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#1
IP: 204.157.20.43
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Selecting an Alternator
Are there any rules of thumb that will help in selecting a properly sized alternator?
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#2
IP: 204.157.20.43
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I have heard (and am finally paying attention to) four rather simple rules of thumb regarding alternator sizing:
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#3
IP: 209.183.153.18
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bigger alternator effect on A4 engine
It's been suggested to me recently that putting a bigger alternator on an Atomic 4 is asking for trouble because the crank is only supported by two main bearings (front and back with nothing in the middle), and the additional side load on the crank will cause stresses on it which will likely cause it to fail in the long unsupported middle section.
I've just put a 70A Balmar (the 621) on to support the bigger house bank required for a new refrigeration installation this past offseason, and I know I can jumper the temperature control on the regulator to reduce the alternator output, but that would be a shame, given that a major reason for putting it on (aside from 3-stage charging) is in response to the rule of thumb that alternator capacity should be 25% of the bank's Ah rating. I haven't been able to find a cutaway drawing of the A4 to check out the bearing story. Can you comment? Thanks. |
#4
IP: 38.118.52.41
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Mark,
This question is revisited at least a couple times each year within the Atomic 4 fraternity. The short answer is that the Atomic 4 crank is indeed designed with no center main bearing. However, the engineers really did a good job in designing the crankshaft to withstand all of the normal stresses which they envisioned, up to the rated HP of the engine plus a generous safety margin. As of the time Universal was sold in the early 1990's, their reported failure data showed that the number of crankshaft failures was less than the theoretical number of failures to be expected simply from QC defects of a crankshaft during manufacture. The failures that were reported were usually associated with a bubble in the casting from the casting process. Our own experience tends to support the Universal assessment. We have only had the opportunity to investigate 3 crankshaft failures in over 15 years of servicing and rebuilding Atomic 4's, and each one had some preexisting defect which set up a premature cycle of fatigue. Fatigue crack analysis is interesting because it indirectly demonstrates (after the fact of a failure) how much of the cross-section of a particular structure can be sacrificed prior to the ultimate failure, hence supporting the design claim of a particular margin of safety. In each of the cranks we analyzed, the fatigue zone of the crack (meaning the part of the crack that had existed for quite some time before the ultimate failure) was almost 50% of the total fracture surface. This means that a crankshaft can reasonably be expected to survive for a relatively long period of time even with up to half of its design strength sacrificed by the fatigue crack. NOTE: The fact that a fatigue crack is developed over many years before an ultimate failure occurs means that "wet-magging" a crank during overhaul would normally have a good chance of revealing a fatigue crack before the crank would ever fail. More importantly, if a fatigue crack is not discovered during overhaul after many years of service, it would go a long ways towards confirming that no manufacturing flaw exists in that particular crank. The naturally aspirated up-draft design of the carburetor on the Atomic 4 makes it virtually impossible to "over-torque" or "over-boost" the engine. The engine simply gets to an RPM on the power curve where it says: "I don't care what you do with the throttle; I can't give you any more power". This design concept is very friendly to internal stress-bearing members of an engine, the crankshaft in particular. In summary, in the unlikely event that your crankshaft would ever fail, it is far more likely that it will do so from a pre-existing manufacturing flaw than from your Balmar alternator. Don |
#5
IP: 216.58.96.134
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I've been using a Balmar 912 (nominal 90 amp) for 6 years now with no problems, using a smart 3-stage regulator. The batteries (two 225 amp-hour golf cart batteries in series) take around 55 to 60 amps initially (I have to run the engine at around 1700 RMP to get this much into them), and after about 1/2 hour, things start to taper off.
The alternator is driven via the accessory drive, which is gear driven from the crank via an idler gear. I wouldn't be worried about that end of things. The place to worry is the bearings on the aux drive for the alternator pulley, if you put on too big an alternator on, and try to tighten the belt too much to prevent slippage. Incidentally, re belt tightening - I bought the belt tensioning device from Indigo Electronics a few years ago, and it makes life MUCH simpler.
