Canal Boat - - Back Cabin -

To blast, or not; CO wor­ries; sticky loo valve; split­ting the charge; what horse­power?

QMy al­ter­na­tor’s in­ter­nal reg­u­la­tor al­lows the volt­age to rise to 14.7v, but I have lead acid bat­ter­ies which, I un­der­stand, should not be charged at more than 14.4v. The al­ter­na­tor is a pat­tern re­place­ment; it has the main B+ out­put, the W ter­mi­nal (for rev counter – not re­quired) and just two other ter­mi­nals: L (for the warn­ing lamp cir­cuit) and a small + (for con­nec­tion to the bat­ter­ies while the en­gine is run­ning). Would it be pos­si­ble to in­sert some­thing into the path of the feed to the small + ter­mi­nal to force the al­ter­na­tor to bring down its out­put volt­age?


ATONY REPLIES… I as­sume that the small ter­mi­nal is for a bat­tery sense ca­ble, in which case in­creas­ing the volt­age on it is likely to re­duce the al­ter­na­tor’s charg­ing volt­age. It is easy to fool the reg­u­la­tor into boost­ing the out­put volt­age by in­sert­ing a diode in this ca­ble to cause a volt­drop; how­ever, rais­ing it is a dif­fer­ent thing all to­gether. You may be able to pur­chase a volt­age booster, but you are only look­ing at 0.3-volt and ob­tain­ing that with sta­bil­ity across the op­er­at­ing tem­per­a­ture range is un­likely to be easy. You might be wor­ry­ing un­nec­es­sar­ily. Mod­ern lead acid bat­ter­ies have changed from a lead-an­tin­omy plate al­loy to lead-cal­cium or lead-cal­cium-sil­ver. The cal­cium in­creases the bat­tery’s gassing volt­age sig­nif­i­cantly so it may well be 14.8 volts – but check with the bat­tery man­u­fac­turer’s sheet.

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