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Alternator paralleling


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#1 Schnid

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Posted 13 September 2010 - 07:38 PM

Can anyone tell me if alternator paralleling does in fact reduce battery charging times by a realistic amount? Having read one or two threads on the subject (alternator paralleling that is) I’m afraid I’m none the wiser.

I have a 70A alternator feeding my domestic batteries (4 off, 110 Ah) and a separate 70A alternator for my starter battery

Aqualine, on their website now offers Smartbank as an optional extra and says that the Smartbank system is “a clever box of tricks that links the two alternators to increase their output and reduce your engine running time for charging.”

As I’ve been considering buying SmartBank Advanced for some time now I’m hoping that this is true..

However, I asked Merlin, the supplier of Smartbank, to confirm that it would be suitable for my set up and the response I had was:

“This (Smartbank) is probably going to be of small use as if you use the two alternators together may result in both alternators charging and giving equal output there for raising your charging power however more than likely they will fight with each other and this will either result in one doing all the work and the other will do nothing or worst case scenario they will constantly flip and reduce the charge rate.

In my opinion you have a good system using two alternators on separate banks and your best bet would be to opt for the Smartgauge to give you the ability to monitor, and if you want to increase your charging capabilities go for a high output low RPM alternator like the Balmar series.”


Who is right?


John

Edited by NB Alnwick, 14 September 2010 - 10:35 AM.
inappropriate font sizing removed.

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#2 Arnot

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Posted 13 September 2010 - 09:51 PM

Can anyone tell me if alternator paralleling does in fact reduce battery charging times by a realistic amount? Having read one or two threads on the subject (alternator paralleling that is) Iím afraid Iím none the wiser.

I have a 70A alternator feeding my domestic batteries (4 off, 110 Ah) and a separate 70A alternator for my starter battery

Aqualine, on their website now offers Smartbank as an optional extra and says that the Smartbank system is ďa clever box of tricks that links the two alternators to increase their output and reduce your engine running time for charging.Ē

As Iíve been considering buying SmartBank Advanced for some time now Iím hoping that this is true..

However, I asked Merlin, the supplier of Smartbank, to confirm that it would be suitable for my set up and the response I had was:

ďThis (Smartbank) is probably going to be of small use as if you use the two alternators together may result in both alternators charging and giving equal output there for raising your charging power however more than likely they will fight with each other and this will either result in one doing all the work and the other will do nothing or worst case scenario they will constantly flip and reduce the charge rate.

In my opinion you have a good system using two alternators on separate banks and your best bet would be to opt for the Smartgauge to give you the ability to monitor, and if you want to increase your charging capabilities go for a high output low RPM alternator like the Balmar series.Ē


Who is right?


John

Merlin are on the right track but probably for the wrong reasons...

A 440Ah leisure bank wont like taking more than about 88A for any length of time, it will just tend to get warm and this will shorten your battery life.

If you do parallel two 70A alternators onto a 440Ah battery bank it wouldn't even demand more than one alternator could produce for more than a few minues, after this there would be no benefit.

If you want to increase your charging capabilities then a high output low RPM alternator would help - however;

The major benefit of most special alternators such as the Balmar is that they come with a far better regulator then the standard automotive alternator fitted to most narrow boat engines and this can probably be achieved fairly cheaply and easily by modifying your existing domestic alternator.

I am guessing here but suspect you have an Isuzu engine and if this is the case then it probably has a variety of Lucas A127 alternator fitted and this can be fitted with the "tractor" regulator which should reduce your charging times significantly.

A monitoring system of some description is an excellent idea, then you will actually know what is going on and be able to use your system to best effect. Have a look at the Smartguage or the Victron BMV-600S.

Regards

Arnot
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#3 blodger

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Posted 13 September 2010 - 10:28 PM

Well maybe, but in the computer world "font size" is surely the more commonly used term ? In Microsoft land, for example, the Office suite surely refers to "font size" not "type face size".

As I'm looking at it on a computer, you seem to be splitting hairs, and I'm not really convinced of the greater "rightness" of your offering!

Back on topic, I think the man who set up his own alternator paralleling still watches these forums - I wonder if this will nudge him into contributing again ?

I enjoyed the alternator paralleling thread; it was both practical and entertaining and frustrating for some who were trying to implement what was emergant.
The conventional wisdom and, I stand to be corrected, is that if two alts are working in tandem then one is likely to take the lead and the other virtually shut done pretty quickly so that not a lot gets gained by any extra fancy electrickery.
I had a single 70a alt charging the starter batt and via a split charge relay to the domestics.
I added a matching alt automatically relay connected to charging the domestic bank. The green alt is charging light as apposed to the red charge warning light stays on all the time on both alts.
I can run a washing machine with the engine running with this set up through an inverter which was the aim. I never investigated further about which alt supplied the most, etc, cause it did what I wanted it to do.
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#4 Sir Nibble

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Posted 14 September 2010 - 06:57 AM

Probably the best answer is, it might. Alternator paralleling, slow speed machines, remote regulators and suchlike are all good solutions to various problems. The difficulty is identifying which problems you have! If you intend to fit a battery monitor then that would be the place to start as that would be a source of information to help guide the selection of any enhancements. Gibbo will be along soon no doubt and his is the word of the lore.
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#5 Gibbo

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Posted 14 September 2010 - 08:09 AM

This one keeps coming up and it takes a long time to get to the final answer because it depends on so many variables.

