Alternator problem

[srp]

I have always had to rev the engine to get the alternator warning light to go out, but yesterday, starting the engine for the first time since Christmas and with a slightly under-par battery plus a spare and jump leads, the light wouldn't go out at all.

Is it more difficult to get the alternator to kick in if the battery is not fully charged?

Plan A is to make up a second warning light with something like a 15w car bulb and a couple of leads plus a switch, connect it across the warning lamp terminals and switch it on for a second or two. I've brought the battery home to charge it up properly.

Plan B is to ignore the fact that the charging light is not on and just run the engine for the 3 hours or so it will take to get it to it's new mooring. Will I damage anything by doing this?

I think the problem is bacause the alternator is obviously not original, probably came from a car via the scrap yard, and the pulleys may not be correct size (one of many bodges by the previous owner who was a bodger extroadinaire).

Plan C would be to get another alternator, but this might not be the easy option that it sounds because of the difficulty of putting right the bodges done to get the present one to fit. I will do it eventually, but I will need to make up some replacement brackets and adjuster to fit it properly.

 

[earlybird]

I don't think that a low battery would cause your problem, neither would a larger warning light cure it. If it's not a loose connection,
I'd look at the alternator brushes as a first port of call, and/or get the alternator tested by the local auto-electrician

 

[Davegriff]

Belt tension?

 

[lw395]

First check the belt, make sure the alt is going round.
How fast is the alternator going round?
A smaller pulley may help.
Having to apply a few revs to start the alt is not the end of the world, it allows the engine to get going before loading it.
Checking the brushes is a good start, but in general the light won't come on if the brushes go.

 

[charles_reed]

I have always had to rev the engine to get the alternator warning light to go out, but yesterday, starting the engine for the first time since Christmas and with a slightly under-par battery plus a spare and jump leads, the light wouldn't go out at all.

Is it more difficult to get the alternator to kick in if the battery is not fully charged?

Plan A is to make up a second warning light with something like a 15w car bulb and a couple of leads plus a switch, connect it across the warning lamp terminals and switch it on for a second or two. I've brought the battery home to charge it up properly.

Plan B is to ignore the fact that the charging light is not on and just run the engine for the 3 hours or so it will take to get it to it's new mooring. Will I damage anything by doing this?

I think the problem is bacause the alternator is obviously not original, probably came from a car via the scrap yard, and the pulleys may not be correct size (one of many bodges by the previous owner who was a bodger extroadinaire).

Plan C would be to get another alternator, but this might not be the easy option that it sounds because of the difficulty of putting right the bodges done to get the present one to fit. I will do it eventually, but I will need to make up some replacement brackets and adjuster to fit it properly.

You really can't do anything meaningful without a voltmeter.
Check, at the alternator that it is producing a charge - if not take it off to an auto electrician and have him bench test and rectify it. If you're in the S of England expect rectification to cost c£50, in more moderate areas £30, he'll probably need to replace the on-board regulator and, perhaps, the diode bridge.
Until you've done that simple test you're no farther forward.
As you've got a short-run problem, to get to the mooring, providing the belt is turning the engine waterpump (assuming indirect cooling) you'll have no problems with a 3 hour run - if the belt is NOT turning the engine waterpump don't try that.
No need to think of a new alternator at this point and forget about the proposed jury rig - the "ignition" light is just a warning light though, on some installations, you need a working bulb to excite the regulator into producing a charge.
Good luck!

 

[halcyon]

No need to think of a new alternator at this point and forget about the proposed jury rig - the "ignition" light is just a warning light though, on some installations, you need a working bulb to excite the regulator into producing a charge.
Good luck!

It could be bad connection in the warning light circuit, giving a low rotor magnetic field, thus low output from field diodes, which is why the OP has to rev the engine to get the warning light to go out.

But as said, nothing can be done without a voltmeter.

Brian

 

[Gumpy]

Short out the light
Start engine
Remove short
If light comes back on you have a broken alternator.
If light stays out add a 47ohm 5watt resistor in parallel with the lamp as there is not enough current available to excite the alternator.
The original symptoms of having to rev the engine are a classic sign of the wrong size warning lamp.

