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Old 06-18-2012, 11:18 PM   #1
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Teach me about alternators

Okee-Dokey Y'all,

As the ending of the winter DC upgrade project is upon me, the final step was to route the alternator output to the house battery back (and TBH, I might need to tweak where it's routed to now... more on that in another thread). For the past three years, I had seen a manual in my paperwork for Skinny Dippin' for a Balmar 110A alternator and assumed that was what was installed. Had I ever looked close enough to verify? Apparently not because when I we to tie onto the alternator this weekend, I have found a Motorola Marine 80A alternator (sticker says output is 77A) perched proudly upon Dr. Perky (my engine) and NOT the Balmar. *heavy sigh*

So while I cannot afford to put $700 into a new 110A externally regulated and new Balmar, I do want to learn what I can about alternators. So, as always, I turn to you guys for initial advice.

Questions:
  1. How good or bad is the Motorola? It's a 2-wire and I must assume it's internally regulated.
  2. Can I add an external regulator to it?
  3. I fired it up after my plugs-out battery test and it was pushing a good 30-40A, but it was getting warm. Hot? I didn't let it run that long (15 minutes). Is this a warning sign?
  4. Whoever installed it ran the hot wire to the lug on the starter motor and then installed an 80A fuse on the ground. For what I know about electricity this raises a red flag. Am I missing something?
  5. What should I look for in a new alternator? I really don't want to drop $700+ on a Series 7 Balmar, but will one of the "lighter duty" alternators do the job for me? The amperage numbers are similar.
  6. What is a good size? TBH, I think 80 is about right, but I'm a bit scared it's going to boil my batteries over a long day under power.
It's funny how that on the very last day of this big (for me) project is THE DAY that I find something to undercut all of the incredible confidence I had with it's completion. Now I am paranoid all over again. The upside, I suppose, is that a dead alternator on a diesel won't leave me stranded. At least I don't think it will. The engine needs no electricity to operate... Just fuel and air.


Thanks everyone.
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Old 06-18-2012, 11:29 PM   #2
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I'm not familiar with motorola alts.This may help with some questions.
12 Volt Electrical Systems - BoatTECH Guides | BoatUS

If your engine has a fully mechanical injection pump then it will run until fuel flow stops assuming everything else is in good condition.
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Old 06-19-2012, 07:12 AM   #3
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Nothing wrong with the motorola for charging the starter battery and it will get hot when it is working hard...not red hot but too hot to touch.

A little small for a big house bank....it would need supplimental charging from some place.

The problem with high amp alternators is "CAN your engine support one" as recommended by the engine manufacturer due to the increased pressure on bearings.

You can get higher output alternators for less than $700

here's a few National Quick Start Sales, High output alternator, Alternator & Starter Parts - Dual Rectifier Special Application External Regulated, Alternators.for Diesel Marine and other apps

As long as you're diesel..I wouldn't worry about the "marine" hype...the conditions under the hood of a truck with moisture and road salt is way harsher than my engine room.
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Old 06-19-2012, 08:18 AM   #4
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You would have to define a big house bank. I have four GC2 6V batteries with 440AH. My plugs-out test had me using about 150-ish amps per day, but I still have some tests to do regarding daily usage. That said, an 80A alternator charging at half capacity would only take four hours to replenish that use. I say "only" to define our average daily trip from port to port to anchorage would normally be longer than that. In addition, we have a 55A Iota for charging at the dock.

I am trying to hold off a rebuild of the genset for now. I am trying to get a good balanced system that doesn't rely on it and I think having a reliable alternator is a big part of that. I just don't want to buy new if I don't need to or buy too big (or too small).

So are you saying that I could goto a truck supply store and get a good one for my situation?

