Problems with 12V super glow (1 Viewer)

Joined
Feb 3, 2010
Messages
172
Location
Copenhagen, Denmark
Hi,

Im trying to figure out my 12V super glow system. I used this thread for information:


But the presented information in that thread does not match up to my measurements at all.

My main problem of understanding is the voltage strap, current sensor or whatever it also might be called:

20200407_233248.jpg


a) The green wires go to the glow plug timer and are used for voltage measurement
b) To the left the main heavy wire (directly from the glow plug relay) is connected and supplies the entire current to the glow plugs
c) To the right, the "bar" is connected which joins the 4 glow plugs.

I hope some of you recognize this strap and understand its function, since I dont.

Some info:

The strap is from a 1984 Toyota Hiace with an L engine (2,2 liter diesel engine, 4 cylinders) with the super glow system. It has 2 glow plug relays and uses the 6V or 7V glow plugs.
The car is disassembled at the moment and I am making tests using a multimeter and a powerful DC power supply (to imitate the battery) which enables me to play with all the components. I am doing a frame off restoration of the car and before disassembly I had issues with the glow plugs since starting became difficult and I needed to pre glow several times (turning key several times) before I could achieve a smooth start. With only 1 key turn the engine would shake like mad and first stabilize after 10 seconds of running and become calm.

I need to fully understand whats going on!

In the link above it is mentioned that the strap acts as a resistor having approx the same resistance as the 4 (or 6 plugs) plugs combined. Since they are connected in series, the plugs will get half the battery voltage (6-7V) and the strap will get the remaining (6-7V). So the strap enables us to use the 6-7V plugs.

My problem is, that I measure almost no resistance in the strap, it is very close to 0 ohm = it acts as a perfect conductor. In the link above it is stated that the resistance is 0,5 Ohm and I dont measure that at all!!!

When I play with my DC power supply and connect only 1 glow plug to the strap, I draw 15 Amps when cold and after 5 seconds when the plug is yellow hot it only draws 7 amps. During that test, the voltage drop across the strap is 0,07V ... almost nothing and I have the FULL voltage on the plugs and not the reduced voltage. Put it differently: If I want 6V at the plug I need to adjust my power supply to 6,07V ... and not 12V as stated in the link above.

My DC power supply does not go above 20 Amps: I cannot test all 4 plugs at the same time since that would require at least 28 Amps (4x7 Amps).

Can anyone explain what is the ups and downs in this matter?

PS: Please note: Imagine that 4 plugs get yellow hot within lets say 5 seconds. In total that should equal 4x6x7=168 Watts. If the strap should draw the same amount (50/50 split as mentioned in link), it would be VERY hot to touch. The strap has a plastic coating and NEVER gets that hot.

Lucas
 
Joined
May 26, 2018
Messages
195
Location
Portland, Oregon
Looking at the drawing in that link and the picture you posted, it looks like the resistors are not there? Or are they on the other side of that bar? a plain piece of metal and wire should show little resistance just like you measured.
 

tlaporte

SILVER Star
Joined
Dec 17, 2003
Messages
872
Location
Pasadena, CA
Hi,

Im trying to figure out my 12V super glow system. I used this thread for information:


But the presented information in that thread does not match up to my measurements at all.

My main problem of understanding is the voltage strap, current sensor or whatever it also might be called:

View attachment 2264236

a) The green wires go to the glow plug timer and are used for voltage measurement
b) To the left the main heavy wire (directly from the glow plug relay) is connected and supplies the entire current to the glow plugs
c) To the right, the "bar" is connected which joins the 4 glow plugs.

Are you sure that (b) above is correct, that that is connected directly from the glow plug relay? I'd have to look back at the diagrams or go out and look at the superglow on my HJ47, but I thought it was connected to the resistors mounted on the inlet manifold.

I believe what you have there is simply the sensor strap, unless things are very different between the 2L and the 2H and B-series Superglow systems.

Have a look again at the diagram in the first post in Tom's thread that you linked, and I believe that what you have there in the photo is labeled "Sensor Strap part #28631 0.5R"

There should be two additional resistors that are in front of the sensor strap in the circuit. Glow Plug Relay #1 sits behind one of the resistors, and Glow Plug Relay #2 sits behind both of the resistors.
 
Joined
Feb 3, 2010
Messages
172
Location
Copenhagen, Denmark
Thanks for your quick reply.

The Hiace has only 1 manifold resistor and not 2. So it fits exactly your drawing. I actually found the same drawing for a Hilux LN50 from the same year range.

Yes, what I have is similar to "Sensor Strap part #28631 0.5R" As I understand 0,5R=0,5 Ohm which is A LOT when you try to draw lets say 30 Amps through. My glow plugs pull 7 Amps each when hot (4x7=28 Amps for all four). With 30 Amps and 0,5 Ohm you have a voltage drop of 15 volts!!! And thats in the sensor strap alone!!! If I would draw 30 Amps through my sensor strap I would have a theoretical voltage drop of 0,3 Volts (measured with my DC power supply)!!

As I understand according to your drawing:

Glow plug relay 4 is energized first (thats the big heavy one). When it finishes, glow plug relay 5 is energized and takes care of the afterglow process.

As I understand from reading the internet these to relays are never energized at the same time. Is that correct?

When we look into the drawing you can see that the glow plug relay 4 is connected directly to the sensor strap! BUT, it also has a bypass wire to the intake manifold resistor (like you suspected). But if glow plug relay 5 is not energized NO energy whatsoever will flow that way and all the power draw goes directly to the glow plugs.

Now lets imagine that glow plug relay 5 (the smaller relay) is energized. If glow plug relay is not energized at the same time, all the energy will pass through the intake manifold resistor and onwards to the glow plugs (by using the bypass wire in the drawing). In that situation yes, there will be a considerable voltage drop across the intake manifold resistor resulting in a lower voltage at the glow plugs (after glow).

Please correct me if Im wrong :)

Lucas
 
Last edited:
Joined
Feb 3, 2010
Messages
172
Location
Copenhagen, Denmark
Looking at the drawing in that link and the picture you posted, it looks like the resistors are not there? Or are they on the other side of that bar? a plain piece of metal and wire should show little resistance just like you measured.
Correct, the resistor(s) are not shown in my picture. I have 1 resistor and it is screwed into the intake manifold from underneath. The resistor is located between the strap and the relay(s).

As for plain piece of metal: Yes, the resistance is very low. If I would have a bigger resistance in my strap (lets say 0,5 Ohm) that piece of metal would become burning HOT when I look at the size and volume of the strap.
 

Users who are viewing this thread

Top Bottom