__________________
Larry Bradley C&C Corvette 31 "Lady Di" Clark's Marina Gananoque, ON, Canada in the beautiful Thousand Island of the St. Lawrence River |
#6
IP: 76.24.202.79
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alternator selection
[as i am new to this forum and also to computers, this may not look too good but i do have over twenty years experience working on and using the Atomic 4 both earlyand late types including six trips to Florida in a Bermuda 30. After talking to Balmar and studying their literature, I have come to understand that the overriding consideration is alternator speed. The Atomic 4 suffers from a fundamental design defect in that the accessory drive sheave can only drive the alternator slightly over engine rpm, about 1.3:1 believe. The reason your alternators are running so hot is that they are running so far below design rpm. It is pointless to put a big alternator on that tiny sheave. I bought the PTO flywheel from Moyer Marine, then went to the McMaster book and ordered a double sheave for 1/2 inch belts and then fabricated a bracket to run the length of the (old type) head which carries the Balmar 712 up front. I ran this at 2 to 1 (backwards) all the way to Florida, cool enough to hold my hand on it. I am now moving up to 3 to 1 (9.75 inch double sheave). My wife likes the 1600 w toaster oven so I need big output from the inverter. Thats all for now. Thanks to Don Moyer and his organization for preserving this beautiful technology.[/B][/B]]
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#7
IP: 216.14.224.14
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New Alternator and Smart Regulators?
Hello, I'm rewiring my old 78 Ranger 33 this winter, adding a 200Ah house battery bank (probably gel cell), and replacing the stock alternator. Two questions:
Will the 55A alternator be sufficient or do I go with the 120A high-output alternator? After reading Don's old post in this thread, I'm leaning toward the bigger one. These are internally regulated. Everything I've read says to use a multi-stage smart regulator to get full charge without damaging the batteries. My goal is to keep it simple, but the batteries are going to run $600-700. Do I invest another $300 in the smart regulator? And if I do that, do I need an alternator that is not internally regulated? Thanks for the help! |
#8
IP: 128.183.140.38
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Keep in mind, as Hanley has frequently pointed out, that you're not going to get 120A out of any alternator driven off of the accessory drive. You just can't spin them fast enough to get the rated output. It will run cooler, however, and probably last longer, so that's a reason in favor of a higher rated alternator.
Hanley had to mount a huge pulley on the front take-off and mount the alternator up there in order to get a 3-to-1 ratio to spin the alternator fast enough. And he found that it was lugging the A4 too much. You've essentially turned it into a 30HP generator, with little power left to push the boat! He has since backed off to a smaller 2-to-1 rig. As for the multi-stage smart regulator, you really want to go that way. Not only will it help maximize your battery life, but it will minimize the amount of engine run time required to charge the batteries. The built-in internal regulators are essentially automotive regulators, and back-off to a trickle charge way too soon. Any decent alternator shop should be able to modify an alternator to bypass the regulator and bring out the feild terminals. Just be sure they know its for marine use so they install the proper seals to protect against igniting any gas fumes. The smart regulators will pound the amp-hours into the batteries at the fastest rate they will accept it, until they're about 80% charged. Only then will it back off to a slower charge rate for the last 20%, and then back off to a trickle/sustaining charge. This minimized engine runtime becomes important when you're passage making, and have to run the engine so many hours each day to maintain your "power budget".
__________________
@(^.^)@ Ed 1977 Pearson P-323 "Dolce Vita" with rebuilt Atomic-4 |
#9
IP: 216.14.224.14
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Quote:
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#10
IP: 199.173.226.236
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"Marine" heavy duty externally regulated alternators are very expensive. Delco makes a number of 1 and 3 wire alternators that fit the A4 and can be modified for external regulation, as can the stock Motorola. They are all over FleaBay and also found on this very website.
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#11
IP: 199.173.226.236
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http://www.morganscloud.com/category/electrical/
Follow all the AGM discussions on there. You may end up thinking twice. Quote:
Last edited by joe_db; 11-19-2011 at 09:05 AM. |
#12
IP: 64.134.234.210
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Quote:
Will you have SHORE POWER available on a "regular" basis?
__________________
-Jerry 'Lone Ranger' 1978 RANGER 30 |
#13
IP: 24.224.206.117
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I've had a Delco 90 amp with internal regulator on mine for 4 summers and am pretty pleased with it. I use the boat during summer almost every day and we spend most weekends aboard, either on a little cruise or in the surrounding area. Running two marine starter batteries and always have starting and light power.
Also have a 1000 watt inverter. The only thing about that is that I need the engine running to run the vacume cleaner. I think if I was cruising I'd have a larger battery bank, but for what I do it works fine. It's nice to have something that will throw a charge back into those batteries.
__________________
Mo "Odyssey" 1976 C&C 30 MKI The pessimist complains about the wind. The optimist expects it to change. The realist adjusts the sails. ...Sir William Arthur Ward. |
#14
IP: 72.45.14.161
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FYI : I am unhappy with my AGMs and will go back to gels next replacement.
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#15
IP: 72.83.115.32
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Quote:
Joe, What's the source of your chart?
__________________
@(^.^)@ Ed 1977 Pearson P-323 "Dolce Vita" with rebuilt Atomic-4 |
#16
IP: 72.174.74.80
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Quote:
I'm definitely concerned about robbing power from the prop - I think I'm over-propped already. |
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