Very hot resistor....why?

[tankie88]

I have a brand new Alt on the L/H side and a rebuilt Alt on the R/H side.All was working ok for months.Now,when I start up the glow plug light does all the right things and it starts.Then not charging properly with squeeling belt.All of a sudden it will go into the green and charge.After a while the needle drops no charge,horrible smell and the resistor on the back fire wall is red hot.Anyone any ideas??

 

[gimpyrobb]

Sounds like a bad regulator or battery. I would start with load testing the batteries.

 

[doghead]

The resistor is used to supply the GP relay.

If your relay is bad(dirty contacts), there may be extra resistance, causing extra load(heat).

Try measuring the voltage across the two big terminals on the GP relay while it is energized. Ideally there should be none. Any voltage indicates bad contacts.

 

[Skinny]

From your description, it sounds like your GP system is turning on after the initial cycle on start up. If the GP's come back on, your volt meter will go down due to electrical load. Your GENs may complain too if the truck is at an idle, belts loose, idle speed low, etc.

That would be the only reason I could think of the resistor being used outside of the initial GP cycle. Sure the relay may be stuck on but you would probably never see the voltmeter go into the green if that's the case.

 

[Westech]

Is it really glowing red hot? Or just hot? Mine will smoke a tad if it is covered in dust or water ect... I would just bypass that junk and have the relay fed 12v off the junction on the fire wall. Change out the relay and flow plugs if you have not done so in a few years and I bet she will work just fine.

 

[Westech]

Mine as in before I tossed it in the trash.... (Resistor)

 

[tankie88]

The relay is new and the glow plugs are not that old.The resistor gets that hot it will burn your hand.

 

[Westech]

If it is not glowing your fine.... It will get hot during normal operation

 

[gimpyrobb]

Make sure you do the Doghead mod!!!!!

 

[Westech]

Gimp wtf ? That has nothing to do with glow plugs. Don't make me come down there!!!

 

[tim292stro]

To quote your thread title: "Very hot resistor....why?"

Because that's what resistors do - they convert electrical power to heat. Same principal as your glow plugs. The amount of temperature rise is a function of design.

The purpose of the ballast resistor is to drop the voltage by 50% from the 24V batteries down the to 11-10.5V your typical glow plug will need. A good ACDelco 60G glow plug is about 200Watts, 8x of them is 1.6kW - about as much as your average plug-in room heater will draw - since the 1.6kW is only the lower half the the power drawn (ballast resistor uses the other half of the voltage), that means you are using ~1.6kW just to get the voltage right for the plugs - and that power dissipation is condensed down to that tiny space on your firewall (not a big heater with lots of surface area). The glow plug controller should keep the heat times short enough for that resistor to be okay, but check to be sure that is true (bad cards are common, stuck relays are common).

You could replace your ballast resistor with two DC-DC regulators (one per side of the engine) and you wouldn't have so much of a heat issue, and you'd also relieve the potential for a single Glow-plug failure leading to a cascade failures of all 8 plugs - and it wouldn't be so hard on your batteries (DC-DC regulators are WAY more efficient, >89% for DC-DC regulator vs ~50% for a simple ballast resistor). This will cost money (about $250) and under-hood space...

 

[Skinny]

the glow plug light does all the right things and it starts.Then not charging properly with squeeling belt.All of a sudden it will go into the green and charge.After a while the needle drops no charge,horrible smell and the resistor on the back fire wall is red hot

Obviously trying to diag across the internet is tough but it sounds like you have old slipping drivebelts and a glow controller than is cycling back on when it shouldn't be. Am I the only one that is reading that here? No one really has addressed why the voltmeter would go from green to red after proper operation followed with the resistor being red hot.

 

[doghead]

How long after it starts does the GP controller cycle? There is a short "after glow" cycle too.

 

[Westech]

mine will glow two times after the main start glow when it is butt cold out.

 

[Skinny]

mine will glow two times after the main start glow when it is butt cold out.

Good call, what is the weather like across the pond this week? I think you start to get that after glow when it gets into the 40's or lower. Your mileage may vary...plus you have that whole metric thing to convert to.

Chip Chip

 

[scottladdy]

Antennaclimber's classic video.

http://youtu.be/MTkOl947aTk

Afterglow starts at 1:55 approximately.

 

[Westech]

We are at -12*C here. She is chilly and it'd about 6 weeks too soon for this weather.

 

[Skinny]

At that temp, you may get a slightly longer after glow
If that's the case, the OP may just need to tighten is alternator belts. I wouldn't trust the GP card though.

So I was walking around in the 70 degree t-shirt weather yesterday down here in North Carolina...

 

[tankie88]

Mine normally cycles twice after the main start as well.But I also get relay chatter.

 

[Westech]

my relay chatters also after the last glow. Did I miss the place where this chatter has been explained?