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>>

AuthorMessage
Ray
Ray

Posted: Sun Jun 03, 2012 10:42am

Post Subject: Alternator outputs

Hi Tony, I have just fitted two new 135 amphr "wet Pb" batteries which are fully charged. With no load on the batteries the alternator, 70amp fitted to my Isuzu 35 engine, had an output of about 4amps with engine revs from 850 to 1500 rpm. With a 1500 watt load the output was 41.7amp at 850 eng.rev increasing along a curve plot to 55amp at 1400 eng.revs, plateau-ing out at 58amps at 1800 eng.revs and upwards. The engine pulley is 6.25" dia. and the alternator pulley 3", ratio being 2.1:1. I would like to peak the alt. output at my engine cruising revs of about 1300revs. This would need an alt. pulley dia. of about 2.5". Do you think this is practical and are pulleys available at about this size? Would the change of ratio affect the tachometer readout because the tach. input is connected to same alternator, which would be reving quicker for a set engine speed. Hope my queries are clear!!

Tony-B...
Tony-B...

Posted: Sun Jun 03, 2012 11:30am

Post Subject: Alternator outputs

We certainly could obtain pulleys of about that size when I was on the hire fleet, but it is not just the diameter you need to worry about. You also need to ensure the shaft diameter is correct and the belt groove profile matches the other pulleys and your belt. You should use a notched belt at that sort of diameter because it will bend around the small radius easier than a standard belt. You need to locate your local vehicle electrical specialist and ask them to source the pulley for you. You might also need them to change it for you because modern alternators seem to demand an impact wrench to loosen the nut. You will have to give them the make and model number of your alternator. I have tried Googling for you but I could not find a site that listed spare pulleys but I know they are available so a session on the phone would be required. The vast majority of rev-counters have some method of calibrating them to the engine so you will have to look at your documents to see exactly how you do yours. Before you do too much I think that you should wait a few days. It seems to me as if your batteries have surface charge on them, otherwise I would expect a 1500 watt load to force the alternator to full output when the revs were adequate. That is assuming the ammeter is measuring the full alternator output. Tony Brooks

Ray
Ray

Posted: Mon Jun 04, 2012 9:19pm

Post Subject: Alternator outputs

Many thanks again Tony for your advice. I didn't expect a response this bank holiday weekend, wow! Regards, Ray

Like us on Facebook



Follow us on Twitter

Cache: Disabled for this object  Total Queries: 43.  Total Objects: 162.  Total Unserialized: 3. Total Runtime: 0.26 seconds.