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Old 09-11-2011, 00:12   #1
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High Output Alternators

Currently researching HO alternators for charging a house bank of AGM's rated at 450 amps. Theoretically, I need one that is rated at 30% to 40% of the bank's rated amps, say 160 amps. How much HP will it need from the engine?

Balmar's rule of thumb for sizing a HO alternator's drive horsepower is 1HP for every 25 rated amps. They don't mention volts but the higher voltage required for charging AGM's may come in at fewer amps per HP. Based on the above, my new alternator will require 160/25 HP, about 6.4 HP plus for the AGMs, say 7HP.

I can only find perhaps 4-5 horsepower from a direct coupling onto the PTO of my little used Volvo Penta MD2030 (29hp max). I'll have to find the rest from a really adequate solar energy system, including panels and wind/water generators.

My boat is a beamy timber 33 footer by John Alden. Waterline is less than 25ft so space and weight considerations are paramount. Speed through the water also limits the output of water generators. I'm already maxed out on battery weight and space for the solar panels etc. I have 3 x 75W and 2 x 65W solar panels and plan to buy an Airbreeze and a used wind/water generator which should be sufficient to drive the fridge/freezer a lot of the time. Cruising in the tropics (Australia) demands a small fridge-freezer as well as all the usual trappings of modern life – computers, radar, chart plotter etc. Every 24hrs under sail I expect to consume at least 225 Amps which is 50% of the rated capacity of my House bank (Starter bank is charged separately).

I can't believe I am the only one amongst the cruising crowd that is facing this sort of situation. It would be good to hear from some of the others how they manage large power requirements on a smallish cruising yacht like mine.

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Old 09-11-2011, 00:31   #2
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Re: High output alternators

I can't be definitive but in the tropics the wind generators don't do a lot. Roaring 40's definitely way to go.

Nigle Calder indicated you would rarely see the high capacity Balmers putting out 160 amps and only for a short time because of overheating and he recomends cutting them back a bit and adding cooling to be effective. Think the article was in a pommie sail mag.

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Old 09-11-2011, 08:47   #3
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Re: High Output Alternators

Cutterman:

Well you don't NEED 160 amps but your batteries can ACCEPT 160 amps. As downunder said, you will rarely see 160 amps from a 160 amp alternator and if you do, it won't be for long.

I suspect that the majority of the time you will be charging in the low hundred range, say about 120 which should stay within your PTO spec. You can also set Balmar's regulator to limit the current output.

Another solution is to drive the alternator from the belt system. But it will take a dual belt system to handle the power, which could be expensive to retrofit.

Also with the PTO drive you can fit a large case alternator which is preferrable to the small case which is probably all that will fit the belt system.

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Old 09-11-2011, 09:54   #4
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Re: High Output Alternators

450 amps x 13.7 volts is 6165 watts which is 8.2 horsepower. You may need a clutch PTO that does not use belts.

I think it's also overkill for charging batteries....unless it's a diesel-electric submarine.

You also have to consider that it is easier on a battery to be charged slower.

A better alternative would be small generator powering a large battery charger.

Or as others have said wind, solar or both, capable of more than keeping up with your average house load.
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Old 09-11-2011, 10:14   #5
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Re: High Output Alternators

Any alternator over 75 amps (maybe 100) needs a double belt. If you go into 150 amp alternators you need very good mounts etc. You dont have to have one that big for your battery bank, especially if you are going to supplement it with solar etc. I have driven 100 amp Balmar alternators with a 6hp kubota engine with no problem. The engine works hard for maybe 15 mins and then the heat etc end up with the alternator backing off in output anyway. At that point I was able to back the Kubota off to a low rpm sweet spot that was very quiet.
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Old 09-11-2011, 10:14   #6
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Re: High Output Alternators

A 450 AH battery bank on a 33 footer sounds like overkill, especially if you have 355 watts of solar and plan to add a wind generator.

I run my 46 footer, which has a separate freezer and fridge, on 260 watts of solar plus a wind generator with a house bank comprised of only two 4D batteries. Although I have a 100 amp alternator on the engine, I could get by with one half that size.

Bottom line, there's no way you should need a 160 amp alternator.
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Old 09-11-2011, 10:14   #7
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Re: High Output Alternators

I don't know where you came up with the consumption figures. A 450 amp-hr bank is more than sufficient for us on a 45 ft boat, and we consume less than 150 amp-hrs per day under way and less than half that at anchor. We have 220 watts of solar and a wind generator, and most pasages we don't need to use the engine to charge at all. The use of led lights and netbooks has cut our consumption down considerably in recent years.

