Constant dim battery light on

[MIGHTY 8]

Hello,
Can someone provide additional help with why this could happen and what detrimental effects it may lead to? And of course, what steps to correct it.
Thank you all,

Gabriel

[ORFORD2004]

Bad ground or check the voltage at the battery. You should have at least 13.5 v

[RRoller123]

Weak alternator output I think will do this as well.

[AriK]

Bad ground or check the voltage at the battery. You should have at least 13.5 v

Weak alternator output I think will do this as well.

If these results are ruled out and the light is only noticeable at nights you may likely consider this as one of
Fiat's standard features.

[So Cal Mark]

this indicates a bad diode in the alternator

[RRoller123]

serviceable by owner? or requires alternator replacement?

[AriK]

i assume OP means that light stays lit with key off.

[djape1977]

+1
bad diode

[mattyd7]

I have this problem as well. It is hard to see in the daytime, easy in the dark. I get plenty of voltage out of the alternator, so it is not a charging problem. Last time it was at the Fiat specialist for something I had them put some time into solving it, and they assumed bad diode but checked and said that wasn't it. Took the alternator out and everything for me. Redid all the grounds. Still does it. Since it charges perfect, I've chalked it up as something I have to live with. If you figure out something else that caused yours that I didn't mention, please post because I wouldn't mind getting rid of that light!

I've done the brown wire fix, headlight relays, a lot of electrical improvements and rewiring in general since owning the car, and none of those have improved or worsened the light.

[djape1977]

there's a replacable part in alternator called diode plate. it contains 3 diodes. it can be replaced if you know how to solder.

alternator, as it's name suggests, produces alternating current (AC), while the electrical system in the car uses direct current (DC).
diodes are there to "flatten" AC into DC. when one of them goes bad, you get a dim red light. pretty soon afterwards, next one will go and you will no longer have DC power supply, but mostly AC which will no longer charge your battery sufficently. when third goes off, you have no charge at all

[AriK]

Great info. Thanks for posting that.

[MIGHTY 8]

Thank you all so much for your input!
Will keep you posted!

Gabriel

[RRoller123]

Likely a standard AC-to-DC Diode Bridge, I think. Here is a simple pic of how these work. They basically flip the bottom half of the cycles to approximate DC current. Then a Capacitor flattens out the curve.

http://3.bp.blogspot.com/-rX5SBYQWPPo/U ... ifier4.jpg

[hayesbd]

Alternators are voltage regulated and there is a standard voltage set point range for the nominal 12V automotive system, namely 14.2 to 14.4 volts. You should see this voltage when running the engine at any decent speed above idle, regardless of what electrical load you have. This set point value was determined to be good enough to charge the battery quickly enough without excessive tendency for the electrolyte to boil dry too soon. If you see 13.8 under steady cruise conditions, there is likely a diode problem as mentioned before. You won't have a huge problem for now at this voltage, but eventually you will have to fix things, especially if you do lots of short trips since recharging the battery at 13.8 volts is much slower than at 14.2.

Interestingly enough, modern computer controlled charging systems often have a variable set point to reduce the fuel consumption and wear/tear on the battery and alternator. When cruising along in daylight on the freeway, sometimes the voltage set point even drops to the "nominal" battery voltage of 12.6V. At night, these systems often switch to a steady set point of 13.8V (at least on GM cars).

I added a Walmart volt meter to my spider by hiding it in the ashtray, which I don't use. It has a switch that is engaged only when I flip open the door. I found this to be a nice way to monitor the system's health while cruising along without spoiling the normal look of the interior.


Brian

[DieselSpider]

serviceable by owner? or requires alternator replacement?

The cost of the diode, regulator and bearings come so close to the $59 for a replacement alternator for a Spider that its hardly worth the effort.

One of the three local major parts vendors Advance, Oreilly or AutoZone can usually get one in 24 hours and it will carry a lifetime warranty.

You may get a hint of the diodes/rectifiers going when you see the displays on digital devices wavering when plugged in to the accessory outlet with the engine running.