How much does it take to damage alternator?

[davidej]

I can't help feel this is all a bit exagggated.

I confess to having accidentally turned off the batteries at the breaker while the motor was running - on several occasions- by turning the knob to off when I meant to select both. No damge so far.

Is it a bit like turning up in Belgium with red diesel? Everybody says nasty things will happen but nobody actually knows anybody who has suffered that fate.

 

[Talulah]

I hope you have suitably rated fuse in the alternator connection close to the battery

I don't but why would it be necessary? Genuine question.

 

[VicS]

I can't help feel this is all a bit exagggated.

I confess to having accidentally turned off the batteries at the breaker while the motor was running - on several occasions- by turning the knob to off when I meant to select both. No damge so far.

Is it a bit like turning up in Belgium with red diesel? Everybody says nasty things will happen but nobody actually knows anybody who has suffered that fate.

It can happen and it does happen. The cost of an alternator overhaul and the inconvenience of alternator failure in some faraway place in the middle of a holiday makes it one of the risks to avoid.

Very likley that if the alternator is lightly loaded, ie batteries charged and/or engine at idle, no damage will result.
The risk is probably greatest when a substantial charging current is interrupted

 

[ianj99]

I can't help feel this is all a bit exagggated.

I confess to having accidentally turned off the batteries at the breaker while the motor was running - on several occasions- by turning the knob to off when I meant to select both. No damge so far.

Is it a bit like turning up in Belgium with red diesel? Everybody says nasty things will happen but nobody actually knows anybody who has suffered that fate.

The reason few owners experience a problem is no doubt simply because the batteries are well charged when the switch is inadvertantly operated. Thus the alternator is not producing much current to interrupt so any surge is well within the diodes capabiity to block.

 

[lw395]

I can't help feel this is all a bit exagggated.

I confess to having accidentally turned off the batteries at the breaker while the motor was running - on several occasions- by turning the knob to off when I meant to select both. No damge so far.

Is it a bit like turning up in Belgium with red diesel? Everybody says nasty things will happen but nobody actually knows anybody who has suffered that fate.

The bloke who bought my Yanmar Alternator said it had happened to him. The money he gave me was real enough.
And more than enough to pay for the bigger Mondeo alternator I'd replaced it with.

 

[Graham_Wright]

………I hope you have suitably rated fuse in the alternator connection close to the battery ………

If you do, (use a fuse) could it also be used as a current meter shunt?

I have a selection of big current fuses here (at work) but only a cheapo meter which reads 0 ohms ±5!.

If there were a usable voltage drop, it would save the loss in a dedicated shunt. (O.k., I know the resistance would vary with current but we are not talking about scientific precision here).

 

[prv]

I don't but why would it be necessary? Genuine question.

Because otherwise a short from the positive stud on the alternator to any of the large quantities of nearby metal (including the alternator body itself mere millimetres away) will be a direct short through heavy cable from an unfused battery. I've never experienced such a thing but I imagine it's rather like running an arc welder randomly across your engine and will cause a fire if not an explosion. The cause of such a short could be either stray metal (a spanner?), the nut on the stud vibrating loose and releasing the cable, or maybe part of the engine shifting (alternator losing belt tension and swinging down?). And it could happen at any time, not just when the engine's running and you're aboard.

I too shunned the 1-2-both switch and have a connection direct from alternator to battery, but there's a megafuse as part of the connection to the battery post.

Pete

 

[VicS]

Because otherwise a short from the positive stud on the alternator to any of the large quantities of nearby metal (including the alternator body itself mere millimetres away) will be a direct short through heavy cable from an unfused battery. I've never experienced such a thing but I imagine it's rather like running an arc welder randomly across your engine and will cause a fire if not an explosion. The cause of such a short could be either stray metal (a spanner?), the nut on the stud vibrating loose and releasing the cable, or maybe part of the engine shifting (alternator losing belt tension and swinging down?). And it could happen at any time, not just when the engine's running and you're aboard.

I too shunned the 1-2-both switch and have a connection direct from alternator to battery, but there's a megafuse as part of the connection to the battery post.

Pete

Just an example but what comes to mind is the possibility that the oil filter might be very close to the alternator .. it is on some older Volvo petrol engines. It would be easy to short the main alternator/ battery connection to earth while changing the oil filter.

Even if you have a mega fuse in the battery connection you ought to have fuse in the alternator connection rated to protect the wiring between the battery and the alternator.

 

[Talulah]

Because otherwise a short from the positive stud on the alternator to any of the large quantities of nearby metal (including the alternator body itself mere millimetres away) will be a direct short through heavy cable from an unfused battery. I've never experienced such a thing but I imagine it's rather like running an arc welder randomly across your engine and will cause a fire if not an explosion. The cause of such a short could be either stray metal (a spanner?), the nut on the stud vibrating loose and releasing the cable, or maybe part of the engine shifting (alternator losing belt tension and swinging down?). And it could happen at any time, not just when the engine's running and you're aboard.

But that would apply to most people with a standard set up as well unless they had a fuse between their starter motor and battery. (Some do of course.)
It would only not apply to standard set up if you turned off the battery switches inbetween each engine use.

 

[prv]

It would only not apply to standard set up if you turned off the battery switches inbetween each engine use.

True - but most people with a 1-2-both do turn it off when leaving the boat, and probably when working on the engine (they should, anyway). My alternator terminal is live at all times (just as it is on my car). I suppose the isolator you mentioned fixes this; I hadn't noticed that first time round.

I was going for maximum simplicity in use, with all controls (including engine) on the electrics panel. That precludes routinely-used isolators elsewhere; I only isolate my battery if working on the electrics.

Pete

 

[basil421]

1 2 Both

This is why with a 1,2 both,off switch it is important to always switch via the both position, never via the off position when cahnging batteries over while the engine is running

This is an issue which concerns me also. My Yanmar 1GM10 powered system charges the two batteries via a 1,2,Both isolator and I religiously switch via the "both" position. However, I've recently noticed that when switching from "2" to "Both" there is a momentary disconnect. This also happens going the other way. "Both" to "2". No such disconnect occurs between "1" and "Both" so I'm wondring if there is a fault with my 1,2,Both Isolator.
see attached picture of Isolator.
If anyone is familiar with this Isolator I'd appreciate any comments. Should I replace the Isolator or can it be repaired?

 

[Graham_Wright]

Spli charge diode for Landrovers £10 new. RRP £120.
Any use for boats?


http://www.ebay.co.uk/itm/Land-Rove...arts_Vehicles_CarParts_SM&hash=item1e6c3a3090