How do you limit amps for charging?

Discussion in 'OnBoard Electronics & Controls' started by Raftman1979, Oct 20, 2008.

  1. pistnbroke
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    pistnbroke I try

    Sorry Fanie you are making the classic mistake ...yes low internal resistance of 0.002 ohm will allow large discharge currents BUT when charging the alternator has to overcome the at least and rising 12.5v of the battery with its max 14.4v output . the internal resitance is not relavent when you consider the resistance of the connecting cables and resistance of the alternator internals ..this differecnce of only 1.9v soon reduces to zero as the battery charges to its fully charged state at 14.4v...
     
  2. robherc
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    robherc Designer/Hobbyist

    Here, let's solve the entire argument at once.

    1. The alternator puts out 75 amps at closed-circuit conditions (i.e. 0 volts) and 14.4 volts (regulated) at anything from about 0-10 amps.

    Therefore, if you still have 6+ volts energy in your batteries (which would be under 1/4 charge), you should still be WELL under 35 amps transferred from the generator due to the lowered voltage differential (6 volts is a lot more than 0).

    If you're still worried about it, buy a 15V, 1F capacitor from Wal-Mart (intended to cusion the load of a too-big amp & subwoofer on your car battery) and install it in parallel with the batteries. The capacitor will soak up any excess amperage until the batteries' charge (and thus resistance) comes up a bit & everything balances out. The capacitor will also help smooth out the draw on the batteries during the surge every time you turn any electronic item on your raft on/off.
     
    Last edited: Jan 17, 2009
  3. pistnbroke
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    pistnbroke I try

    I think you should delete all that post robherc every word is rubbish

    The alternator output is 75 amps at 14v if you put sufficient load on it with say a carbon pile variable resistor. Alernators usually run to 12000rpm so you need at least 6000 for full output..It is self regulating for current and cannot be overloaded. where you might ( ha hal) be confused is that a professional would short out the voltage regualator for this test .

    Your battery is considered fully discharged at 10.8v with a 1/10 amp hour load...whats all this 6v and 1/4 charge crap and that capacitor will do nothing ...

    so go find your delete button and remove the techocrap
     
  4. Fanie
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    Fanie Fanie

    No classic mistake.
    LA batteries needs to be voltage limited or they may be damaged
    SAL batteries should be voltage and current limited or they may be damaged

    Both is a function of the charger you use and for the battery type.
    An alternator's composition / size & ,materials used determine the max amount of power it can output. It's like a small 24VA transformer can say deliver 2A max at 12V, a 240VA transformer can deliver 20A at 12V. If you add a regulator on both then the regulator would determine what gets put out in terms of voltage and current, if it is designed to do it.

    It is during this time you call 'soon' that the current may be excessive. A large battery may take quit long to get it's voltage lifted, and in the case of a SLA you can damage it if you put an alternator on it.

    BS. Alternators are designed to de able to supply full power (voltage and current) at much lower rpm. When you rev the car engine up, only the frequency of the three phase increase.
     
  5. pistnbroke
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    pistnbroke I try

    I think you are on a different techo planet ..jump of and return to earth ...alternator ok for all types of battery you will find on a boat . What your are quoting is techo crap and no help to anyone ...please stick to what you are qualified to comment on or you just confuse people and cost them money ....

    Enough qualifications on auto electrices to shut down this site !!!
     
  6. Ratch
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    Ratch Junior Member

    Have an idea :idea:

    If you add 2 diodes in series and assuming that the alternator is set for 14.4v then you have reduced the charging voltage by 1.2v to 13.2v and this is normally what is used for float charging. Having the diodes in circuit while bulk charging will also lower the amount of amps that can be delivered to the battery due to the lower voltage.

    I still think you can hook the alternator up directly to the battery without worrying about all this stuff.
     
  7. CDK
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    CDK retired engineer

    Sorry pistnbroke, you're not only rude, but also wrong. Fanie is correct.
    The 14.4 v. threshold from an ordinary alternator can and will damage gel batteries. When charged with more than the current printed on the label (1/10 to 1/20 of the nominal capacity), or over 14,0 v. the safety valve opens because of the internal gas pressure. This ruins the battery and if you return it, the supplier will waive any warranty claim because you maltreated the battery. I learned this the hard way by connecting 20 pcs. 12V/10Ah in parallel with over 400 Ah of ordinary LA batteries. All 20 died within one month, the wet batteries were still in good health..
     
