MORE INPUT FROM A RECENT CRUISE - THE UNINTENDED CONSEQUENCES
Kyle, I have just experienced almost exactly the SAME conditions you just described.
To back up a bit, I believe we put larger alternators with external regulators into our boats to REDUCE engine charging times, and get as much amperage, as quickly as possible, within the 50% to 80 or 85% range of the house bank.
Accordingly, with house banks at around 400 Amp Hours and 70, 90, 100 and 125 amp alternators being installed, three things seem to be happening, which are THE UNINTENDED CONSEQUENCES of this “new” arrangement of charging:
(1) The alternator works like a bandit when the engine first starts on the depleted house bank because the regulator is telling it to charge. The voltage is low at the bank, and the voltage begins to rise as the regulator tells the alternator to pump in maximum amperage with the rising voltage. This usually lasts between 23 to 36 minutes on the Balmar Max Charge we have on Aquavite.
(2) The alternator gets really hot when the engine starts IF YOU’RE MOTORING AT CRUISING SPEED. If you’re idling at anchor (or motoring/cruising at a lower rpm) at 1,500 rpm it doesn’t seem to be an issue.
(3) The maximum output I’ve seen from our 100A alternator is 50 Amps when charging a depleted battery. I am becoming convinced that this is the limit of the acceptance of a 50% discharged reasonably sized house bank of around 400 AH, maybe only based on wet cells, deep cycle, that we have on board. AGMs will take many more amps.
This happened to us this past weekend: two nights on the hook from a Friday arrival at 1800 to departure on Sunday at 1500 hours, no engine use at all. Fridge on, some lights, radio, and inverter use for popcorn and the computer for DVDs. The Link 2000 showed 11.97 V (sound familiar, Kyle???) and <–>170 AH on the house bank which is 360 AH. We had essentially used just 50% of the house bank, which then needed to be recharged.
The alternator got very, very warm when we started motoring at cruising speed. It was pretty amazing that it happened just after Kyle’s original question on this subject, and I appreciate his input VERY< VERY< VERY much because it gave me a sense of comfort when it happened to me!
Because we did not have to motor too long, I simply opened the alternator door to the head and let it vent. If we had had to motor, as we do sometimes, for a longer period, and we did need to replenish the batteries, I would have made the decision to utilize the amp manager feature of the regulator to simply reduce the load, ON THE ALTERNATOR, and NOT on the engine!
That’s what so crazy about this arrangement: Even with a good sized alternator which is way above the acceptance rate of the house bank (110A over 50 Amps max charge rate at a rising 12+ volts to the bulk voltage of 14.5 in the program’s algorithm) the alternator is putting out so much it heats up. Which is contrary to exactly what we’re trying to do by pushing lotsa amps in as short a time as possible. The next step is the REDUCE the alternator output using the Amp Manager, which would make the charge period even longer!!! Another option would be to run the engine for an hour each day to reduce the drain on the house bank by pumping in 30 to maybe 50 amps at 1,500 rpm for an hour. This is exactly what we’ve been trying to AVOID! Like a Catch 22!
I’ve had a discussion with a C36 owner from Connecticut on the “larger the better alternator”, arguing the point that a huge alternator (125A) on an M25, even M25XP, is kinda overkill and could hurt the bearings on the engine. He replied that the larger alternator didn’t have to work so hard. There is truth to that IF the acceptance of the reasonably sized house bank is the limiting factor.
So, now that we’ve put in the large house bank, the larger alternator, rewired the alternator output to the house bank avoiding the dumb 1-2-B switch, and installed a new regulator, we’re almost in the same place as we were when we had the dinky old OEM 55A alternator with internal regulation and one house battery of Group 27 size [a marina hopper stuck out at anchor for a night – can you visualize this???], not to say “bank”: run the bloody engine for an hour or two every day ANYWAY! Oh joy, Oh rapture, back to the Dark Ages!!!
It’s an interesting system balance, but it is very nice to know, first, that we are not alone in this, and second, it is a system issue that warrants careful consideration in actual day-to-day use.
I go back to my earlier reply recommending the amp manager feature, which is relatively easy to deal with. That would be appropriate IF Kyle’s and my recent experience required motoring at cruising engine speed right after a deep discharge. OR one could motor slower for the first hour. OR both. Reducing the input amps to the house bank from the alternator is just what we’re trying to avoid.
I don’t think it is the alternator from Blue Circle, unless just Kyle and we have these on our boats. It would be interesting to hear from those with other alternators what their experiences have been in these situations. In 2004, before we put in our new alternator, the OEM 55 A Motorola with an AutoMac which had NO trouble amping back when we were motoring at cruising speed up in the Delta. It was probably only putting out 25-30 amps.
It’s all such a delicate balance…
A battery monitor, our Link 2000 (A Link 10 would do for you, Kyle) has shown me two important things:
1. My energy budget numbers are almost exactly on target (see my post on that earlier) for amps being taken OUT
2. My energy budget for RECHARGING was WAY, WAY OFF. It takes much longer to charge, even with a shorepower charger, than I had thought. This is IMPORTANT to know for REALLY extended cruising. The “steadily diminishing law of returns” from my earlier post on that subject goes like this:
"Helpful Hints: Electrical Systems: For extended cruises for those with OEM stock alternators and no external regulation, there is inherently a steadily diminishing law of return in battery charging even if you motor a lot everyday. If you do an energy budget, even if you motor for eight hours a day, you will be drawing down your batteries, regardless of how much you’ve increased your house bank. You WILL need to stop and plug in every week or so. Do the math. If you really want to stay out “forever,” add solar and a new high(er) output alternator and smart regulator. We minimized use of electric lights with our lamp oil trawler cabin light and lamp oil anchor light hooked onto our Garhauer dinghy davit, but most of the energy use is from the fridge. With our large 315 amp hour house battery bank and a separate start battery, we were very comfortable being out in two different situations. The first was for a few days without motoring or plugging in. We turned off the fridge at night, so we only used 30 to 40 amp hours a day and could go three or four days without running the engine. The second was knowing we’d be motoring for at least five hours or plugging in at a marina. So, before you go, make sure your electrical system is up to snuff so you can really relax and enjoy the peace and quiet without having to worry about your boat systems."
This now seems to be true also of the newer arrangement of larger alternators and external regulators if you use the amp manager feature to reduce alternator output.
{Ed. by Stu] BETTER YET: Use the Small Engine Mode ; see page 2 of this topic.
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Topic: Alternator heat, Regulator Controls, Small Engine Mode (Read 27207 times)