I'll ask one of the mods to pin this so that we don't keep answering the same question.

Will paralleling alternators reduce charge times?

It depends upon:-

1. The size of the alternators in relation to the battery bank.
2. How far the batteries usually get discharged.
3. How fast the alternators are spun.
4. What other loads are being powered during charging.

Answers.

1. and 2. If the alternators are very small (say less than about 15% of the battery bank size for each alternator) then paralleling them will almost certainly reduce charge times. There is a rule of thumb called amp.hour law charging (which is actually a play on what really goes on but it suffices for this purpose). This law states a battery will safely accept a charge current in amps equal to the number of amp.hours that need replacing. So a 400Ahr bank, at 50% SoC needs 200Ahrs replacing therefore it will accept a charge current of 200amps. After a short while that bank will have increased to 51% SoC, so now it will accept 196 amps. And so on.

It can thus be seen that the idea of an alternator sized to 10% or 15% is complete crap. An alternator much bigger than this can be used and will result in massively reduced recharge times. If the batteries only ever get discharged to 90% SoC then at that state, the same 400Ahr bank will only safely accept 10% of 400 = 40 amps. So there is no point whatsoever in fitting an alternator bigger than this or in paralleling two 70 ampers. It would achieve nothing. But how many people only discharge to 90%?

On a 400Ahr bank, with twin 70 amp alternators, parelleling them will almost certainly reduce recharge times. Anyone who says otherwise simply hasn't understood what is going on.

3. A huge problem on the inland waterways is alternators not being spun fast enough. Most marinisers (read engine painters) don't pulley the alternators up high enough. They have many excuses for not doing so, but whatever their excuse, it doesn't change the fact that they don't pulley them up properly. They might feel justified in leaving the alterntor spinning too slowly, they might be just saying things to justify their laziness in not being bothered to change the pulleys, but it doesn't change the reality. This isn't just my opinion, this is fact. Adverc reach exactly the same conclusion on their website. This means that the alternator does not produce anywhere near its full capability at tickover. If the engine is being run at tickover just to charge batteries then paralleling the alternators will almost certainly result in a massive increase in charge rate. On many off the shelf "canal boat" engines you typically double the charge curent at tickover by paralleling them.

4. A 70 amp alternator (even assuming it's pulley'd up properly) isn't going to put much charge into a battery if there is an inverter running at the same time pulling 71 amps from the batteries. In fact there will be a continual 1 amp discharge. In this case, paralleling up the other alternator will turn this into a charge.

So you can see from the above that paralleling them can make a huge difference in many instances.

Alternators don't "fight each other" if paralleled. During the bulk stage (ie when the extra current is needed) they both work at full hoot. When acceptance is reached (ie the regulation voltage of the alternators), one of them might shut down completely. This is no issue, it has only shut down because its charge current is no longer needed to maintain the battery voltage at acceptance. If its current was needed, it wouldn't have shut down in the first place because the voltage wouldn't have reached acceptance. If loads are put on that exceed the capability of the remaining alternator, then the other one will instantly fire back up again. Whether one alternator shuts down or not depends upon its regulator and in particular whether it is battery sensing (most external regs) or machine sensing (most internal regs). Machine sensing ones rarely shut down, battery sensing ones often do shut down.

One issue that can rear its head is that the alternator shutting down can cause its charge warning light to come on and/or its tacho to stop working. This is a difficult (though not impossible) one to crack. With SmartGauge and SmartBank Advanced there is a feature built in to stop this happening.

I see the external reg issue has come up again. With modern alternators they do nowt. Absolutely nothing. All they ever did was increase the charge voltage. That is it. The rest is marketing bullshit. Modern alternators already charge at the same voltage so adding one does nothing. Some mention the virtue of converting to battery sensing as this compensates for the losses in under sized battery cables and dodgy battery isolators. I maintain it is better to get rid of the losses that battery sensing tries to bodge its way round. This is achieved simply by replacing the battery cables with correctly sized cables and putting in proper battery isolators.

When I used to actually wire boats up, as opposed to designing the equipment, I paralleled up literally hundreds of alternators, probably thousands. Every single one I did saw a reduced charge time of at least 20%, many as much as 30% and several by 50% or 60%

Finally, don't think of it as paralleling the alternators. Think of it as paralleling the batteries. A subtle difference, but realise that, as a result of this subtle difference, if an alternator packs up, you will still get charge to both battery banks without lifting a finger. You can also emergency start the engine from the domestic bank via the split charge relay.
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