Is a 60 amp alternator enough to charge 345ah domestic bank

[john_morris_uk]

Without criticising individual contributors there are a couple of basic misconceptions with some of the responses.

The first misconception appears to be when some people talk about 'boosting' the output of an alternator. A 60 amp alternator will NEVER produce more than 60 amps - it just can't because of the physics of the way that it is built. You can't even assume that it will generate anywhere near 60 amps for any serious length of time. With its normal alternator regulator, and assuming that the batteries will accept the charge, then it might get somewhere near to 60 amps for a few minutes, but then internal heating etc will derate itself and the output will fall. Manufacturers are a bit disingenuous when they 'rate' alternators and the quoted value will only be achieved under the most optimum conditions.

The boosting of the 'smart' alternator regulators will force the charging current to be at its maximum for longer, but we then come up against the physics of the batteries. The chemical reaction that occurs between the lead and acid etc can't be forced to occur faster than nature allows, and as the charge moves from the surface of the plates to deeper into the plates, the process slows down. No matter what you do, the batteries can't be forced to accept charge above a particular rate without excess gassing. The so called 'smart controllers' are much better than the standard alternator regulator at getting the batteries to accept charge, but they can't alter the physics of the batteries. Power in has to be more than power out in the charge discharge cycle and you can't achieve full charge in twenty minutes of motoring out of the anchorage no matter how big the alternator and how clever the charger controller.

This leads to the final bit of misunderstanding. Having a smaller alternator might not be optimum - but it will still work. I despair when I read people suggesting that a 65 amp alternator won't charge a large battery bank. Of course it will - but it won't be optimum and it will take longer.

To the OP: The alternator might not be ideal but it will be ok. A smart alternator charge controller (Sterling etc ) will help considerably.

The real solution is to measure daily power needs and budget to replace the power used accordingly. In other words how many amp hours is used by EVERYTHING on board - and then find a way of putting it back (plus a bit)

In the Med' some solar panels will make a lot of difference! Most long term sailors end up with a mixture of solar/wind and topping up with engine/generator as required.

FWIW we have a battery monitor that allows us to see how much power in and power out from the batteries at all times. Saves guessing!

 

[halcyon]

I can't emphasise enough what a difference the AtoB made though. Previous to fitting this it was really hard to get the batteries to fully charge without shore power (even by running them for 4 or 5 hours), hence my comment that an alt on it's own is no good.

But you are not increasing alternator output amps, only volts, in fact you have less amps due to switchmode effiecency.

Brian

 

[Bobc]

Without criticising individual contributors there are a couple of basic misconceptions with some of the responses.

The first misconception appears to be when some people talk about 'boosting' the output of an alternator. A 60 amp alternator will NEVER produce more than 60 amps - it just can't because of the physics of the way that it is built. You can't even assume that it will generate anywhere near 60 amps for any serious length of time. With its normal alternator regulator, and assuming that the batteries will accept the charge, then it might get somewhere near to 60 amps for a few minutes, but then internal heating etc will derate itself and the output will fall. Manufacturers are a bit disingenuous when they 'rate' alternators and the quoted value will only be achieved under the most optimum conditions.

The boosting of the 'smart' alternator regulators will force the charging current to be at its maximum for longer, but we then come up against the physics of the batteries. The chemical reaction that occurs between the lead and acid etc can't be forced to occur faster than nature allows, and as the charge moves from the surface of the plates to deeper into the plates, the process slows down. No matter what you do, the batteries can't be forced to accept charge above a particular rate without excess gassing. The so called 'smart controllers' are much better than the standard alternator regulator at getting the batteries to accept charge, but they can't alter the physics of the batteries. Power in has to be more than power out in the charge discharge cycle and you can't achieve full charge in twenty minutes of motoring out of the anchorage no matter how big the alternator and how clever the charger controller.

This leads to the final bit of misunderstanding. Having a smaller alternator might not be optimum - but it will still work. I despair when I read people suggesting that a 65 amp alternator won't charge a large battery bank. Of course it will - but it won't be optimum and it will take longer.

