twin alternator installation

Discussion in 'Electrical Systems' started by Timothy, May 12, 2009.

  1. Timothy
    Joined: Oct 2004
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    Timothy Senior Member

    I don't know if this is the right forum to ask this question but I will give it a try.I wish to install an additional 200 amp balmar alternator on my Perkins 4-108 . I am already running a 200 amp Balmar on two belts for the house bank and on another belt a 60 amp alternator for my starter battery and the water pump. I have no more space between the center board trunk and the power take off to install any more pulleys on the power take off so I must run the additional 200 amp altenater on the same two belts as the original 200 amp altenater . I think I can do this as long as I maintain sufficient surface area on the altenator pulleys. I have devised a way to do this in the space that I have but it requires that the bets turn around snub idlers with their backs bearing on the pulleys. I do not want to change the pulleys on the power take off or the pulleys on the alternators which are for half inch v belts. Can I use flat pulleys for the idlers (tension but no load ) or do I use all v pulleys and double v belts? Thanks in advance for any ideas.
     

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  2. mydauphin
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    mydauphin Senior Member

    I don't knowing anything about the pulley question, and I may be wrong in saying this, but why not replace 60 amp with 200 amp. Certainly 400 amp should be enough. The spend a little time mankind sure regulators work correctly...
     
  3. Timothy
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    Timothy Senior Member

    I would do that if I had room for the additional pulley on the power take off but I do not as the engine is too near the after end of the centerboard trunk.
     
  4. Landlubber
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    Landlubber Senior Member

    That is going to take about 10 hp from the engine, are you sure the 4108 crank can handle that from the front pulley.

    Do you really get 200A from the one you have now, most auto regs only supply half that or less, maybe the answer is to make better use of what you "currently" have.
     
  5. Timothy
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    Timothy Senior Member

    I think the crank can handle it, not sure about the bearing.If any body knows for sure I would like to hear from them. I am using Balmar's smart max regulator which with the addition of their controller allows for two alternators. I have agm 8d battery's which accept any amount of charge. The idea is to charge the battery's quickly at anchor while maintaing load on the engine. At 1200 rpm on the engine the alternator at present puts out about 150 amps. As I have separate cold plate 12v frig and freezers each with their own compressors it would be nice to have the power. Balmar makes a 360 amp alternator which they inform me would be fine on my engine but it is over $2000 . Scince I already have the two 200 amp alternators I want to go with them if I can.
     
  6. Landlubber
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    Landlubber Senior Member

    Hey Tim, you seem to be understanding of what is required, send Pistnbroke a PM, I am sure he will assist you, and let us know the result, interesting.
     
  7. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Leave out the pulley between the alternators. Bending a CV-belt backwards 180 degrees is not healthy for the rubber-canvas bond. With a multi-V or timing belt you can do this without shortening the life, but a normal V-belt is not suitable for such acrobatics. Without the idler an angle of over 100 degrees is covered, that should be enough for a twin belt construction and a 10 hp load.
     
  8. Timothy
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    Timothy Senior Member

    -CDK Thanks. I more or less thought that to be the case but was worried that there would not be enough surface area on the alternator pulleys without it. I have seen double V belts (back to back V) advertised that apparently overcome this problem but that require pulleys of no less than 4" diameter.
     
  9. Arnot
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    Arnot Junior Member

    You might have a couple of other problems here...
    The torque requirement of two 200A alternators is going to be very high at lower speeds and assuming that battery charging is an important priority, you will want to keep the engine speed as low as you can to reduce noise and fuel consumption.

    The potential problems are;
    1) It is likely that at low to medium engine speed, the torque requirement of the alternators when the batteries are flattish will exceed the engines ability to provide it and you will hit a rev limit until the batteries are more fully charged. The symptom is that the engine does not respond to the spped control apart from making a larger cloud of black smoke.
    2) There is a limit to the torque that two "V" belts can transmit and I suspect that you are already near this. If you add another alternator you will probably find that the belts quickly stretch and start to burn.

