archspeed
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 posted on 25/1/09 at 05:51 PM |
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Savage Battery Light - Problem - Help Please!
Hopefully this is me being stupid!! but the problem I have is this:
I've got a set of savage switches, including a battery "charge light". Problem is, when I start the engine, yhe battert light
doesn't go out!! If I put a normal bulb in instead, the bulb lights - then goes out when the engine started!
So me thinks it must be a problem with this savage light....
Theres only 2 connectors, + and - ,
Is it somthing to do with it being LED? and the bulb being a bulb? Do I need another resitor or somthing wiring in?
The instructions that came with it say nothing...
Thanks as allways for any help..
Kevin
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BenB
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| posted on 25/1/09 at 06:03 PM |
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For the ignition light to go out you need the alternator to start working. For this to happen you need to pre-excite the coils. This is normally done
using the ignition light cable (via a bulb). The resistance (and behaviour) of this bulb is quite important. My regulator, for example, on the ST1100
won't work without the specific Honda part (or just being a short circuit as I've got it). The LED will have a totally different
characteristic to the bulb so it's not surpising it won't work.
Most bulbs have a resistance of less than 10 ohms when cold but this decreases as they get hot. You could try replacing the bulb with a 5 ohm resistor
and put the LED in parallel (you will still need a series resistor if you do presently).
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prawnabie
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| posted on 25/1/09 at 06:04 PM |
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Hi
Older alternators need a bulb of about 2 watts to enable charging. The led isn't allowing enough current to be pulled through.
Best thing to do i found is to wire up a small warning lamp behind the dash and keep the savage light up front.
HTH
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archspeed
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| posted on 25/1/09 at 06:46 PM |
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That does all make sense.
Thanks Loads.
Kevin
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:{THC}:YosamiteSam
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| posted on 25/1/09 at 07:21 PM |
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i had similar probs with the dax when i had the zetec in - got a OEM alt to match and did have a LED with the pinto - soon as i changed to the new alt
it wouldnt go out... strange - but when i revved the engine it would then go out - i had to go about 3000rpm or so to get it to go out (as said -
excite the coils to get it to start) there will be a way round it electrically
i took it down to electro diesel north east as it had me baffled - he thought it *may* be the alt pulley which was not standard size (minutely
different)
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02GF74
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| posted on 26/1/09 at 10:27 AM |
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quote:
Originally posted by BenB
Most bulbs have a resistance of less than 10 ohms when cold but this decreases as they get hot. You could try replacing the bulb with a 5 ohm resistor
and put the LED in parallel (you will still need a series resistor if you do presently).
oooh Ben, I know you know better than that!
Metals increase in resistance as they get hotter - this is why domestic filament light bulbs blow when you hit the switch; known as postive
coefficient of resistance.
... back to OP
Diodes are directional too but as your lamp comes on, then you have wired it correctly. As ^^^ say, there is too little current being drawn and the
option is to fit a bulb in parallel or fit a resistor. Bulb is ok but do you want light behind your dash? (you could always paint the glass
black).
I have this in my kit car - cannot remember the value of resistor though - and am about to do the same in my Land Rover. I'm going to try with
a value of 100 ohm 2 W resistor - this does get quite warm.
Note a 5 ohm resistor is way too low - you need about 200 mA so 60 ohm is fine; the resistor will need to dissipate around 3 W ;
68 ohm one of these
I went for 100 ohm 2 W as it is cheaper but that may have been a mistake - I wasn't aware ofthe 3 W resistors at the time.
[Edited on 26/1/09 by 02GF74]
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BenB
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| posted on 26/1/09 at 11:19 AM |
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Good point. I always get confused with temperature and resistance.
Cos the way I look at it (perhaps stupidly) is that the electrons are going to be more active at higher temperature in the metal therefore it's
easier for current to flow.... 
Damn physics proving my theories wrong again!!
Maybe it's a quirk of the ST regulator... but I had to use a zero-ohm resistor. I attached a pot (flipping big one) and wound it down. I needed
a couple of ohms only to get the alternator to work....
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