Date: 11 February 2018. Upsizing the
Alternator - My Mistake.
article is longer than usual. You might wish to pour yourself a
beverage before beginning.
all, "everyone" says get a bigger alternator. I did so. Though my
reasoning was correct errors were made. As with most things, there
was not a single flaw that caused the problems I experienced.
Instead a litany of Good Ideas morphed into mistakes. I was
fortunate to catch this before a catastrophic failure incurred.
Here's what I did wrong.
says it is a Good Idea to get a bigger/better alternator. So I did.
The original alternator that came with my 18hp Kubota engine was 15
amps. I wanted a faster charging system. My friend Rich over on the
east coast sent me a 55 amp alternator. Thank you Rich.
This is the
55 amp ↓ alternator. I take pictures of the labels then transfer the
information into my Log Book.
Like most boaters, Rich had a
spare alternator "just in case" something went wrong with his
original. Usually what happens is we will have a failure. We buy the
new part for immediate installation.
Starters, pumps and
alternators are often rebuilt or repaired.
Later when we have time we repair/rebuild the original. That
rebuilt item becomes an addition to the Spare Parts inventory.
Those of us on limited budgets can amass a decent number of
backups over time.
This collection of spare parts can often be
attributed to a bunch of mechanical breakdowns.
event, I wanted the 55 amp alternator installed on my 18hp Kubota. I
did not realize a 55 amp alternator has TWO BOLTS to adjust the
tension. The original mounting used the top bolt only. This upgrade
was the beginning of my alternator problems.
bolt is supposed to be long and attached from front to back of the
alternator. Two anchoring points at the bottom secure the alternator
in place. Undue stress was placed on that single bottom bolt because
it only attached at the front.
The original alternator mounts with
a single bolt at the top of the unit on the curved slider
The 15 amp alternator was mounted to the engine with a single bolt.
The 55 amp was supposed to be
mounted with two bolts spanning three attachment points. The one at
the top pivots. That adjusts the belt tightness.
For a 15
amp alternator that's all you need. When I upgraded, the 55 amp
alternator requires a second longer bolt to hold the unit in place
on the engine.
bolt is at the bottom. You can see it just above the red oil filter
on the right. →
is 4 1/2" long. It should attach to two places on the engine block.
Instead it was bolted through one, and then through to the other
side of the alternator. The back side is where the problem incurred.
On a larger
engine there would be a place to attach a big alternator properly.
That was not true for my Kubota 18hp tractor motor.
initial install was
faulty my upgrade was doomed.
I did not
notice that the original was wrong. My alternator was not attached
front and rear at the bottom. Thus when I upgraded further to a 110
amp alternator the torque was simply too much.
You get what you inspect, not what
mistake was in not noticing the second bolt attachment on the
original install was wrong. I should have seen that.
the original mechanic should have said something too. Just because a
client wants something, we depend on wise counsel too.
The Person to blame is often found
in the mirror reflection down in my cabin.
Regarding the alternator fiasco, there is plenty of blame to go
around. Ultimately however, it is the boat owner who assumes
responsibility for any mistakes made. This alternator upsizing was a
Good Idea as I understood it. The unintended consequences bit me on
Almost all failures are not the
result of a single misstep. My problems were the culmination of
error piled upon error. Regarding the alternator upsizing saga, I
made several mistakes. So here is my cautionary tale of woe.
Fitting the alternator bracket was a problem. That
was solved by having a new bracket welded.
See the previous article
Alternator Bracket Pattern (how to)
For the record, the above photo was taken during the examination
process. I never ran the engine with the alternator mounted like
alternator has to mounted in alignment with the pulleys or belts on
your engine. On my Kubota, the fan belt makes the water pump work.
That keeps my engine cool. All these parts have to work in
coordination. When one part goes belly up, disaster and breakdowns
This is the front of the engine looking aft. The 55
amp alternator is mounted.
Mistake Number One: The
55 amp alternator took a lot of power from my small engine. She
would bog down (RPM's decreased) and I lost 1.5 mph in speed when
underway. That's when Edwin came up with a solution.
Edwin's solution was the addition of a switch. I
turned off the power generation while underway. At anchor I could
use the alternator. Of course running an engine at idle is not
The thing is this: I wanted to be able to run my air conditioner at
anchor without a generator. I do not have enough solar for an a/c
unit. It gets hot here in Florida so I spent a lot of time
considering options. The upsized alternator seemed like a Good Idea
at the time.
There was a catch though. Details follow...
Alternators are rated at their
Maximum output. Thus a 55 can briefly put out 55 amps. That
said, an alternator will "throttle back" when it gets hot.
