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alternator 1987 350 alpha

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redsnapper386

Regular Contributor
guy's,i have a 1987 350,alpha-1 with a delco 61 amp alt with the thunderbolt ignition.is there a maximum amperage alt to use,or should i stay with the 61 amp.can i use a 70 amp,which is what mercruiser offers now.need advice.also,i use 2-batterys with a battery switch.thanks.
 
Re: alternator

I would think you can use a larger one, It will just charge the battery quicker.

If you have no additional accessories that cause a draw then leave it alone............
 
Re: alternator

Yep replaced mine DB electrical i lost count how many things i bought from him just get the right number of wires if in doubt just send them the numbers off yours.

You need one marked j 1171 thats the sae number for marine electrical parts.
 
Re: alternator

redsnapper386 said:
guy's,i have a 1987 350,alpha-1 with a delco 61 amp alt with the thunderbolt ignition.is there a maximum amperage alt to use,or should i stay with the 61 amp.can i use a 70 amp,which is what mercruiser offers now.need advice.also,i use 2-batterys with a battery switch.thanks.
Click to expand...

with a carb engine you don't need more than 60amps. If the batteries where both run down the most they would use to charge would be about 10amps each ..that still gives you about 30 amps for the other equipment. alternators rated 60 amps can output about 55amps max..

as the alternator gets hot approaching the higher output, the voltage drops, this reduces current output.

with fuel injection you would need a larger alternator .
 
Re: alternator

If you're on the hook a lot and take short trips to get there, hi outputs are great. Having said that, making the change to gain only 9 amps just isn't worth the effort or extra cost IMO. If you do change up, make sure the existing charge wire is properly rated for the extra output.
 
Re: alternator

Think of the batteries as a bank account that you draw from. The alternator's job is to keep the account from getting so low that you go bankrupt. If you take it out faster than it goes in, you are in trouble. If that is the case, you need an alternator with more output. Remember that the alternator's amp rating is for it's maximum possible under the best conditions. Chances are that you can't even spin it fast enough with your marine engine to ever approach the 61amps on the label. At WOT, you might be making 45-50. At idle it is barely putting out anything. Cruise speed you are likely seeing about 30-35 amps. This is important to consider when doing the calculations for your energy needs. If you are overnighting or away from the dock for extended periods this is very important. If you are only using the boat for day trips, you need not be concerned. The most important thing is that you have at least one battery that is fully charged at all times to start the engine. The alternator is only one part of your charging system, and it should be in condition to do at least that much. You can get along with no music or water pressure, but you gotta be able to start that lump.
In almost every situation a larger battery bank will trump alternator size every time. Do you have a two bank system? One battery should be for engine start only and one for the house loads. I have installed several systems over the years on both power and sail. In every case, I went with two or three bank systems that adhere to ABYC standards. Most boats that you buy do not have adequate charging systems from the factory.
 
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Re: alternator

j cat said:
with a carb engine you don't need more than 60amps. If the batteries where both run down the most they would use to charge would be about 10amps each ..that still gives you about 30 amps for the other equipment. alternators rated 60 amps can output about 55amps max..

as the alternator gets hot approaching the higher output, the voltage drops, this reduces current output.

with fuel injection you would need a larger alternator .
Click to expand...

This is about as misleading as it could possibly be. Sorry man, it's just not possible to make these kinds of general statements.
I have a carb engine but need a bigger alternator (100 amp Balmar) to run my electronics, baitwell pump, plus keep my start bank topped up.
 
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Re: alternator

o2batsea said:
This is about as misleading as it could possibly be. Sorry man, it's just not possible to make these kinds of general statements.
I have a carb engine but need a bigger alternator (100 amp Balmar) to run my electronics, baitwell pump, plus keep my start bank topped up.
Click to expand...



with the adding of other equipment the alternator to be used would be of a higher output. that has to be determined by what the owner is operating for power needs. he did not indicate that he had power issues. or stated anything about adding more load ..

with some owners 100 amps would not be enough.. with the use of inverters and high power audio systems etc you would have to compute your needs with YOUR special loading added..

for me this adding of additional load is just common sense , that you have to use a larger alternator to drive all of these added devices.
all he added was a battery ..so he stated !
 
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