C7 intake grid heater voltage drop. Normal?

[GeneralDisorder]

Video of the 14v gauge on cold start with the intake heater running. If you set the high idle it draws more power as more air is pulled across the heating element. Voltage goes back to 14v when the grid heater turns off.

Having no frame of reference for normality I figured I would get opinions on this behavior.

2008 A1R with 260a alt. Seems like the more powerful alt should be able to maintain closer to 14v than what I'm seeing but again I have no frame of reference. I just can't imagine how low the voltage must get on the 100a alternator trucks.....

Video of the 14v gauge on cold start with the intake heater running. If you set the high idle it draws more power as more air is pulled across the heating element. Voltage goes back to 14v when the grid heater turns off....

Rick

 

[Ronmar]

Wonder what it is actually doing at the batteries?

 

[Ronmar]

Hey, I know why the intake heater is pulling your 14V down so much…

Because it is supposed to be connected to 28V, not 14…

TL507 is the feed to the intake heater. It is supposed to be connected to the “24 battery” terminal on the LBCD. From there it runs thru a fuse and to the intake air relay/contactor, then thru the heater and on to engine block ground X10…

 

[GeneralDisorder]

Ya know I wondered about why it wasn't a 24v heater. I have been doing searches on the C7 heater trying to find specs like amperage draw, etc..... Well I know for a fact that I didn't swap them but someone had been in there for sure at some point because I clearly remember at least one of the studs missing it's lock washer and of course they were all nasty and broken free from the epoxy before I tried to clean them... Truck formerly lived in TX and the inlet heater probably never got used. I'm sure someone from the E4 mafia or someone with skeeter wings is responsible for this screw up.

I will check that first thing before I run the truck again. I should have reviewed the schematics. It makes so much sense now that you pointed it out to me! Thanks!

And that's exactly why I asked. Because it didn't seem right to me.

Rick

 

[Ronmar]

It will also probably work a lot better on 24V

 

[Suprman]

The solenoid relay for the grid heater is a common failure it gets water in it.

 

[jasonjc]

Can't speak for the c7, but the 6.7cummins in our bus at work, will pull the volts down like that or more and we have 320 amp alt with 3 group 31 batteries.

 

[coachgeo]

The solenoid relay for the grid heater is a common failure it gets water in it.

is it a 12v relay that switches on 24v electrical path?

 

[Mullaney]

is it a 12v relay that switches on 24v electrical path?

.
Why not? The starter on the LMTV won't engage with fully charged 24v batteries IF the 12v batteries are low. In my particular truck, the right front battery (of four) is the one that measures lower than it should be.

Seems to be no reasoning to that situation either.

 

[Ronmar]

Yea that solenoid is right at the back end of the head so water down the back of the cab can get to it.

Not sure if its coil is powered by 12or24 but the ECU is controlling the coil current path…

 

[Ronmar]

Can't speak for the c7, but the 6.7cummins in our bus at work, will pull the volts down like that or more and we have 320 amp alt with 3 group 31 batteries.

To get the same heat/wattage out of a 12v unit you need to pull twice the current…

 

[Ronmar]

Ya know I wondered about why it wasn't a 24v heater. I have been doing searches on the C7 heater trying to find specs like amperage draw, etc..... Well I know for a fact that I didn't swap them but someone had been in there for sure at some point because I clearly remember at least one of the studs missing it's lock washer and of course they were all nasty and broken free from the epoxy before I tried to clean them... Truck formerly lived in TX and the inlet heater probably never got used. I'm sure someone from the E4 mafia or someone with skeeter wings is responsible for this screw up.

I will check that first thing before I run the truck again. I should have reviewed the schematics. It makes so much sense now that you pointed it out to me! Thanks!

And that's exactly why I asked. Because it didn't seem right to me.

Rick

Another possibility you should explore is that I believe they make the heaters in 12 or 24v config. Someone may have shifted yours to a 12v heater. It looks like 2 heater grid units side by side so may be wired parallel for 12v operation or in series for a 24v installation…???

 

[GeneralDisorder]

Well - I did confirm that the heater is currently hooked to the wrong terminal. It's on the 12v load terminal, and should be connected to the 24v batt terminal. On my truck and in my schematic it is TL508. I'm going to move it today.

Wiring looks all original CAT and the solenoid is labeled 24v. Just a single big cable to the heater. Truck had less than 2k on it when previous owner got it and he changed nothing regarding the LBCD or grid heater.

Might be what caused the demise of the LBCD capacitors.... not sure why the 24v caps would be blown also though.

Still plenty of questions on this one.

 

[Ronmar]

I wouldn't think it would effect the caps as it should only be DC as with a resistive heater there is nothing to generate any noise….

my info shows TL508 at the solenoid end of that power cable.

what I was talking about earlier, if the heater elements are a pair in series, and say one failed(no heat) some bright light may have got field expedient on its ass and bypassed the bad element and reconfigured it for a single 12v element(half heat is better than no heat)…. I would look at the heater end of the wiring just in case…

 

[GeneralDisorder]

I checked the heater end of the wiring - it's just a single terminal from the solenoid into the heater. And it looks untouched and stock.

You are correct - TL508 is the solenoid side of the wire after the fusible link. TL507 connects to the LBCD.

I swapped it back and fired it up. No more issues. No wavering of the 14v gauge. The 28v gauge took a second to reach 28v - current inrush of the cold heater I assume. It quickly climbed up to 28v though and stayed there. I'll post a video in a bit. It started quickly, but the temp is currently 50 degrees.

You're right that there *shouldn't* be any effect on the caps - if it was connected correctly. But it was connected to the 12v load terminal. Not the 12v batt or 24v batt terminal. So it was drawing from the side where the 12v caps are connected. That doesn't entirely explain the 24v caps being wasted though. I'm not really sure what conclusion to come to. I hope I didn't hurt the replacement LBCD. I only started it the one time. Today after I realized the possibility of the wiring issue I raised the cab and lowered the spare by hand to make my assessment and adjustments.

I found a picture I took of the LBCD 24v batt terminal before I touched the original to clean up the terminals and there's no inlet heater wire. So definitely this has been this way for minimum 3,000 miles. I smell the work of Private Snuffy......

 

[Ronmar]

Ahhh PVT Snuffy, not the sharpest tool
In the shed but a dam fine shot!

You may have pushed the 200A current limit pulling that heater current thru it for that start, and the restriction to the flow from the diodes at that flow rate certainly explains the voltage drop at the meter….

you didn't run it that way for long so you are probably ok… especially since the diodes on the old one were still passing current OK…

Dont see it effecting the caps though, and like you mentioned, certainly not the 24V ones.

another fine example of not taking anything for granted. When I got mine, 3 of the 4 front brake shoes were on backwards…. That Snuffy guy gets around…