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Alternator Wiring Query


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Hi Folks. Please can I have some advice. The alternator for our leisure batteries is wired independently, with the exciter feed/on/off switch and warning light wired in straight to the batteries, live!  I have never had much of a problem with this arrangement so far, but it is easy to knock the switch on, or forget to turn off or on by accident. Could I wire in a warning buzzer in parallel with the bulb? or perhaps replace the bulb with an LED and buzzer in parallel, or would this confuse/damage the alternator. How are second alternators usually wired in please? I guess if there are any spare 12v terminals on the engine on off switch (are there likely to be?) I could use a relay, with switching controlled by the engine side and the feed directed through the relay switch?  We inherited this arrangement when we bought the boat. The iengine is an LPWS4 Lister with an oldish control box if that helps!

Thanks,

Plonk

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Normally there is a relay that is operated from the engine battery /ignition switch, and the relay contacts are used to connect domestic battery positive to the warning light (and then onwards to the domestic alternator).

 

You mention the existing setup being wired direct to the domestic battery positive, but there should be a fuse in there, close to battery positive, just in case something short circuits.

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1 hour ago, Plonk said:

Hi Folks. Please can I have some advice. The alternator for our leisure batteries is wired independently, with the exciter feed/on/off switch and warning light wired in straight to the batteries, live!  I have never had much of a problem with this arrangement so far, but it is easy to knock the switch on, or forget to turn off or on by accident. Could I wire in a warning buzzer in parallel with the bulb? or perhaps replace the bulb with an LED and buzzer in parallel, or would this confuse/damage the alternator. How are second alternators usually wired in please? I guess if there are any spare 12v terminals on the engine on off switch (are there likely to be?) I could use a relay, with switching controlled by the engine side and the feed directed through the relay switch?  We inherited this arrangement when we bought the boat. The iengine is an LPWS4 Lister with an oldish control box if that helps!

Thanks,

Plonk

I am not 100% clear about how the domestic alternator is wired. I think that you mean that you have a separate energise switch to illuminate the charge warning lamp and start the alternator charging and this is not fed from the ignition switch 9if you have one) but from the domestic battery positive  hopefully via a fuse as @nicknorman said.

 

If so leaving the switch on when the alternator is charging is fine, that is basically what a conventional system does. The downside is that if you turn the switch on with the engine stationary the warning light illuminates and you suffer a 0.25 amp discharge, a bit more if you install a buzzer in parallel with the bulb. This should not damage the alternator but will discharge the batteries over  a long period.

 

The following assumes the engine and domestic bank negatives are linked as is normal.

 

You have a number of options:

 

Do the job properly and wire via a relay as @nicknorman explained.

Wire your existing switch  feed form the "ignition on" terminal on the ignition switch.

Change the switch for a push button that you hold down until the warning lamp turns itself off and the release.

 

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14 hours ago, Tony Brooks said:

I am not 100% clear about how the domestic alternator is wired. I think that you mean that you have a separate energise switch to illuminate the charge warning lamp and start the alternator charging and this is not fed from the ignition switch 9if you have one) but from the domestic battery positive  hopefully via a fuse as @nicknorman said.

 

If so leaving the switch on when the alternator is charging is fine, that is basically what a conventional system does. The downside is that if you turn the switch on with the engine stationary the warning light illuminates and you suffer a 0.25 amp discharge, a bit more if you install a buzzer in parallel with the bulb. This should not damage the alternator but will discharge the batteries over  a long period.

 

The following assumes the engine and domestic bank negatives are linked as is normal.

 

You have a number of options:

 

Do the job properly and wire via a relay as @nicknorman explained.

Wire your existing switch  feed form the "ignition on" terminal on the ignition switch.

Change the switch for a push button that you hold down until the warning lamp turns itself off and the release.

 

The downside of your last sentence is that you won’t know if the alternator fails whilst in operation. Maybe this doesn’t matter too much because you will know next time you start the engine, but I thought it worth mentioning.

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Thanks guys, I will locate a 12v live on, on the back of the ignition switch. I think Ihave a relay kicking around somewhere, bought for a different purpose a while ago. I will also trace the wiring back to check for a fuse. I have no idea what they were thinking wiring it as it is currently. 

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14 minutes ago, Plonk said:

Thanks guys, I will locate a 12v live on, on the back of the ignition switch. I think Ihave a relay kicking around somewhere, bought for a different purpose a while ago. I will also trace the wiring back to check for a fuse. I have no idea what they were thinking wiring it as it is currently. 

They were thinking what anyone thinks when carrying out a quick and dirty bodge.

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