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  8. robherc
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    robherc Designer/Hobbyist

    WRONG, and you PROVED IT YOURSELF! Go back to High School and quit trying to insult people who actually have a CLUE what they're talking about!!!

    1. If you "short out" your voltage regulator, and put a high enough load on the alternator, the potential voltage drops to (nearly) 0...thus giving you 75 amps at (nearly) 0 volts...check your High School textbooks....somewhere around chapter 1 or 2 "Voltage and Current" and "Ohm's Law"

    2. Anytime you wire a capacitor in series with a battery, the capacitor does a LOT of power-conditioning for the battery. It absorbs excess charging voltage to smooth the current taken up by the battery at the beginning of a charge, and it is the first to give out current/voltage for the high-draw "surge" that almost all appliances (even the LEDs he'll be using at night) require to reach their peak efficiency immediately after having been energized. (check your High School textbook again, I'm sure you'll be interested in chapter 5 "Capacitors" and chapter 7 "Initial Loads")

    3. I don't know about "deep-cycle" betteries' power levels, but I know I've started my car (over 100 amps to crank it) off a 550CCA battery that was reading below 10V (about 9.8V actually), and it was about -3C out when I did it, so somehow, the <55CCA you're saying it should've had left almost a full Voltaire higher than that doubled itself in a lower-charge battery! (were you thinking LiIon? 'cuz for NiCD, and NiMH the voltage at discharged state is even lower than for Lead-Acid, and I've seen Lead-Acids work SOME down to 8.5-9V...just not well at all)

    4. My Favorite "...with a 1/10 amp hour load" now that's just precocious! How, EXACTLY, do you measure a 1/10 amp hour load...with a time machine?!?

    Wow, can you just shut up here please? You're beginning to offend the last few examples of intelligence in the "great" human race! YOU are the one confusing people, and I PRAY they have the sense not to listen, or you'll cost them money for sure.

    Now, for everyone else:
    With 2 deep-cycle batteries in parallel, I think he SHOULD be fairly safe running the alternator. If there are still any concerns, he could simply use a charge controller, or a capacitor, or almost any on the ingenious (if a bit unconventional) ideas I've seen in here. Most of your ideas would work to control the current, but as he already said he doesn't mind paying for a high-quality solution, I think "correct" answer to the original question here would be: "What is a Charge Controller" ... available at any marine supply store/website.

    P.S. Sorry everyone else had to listen to that rant, I just couldn't handle reading the nonsense & insults spewing from that individual anymore. :eek:
     
  9. robherc
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    robherc Designer/Hobbyist

    CDK, thanks for the useful info...I'll think about that & see if I come up with anything else that might help here. :)
     
  10. pistnbroke
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    pistnbroke I try

    Unfortunatly misunderstanding of alternators and batteries is a problem workld wide.People get very set ideas based on folklore . My knowledge comes from 30 years as a consultant on auto electrical equipment to car makers and canal boats. I have enough qualifications both low level through to degrees in this subject and dont tolerate technocrap....

    I/ you should not be connecting batteries in parallel as one runs the other down ..you can get away with it for a time if they are both new and identical and used on a daily basis....

    2/ a lead battery is only fully charged when it gets to about 15-15.3v . Unfortunatly it gasses at 80% charged so modern alternator limits to 14.4v. Thus what we call fully charged is in fact only 80% compaired to the odd days of dynamo systems..when we topped up the battery with water every week !!

    3/ putting two diodes in series is not a good idea in most circumstances as this drops the voltage to 13v ( 14.4-1.4 ) which is a bit low . If you only charge your battery to 13.6v it will only last 6 months as it will be sulphated for most of the time and this will become permanent sulphation. I cold see one diode being usefull for float charging a small gell battery say 12v/10ah but no good for a starting/aux battery.
    4/ if you put a capacitor in series with your battery ( did you mean parallel) then once the capacitor is charged (seconds at most) you will have no charge current...two metal plates seperated by an insulator in series ...??? eh?
    4/ the details of load testing the alternator come from the alternator manufacturers with whoom I have worked for 30 years ..you put sufficent load on to pull 75a at 14v and you need plenty revs
    5/ I would not use an alternator to charge a 12v 10 ah battery as inital currents could be high but as an alternator was not designed to charge small gel batteries its not important ...anything over 30 ah will be fine.
    6/ If you connect 20 gel batts in parallel it only takes one weak one to run all the others down and they dont recover well if over discharged..sillly idea anyway ..must have cost a fortune....
    7/ a current of 1/10 of the amp hour capacity means to those qualified in this subject that for example a 100 ah (10 hr rate ) battery would be charged at 1/10 of 100 ah in amps eg 10 amps ...its quite common to quote the charge current as a fraction of the AH capacity in amps