Unless your fridge is really inefficient, I would guess that you would be quite happy with a belt-driven 100 amp alternator.
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Old 09-11-2011, 10:31   #8
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Re: High Output Alternators

I am a bit of a poweer miser but I found a 400 odd amp bank too small. I only draw the bank down 50% and my daily usage is well under 100 amps so I get 2 days or so out of a full bank. I've now got a bit over 600 amps in the house bank. Works a lot better. Most of the cruisers I know have at least a 600 amp house bank.
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Old 09-11-2011, 10:56   #9
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Re: High Output Alternators

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Originally Posted by Vasco View Post
I am a bit of a poweer miser but I found a 400 odd amp bank too small. I only draw the bank down 50% and my daily usage is well under 100 amps so I get 2 days or so out of a full bank. I've now got a bit over 600 amps in the house bank. Works a lot better. Most of the cruisers I know have at least a 600 amp house bank.
Do you have any solar or wind power to keep your bank up?? My guess is that with 375 watts of solar your net usage would be negative most days, and all you need from your battery bank is to keep things going during the night.
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Old 09-11-2011, 11:01   #10
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Re: High Output Alternators

Quote:
Originally Posted by Vasco View Post
I am a bit of a poweer miser but I found a 400 odd amp bank too small. I only draw the bank down 50% and my daily usage is well under 100 amps so I get 2 days or so out of a full bank. I've now got a bit over 600 amps in the house bank. Works a lot better. Most of the cruisers I know have at least a 600 amp house bank.
I think things are different on a boat with solar/wind generation. It would be extremely rare for my house bank ever to dip below 75%, even on a windless night. On most days I'm up to a full charge by noon, and the solar shuts itself down half the time between noon and sunset even on hot days when both refrigeration compressors are running.

Regardless, the OP is currently running five solar panels and is contemplating the addition of a wind generator. There's just no way he needs an alternator larger than 100 amps.
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Old 09-11-2011, 11:31   #11
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Re: High Output Alternators

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Originally Posted by donradcliffe View Post
Do you have any solar or wind power to keep your bank up?? My guess is that with 375 watts of solar your net usage would be negative most days, and all you need from your battery bank is to keep things going during the night.

I have a KISS wind generator and a Honda EU2000i. When I bought this boat (2004) solar panels were too expensive. They have come down now but I have yet to spend any time in a spot where I could get solar installed. I get down to the boat in FL, paint the bottom, throw it in the water and off I go. It is difficult to get any major work done when cruising and at the end of the season all I want to do is haul the boat and go home. I keep talking about getting solar panels though, maybe this season.
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Old 09-11-2011, 11:49   #12
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Re: High Output Alternators

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Originally Posted by Bash View Post

Regardless, the OP is currently running five solar panels and is contemplating the addition of a wind generator. There's just no way he needs an alternator larger than 100 amps.
The only things I can figure on consuming 225 ah's in 24 hours are;

1- He's running a gourmet kitchen/galley with a Sub Zero household refrigerator and then running it through an inverter.

2- His math is off
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Old 09-11-2011, 12:22   #13
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Re: High Output Alternators

He mentions 225Ah in 24hrs under sail. An autopilot at 6 amp average, some nav equipment and a refer/freezer will get one close to that.

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Old 10-11-2011, 01:45   #14
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Re: High Output Alternators

Wow, what a lot of replies! My thanks to all.

Just spent an hour taking up your points but the reply has disappeared into cyber space.

Will get back to you when I have more time.

Cheers,
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Old 14-12-2012, 00:48   #15
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Re: High Output Alternators

It is now more than a year after my first post and I have not had time to get back to you as promised so here is a quick note to say what I have done and make some comments on your answers.

Consumption estimate may be over-generous but seems better to err that way than the other. Production of solar panels can be very low in the tropics, especially if you are up a creek hiding from a cyclone for a few weeks. My capacity is designed to be marina proof. And bear in mind that fuel capacity on a boat as small as mine is often very limited. Anyway, marinas are few and far between in many of the most interesting parts of Australia and ditto for SE Asia.

People tend to use their own experience when comparing an alternative system, rather than look at the particular circumstances pertaining to the alternative.

The result of my research has been two high output 70amp alternators running off the PTO for charging the 450 Ahr house bank. One replaces the Volvo alternator and the other is driven by a larger pulley in front of the one on the crankshaft. Their pulley ratios are matched so that both alternators run at the same speed.

Balmar warned me about the vibration problem but seemed reassured when I sent them a photo of the mod. I also mimicked the volvo attachment arrangement which clamps alternator to the front end of the bracket. This requires very little torque to hold the alternator solidly after adjusting the belt.

There is a DC-DC charger that tops up the start bank whenever the house bank reaches 13.8v - whatever the source of energy. The start battery is one of two 55Amp Lifeline Start Batteries. They can be paralleled together and/or connected to the house bank in emergencies.

The Balmar controller can be used to reduce the output of the alternators by up to 50% when the engine is being used for propulsion. When being used just for charging, the engine should be producing 4 or 5 HP depending on the state of charge of the batteries and the amount being used by peripherals such as the fridge/freezer (up to 6 amps) and the 8gph water maker (27 amps)

There is also a delay and ramp up facility available when starting the engine so that the demand from cold output does not stall then engine at tick-over speeds.

My consumption figures allow for a wider range of conditions than I expect to experience most of the time. Looking at your responses in that light, I reckon I'll be less likely to be caught out than some when faced by the sort of conditions I've allowed for.

Thank you for your interest and advice.
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