flibble
|
| posted on 6/12/08 at 10:42 PM |
|
|
Charge indicator bulb
Hi people,
Im currently trying to replace my old 1.7 crossflow with a Saab 2.0 turbo (b204l) and trying to get on with the electrickery side of things.
Now, I've decided to make a loom from scratch (original sensors & ecu though) and as elecrics arn't my strong spot I'm
struggling a little.
I decided to make the most basic loom I can to get the engine started to begin with, and here's my question (finally)..
Is a charging light needed for the battery to actually receive a charge from the alternator as I'm half sure I read a few times that the bulb is
actually needed for some reason about it kicking off the charging process and if bypassed with a wire it ruins the circuit?
I dont understand how a bulb being in a circuit is any different (for flow of electricity) than just having a straight wire??
Sorry to ramble but its late, i'm drunk and I'm sure none of that made sense... 
Cheers, Kev
|
|
|
|
|
Antnicuk
|
| posted on 6/12/08 at 11:09 PM |
|
|
i have an issue with mine, the light doesnt go out when the engine is running. I have been told that there are several different alternator systems
and it depends on which type you have as to whether it needs the bulb in the circuit.
Mine still doesnt work though so i may be talking out my a**e
600 BHP per ton, Stylus Brought back from the dead! Turbo Rotary Powered!
|
|
|
Chippy
|
| posted on 6/12/08 at 11:32 PM |
|
|
Can't see that the lamp serves any purpose other than it tells "IF" the alternator is charging, so really it's quite handy to
have one. Cheers Ray
To make a car go faster, just add lightness. Colin Chapman - OR - fit a bigger engine. Chippy
|
|
|
SteveWalker
|
| posted on 7/12/08 at 12:13 AM |
|
|
I think that the bulb allows current to flow to produce a magnetic field for the alternator to begin operation. Once the alternator is producing power
it is self sustaining.
I have seen some motors in the past that had a similar system, but they would still start without it, as long as they'd been run recently enough
that there was still residual magnetism in the cores.
|
|
|
sparrks
|
| posted on 7/12/08 at 12:15 AM |
|
|
the builb is there to show charging or not and if you didnt have it it would be like dead shorting the wire down to earth .ignition on engine not
running you have 12v to the builb and earths out through the ault. with the engine runnung the terminal on the ault becomes the same as the ault
output ie 14.5v you then get voltage to both sides of the builb wich turns the builb out
hope this helps you mate
|
|
|
BenB
|
| posted on 7/12/08 at 12:50 AM |
|
|
You need the bulb.
As well as indicating when the alternator is making juice the flow through the bulb pre-excites the circuit to create the current. No flow through the
bulb= no charging.
Which is why the bulb blowing is seriously bad news because you not only lose the ability to see that you're charging but you lose the ability
to charge at all.
You can miss out the bulb a straight wire because bulbs have a pretty low resistance but some charging circuits won't work without a seriously
low resistance. On my ST charge circuit I had to omit the charge bulb in the end and just have zero resistance- even the lowest resistance bulb I
could find was enough to prevent the alternator coils working....
|
|
|
Antnicuk
|
| posted on 7/12/08 at 10:04 AM |
|
|
my main concern about not having a bulb was that if the alternator belt snaps while on track, or the road for that matter, i have no water pump
either! 
not sure what else your belt drives
600 BHP per ton, Stylus Brought back from the dead! Turbo Rotary Powered!
|
|
|
flibble
|
| posted on 7/12/08 at 01:04 PM |
|
|
Blimey, that was fast!
Bulb it is then, I had to do it properly sometime so I guess it may as well be from the start!
Cheers all
Still cant quite get my head around quite why it works though so I'll put it down to magic
Kev
|
|
|
triumphdave
|
| posted on 7/12/08 at 02:35 PM |
|
|
When I did my dash I used LEDs for warning lights,the charging light LED didnt work to well.I had to rev the engine quite hard to get it to go out,and
was told you needed a proper bulb to excite the circuit.
If you always do what you have always done you will always get what you have always got
|
|
|
02GF74
|
| posted on 8/12/08 at 04:08 PM |
|
|
quote:
Originally posted by triumphdave
When I did my dash I used LEDs for warning lights,the charging light LED didnt work to well.I had to rev the engine quite hard to get it to go out,and
was told you needed a proper bulb to excite the circuit.
yes, that is because the current drawn by LED is about 1/10 of that for the bulb - the solution, and I am using the same set up, is to connect a
resistor across the LED.
The bulb is in effect a resistor that allows current to flow from the battery to the alternator 's field windings. This guaratnees the
alternator will product current; ther may be enough residual magentrism in the coil but you don;t rely on that.
As a side effect of using a bulb, the lamp will be lit when the ouptut from m the alternator is low as explained above.
Note that some modern alternators may have a different set up that do not use the charge lamp in this manner hence it is important to state the
make/model of alternator.
The charge lamp should not be replaced by a wire as effectively this will short the battery to ground.
|
|
|
