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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Gas > Atomic 4
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Old 09-28-2007
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high output API Alternator

I currently have 2 banks of batteries, a total of 5 batteries. The existing 35 amp Motorola alternator is very slow to recharge the batteries. I want to replace the alternator with a larger API brand alternator to decrease battery recharging cycle time. I heard about a great alternator for such an application. I was told it is an API small frame internally regulated, single foot, single output alternator rated at 120 amps. However, I am unable to identify the model number. Has anyone installed one of these? Anyone know the model number? Has anyone had any problems with this particular alternator? Thanks.

Steve H.
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Old 09-28-2007
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You don't say how big your battery bank is in amp hours but as a rule of thumb for wet cells (not AGM's) your alternator should be rated at 25% of bank amp hours. 35 amps is clearly inadequate.
For proper charging AND battery life for deep cycle bateries you alternator should NOT be internally regulated but instead should use an external 3 stage regulator. Balmar and AmplePower are good examples of brands that you shoud look at for both alternators and regulators.
If you've had a large bank with a small alternator for some time...chances are the batteries are heavily sulphated and a a battery charger with an EQ setting may be needed to restore them to taking a proper charge.
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Old 09-28-2007
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There are several folks out there building higher output alternators based on the old Delco Remey 10DN Alternator (around 100 amps) When you start getting around a 100 amps, you've reached the limit of what a single belt pulley system can handle. I speak from experience as the previous owner hung a 105 amp Lestek Alternator on our boat and belts don't last long.

You could get the standard externally regulated Delco Remey Alternator rated at around 65 amps for around $65 from about any alternator repair shop. I bought one this summer as a backup to the two alternator system on our boat (one for the starter battery, one for the house bank, both small case Delco models.)

Ditto on what Cam said about standard automotive regulators not charging deep cycle batterys well. Even with your existing low output alternator, you would see an improvement in your battery's health by investing in a smart charger regulator.

I don't know anything about the API alternator, so can't help you there.
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Battery bank sizes

Thanks for the responses so for.
House Bank = 4 wet deep cells...244 amps total
Starter Bank = 1 wet deep cell...62 amps
Definitely plan on using a marine grade alternator. The API Alternator I am looking for is better sealed and intended for marine applications.

To date have not had heavily sulfating, probably due to two facts: 1.) The boat spends 99% of it's time in the slip with the shore power plugged in. However, when I start taking week long voyages the risk clearly applies. 2.) I already have a Truecharge microprocessor controlled multi-stage battery charger wired into the the boat's shore power breaker box.

I will look into the smart charger external regulator.

Thanks....Steve H.

Cam--Is there some other form of battery charger you were referring to?

Last edited by skhorleb; 09-28-2007 at 11:07 AM. Reason: added details
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Steve...no...the Truecharge models are good chargers...all except the 10 and 10TB have an EQ cycle as well and if you've never used it, it is a good idea to do so once in a while...I used to do it monthly when I was living aboard.
That said...the fact that you are plugged in with a good charger 90% of the time leads me to think tht our batteries shoul be OK. With a roughtly 300 amp hour total, you need an alternator in the 80-90 amp area...anything else would be overkill unless you plan on further enlarging your bank or switching to AGM's which can accept unlimited amps. A 200 amp alternator will NOT charge your batts any faster than an 80Amp one given your present size and configuration.
With your size house bank...244A/H's...you can use 122A/H's before you need to recharge. Your battery bank will ACCEPT about 60Amps of current in bulk charge stage so you can recharge to about 90% full in about 2 hours of engine running time with ANY alternator over 60 amps.
If that is not quick enough for you...your only alternative is to changeover to AGM batteries and a 120amp alternator which will get you done in half that time.
Hope this is helpful to your decisions.
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Ummm,
Atomic 4 + >100 amp alternator= HP and RPM problem.

Not only will belts be a problem, you might want to check what RPM the regulator kicks in at. Then wander over to moyer marine to see what the HP rating and torque is @ that RPM.

I wouldn't go any higher than 60-80.
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Old 10-15-2007
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Steve,

I'm using the API 120 alternator on my my A-4 charging (4) 130 Ah Trojan lead acid batteries as a single bank. I have changed the pullies to 1/2" to keep the belt from slinging dressing all over the place. I'm also running an Indigo Electronics 3 blade prop. I can cruise at at 1900 -2000 rpm with 2450 rpm at WOT. At 2000 rpm the API 120 amp alternator is ONLY putting out around 60 amps. It's also costing me almost 2 hp of the 20 hp an A4 makes at that rpm.

When at the dock I have a true charge 40 on 24/7. I keep the frige on all the time so the charger keeps the batteries topped of and the beer cold as well.


I plan to ditch the API unit in favor of a Balmar 70 or 90 amp unit with an external regulator.With luck I'll find an alternator that will produce the juice at a lower rpm than the API. I am also going to downsize my house bank to (3) 110 ah AGMs.

If you still have the typical too large prop on your A4 your max rpm is around what, 1400-1500 rpm? At that rpm your 120 amp alternator will only produce around 30 -40 amps.

you can't go wrong with Don Moyer at moyermarine for all your A4 needs.

Mike

Last edited by Mike244; 10-15-2007 at 09:18 PM.
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