Electrics

[Mike]

I've finally managed to change my main batteries. I turned off the mains charger which was on float charge, then turned off the battery isolator. I removed the leads and lifted the old batteries out. While lowering in the new ones, the leads touched and there was a brief spark. On checking with a meter, there was 12 volts at the leads before they were touching the new batteries. This had to be coming from the engine start battery. Surely this is wrong, are the two circuits not supposed to be independant? My engine has two alternators, so I assumed they were totally separate.

Any lecky experts out there please?

 

Mike

Stargazer, K&A

[Chris M]

I've finally managed to change my main batteries. I turned off the mains charger which was on float charge, then turned off the battery isolator. I removed the leads and lifted the old batteries out. While lowering in the new ones, the leads touched and there was a brief spark. On checking with a meter, there was 12 volts at the leads before they were touching the new batteries. This had to be coming from the engine start battery. Surely this is wrong, are the two circuits not supposed to be independant? My engine has two alternators, so I assumed they were totally separate.

Any lecky experts out there please?

 

Mike

Stargazer, K&A

 

Maybe you are experiencing capacitive discharge from your battery charger or an inverter if you have one?

The way to rule that out would obviously be to isolate ALL batteries and then check for a voltage in the system as you did before.

I have a cheap 2kw inverter in my boat. If the terminals on that touch with no battery connected there is quite a hefty spark.

[NB Willawaw]

It sounds like you isolated the wrong bank.

There should be an isolator on each bank including your starter bank.

Are you sure you didnt isolate the starter bank by mistake and then got a discharge off the smoothing capacitors in the charger by touching the leads for the domestic bank together ?

 

If the domestic bank was really isolated, it would be totally dead at the lead ends (unless something is permanently connected and not routed through the red key - you haven't got a diesel heater onboard have u ?). I've found boats that have this connected straight across the batteries, although I can't think how this would store up a 12V charge !

 

Theres somethings strange going on - suggest you try following the cables to see how they are connected.

 

Mark

 

I've finally managed to change my main batteries. I turned off the mains charger which was on float charge, then turned off the battery isolator. I removed the leads and lifted the old batteries out. While lowering in the new ones, the leads touched and there was a brief spark. On checking with a meter, there was 12 volts at the leads before they were touching the new batteries. This had to be coming from the engine start battery. Surely this is wrong, are the two circuits not supposed to be independant? My engine has two alternators, so I assumed they were totally separate.

Any lecky experts out there please?

 

Mike

Stargazer, K&A

[DHutch]

Maybe you are experiencing capacitive discharge from your battery charger or an inverter if you have one?

The way to rule that out would obviously be to isolate ALL batteries and then check for a voltage in the system as you did before.

I have a cheap 2kw inverter in my boat. If the terminals on that touch with no battery connected there is quite a hefty spark.

Yeah, sounds plausable. IF the inverter or charger by-passes the isolation switch.

- I've got a nasty kick of a computer PSU before now, days after it was unpluged.

 

With the leads disconected connect a load accross the, such as a (filament) bulb.

- If this is the case it should light, then fade after time, untill the cap is disscharged.

 

 

Daniel

Edited April 29, 2006 by dhutch

[Sir Nibble]

How big a brief spark?

The trouble with a voltmeter is that it will show you that there is a potential difference between two points that may well collapse totally should you attempt to draw any current. For instance, it is possible that you may be reading 12V through the alternator warning light or a relay coil. This is why I always prefer to work with a testlamp, and why (with respect) amateurs often find meter readings more confusing than enlightening.

Whereabouts on the K&A?

[Guest]

How big a brief spark?

The trouble with a voltmeter is that it will show you that there is a potential difference between two points that may well collapse totally should you attempt to draw any current. For instance, it is possible that you may be reading 12V through the alternator warning light or a relay coil. This is why I always prefer to work with a testlamp, and why (with respect) amateurs often find meter readings more confusing than enlightening.

Whereabouts on the K&A?

 

Thought it was just me! Multimeters can lead us right up the garden path sometimes. You can get a voltage reading through a pencil line with a meter. a test lamp applies some load.

Edited April 28, 2006 by Guest