To the OP: The alternator might not be ideal but it will be ok. A smart alternator charge controller (Sterling etc ) will help considerably.

The real solution is to measure daily power needs and budget to replace the power used accordingly. In other words how many amp hours is used by EVERYTHING on board - and then find a way of putting it back (plus a bit)

In the Med' some solar panels will make a lot of difference! Most long term sailors end up with a mixture of solar/wind and topping up with engine/generator as required.

FWIW we have a battery monitor that allows us to see how much power in and power out from the batteries at all times. Saves guessing!

Great post, spot on.

This is exaclty what I found. After an intial period, my alternator was dropping amp output quite considerably, and not charging at anywhere near 60A (more like 10-15A). The Sterling pushed it back up to around 50A, and boosted the charge voltage from 12.9v to 14.4v.

 

[ianj99]

One point not made, is to alter the alternator gearing by fitting a smaller pulley to it.

Your 60amp alternator may never reach this output at the engine revs normally used. So gearing it up and fitting a Sterling regulator may be more effective than changing the alternator.

You can buy smaller pulleys on Ebay.

Ian

 

[john_morris_uk]

One point not made, is to alter the alternator gearing by fitting a smaller pulley to it.

Your 60amp alternator may never reach this output at the engine revs normally used. So gearing it up and fitting a Sterling regulator may be more effective than changing the alternator.

You can buy smaller pulleys on Ebay.

Ian

You can check that the gearing is ok by playing with the engine revs and watching the charge rate. No point in spinning the thing faster than necessary and its quite rare for the pulley ratio to be completely wrong. The builders usually think about these things a bit - but its worth double checking by playing with the engine revs and watching the charge rate. If you find you have to have the engine revving hard to get to the plateau beyond which no further increase in revs gives more amps out, then a change in pulley ratio might be worthwhile. Just make sure you don't gear it for tick-over speed and then over rev the alternator when you are motoring hard.

 

[ianj99]

The builders usually think about these things a bit

yeah right!

Boat builders use whatever comes with the engine and engine manfacturers will assume you'll be using the full rpm.

If you do most of the time, then fine, no need to change the pulley.

But if, as I do, you rarely use more than 1/2 -2/3rds engine rpm then without a smaller pulley, the alternator could never reach its rated output. The alternator isn't going to fly apart because its over revvved a bit for a short time but the only way to check, as you say, is to measure the current into a flat battery.

The pulley size reduction is limited anyway by the minimum diameter for a given size of belt. However even a 20% increase in rpm could mean the existing alternator is perfectly adequate.

 

[john_morris_uk]

Boat builders use whatever comes with the engine and engine manfacturers will assume you'll be using the full rpm.

No need to be sarcastic. Engine builders actually don't assume that you will be using full rpm - and despite what you suggest, the engineers do think these things through. It is possible to over rev alternators.

If you go into the details of alternators and outputs, then you will find that there are suggested limits by the manufacturer for the rpm.

There will be a sort of plateau in the charging output vs rpm graph and revving the alternator beyond this point is a waste of energy. Its worth checking that your normal cruising engine rpm spins the alternator fast enough by checking the charging current when you lower and increase the revs a little, but to state that spinning the alternator even faster will give you more output just isn't necessarily true.

 

[ianj99]

Its worth checking that your normal cruising engine rpm spins the alternator fast enough by checking the charging current .

That's right, tell me off and state the bleedin obvious...

My posts were perfectly valid and don'r require correcting by you.

 

[grumpygit]

Without criticising individual contributors there are a couple of basic misconceptions with some of the responses.

The first misconception appears to be when some people talk about 'boosting' the output of an alternator. A 60 amp alternator will NEVER produce more than 60 amps - it just can't because of the physics of the way that it is built. You can't even assume that it will generate anywhere near 60 amps for any serious length of time. With its normal alternator regulator, and assuming that the batteries will accept the charge, then it might get somewhere near to 60 amps for a few minutes, but then internal heating etc will derate itself and the output will fall. Manufacturers are a bit disingenuous when they 'rate' alternators and the quoted value will only be achieved under the most optimum conditions.

