darbon 0 Report post #1 Posted November 15, 2013 Hi all. I'm looking at a 100amp 12v second alternator for a BMC 1.8. Would this amperage Alternator be ok for the engine? Suggestions welcome. D Share this post Link to post Share on other sites
Arthur Brown 69 Report post #2 Posted November 15, 2013 I suspect that a 1.8 will drive both easily BUT if using only one belt don't expect it to last long and even if using two belts remember that taking 2 -4Kw off the engine will restrict the power available for propulsion. Share this post Link to post Share on other sites
alan_fincher 2809 Report post #3 Posted November 15, 2013 (edited) You say second alternator, so are presumably also going to be retaining an existing lower powered on? What current is that, and do you plan to use it just for starter battery charging.I think the issue with ones as big as 100 amps will not be so much the load they place on the engine, but coming up with pulleys and belts to drive it adequately. Generally people seem to thing only up to about 70/80 amps is really sound with a standard 10mm "V" belt. Edited November 15, 2013 by alan_fincher Share this post Link to post Share on other sites
darbon 0 Report post #4 Posted November 15, 2013 Yes, I have a 30amp standard alternator at present. I have a triple crankshaft pulley from Calcutt boats, so each would be driven separately. I'd heard that 70-80 should be around max for a 10mm V. But I've also read that a 100amp alternator won't crank nearly that amount at idle/low revs. In case it makes any difference, I have a 180amp sterling alt-batt charger. I'd quite like to use as much of that 180amps as possible! Cheers Share this post Link to post Share on other sites
Arthur Brown 69 Report post #5 Posted November 15, 2013 Can you use two of the slots on the Calcutt pulley for a matched pair of Vee belts for the big alt. Share this post Link to post Share on other sites
darbon 0 Report post #6 Posted November 15, 2013 Sorry, make that 130 amp alt-batt charger Can you use two of the slots on the Calcutt pulley for a matched pair of Vee belts for the big alt. Good idea that man!! Share this post Link to post Share on other sites
nb Innisfree 601 Report post #7 Posted November 15, 2013 FYI we have twin 13mm V belts driving 24v 100a alternator, 6" crank pullies 3" alt pulIies, never slips or needs adjusting. Engine LPWS4. Share this post Link to post Share on other sites
Phil Ambrose 824 Report post #8 Posted November 15, 2013 My Thorneycroft type 80 drives a 90amp alternator with a single V belt, never had any issues with belt slip or belts wearing out. Phil Share this post Link to post Share on other sites
Chris-B 110 Report post #9 Posted November 15, 2013 most important thing is to ensure you fit a positive tensioner on the alt otherwise belt slip is a regular occurance Share this post Link to post Share on other sites
