Beta Marine 25 High Output Alternator Options

[Bestline]

I have a new Beta Marine 25 hp diesel with a 70 amp externally regulated small case alternator, this is unlikely to be sufficient for my needs but given the small engine bay and lack of space for a large case alternator what are the options? Beta Marine isn't very forthcoming on pulley upgrade info from what I've seen on their site but a 140 or 210 amp small case alternator will undoubtedly require a wider belt that the stock one on there now. Anyone have this issue with their small Beta? As far as alternator cooling can I just run the engine with the cover off and an electric fan blowing on the alternator when giving the house bank a high dose of amps? The whole boat has been refit before having done much cruising so I'm not sure what my actual daily usage will be yet.

[Adelie]

At about 100A you would need a serpentine belt and pulleys. Figure $500-1,000.

The regulator and alternator are
Going to be upwards of $1,000 if I recall.

You ventilation arrangements sound adequate.

Why do you need such a high amperage alternator? The only 2 obvious reasons are that you have LFP batteries for your house bank or you have a really large bank of AGM batteries for your house bank.

If it’s AGMs the extra large alternator will shave perhaps 30min or so off a 6-7hr charging cycle starting at 50% discharge. The bank will very quickly reach max voltage and the charger will taper current.

If you have flooded lead acid (FLA) they are current as well as voltage limited and you might save minutes.

With Gels high amps, even starting from a deep discharge condition may damage the battery.

[Bestline]

I might not need the output yet but unsure what the future will hold. From what I understand modifying an existing alternator involves doubling or tripling its initial output so, most likely if I had a 210amp alt it would be set to charge at lower rates. I've got three Firefly carbon foam batteries group 31s IIRC which are rated at 112 ah I think. Ideally, I'd like to have a freezer aboard and be able to run power hungry laptops but we'll see. Kind of inclined to have backbone systems like power generation leaning into overkill territory as its easy to use less.

This is probably inexperience talking, though.

[GILow]

Originally Posted by Bestline

I have a new Beta Marine 25 hp diesel with a 70 amp externally regulated small case alternator, this is unlikely to be sufficient for my needs but given the small engine bay and lack of space for a large case alternator what are the options? Beta Marine isn't very forthcoming on pulley upgrade info from what I've seen on their site but a 140 or 210 amp small case alternator will undoubtedly require a wider belt that the stock one on there now. Anyone have this issue with their small Beta? As far as alternator cooling can I just run the engine with the cover off and an electric fan blowing on the alternator when giving the house bank a high dose of amps? The whole boat has been refit before having done much cruising so I'm not sure what my actual daily usage will be yet.

As others have asked, does your house bank actually support faster charging? Best make sure of that before wasting a lot of money on high output alternators.

Secondly, we don't know where you are or what sort of boat you have. This info would help, for instance, solar may be a better option for you.

Finally, I've lost track of the information, but somewhere on this forum i read a good analysis of what sort of alternator output was practical from various engines. At the size of your engine you may find the engine limits what you can extract without serious complexity.

[Adelie]

I would suggest updating your profile with your general location and your boat make & model or “Looking” in the "Boat" category. This info shows up under your UserName in every post in the web view. Many questions are boat and/or location dependent and having these tidbits under your UserName saves answering those questions repeatedly. If you need help setting up your profile then click on this link: https://www.cruisersforum.com/forums...ml#post3308797

I would happily help more if the link above is not enough.

[Adelie]

So 3 Fireflies is about a 350Ahr bank.
As Fireflies let’s assume you are using up to 75% of capacity, 261Ahr.
So you need to put 261Ahr back in the battery to get it to 100%.
If you had a 261A alternator with a smart regulator it would put out 261A for 30min or less. The battery would be at about 60-70% and it would have reached maximum allowable voltage, about 14.2-14.4v.

At this point the regulator will hold the voltage steady and Amps will taper to almost nothing over the next 5-6hr.

If you have a 120A alternator it will run full power for 1hr or less, hit max voltage then Amps will taper to almost nothing over the next 5-6hr.

If you keep the stock 70A alternator it will run full tilt for 90min or so then Amps will taper to almost nothing over the next 5-6hr.

