BMC 1.5 problem update

[Strathglass]

Sorry It\'s only malt up here NM

single malt

 

[stubate]

and i thought i was sad

looking at forums after midnight !!
stu

 

[Strathglass]

Re: and i thought i was sad

Yes I know, very sad.
Got the flu and just can't stop coughing. So was doing some work on the PC as I couldn't get to sleep, but monitoring some of the forums every so often. Still feel quite rough, but over the worst of it. I was really surprised that at that time in the morning there were still over twenty people logged in.

I did manage to do some voltage and current measurements today on a Ford 1.8D today. The voltage drops are quite high. Probably post a summary of my measurements if there is any interest. I will certainly be adding a relay on the glow plug circuit on the boat. At the moment all the glow plug current passes through the ignition key.

Thats's my story and I'm sticking to it

Iain

 

[Chris771]

Re: and i thought i was sad

You have a Mickey Mouse installation there Iain if all the glow plug current goes through the ignition key. As the current will be about 25 Amps it is a wonder the inslulation on the wire is not melting.

The correct way is to have a heavy duty relay taking the +12v feed from the starter solenoid on a thick cable (about 6mm/sq) to a heavy duty (at least 30 Amp) relay mounted on the engine. The output of this relay then goes directly to the tops of the glowplugs (YES all in paralell - as Steve so rightly pointed out) the total length of the high current cable is then only a few inches long and there is negligeable voltage drop. The feed from the preheat or ignition key switch is then used to energise the coil of the relay and only carries about 500 milliamps or less depending on the relay.

When I marinised my XLD 416 many years ago I did not get the Ford Cold Start relay with the engine. I priced it then at over £50, so I bought a heavy duty 35 Amp rated relay from an Auto Electrical Dealer (£6) and built myself an adjustable self timer using a 555 Timer chip and a Power MOSFET transistor, complete with pretty indicator LEDs (another £5 or £6). This circuit was mounted in a small Aluminium project case on the engine. The trigger circuit drew only about 5 milliamps (5/1000 of an amp) from the ignition circuit . The act of switching on the ignition triggered the preheat circuit and once the LED went off I turned the key to Start to rotate the engine. I measured the preheat current out of curiosity between 23 and 26 Amps depending on temperature. As the glowplugs get hot, the resistance increases and the current falls to about 12 Amps when they are smokin. I found by trial and error that about 30 seconds was the ideal preheat time for winter starting and just left the auto timer set to that. In summer 20 seconds would have been plenty.More modern glowplugs heat much more quickly. A Landcruiser I had about 6 years ago took three seconds and my present Mercedes engine takes about 8 seconds, it all depends on the glowplugs you are using.

I recommend that you get a relay fitted before something melts or you start a fire if all the current is going through the ignition switch. To be a purist you should fit a reverse biased quenching diode across the relay coil to prevent the large spike which caused when power is suddenly removed from it. Another point to bear in mind is that the voltage drop along the present cable is reducing the voltage at the glowplugs. They then take longer to heat, which means that you also have to heat the wiring for longer, as all the energy from the voltage drop along the wire has to be dissipated as heat......SCARY!!! On the plus side it will help to get rid of moisture and condensation on the ignition panel.

Hope this helps

Chris

 

[Strathglass]

Re: and i thought i was sad

Chris,
Your figures are a bit low.
Each glow plug can draw over 17.5 Amps when fed individually from a battery at 12.5 volts. (this drops to 13 Amps after 5 seconds.
The losses through a normal Ford vehicle instalation reduce the voltage at each glow plug to 10.2volts. At this, the current through each glow plug is initially 13 Amps. Thus the current for four glow plugs in parallel will be over 50 Amps.

I have fitted four Ford XLD1800 engines to different craft both to yachts and a twin engined cruiser. In all cases I have used the Ford harness and the relay control system. I am currently wiring the XLD I have fitted to my own yacht and already have 6mm wire to the glow plugs. But have not wired the ignition switch etc yet. I do not wish to add a delay system as I prefer to have control over this myself.
Any relay used in a glow plug circuit should be capable of switching in excess of 50 Amps.

One of the problems of this forum is that people do not appreciate the extremely high skill levels and the depth of experience of many of the posters. There is also the opposite problem of beginners asking apparently silly questions because they do not understand some basic principle.

I resisted from making any comments on the series /parallel glow plugs posting as it was being adequately dealt with on the forum and I did not wish to teach my granny to suck eggs.

Somewhere in the past I used to design, commision and supervise the building of test systems for complex military items. Often the steady state DC currents involved were in excess of 100 Amps and stiff military safety standards had to be complied with. I am very aware of the potential dangers of underrating components.

That is the very reason why I said that I would measure the real currents through the glow plugs on a Ford Engine.

ps. it's still very cold up here the snow has just started to fall again.

Iain

 

[stubate]

very well put !!

iain
the prob with posting here, as i have found out to my cost, is that in trying to put forward a simple solution derived from, as you quite succintly put it, many years of experience, often arouses the arm chair expert who picks up on a point that was used in attempting to get the message across simply and trys to show how clever they are.
the debate then degenerates into using any means or argument to attempt to get their very often misconstrued or invalid point across.
stu

 

[PeteMcK]

All....Except!!

That most unendearing of all diesels, the 2.25L Landrover. Lose one heater, you lose 'em all. Even with all four working, starting was never a certainty.

 

[Chris771]

I stand corrected

Iain,

Quite possibly the figures I measured are low compared to the XLD 418, I had a 416 and I know that the 416 took longer to heat than the later 418. Possibly it has different faster warming glowplugs which would take more current.

I don't really know and readily accept what you have measured. In my case I did not do the measurements particularly scientifically, (ie with individual plug on a battery) I simply took a feed from the solenoid supply to the plug rail and measured the current with a suitable meter. I never measured the voltage at that point with the glowplugs on load, but even with the large main feed from the battery about 2 metres away there would have been some drop.

I just took the simplistic approach found the initial current in my circuit was in the upper 20s so made sure that the relay could cope with about 50% more. It just happened that a 35 Amp relay was cheap and the price went up considerably for a 50 Amp relay.

In the event it worked for about 8 years after installation, so was adequate. That was why I mentioned that different engines warm at considerably different speeds. As the glowplugs probably require a vaguely similar amount of energy to heat, then quicker ones will therefore require more current to heat rapidly.

I suppose that I should have made more of a point that the figures I obtained applied to a particular engine. I did notice a thread elsewhere a few days ago saying that XLD 418s should only be preheated for a maximum of 20 seconds, so that would indicate more current than mine used to consume.

Thanks for pointing out that I should not have generalised, you have obviously worked out the requirements for your engine and rated accordingly. Probably the most important point of our posts is to make others of a less electrically inclined persuasion; aware of the necessity to correctly rate components and fit an adequately rated relay and avoid any possibility of causing a fire by passing the full current through thin wires.

Chris