Alternator buggered, now charging drama 100 series TD

An alternator won't charge a dead flat battery as it needs power to "excite" the diodes.
An old fashioned generator will cahrge a flat battery.

Excite the field winding actually, not the diodes.

Well I'm excited.... lol

im going with this one

something up with the install or alternator still

I'm no rocket scientist either, that's why I use an auto sparky to do the job!

I wouldn't know one alternator from another but the new one does appear identicle to look at....as the other.

The batteries were both new about 6months ago...and she started just fine on Sunday before driving home when the battery light came on. Then it wouldn't start. (a 2 hr drive)

That's a bit weird because having started fine, I didn't have any lights on or anything but they went flat????

Anyway, we'll see what the sparky says today and go from there. He has been charging the batteries overnight.

Go to the top of the class!

If the battery was flat how was the engine started anyway? Even if it was started by jumper leads there would be excitation voltage available. Maybe a possible "black start" for a diesel rolling down a hill, but otherwise.............!

More to this than meets the eye.

Al,

I know older diesels will push start, but will a modern diesel roll start if there is not enough voltage/power to run the computer (engine management system)?

not sure who told you that but ive had plenty of dead flat batteries jump started ( we have to have the lights on to drive around for work and sometimes they get left on till the battery couldnt be any flatter)

and while it does the battery no good, after jump starting we dive them round for a bit and they get charge back into them no worries

Tony, I was relating to Muzbry and saying that even with a dead-flat battery, if a The engine jump-started then the application of the support battery will provide voltage to excite the alternator and get charging going.

I also did say "possible" black start to avoid descending into too much detail. Certainly diesels with engine management systems will need 12V available to get going and even older ones will gave fuel cutout solenoids to be energised before a start will succeed.

Who told who what get Outmore?

first post and follow up and also it was posted further up that an alternator cant charge a dead flat battery

Well yes, of course it can. Or rather, an alternator can feed current to a dead flat battery but whether it succeeds in raising a charged state in the battery depends on the condition of the battery. If it is truly dead-flat it may be just that .....dead, permanently dead, and un-chargeable!

Some "intelligent" battery chargers do however require some voltage to be present in the connected battery before they will begin to charge.

Alternators require voltage!

Thanks Shaker

Yes Shaker, they do need the application of an initial voltage in order to energise the field winding but it does not necessarily need to be a full 12V or much current.
Even a battery which might be described as "dead flat" in that it only has a couple of volts and can supply very little current can still supply sufficient to the alternator field to get it up and going. Providing of course that no other loads are sapping everything from the battery. It is even possible to kick-start an alternator by hooking up a couple of 1.5v D cells to the field. I wouldn't want to have to rely on it routinely mind you but would rig it if there were no other way to get going.

Last christmas I ran mine flat by leaving the parkers on for the day. A volt meter gave a reading just over half a volt, so it was flat. Using a jump start pack, borrowed from a car yard across the road, it started straight up. 96 diesel Patrol.
This battery was in poor condition, but lasted till last week when I got a new one. Just needed to throw a charger on it every few weeks.

It was the same as with the buggered one but now after a recharge overnight, it all seems to be fine.

Was charging at about 10v now over 14v

Looks like the trouble was low batteries...and I have 3 because the TD has 2 for cranking and I have 1 for the accessories.

After a recharge over night, the alternator seems to be doing its job.

Thanks for all the replies.

Bucky, with an engine and battery in good condition, a normal start with cranking of only several seconds, very little energy is taken from the battery. Less than 0.5ah. With the alternator now charging at about 30 amps that energy is replaced within a couple of minutes. All is good. This scenario changes dramatically when (a) the engine does not readily start and needs to be cranked for some extended time or (b) the alternator is playing up and not putting in its proper charge or (c) the battery is under the weather and not accepting or holding a charge. That then is another story and some maintenance is indicated.
So even stop-start running is acceptable provided that it is not ridiculously extreme. Those who are operating in stop-start mode such as delivery couriers have no problems unless their vehicles are crook whereupon they attend to it.

So you had good reason to question your "wise man"s proclamation.

Incidentally, the alternator does not necessarily produce "all that energy" for hours unless the battery has been well depleted (as is the case with an auxiliary battery after feeding a fridge overnight) . Once the alternator replaces the batterie's delivered energy and the battery voltage has risen to the "fully charged" value then current reduces to little or no amount and the alternator is simply idling. Apart from small loads such as engine management or radio etc. no energy is going anywhere.

Al
Then can I safely say, if the vehicle/batterys don't need power then the Alternator will only produce and little more than a trickle ?

Eureka ! !!!!!

Finally

Cheers
Bucky

Yep Bucky, you got it!

Al said

"Apart from small loads such as engine management or radio etc."

I don't know what constitutes a "small load", but on my D4D Prado - ie, diesel, no electric ignition, but lots of electronic trickerey to go wrong in the bush, the engine need 13 amps just to keep it running. Saw it on a diagnostic test printout, with no other electrical loads switched on or connected, just idling in neutral. I was quite surprised.

A petrol motor would need even more, I imagine, due to ignition.

Cheers

Frank

Yes Frank, I think 13 amps is getting to be a rather larger "small load".

I am grateful that my old Troopy has no electronic trickery .