Glowplugs current

[Lady Campanula]

'How long is a piece of string'....

I know, but would peeps care to suggest a 'ballpark' range of current draw, four cylinder engine? Each, so I can multiply up, or four if you want to spare me the effort!

 

[Bodach na mara]

BMC Captain plugs took 6 amps each, but the plugs in my Ford Focus diesel take 10 amps each.

 

[Marsupial]

Volvo manual for tyhe MD22 says current drain should be 27A dropping to 14A after 10 secs and thats for only 1 (one) glow plug.

 

[Playtime]

Volvo manual for tyhe MD22 says current drain should be 27A dropping to 14A after 10 secs and thats for only 1 (one) glow plug.

I would agree with this, from observation! My 'ignition' switch failed once (on an MD22) with the glow plugs switched on. I was convinced that the alternator had failed.

50A for four is the ballpark, allowing for some volts drop etc.

 

[Jcorstorphine]

Results for Ford XLD 1600 Fiesta)

According to the good book from Haynes, the current is 8 amps per plug for a 1600 cc Ford.

JC

 

[sarabande]

glow plugs are wired in series, so if one fails (or the lead fails), then they all go on strike.

Are ye looking at the ammeter as you turn the engine switch ? What sort of discharge is showing ?

 

[VicMallows]

glow plugs are wired in series, so if one fails (or the lead fails), then they all go on strike.

Wherever did you get the idea that they are in series? ... Pretty difficult to implement even if one wanted to. True though that if 1 fails the engine may be very difficult to start and another, probably of same vintage, may well decide to fail because it now has a bit more current available due to lower circuit losses....and so on.

Vic

 

[sarabande]

sorry Vic, years of looking at one little wire running from one plug to the other on a variety of engines, including the old BMC Captain marinised taxi engine.

Why should it be difficult to arrange ? The circuit goes in to the plug at the head, down through the heating element, back up to th ehead, along to the next plug.

Genuinely puzzled.

 

[rob2]

Well the two on my mini-14 are in series, though the warning lamp doesn't work the other anunciator lights dim. I always thought the engine was a good starter til I replaced the plugs - now it starts so easily!

Rob.

 

[Heckler]

glow plugs are wired in series, so if one fails (or the lead fails), then they all go on strike.

Are ye looking at the ammeter as you turn the engine switch ? What sort of discharge is showing ?

Not necessarily Tim, on the old Mercs they were, but the vast majority of donks are singly wired, so if one fails the rest continue to work.
Stu
PS saw the next post, usually you see the link going from one to the next to the next etc, it can be confusing, if they are on top they are in parallel, if they go to the top and exit from the bottom then serial. As I said the old Mercs were like that

 

[Bodach na mara]

sorry Vic, years of looking at one little wire running from one plug to the other on a variety of engines, including the old BMC Captain marinised taxi engine.

Why should it be difficult to arrange ? The circuit goes in to the plug at the head, down through the heating element, back up to th ehead, along to the next plug.

Genuinely puzzled.

The wire linking plug to plug on the Captain is a single core wire. The current goes through the plug to the cylinder head (earth) and back to the battery. They are thus all in parallel.

 

[LadyInBed]

'How long is a piece of string'....

I know, but would peeps care to suggest a 'ballpark' range of current draw, four cylinder engine? Each, so I can multiply up, or four if you want to spare me the effort!

A good glow plug shows resistance that is approximately less than 6 Ohms
Voltage down the left Resistance along the top gives Current in table So take your pick!

V/R=I	10	9	8	7	6	5	4	3	2	1	0.5	0.3	0.1
11	1.10	1.22	1.38	1.57	1.83	2.20	2.75	3.67	5.50	11.00	22.00	36.67	110.00
11.5	1.15	1.28	1.44	1.64	1.92	2.30	2.88	3.83	5.75	11.50	23.00	38.33	115.00
12	1.20	1.33	1.50	1.71	2.00	2.40	3.00	4.00	6.00	12.00	24.00	40.00	120.00
12.5	1.25	1.39	1.56	1.79	2.08	2.50	3.13	4.17	6.25	12.50	25.00	41.67	125.00
13	1.30	1.44	1.63	1.86	2.17	2.60	3.25	4.33	6.50	13.00	26.00	43.33	130.00
13.5	1.35	1.50	1.69	1.93	2.25	2.70	3.38	4.50	6.75	13.50	27.00	45.00	135.00
14	1.40	1.56	1.75	2.00	2.33	2.80	3.50	4.67	7.00	14.00	28.00	46.67	140.00

 

[Marsupial]

A good glow plug shows resistance that is approximately less than 6 Ohms
Voltage down the left Resistance along the top gives Current in table So take your pick!

V/R=I	10	9	8	7	6	5	4	3	2	1	0.5	0.3	0.1
11	1.10	1.22	1.38	1.57	1.83	2.20	2.75	3.67	5.50	11.00	22.00	36.67	110.00
11.5	1.15	1.28	1.44	1.64	1.92	2.30	2.88	3.83	5.75	11.50	23.00	38.33	115.00
12	1.20	1.33	1.50	1.71	2.00	2.40	3.00	4.00	6.00	12.00	24.00	40.00	120.00
12.5	1.25	1.39	1.56	1.79	2.08	2.50	3.13	4.17	6.25	12.50	25.00	41.67	125.00
13	1.30	1.44	1.63	1.86	2.17	2.60	3.25	4.33	6.50	13.00	26.00	43.33	130.00
13.5	1.35	1.50	1.69	1.93	2.25	2.70	3.38	4.50	6.75	13.50	27.00	45.00	135.00
14	1.40	1.56	1.75	2.00	2.33	2.80	3.50	4.67	7.00	14.00	28.00	46.67	140.00

let's assume this table is correct, the maths and the science works for me.

let's assume the Volvo manual is correct (it assumes a fully charge battery)

this indicates that glowplugs are not as simple as we (I) thought, they must have an inverse thermocouple effect that means the resistanace increases as the temperature increases giving the readings quoted in my last post on this thread.

even so an MD22 (whole engine) is drawing 108A for 10 seconds at start up, which then drops to 56A - poor battery, the next thing that happens to it is the starter motor . . .

 

[oldharry]

sorry Vic, years of looking at one little wire running from one plug to the other on a variety of engines, including the old BMC Captain marinised taxi engine.

Why should it be difficult to arrange ? The circuit goes in to the plug at the head, down through the heating element, back up to th ehead, along to the next plug.

Genuinely puzzled.

No, the circuit takes power to all four terminals, the circuit being completed through the plug heating element to the engine block, same as a spark plug grounding through the cylinder block. Very rarely are they wired as you describe, and can be identified, by a second terminal near the bottom of the plug which goes to the top of the next one. The last plug in the 'chain' the lower terminal will be connected to the negative return'

Spark plugs have separate leads, because they have to be energised at different times to each other. Glow plugs need to be energised all at the same time.

 

[sarabande]

thanks all. Waylaid by years of my Mercedes 190, and various Landrovers.

I'll read the engine manual with even more enthusiasm than normal next week.


Parallel it is.