Generally speaking, figure a 55 amp alternator will roughly
provide 25 amps from now until Sunday if your battery voltage is
Now this is a Rough Estimate. Of course with
external regulators (above my budget range) you can expect better
results, i.e. more amps in to your batteries. Nigel Calder knows all
this stuff far better than I. He is also better at explaining it. If
you have not yet bought
Calder's Boatowners Mechanical and Electrical Manual
4th Edition, please do so. His tome is truly
the Bible for boaters.
Every live-aboard boat owner I know has
Calder's. Indeed, I would not be without my copy.
← Affiliate link.
This was my Theory: Because the 55 amp alternator could not put
out consistently 55 amps, the theory was that a larger
alternator (the 110) could put out 55 consistently. So if I
upsize the alternator I could have air conditioning with just
the cost of diesel. My Kubota sips fuel.
I need about 50 amps to run
the air conditioner. Thus a 110 amp alternator could
theoretically keep up with the power requirements of my Haier 5k
btu a/c unit. Putting out 50 amps would not overheat the
larger 110 amp alternator.
So I went shopping!
I got a ride to Will's Starter and
Alternator shop in St. Pete where I met Tony. Phone: 727-531-4667
Will's is the type of shop those of us who appreciate
tradesmen will enjoy. They have the equipment necessary to test
items. The men behind the counter were knowledgeable. I was amazed
by the sheer number of starters and alternators in stock. Literally
the walls were lined with 'em.
Will's Starter and
Alternator has bunches of parts on the premises.
The facility also tests items. They will tell you if
yours is okay or in need of a rebuild.
I was concerned that the 110 amp unit would have the
same *Case and bolt pattern as the 55 amp one I was replacing. Tony
(the fellow behind the counter the day I visited) assured me
external dimensions were identical.
*Case: When changing your
alternator you need to verify the outer dimensions of the new
alternator matches what you are replacing. This is called the Case
or Frame by professionals.
Will's Starter and Alternator does
offer a guarantee. They also mark their units.
ALTERNATOR BRACKET ATTACHMENT:
That is my newest double belted alternator (single
Side Note regarding belts
and alternators: When you get to 100 amps, you move from
single belt to either a double v-belt as I purchased or
serpentine style belt.
belts seem to be the better regarded of the two styles.
It is absolutely NOT RECOMMENDED that you attach one
belt and go with it. I did so anyway. That is because this was
intended as a temporary measure until I could retool with the
serpentine belt pulleys. Those are flat with ridges whereas my pulleys
are v-shaped to accommodate the fan belts I use.
When using just one fan belt ALWAYS attach to the
pulley closest to the hub. Please note that experts will tell you this
is not ideal. You really do need to use both belts.
The bumpy parts of the
fan belt are v-shaped. Thus the name v-belts. For me, and I'm
not a mechanic, I simply call this type fan belts. It looks
like those I used in my car all those years ago to make the
fan blow on the radiator.
The plan was to replace the fan belt with a
serpentine belt. Serpentine is a fancy word for a flat rubber belt
that is approximately 1.5" wide. Larger units would have wider
The Fatal Flaw in my plan was
discovered prior to pulley replacement.
Did you notice
that every step seemed logical? Each decision made progress toward
my goal of having the ability to run an air conditioner at anchor.
There were costs every step of the way. I was of
course motivated to make it all work together. A bit of ego was
involved too. I wanted to be right.
Boat projects tend
to grow exponentially. They become more
expensive and take far more time than you imagined. Always!
The alternator bracket from the original 15 amp
charger doesn't fit properly.
The original bracket could not accommodate the 110
amp alternator. The torque (spin strength) was too much for the
smaller brace. That is one of the reasons I had a new stronger
bracket made at Lisotte's Welding shop. The new bracket was
So one Sunday I wanted a parfait from McDonald's. I
untied and headed down the river. Along the way I flicked the switch
to start the alternator charging my battery bank. All was well for
about two minutes. Then I heard a sound. Nothing particular, just a
A quick glance out the
side of my boat showed zero exhaust water. Quickly I pulled off the
channel and anchored. I shut down the engine and hoisted my anchor
When anchoring in the daytime you
are supposed to display a black ball. That indicates you are
Very few boats display an anchor ball. It is the
right and proper thing to do.
Anchor balls are the same
size and shape as the radar reflector balls many sailboats
use. I found an old radar reflector at a marine nautical flea
market for $2. Then I spent $5 on a can of black plastic spray
paint. Several coats of paint later my neighbor had his own
Mine is plastic and folds
flat. His, a former radar reflector, will not fold.
