electrical question

[durecell]

so I know that you will get a certain about of rpm drop when you load down the alternator. turn on the head lights, heater, etc.

my question is that 200 to 300 RPM drop seems excessive. when your idling at 900RPM anyway and now im down to 600 that makes the engine shudder a lot. is this normal? or is the alternator weak or is it maybe the battery. the alternator is of un know age. the battery is smaller but was a good price from the wrecking yard. it starts the car fine. its just a little annoying. I have cleaned all my connections including all the ground connections I can find. any thoughts on this?

[Gottolovem]

What do you mean by smaller battery is the load rating wrong.
Do you have another known battery to swap out and see if there is a difference.
I agree 200 to 300 hundred rpm is wrong my car has no noticeable drop however I keep my idle at 1000 rpm.

[durecell]

yes the load rating is not what is recommended. the battery was free. my dad picked it up at the pull and save and just gave it to me. it holds a charge ok except when it got really cold a couple of weeks ago. I had to charge it up to start the car. but other then that when its not sub zero it starts fine with no hesitation. just don't like the rpm drop so much.
I keep my idle at 900 cause it idles smoother and I read on a post by petros that that's what he recommended. it will idle fine at the factory 650 rpm recommendation but then when you turn on headlights and heater it darn near dies. so I keep it at 900. I figure the higher the idle is the more gas you use and when you idle a lot in stop and go traffic and traffic lights that id try and squeeze all I can out of her. my 86 pickup ideals fine at 650 rpm even with the heater and lights on, but I know the alternator in it is only a few years old and the battery is brand new.

[Petros]

I doubt that an excessive load on the alternator is internal to it. the alternator usually works or it does not, I have also had them put out very weak output, but it did not cause excessive load on the engine.

If the battery is marginal and will not hold a charge the voltage regulator may respond by going to full charge mode causing it to bog down. I do not think that a smaller battery would by itself cause it, if it is a good battery it should operate normally. with an undersized one it just means you have much less battery reserve for those really cold days. I would take the battery to an autoparts store or a battery shop and have them load test it, most will do it for free. If it is weak and will not hold a charge than you need a good battery (and they will be happy to sell you one).

A marginal battery will cause you all kinds of odd electrical behavior, a good strong one will make it all go away. But have it tested first just to make sure.

[durecell]

thanks petros you always seem to have the answers im looking for ill try the battery. I have one in my pickup I could swap over see if that helps. I know that one is good.