Relay Question

[jim-d]

Not for C-10 but an interesting question.

We have a bus at work.  It drains the battery overnight.  Sometimes it does, sometimes it dosen't.  Took it to the shop.  They said pull out this fuse, a 50 amp one.  So every night the driver parks the bus & pulls out the fuse.  The battery never dies with the fuse pulled out. 

So don't go screaming on the mechanic, this is Atco, NJ.  Using 3 syllable words will get you elected mayor, or a burning cross on your front lawn.  Kind of depends..............

Sounds like a stuck relay to me.  I do not have a wiring diagram.  So the question is, how can you figure out which relay is attached to which fuse without a diagram.  Is there a way to test a relay to see if it's on at the relay or at the relay block?  The set up is what you expect, a block of about 20 fuses right next to a block of about 8 relays under the hood.

I asked the person who shold know, fat chance around here, if the bus will run with the fuse pulled out...YES.  When the bus is running, what is missing with the fuse pulled out...some of the tail lights.  Seems like something missing for a 50 amp fuse.

Any ideas?

Thanks

[connie_rider]

I am not an electrical guy, so someone can shoot this idea down.
Besides the 50 amp fuse, there must be others/smaller fuses..
Assuming you don't have something that stays powered when the bus is off, pull the 50 amp and put a volt meter across it.
Should read 12 volts.
Next pull the smaller fuses until you loose voltage. That circuit will be where the fault is.

Ride safe, Ted

[rwulf]

That's a great idea!

[jim-d]

Thanks, not sure I fully understand.  Is a big fuse like that usually in front of the relay or after it?  The fuse should be in front of the relay, right?  If so you will always get power arcing the fuse socket.  Shouldn't matter pulling other fuses, the box is always hot.

If smaller fuses are down stream, it still doesn't tell me which relay is providing the power.

I'm looking for a stuck relay, one that won't open when the triggering power source is off, not convinced it is a short circuit.  If the relay worked it would not drain power when off, a short should  blow the fuse.    Can't figure out how to test a relay to see if it's open or closed while still plugged in.  This is mounted in a truck so I can't  get to the pins on the relay to test for open or closed here. 

That's where I need to go.

[connie_rider]

Like I said, I am not an electrical guy, so someone can shoot this idea down.
I was guessing that the big fuse was a Master Fuse.
The smaller fuses would be after the Master fuse in the circuit, but before the components.
And I think, before the relays for those components.
Fuses are installed in the Positive wire, before the component. (so that they protect the component)

Another option would be remove the positive wire from the battery. Put the volt meter across that.
Should read 12 volts if something is turned on.
If everything is off, (and if you don't have a clock in the bus) you should read no voltage.
Pull the 50 amp fuse and see if the voltage goes to0.
Replace the 50 amp and voltage should come back.
Then remove smaller fuses, looking for the fuse that kills the power.

NOTE: You may not have a stuck relay. You may have a short.

[Daytona_Mike]

i doubt very much it is a relay.  You would know what is on if a relay was left or stuck on.
You may have a current draw .
Borrow a current (amp) meter and put it inline  from the positive post to the battery and see if there is a draw.
if there is  a draw then you can pull fuses until the draw stops.
You found the culprit at that point.

[jimmymac]

i doubt very much it is a relay.  You would know what is on if a relay was left or stuck on.
You may have a current draw .
Borrow a current (amp) meter and put it inline  from the positive post to the battery and see if there is a draw.
if there is  a draw then you can pull fuses until the draw stops.
You found the culprit at that point.

This. Amp meter.
There are other ways to find it, but the amp meter is the correct way.

[GeeBeav]

This. Amp meter.
There are other ways to find it, but the amp meter is the correct way.

Preferably a clamp-on type. It clamps around the battery cable so you don't have to break the circuit.

[Leo]

How big of a bus?   I worked nights at a school bus Company in Lansing, IL.  They had 700 buses and many Gov contracts.  They also had a motorcoach company.   I would often find bad diodes in the Alternator.  The above suggestions of a meter (or even a light bulb) in series with the battery lead is a good indicator.  If you are lucky enough to get to the vehicle when it is cold, you may be able to feel the Alternator being warmer than the other parts under the hood.  Smack the alternator with a club and if you see a change, that is a sign of a shorting diode.   Removal of the B+ lead will usually eliminate the draw.  If it does, you found the problem.  Good luck

[connie_rider]

Good point Leo.
I bad diode in the Alternator could easily be the culprit here.

Ride safe, Ted

[jim-d]

i doubt very much it is a relay.  You would know what is on if a relay was left or stuck on.
You may have a current draw .

I was going this way becasuse last x-mas eve my girlfriends Civic died in her parents drive way.  AAA sais it was a dead batery.  I drove over with a new battery & it was dead in the morning.  Dealer said it was a stuck relay to the AC so nothing was ever on that you could see.

Kind of like the alternator idea.

Ill try the fuse idea but for a short, wouldn't it stop drawing when the bus is turned off if everything else was working, or blow the fuse first or wouldn't you smell something burning?  Thing withthe short is everything is working fine whenthe big fuse is in & the bus is running.  Nothing that won't turn off & all the lights and accessories work.

The only experience I have with a short was a cheap phone charger that would blow the fuse everytime I plugged it in.  If it was in when the car was off that would have been a power draw but the fuse always went first.

The bus is a 2011 ElDorado 18 passenger on a Ford E450 super duty chassis.  Gas engine.

[Bikenagain]

Try looking at the voltage regulator / rectifier. On a few bikes I have worked on over the year  the owners have had the problem of if the bike had been let sit for 2 or 3 days the battery had gone flat and in each case the rectifier had been RS, replaced the rectifier and problem solved. Just google testing voltage rectifier and how to test it will come up.

http://answers.yahoo.com/question/index?qid=20100929121546AASItlM

[jim-d]

Thank you fr all the good advice gentlemen.  I'll be off on a new electrical adventure Monday.

[bbroj]

A short doesn't always mean blown fuses. If it is a low or no resistance short, you will likely blow a fuse. A high resistance short, green crud at the bottom of a light bulb socket for instance, will allow everthing to work correctly and just slowly bleed the power overnight. The suggestions for drilling down to the culpret circuit already posted are exactly what I would suggest, so no need to repeat. However, I'm leaning in the direction of Leo's idea of a bad diode in the alternator.