The charg­ing is a bit con­fus­ing

Canal Boat - - Back Cabin: -

QI have a sin­gle al­ter­na­tor, 65-amp Lu­cas type, and a Cyrix split-charge elec­tronic re­lay. All my ca­bling is shrink-wrapped, con­duited and sup­ported. Is it okay to con­nect the Cyrex to the starter per­ma­nent live on the switched side of the iso­la­tor? If not, can I con­nect straight to the starter bat­tery. The Cyrix is con­nected cur­rently with the starter bat­tery as the pri­mary bat­tery.

Would tak­ing the al­ter­na­tor live wires up to the iso­la­tor (mounted on in­stru­ment /con­trol panel) mean a long run and cre­ate a greater pos­si­bil­ity of volt­age drop? SI­MON, via email

ATONY REPLIES... I think the Cyrex is noth­ing more than a volt­age sen­si­tive re­lay. That means (like any other charge split­ting re­lay) minimising the cur­rent pass­ing through the con­tacts.

The in­struc­tions talk about charg­ing the en­gine bat­tery be­fore the re­lay closes to charge the do­mes­tic bank, but (in my own and sev­eral other peo­ple’s view) this is of lit­tle value. If you min­imise the cur­rent through the con­tacts it re­ally does help max­imise the re­lay’s life.

Starters draw a huge cur­rent but for such a short time (on en­gines in rea­son­able con­di­tion) that the dis­charge is only a few amp hours; so the en­gine bat­tery will be fully charged prob­a­bly within half an hour of start­ing. A de­lay of prob­a­bly no more than half an hour while very dis­charged do­mes­tic bat­ter­ies charge a lit­tle is of lit­tle con­se­quence to en­gine bat­tery charg­ing.

If you wire the al­ter­na­tor to the en­gine bat­tery then as soon as the re­lay closes you will not only have the full al­ter­na­tor out­put flow­ing through the re­lay con­tacts, but also an amount of cur­rent be­ing pro­vided by the starter bat­tery (that is all but fully charged). Ex­pe­ri­ence shows this can burn out the re­lay con­tacts, and the larger the al­ter­na­tor, the more likely. You avoid this prob­lem by send­ing the al­ter­na­tor charge to the bat­tery that will be the most deeply dis­charged, so the bulk of the charg­ing cur­rent never passes through the re­lay. So con­nect the al­ter­na­tor out­put to the do­mes­tic mas­ter switch.

If by iso­la­tor you mean the bat­tery mas­ter switches, then I think it is a ter­ri­ble idea to put them on the in­stru­ment panel. It means long ca­ble runs with volt-drop prob­lems, as well as be­ing easy to ac­cess and there­fore to turn off ac­ci­den­tally with the en­gine run­ning, which could ruin the al­ter­na­tor. Keep them close to the bat­ter­ies and hid­den, apart from the manda­tory no­tice.

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.