No Glow plugs

[cruiser_guy]

There are 3 wires coming off the - post on the LH battery, I know 2 of them are for headlights, as I've had to fix it before...

You're looking for wires coming off the positive " + " post NOT the negative " - " post.

Give us a picture of the POSITIVE posts.

 

[brownbear]

eric, I will do the math soon. Here is a calculator for for future reference... might be useful.

http://www.sengpielaudio.com/calculator-ohmslaw.htm

now the plugs are four in parallel, so they have a different "cold" resistance to "hot" so the draw is greatest at the start of glowing. The fuses are called slow blow device though and I am sure a fusible link acts this way, meaning it can go above its rating for a short period with out burning. But if time extends it blows. So a short to ground would blow it.

 

[brownbear]

Yep, but what amp rating does he need?

Ok Math time,

A 24 volt glow plug at 20 degrees is 1 ohm per plug, when hot they are about 4.8 ohms.

So basic parallel math says, 4 plugs at 1 ohm resistance equal 0.25 of an ohm. So a 24 volt system when you first turn on the glow system for an instant you use 96 amps of current.

BUT they ramp down considerably when they get hot, almost instant would be my guess. But the intial current is that high.

Now hot they use quite a bit less amperage, So 4 plugs at 4.8 ohms each hot, equal 1.2 ohms total in parallel. So 24 volt system times 1.2 ohms equals= 20 amps draw once they are glowing.

Now If I was to pick a fusible link I would have to also consider the wire it was on.

If the wire is 10 gauge wire then it can handle approx 100amps.
12 is 60 amps
14 is 40 amps.

Not sure if you can figure out what wire size you have or not. There are charts online to help. Or go to the auto store and look at sizes and try to compare.

I am guess it is 12 or 14. On the BJ60 they use a 60 amp fusible link I think.

But you 24 volts. So You could use a 40 amp fusible link. If it blows go one size bigger.

Also ensure one thing first, MOST IMPORTANT, disconnect the wires at the relay, and the busbar and making sure the ends do not touch ground, try using your meter set on ohms to see if the cable has any shorts to ground that caused the fusible link to go. Also with all the busbar off on each glowplug take your meter to the top and the other probe to the engine, ensure that each glowplug is about an ohm. If it is 0 or .2 you have a bad plug that is shorting direct to ground. So your next fisible link may fail.


Any questions?

 

[brownbear]

You may ask, why is the fusible link 40 amps when the plugs draw 96 to start?

Well the fusible link is just a smaller wire designed to fail first, like a shear pin. It can handle bursts of higher power, but if the higher power was left on it will get hot and melt. Much better than the actual wire melting.

SO yes IMOP a 40 amp fusible link can handle a burst of 96 amps, but only momentarily. Which is what I think the glows do.

But I am not an auto mech, so take this with info for what it's worth, 2 cents...

 

[Eric Winkworth]

thanks brown bear, it is warmer out today, so I'm going to get this fixed up...

 

[Ron R]

Eric,
if you can't find the break in the wire or find the fusable link, then maybe it's worthwile to (temporarely) create a direct connection (use a fuse near the batterie) between the batterie and the glow-relay if not untill y've sorted out the problem, then at least to find out or this is the reason for your problem.

 

[brownbear]

Eric,
if you can't find the break in the wire or find the fusable link, then maybe it's worthwile to (temporarely) create a direct connection (use a fuse near the batterie) between the batterie and the glow-relay if not untill y've sorted out the problem, then at least to find out or this is the reason for your problem.

A fuse, like a square heavy one in a GM. May not have the slow blo feature enough. It might blow to quick. Where a fusible link probably allows more heat over a longer period.