Alternators - What's the Difference ?

[Jamel]

Originally Posted by GordMay

Battery life is directly related to how deep the battery is cycled each time.
If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD.
If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%.
However, a battery that is continually cycled 5% or less will usually not last as long as one cycled down 10%. This happens because at very shallow cycles, the Lead Dioxide tends to build up in clumps on the the positive plates rather in an even film.

Typical Cycles vs Depth of Discharge chart ↓

Thankyou Mr GordMay! Your post above has put me firmly on the right track and your earlier reference to Nigel Calder had me diving for the bible "Boatowners Mechanical & Electrical Manual by Nigel Calder"( never leave without this one onboard!)

Nigel goes into great depth about power usage, alternator sizing to battery bank capacity.....all inter- related. He sums up, in a nutshell, Quote "Most of todays mid size cruising boats charging batteries on a daily basis will use 100AH between charges, requiring 400AH of batteries and an alternator size of 133amps to 200amps" ( relates to 1990s cruising boats)!


Personally,I like the idea of extended battery life and at a dicharge of 25% of battery capacity each day.
In my case I'm calculating a discharge of 200AH use per day between charges...why? Because these days we run so much ..stuff! Bear in mind The boat is new to me, I have a long ocean passage to make initially. I'm allowing 100AH for daily use of fridge, lights, radios,laptop ipods to charge( I have a young crew) and ofcourse the big drain will be the autopilot which will steer the boat 24/7, unless someone (who?) wants to steer! So allowing 100AH per day between charges for autopilot + 100AH to run the other stuff total is 200AH or 25% of battery capacity!

I wish to put this deficit back each day as quickly as possible i.e. run the motor for approx 1 hr per day. What I'm going to do is fit a 200amp alternator + external reg + serpentine pulleys and belts = Electromaax combo @ $1785. Decision made!!

[Maine Sail]

Originally Posted by ADMPRTR

The following is an off topic battery question but is partly relevant:

Does going with a higher than required battery capacity extend the life of the batteries because they don't discharge as much (as a percentage of their overall capacity)?

Yes

Originally Posted by ADMPRTR

i.e. if the house required 50Ah per day I believe it would normally dictate a 200-250 reserve capacity to discharge to 25-20%. If 400Ah batteries where installed (resulting a a daily discharge of only 13%) would it be a waste of money or a strategy to extend the life of the batteries?

No not at all. It is actually a smart move. I do this with my customers whenever they have the room for more batteries. Took one customer from an average of 2 years on a bank to 5+. Same batteries, same model same daily usage just more Ah's and shallower resulting bank discharges.

Originally Posted by ADMPRTR

Essentially, does a shallow discharge help or hinder battery longevity?

Cycle life is directly translatable to the depth of discharge. The shallower the discharges the more cycles you get.

Originally Posted by ADMPRTR

If the above is true (and to bring us back on topic) would either scenario described above require the same size alternator or would the larger bank require a larger alternator even though only 50Ah are being replaced?

Nothing "requires" a bigger alternator but unless you're up against bank acceptance then a bigger alt will get your bulk current back faster than a smaller one. A 400 Ah bank of wets can theoretically accept 100 amps in bulk or about 25% of C20 (20 hour Ah capacity). most boaters are limited by the belt as to what they can put back into the bank. Electromaax is making some very sweet serpentine pulley kits that allow up to 200A on a single 4 grove serp belt all with less tension then a v-belt.


Our CS-36T uses about 16-25 Ah's /day (net) with a 375 Ah bank. We have strongly focused on conservation, LED's and engine driven refrigeration, all computers run off 12V and we've been using a lot more iPad as opposed to laptops as they are much less power hungry.

The bank is CHEAP deep cycle batts, $204.00 for the entire bank 5 years ago, and they are nearing the end of year five now. They have been charged with a dumb regulated alternator, blasphemy I know, and 80W solar panel.. They have also been left ON THE BOAT each winter, I know more blasphemy.

I did a controlled 20 hour load test this past spring and they were still at 97-98% of the 20 hour capacity. CCA capacity is still above the rating on the battery according to both a Midtronics and Argus analyzer.

