Jamesc2123
Jamesc2123 Reader
12/21/11 9:32 a.m.

This is probably an easy one, but its just not something I've heard of or had to deal with before.

Car is a 1991 CRX. I clicked on the high beams the other day and they came on for a few seconds, then both blew out. They use single filament beams, so the high beams are a second bulb/housing than the lows, which are working fine. I replaced the bulbs, turned the high beams on, and they blew out in about 5 seconds.

woohoo, that was a fun way to spend 30 dollars...

Probably related is the fact that my wipers and dashboard lights get faster/brighter as RPMs climb, so I'm thinking my alternator is overcharging my system somehow. But my turn signals, low beams, taillights, etc are all working fine.

So what do I check for, and how do I know to replace it?

Dr. Hess
Dr. Hess SuperDork
12/21/11 10:03 a.m.

Over voltage will blow headlights, certainly. However, did they blow out with the car off or with the motor running?

Start with a volt meter. Put it across the battery and rev the motor. If you have more than 14.7V, replace the regulator or alternator, depending on your configuration. I am gonna guess an internal regulator, so replace the whole unit, but I don't know honduhs. Next, put the meter on AC Volts and check across the battery. If you read anything there, the diodes in the alternator are shot.

DILYSI Dave
DILYSI Dave SuperDork
12/21/11 10:09 a.m.

I'm betting you've got a bad ground somewhere.

Cone_Junky
Cone_Junky HalfDork
12/21/11 10:13 a.m.

Had the same problem on my VW. Both headlights would blow out at the the same time randomly. Rewired and relayed them, still did it. Tested alternator and battery, everything looked great. But one night driving home I noticed my headlights would occasionally go super bright. Replaced the intermittently failing voltage regulator and the problem was solved.

N Sperlo
N Sperlo SuperDork
12/21/11 10:41 a.m.

My bet is on voltage reg.

wclark
wclark New Reader
12/21/11 10:57 a.m.

+1 for the voltage regulator.

a401cj
a401cj Reader
12/21/11 11:28 a.m.
DILYSI Dave wrote: I'm betting you've got a bad ground somewhere.

i hope that was meant as sarcasm

DILYSI Dave
DILYSI Dave SuperDork
12/21/11 11:49 a.m.

It was not. Why do you hope that?

That generation of Hondas have a history of grounding issues. If there is a bad ground, then it could be pulling too much amperage through the circuit, and blowing the bulbs.

Dr. Hess
Dr. Hess SuperDork
12/21/11 11:59 a.m.

Bad grounds pull less amperage. Bad ground = poor connection = resistance = heat at the bad ground = less amps flowing in the circuit.

However, a bad ground in the wrong place could cause the voltage regulator to overcharge the system.

stuart in mn
stuart in mn SuperDork
12/21/11 12:14 p.m.
Probably related is the fact that my wipers and dashboard lights get faster/brighter as RPMs climb, so I'm thinking my alternator is overcharging my system somehow. But my turn signals, low beams, taillights, etc are all working fine.

The evidence suggests a bad voltage regulator. Do you notice the fan blower changing speeds as well? Measure voltage at the battery and rev the engine, it shouldn't go any higher than a little over 14 volts. If it does go higher than that the regulator is toast.

mad_machine
mad_machine SuperDork
12/21/11 1:47 p.m.
Dr. Hess wrote: Bad grounds pull less amperage. Bad ground = poor connection = resistance = heat at the bad ground = less amps flowing in the circuit. However, a bad ground in the wrong place could cause the voltage regulator to overcharge the system.

I have seen it on one of my fiats where a bad ground power back through the highbeam circut when the lows were on.. and no.. the lamps did not last long when that happened.

I would take the lamps out and connect up a meter to check the voltage at the lamp socket. With the car running and the highs engaged, you will be able to tell if you are supplying too much voltage to the lamps

Jamesc2123
Jamesc2123 Reader
12/21/11 2:48 p.m.

So the voltage regulator would be contained inside the alternator, not a separate unit like a motorcycle, and if it were bad I would need a new alternator?

The dash lights get brighter and wipers speed up as the RPMs rise. As far as i can tell, everything else stays the same (low beams, blower motor, etc.) but I could just not be noticing.

I'll have to wait until I'm home this weekend to use my multimeter to check the volts. Should I be worried about damaging other systems the next few days if there is too much voltage getting to other parts?

a401cj
a401cj Reader
12/21/11 3:11 p.m.
DILYSI Dave wrote: It was not. Why do you hope that? That generation of Hondas have a history of grounding issues. If there is a bad ground, then it could be pulling too much amperage through the circuit, and blowing the bulbs.

because that is answer posted for every single electrical question period. I even use it at work myself (EE) when I don't feel like taking the time to give a thorough answer. It's almost as bad as saying 'the flux capacitor'

iceracer
iceracer SuperDork
12/22/11 9:29 a.m.

Bad grounds was one of the first thing the instructor would mention when I attended classes in electronic fuel injection etc.

Sky_Render
Sky_Render Reader
12/22/11 9:31 a.m.
DILYSI Dave wrote: I'm betting you've got a bad ground somewhere.

A bad ground would cause under-voltage, not over. As reference, see these articles, written by yours truly:

http://www.motoiq.com/magazine_articles/id/1787/electrical-basics-and-automotive-grounding-systems.aspx

http://www.motoiq.com/magazine_articles/id/1952/basic-electrical-troubleshooting.aspx

If your voltage is too high, you need a new voltage regulator. Different cars have them installed in different locations. On some cars, they are internal to the alternator, on others, they are external or part of the logic module. On many vehicles, you can simply install an external regulator and be done with it.

If you need a recommendation on one, buy one for an old Muscle car from Summit Racing.

EDIT: This might work, even if it is for old-school Mopars: http://www.summitracing.com/parts/DCC-4529794/

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