Larger alternator or dual alternator? Bavaria 38 2002 - Volvo Penta D2-55A

[Seagoon]

I have a 500Ah AGM house battery bank and am looking at doing some longer passages and remote cruising. I have some solar and wind charging installed but I still have the stock Valeo 60-amp alternator installed.

I have been thinking of a larger alternator such as the Volvo 115A offering or a Balmar, and/or a dual alternator installation to more efficiently charge this bank.

Volvo seem to only do dual 60A kits for the D2-55A, with single or dual 115A kits only for later models - see https://www.volvopentashop.com/epc/en-US/Details/AccessoriesCatalog/2784?path=1532%2F2783%2F2784

Has anyone worked out why the Volvo dual 115A is not for the D2-55A?

Has anyone had success with higher output single or dual alternator installations on D2-55As?

[tiger79]

Has anyone worked out why the Volvo dual 115A is not for the D2-55A?

I think the D2-55A uses an ordinary V-belt to drive the alternator, whereas later versions of the engine have a multi ribbed poly-V belt, which is necessary to drive the larger output alternator.  With an ordinary V-belt, around 90A is the maximum 12v alternator which can be reliably driven - larger than that and there's excessive belt wear.

If you change the pulleys, you could no doubt fit a 115A alternator to your engine.

[IslandAlchemy]

Neither.  Fit a Sterling Alternator to Battery charger (AtoB).

It will give you far more charge than a bigger alternator.

I had (until recently) a Valeo 60A alternator on a VP engine and 675Ah of house batteries, and it worked perfectly.

[tiger79]

Neither.  Fit a Sterling Alternator to Battery charger (AtoB).

It will give you far more charge than a bigger alternator.

Well, an A-to-B charger will help to maximise the charge rate by increasing the charge voltage at the batteries, but it can't magically create any more charge than the alternator is capable of producing.  A typical 60A alternator, with the engine running at cruising revs, might be able to produce 40-50A.

[IslandAlchemy]

An alternator on its own will not produce 40-50A for 2 hours.  It will produce it for about 20 minutes, and then reduce down to a fraction of that.  The Sterling unit basically makes the alternator pump the full output into the batteries until they are full (taking a breather every 15 minutes to let the batteries cool and settle down).

It works.

[sy_Anniina]

If you have or can borrow a clamp ammeter capable of DC-measurement, I would suggest you to measure the true charging current you get from the current alternator. I suspect IslandAlchemy is correct here, but measuring your own alternator output you can be sure.

Based on findings of collagues, my guesswork is your current alternator does supply about 30A to your 500Ah battery bank after short initial rush close to 60A.

Changing to bigger alternator only (with identical charge controller) will still produce the same steady-state 30A current, just the initial rush will be bigger.

If increase 30->60A is enough Sterling AtoB or other regulator (like Sterling Pro RegDW) is enough

If more is needed, you need to upgrade both the alternator and the regulator.

BR,

Tommi
s/y Anniina

[tiger79]

An alternator on its own will not produce 40-50A for 2 hours.  It will produce it for about 20 minutes, and then reduce down to a fraction of that.  The Sterling unit basically makes the alternator pump the full output into the batteries until they are full (taking a breather every 15 minutes to let the batteries cool and settle down).

No, the A-to-B charger only increases the charging voltage at the batteries (to 14.4v in the case of the OP's AGM batteries).  If this is higher than the alternator's output voltage, the charging current will be greater, but the actual current will depend on the ability of the batteries to absorb that current.

[IslandAlchemy]

From the Sterling literature....

ProAlt AtoB optimises the available output of the alternator (that varies with engine speed) and converts the output to mimic that of a mains powered multi stage battery charger.

How it works

In order to maximise the alternator output current, the alternator-to-battery charger pulls the alternator output voltage down to about 13V. Then this low voltage is amplified to a higher voltage suitable for effective battery charging, i.e. 14.1V to 14.8V.
The unit’s intelligent software automatically calculates the optimum charge in any cycle and absorption time. When the batteries have been fully charged, the voltage is reduced to float voltage (appr. 13.5V to 13.8V).

It is designed to pull this voltage down a little in order to enable the standard alternator regulator to produce its full current.

[tiger79]

Don't necessarily believe the Sterling hype.  The A-to-B charger is a clever bit of kit, but it can't generate any more electricity than the alternator can generate, at any given engine speed.  Alternators generally achieve their rated output at 6000-7000rpm, depending on pulley sizes this could be 3000ish engine rpm. 

The A-to-B charger achieves better charging purely by increasing the charge voltage at the batteries to an optimum level (the same thing can be achieved by adding a "smart regulator" but that requires some alternator modification whereas the A-to-B charger needs no alternator modification and hence preserves warranty).

One thing the A-to-B charger does do is allow the charge voltage to drop to a float level, which is something that add-on regulators don't do.

