professional.

Since no two regulators will have exactly the same threshold(s) this means that some of the paralleled regulators will tend to cut down or shut down before others and leave the job of finishing the charge to them but by that stage the current requirements are within the capacity of the one(s) that continue(s) to remain on line.

Exactomondo Bill. Now I wish others indulging in electrical circuit voodoo would listen. Folks its a science, rules apply , these are the rules, they apply , end of story.


Dave

[hellosailor]

Dave, we all know there are rules and they will apply.

What no one knows--unless they've done a lot more testing and investigating than the average user--is:
WHICH charging source will cut out first?
What difference will that make to the equipment (wear, lifetime?)
What difference will that make in the charging time?

Little things like that. Which may arguably be insignificant. End of story? Sure, like a 1950's b-grade sci-fi movie that says "The End?" in the last scene.

Suppose you have two alternators, 55A and 75A. And the 75A cuts out 1/100th of a volt sooner. So, now you're going to finish charging on the lower power alternator, taking longer, placing more heat and wear on it as well. Maybe that's only a ten minute difference, maybe it is a half hour difference. Who knows? Yeah, you can run some numbers, try not to complicate those with two more charge inputs, from a windgen which may now be dumping, and a solar which may have shut down because it also lost the "hundredth of a volt" decision.

We all know what might be happening. We all know what could be happening. It would just be nice to have some numbers and to know what actually IS happening in any given case. And there's no simple way to predict that, given the current lack of integrated charge controllers.

What we've got is the back of the envelope, the ballpark guestimate. Sometimes that's enough, sometimes...one might want to come closer than that.

Horseshoes, anyone?