Can high amp alternators harm batteries?
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Can high amp alternators harm batteries?

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    Senior Member Rivernut's Avatar
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    Default Can high amp alternators harm batteries?

    I see 12V alternators up to 300 amps for sale. What happens if the battery is run low and the boat takes off at full throttle? Does the battery really get hundreds of amps thrown at it? Traditional high amp battery chargers have 40 amps as the cut off with bursts of 60-100 amps for starting. What's the most amperage an M-30 AGM battery will accept when drawn down? Does it get to even 50 amps before the voltage hits 14.3 and backs off the regulator?
    Last edited by Rivernut; 07-19-2010 at 05:02 AM.

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    gn7
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    I have asked this very question about batteries that SUPPOSEDLY require special low amp chargers. What happens when even a 100 amp alternater is used and my Optima battery is almost dead and a you jump start it. All I got was a shrug and stare.



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    Lord of the Drinks Havasu Hangin's Avatar
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    I think it probably depends more on the regulator. I believe the high amp alternators only put out what the draw is on the system, based on the regulator.

    How many amps the regulator allows to re-charge a dead battery is probably small compared to an AC charger. You can always tell a high amp charge by how warm the battery gets- I've never been able to get a battery warm with an alternator.
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    Senior Member Uncle Dave's Avatar
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    they can but rarely do. Certain battery chemistries are more susceptible to damage than others.

    Couple of things-

    You'll need a serpentine belt vs a 1/2 inch v belt to drive any alternator over 100 amps effectively, much less 300.

    My Ilmor 710 has a 165 AH alternator and Ive never seen it go above 14V when charging a 70% depleted Odyssey 2150. (I left the air conditioner on most of the night)

    AGM's much lower internal resistance gives them a habit of taking everything your alternator can throw at them and can cause alternator overheating due to the constant high load. Where lead acids will only accept a charge to a certain point.

    If you are really concerned about it you can buy kits that limit voltage.

    Read more about high performance alternators at http://www.balmar.net/


    Uncle Dave

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    cfm
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    I thought the alternator can only put out what the battery draw is ? Meaning, what the battery will accept (edit in:at a time.) Based on this thought, the initial draw can be quite high but will even out at a much lower amperage very quickly.

    Say if you had 50amp draw from accessories - the alternator wouldn't produce more than 50 amps even if alt is rated for 200amps.

    Same for batteries, they will only accept (ask for / demand) so many amps even if in need of alot more charging.

    Above is my assumptions / lack of knowledge in this field.
    Last edited by cfm; 07-19-2010 at 08:47 AM.

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    Senior Member ap67et10's Avatar
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    first off, there is no need for an alternator above 65amp in your boat, unless you run multiple batteries and/or a modified stereo system. However you can cause far more damage to a battery by having it operate in a discharged state, with too small of an alternator. meaning, if you are running your engine, and blasting your stereo and can only get a running voltage of 12.5-13.5V, you are asking for premature battery failure. At that time you need a higher amp alternator. Your alternator needs to be able to support every accessory on your boat/car and maintain a 13.5-14.5 v charge on the battery, if you see less than that, your battery is now supporting part of the constant load in a system and its not designed to do that. (some batteries are, but most people don't run those). When you have your 300amp alt. and you fire up the boat, it will output a large amount due to the discharged battery from starting and also from it being static before starting. once at 13.5-14.5V it will only be outputting what the battery can take in. And theoretically if you had a completely charged battery that maintained 13.5-14.5V (obviously batteries static charge is around 12.6V) you would see no output on the alternator....no matter what size. Also, if you were overcharging a battery with too many AMPs, it would be seen in the voltage readings. if you had an amp clamp on the cable from the alt. and were reading 200amps constant (can just about guarantee you won't see that) and only see 13.8v on the battery, well the battery isn't being overcharged. if you have no accessories on, you better start looking real close cause you have a MAJOR wiring/resistance/current draw issue. If you were actually putting out too many amps, it would be seen in a 16-18V reading on the battery....which can be bad, however most batteries are more resilient to a 16-18v charge than you'd think.

    Andrew
    Last edited by ap67et10; 07-19-2010 at 10:18 AM.

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    Senior Member Uncle Dave's Avatar
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    Quote Originally Posted by cfm View Post
    I thought the alternator can only put out what the battery draw is ? Meaning, what the battery will accept (edit in:at a time.) Based on this thought, the initial draw can be quite high but will even out at a much lower amperage very quickly.

    Say if you had 50amp draw from accessories - the alternator wouldn't produce more than 50 amps even if alt is rated for 200amps.

    Same for batteries, they will only accept (ask for / demand) so many amps even if in need of alot more charging.

    Above is my assumptions / lack of knowledge in this field.

    AGM's will draw more than they should for best battery life.

    In other words they will accept a charge rate that is 80% of their total capacity even though 20-30% of total capacity is best for overall life.

    The trick is really temperature compensated charging. (Xantrex)


    Uncle Dave
    Last edited by Uncle Dave; 07-19-2010 at 11:47 AM.