[IslandAlchemy]

I don't believe the hype.  I have one and believe what I see happening.

When I got it, the people at the boatyard said "it's just a box with flashing lights and won't help you.  What you need is a bigger alternator".

Well, I fitted it, and it took my batteries from 12.2v to float in 2 hours every day for 10 days during the second half of a transat from the Azores to the UK, where before we were having to run the engine for 6-8hrs/day just to get the batteries to break-even.

[tiger79]

I don't believe the hype.  I have one and believe what I see happening.

If you had an add-on smart regulator you'd see a similar effect, it's simply a case of getting the charge voltage correct at the batteries.

[tiger79]

Well, I fitted it, and it took my batteries from 12.2v to float in 2 hours every day for 10 days during the second half of a transat from the Azores to the UK, where before we were having to run the engine for 6-8hrs/day just to get the batteries to break-even.

12.2v is generally considered to be 60% state of charge.  To fully charge your 675Ah of batteries would therefore need at least 270Ah (40% x 675).  Your 60A alternator simply can't supply that in 2 hours.

[Symphony]

I don't believe the hype.  I have one and believe what I see happening.

When I got it, the people at the boatyard said "it's just a box with flashing lights and won't help you.  What you need is a bigger alternator".

Well, I fitted it, and it took my batteries from 12.2v to float in 2 hours every day for 10 days during the second half of a transat from the Azores to the UK, where before we were having to run the engine for 6-8hrs/day just to get the batteries to break-even.

Something does not quite add up here. Firstly how were you taking your batteries from fully charged down to 12.2v in just one day while on passage. As tiger 79 suggests this is anything up to 270ah from a 675Ah bank. Secondly the very maximum your alternator can put back is 120A in 2 hours although in reality it will be substantially less. You AtoB works by boosting the voltage so shortening the initial charging time but to get a bank up to full charge from 60% takes substantially longer as the limitation is the rate at which the bank can absorb the charge, independent of how much the alternator is theoretically capable of producing.

I have no problem with accepting that in 2 hours you could replace a typical day's usage on passage - that is 60-75Ah, particularly if you had, like most ocean passage makers, alternative power sources such as solar or a wind generator. However fully charging a bank as you described is simply not possible.

[IslandAlchemy]

Believe what you like. I'm telling you what actually happens, not some theories.

On the passage, we had autopilot, 2 fridges and instruments on 24/7, and nav lights on for 12hrs/day.  Also had people watching films on the telly and listening to music.

Even with my batteries fully charged, they will pull down to about 12.5v with that lot on, as we have Trojans, not 12v leisure batteries.

[Symphony]

Much as you may not like "theory" it is fact. You cannot get more than 60 amps out of a 60A alternator, so the maximum you can get in 2 hours is 120A if your batteries will take it. In reality you are unlikely to get anywhere near 60A except initially, and at high revs.

So, either your consumption is substantially less than you are suggesting or your batteries are not being fully charged. Suggest instead of guessing you monitor your real consumption and the real amps that you are putting back in. This alone will tell you whether you are replacing the consumption in your 2 hours charging time. Also taking a reading of voltage as state of charge while the batteries are in use is misleading. Using this measure is only applicable on a rested battery with no load. To check, just turn off all the loads and the engine and watch the battery voltage reading rise.

BTW I am not disputing that that your A to B will charge faster, but the amount of amps the alternator can produce is the limiting factor. The type of battery is not particularly relevant. The advantage of batteries like Trojans is they are more tolerant of deeper discharge and more discharge cycles.

[tiger79]

Believe what you like. I'm telling you what actually happens, not some theories.

I don't think you are telling what actually happens, because I think you're rather confused.

Earlier in this thread, you posted this...

Well, I fitted it, and it took my batteries from 12.2v to float in 2 hours every day for 10 days during the second half of a transat from the Azores to the UK, where before we were having to run the engine for 6-8hrs/day just to get the batteries to break-even.

But on 22 Feb 2017, you posted this...

From 12.2v, they will take about 3-4 hours to get back to float charge (60A alternator and Sterling AtoB).

So how long does it really take?  2 hours?  4 hours?  See why I think you're confused?  And note that getting to float charge doesn't mean the batteries are fully charged, it just means that the Sterling charger has decided to go into float.

The Sterling A-to-B charger is a clever bit of kit, useful for some people, but it can't overrule the basic physics of your alternator.

[Jeff Jones]

Hi Seagoon. I looked at and costed increasing my VP 2030 70Amp alternator upto 115Amp it is do-able and would require replacement of the V belts and pulleys to Serpentine (ribbed belts) as well as a new alternator. it wasn't cost effective for me - and so it was one of the reasons I my case i replaced the engine..for a D1-30 which came with the up rated alternator as standard.

What you want to achieve requires a mix of work. You can use your engine to bulk charge the batteries and then relay on increased solar to top off. You'll need to calculate what power you actually use and therefore what you then need to put back into your batteries.

