Large Alternator or Additional Alternator Regulator - Which is better?

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swanny

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New engine and going for two alternators! However, with a short charging period am I better to still use my Sterling Pro Digital Alternator Regulator with a smaller amped Alternator or go for a large, say 150amp alternator instead. I understand that the Alternator will sense what is in the battery and step down whereas the sterling unit will keep it on boost charge until stepping down so charging quicker. What is better? Simpler but longer or Quicker but more complicated???
 
Not quite as simple a question as you may expect. The second alternator kit on a Yanmar uses a single belt pulley. This limits the alternator size to about 100 amps. Hence you can't really go for the 150 amp alternator and reap the rewards without suffering excessive belt wear.
Hence that may answer your question on alternator size depending upon your setup.
Questions previously brought up about external regulators have created a heated response.
IMHO they are a must but others would disagree. There are no alternators internally equipped with mutli stage regulators that I know of so stick with an external multi stage regulator.
 
Re: Large Alternator or Additional Alternator Regulator - Which is bet

They are addressing two different needs - a larger alternator gives you the potential to put out more amps whilst the regulator simply controls the way in which this is done (ie the output voltage) and gets round some of the problems inherent in the normal alternator control circuits.

The alternator control circuit controls the output voltage of the alternator and that in turn controls the current drawn. So if, for example, you batteries were maybe 200 amp hours capacity and were half discharged, the voltage might be 14 to charge them and the alternator putting out 30 amps whether it was a 150 amp alternator or a 60 amp one. Theses figures are plucked out of the air for illustration by the way.

To put it another way, putting a much larger more powerful engine in your car would be a waste of time if you were limited to 70 mph on the motorway, wouldnt it?

So what dictates whether you can use a 150 amp alternator is the capacity and internal resistance of your battery bank. If the max that it takes is 40 amps, why bother having a bigger alternator?

Both the big alternator and the small one would benefit from the alternator controller assuming your boat circuits have been wired in the usual way.
 
You're unlikely to be able to use the output of a 150a alternator unless you have some 600AH of battery capacity, and it's discharged well below 50% . Even then, you'd need 14.4v or so at the battery to overcome its internal resistance, and a double drive belt to take the load. The less the battery capacity, the higher its internal resistance, so the lower the amps charge it will accept at 14.4v.

So, usually first step is to ensure you get 14.4v at the battery when it needs it; this often calls for a smart voltage regulator sensing battery voltage. Then, measure what amps that's pushing out when they're discharged 50% with typical loads on the circuit. If it's only 60a or so, no point in fitting a higher amp alternator without a bigger battry bank . . . .
 
The regulator I have does sense battery voltage - designed to overcome voltage drop through the split charge diode. Am I right then in thinking that the only time I would need or use a larger alternator would be with a larger battery bank - currently house batteries are 324amps - or if the bank is being charged and there is large loads being run from the system at the same time? The cost for a the larger extra alternator is negligble compared to say a 100amp one. And, I am fitting upgraded poly v belts or whatever they are so the engine has no problem powering them. I guess I am trying to think ahead also. I will fit (either now or later) an electric windlass and perhaps, perhaps, a bow thruster. I still like the idea of the Sterling Regulator and it is after fitted already on the old alternator. I am guessing that this unit senses the battery needs and controls the alternator accordingly. I mean, with a 150amp alternator it will not simply allow the alternator to push this amount of amps into the batteries until say 80% charged. I hope it will still only let the alternator put out what is needed, albeit at a higher level for longer. Boy it's complicated but I LOVE IT! They say the two best times of boat ownership are buying and selling but I have to say, upgrading is hard to beat and the financial loss is about the same!
 
Also depends upon what battery type you have.
Fit AGM batteries and these will recharge much quicker having a much lower resistance than Lead acid and hence make use of a higher powered alternator.
 
