B3350

[SDT]

I thought I read that glow plugs usually have a voltage rating that is lower than battery voltage. So I was surprised when Whitetiger said the voltage on the glow plugs should be battery voltage, or close to it.

Point to check the glow plugs and verify the rated operating voltage is a good one. Heat generated is proportional to the square of the applied voltage. 10 volts on a 12 volt glow plug would produce roughly 44 percent less heat. (this is because heat produced is a function of the square of the voltage applied)(for a 1 ohm glow plug, that would be 100 vs 144 watts)

As far as voltage drop in the wiring supplying the glow plugs being 2 to 3 volts, in my opinion if that were the case the electrical engineer who sized the wiring should be doing other work. Unless of course, the drop is by design, but that is often accomplished by inserting a resistor in series with the glow plugs.

These two things leave me scratching my head...

9-10 volts is all that can be expected at the bus bar due to voltage drops across components between the battery and the bus bar.

Trust me. I have inspected the electrical system.

SDT, EE, retired

 

[whitetiger]

9-10 volts is all that can be expected at the bus bar due to voltage drops across components between the battery and the bus bar.

Trust me. I have inspected the electrical system.

SDT, EE, retired

On the several I have checked, the voltage at the glow plugs in a B3350 are within .5 volt of battery voltage. I put a volt meter across the battery terminals to monitor battery voltage and a meter between the battery negative post and the glow plug, then turn the key switch to Glow position. I have then rotated the meters and retested them for accuracy.
There is no reason for this simple straightforward system to have a large voltage drop.

 

[SDT]

On the several I have checked, the voltage at the glow plugs in a B3350 are within .5 volt of battery voltage. I put a volt meter across the battery terminals to monitor battery voltage and a meter between the battery negative post and the glow plug, then turn the key switch to Glow position. I have then rotated the meters and retested them for accuracy.
There is no reason for this simple straightforward system to have a large voltage drop.

Actually, there is such reason.

Divide the nominal resistance of a glow plug, which is quite low (but I'm not going to take the time to look it up), by 4 to determine the resistance of the load. Divide the battery voltage by the resistance of the load which will be below 1 Ohm, to determine the load current, ignoring the IR of the battery, which is low but not 0, and the resistance of the wiring harnesses, connectors, relay etc., which will be considerably higher than the IR of a good, fully charged battery.

I expect that the nominal load current is 15-20 amps but I'm not going to take the time to verify this.

Inspect the wiring size(s) and length(s), which I am not going to take the time to do, and I expect that you will determine that a voltage drop of 3 or 4 volts across the wiring, connectors, etc., is to be expected.

I certainly do.

SDT

 

[Henro]

Actually, there is such reason.

Divide the nominal resistance of a glow plug, which is quite low (but I'm not going to take the time to look it up), by 4 to determine the resistance of the load. Divide the battery voltage by the resistance of the load which will be below 1 Ohm, to determine the load current, ignoring the IR of the battery, which is low but not 0, and the resistance of the wiring harnesses, connectors, relay etc., which will be considerably higher than the IR of a good, fully charged battery.

I expect that the nominal load current is 15-20 amps but I'm not going to take the time to verify this.

Inspect the wiring size(s) and length(s), which I am not going to take the time to do, and I expect that you will determine that a voltage drop of 3 or 4 volts across the wiring, connectors, etc., is to be expected.

I certainly do.

SDT

SDT, you are disputing actual specific measurements taken and reported by a respected, knowledgeable and very experienced Kubota Technician...

Remember, Whitetiger did ask about size of wires connected to the relay on the B3350. Perhaps yours is one that has the wrong size wiring, and there actually IS an excessive voltage drop in your wiring.

It makes no sense that a manufacturer would build a system using 12 volt rated glow plugs, and wire it in a way that would only supply 10 volts (or less) to those glow plugs. No way the glow plugs could produce the rated heat, and they are in place to produce the rated heat...

 

[SDT]

SDT, you are disputing actual specific measurements taken and reported by a respected, knowledgeable and very experienced Kubota Technician...

Remember, Whitetiger did ask about size of wires connected to the relay on the B3350. Perhaps yours is one that has the wrong size wiring, and there actually IS an excessive voltage drop in your wiring.

It makes no sense that a manufacturer would build a system using 12 volt rated glow plugs, and wire it in a way that would only supply 10 volts (or less) to those glow plugs. No way the glow plugs could produce the rated heat, and they are in place to produce the rated heat...

Actually, it is not uncommon for manufacturers to size wiring knowing that there will be significant voltage drop in the circuit in order to save the cost of additional copper.

Trust me in this regard as for years I was a design engineer for a major US automobile manufacturer in a previous life.

I am not uncomfortable with a 3 or even 4 volt drop in this circuit given the intermittent duty.

Someday, when time permits, I will measure the voltage at the glow plugs in my B1750, L6060, M9960 and RTV X1100C.