Having larger alternators will only help with bulk charging...you'll end up running your engine for extend periods just to top off and you'll with the alternators never get you batteries truly full.

All alternators suffer from heat, the heat reduces the current output irrespective of what it is charging...also the batteries have an acceptance current they will draw when charging (which varies dependent on how low the batteries are)...again heat can play a part in reducing the charge acceptance, and cables getting hot carry less current and so it can spiral.

id recommend the Battery University on the web for detailed info.

Normally an alternator will produce its best current when its cool... but in the engine bay you might want to add some secondary cooling.. but i think your best bet would be to increase any solar you might have as a first step..you can spend £1500-2000 in getting pulleys and alternators brackets made. best to put the money into solar in my opinion.

 

[Salty]

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..................best to put the money into solar in my opinion.

I couldn’t agree more, and in addition solar has no moving parts to wear out, and just keeps on working all the while there is some sunshine.

Obviously the down side of photovoltaic systems are that they don’t generate at night, and don’t produce much energy during the daytime if the weather is overcast, but they do very much provide a useful charge for the batteries. My boat is kept on a swinging mooring when I’m not actually sailing it, so connection to shore power is not an option. For the last couple of seasons from 1 April thro to 31 October, a single 100 watt solar panel along with occasional running of the engine when leaving or entering the port has provided for all of my electrical needs. Even over winter while the boat is ashore and during which time I usually spend two or three days a week onboard carrying out maintenance tasks, the only use I have for mains power is for operating mains powered machinery (and an electric blanket on chilly nights !!!). On very rare occasion during the winter lay up I switch on the mains powered battery charger just to give the batteries a boost, but that’s about it. Having said that I think sometimes that a bit more solar panel would be useful so I’ve just bought a second 100 watt panel which should do the job with quite a bit to spare.
(Battery bank consists of 2 x 240 amp hour lead acid domestic + 1 x 100 amp hour engine start battery + 2 x 120 amp hour batteries used to run the electronic antifouling system but that system is switched off during the winter while the boat is ashore).

Another problem with solar panels of course is where to put them where they will not be in the way, and will not get trodden on or damaged. Initially I placed the panel on top of the hatch garage, but It wasn’t entirely satisfactory there because it got shaded by the boom or by the main sail. I tried putting it foreward on top of the fore hatch,  but that too wasn’t very satisfactory and I was afraid it might get washed away if we took a big greeny across the foredeck. Finally I took the plunge and had a stern gantry made, and that is just perfect, albeit a bit on the expensive side (£800), but less than the price of a new engine with a larger alternator, and all of the electricity the panel now generates costs nothing more for it to be produced.

[Jeff Jones]

Hi Salty... thanks

I installed 2x 42w Solara semi-flexible solar panels, in the same locations 1 on the garage and 1 forward of the front hatch, they are wired in parallel because of foreseen shading. I have been really surprised with the performance with best power seen is 78Watts and 20vdc normally put also voltages up to 23/24vdc in bright sunlight.

I have 300amp/hr of full river AGM's and they are kept well topped up from solar alone.

When I say spend a week on board (based on a swing mooring) I normally run the engine to bulk up the batteries before I leave and then let the solar top of until the next time on board. I don't have to worry about the batteries anymore being able to run a tv and heating whilst on the mooring at night and on bright day even turn the fridge on.

Had the solara panels now for over 14months and no degrading of power out or walkon panels...(hope am not tempting fate)

[IslandAlchemy]

Can I suggest that you re-read the original OP.

He says that he cannot get the required charge from his current 60A alternator, and the only option on his engine is to add another 60A, which is neither a good solution or particularly cheap.

My suggestion of replacing the split charge diode with an A to B charger still stands as the best and most cost-effective way of getting his engine charging boosted.

I doubt very much that he will want to put a new engine in to get a bigger alternator (utter madness), and adding solar is a completely different solution to a completely different problem.

[Symphony]

That is just one alternative that will indeed as you pointed out shorten charging times. However the limitation is still the 60A output from the alternator. The real question is about what daily consumption he anticipates and how best to replace that. Changing to a 115A alternator will increase the voltage of the charge just as your A to B does plus give the potential of greater charge rate if the batteries can take it. The move to 115A alternators is in part to deal with the more common use of larger capacity AGM house banks fitted to newer boats.

On older boats such as the OPs solar is probably a much better solution as it reduces the need to run the engine - running an engine for 2 hours a day on light load for charging is just about the worst thing you can do to it plus solar is "free". Particularly effective in warmer climates and clearly a popular solution.

So, the process is to assess expected usage, then seek ways of minimising that and finally consider the alternative ways of balancing the demand and supply. In my view running the engine daily is right at the bottom of the list of preferences. However, if you do run the engine, either the A to B with the existing alternator or an upgraded alternator will reduce running time.