The boosting of the 'smart' alternator regulators will force the charging current to be at its maximum for longer, but we then come up against the physics of the batteries. The chemical reaction that occurs between the lead and acid etc can't be forced to occur faster than nature allows, and as the charge moves from the surface of the plates to deeper into the plates, the process slows down. No matter what you do, the batteries can't be forced to accept charge above a particular rate without excess gassing. The so called 'smart controllers' are much better than the standard alternator regulator at getting the batteries to accept charge, but they can't alter the physics of the batteries. Power in has to be more than power out in the charge discharge cycle and you can't achieve full charge in twenty minutes of motoring out of the anchorage no matter how big the alternator and how clever the charger controller.

This leads to the final bit of misunderstanding. Having a smaller alternator might not be optimum - but it will still work. I despair when I read people suggesting that a 65 amp alternator won't charge a large battery bank. Of course it will - but it won't be optimum and it will take longer.

To the OP: The alternator might not be ideal but it will be ok. A smart alternator charge controller (Sterling etc ) will help considerably.

The real solution is to measure daily power needs and budget to replace the power used accordingly. In other words how many amp hours is used by EVERYTHING on board - and then find a way of putting it back (plus a bit)

In the Med' some solar panels will make a lot of difference! Most long term sailors end up with a mixture of solar/wind and topping up with engine/generator as required.

FWIW we have a battery monitor that allows us to see how much power in and power out from the batteries at all times. Saves guessing!

Very well put.

Pulley size will not be far out of ratio for sure. Once the alternator has reached it's cutting in voltage it will only need up to a further 20% of revs for it to reach the optimum output in relation to what the batteries will accept. I would say most if not alternators on marine engines all are fitted with an automotive regulator and this is the bit that needs attention.
Driftgate/Adverc/Sterling are a few among many that will vastly improve your alternator for your marine requirements. Most also have soft start to boost mode so not to destroy the belt(s) and battery temperature sensor to prevent heavy gassing of the batteries which will shorten there life dramatically.
FWIW I also think the OP's alternator size is fine, especially with a smart controller.

_____________________________________________________________________

 

[whipper_snapper]

That's right, tell me off and state the bleedin obvious...

My posts were perfectly valid and don'r require correcting by you.

Welcome to the forum. I can tell you are gong to fit right in!

 

[stevensuf]

the maximum recommended charging rate for 300 odd amp hours would be 60 amps, putting in a 90 amp charger will overheat the batteries, when no smart regulator is used, using a smart reg will most likely drop the charging rate down once the batteries start to heat up to 60 amps or less, so using a larger alternator on normal lead acids would be a waste of time, if agms then thats a different matter, they can accept more amps in without over heating.

 

[Bob_Ranft]

Alternator Regulators

I also have a Yanmar 3YM30 with the standard 60 amp alternator. When I was looking for a battery monitor I came across a very interesting article on the Smartgauge web site. On the subject of alternators and regulators they basically say that about 10 / 15 years back many alternators only charged at 13.6 to 13.8 volts and an external regulator would provide a considerable improvement to the overall charging scenario. Fast forward to present they say many alternators now charge at 14.4 volts and with such an alternator an external regulator will make no difference whatsoever.

I understand the standard 60 amp alternator on the Yanmar 3YM30 charges at 14.4 volts.

Only passing on information here from a web site belonging to folks who are supposed to be experts on the subject. www.smartgauge.co.uk

Click on Technical Information and stroll down page 1 to "Are Alternator Regulators Really Required". It's a long article, but makes interesting reading.

Bob

 

[charles_reed]

some advice please for my father in-law.
He has just fitted a new Yanmar 3YM30 (29hp) to his Moody 336 in Greece (found an excellent engineer)

They are currently cruising the med - hence they rarely plugin to shore power.

He has 3 x 115ah domestics & a regular cranking battery (all recently new)
Question is - will the 60amp modern Alternator be sufficient??

He is wondering if some form of Alternator 'booster' should be added?

