24volt alternator, what watt warning bulb/holder do I need?

[Trevorleach]

Old Ford industrial engine in an even older orange crash/emergency lifeboat thing, I am rewiring it and need an alternator warning light, believe it or not I am having trouble finding a cheap lamp and 24v bulb to match.
So am going to take a punt on some quality ebay lamps! but the bulb wattage is going to stump me I know, any ideas?

 

[skotl]

Don't overthink it - current is drawn by the device so a (for example) 5W bulb will draw 5W, aka 0.2A*

So if you're buying an ebay indicator lamp then it's just going to work - 1W, 2W or 5W wouldn't seem unreasonable

* P=IV (roughly) so Power in Watts is the number of amps (I - don't ask...) times number of volts (V). Hence a 5W bulb at 24V will draw 5W/24V = 0.2A

 

[m_c]

I'd probably go for 4w.
12V traditionally was a 2.2W bulb, so I'd say the typically larger 24V alternators will handle a similar current.

However with the demise of bulbs, you might find you'll have to use a suitable 5W wire wound resistor instead in parallel to the bulb.

 

[Morrisman]

I have some old Landrover bullet style tail lights that I seem to recall are 24 volts. Bought them many years ago but never used them.

 

[joebog1]

Its more important that you "excite " the alternator. So really any small 24 volt bulb will do.
The size of the bulb doesnt have any bearing on what charge current the alternator makes,
NOR the voltage it produces. Alternators are not self exciting, so need that wee current to make a small amount of magnetism
to start the cycle / principle off. If the bulb is too weak ( i.e. not enough watts ) it will still glow very slightly when the alternator is running.
Once an alternator is actually going at normal revs, you can actually disconnect the bulb and the alternator will still work.
As it goes out when the battery is charging. No modern car ( that I know ) has any sort of instrumentation thats meaningful.
As any car freak will tell you, " the oil light came on when I looked in the mirror and couldnt identify the crap on the road ".
25 seconds later the knocking bearings told them :-) .
2 watts to probably 5 watts will work fine.

Joe

 

[Trevorleach]

Thank you for the replies, cheap land rover light now on my shopping list.

 

[8ob]

Old Ford industrial engine in an even older orange crash/emergency lifeboat thing, I am rewiring it and need an alternator warning light, believe it or not I am having trouble finding a cheap lamp and 24v bulb to match.
So am going to take a punt on some quality ebay lamps! but the bulb wattage is going to stump me I know, any ideas?

Is this engine a pull stop or solenoid stop? If it’s a solenoid stop you need to make sure you use an ignition barrel that separates out the charge indicator lamp side from the ignition system or fit a blocking diode. One can back feed the other and it won’t shut down.

Bob

 

[johnik]

most trucks are 24 volt,see what they use

 

[Trevorleach]

most trucks are 24 volt,see what they use

All super high tech whizz bang machines these days, bulbs anywhere are a real rarity.

 

[Trevorleach]

Is this engine a pull stop or solenoid stop? If it’s a solenoid stop you need to make sure you use an ignition barrel that separates out the charge indicator lamp side from the ignition system or fit a blocking diode. One can back feed the other and it won’t shut down.

Bob

Pull stop.
It is the simplest circuit you can have, two battery cables, one wire to trigger starter and the other to turn on the alt light, well I say alt light as it did not have one as the wirjng was like a joke, hence my involvement.

 

[Trevorleach]

It is only to energise the rotor windings (provides a magnetic field) until the alternator starts to generate sufficient voltage, so I expect 4-5W would suffice, possibly less - but bot a tiny wattage led lamp! - it is, after all, only an indication lamp for the driver (apart from the excitation current).

That was the issue I was having, they all seem to be led these days.

 

[PhillipM]

I just use a ballast resistor with the LED lamps

 

[Trevorleach]

I just use a ballast resistor with the LED lamps

I did think of something like that (but that stuff is above my pay grade) but it is a boat operating on salt/brackish water that literally no one looks after/gives a toss about, and has had one bodge repair after another, plus not even the cubby is waterproof!

 

[Trevorleach]

Well rewired engine, used an old Rubbolite trailer sidelight with a 3 watt bulb as the alt warning lamp, which of course will not go out with engine running, I guess alternators kept under water do not fare to well!
But another guy did say to me the alt might need flashing to wake it up, something I have not had to do since working on old crappy ERFs with Gardner engines, so thats this weekends fun, if no good it gets a new one.

 

[Matrixx]

On generator's it is dependant on the type of alternator, they require different resistances depending on the alternator design.

 

[m_c]

I'd try a 5 or 10w bulb, as the alternator maybe isn't getting spun fast enough to be excited with just a 3w bulb.

 

[Trevorleach]

Well I splashed out (90 quid) and fitted a new generic 24v alternator from ebay, and it works a treat.
The alt was a bit like a fit all Lucas A127 in 24v, bit of shimming with some washers and we had decent belt alignment.

 

[Trevorleach]

Fitted new belt today, so that is me done with this one, hints of stern glands need doing as I am slowly backing away!
Pic is old belt, plus notice adjuster at end of its slot.