boatmike
regular
Reged: 30/06/2002
Posts: 4218
Loc: Solent
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Joe,
Thanks for the input so far. Are you able to say what the output of the 110A alternator would likely be in practice? Is 50A reasonable?
I have a conventional diode splitter with the sensing wire at the batteries on the 50A and have been getting voltages of 16.5 - 17 indicated with about 25A on boost which seems to suggest the wiring is indeed marginal anyway. I would expect 14.8 plus about 1.5 for diode plus cable maximum (?). If I fit a 110A I will seriously examine/replace the cabling but how big should it be? In am assuming for that amperage I will need 25mm2 battery lead. Also would you expect the single 1/2" belt drive to be man enough? I see the driftgate alternator is fitted with one as standard but am considering fitting twin pulleys is this OTT?
If I assume 50A at 15.5V thats 775W which is a little over 1HP assuming I have got my sums right (?) assuming 100% efficiency. 110A would be 2-2.5 HP theoretically but I think the sterling will need the trip switches re-set for the bigger alternator (I will have to look up the installation manual again) and will not allow a higher rate of charge than the batteries will tolerate which will probably be no more than 50A. Either way I will fit a switch in the activation line of the stirling to allow me to reduce the charge rate when I need maximum output of the engine to drive the boat.
Edited by boatmike (10/05/2008 08:15)
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boatmike
regular
Reged: 30/06/2002
Posts: 4218
Loc: Solent
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Jerry,
I hear what you say but I believe the alternator is "fried" due to running too hot for too long and it's on the small size anyway. I would rather err on the side of a new bigger one if the bill comes to less than £200. I do have things like fridge running constantly and use the eberspacher and cabin lights a lot in cold evenings so tend to hammer the batteries.
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boatmike
regular
Reged: 30/06/2002
Posts: 4218
Loc: Solent
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Crossed posts there John but you will see from my recent posts that you are confirming my view. Alternator too small. Cabling probably needs replacing with bigger especially as its quite a long run of cable, and Sterling will need to be set up for new alternator. How big is your alternator and does it run off a single 1/2" belt OK?
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Captainslarty
regular
Reged: 12/08/2007
Posts: 1949
Loc: Currently La Coruna Spain
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You have a problem with your cabling Mike. 17v is too high really.
for the 50 A unit, 25 mm2 is adequate, for the 110, 35 as a minimum, I use 50mm2 on a balmar 130. with SHORT runs.. you say you have a lot of cable length ? if so, definitely 50mm2.
a lot of your problem, knowing the voltage now (And presuming that is AT THE ALTERNATOR - not at the batteries !) then the cabling is inadequate.
The diode splitter will drop 0.6 to 1v. easilly made up at the alternator. I would aim for a max voltage at the alternator of 16v. assuming 14.8 max at the batteries i(f wet cell)
The other thing to consider, is how are you reading the output current - with a splitter you have two banks, are you monitoring just one, or both ?.
Max recommended size of alternator on a single belt is 130 Ah.
the output from the alternater to a disharged bank (Assuming a 110 unit and proper cabling - ) should peak up to 90 amps for a short period (You will very rarely if ever get the maximum due to heat and the fact the alternator was not designed for marine use - ie, a higher voltage than automotive and much more use)
My 130ah alt can peak at 115 for short periods - that is controlled by a balmar reg also.
The stirling unit should not need any adjustment - afaik the dip swiches are only for the battery bank TYPE. there is also a fuse that can be fitted in two positions for either neg or pos field reg alternators.
No problem on the switch, there are deatails in the stirling reg manual afaik.
Hope that helps..
I would firstly change to 50mm2 cable, keep the runs as short as possible. try the older alternator first.. the cable will be oversized a tad for your existing alt, but thats better than undersized and allows you to go up in size on the alternator without changing calbing again.
Hope that helps Mike.
Ps Charles Stirlings instruction re voltage drop and cabling are very comprehensive (Assuming the pro digital unirt) - have a browse through that as well.
Cheers n beers
Joe
--------------------
PM me for info re SSB's etc. Bought, sold, repaired, fitted and optimised.
Edited by Captainslarty (10/05/2008 10:09)
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boatmike
regular
Reged: 30/06/2002
Posts: 4218
Loc: Solent
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Thats very helpful Joe thank you. I am sure you are right about the cabling. You can see from my earlier posts that I had already reached that conclusion. I just looked up current ratings for cable and agree with your sizing. The charge cable will end up bigger than the starter motor cables but I guess they only have to pass current for a short burst. The charging line cables have to pass current for extended periods....
Yes the voltage mentioned is at the alternator and showing up on the engine panel. I actually have three batteries on a 3 way split diode. There is a shunt on each line from the diode splitter to each battery which is also showing a high voltage (15V) but I am advised that this is probably due to the sensor wire going to the battery side of the diode rather than the battery terminal itself. This I shall also change. The shunts are wired directly to a Stirling battery management panel which allows me to see volts and amps to each battery. The sensing wire goes to the battery supplying the fridge, eberspacher, lights etc, which is going to be the highest discharged. The second battery serves instruments and essential services, The third battery is for engine cranking only and seldom gets heavily discharged.
There are 2 sets of dip switches on the Stirling. One is set for voltage re wet or gel batteries. The other controls the charging cycle. for a small alt on big bats it extends the boost cycle time. The other way around reduces it. They are the ones I will need to reset to avoid boiling batteries with a bigger alternator.
I can't try the old alternator Joe, it does not work! The whole point of the exercise is to aviod spending money on repairing it when it's too small anyway. I think in a way it's a blessing in disguise that it has failed as I now have an excuse for buying a bigger one and upgrading the installation generally.
Thanks a whole lot for your very helpful input (and that of others of course) that in true forum tradition has helped me to get the details clear in my mind. I shall post again when the project is completed and tell you how I got on.
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Captainslarty
regular
Reged: 12/08/2007
Posts: 1949
Loc: Currently La Coruna Spain
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Nice one Mike.
Hope you get it all sorted out - I am sure you will.
happy charging and have fun
Joe
--------------------
PM me for info re SSB's etc. Bought, sold, repaired, fitted and optimised.
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