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Old 06-19-2012, 08:44 AM   #5
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Quote:
Originally Posted by GonzoF1 View Post
You would have to define a big house bank. I have four GC2 6V batteries with 440AH. My plugs-out test had me using about 150-ish amps per day, but I still have some tests to do regarding daily usage. That said, an 80A alternator charging at half capacity would only take four hours to replenish that use. I say "only" to define our average daily trip from port to port to anchorage would normally be longer than that. In addition, we have a 55A Iota for charging at the dock.

I am trying to hold off a rebuild of the genset for now. I am trying to get a good balanced system that doesn't rely on it and I think having a reliable alternator is a big part of that. I just don't want to buy new if I don't need to or buy too big (or too small).

So are you saying that I could goto a truck supply store and get a good one for my situation?

Tom-
I forget the "recommended" rate of charge for a bank (was posted not too long ago)...but the typical alternator is only putting out about 1/2 or less at typical trawler eng rpm cruise speed...so lets say 40 amps...take out 150 amp hours and that's 4 hr of running minimum and also (with the typical regulator) you drop off to a trickle of ampsas the voltage "approaches) full charge so add a few more hours of running.

So you might get by..a lot of us do without gigantic alternators..

But yes...the truck store might be able to set you up...finding the right pulley might be a bigger challenge.
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Old 06-19-2012, 08:47 AM   #6
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Tom: A suggestion would be to read Nigel Calder's 3rd edition. He has a good write up on alternators and voltage regulators.

That being said, keep the system simple. I would use your current alternator and have it wired for an external regulator. Very simple and at the same time have the brushes and bearings changed (cheap). Get a good 3 stage external voltage regulator. Put the system together and see how it works. You won't be into it for lots of dollars and if the alternator is to small then keep it as a spare and get a larger one. Your external voltage regulator will work on both. If you do go with a larger alternator to say 100-120 amps plus (these values are arguable), then you will need to change your belt/single pulley set up to something larger so keep that in mind.

You asked originally about the alternator getting hot, they do. Alternator output is rated at 122įF (that temperature is measured in the air around the alternator not the alternator itself). As the temperature goes up, your output falls off. A good external voltage regulator will have an temperature sensor to reduce the output of your alternator so it won't be damaged. The actual alternator temperature can easily get up over 150 degrees.
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Old 06-19-2012, 11:45 AM   #7
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Tom
Your Motorola 72a is a reasonable size for your 440ah bank since flooded-cell batteries accept a charge rate from 10% to 20% of their capacity. Since your bank is 440ah it will accept a charge rate between 44a and 88a. Any higher charge rate requires a voltage high enough to boil off electolite and will probably shorten battery life.
Your existing setup will charge your bank but an external smart regulator would do it faster by running your alternator hard enough to keep the batteries at an optimum acceptance rate, as detemined by battery voltage and temperature but will protect the alternator by monitoring its temperature.
I would guess your internaly-regulated alternator would take around 6 hours to restore 150ah and the smart regulator setup would take around three hours, assuming no other house loads like refer and nav electronics.
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Old 06-19-2012, 12:52 PM   #8
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Can a three stage external regulator be used with a one wire Delco alt?I have always sized the alt to the bank and ran it through an isolator.I will run a combiner on my next boat.
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Old 06-19-2012, 02:16 PM   #9
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Good stuff guys. Thanks! I brought Calder's book back from the boat to read, but like everything, I do like to also run it past y'all as a backup plan.

I also have always had soft plans to pull the Motorola and run it by a rebuild shop for a once-over. At that point is when I think I will see about wiring it for an external regulator. However, it is good to know that at least for the short term, assuming the Motorola is in reasonable shape, I am good. I will monitor it for a little while and make sure it's not overheatiing.

