very strange alternator issue on sisters car

[phoebelala]

Anyone offer any wisdom on this one?

Sister is skint cos her husband took off and I bought her a little car a year ago. (kia pride) like new with 10K miles on it.

shortly after buying it the alt went and a new one was duly fitted.

recently is has started squeeling or the belt has, but..and this is the strange bit.......only at night when the headlights are on?

Its a big joke saying the car is scared of the dark but can anyone suggest why the extra load on the electrics would cause the belt to slip?

Well strange

Al.

[Phaeton]

Has it only started happening since the nights have got colder? Once had this on an ols car & changing the belt cured it, on inspection the belt seemed quite brittle so all I could assume was brittle belt, cold steel equalled slipping hence squeal.

Does she start the car with the headlights on? After starting & with lights on there is quite a big load on the alternator. Try asking her to start without the lights & give it a minute before she puts the headlights on. This will do 2 things, firstly allow the battery to recover slightly & also allow the belt to warm which may give it a bit more grip.

BTW all the above could be absolute cobblers but it sounds reasonable.

Alan...

[phoebelala]

BTW all the above could be absolute cobblers but it sounds reasonable.

Alan...[/QUOTE]


Belly laughs,

Thanx for that. yeah, she starts it and runs if for a while then switches lights on and it squeels. I drove it myself today in the daylight for 5 mins then turned on the lights and it squeeled. I did not investigate under the bonnet as it was still red hot. I expect it will be slipping due to load when the lights are on but did not realise the alt has extra resistance to turn when the lights are on.

[M35A2]

It sounds to me like a worn or loose belt. If the car has sat all day and the engine is cold, everything has shrunk slightly, and this will make the belt slip. Have a look at the belt and see if it's loose. It should only have about 1/2 inch play at the mid point at the longest stretch between pullys (if that makes sense?)

[phoebelala]

It sounds to me like a worn or loose belt. If the car has sat all day and the engine is cold, everything has shrunk slightly, and this will make the belt slip. Have a look at the belt and see if it's loose. It should only have about 1/2 inch play at the mid point at the longest stretch between pullys (if that makes sense?)

Oh yes, it all makes sense thanks, I have changed a few in my time. what I have trouble with is why only with the lights on.

It actually squeels if the engine is fully warmed up but ONLY if the lights are on which is the strange bit.

I will check the belt in the AM with the engine cold as Sis is staying at our house 2nite

Al.

[MattF]

It actually squeels if the engine is fully warmed up but ONLY if the lights are on which is the strange bit.

Not strange, just the basic way an alternator works. The more current it has
to supply, the greater the strength of the field internally, hence it has more
resistance to rotation.

[div3r]

You beat me to it but I typed this so here it is.

What you are suffering from is BEMF or you don’t get something for nuffing, the more you load your electrical system the more torque is required to turn the alternator, you will find it will be worse as you accelerate the engine particularly, if you have the lights on, the heater fan going full blast, and the rear window heater on, if you reduce the electrical load it will magically disappear the solution is to tighten the belt to specification or you may need a new belt. WARNING Do not tighten the belt to much or you will nacker the bearing on the alternator.

[phoebelala]

Not strange, just the basic way an alternator works. The more current it has
to supply, the greater the strength of the field internally, hence it has more
resistance to rotation.

Bingo, thats what I was hoping to hear. I honestly thought an alternator supplied the same current all the time. (max) and the surplus was burned off as heat thru a regulator/rectifier.

This explains everything.

Thanx to all who have offered assistance, will fix it in the AM.

Al.

[MattF]

I typed this so you going to read it !!!

Ain't it a bugger when someone just pips you to the post.

[phoebelala]

I typed this so you going to read it !!!
What you are suffering from is BEMF or you don’t get something for nuffing the more you load your electrical system the more torque is required to turn the alternator you will find it will be worse as you accelerate the engine particularly if you have the lights on the heater fan going full blast and the rear window heater on if you reduce the electrical load it will magically disappear the solution is to tighten the belt to specification or you may need a new belt WARNING Do not tighten the belt to much or you will nacker the bearing on the alternator.

Again, very sound advice, thank you. I will be sure not to overtighten.

Thanx Plenty

Al.

[div3r]

I must learn to typpe ffaster

[MattF]

Some of us have had quite a bit of practice by trying to beat Vince to the first
post.

[BUSHWHACKER]

Some of us have had quite a bit of practice by trying to beat Vince to the first
post.

I'm chillin'.

[MattF]

I'm chillin'.

We'd noticed. We've been able to post at a leisurely rate of late.