Alternator problems .....continued

[chubby]

Cheers Pete

 

i really can t follow what means , i m sorry . Ive got two warning lamps & if it required pulling instrument panels out to get to the connections at the back then im just way way out of my depth & im if im honest im afraid now of causing damage to stuff .

 

I think im going to have to put my hands into my pockets & get someone in to look at it as its behaving in a way i just don t understand . It comes on ok & then shuts itself down & i don t have the first idea why .

cheers again

[smileypete]

Righto, could also get a 12V panel lamp (not LED) from halfords etc, connect one end to domestic batt +ve, then the other end to domestic alt warning lamp connection, having disconnected it from the engine loom first.

 

cheers, Pete.

~smpt~

Edited January 2, 2015 by smileypete

[chubby]

 

 

Ive got a " test lamp " . Rigged up with a cabin light . Its the most well used piece of equipment on my boat , especially as it saw active service during my eberspacher episodes .

 

Is this what youre referring to ? One side is neg , one is pos .

 

Your saying pos to pos tho ?

 

Im sorry if i appear dumb , but my brains been fried by this issue & if connect up the wrong thing to wrong thing i may damage stuff .

 

If its ok & is suitable i ll use it

 

cheers

[smileypete]

Have a break for now then, come back to it tomorrow or Sunday.

 

cheers, Pete.

~smpt~

[Loafer]

Can anyone point me to info, on here, that 'sorts' the problem of having to 'blip' the throttle to get an alternator going?

[MtB]

Can anyone point me to info, on here, that 'sorts' the problem of having to 'blip' the throttle to get an alternator going?

 

The fix is to fit a bigger crankshaft pulley.

 

Or tighten the vee belt if it's loose.

 

 

 

MtB

[nicknorman]

Yup, a well-marinised engine doesn't suffer from this problem. Start our engine at idle, the alternator can produce around 150A straight away. As MtB says, it's all down to the pulley ratios.

[Keeping Up]

Can anyone point me to info, on here, that 'sorts' the problem of having to 'blip' the throttle to get an alternator going?

Often a resistor, or a second bulb, in parallel with the warning light (or else just changing the bulb to a more powerful one) will sort it.

[bizzard]

I said a bigger bulb about 49 posts ago, or was it on the other thread of Chubby's.

[Sir Nibble]

Well I have looked up diagrams online though I can only get the latest ones which are slightly different. I see a relay in there on the warning light, not sense circuits! I suspect the wiring has been messed with. Oddly, the relay in question is ignition controlled but only breaks the warning light line on the -ve side, the lamp being ignition fed! So what that example of redundancy is doing I cannot imagine. PM incoming.

[Loafer]

Yup, a well-marinised engine doesn't suffer from this problem. Start our engine at idle, the alternator can produce around 150A straight away. As MtB says, it's all down to the pulley ratios.

 

Hmm. I'm certain that the original alternators are no longer on this engine, so I'm guessing that the 'standard' alternator pulleys are a little too large. We don't need to blip the throttle much, maybe to about 500rpm (idle is about 250, max 1200) but I like to sort things like that. Is it easy to get smaller alternator pulley wheels?

 

The drive wheel on the engine is mahoosive. About 18" across. Thanks chaps.

[MtB]

What's the effective diameter of the alternator pulley now?

 

With a flywheel pulley that big it could be that the ratios are fine and something else is wrong...

 

MtB

[Loafer]

What's the effective diameter of the alternator pulley now?

 

With a flywheel pulley that big it could be that the ratios are fine and something else is wrong...

 

MtB

 

I'm not sure Mike, I'm not able to measure it at the moment. Is it worth measuring both the drive pulley and the alternator pulley diameters to publish here, and hope for an informed opinion?

 

The 'problem' has existed since we bought our boat, and has been easy to live with. Sometimes a throttle 'blip' will sort one alternator but not the other, until a slightly bigger blip wakes up the slack one! I know that because I have an ammeter for each alternator. (Shunts and mV meters)

 

Having heard of others with the same problem, I just thought it was normal with lower-revving engines and not to be concerned about!

PS to my last, I do recall that with discharged batteries, on first engine start, I do need to lift the engine rpm to about 500 to get max current from each alternator.

[Sir Nibble]

Sounds to me like all you need are bigger bulbs.

[MtB]

Yes, post both diameters. The ratio of one to the other x the engine speed = alternator speed. This needs to be high enough to meet the manufacturer's minumum speed spec. with the engine at tickover.

 

I think...

 

Maybe the alternator experts could explain what makes an alternator start charging at a particular speed. I don't actually understand now I come to think about it.

 

MtB

[Loafer]

Sounds to me like all you need are bigger bulbs.

 

You mean higher wattage, i.e. larger current?

 

I would love a quick and dirty explanation of why that works, it it isn't too much trouble. (Please tell me to go forth and Google myself. I just like the personal aspect to this forum!)

Edited January 3, 2015 by Loafer

[MtB]

Yes.

 

ISTR Snibs suggesting two bulbs in parallel or just one twice the wattage recently. Or maybe that was Bizzard.

 

 

MtB

[Loafer]

Yes.

 

ISTR Snibs suggesting two bulbs in parallel or just one twice the wattage recently. Or maybe that was Bizzard.

 

 

MtB

 

I saw that too, but I can't work out how it fixes the problem!