    1/10 of the AH capacity in amps woud be a normal charge rate for a fully discharged battery and take 14 hours to charge it

    perhaps a trip to the libary for a good auto electrical book would be a good idea for some of you
     
  11. Landlubber
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    Landlubber Senior Member

    pistnbroke,

    Well mate, it seems that the arm chair admirals are at it again......i read many articles on this forum, 99% are crap, there are some very good and knowlegable people here (PAR, Guillermo, Rick in Melbourne etc etc), and there are many comments by people that have obviously had no real boating experience other than a ride on the harbour ferry to visit Grandma.......

    1/10 of the capacity has long been the best maximum "normal" rate............
     
  12. pistnbroke
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    pistnbroke I try

    thanks for that Landlubber when I first found this sight I thought great a lot of knowledgable people but as you say 99% write crap to quote yourself ( moderator note that )
     
  13. CDK
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    CDK retired engineer

    Quotes from post #25:

    "I/ you should not be connecting batteries in parallel as one runs the other down ..you can get away with it for a time if they are both new and identical and used on a daily basis...."

    Solar systems often need 1000 AH or more storage capacity to bridge cloudy days. The only way to do that is parallel wiring. According to your statement, if one cell in one battery fails, you should replace all of them at the same time. But you would be throwing away a lot of good batteries then.
    The university in Amsterdam where I studied 45 years ago, had a battery room with several hundred single sell glass batteries, each the size of a large aquarium. Back then they did not even throw the one away that failed, but replaced just the single plate or separator. Most of the time draining and removing the sludge was enough to bring a battery back to life again.

    "2/ a lead battery is only fully charged when it gets to about 15-15.3v . Unfortunatly it gasses at 80% charged so modern alternator limits to 14.4v. Thus what we call fully charged is in fact only 80% compaired to the odd days of dynamo systems..when we topped up the battery with water every week !!"

    Battery voltage is temperature dependent. To determine the state of charge you need to test the specific weight of the electrolyte. Alternators set at 14.4 volts without temperature compensation cause damage to modern sealed car batteries in a warm climate. Companies like Varta and Exide have reduced their aftermarket warranty period in the Mediterranean from 3 years to 12 months.

    "6/ If you connect 20 gel batts in parallel it only takes one weak one to run all the others down and they dont recover well if over discharged..sillly idea anyway ..must have cost a fortune...."

    These were new 12V/10AH units, left over from another well paid experiment. I used them in a solar system with a Siemens microprocessor charge controller. These devices must be programmed and have different settings for open, sealed and gel batteries. Because the majority was wet, sealed I did not change the settings. Unlike wet batteries, the gel types do not offer much resistance to an excessive charging voltage because the electrolyte cannot freely move around. Instead, hot spots form, followed by a gas bubble, leaving a 'dead' spot on the negative plate. That is why these batteries only reach their designated lifetime when both current and voltage are monitored. A crude 14.4 volts alternator quickly and silently kills them.
     
  14. robherc
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    robherc Designer/Hobbyist

    Perhaps READING my post before going off half-cocked would be a good idea for you???
     

  15. Fanie
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    Fanie Fanie

    The original question was how to limit amps for charging.

    For LA batteries a current limit is not required. LA batteries love the high current bump at the beginning of the charge and the current falls off when they reach 13.8V to 14V.

    SLA batteries are different from LA batteries and they need to be voltage and current limited. SLA batteries wants to be charged to 14.6V while their current gets kept below the spec.

    An alternator is not really a good option to charge SLA batteries with. Even if you can adjust the output voltage to 14.6V you still have the current limiting to consider.

    Whichever way you look at it, SLA batteries needs some electronics to do their charging with.

    Despite their seeming drawback with the charging, SLA batteries are in my opinion much better than LA batteries. They are maintenance free, always clean, charge up faster than LA (despite the charge current limit) and if looked after gives years of good service. My personal choice.

    Both LA and SLA's doesn't like to be left discharged for some time. SLA's have a better shelf life than LA, but they should be kept fully charged.

    Many boaters buy small solars for their boats for only one purpose, keep the battery full. Good idea if the boat is not attended to or used full time, and even then...

    So in my opinion an alternator is not good for SLA's.
     
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