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Old 06-19-2012, 03:46 PM   #10
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Tom: your Motorola is probably putting out more like 30-35A under normal cruising conditions. That is just barely ok to charge your House bank. Hopefully part of your DC upgrade includes installation of a battery monitor (eg Victron BVS or similar) that will show you exactly what your alternator is putting out. Don't worry about 'the alternator boiling the batteries': the alternator will only put out what the battery bank demands. Alterntors don't boil batteries, faulty regulators do so moving to a quality external reg with BOTH battery and alternator temperature sensors is a very good idea and these days should be regarded as standard practice. AV8r is right in saying that up to 88A output is fine. To achieve that at standard cruising rpm think more like a 110-130A alternator (note your manual refers to a 110A as standard so that's a clue right there). Balmar alts, while good, are VERY expensive. Take a look at Leece-Neville: you could buy 3 of those for one Balmar and they are highly regarded by truckies, readily available, etc..
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Old 06-19-2012, 04:00 PM   #11
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There is no question that bigger is better when talking alternators and DC charging systems. The heat issue ends up being the biggest enemy of the solid state parts as well as bearings etc on the alternator.

Using a large frame unit, then de-rating it via a smart regulator will ensure a long life for your system. Always use temp sensors on both the alternator and battery bank.

My boat came with a stock 60A small frame and when I asked it to try and charge a house bank around 500Amps, it simply could not do the job.

I then upgraded to a small frame on steroids 120A unit coupled with a smart regulator, which did an adequate job, but got REALLY hot.

Since my motor has a serpentine belt, it was a fairly simple matter to fit a large frame 200A unit, which charges my now very large 1350AH bank quite nicely. I have de-rated the alternator to 160A so it never runs at the max design in any circumstance.


If you have room and pulley/belt ability, just get a truck alternator - Ebay has lots of choices Leece/Nev 160-200A units are around $200.


It is always easier on the entire system to use less charging than you have available.
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Old 06-19-2012, 04:18 PM   #12
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I completely agree with bshanafelt !
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Old 06-19-2012, 09:12 PM   #13
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Tom,

Another option is to have your local rebuilder build an alternator to suit. My guy gave me several frame sizes to see which one would fit best. He then built me a 140 amp machine.

I have the regulator set somewhere around 80 amps. We are on our sixth season with no problems. cost of the alternator was less than $100.

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Old 06-19-2012, 11:22 PM   #14
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Short answer, no. The prestolite has an internal regulator that simply tries to maintain a specific voltage such as 13.8, 14.1, or 14.6. A shop may be able to remove the regulator and provide a terminal to connect the external regulator but you would want to dicuss it with them.
A single-wire alternator is a good cheap piece of equipment to have as an emergency replacement, though, if it will bolt right up.
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Old 06-20-2012, 12:34 AM   #15
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Quote:
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Ben2go
Short answer, no. The prestolite has an internal regulator that simply tries to maintain a specific voltage such as 13.8, 14.1, or 14.6. A shop may be able to remove the regulator and provide a terminal to connect the external regulator but you would want to dicuss it with them.
A single-wire alternator is a good cheap piece of equipment to have as an emergency replacement, though, if it will bolt right up.

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Old 06-20-2012, 06:59 AM   #16
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More good stuff guys, thanks. I'll look into a few of these ideas. I am surprised how expensive the regulators are. At least the Balmar multi-stage. Any others out there I am missing?

I'm not sure what frame size we have now, nor if I have the room for a dual or notched belt system. The crank pulley is already pretty close to where the generator sits. Although, a serpentine belt that ran the water pump, alternator, and the thruster would probably work. Moreover, I don't know that I have ever laid eyes on a "large frame" alternator, so I don't know how large is large. I would hazard a guess that the price is large too.

The end game here, at least in the short term, is not to be totally off-the-grid. Like I said, my genset is down and I just need a way to keep the batteries topped off enough to not be forced to spend every night in a marina. I mean, we are still mainly weekenders. So if we can have an alternative way to keep the house bank charged, even if not TOTALLY topped off, we are doing much better than before. At the very least, not start a night at anchor in the hole from the trip. That's always bothered me.

I'm going to check around some more, read some more, and see what my options are. Hey, once my genset is fixed... who knows.