I don’t believe that you will find a small frame alternator that pull puts out 261A and doesn’t fry itself for the first six months. Probably the best you’ll find is a 120 to 150 amp alternator. That means starting at 25% you will save approximately 30-45 minutes per charging cycle using the high output alternator. Starting at 50%
You will probably save 15-30min.

AGMs (including Fireflies) need to be bulk charged at a minimum of 0.2C. 0.3-0.4 is better.
You 348Ahr bank has a C of 348A. So 0.2C is 70A. Looks like you stock alternator is meeting minimum requirements.

If you really want a bigger alternator get a 90A which won’t cost an arm and a leg and keep the stock as a spare. Use the same pulleys and save the cost of the serpentine system.

Take the money saved and buy more solar panels and a stern arch or Bimini frame to mount them on. Solar is the best source for the long tapering charge of lead batteries, running the engine for 6-7hr every day will be a noisy aggravation and expensive in fuel.

Using a combination of stock alternator and moderate solar you can keep you batteries fully charged for the least cost and aggregation. When the batteries are lowest first thing in the morning run the engine to bulk charge the batteries. When max voltage is reached and current tapers off let the solar quietly finish. Late in the afternoon when batteries are almost full and the is excess solar power turn down the temps in the fridge & freezer to over-cool them. A but before sundown return the temps to normal and they will coast without using power for 2-5hr.

The thing about lead batteries is that you can’t get around the 5-6hr tapering charge, you could up the voltage but that would damage the batteries and shave years off their live.

And there is the question of whether Fireflies will continue to be available? They are a very expensive form of lead battery and LiFePo batteries are approaching the point where they cost the same but are 1/2-1/3 the weight. When this bank dies is it more likely to be replaced with more Fireflies or with LFP?

If you plan on eventually replacing the current bank with LFP then a bigger alternator would be more useful but solar panels would be able to provide more charging since LFP will accept full output almost until they are full.

Regarding daily usage.
Fridge and freezer will be about 50Ahr/d each. I don’t see having room for a separate freezer until the boat reaches about 40’ length.
Autopilot uses about 50Ahr/d. Better investment would be a windvane.
House loads would be about 50Ahr/d unless you have an electric galley which would use 75-125Ahr/d depending on you cooking habits.

Let’s assume you use about 150Ahr/d normally. That means charging starts at about 57% so bulk charging at full amps is going to last 15-30min using stock alternator then it will start to taper some. A high output alternator is going to bulk charge for 10-20min before amps starts to taper for the next 5-6hr.

[FPNC]

Call or e-mail Beta USA in North Carolina, USA. They will be happy to give you all the information regarding retro-fitting a 120 amp large frame alternator to your Beta 25. There are kits available.

[GILow]

Originally Posted by FPNC

Call or e-mail Beta USA in North Carolina, USA. They will be happy to give you all the information regarding retro-fitting a 120 amp large frame alternator to your Beta 25. There are kits available.

With all respect to Beta, they are hardly likely to check if the conversion is actually worth doing.

In this case, as well articulated by Adelie, it’s hardly worth the effort.

[ItDepends]

Originally Posted by Bestline

I might not need the output yet but unsure what the future will hold. From what I understand modifying an existing alternator involves doubling or tripling its initial output so, most likely if I had a 210amp alt it would be set to charge at lower rates. I've got three Firefly carbon foam batteries group 31s IIRC which are rated at 112 ah I think. Ideally, I'd like to have a freezer aboard and be able to run power hungry laptops but we'll see. Kind of inclined to have backbone systems like power generation leaning into overkill territory as its easy to use less.

This is probably inexperience talking, though.

If you have 3 Firefly g31 batteries, you have about a 350 A-hr battery bank. Firefly's recommendations is to charge these between 0.2 and 0.5C, so your charge rate should be not less than 70 Amps, but should not exceed 175A.

Also, be aware that alternators of the size you are suggesting use a LOT of horsepower. A 200 Amp alternator running full tilt will take on the order of 8 to 10 HP. Thats a LOT to pull off a 25HP engine. There are ways to manage this, but if you do not, you might find yourself starved for maneuvering power.

Also, you will want to be SURE that the front crankshaft bearings are rated to have this much power taken off the front pulley. Most engine makers will have a specification for this, although you might have to search for it, or ask.