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fin
New member
Username: fin
Post Number: 1
Registered: 07-2008
| | Posted on Saturday, July 12, 2008 - 07:25 am: | 
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hi im in need of some advice.im running a dorman 3lb in my norrow boat tug. we r living aboard so i have up graded to a 160amp bosch alternater and sterling digal reg. but even with a 40 cm pulley on the fastest pulley on the end of the engine and the smallest i can find for the alternater it still will not spin fast enough.when i rev the hell out the engine i can get the charge light to go out but the voltage drops to 12.9 when on the move rather than 14.7. how can in crease the speed. tryed many pulleys on differant parts of the engine still no joy.the old alernator wasnt much better ran out of ideas. is there a way round this as most old engines dont rev that high i cant be the only one. |
oslin04
Member
Username: oslin04
Post Number: 17
Registered: 10-2006
| | Posted on Saturday, July 12, 2008 - 08:10 am: |
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Hi fin,
Have you thought of welding or bolting a large pully on to the engine pulley there are a lot around providing you have room, you might try a compresser or machine tool pully, if not it would be possible to to attach a small reduction gear train mounted seperatly and driven by a belt from the alternator and a belt from the engine, gearing up rather than down but that would require a lot of bracket making,
one last thought if you can find an alternator from a Gardener engine they have high output at low revs and produce full charge on tick over but they are expensive for that reason.
hope this helps
Keith |
jb_castagnos
Senior Member
Username: jb_castagnos
Post Number: 380
Registered: 07-2002
| | Posted on Saturday, July 12, 2008 - 09:38 pm: |
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I don't know the layout of your engine, but if the waterpump turns faster than the crank, you could put a large pulley on it and get a double step up. You could also look for the largest alternator diameter you can find. The large rotors have more surface speed and will charge at a lower rpm. A small alternator, even though high output, depends on high speed. An alternator turning too slow will run "full field" and tend to overheat, newer alternators will protect themselves, older units will destroy themselves. |
martyn pitman
Visitor
| | Posted on Thursday, September 11, 2008 - 12:01 pm: |
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I dont think you have a pulley problem it may be a alternator/wiring/regulator problem. Most alternators need to be spinning at least 1500/1700 rpm to start charging and produce full charge by 5500 rpm ish. therefore if you have a 400mm pulley and the engine is at idle cant remember what a dorman 3lb is but lets say a low 400rpm if you were to have a 100mm pulley on the alternator you would be getting 1600rpm on the alternator and therefore should work.
I would suggest using a 70mm pulley on the alternator and the 400mm on the crank this would give you 2285rpm at idle and would be well into full charge at normal canal speeds.
Hope this helps
martyn
marinepowerservices.co.uk engineer |
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