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Old 06-20-2012, 07:41 AM   #17
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Tom: I checked with Leece Neville and they make a SMALL FRAME 140A alt that would be perfect. (BTW, large frame alts are not actually much more $$ for the alt....BUT there is additional cost in having a custom mounting frame made up & installed.) Don't underestimate the real $$ savings in reducing your dependence on the genset...plus the noise-reduction benefit you have already commented on. Balmar regs are a bit more because they are so flexible across different battery technologies and charging profiles. They also take battery and alternator temp sensors, which as noted above should be regarded as essential requirements these days. You could get a price on the AMPLE equivalent: not sure if they are any/much cheaper.
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Old 06-20-2012, 12:31 PM   #18
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If you decide to upgrade the capacity of your Alternator, it will mean a number of 'other' costs as well.

First you must determine if your pulley/belt arrangement will be adequate. The normal rule of thumb is a single belt will safely give 100A or less. Dual belts or serpentine for greater than 100A. Determine if the side loading of the main bearing or waterpump you take off will be a problem.

As mentioned, if you change frame size, there can be mounting brackets etc to install/design.

Next, if you trade out a stock 60-70A internally regulated unit for a high-amp one, the cables will need to carry the extra juice - this normally means wire that is big enough - be sure to check a table or two for sizing properly - Don't forget fusing.

Of course, the Regulator will need to be a multi-stage unit. Balmar, Ample etc make some good equipment which will survive the marine environment well. The nice thing about these regulators is they are fully programable for the different stages of charging, battery types etc.

Then will come the 'how do I keep my start battery charged?" issue. These days an echo charge unit is hands down the best solution to the problem - Balmar, xantrex etc make good ones. This gets rid of the battery isolator - which never works well and makes more unwanted heat.

By this time you have spent some $$ and time designing a good DC system, so you will have already determined your usage needs and sized the house bank appropriately, and may decide it is time to make the bank bigger - thus necessitating buying an entire new house bank of AGM batteries to accept all these amps you now can produce.

You must also have a way of monitoring the beast - a link or other 'smart' monitor is pretty important to the health of your system.

It is a slippery slope when you really look at what is necessary to 'oversize' things.

The good news is you may just not need a generator after you get your DC system in shape.

below is a schematic showing the arrangement on my boat.

I have the ability to stay anchored in one location for up to 6 days and still be above 50% of Bank capacity. We usually stay 3 days max in any one place, but the option is there.

Good luck
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Old 06-20-2012, 12:55 PM   #19
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Will that L/N 140A work with a single-groove V-belt? Link?

The genset thing has nothing to do with OVERALL savings (even though that will be nice), just short-term savings. It's broken now and don't want to pay the $1000 to fix it until the Fall.

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Old 06-20-2012, 02:19 PM   #20
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On my Cummins 6bta's, I have that L/N 140A unit on a single wide belt on one engine. I did need a new pulley....no big deal. The genset comment certainly does have to do with overall savings: I wasn't thinking at all about your immediate repair bill but about the fact that you will need to run it a LOT less. bshanafelt is right (again) in saying you may not need your genset AT ALL...so even needing a $1,000 repair, you may be able to sell it and fund the upgrade works: IF your estimate that you only use ~150ah/24 hours is right and that when you cruise, you typically do a 4-hour run from dock to anchorage and a couple of hours moving between anchorages, and you are back at the dock with shorepower charger operating between cruises, with the setup described so well by bshanafelt's diagram you won't need a genset at all. We're assuming here you have a decent inverter already. Only reason to have a genset would then be to run air-conditioning and/or an electric water heater if engine coolant heat exchange isn't doing the hot water heating for you. bshanafelt's diagram is just about a perfect setup for a single-engine install in my view: I'd maybe quibble about the battery technology (if access is ok & you don't mind topping up with water occassionally, I'd prefer cheap wet batteries to AGM for the House bank and an Optima spiral-wound AGM for the Start/Davit battery)....but those are very minor points.
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