 

[srp]

Short out the light
Start engine
Remove short
If light comes back on you have a broken alternator.
If light stays out add a 47ohm 5watt resistor in parallel with the lamp as there is not enough current available to excite the alternator.
The original symptoms of having to rev the engine are a classic sign of the wrong size warning lamp.

I'm hoping it is the wrong wattage warning light, and maybe coupled with the wrong size pulley (if the original came from a petrol engined car which revs faster than the old fashioned Perkins 4108 it may well not have the correct pulley on it). The belt was new last year and the water pump is pumping water ok.
I have just borrowed a multimeter, so will check the alternator output on the next visit after the battery is charged.
I hadn't thought of the brushes, so thanks to those who suggested this as a possible. May be the brushes are a bit sticky in the slides or the springs are a bit feeble, so I'll have a look at them.
The alternator itself is a Delco I think (it says Made in France on it), and has two connections, which I presume are Output +ve, ignition +ve, and the frame is obviously the ground.

 

[ghostlymoron]

I'm hoping it is the wrong wattage warning light, and maybe coupled with the wrong size pulley (if the original came from a petrol engined car which revs faster than the old fashioned Perkins 4108 it may well not have the correct pulley on it). The belt was new last year and the water pump is pumping water ok.
I have just borrowed a multimeter, so will check the alternator output on the next visit after the battery is charged.
I hadn't thought of the brushes, so thanks to those who suggested this as a possible. May be the brushes are a bit sticky in the slides or the springs are a bit feeble, so I'll have a look at them.
The alternator itself is a Delco I think (it says Made in France on it), and has two connections, which I presume are Output +ve, ignition +ve, and the frame is obviously the ground.

A good multi meter is the most useful thing you can have on a boat (next to sails). I recently bought a smashing one from CPC for a tenner. This is the one I bought http://cpc.farnell.com/unbranded/st-912/compact-digital-multimeter/dp/IN05460?Ntt=IN05460

 

[srp]

A good multi meter is the most useful thing you can have on a boat (next to sails). I recently bought a smashing one from CPC for a tenner. This is the one I bought http://cpc.farnell.com/unbranded/st-912/compact-digital-multimeter/dp/IN05460?Ntt=IN05460

I've already got one. It's in the workshop 80 miles and a ferry trip away (I always forget something important). However, I have borrowed one for a few days, so I should be able to get some more information when I next row out to the boat.

 

[VicS]

I've already got one. It's in the workshop 80 miles and a ferry trip away (I always forget something important). However, I have borrowed one for a few days, so I should be able to get some more information when I next row out to the boat.

Get a couple of inexpensive ones eg from Maplin so you have one at home, one in the boat and one in the workshop


http://www.maplin.co.uk/domestic-multimeter-37279

 

[charles_reed]

Get a couple of inexpensive ones eg from Maplin so you have one at home, one in the boat and one in the workshop


http://www.maplin.co.uk/domestic-multimeter-37279

More or less as I do, though I've two on the boat in case I'm taking readings @ two points. Even in Maplins they're less than £20 and using them means you'll have far fewer embarrassing electrical experiences and save an awful large sum of money.

 

[srp]

Update - went out to the boat again today (in the snow!) with the now fully-charged battery (12.9 volts 24 hours after disconnecting the charger). Connected up and the engine started on the second 4 sec cranking attempt. Alternator warning lamp didn't go out (as expected!). Battery voltage was now 12.65 volts.
Pulled the leads off the warning lamp and connected them to a 12v 15w lamp and immediately noticed a v slight drop in engine revs. Reconnected the original warning lamp and it didn't illuminate. Measured the voltage at the battery and it showed 14.4v so is presumably working ok.
So it looks as though the panel warning lamp is too low a wattage for the alternator - unsurprising as it is obviously not an original alternator. Possibly the problem is made worse because the alternator is not being driven at the correct speed.