Being at anchor just off the channel on Boca Ciega Bay in St. Pete
is not the place to be on a weekend.
Every idiot was out there. Including me! For the record I almost
never go anywhere on a weekend. The alternator fiasco is yet another
reason why not. I knew better. It was the lure of a McDonald's
parfait... I love those things.
McDonald's parfait ↑
that I doctored up with extra strawberries last year. A
parfait is a real treat.
So I began troubleshooting. That
is when I discovered the broken bolt. The bolt at the bottom of my
alternator was supposed to be attached to the engine in two places
(front and back) had sheared off. When I tried to loosen it I
discovered the bolt was broken. A 3/8" stainless bolt sheared in two
is not a good thing.
Then things got worse. A boat went right my my
transom throwing one heck of a wake. I came up out of the bilge
rubbing my sore spots and got on the VHF radio. I called the navy blue
Mainship that had passed me so closely and said "Nice wake buddy".
Note to other boaters:
do not tick off anyone who is in the bilge. We are already
not having a good day and you do not want to annoy us by
being stupid. But Mr. Mainship had never heard of that rule.
That's when Mr. Mainship put on
his "instruct the woman on the radio attitude". Believe me when I
say you will find that type on more than one occasion. He proceeded
to tell me if I was at anchor I should put up a black ball so that
Real Boaters will know I'm at anchor.
Can you feel my blood pressure
Quickly I popped my head out the
side and checked. Yep, mine was there. And flying high.
I got back on the radio and
suggested he "Look up. I am displaying."
Radio silence. Not a word out of
The next boat slowed down as it
approached me however by then I was back underway. I'd fixed the
So anyway, during the examination to see what had
happened, I spotted the reason why. That long bolt was not attached
to a mounting point at the rear of the alternator. All of the torque
was on that one point in the front. It was a recipe guaranteed to
With a 15 amp
alternator, no issues could occur. The 55 was "pushing the envelope"
and then I made things worse. I got a Good Idea and upsized to a 110
amp alternator. The process was doomed from that point onward.
Although when testing at the dock the 110 pulled down the engine
RPMs, the alternator did put out lots of power. It was the stress of
being underway AND running the alternator that created the failure.
That combination was too much.
important. The alternator belt plays a part in the cooling system of
The large round hub at the bottom center
↑ marked 07220 turns the
time the engine is running. That is the crank shaft pulley. Belts
run off that.
The belt is tensioned (tightened)
by moving the alternator. Another thing to remember is that your
belt stretches. According to
Calder's, for the first one hundred hours the belt continues to
stretch. That's why you have to keep tightening the belt via the
alternator bracket when it is new.
On the bright side however, by the
time your 100 hours is finished you'll be an expert at tightening
that dang belt.
Having spare belts is Very
Important. For details please see the
Expert Advice versus Intuition
(spare parts inventory) article.
That day stuck out there on Boca
Ciega Bay, well, I found another long bolt and put it in at the
bottom. It was Wrong, but it would work long enough for me to move
the boat to safety. The good thing is that I discovered a serious
issue. I was able to rectify the current problem without help. Betsy
(my 18hp Kubota) could have been ruined.
Of course I shut off the
alternator using the switch. After adjusting the alternator to
tighten the belt, I was on my way. I babied Seaweed back to her dock
to rethink the mess.
I had spent a lot
of perfectly good money on a
system that simply will not work on my engine.
For the record, there were at least a half dozen
experienced mechanics aboard Seaweed between the time the 15 amp
alternator was upsized and the failure. No one noticed this small
error. It simply slipped by us all. I do not blame anyone except
myself. As soon as I saw the broken bolt I knew what the issue was. My
Any other person would have realized immediately the
why as soon as that bolt snapped. It really was that apparent. IF I
had not had that Good Idea to upsize my alternator... well, there's no
Often times it is
little things that bite us on the transom. I bet y'all will
check your alternators before you run your boats again. That
is a good thing.
It is always better to
learn from others. Frankly that is why I listen and learn from
so many far more experienced boaters than I. It's less costly
That is my tale of woe. It is not entirely a bad one. I learned
something. One of the things I like about boating is that there is
always something to learn. I enjoy the challenges. I also like the
blissful times at anchor. After consideration I opted to return to
the beginning. The original 15amp alternator is back on *Betsy.
*Betsy is the name of my engine.
And life is good afloat.
Did you upsize your alternator when you bought your
And, do you have a spare alternator in case yours quits?
© 2018, 2020
In the Bilges,
Alternator Bracket Pattern (how to)
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