Until such time, I will agree to disagree as this is not that important to me and has already taken too much of my time.

SDT

 

[Henro]

Actually, it is not uncommon for manufacturers to size wiring knowing that there will be significant voltage drop in the circuit in order to save the cost of additional copper.

Trust me in this regard as for years I was a design engineer for a major US automobile manufacturer in a previous life.

I am not uncomfortable with a 3 or even 4 volt drop in this circuit given the intermittent duty.

Someday, when time permits, I will measure the voltage at the glow plugs in my B1750, L6060, M9960 and RTV X1100C.

Until such time, I will agree to disagree as this is not that important to me and has already taken too much of my time.

SDT

OK, but then how does it make sense that they would use a 12 volt rated glow plug if that were the case?

Having trouble seeing the logic there. I have read that some tractors actually have a resistor used in series for the purpose of dropping the voltage down to that required by glow plugs that have a lower than 12 volt rating.

If smaller wiring was intentional on the B3350, how would that explain Whitetiger's measurements? The tractors he checked would have had to have defective glow plugs, following your logic.

These are the questions that pop up into my mind.

Not meaning to be argumentative. Just explaining where my thinking is at...

 

[Russell King]

OK, but then how does it make sense that they would use a 12 volt rated glow plug if that were the case?

I do know that NGK and Kubota design the glow plugs to operate below 12 volts. My older L185 has a resistor in the circuit when at the glow only position. When cranking the glow plugs are still active but the resistor is bypassed in the crank position. I have measured the voltage at the plugs in both positions but don’t recall the exact voltage value. They do the voltage reduction to lengthen the life of the glow plug.

I will try to measure the voltage between the battery negative post and the glow plug terminal this weekend sine the indicator and glow plugs are relatively brand new.

(Why is brand new newer than new?)

 

[Henro]

I do know that NGK and Kubota design the glow plugs to operate below 12 volts. My older L185 has a resistor in the circuit when at the glow only position. When cranking the glow plugs are still active but the resistor is bypassed in the crank position. I have measured the voltage at the plugs in both positions but don’t recall the exact voltage value. They do the voltage reduction to lengthen the life of the glow plug.

I will try to measure the voltage between the battery negative post and the glow plug terminal this weekend sine the indicator and glow plugs are relatively brand new.

(Why is brand new newer than new?)

No doubt that SOME Kubota tractors use glow plugs that are rated at less than 12 volts and use a series resistor to drop the voltage to rated voltage, often around 10 volts or so from what I have read.

BUT Whitetiger, a very experience Kubota technician, has indicated the B3350 glow plugs should have 12 volts applied to them. AND has measured this himself on two or more of those tractors. I do not know,but have no reason to doubt Whitetiger.

I do not have a B3350 tractor, so have no personal interest. BUT I do have intellectual curiosity.

Just cannot rationalize why applying 10 volts to a glow plug rated to operate at 12 volts would make any sense...

Perhaps someone can verify what the rated operating voltage of the glow plugs used in the B3350 is. If it is 12 volts and 10 volts is applied, this does not seem to make sense...

 

[D2Cat]

Maybe they apply less voltage to prevent the GP from melting the tip. On the Ford 6.9 diesels the tips melting was a problem. When it happened in most cases the head would have to be removed to get the broken tip off the top of the piston.

I know some folks would turn the engine over and hope the compression would blow the piece out. Sometimes it did and you could end up with a hood that looked like a 22 was shot through it!

 

[PoTreeBoy]

No doubt that SOME Kubota tractors use glow plugs that are rated at less than 12 volts and use a series resistor to drop the voltage to rated voltage, often around 10 volts or so from what I have read.

BUT Whitetiger, a very experience Kubota technician, has indicated the B3350 glow plugs should have 12 volts applied to them. AND has measured this himself on two or more of those tractors. I do not know,but have no reason to doubt Whitetiger.

I do not have a B3350 tractor, so have no personal interest. BUT I do have intellectual curiosity.

Just cannot rationalize why applying 10 volts to a glow plug rated to operate at 12 volts would make any sense...

Perhaps someone can verify what the rated operating voltage of the glow plugs used in the B3350 is. If it is 12 volts and 10 volts is applied, this does not seem to make sense...

I think there are 2 basic series of Kubota glow plugs. Many of the older tractors had a glow indicator that was really a resistor in series with the glow plugs that visibly glowed in the preheat position. That indicator dropped about 2 volts which left about 10 volts for the glow plugs (most glow plugs are in parallel but I think there were a few in series). Then, when the ignition switch is in the start position, full battery voltage is applied to the glow plug. But, because of the heavy draw on the battery from the starter, less than 12 volts is available to the glow plugs. This is similar to the resistor setup on old points and coil automobile ignition systems.

The newer tractors have quick heat glow plugs and no resistor. I think there may be an internal coil that uses the fact that most conductors increase in resistance with temperature. This increases the resistance of a hot glow plug, reducing its current draw.