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Old 02-22-2018, 10:22 AM   #1
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What amperage alternator

I have twin Perkins engines. Each engine has a 65 amp alternator. One for house batts, the other for start batt. Iím considering getting a much larger amperage alternator for the house batteries. Is there a down side to this? Pros vs cons.

Thanks,

Sam
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Old 02-22-2018, 11:01 AM   #2
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I have a 220 amp alternator with 3 stage external regulator for the house bank. Depending on the amp capacity and type of battery, there is a limit to the rate you can charge them at. Also, larger amperage alternators require either thicker, multiple or serpentine belts to handle the additional load. Power cable sizes will likely need to be increased to handle increased amps. Finally, there is the mounting bracket and the space it must fit in. It's very worth while, but often not as simple as buying a new alternator.

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Old 02-22-2018, 11:08 AM   #3
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Quote:
Originally Posted by Sam View Post
I have twin Perkins engines. Each engine has a 65 amp alternator. One for house batts, the other for start batt. Iím considering getting a much larger amperage alternator for the house batteries. Is there a down side to this? Pros vs cons.

Thanks,

Sam
Options galore.

Flywright did a modification (much bigger alternator and new belt drive setup) similar to what you desire. He has a Californian and Perkins engines.

Another consideration is increasing the size of your alternator(s) to somewhere around 110 amps such that the same motor sheave and a single belt can be used. Then add a combiner or switch such that both alternators can power the house bank.

Do you have a genset?
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Old 02-22-2018, 11:12 AM   #4
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How big is your house bank? What type of battery?
A normal single belt pulley setup is only good up to about 100 amps. Above that you need either a second belt or serpentine belt kit.
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Old 02-22-2018, 11:52 AM   #5
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To summarize the foregoing good advice and add some of my own:

1. Keep the alternator at or below 100A if driven by a single belt.
2. Don't use an alternator any bigger than 25% of your house bank AH capacity if flooded cells, maybe more with AGMs.
3. You need a three stage external regulator to get the most out of an alternator. These require the appropriate connections on the alternator to hook up.
4. Some standard HO alternators have these connections on some models like Leece Neville. Specialty HO alternators like Balmar, Hehr, etc have them.
5. You need to wire the regulator's voltage sense wire directly to the batteries.
6. A 100A HO alternator with external regulator feeding a 400AH battery bank will probably charge 3-5 times faster than what you have now.

One approach is to replace one of your engine's alternators with a HO and external regulator. Wire it directly to the house bank with big wire- #6 minimum. Use the other engine's alternator to charge both starting batteries. Lot's of other ways to do it though.

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Old 02-22-2018, 12:18 PM   #6
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All very fantastic advice. Thank you so very much.

The house batts consist of two 8D deep cycle batts. Start battery a larger standard ? start battery about the same size as the 8D's.
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Old 02-22-2018, 12:58 PM   #7
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I faced a similar dilemma although with a Cummins 6BT. David's recommendations are spot on. A couple thoughts, I used a Zena marine alternator in 250A. It's a Leece-Neville that has been beefed up, it has an external rectifier bridge to relocate some heat, mine has a 2" hose that divides ambient air from a 250cfm blower between the back of the alternator and the battery box. My bank is 1150AH in AGM, so it will take whatever the alternator can throw at it. It's regulated with a Balmar 612 with temp sensor for alternator and battery, and it pretty much takes care of itself. I'll see in the 180A range when charging the bank at 60% SOC. The alternator loads at 90% for an hour then is down in the 65% range. The Balmar does a terrific job and can be tweaked to the precise needs of your individual configuation. It also has a belt setting, so if you have an alternator >100A, you can limit it to keep the belt wear under control, and not worry with overheating a marginally-sized alternator.

Don't overlook your running load; you'll have a standing 12V load under way that must be met before anything is going to go to the bank. Most importantly, don't be short-sighted and focus on a part of the system. It is, after all, a system, and as such you need to consider every part as it relates to the other in order to accomplish the objective.
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Old 02-22-2018, 01:01 PM   #8
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Two 8D have roughly 440 amp hours. FWIW most 8Ds are not really deep cycle and replacing them with four GC batteries wired in series/parallel will give you much better battery life and two GC batteries will fit in an 8D's battery box.

Did you say that you have one starting battery that serves both engines? That makes it easy to wire up a HO alternator as described in my previous post.

But in any case, that means that you can use a 100A HO alternator to charge your 440 AH house bank.

David
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Old 02-22-2018, 01:06 PM   #9
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If I can add my 2 cents look also how you use your boat. I mean do you often go from the dock for 2h at the anchor and back to the dock? Do you often 1 day at the anchor, than run 1h and stay again at the anchor? In summary do you need to charge your battery the fastest as possible or not really?

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Old 02-22-2018, 02:21 PM   #10
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Without converting to or adding an LFP bank, increasing alt output will have a very limited impact on total time required to get to 100% full.

Even with high-CAR AGM, the high amps acceptance stage is under 20% of the total time required from 50% to Full.

