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Author Topic: Second alternator  (Read 3212 times)

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Second alternator
« on: July 30, 2001, 10:45:25 PM »

I know sooner or later I'm going to have to install a separate cranking battery.  Until then, here is a question that came up for me when I went to one of Nigel Calder's workshops here in Seattle:
  • Dual alternator setup

 Has anyone installed a second (high-output, "special" winding) alternator to charge the house bank?  (With the original alternator relegated to charging the cranking battery.)  The two circuits (house/cranking) would then be totally separate, except for an emergency switch.
 Is there even room in the C34 engine compartment to install a second alternator on the Universal M25XP?
 Fulvio Casali
 Seattle WA
 #929 (1989)


  • Guest
Second Alternator
« Reply #1 on: August 06, 2001, 05:04:56 PM »

The first answer is that there really in no good way to add the second alternator on a C34 engine of any size without going to an awful lot of trouble. The second answer is that the benefits of such a setup aren't nearly enough to justify the expense and trouble that you will go to to add a second alternator.
 The better way is to replace your original weak-hearted alternator with a good quality high output, externally regulated, marine alternator which is connected directly to the house bank, and then use an electronic combiner between the house bank and the starting battery. If you already have a Freedom inverter with an EchoCharge output, you don't even have to add the combiner: the EchoCharge output works with any source of charge voltage applied to the terminals of the inverter, which are of course connected to the house bank. The electronic combiner will allow faster recharge if your starting battery gets significantly discharged, but this is not the norm.  As I mentioned only in passing, you should also use an external "3 step" voltage regulator with your high output alternator.
 A second alternator is just another belt to maintain. Quality alternators and voltage regulators are quite reliable, so if you use good stuff on the one alternator system and maintain your belt tension properly, you will generally never notice any improvement in reliability of a 2 alternator setup versus one good alternator and appropriate means to connect it automatically to the house bank


  • Guest
Second alternator
« Reply #2 on: August 09, 2001, 02:31:57 PM »

Got it.
 I have a Freedom 10 with a Link 2000 remote, so I'm already covered on the 3-step charge regulator side.  The Freedom is an older model, though (1995), so I don't think it comes with a built-in Echo~Charge, like some newer ones.
 I'll keep the Echo~Charge in mind when I install the cranking battery.  My only remaining question concerns the different battery types.  My house bank is made up of 2 deep cycle sealed wet cell batteries, whereas the usually recommended cranking battery is a non-deep-cycle gel cell.  How does this mixed configuration affect the charger and the whole system.
 I found some literature at, by the way.
 Fulvio Casali
 Seattle WA
 #929 (1989)


  • Guest
second alternator / batteries
« Reply #3 on: August 11, 2001, 09:32:18 AM »

You don't want to mix battery types. The Gell types don't want to be charged at 14.2 volts like the wet cells do and in doing so will damage them.
 The wet cells don't want to be charged at 13.8. Doing so will undercharge them and reduce their life.
 If you must install them in an inaccessable location, look at the spiral wound type batteries. More expensive but completely maintenance free. OPTIMA is one brand that comes to mind.
 Where were you thinking of installing a starting battery.
 Mike Senko
 S/V Puffin #495

Stu Jackson

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Different Battery Types
« Reply #4 on: August 12, 2001, 08:26:33 PM »

Don't mix types of batteries because gels and wet cells require different charging rates.  This is from the West Marine Advisor, and is basic to batteries:  (
 1) Gel batteries charge at different voltages than flooded-type and AGM batteries, and 2) the voltages stated are temperature-dependent. This makes it difficult to recommend precise charging voltages, since they vary according to the temperature of the battery. Most of us generally operate our boats in temperatures between 50°F and 90°F, and the values used in our Advisors reflect that. Higher temperatures require lower voltages, and lower temperatures require higher voltages. Note: In the following section, we define the capacity of the battery bank (in amp-hours) as C.
 The "Ideal Charge Curve"
 Rick Proctor, founder of Cruising Equipment Co., is one of the leading innovators in the field of marine electrical systems. He coined the term "Ideal Charge Curve" to describe the best way to restore energy to your batteries. Here's how each phase of the process works:
 Bulk Phase: Charge at a rate up to 20%-40% of C to a voltage of about 14.4 volts (gel: 14.1V).
Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

"There is no problem so great that it can't be solved."


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Mixing Battery Types
« Reply #5 on: August 13, 2001, 05:06:11 PM »

The one notable exception to the general rule of not mixing battery types is the combination of normal flooded ("wet") cells and Lifeline AGM batteries. At temperate ambient temperatures, you can successfully mix Lifelines and flooded, at least as far as sharing a charging source, because the nominal charge voltages are relatively close for the 2 different types. What I do in these cases is select a charge protocol for the Lifeline AGM (if available) and let the flooded cells be just slightly under-charged in the float mode. The bulk and absorption voltages are close enough to not worry about the differences.
 In the case of an older "black" Freedom inverter, what you would do in this case is set the battery type selection to "warm flooded" in those instances where you only have 4 choices: i.e. - when used with the basic "dip switch" remote control head. If you have a Link 1000 or 2000 interfaced to it, you may have additional options if the serial number of the inverter is greater than 100,000. (Below sn 100,000 you are still limited to the 4 battery choices: cold gel; warm gel; cold flooded; warm flooded.)In the case of a Link product with a "black" Freedom with sn > 100,000 you can set the temperature to a level that will cause the bulk and float voltages to be correspondingly adjusted. In these cases, you can "tweak" the float voltage to be whatever you want, and take the bulk/absorption voltage that goes with the float voltage that you get with the declared temperature. Often, you have to do this anyway to get the voltages exactly right because the older Heart tolerance on charge voltages is a hefty +/- .2 vdc. A .4 volt error in float voltage can get you high enough to completely destroy any sealed battery ( AGM or gel ) in an amazingly short time.
 Never mix these battery types in any individual bank, but it is OK to have an AGM house bank and a flooded start bank, or visa versa, as long as you configure your charging sources appropriately.
 On the subject of AGM starting batteries, the Optima is a good performing product, but has a poorer warranty (max of 36 months with a whole list of "stipulations" that void the warranty) than the Lifeline GPL-1400 (60 months). The Optima is more starting battery than any C34 needs (about 700 to 800 CCA, depending upon model). The Lifeline GPL-1400 is an honest 550 CCA and quite rugged: I have successfully and repeatedly started 135 hp, 400 cubic inch marine diesels with 1 of them, and I have used a pair of them to start 450 hp CAT diesel engines in large motor coaches.
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