Bruce wrote: > Thanks Roger. I note that the next engine will have a 175 A domestic > alternator, so in six years they've gone from the 90 A beast on Sanity > to nearly three times that capacity.
Out of interest, what size battery bank are you having that will be charged by this hefty alternator? Is it the only alternator or have you another dedicated starter battery alternator also? Let's do some crude calculations. You say 175A and, I assume, a 12V system. That's 2100W at full chat. Take an overall efficiency of say 85% (I've no idea if this is correct but I suspect it won't be too far adrift). This means that to generate 2100W (2.1kW or 2.82 hp!!!!!) the belt has to deliver 2415W. Thus 315W is waste. Now, some of this will be energy in the form of noise and windage but there will be heat generated internally and by the friction of the belt around the pulley. So, just for a giggle, let's assume that 300W is generated as one source of heat or other. Three hundred watts of heating continuously coming from the alternator alone and it could be sitting in a very hot ambient already. My figures might be horribly wrong (possibly on the low side) and your alternator doesn't charge at full chat continuously but, I hope that you can see the point I'm trying to make. > > Looks like I'm lucky to have got the time I did out of the present > kit, though my practice of never discharging below around 12.2 V if I > can possibly help it may have something to do with it, I guess. I'm pretty sure that this will have helped. Don't forget that the lower the charge current that you are requiring from your alternator the less heat it will generate within itself and, therefore, the less it will be affected by a warm ambient air surrounding it. QED, a small alternator working less hard will survive high ambients better than larger alternators working very hard. In some ways I'm surprised that marine engine installations haven't gone over to the water cooled alternators that poeple like Bosch have had in the automotive field for many years now. It enables an alternator to be fitted in a more hostile environment and yet still be adequately cooled and has the side benefits of being quieter (no fans whirring air around) and wasting less energy (losses due to pumping the air around). Note to Beta for their cocooned engines ;-))) Roger
