Forums » Ask a Question

Use this forum to post your questions to our experts – you need to be logged on to do it (you can register here ), then scroll down to the bottom of this page and click the blue Post Thread words

If you can help answer the question, feel free to post a reply – you need to be logged on to do it (you can register here ), then hit the reply button on the thread.


To go back to the experts page click here>>


Posted: Thu Dec 25, 2008 8:32pm

Post Subject: Alternator

I have a Lister-Petter LPSW3 engine fitted with original 45amp alternator. This is fitted to an 90amp Sterling Alternator to Battery charger in turn charging one 110 amp starter battery and three 120 amp domestic batteries. I would like to fit a larger amperage alternator and would like to know if it is feasible to fit a larger alternator from a road vehicle as most modern cars seem to be fitted with large alternators these days. Also what would be the maximum size I could fit without having to change pulleys and belts.


Posted: Fri Dec 26, 2008 9:59am

Post Subject: Alternator

Dear James, I am fairly sure your engine electrics will be "earth return" even though they may look as if the starter and alternator have negative cables fitted to them. Set a meter to 20 volts DC and connect it between the engine battery positive terminal and a metal part of the engine. If it reads battery voltage you can fit a typical vehicle alternator. As far as I know most modern alternators use the same sized shafts so your original pulley should fit the "new" alternator but double check the exact size of the V so you can make sure the "new" alternator pulley has the same sized groove - just in case you can not change the pulleys. I would be reluctant to try to drive much more than a 70 amp alternator via a single V belt and take 90 amps as the absolute maximum before belt problems are likely. If your boat is equipped with a revcounter you will need to get an alternator off a car with an alternator driven revcounter, although many modern petrol engines use that method it might be easier to choose one from a diesel car that has a revcounter. You will need to ensure the "new" alternator has the same handed mounting brackets and they are of the same type (although it is usually possible to change a left handed alternator to right handed by removing the "through screws", twisting the front bracket and drilling out a thread. The gap between the front and back alternator my be slightly different but the bush in the back bracket can usually be gently knocked through the bracket to suit fit but make sure you support the bracket whilst doing this. If the "new" alternator is significantly "fatter" you may have to extend the slotted bracket and fit a longer belt but much depends upon the exact setup on the engine. It seems as if the Sterling unit can handle a 90 amp output so as long as you stay with my recommendations it should be fine but check with Sterling if you decide to fit a 90 amp alternator because when cold it is likely to deliver rather more than 90 amps. Tony Brooks

Most Read

Newsletter Sign Up

Canal Boat monthly newsletter
Sign up to receive our regular email newsletter

Our Privacy Policy

Like us on Facebook

Follow us on Twitter

Cache: Disabled for this object  Total Queries: 43.  Total Objects: 162.  Total Unserialized: 3. Total Runtime: 0.24 seconds.