    It might be an idea to see if your present alternator is actually delivering what it should, it may be that there is some inadequacy in the installation that is preventing this. Alternatively you may just have to learn to be patient ;-)

    Regards

    Arnot
     
  10. Timothy
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    Timothy Senior Member

    I realize that the limit for half inch belts is supposed to be 100 amp per belt but Balmar makes a 310 amp alternator that runs on two belts and produces 300 amps at 5000 rpm (alternator). I use a field disconnect switch on the regulator and only charge battery's when at anchor or under sail.So far I have no problems with belts( replace once every two years running about two hours a day). I tried too install one of the 200 amp alternators on an old Lister Peter 6 hsp single banger, It worked but I experienced the over loading problems you describe. Do you really think if I install the second alternator presuming the belt problem can be dealt with, that 10 hsp from a 50 hsp engine run at mid rpm is over loading the engine. I know we are talking torque. But?
     
  11. Arnot
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    Arnot Junior Member

    It is going to depend on the gearing of the alternators, the torque curve of the engine and the torque curves of the alternators.

    The gearing is a function of the size of the pulleys on the engine and the alternators, the torque curves you are going to have to find out from the respective manufacturers.

    I am far from sure that you will have a problem, it's just that if you do then you will have wasted a lot of effort and money! It's best to be as sure as you can on this one.

    As you identified, it is about torque, and a 310A alternator delivering full pwer at 5000rpm will take the same torque as a 165A alternator delivering full power at 2500rpm. The question is do you really want to have to run your engine at the sort of speed necessary to achieve this? Alternators, as they start to come on charge, tend to draw a large amount of torque. I have attached a pdf from Prestolite that illustrates this well and is pretty much what they all do!

    FWIW, this sort of thing falls right into the middle of my day job and I have nightmares about running twin alternators from a single drive pulley, there are all sorts of potential problems as well as the ones I mentioned such as a minor variation in pulley size or regulator time constant causing a "beat" effect between the two alternators.

    Just as a thought, could I suggest that you get hold of a good clamp on ammeter and voltmeter and plot the voltage and current against the engine speed? You may well find that in practice you can get a good increase in charging current by altering the gearing or regulation system wiring.

    Correctly configured, a 200A alternator should maintain a battery bank of 1000Ah and unless yours is significantly bigger it is doubtful that another alternator will help. Batteries are generally more or less self limiting as far as the charge current they will accept and convert into stored charge.

    Regards

    Arnot
     

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  12. Timothy
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    Timothy Senior Member

    My battery bank is indeed 1000 amp hours. I originally had Surette batteries which were very good but like all lead acid battery's their charge acceptance rate was limited to about 25% of battery capacity and only up to about 80% charge (hence the 200 amp alternator) I have recently changed to AGM battery's which can be recharged given enough juice in half an hour according to an article in Professional boat builder by Nigel Calder. So I thought since I already have the other 200 amp alternator I would give it a try. Apparently the problem most encountered when switching to agm batterey's is that the existing alternator that was sufficient for the lead acid battery's soon over heats and burns out because of the increased demands of the agm battery's. The part of the hype for agm battery's that I can confirm is their ability to hold a charge when unattended. I went to Thailand for six months and left my boat on the hard through a Canadian winter and when I returned the battery's were still over 12 volts. I think from the responses I have received I am better off keeping the second alternator as a spare and waiting for that 270 watt solar panel Sanyo keeps promising to be available and at a reasonable price. At 31" by 61" it would make a nice Bimini.
     

  13. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    Timothy, I thought of something like your idea and am looking into Outback has a battery charging system that will get most very watt produce. Outback Power FLEXmax 80 MPPT Solar Charge Controller, would be attach to 200 amp alternator without regulator to let it produce max voltage and amps then let outback bring voltage down. Perhaps multiple of these would work for you. It is a matter of effiecieny in generation and conversion. I am using BO panels that produce 44 volts.
     
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