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Joined: Mar 14 2017
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Hello folks,

I know the majority of you have the V8 model but I was wondering if anyone out there knows what current draw I should see when the glow-plugs are active?

I am learning how to use my new tool but I appear to be drawing over 90 Amps when the glowplugs energize. Is this about right? The glowplugs are about 6 months old.

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Joined: Sep 14 2016
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PicoTechnology, the oscilloscope people, suggest 100 amps initial spike quickly dropping to 70 amps then further to 45 amps over the next 5 seconds and holding until the glow plug relay switches off after around 11 seconds. Their page (https://www.picoauto.com/library/automotive-guided-tests/glow-plugs/) implies a four cylinder engine so your figures don't seem too unreasonable for a 6 pot.

I imagine the details and actual current according to the type of glowplug and car engine involved.

Clive

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Sounds about right for a setup where they are all switched on at the same time. Some newer cars pulse them individually, which had me really confused how they were getting away with a weedy main feed to the control unit until I worked it out.

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Joined: Feb 11 2018
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I think they about 13amp each.

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Joined: Dec 30 2015
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Sloth wrote:

Sounds about right for a setup where they are all switched on at the same time. Some newer cars pulse them individually, which had me really confused how they were getting away with a weedy main feed to the control unit until I worked it out.

What is the advantage in that? Surely it just means that it takes longer to heat all the cylinders? Or do they shove $MANY_AMPS down each one for a very short time?

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Joined: Mar 14 2017
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Thanks for the replies, much appreciated. Assuming I'm using the tool correctly (clamp style DC ammeter as recommended in the other post) then mine is drawing about 90 amps for the full duration that the glow plugs are energized, then it drops right off.

If that 13amp per plug is correct then I should only see 78 amps plus any other loads (12 amps?)

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Joined: Feb 11 2018
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Fans, brake pump, etc could also be adding to it

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Did you zero the meter with it close to where you were clamping? In DC mode, other magnetic fields can influence DC clamp meters quite a lot. So best to zero it close to the cable, then clamp on.

But as tanis says - if you're clamping on the main battery cable (or ground), it could be other things sucking the amps too.

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It sounds about right to me, at the very least I'd expect over 10 Amps per heater. I had a Peugeot 406 HDi company car a few years ago and with additional kit installed if it was left for more than 4 days (like over a bank holiday weekend) it would need a jump start. When the ignition was first switched on, it would crank over fine but not start as the heaters hadn't had time to do their thing. If I turned the ignition on and waited for the glow plug light to go out, I could see the panel lights dim as the heaters drew the last remaining current from the battery so then it would no longer have enough to spin it over on the starter.

I'd be more concerned if it was drawing a lot less as that would suggest that not all of the glowplugs were working.

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Joined: Jan 16 2017
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Morat wrote:

Sloth wrote:

Sounds about right for a setup where they are all switched on at the same time. Some newer cars pulse them individually, which had me really confused how they were getting away with a weedy main feed to the control unit until I worked it out.

What is the advantage in that? Surely it just means that it takes longer to heat all the cylinders? Or do they shove $MANY_AMPS down each one for a very short time?

Thick wire is more expensive, and if your producing thousands of them it makes a difference.
Lower current draw on the battery probabbly a good thing as well, given you'd be pulling loads out to run the starter afterwards. Might be just enough to make the battery last a bit longer or manage to start when it otherwise wouldn't.

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Joined: Mar 14 2017
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Meter was zerod yes and placed around the battery earth cable. Interestingly I get different figures depending on which direction the instrument faces?

Either way, I am feeling comfortable with the current draw. The vehicle is acting in a similar manner as described for the peugeot, you can hear the ABS pump labour and see the dash lights lose some of their sparkle as the battery discharges.

As you may have guessed I am suffering from a flat battery issue. However, in my case I suspect the battery is at fault. Unfortunately Halfrauds little battery test box does not agree and so they are so far refusing to honour the 5 year guarantee (battery is not quite three years old yet).

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Joined: Feb 11 2018
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Failing or failed diodes in the alternator can cause battery to go flat.

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Joined: Dec 30 2015
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There are no good batteries for our P38s at Halfords.
Bend to the inevitable! Buy the Hankook of Power!

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Joined: Feb 11 2018
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Like morat says

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Halfords battery in a DSE, there's a recipe for a non start if ever I heard one......

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Joined: Mar 14 2017
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This was the biggest they did and is bigger than the one they specify for it (which means cock-all, I know).

Either way, I have cut my loses and ordered a Hankook. In fact I think they may have tried to deliver it today to my parents place as a delivery van pulled up across their drive, but then drove off again. This was about the same time I had a missed call on my mobile. As it's a road without house numbers I'm guessing he must have been phoning me for directions...

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Ooh crikey, that Hankook is a big bugger. The restraining strap is bulging and the leads had to be stretched a bit to reach the posts!

However, it certainly does the job! Starting is now pretty much instantaneous. In fact it spins the engine over that fast I reckon I could legitimately claim it to now be a hybrid by pulling the fuel pump fuse and driving it around on the starter motor.

The old battery provided sterling service for two and a half years but didn't have the welly behind it that this one does. It is however still under warranty so I haven't finished with halfrauds just yet.

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Welcome to the club :)
I reckon Chinese submarines use MF31s!

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Joined: Feb 11 2018
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Question!

How have you fitted it as it has centre terminals. My leads only just reach the standard layout

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It was no problem on my 98 as the cables were long enough. On the Ascot, same year as yours, I had to alter the run on the positive so it runs over the bundle of cables going into the ECU box (not sure if you even have that bundle on a diesel though) and extend the negative. The negative had been butchered as someone had fitted a battery isolator before I got it so needed replacing anyway, so I just got a pre-made negative cable that was slightly longer.