alternator charging problem

v8man · Post by **v8man** » Sat Jun 23, 2007 3:26 pm

hi Guys,

got a problem on charging circuit again ,
thing is only charges on a cold engine when engine goes to normal temperature it stops charging ,
on cold charging at 14.53
hot engine goes back to battery voltage

is it the regulator ?
it is a denso A127i 85 Amp alternator with abou a 1000 miles to it almost new

cheers
Gil

ChrisJC · Post by **ChrisJC** » Mon Jun 25, 2007 7:01 am

Assuming you've been measuring at the back of the alternator, then yup I would try a different alternator. Does it have the regulator built in?

Chris.

v8man · Post by **v8man** » Mon Jun 25, 2007 8:03 am

hi

yes it was measured at the back to ,and yes it is a built in regulator and alternator fan is inside to

cheers
Gil

ChrisJC · Post by **ChrisJC** » Mon Jun 25, 2007 2:54 pm

Get another one I reckon.

Chris.

v8man · Post by **v8man** » Wed Jun 27, 2007 2:41 pm

thanks for the replys gents

alternator is ok as per the alternator shop,
looks like the problem is whem the high speed fans come on
as the voltage starts droping (85 amp alternator)
any ideas guys

cheers

Gil

ian.stewart · Post by **ian.stewart** » Wed Jun 27, 2007 3:02 pm

Big Fans draw BIG current, My little fans draw nearly 40 amps,

v8man · Post by **v8man** » Wed Jun 27, 2007 3:47 pm

thanks
they are 50 amp fans ,
the alternator still has 35 spare amps

going to over see all connectors

cheers

Gil

ian.stewart · Post by **ian.stewart** » Wed Jun 27, 2007 4:03 pm

You say 50amp FANS, is that 25 amps each or 50amps each?????

r2d2hp · Post by **r2d2hp** » Wed Jun 27, 2007 5:34 pm

When you measure the battery is that at tickover with the fans on. If so then it would not be able to supply the current drawn by the fans and you will see battery voltage drop.

v8man · Post by **v8man** » Wed Jun 27, 2007 6:12 pm

two fans 25 amps each
yes at idle so that means alternator is not up to standards

cheers

Gil

r2d2hp · Post by **r2d2hp** » Wed Jun 27, 2007 7:04 pm

I don't think an alternator will supply 50 amps at tick over therefore the voltage across the battery terminals start to fall as the fans come on. If you raise the engine revs then you should see the voltage increase to something between 13.5 to 14.5 which would indicate all is working well.

If it stays below 13.5 volt then it suggests something is wrong with the charging circuit.

Ian Anderson · Post by **Ian Anderson** » Wed Jun 27, 2007 7:34 pm

What else is running?
Fuel pump - up to 10 amp
Ecu 5 amp
Aircon 30 amp
Radio - anything up to 15 amp depending on wattage
Lights
Brake Lights

Ian

v8man · Post by **v8man** » Wed Jun 27, 2007 8:50 pm

thanks guys for your comms
going to check tomorow as it is to late to start the beast and due test at 3000 rpm to see if any changes ,
i`ve changed all wiring from alternator charging circuit as old ones were bad ,going for a drive tomorow to see if any changes
fuel pump is a carter on
radio off
ac off
lights off
just 2 high speed fans on
carb car no ecu

cheers

Gil

v8man · Post by **v8man** » Thu Jun 28, 2007 6:56 pm

test at 3000 rpm hot engine fans on high speed today shows 14.56 volts
might be ok
have to go for a long drive to see if alternator still charges after a long drive

cheers

Gil

ramon alban · Post by **ramon alban** » Thu Jun 28, 2007 10:24 pm

Whichever way you look at it 50 amps is a heavy load and and if the alternator is capable of supplying 85 amps then providing very little else is switched on then there would be sufficient excess capacity to charge the battery at proper charging rpm, but that also assumes that the battery is in peak condition without too many cranking events taking place in the immediate prior time frame.

In the following article there is a section on charging capacity and one of its points is that the original charging capacity would be expected to supply 125% of the maximum expected original load.

If the fans are additional to the original design load then they would severely compromise that rule.

The section on charging capacity (page 4 of the pdf) may throw light on a solution to the problem.

http://www.vintagemodelairplane.com/pag ... ery01.html

On the other hand the bottom line may well be to ensure that the battery reaches a proper state of charge before taking any measurements.

That is also covered in the essay.