Having forked out for a new engine he would like to avoid the cost of a bigger alternator if possible.

ps - he does have a great big solar panel on a frame off the transom too

Yes it is, but I'd suggest a smart controller Adverc (or Sterling) and replacing the alternator when it burns out (usually after 5 years in my experience).

Providing you use a serrated heavy duty belt on the 3YSM (I have one with just this set-up) you can just drive a 110 amp alternator, though a 90 amp Lucas one from Adverc might be a more economical bet.
As already suggested the output/rpm curve is more important than the quoted max output - I found the "best" alternator was a 100 amp Magnetti-Marelli as fitted to an horrid cast-iron Fiat Ducato motor - that only revved to 2400rpm so the alternator produced far more than the current 110 amp alternator I have fitted at normal revs of 2000-2400.

My first alternator (on the 3GM) was a 35amp Hitachi and events transpired as I reported.

 

[pvb]

I also have a Yanmar 3YM30 with the standard 60 amp alternator. When I was looking for a battery monitor I came across a very interesting article on the Smartgauge web site. On the subject of alternators and regulators they basically say that about 10 / 15 years back many alternators only charged at 13.6 to 13.8 volts and an external regulator would provide a considerable improvement to the overall charging scenario. Fast forward to present they say many alternators now charge at 14.4 volts and with such an alternator an external regulator will make no difference whatsoever.

Not so - many external regulators can increase the charge voltage at the battery to 14.8v. Most use battery sensing as well, to negate any voltage drop in cabling, diodes, etc. In addition, many include temperature sensors which allow temperature-compensated
charge voltage and/or alternator overheat protection.

 

[Bosun Higgs]

Without criticising individual contributors there are a couple of basic misconceptions with some of the responses.

The first misconception appears to be when some people talk about 'boosting' the output of an alternator. A 60 amp alternator will NEVER produce more than 60 amps - it just can't because of the physics of the way that it is built. You can't even assume that it will generate anywhere near 60 amps for any serious length of time. With its normal alternator regulator, and assuming that the batteries will accept the charge, then it might get somewhere near to 60 amps for a few minutes, but then internal heating etc will derate itself and the output will fall. Manufacturers are a bit disingenuous when they 'rate' alternators and the quoted value will only be achieved under the most optimum conditions.

The boosting of the 'smart' alternator regulators will force the charging current to be at its maximum for longer, but we then come up against the physics of the batteries. The chemical reaction that occurs between the lead and acid etc can't be forced to occur faster than nature allows, and as the charge moves from the surface of the plates to deeper into the plates, the process slows down. No matter what you do, the batteries can't be forced to accept charge above a particular rate without excess gassing. The so called 'smart controllers' are much better than the standard alternator regulator at getting the batteries to accept charge, but they can't alter the physics of the batteries. Power in has to be more than power out in the charge discharge cycle and you can't achieve full charge in twenty minutes of motoring out of the anchorage no matter how big the alternator and how clever the charger controller.

This leads to the final bit of misunderstanding. Having a smaller alternator might not be optimum - but it will still work. I despair when I read people suggesting that a 65 amp alternator won't charge a large battery bank. Of course it will - but it won't be optimum and it will take longer.

To the OP: The alternator might not be ideal but it will be ok. A smart alternator charge controller (Sterling etc ) will help considerably.

The real solution is to measure daily power needs and budget to replace the power used accordingly. In other words how many amp hours is used by EVERYTHING on board - and then find a way of putting it back (plus a bit)

In the Med' some solar panels will make a lot of difference! Most long term sailors end up with a mixture of solar/wind and topping up with engine/generator as required.

FWIW we have a battery monitor that allows us to see how much power in and power out from the batteries at all times. Saves guessing!

Which might explain the "why" but doesnt tell him the "what" John.

The normal rule of thumb is the alternator to be 25% of the battery bank rating for flooded lead acid batteries and 40% for gel types. So for 345 aH battery capacity and assuming flooded lead acid, the max useful alternator size is about 85anp. So it would be worthwhile but not absolutely necessary for him to upgrade his alternator to ( say) 90 amps which will just run with one pulley belt. The batteries will accept that level of charge.