Adding that third 12V battery, that I didn't really "need", for only $68.00, was some of the best money I've spent. I fully expect at the least 6 year or perhaps 7 years out of this bottom of the barrel, inexpensive Johnson Controls battery bank.

We run the engine 30-40 minutes per day for refrigeration and most all our charging needs are satisfied with a 50A dumb regulated alt and 80W solar panel.

The contributing factors to this bank performance from "non-premium" batteries I attribute to over-sizing the bank for shallower discharges, conservation so we use less capacity which helps with the shallow discharges, and solar topping the batts back to 100% while the boat is on the mooring and a good, well calibrated battery monitor to know what's going on. The solar helps prevent sulfation by keeping the batteries full often..

Seeing as this is a personal experiment my parameters for this "cheap bank" real world experiment was that I would never equalize this bank and I never have. I have "abused" them based on what some consider "abuse". A dumb regulator, stored on-board each winter in Maine and only charged up once over the winter, and buying the least expensive deep cycle batts I could find, Wal*Mart. They have also only ever been charged via solar and a 6A Guest portable charger other than the alternator. The Guest Charger is only ever used for the mid winter top up and I let it run for a day. I have been keeping up with water but other than that it has been "abuse" by some folks standards.

As a marine electrician I get to see lots of systems and lots of failed banks. Deep discharges, alternator only charging, banks not regularly getting back to 100%, all tend to contribute to shorter life. I also see a direct correlation with shorter life to banks left of float chargers at docks 24/7. I know that may sound weird too but that's what I see. Solar is only charging a few hours a day then the batts get to rest. It is my suspicion that this is a better scenario for the batteries than 24/7 float but all I have to go on is real world field experience. I replaced 12 batteries this week alone, so I get lots of that....

[Kettlewell]

Listen to Maine Sail--knows what he writes about. But, I would venture to wonder if longer life in the case of shallower discharges = least cost per amp hour? In other words if your batteries cost twice as much (doubling your capacity) do you get twice the life from them, assuming the same daily discharge level? If the answer is no, you are only gaining time between battery changes, not actually saving money. In my experience, you also have to allow for bad stuff happening (alternators die, regulators die, batteries crap out early for some reason, etc.) which can kill your wonderful expensive battery bank very early, meaning you would have been much better off killing your crummy cheap battery bank early. Don't know if this makes sense to you. Just for example, I had a regulator fail so that it overcharged my battery bank enough to destroy one of my batteries on a long motoring run at night when I wasn't monitoring the instruments very carefully because I was asleep most of the time and someone less experienced was on watch.

[Kettlewell]

Here's a good cheap source for that Delco 10SI alternator.

[billwa]

Originally Posted by atoll

one of the problems sailing downwind on an east west axis is that solar panels are in the shade

I just installed solar array on my Ketch - the problem here are even worse I imagine. I set it up fully expecting only half power from my array when sailing.

One of the things that should be considered with price effectivness of batteries is the maintenece requirement.

As a newb, I put in a whole bank of 4 T105 Trojans (210 ah). Not knowing any better, I didnt top them up with water for a couple of months, and lost the whole bank.

So, if your lazy or forgetfull, or would rather be sailing than keeping an eye on your battery - traditional lead acid might not be the most cost effective.

I replaced the whole bank with a single sealed lead acid (70aH). No thought went into this, I just had one in the shed. This has been great for day sailing. It also seems to accept more charge per amp hour than the Trojans, which has been a bonus. And I dont have to top it up with water all the time.

This season, I intend to replace all the T105s with sealed lead acid.

[Jamel]

I do advocate a suite of charging options as posters indicate i.e. solar & wind gen as well as alternator.
People cite that alternators may burn out and leave you without charging capacity if thats all you rely on. Well, lets be fair here, the sun don't always shine and de wind don't always blow! The Pacific trip I'm doing "rolling down the trades" with following winds may hardly turn a wind gen and the rolling of the vessel may give only intermittant direct sun on panels ( at best 5 hours good charge when stationary, sailing, pitching and the trade winds roll will I suspect reduce that even more).
So for me, it's 200amp Electromaax alt + ext reg + serp belt & pulleys! I consider that a good investment in the enjoyment of my boat and how I will be using it, far away from the shore power umbilical cord brigade!