Split Charge Relay

[theia]

Have fitted a Lucas split charge relay and followed the instructions to the letter. However the second battery seems to lose it's charge after 2-3 days. I don't think it's the battery itself. Any ideas what could be the cause?

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[alan54]

Is it a relay or a diode splitter ? if its a relay i suggest it could be faulty, more than likely the battery is on its last legs and not holding a charge !
good luck
radar

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[Birdseye]

difficult to say without more detail, but if you have got the relay connections wrong so that the second battery is powering up the relay all the time, then this might have the effect you describe.

the relay should be activated by the ignition switch so that it connects the domestic battery into the charging circuit only when the engine is running. othertimes, there is no connection between the engine battery and the domestic.

as a test, charge the second battery fully and then disconnect at the terminals for 3 days. if it still goes flat - battery duff. itf it doesnt, then you have some external load on the battery which may be miswiring of the relay.

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[philip_stevens]

The relay should really either be energised after the engine has started, by wiring into the ignition warning light supply - when the light goes out, the relays are energised, or by fitting another oil pressure switch, that is NO (normally open) when the engine is stopped, and will be closed when the oil pressure has been raised by the running of the engine.

If you take the supply for energising the relays from the ignition switch, the batteries will be paralleled before the engine has started.
Not good, as, if the engine starting battery is lower than the other battery, there is a chance of burning out the wiring and relay contacts as the engine starter will try to get extra current from the better battery.

<hr width=100% size=1>regards,
Philip