The digital regulator etc from Sterling and the like will shorten the charging period by keeping the alternator running at / near full output for longer. But it will cause a lot more heat generation - my alternator in the UK becomes too hot to touch using a Sterling jobbie. And thats 60 amp into about 300aH capacity.

But really its a suck it and see situation. How much leccy does he use? How long can he run before he has to start the engine to re-charge the batteries? In short, if he has to switch on the engine too often for his liking, then he could usefully uprate the alternator. But if it works OK now, then why change.

 

[ianc1200]

We have 4 x 110 AH house batteries, 2 x 110 starter batteries (have a main and wing engine). The main engine has 90A & 110A alternators, and there is a Sterling AtoB 210A unit, there are two 30W solar panels. Point of all this is we rarely see anything like 70A charging, usually well below 30A. (the boat is a displacement motor cruiser used on upper Thames).
IMO having the second alternator or anything beyond 60A doesn't achieve much.

BTW, best bit of kit I have in this regard is a Smartguage which really tells me what I need to know about the state of the batteries.

 

[sailinglegend420]

To summarise and add a few points - bearing in mind the original poster was talking about the Med.

1. A 60 amp alternator will output much less when hot - you need a more expensive marine alternator like Balmar when 60 amps means 60 amps.
2. If the alternator is about 15 years old it may only output 13.8 volts.
3. Modern car alternators may be 14.4 volts - but their internal regulator sets the voltage regulation at the alternator and not at the battery. A big problem with split diodes or power loss on the cables.
4. SmartGuage suggest that you don't need a regulator because they are trying to sell you their solutions. Note that they were bought by Merlin who's customers are now more automotive - MOD - ambulance services than their original marine customer base.
5. An external regulator will give you benefits like battery voltage sensing, programming for different battery types, dropping to float voltage - essential if you have sealed batteries, allow you to add an alternator and battery temperature sensor to drop the alternator output if necessary, and they may delay the alternator output for about a minute to limit the load on the engine at start up.
6. Larger alternators will help with larger banks and are essential to get the best from AGMs - but may over heat some batteries. Batteries will eventually limit their charge acceptance rate to about capacity divided by 4. So for 100 Ah battery use a 25 amps alternator. A 100 amp alternator would be a waste of money, and will take 4 HP from the engine. It may also need a larger belt or different pulleys.
7. Running the engine for just a few hours will only get the batteries up to about 80% charge, which will cause sulfation if not raised to 100% at least once a month. Other than shorepower large solar panels are the best answer, but they must replace the lost Ah each day and have spare capacity to add charge and bring the batteries back up to 100%.
8. Boosters like Sterling actually suck all the power out of the alternator and convert it to a higher voltage to charge faster. This may cause the alternator's premature failure. Mr Sterling only recommends you use open wet lead acid batteries. which accept his "fast charge" claims by boosting voltages up to 14.8 volts. His boosters/regulators may have settings for "sealed" batteries but many posters on here with sealed batteries have had problems with Mr Sterling!
9. There is only one simple way to accurately determine when a battery is fully charged and that is when the current going into the battery is less than 1% of the Ah capacity at the absorption voltage. So a 100 Ah battery will be fully charged when the charge voltage is above 14.2 volts and the current is about 0.5 amps. Chargers drop down to a float voltage of 13.2-13.6 volts well before this to prevent the battery from overheating, so don’t assume that when you’ve reached “float” your batteries are fully charged.

 

[carrswood]

Dear All

As ever some excellent advice and feedback. Im very grateful, as is the F-I-L.

Many many opinions - not all conclusive; however I think we agree it would be wise to see how the standard alternator performs. He is an experienced sailer who has done much cruising in this Moody 336 - starting from the UK. So at least he already has a benchmark to compare against.

During his travels to date he has not had a problem with low SOC. Yes I would think the "'large" solar panels are really helping the situation - especially as they are in the Med. (sorry I dont know his solar panels rating - but I'm estimating 60-70W).

But also they aren't big consumers of the ah either - so that helps. The Isotherm built in fridge is the biggest consumer but as this is seawater cooled that also helps.

Thanks again