Alternator sizing

[Scott B]

Jason, yes ours is a 2005 as well. I noticed your solar panels at Hope Island last year, Sept. long weekend and meant to ask you about them.

I knew the stock alt was a 60, but thought my was an 80, but will have to wait until the snow melts sometime in May?? If it's not the 80 I'll have to look for a 100 that will fit right in without alterations of any kind.

What did you use for house batteries, golf or other and where did you locate them all. I hoping the 4 golf carts will fit under the seat beside the chart table and the engine batt in the next compartment. I'll have to open up some ventilation to that compartment.

Been up to check your tarps yet? We were up before Christmas and everything was intack. Also talked to the people from the marina at the boat show and she said several boats had their tarps blow off in the high winds over Christmas, but we didn't get a call so was still intact. :dance:

Lots and lots of snow, hopefully it all melts in a few weeks??

Did you ever get anywhere with your heat exchanger. Had mine changed last year and had no issues at all. Even went to Killarney and back.

You're just to the right of centre.

 

[Stu Jackson]

Once again

Scott,

4 gc batteries will give you 440 ah, NOT 880.

 

[Scott B]

Scott,

4 gc batteries will give you 440 ah, NOT 880.

Stu, I did get that several post ago, but I fixed the original post to not confuse anyone.

I have your posts bookmarked and will def. get to reading them when my brain settles down a little.

 

[Bill Roosa]

Alternator size is driven by

The amount of current used and the amount of time you have to put it back in.
So a AA battery trying to provide a 100 AH/day load is going to need the alternator going all the time and it will need to be sized at 100 amps/24 hours= 4.2 amps continuous.
A 100 AH bank will need to recharge every 12 hours (50% discharge) and to put it back in without running the motor longer than 1 hour (design value) the alternator will need to be 50 amp
A 200 AH bank will need to recharge every 24 hours and will need an alternator sized at 100 amps.
All this ignores charging efficiencies and bulk/absorption/float issues you run into when charging batteries so it does get a little more complicated but those parameters just need to be determined and then factored in.

The parameters have to be determined and then you pick the components.
So ask yourself, how long do I want to run the engine each day, determine the load that the batteries will see to provide your lifestyle, then size your batter bank and alternator so you have a least cost system.

 

[Don S/V ILLusion]

Re: Alternator size is driven by

Sizing an alternator based solely upon how quickly one needs to recharge does not consider the impact on the battery bank's capacity to accept it - you cannot force amps back into batteries any faster than they are safely capable of accepting it. This is why I suggested earlier that the alternator be sized at approx 20% of the total battery capacity which is what most battery mfgs recommend. I know Balmar suggests recharging can be done at a higher rate but they also sell large alternators so their recommendation may be a bit biased and in the context of their marketing.

In Bill's example above citing a 200 amp bank and a 100 amp alternator, the practical output of that alternator of 50-70 amps at a bulk rate of recharge into a bank presumably 50% depleted comes close to 25+% rate which can overheat batteries if not temperature compensated.

Deciding on the appropriately sized alternator is therefore a function of:
battery bank size
expected discharge rate (usage)
alternator charge rate ( charge curve of alternator)

 

[Bill Roosa]

Re read my post Don

I believe I said that there where other parameters to deal with. Acceptance (aka bulk, absorption, float charging) of charge is certainly one. But these variables are a) understood and b) fixed. They don't change once you pick a lifestyle (aka set of loads). You can't pick an acceptance rate but you can pick a battery bank size to reduce the amount of current each battery has to absorb and you can pick an alternator (or other source) to provide the number of amps to minimize the engine run time.

I'm not disagreeing with you Don but there are important controllable variables and there are variables that are important that you have to live with no matter what setup you use.

 

[Don S/V ILLusion]

I believe I said that there where other parameters to deal with. Acceptance (aka bulk, absorption, float charging) of charge is certainly one. But these variables are a) understood and b) fixed. They don't change once you pick a lifestyle (aka set of loads). You can't pick an acceptance rate but you can pick a battery bank size to reduce the amount of current each battery has to absorb and you can pick an alternator (or other source) to provide the number of amps to minimize the engine run time.

I'm not disagreeing with you Don but there are important controllable variables and there are variables that are important that you have to live with no matter what setup you use.

My mistake Bill - I didn't read it thoroughly and I thought it strange as I was trying as I know full well you are well aware of all the considerations.
I'll drink one less beer tomorrow night during the game as penance.