Glow plug controller

[jeffhensley]

I just upgraded my Ford 1210 to a Kubota 7200 4 wheel drive. I've been loving it about 2 months, but starting has always been difficult (takes a long time: over 30 seconds). As the weather gets colder, I noticed my glow plug controller hanging down the side (obviously been worked on) and the element was blown. I ordered a replacement and there was immediately improvement to cold weather start. Before it fully started though, this filament blew too. Pretty sure the frame of the controller was grounded to the chassis just as if it were installed correctly. I'm glad it's a cheap part, but before I replace it again, any suggestions what the problem is?

 

[Roadworthy]

I'm wondering about the "glow plug controller". Is this a glow type resistor in series with the glow plugs? If that is indeed what it is the resistance should be electrically isolated from the frame of the unit itself. The resistance comes from a short coil of nichrome wire whose resistance changes as it heats. If either end contacts the housing and the housing is secured to anything on the frame of the tractor you will have a dead short to ground. If you disassemble the thing I think you'll find both ends of the wire coil are isolated from the frame with ceramic or mica insulators. This was a pretty common means of dropping glow plug voltage in older tractors as glow plugs don't generally run at twelve volts. For whatever reason many actually run at 10.5 volts.

 

[jeffhensley]

I'm wondering about the "glow plug controller". Is this a glow type resistor in series with the glow plugs? If that is indeed what it is the resistance should be electrically isolated from the frame of the unit itself. The resistance comes from a short coil of nichrome wire whose resistance changes as it heats. If either end contacts the housing and the housing is secured to anything on the frame of the tractor you will have a dead short to ground. If you disassemble the thing I think you'll find both ends of the wire coil are isolated from the frame with ceramic or mica insulators. This was a pretty common means of dropping glow plug voltage in older tractors as glow plugs don't generally run at twelve volts. For whatever reason many actually run at 10.5 volts.

Yes. The glow plug controller is what you describe. I'll check for grounding and put the hopefully insulated backside of the device back where it goes for the next test.

 

[moship]

Just a thought...

Would it be possible to update the glow plugs to quick rise higher voltage ones and forego the "glow plug controller"? The glow plug circuit design on newer tractors does not use a voltage dropping device in the circuit and the glow plugs turn red/white hot within 5 seconds. The GP on time is controlled by the computer based on coolant temperature, but doesn't drop voltage. In the coldest temps it is energized for a maximum of 10 seconds. GP power is direct from the battery with a 40 amp or higher relay used to turn it on/off.

The benefits would be simpler more economical wiring and very quick start times.

https://www.ngkpartfinder.co.uk/files/NGK_Glow-Spec.pdf

Here's the GP used in my L4740 and a host of other models

Kubota 19077-65512 is actually a NGK Glow Plug Part number: Y-716RS, stock number: 4693 (Rockauto has them for <$15)

Documented my GP findings in the following post: https://www.tractorbynet.com/forums/kubota-owning-operating/407470-glow-plugs.html?highlight=

The hard starting issue which prompted the post above turned out to be an incorrect relay installed by the factory. They installed relays with 1/4" male tabs when it was designed to used 3/8". This resulted in poor electrical continuity.

 

[jeffhensley]

I'll check out the link later. Thanks moship.

 

[Roadworthy]

Going through the list one will note there are no twelve volt glow plugs. Controllers in new tractors may not drop the voltage but if they don't I suspect they pulse it in some way. Feeding full voltage to the glow plugs will shorten their lives. The voltage dropping glow resistor also serves to limit the current to the glow plugs. Without it you will burn out the glow plug position on the ignition switch. To prevent that you would need to add a relay in series with the glow plugs, the relay being controlled by the glow plug switch. You cannot control the glow plugs directly from the switch without some kind of current limiting device.

 

[jeffhensley]

Going through the list one will note there are no twelve volt glow plugs. Controllers in new tractors may not drop the voltage but if they don't I suspect they pulse it in some way. Feeding full voltage to the glow plugs will shorten their lives. The voltage dropping glow resistor also serves to limit the current to the glow plugs. Without it you will burn out the glow plug position on the ignition switch. To prevent that you would need to add a relay in series with the glow plugs, the relay being controlled by the glow plug switch. You cannot control the glow plugs directly from the switch without some kind of current limiting device.

THANKS

 

[moship]

Going through the list one will note there are no twelve volt glow plugs. Controllers in new tractors may not drop the voltage but if they don't I suspect they pulse it in some way. Feeding full voltage to the glow plugs will shorten their lives. The voltage dropping glow resistor also serves to limit the current to the glow plugs. Without it you will burn out the glow plug position on the ignition switch. To prevent that you would need to add a relay in series with the glow plugs, the relay being controlled by the glow plug switch. You cannot control the glow plugs directly from the switch without some kind of current limiting device.

Your assumption they are pulsed, is incorrect and your speculation contained above is just that. The voltage is direct from battery through a relay as I described in the post. Check the wiring diagrams and you'll see what I'm talking about. The old fashion glow plugs you're likely familiar with are different than the newer ones. They are also likely to have different materials of construction versus newer designs. The stock glow plug from the factory is an NGK rated at 11.5 volts. There is no current limiting device in the circuit to the GP, but the GP itself is likely self limiting in that as it heats up current is restricted.

Yes you would not want to leave any glow plug on indefinitely. Newer tractors prevent this by taking away the operators ability to leave the glow plug energized indefinitely, since the on time is controlled by the ECU.

You'll also notice the GP manufactures will list the new ones as being fast acting when digging into the individual spec sheets. Physically they look the same.

For those with the old style glowing dash indicator that is failing, this might be an option.

Please do not run battery supplied voltage directly to the old style GP's...