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    Senior Member Rivernut's Avatar
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    I have 4 m-30's with one of them serving as the crank and accessory battery and the other three as trolling motor batteries for my jet bass boat. I have a Stealth on the fly charging system that takes 40 amps and many accessories such as livewell pumps, 4000 and 1000 GPH bilge pumps, stereo, etc. I just installed a 105 amp 1 wire internet special @ $85 and wondered if I could go even higher. I put 4 gauge wire in, so no fires!

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    cfm
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    Quote Originally Posted by Uncle Dave View Post
    AGM's will draw more that they should for best battery life.

    In other words they will accept a charge rate that is 80% of their total capacity even though 20-30% of total capacity is best for overall life.

    The trick is really temperature compensated charging. (Xantrex)


    Uncle Dave
    Well, that explians why I have not had all that great of 'luck' with AGM's.

    Thank you.

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    Senior Member Uncle Dave's Avatar
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    Quote Originally Posted by ap67et10 View Post
    first off, there is no need for an alternator above 65amp in your boat, unless you run multiple batteries and/or a modified stereo system. However you can cause far more damage to a battery by having it operate in a discharged state, with too small of an alternator. meaning, if you are running your engine, and blasting your stereo and can only get a running voltage of 12.5-13.5V, you are asking for premature battery failure. At that time you need a higher amp alternator. Your alternator needs to be able to support every accessory on your boat/car and maintain a 13.5-14.5 v charge on the battery, if you see less than that, your battery is now supporting part of the constant load in a system and its not designed to do that. (some batteries are, but most people don't run those). When you have your 300amp alt. and you fire up the boat, it will output a large amount due to the discharged battery from starting and also from it being static before starting. once at 13.5-14.5V it will only be outputting what the battery can take in. And theoretically if you had a completely charged battery that maintained 13.5-14.5V (obviously batteries static charge is around 12.6V) you would see no output on the alternator....no matter what size. Also, if you were overcharging a battery with too many AMPs, it would be seen in the voltage readings. if you had an amp clamp on the cable from the alt. and were reading 200amps constant (can just about guarantee you won't see that) and only see 13.8v on the battery, well the battery isn't being overcharged. if you have no accessories on, you better start looking real close cause you have a MAJOR wiring/resistance/current draw issue. If you were actually putting out too many amps, it would be seen in a 16-18V reading on the battery....which can be bad, however most batteries are more resilient to a 16-18v charge than you'd think.

    Andrew
    This particular group tends to think stereos and lights when a whole other market segment thinks, gps, finder, plotters, Ac, Radar, Stereo, lights, screens.

    I can put a 60 amp + load on my systems cruising at night running all my equipment and AC.

    shut the engine off an sit for a while Ive got to make up that drain somehow.

    I need a 165AH alternator.

    Uncle Dave

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    Senior Member ap67et10's Avatar
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    Quote Originally Posted by Uncle Dave View Post
    This particular group tends to think stereos and lights when a whole other market segment thinks, gps, finder, plotters, Ac, Radar, Stereo, lights, screens.

    I can put a 60 amp + load on my systems cruising at night running all my equipment and AC.

    shut the engine off an sit for a while Ive got to make up that drain somehow.

    I need a 165AH alternator.

    Uncle Dave

    This is very true, I tend to forget about all those other accessories, because I would never have them on my boat. But its very difficult to forget about the massive stereos, because thats all you see and hear when on the water. Which is another thing i don't have on my boat though...but thats just me.

    But you are correct...there are many accessories that would cause the need for a larger, more capable charging system.

    Andrew

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    Senior Member Uncle Dave's Avatar
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    Quote Originally Posted by cfm View Post
    Well, that explians why I have not had all that great of 'luck' with AGM's.

    Thank you.
    Curious.....

    Odysseys, Optimas or other ?

    UD

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    cfm
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    Quote Originally Posted by Uncle Dave View Post
    Curious.....

    Odysseys, Optimas or other ?

    UD
    Optima Blue's. A bunch at 1-2yrs and poof...no good...wouldn't hold a charge any longer and my computerized battery tester would indicate '0 battery health' and 'dead cell.' Have run a few red's and yellows for approx 4-5yrs before replacement.

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    all wet cell batteries discharge at the same rate they charge its jus a fact so knowing that why would anyone be scared of using a high amp alt? now i can see if its a 1 wire layin down 120amps allll the time even after the battery is nice and hot, that's jus like leaving a battery charging on high for too damn long, shits gonna heat up inside the battery. i jus count the amp output i think i'll have, tehn try for 10amps over tha with the alt so battery gets recharged from cranking the motor but the motor lives on the alt output , not the battery
    dont know bout gel cells or absorbed glass mat batteries, i know the gel cell will charge fine jus like a wet cell, but the agm does have to have a special charger or it'll overheat internally from what im told. get a battery nice and hot and the cells will flew, touch each other and its replacement time then

    Dare to be different, if it turns out great you can claim you planned it that way.

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