Given the size of battery bank and your future intentions I would suggest a Balmar 110 amp alternator (series 7 with no internal regulator.) I say this because they are designed to give a higher output at lower revs than a standard alternator. I've no experience of the Sterling Regulator. Personally I like the Balmar Maxcharge Regulator.
You could keep your existing regulator for the engine battery although frankly it's bit of a waste.
You haven't said what hp your engine is?

I have no connection with any of the manufacturers named and it's easy to spend other peoples money!
 
At the moment, with 324Ah of domestic batteries, you won't get full use of a 150A alternator, and a 100A alternator would be more than enough. However, if you're decided on having a second alternator anyway, and if you're thinking of further electrical loads in the future, my suggestion would be to go for just the Beta's standard 65A alternator charging the start battery only, and then have a 150A second alternator charging the domestic batteries only. This way, you don't need any diode splitter (so no losses and one less thing to fail). You also have built-in redundancy in the event of one alternator failing. And your alternator will be fine for future increases in battery capacity. Your Sterling regulator should control the 150A alternator only.

To minimise charging time, you really need a bigger battery bank. It would be worth adding 200-300Ah. If you go for a windlass or thruster at some time, you'll be able to run them straight off the domestic bank.

I've been running this sort of set-up for many years on a Volvo 2003T. The standard 50A alternator just charges the start battery, and a 90A Leece-Neville with Adverc control charges 660Ah of domestic batteries. Works well.
 
Electric windlass and bow thruster take big amps, but for only very short durations, so are not big ah users (60a for 10 minutes is only 10ah down the swanny).

Fridges and TVs are another matter; 4a for 12 hours is 48 ah gone. So it's only your domestic battery that needs a lot of tlc to keep its life long and sweet. It's most unlikely that 324ah batteries plus 10a of load will take more than 60a from any alternator, except perhaps for the first few minutes of charging. And, as we've seen, minutes of current don't count in the scheme of things . . .
 
Jim is right. It's a popular misconception that heavy loads require big batteries - it's prolongued heavy loads that need this kind of kit. Windlass anchoring and bow thrusters used even a couple of times a day hardly merit heavy gear.

You haven't talked of your anticipated time alongside, with mains connection. This is how most of us handle battery loads- a good mains phased charger keeps a bank such as yours in good shape - I'd be surprised if you had to run your engine to charge under these circumstances. Of course, loads of time on the hook in foreign or poorly equipped waters is another thing.

Final thought, two alternators represent quite a drag on the engine, and continuous - absorbing about 10% of output in rough terms. You may well never really need it, but you'll pay for it.

If you have space for,say, a 100 amp alternator and fit a smart regulator, plus mains charger, you'll have a better combination.

PWG
 
Also consider the current vs rpm curve of the alternator, together with the rpm range. Do you want fast charging at tickover, with the fridge and heating running? Depends how you use the boat.
What pulley ratio can you get? Usually difficult to achieve optimum alternator rpm. Also the quoted output current will be into 14V, so you will get a bit less if the alternator voltage is up at 15.5V due to smartcharging at 14.6 with 0.9V of drop through a charge splitter. It may be easier to retrfofit a controller than a larger alternator when you later decide you need both!
Hope that helps.
Chris
 
The engine size will be 43hp which is more than enough to compensate for the larger demands of two alternators. I think I should cruise at about 6knots using only say 1400 to 1600 revs. Your right regarding battery bank size and have made me think about demands of fridge and erm...hrmph...CD player which can be on for quite some time in the evenings at anchor (ok, most of afternoon and evenings). I will increase the bank size. In actual fact, I fried my current batteries at the end of this season so I do need to replace them! Long story and reluctantly quite funny. Perhaps I will replace with large bank of AGM's (gulp!) the 150amp second alternator connected to my sterling regulator. this should give me super fast charging off the engine. But which AGM's?? They are very expensive. Any thoughts? Any opinions on the Squadran AGM'S ?
 
