upgrading an alternator

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salty87

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the stock alternator on my boat is a 35 amp (1987 Supra, 454 pcm chevy inboard).<br /><br />i have a couple of amps for the stereo, 2 batteries with an isolator, and a spare jumper pack becuase i can count on it not starting after awhile of playing the stereo or much time at night with the lights on and the engine off.<br /><br />i'm thinking i need to upgrade the alternator. i've got the stereo amps wired to their own battery and the rest of the boat, including the starter, wired to the other battery (stock).<br /><br />i boat on a river, never have to run far and like to sit with the engine off to rest from wakeboarding, with the stereo on. it seems like the 35 amp alternator never makes any headway charging the 2 batteries. the stereo battery will eventually get drained and if the lights are on, the starting battery will too.<br /><br />does upgrading the alternator sound like a solution? what about getting it re-wound? i don't know much about alternators and have never replaced one. thoughts?<br /><br />it's time for new batteries and i don't want to kill 'em with this alternator.<br /><br />thx
 
Walt T

Walt T

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Re: upgrading an alternator

Any alternator will fry itself if you are always trying to charge dead batteries. The starting circuit on your boat should be sacred. Do not use that battery to play with. The second battery that you're using to run the stereo and lights should be a deep cycle. I recommend that the deep cycle not be attached to the alternator in any way, and it should get charged up at home on the trailer. However most folks don't like that idea, so a deep cycle can be attached to the system.<br />First make sure your batteries are okay with a hydrometer.<br />Then have the alternator checked. If it is bad, then upgrade to a 60A if you like. <br />I suggest making the charging wire larger.<br /><br />Before you do anything though, make sure the batteries are okay or no matter how big an alternator you put on you will still have the problem.
 
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ndemge

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Re: upgrading an alternator

you are sucking a lot of power....<br /><br />like he said, you need a good deep cycle for the 2nd battery.<br /><br />If you sit for a long time without much running, put your lights on the 2nd battery.<br /><br />I'd upgrade the alternator for sure. the one in my van is HO from summit, 160 amp.... I wouldn't think a 60+ marine alternator would be hard to come by.
 
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navigator336

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Re: upgrading an alternator

You mention you have 2 amps. I'll take a guess and say they are 200 watts each. Volts times amps equals watts. 400 watts/12 volts = 33 amps IF you are maxing out the amps. Therefore, you are probably pulling less than 33 amps. Let's say it's 20 amps. If you have a standard automotive size battery and it's fairly new and a deep cycle marine one, it may be good for 80-100 amp hours. Therefore, without running the engine, the battery would go dead in 4-5 hours. To re-charge it at 35 amps, it would take about 3 hours of running. So yes, you need a bigger alternator. 60 to 80 amp marine units are pretty reasonably priced (rebuilt). You must have big halogen flood lights on your tower to be drawing down your starting battery very much. If you are running just normal lights and your battery is getting run down then I would suspect your alternator(regulator) and/or battery are marginal. Check the battery voltage with everything off including the engine. Start the engine and recheck the voltage. If the alternator is working well it should read at least 13.5 volts and maybe up to 14.5 or 15. If the voltage starts dropping as the engine runs, the alternator isn't putting out anything.
 
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BRIAN03

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Re: upgrading an alternator

Great Post/ Great answers. I run 3 batteries group 27's with (all) 2 guage wire and 220 amp alternators. Speciality built for my service trucks.You can never have enough power.
 