But those high amps can be useful driving other loads while motoring, like aircon, HO watermaking or eutectic refrigeration.
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Old 02-23-2018, 06:02 AM   #11
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"If I can add my 2 cents look also how you use your boat. I mean do you often go from the dock for 2h at the anchor and back to the dock? Do you often 1 day at the anchor, than run 1h and stay again at the anchor? In summary do you need to charge your battery the fastest as possible or not really?"

This IS Question #1.

Although regardless of the answer a better faster charge can usually be done with a smarter Voltage Regulator .
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Old 02-23-2018, 06:24 AM   #12
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Considering what you have as a battery system, even if you change to 4 GC batteries, I wouldnít waste your money yet. Think and research upgrading your rig (should you have the need for it) and then decide what your charging options are that you need to explore. Look, we arenít sailboats that spend all day under sail with minimal charge going into the banks. We are motorboats that, when we travel, provide a pretty hefty charge 100% of the time. Sure, arguments for needing quick charging when at anchor for many days at a time, but again, your current rig is not capable for this style of boating yet. For weekends at anchor, day to day hopping around, or even a long trip of coastal cruising, you will be fine.

Take a long look at what kind of boating you will be doing and go from there. Simply jacking up your alternators wonít gain you much. Like putting mud tires on a pickup truck and then just driving it back and forth to work. Certainly, that the money and time could be better spent on another project. Sometimes bigger isnít always better.
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Old 02-23-2018, 09:02 AM   #13
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Thank you gentlemen for the advice. It has been well received. I now understand that while possible to charge quicker, changing the charging system now would not be pragmatic. Sailboat and the mud tire analogies were perfect.

Have a great weekend and thanks again.

Sam Nigro
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Old 02-23-2018, 11:38 AM   #14
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One alternative that wasn't brought up: let your current alternators work together by putting in an external regulator that allows both of them to charge the house batteries.
A solenoid is used to parallel the house and starter bank during the charging cycle. Twice the charging capability without messing with the engines, and both engines/alternators are seeing the same loads on the alternators and the belts.
I did this with the dual alternator controller from ample power. Could also be done with the centerfielder from balmar.
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Old 02-23-2018, 11:44 AM   #15
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OEM alternators rarely have the connections to the field coil to use with an external regulator like the Ample Power or Balmar.

Some say to get a local alternator shop to install the connections to your existing alternator(s). I think that is a bad idea because you are asking these alternators to put out 3-5 times more current over a long period. They don't have the diodes, windings or cooling capacity to do this for long.

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Old 02-23-2018, 11:50 AM   #16
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But with a sophisticated VR like Balmar's MC-614, there is temperature protection built-in, including a dedicated sensor,

Plus you can de-rate current output to whatever you like in pretty fine increments.

Yes they're not cheap, but will be put to use on future larger alts, and will even be suitable for LFP down the road.

Not sure about the lesser Balmars or the center fielder, not as adjustable.

Switching over from the stock internal VR is NBD.
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Old 02-23-2018, 11:53 AM   #17
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I was able to make the conversion on mine without a problem - and they're doing great.
I don't understand the "3-5 times more current" - are you saying that his 65-amp alternators are actually only putting out 20 amps, or are you saying that his 65-amp alternators currently put out 65 but if they were externally regulated they would put out 200? Neither of these cases are realistic. By running the alternators in parallel, they would not be run for a longer period of time, but a shorter period of time (2x the current available means half the battery charging time).
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Old 02-23-2018, 02:07 PM   #18
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a shorter period of time (2x the current available means half the battery charging time).
Very common misconception, but completely false.

Say a bank takes 6 hours of charging at 50A available to get from 50% to true Full (via endAmps).

Only the first 60-90 minutes of that will even a high-CAR bank charge any faster, after the 85% point acceptance for any lead chemistry drops radically.

Going to 100A might only save 30-60 minutes, maximum.

The big advantage of a better VR is keeping voltage at Absorb longer, derating Current only when the alt gets hot.

Stock VRs are usually shockingly poor at getting a quality bank what it needs.
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Old 02-23-2018, 02:35 PM   #19
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after the 85% point acceptance for any lead chemistry drops radically. .
"Radically?" Really.

Drop it does, but not that much. But there are some old wives tales out there too regarding how slow LAs are getting to 100%. For many years I've had no problem getting my LAs to 100% quite quickly. Around 94 % they do start to slow down, but after 4 hours or so of cruising with genset off they are nicely at 100%.

Using internet charts and non LA sales jargon isn't always accurate for the real world we cruise in. Thus, the reluctance for so many of us to switch to the much more expensive stuff largely driven by hobby desires or getting the best. In other words, how good is good enough..
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Old 02-23-2018, 02:39 PM   #20
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I did not mean to spark another lecture on the charging to 100% thing; I have a boat and a battery meter, so am aware of this. I wrote my post too hastily.
My question was mean to be related to the "3-5 times more current" comparing an internal to externally regulated alternator. Any thoughts on that?
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