[nicknorman]

The reason a bigger (higher wattage, higher current) bulb works is because the current flowing through the bulb is fed into the alternator rotor windings to magnetise the rotor a bit. This magnetised rotor, when spun at an adequate speed, induces lecccy into the stator windings. How fast the rotor has to spin depends on how much current is generating the magnetic field, ie the wattage of the bulb. Small bulb = weak magnetic field so the rotor needs to spin fast and vice versa. Typically (varies with alternator type) a set of diodes then rectifies the weak stator output and this is used to supplement the rotor / field current. As this current thus increases a bit the rotor magnetic field intensifies which increase the stator output current in a "vicious circle" which means the alternator jumps into life at that critical rpm. As the voltage at the filed diodes reaches 12v (or whatever) this means that not only is loads of field current now available (and it may then be restricted by the regulator) but als the voltage at the alternator end of the bulb is now 12v, same as at the other end, hence no voltage across the bulb and the light goes out.

 

Ed due to stator and rotor confusion!

Edited January 3, 2015 by nicknorman

[Loafer]

The reason a bigger (higher wattage, higher current) bulb works is because the current flowing through the bulb is fed into the alternator rotor windings to magnetise the rotor a bit. This magnetised rotor, when spun at an adequate speed, induces lecccy into the stator windings. How fast the rotor has to spin depends on how much current is generating the magnetic field, ie the wattage of the bulb. Small bulb = weak magnetic field so the rotor needs to spin fast and vice versa. Typically (varies with alternator type) a set of diodes then rectifies the weak stator output and this is used to supplement the rotor / field current. As this current thus increases a bit the rotor magnetic field intensifies which increase the field current in a "vicious circle" which means the alternator jumps into life at that critical rpm. As the voltage at the filed diodes reaches 12v (or whatever) this means that not only is loads of field current now available (and it may then be restricted by the regulator) but als the voltage at the alternator end of the bulb is now 12v, same as at the other end, hence no voltage across the bulb and the light goes out.

 

That sounds good stuff. I'm beginning to get it. In order to test this, can I just attach a 12v-rated bulb to a terminal on the back of an alternator, and the other end to a 12V source (like B+)? Would this effectively parallel my original bulb? If so, which alternator terminal should the bulb be connected to? (Well, one side of the bulb anyway)

 

Furthermore, is there a sensible limit? I'm guessing you can't just short out the original bulb, say, 'cos you'd be shorting your battery bank...innit?

 

Thank you.

[MtB]

Fanx Nick!

 

Presumably it isn't proportional, i.e. doubling the excitation current halves the speed at which the alternator kicks in?

 

(I would describe it as a 'virtuous circle' rather than a vicious one... )

 

 

MtB

[nicknorman]

That sounds good stuff. I'm beginning to get it. In order to test this, can I just attach a 12v-rated bulb to a terminal on the back of an alternator, and the other end to a 12V source (like B+)? Would this effectively parallel my original bulb? If so, which alternator terminal should the bulb be connected to? (Well, one side of the bulb anyway)

 

Furthermore, is there a sensible limit? I'm guessing you can't just short out the original bulb, say, 'cos you'd be shorting your battery bank...innit?

 

Thank you.

Yes you could parallel your existing bulb between the alternator and the B+ with another bulb. I wouldn't overdo it though as I seem to recall that too much current can be damaging, but I can't remember why. Definitely not a direct connection to B+

 

The alternator terminal may be labeled D+ or something like that, but it depends. One way to find out is to switch on the ignition and then disconnect the various wires, the warning light will go out when you disconnect the right one.

Fanx Nick!

 

Presumably it isn't proportional, i.e. doubling the excitation current halves the speed at which the alternator kicks in?

 

(I would describe it as a 'virtuous circle' rather than a vicious one... )

 

 

MtB

I doubt it will be proportional because there isn't a very linear relationship between current in an electromagnet, and magnetic field strength. Probably not too far off linear if well away from saturation though.

[Loafer]

Yes you could parallel your existing bulb between the alternator and the B+ with another bulb. I wouldn't overdo it though as I seem to recall that too much current can be damaging, but I can't remember why. Definitely not a direct connection to B+

 

The alternator terminal may be labeled D+ or something like that, but it depends. One way to find out is to switch on the ignition and then disconnect the various wires, the warning light will go out when you disconnect the right one.

 

Good tip. So when I identify the right one, where the warning light goes out, that's one of the terminals for one side of my additional bulb.

 

Which is the other? I'm thinking battery positive, or B+ on the back of the alternator (i.e. it's output) such that the bulb would be connected to TWO of the alternator's rear terminals, making for a quick and easy job. No?

 

(I'm sorry to grab so much of this post's attention, but I've caused a spark before, and nearly shat myself. I immediately made even more sparks in the panic of trying to prevent any more, and bumped my head, which nearly made me break my neck!)

[bizzard]

I had a Japanese alternator on my engine for about 12 years, which was very good, although I had to rev a bit to excite it. However, that alternator packed in a few weeks ago. I had a good reconditioned uprated old Lucas ACR ( Mini type) alternator in stock so fitted that. I had to rev the engine considerably to excite it, so I changed the warning light bulb and holder which was one of those tiny Pea bulbs of about 2w for a larger 6w vehicle side light bulb and holder. It now excites immediately, almost before I've let go the start key. This is with a split charge relay. The engine is a Lister ST2 with a 10'' pulley on the camshaft.

[Loafer]

I had a Japanese alternator on my engine for about 12 years, which was very good, although I had to rev a bit to excite it. However, that alternator packed in a few weeks ago. I had a good reconditioned uprated old Lucas ACR ( Mini type) alternator in stock so fitted that. I had to rev the engine considerably to excite it, so I changed the warning light bulb and holder which was one of those tiny Pea bulbs of about 2w for a larger 6w vehicle side light bulb and holder. It now excites immediately, almost before I've let go the start key. This is with a split charge relay. The engine is a Lister ST2 with a 10'' pulley on the camshaft.

 

Thanks Biz. Sounds like the solution here. I'll get on the case on Monday and report back here. 6W -ish then!