A lil confussed

[Lild]

So I was checkin over the engine bay, & I noticed a cut to what I assume is the resisters for the glow plug relay. So looked over the tm's, & notice that the positive wire that goes to the relay & fusible link are missing & the resistors are just sitting there takeing up space.

So I took a few pics. & hope some one can help me with either do I fix it back or leave it the way I got it. This is the way I bought the truck.

 

[Warthog]

Someone has bypassed the glowplug resistor. A lot of guys do it to prevent glowplug damage. Leave it as is.

we have covered it many, many times.

 

[Lild]

Thanks, i sorta figured that, but wasn't completely sure.

Thanks again.

 

[MarcusOReallyus]

Feel free to remove the old resisters and clean things up. OR not. Just a matter or preference. Functionally, it's the same either way.

 

[Recovry4x4]

I don't have a strong knowlege of electonics but from my reading I understand that the whole resistor deal was to facilitate slave starting. I fail to understand how it helps for that but just the same, I left my resistor in place and ready for deployment should it be necessary. My bypass was done a little differently than yours and most. Instead of fabbing up that little pigtail wire to the 12V block, I ran a fresh 8GA wire to the front batt.

 

[SpecWarSquid]

The "Battery Booster" resistors are used to balance the draw across both batteries and step down the voltage to the 12VDC range. It's not exactly 12VDC because it depends on a few things; the voltage level of your batteries, the resistances of your glow plugs(which changes as they heat up) and the current flow across them. Voltage = Current x Resistance.

BTW with regards to resistor check in the -20 TM (Electrical Trouble Shooting, 19. Step 5), the check is poorly written and the resistance is wrong. It states "Check resistance between resistors and ground.Resistance should be 0.28 ohms." First off the resistance should be read across the resistors. Secondly each resistor is 0.28 ohms (I verified this, printed on each resistor) and installed in parallel. The total Resistance in parallel, in this case is actually 0.14 ohms (look up measuring "Rtotal in parallel")

The reason I bet as to why everyone thinks there resistors are bad is because of this really low resistance to measure. My Fluke meter's lead when touched together will already read 0.2 ohms, so the regular joe meter isn't going read these resistors very well. I just rebult my resistor pack and the way I checked them was I used a bench power supply and controlled the current. Sure enough my voltage drop across the resistors told me my resistance was 0.14 ohms. Also if you have access to a 4 wire resistance meter, that can read really small resistances. The truth is that these are heavy duty 300 watt resistors that have a relatively low duty cycle (low usage, only at start up). I don't see these failing like everyone says they are. I suppose they could crack due to vibration, they are ceramic. But that problem I would likely think would lead to both resistors opening up and reading inifnite.

HTH

 

[Recovry4x4]

I've never had an issue with the resistor failing, more of the cascading effect of fried glow plugs when one burns out and the voltage goes up in the others.

 

[MarcusOReallyus]

I've never had an issue with the resistor failing, more of the cascading effect of fried glow plugs when one burns out and the voltage goes up in the others.

Yep.

 

[Lild]

I will most likely take them off. One less thing to clean up after a muddy ride. i just wanted to make sure i was in he good with the current set up. Still new to this whole 12/24v deal, still learnin the in's & outs of it.

 

[Warthog]

Dont throw it away. The next owner may want to put it back.

 

[Lild]

I don't plan on sell "bubba" any time soon. I won't throw them away, but most likely sell them along with other do dadds off the old beast that i dont want. But thats for another post on another board some where in the future.

 

[amphi]

……… from my reading I understand that the whole resistor deal was to facilitate slave starting. I fail to understand how it helps for that ………………

The 12v glow plugs seem to be sensitive to high voltage as evidenced by the cascading burnout effect.


It is possible for all of the glow plugs to see more (or less) than 12 volts while slave starting with resistor bypassed.


The following might be the reason for the dropping resistor:


Batteries charging in series drop voltage just the same as resistors in series.


One can consider two extremes while slave starting from a 24v source.


If the rear battery is COMPLTELY shorted: No voltage will be dropped, at the rear battery, resulting in the front battery and the entire 12v truck circuit seeing 24v.

If the rear battery is COMPLTELY open or missing: All voltage will be dropped, at the rear battery, and the front battery and 12v load will see nothing.


Anything in between these two extremes is possible while slave starting.

In a situation where the rear battery’s charge state (resistance) is lower than the front battery, it (the rear battery) will drop less of the 24v and the front battery will see the remainder. With the resistor bypassed the glow plugs will see a higher than normal 12v and possibly be damaged. The reverse is true if the front battery is lower than the rear.


This battery imbalanced will not affect the glow plug voltage while the resistor is in series with the 24v slaved source, assuming all glow plugs are good and connected. In a complete and well maintained circuit the glow plugs should not see more than 12v as the resistor should drop the other 12v.


I’m not saying the bypass is a bad thing, actually it’s is a good thing -- just be very careful when slave starting the dual voltage CUCV -- follow the TM


The TM -10 clearly states:
"If one battery is missing, DO NOT attempt to slave start."

"Wait 3 to 5 minutes after hooking up slave cable to "dead" truck, before attempting to start it. Damage to the truck’s electrical system may result if the truck is started sooner."


See: TM 9-2320-289-10 Section VI 2-86 Page 125 in the pdf


This wait time is an attempt to allow the batteries to receive charging current form the source/slave and become somewhat balanced allowing the 12v circuit to see a voltage close to the designed 12 volts.


Be very careful when slave starting the dual voltage CUCV -- follow the TM.