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salty87

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Re: upgrading an alternator

thanks for the replies!<br /><br />navigator-<br />that math is very helpful, i'm running closer to 1,000 watts on the stereo. no halogens on the tower, that would be cool. i am about to switch all lights to LED though.<br /><br />my old batteries are beat to he!!, i trickle charge them when not in use but have probably done some harm there too. i'm definitely getting some new ones, starting and deep cycle. i'm also going to switch the wiring on the amps and starter to isolate the starting load, put the amps on the house battery.<br /><br />is there somewhere online to get a rebuilt alternator? or should i just look locally? can a shop rewind my 35 much bigger?<br /><br />i've read about this somewhat....i don't understand the diff's between 1 wire or 3 wire, i think that's the options.<br /><br />thx
 
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navigator336

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Re: upgrading an alternator

Shiver me timbers! I'd like to run a slalom course behind your boat with the stereo at 1000 watts!<br /><br />Ebay has rebuilt marine alts I think. West Marine sells them rebuilt by Sierra for $150 (if you know someone with a Port Supply acct. at West Marine they're about $90.00. J.C. Whitney sells rebuilt marine ones for about $95.00. Just search for marine alternators on the web and you'll find plenty of rebuilts. I would guess yours could be re-wound for more output too. I'd just be leary, because the more it puts out, the harder it works and the more heat it generates. If it wasn't designed for the higher heat, who knows. <br /><br />If you have a 3 wire now, by all means stick with it. It will give you a little more output and slightly better regulation as one of the extra wires runs directly to the battery to sense it's voltage and turn the internal regulator on and off appropriately. A single wire is also sensing battery voltage but via the charging output wire. The third wire goes to the ignition so that the alt. field isn't energized when the key is off. A single wire alt. does this internally as well. <br /><br />If you don't mind the weight and can handle the size, Interstate makes a good 4D size deep cycle with about 200 amp hours capacity for $160 each. They're big (about double a group 27).
 
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ndemge

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Re: upgrading an alternator

... the 4D is a big battery.... but for bang for the buck... Golf Cart 6V batteries are the way to go IMHO....<br /><br />Put a amp meter on your power wire when you've got your stereo cranked with some good bass going..... you might be surprised how low amount of power they pull despite the fuse that is on them....<br /><br />don't get me wrong, they will still suck a battery down, but might help you with your math.
 
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bluewater19

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Bondo

Bondo

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Re: upgrading an alternator

That Might be a Great Alt....<br />But, It's Difinetly Not a Plug + Play......<br />And, Even though it Says Marine,<br />I Can't See Any Spark Shielding.....<br />It comes down to the Amount of Power the Battery will Accept, Rather than how Much the Atl. puts out..... <br />160amp is Really Big.....
 
A

airman

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Re: upgrading an alternator

Another important consideration is the regulator. Navigator, your math is good, assuming that the alternator really puts out its rated amperage. Most alternators won't unless you spend some $ on a good marine (external) regulator for it. If you've ever read the specs on an alternator, you'll find that they're usually rated based an a high rpm and a dead battery. I've found that my own 35 amp alternator rarely puts out more than 8 amps unless the batteries (4 90Ah group 27's) are really low. I usually cruise at 1500-1700 rpm though.
 
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salty87

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Re: upgrading an alternator

good stuff, i was looking at ebay and only see 1-wire alts. i looked at my boat yesterday and it's a 3 wire. <br /><br />is it hard to go to 1 wire from 3?<br />should i stick with the 3 wire?<br /><br />i don't want to jump to 160, i doubt there's room for it anyway...i've never seen one though. i've also read that you would need to upgrade some other wiring for that big of a jump. <br /><br />anyway, golf cart batteries would do the trick for sure, and i'd love to have the extra weight (good for the wake, ya know :rolleyes: ) but there's not enough room for 'em. i'll be re-doing the flooring, maybe next year, some battery boxes sunk in the floor will resolve that for me....someday.<br /><br />thx for reading<br /><br />i'll keep looking for a sturdy looking 3 wire. please post any other links you might find or have.
 
Bondo

Bondo

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Re: upgrading an alternator

is it hard to go to 1 wire from 3?
Click to expand...
To Switch,<br />Just Disconnect All of the Voltage Regulator Wiring,+ Toss It.....<br />For the 1 wire you Only need the wire going to the Battery lug on the Starter.....<br />
should i stick with the 3 wire?
Click to expand...
What Ever You Want.....<br />It Doesn't Matter......
 
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