The problem with a large alternator

is that you have to replace the wiring from alternator to board or it overheats.

I found that out the hard way when I replaced a 35 amp Hitachi with a 90 amp Lucas Marine.

More important than sheer output is the power delivery curve - you need a fairly good low-speed output.

I'd tend to stick with one alternator and a smart charger - but then I always carry a spare alternator.
 
Re: The problem with a large alternator

I use a 100a alternator with, sterling regulator and currently, a smallish batt bank (250a/h waiting till I finish work to fit the 'propper' bank). I rarly see more than 50a into the batteries when bulk charging but the big difference the regulator makes is that once into the second step form 80% to full the current stays at 20-40a, without the regulator it goes down to under 10a so the batteries are charged much more effectively right up to the top. Also look at Trojan or Rolls/Surette batteries - twice the life for half the cost and much more robust. Do you really need AGM's? If you do fit flooded cels though you do need a smart regulator because the standard type won't charge them (not enough voltage). The other piont is that the more current you put in during the bulk phase the quicker the voltage rises so if you could charge at 100a plus you might find that it just meant the current would drop of at 70% instead of 80% and you spend longer finishing off the charge. General recomendation is that max charge current is no more than C5, so 20a for each 100a/h of batt bank but then add about 30% because the alternator will be running slower it needs for max output - a 100a alternator rarly in practice gives more than 75-80a. The final piont is check the output curve, often high output alternators only achieve that fig at very high revs you might find that a realistic speeds (under 4000rpm) the 100a & 150a units give the same output and you only get the extra 50 a by going up to around 6/8000rpm which you are unlikely to get on a marine instalation.
 
another thing to think about is the bigger the alternator the more engine power it uses, e.g. a 55 amp alternator uses 3 hp of your engines power. so if you fit a huge alternator you will be sadly lacking in power for manovers or if tide and weather conditions are against you
 
Although you can add a switch across the alternator temperature circuit to put the alternator into 'small boat mode' as Balmar describes it.
Basically if you need the extra power for the prop you can reduce the alternator load. Fit the switch next to your engine panel.
 
Engineer tells me the new larger 100 or 150 will reach it's maximum output with engine revs circe 1400rpm so alternator should in most cases give out good power. I think I will go for the second alternator at 150amp and connect it to my sterling regulator. Reasons - I have enough excess power with the size of engine I am buying not to lose too much propulsion - I think now I am right in saying that even with a 150amp alternator the regulator will only allow the appropriate amount of charge into the batteries and charge them faster - if the regulator goes kaput I still have the normal alternator which is a good size for standard charging. Sounds ok to me.....I er....think.!
 
[ QUOTE ]
- if the regulator goes kaput I still have the normal alternator which is a good size for standard charging. Sounds ok to me.....I er....think.!

[/ QUOTE ]Yes, it's OK - in fact it's even better than you think. The Sterling regulator works in parallel with the alternator's own internal regulator, so if the Sterling regulator were to fail, your 150A alternator would still work (although charging at a slightly lower voltage).
 
One final note:

Your new (service) batteries will hopefully never be depleted again lower than 50% or you'll be frying (again) tonight! So 2 x 130 amp batteries require at most 130 amh to top up.
You probabaly realise that if you had a 130 amp alternator you wouldn't be able to run the engine just one hour and call "job done" It takes time, even with an output controller. It's probable that an alternator of little more than 60-70 amph would achieve top up no slower than the theoretical 130 amph alternator, or even a monster 250 amph output! It's all conditioned by what the batteries can take, which depends on their condition which usually means age, and profile of use (light drawdowns or deep rundowns)

I am concerned that a heavy load from 1-2 large permanent alternators will not only add real drag to your engine output - and all the time - but not actually deliver the snappy battery recovery you may be expecting from such an outlay.

You would be better off going for one capable but not oversized alternator and a shore mains battery charger.

PWG
 
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