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  Author    Right - join Part A to Part B etc, etc, etc  (currently 37,991 views)
Simon Robinson
Posted on: September 23rd, 2013, 05:48:15 Quote Report to Moderator
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Graham - here's the wiring diagram I used. Unfortunately, I didn't use a low current supply for the front screen, which is why the elements burned out! I was hoping that using a 1A fuse would mean there wasn't too much current flowing, evidently it's still too much.

The timer relay I used is this one, it's variable and you can set it to various modes, including one (called mode 3 on the website) which uses a standard toggle switch and resets when you switch it off:

http://www.circuitsolutionsonline.com/cso1-multi-function-relay.html

D&H Mk IV 8313, KGV 215V (aka George) - 75,000 miles and counting since restoration in 2011.
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Simon Robinson
Posted on: September 23rd, 2013, 05:54:33
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Photo didn't upload for some reason, trying again...

D&H Mk IV 8313, KGV 215V (aka George) - 75,000 miles and counting since restoration in 2011.

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Brian
Posted on: September 23rd, 2013, 16:10:04 Quote Report to Moderator
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1a and even the 8a limit on those relays seems quite low for the heaters. Is there a chance you've slow blown the fuse?
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Simon Robinson
Posted on: September 23rd, 2013, 16:53:48 Quote Report to Moderator
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The elements on the screen went gradually, at first only a few were broken and eventually it spread to the rest (as they were drawing more current I suppose) - I tried using a 100 ohm resistor in series to reduce the voltage (before the faults occurred) but then it didn't work at all...

D&H Mk IV 8313, KGV 215V (aka George) - 75,000 miles and counting since restoration in 2011.
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Craig Smith
Posted on: September 23rd, 2013, 17:24:06 Quote Report to Moderator
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This heated screen topic is something that is quite interesting to me..  Could somebody provide the resistance of the screens as supplied?  From that figure we can work out the nominal current draw at 12V and look at ways of perhaps improving element life?  

My current (no pun intended) hypothesis is that it could be that the screen isn't getting the full 12V it is designed for and is thus drawing more current as a result?  

Or could it just be that the elements in the screen are "weak" in places and are simply burning out ?

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Simon Robinson
Posted on: September 23rd, 2013, 20:53:50 Quote Report to Moderator
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I did some basic resistance tests of both screens when they were put in, can't remember the exact readings but the rear should take about 15 Amps and the front was very low, less than 1 Amp. The supply is direct from the battery so should be over 12V - the voltage gauge says when running the system produces about 14V with nothing running.

D&H Mk IV 8313, KGV 215V (aka George) - 75,000 miles and counting since restoration in 2011.
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Craig Smith
Posted on: September 23rd, 2013, 21:25:05 Quote Report to Moderator
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That is a huge difference in current drawn, far greater than the comparative size of the heated area..

Going on those figures, and assuming a steady 12V feed, the respective resistances are 12ohm and 0.8ohm.

At 14V which you would expect when running you get 14ohm and 0.93ohm.

Something around 1ohm seems about right to me;

P=I^2 R gives you 209W at 0.93ohm which seems reasonable, however at 1A and 14ohm it gives 14W - barely enough to light a Neon, and certainly not enough to heat a screen..

I hate to say this but I suspect (and I have absolutely no proof) that you have been supplied with a faulty screen.
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Simon Robinson
Posted on: September 24th, 2013, 08:18:41 Quote Report to Moderator
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I did suspect that it was possibly faulty Craig, but apparently I was the first to actually wire one in so there are no comparisons! If someone else out there has a heated front that's not connected, it would be interesting to see any measurements they have.

D&H Mk IV 8313, KGV 215V (aka George) - 75,000 miles and counting since restoration in 2011.
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Stuart
Posted on: September 24th, 2013, 18:16:50 Quote Report to Moderator
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Quoted from Simon Robinson, posted September 24th, 2013, 08:18:41 at here
I did suspect that it was possibly faulty Craig, but apparently I was the first to actually wire one in so there are no comparisons! If someone else out there has a heated front that's not connected, it would be interesting to see any measurements they have.



Whilst not a direct comparison quite a lot of Midas owners have bought heated front screens, perhaps worth asking the question over on the Midas forum

http://midasownersclub.co.uk/forums/index.php?sid=e2bcc1079d264120eee6580fb6771d45
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Brian
Posted on: September 24th, 2013, 18:39:42 Quote Report to Moderator
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I need to check my window, but as I understand it (I can't recall where I read that, though, so I might just be making it up), the front screen has a circuit for the left side, and a separate circuit for the right side. Did you have the same behaviour on each side?
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Brian
Posted on: September 24th, 2013, 18:40:59 Quote Report to Moderator
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Quoted from Simon Robinson, posted September 24th, 2013, 08:18:41 at here
I did suspect that it was possibly faulty Craig, but apparently I was the first to actually wire one in so there are no comparisons! If someone else out there has a heated front that's not connected, it would be interesting to see any measurements they have.



It might be a few days, but I'll try to get a tester on my heated screen. It's not installed yet, so that should be fine, I just need to dig it out .
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Simon Robinson
Posted on: September 24th, 2013, 18:54:28 Quote Report to Moderator
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Brian - my screen only has two wires, one on either side - it only operates as a single screen. Not sure if yours is different but worth knowing what readings you get.

D&H Mk IV 8313, KGV 215V (aka George) - 75,000 miles and counting since restoration in 2011.
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Graham Bichard
Posted on: September 27th, 2013, 19:35:49 Quote Report to Moderator
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Just had a closer look at the screen I have.  It too only has two wires - one on each end of the screen.  I'm some way off fitting/wiring this but I look forward to the outcome of this discussion.

More important right now - can anyone make sense of how I need to check the position of the door mirrors, for IVA purposes?  It's got me confused  

https://www.gov.uk/government/publications/iva-manual-for-vehicle-category-m1

Sect 08 refers.

In the diagram in the manual (with floor marking 'A', floor marking 'B' and floor marking 'C') does the car get moved around so that the offside is in line with 'a', the nearside with 'c', the centreline with 'b'?

I understand the seat needs to be in the rearmost position for the test, the mirror must move (forward and rearward) with a force of 10kg, it has to be at a certain height (what height though?)

All I'm after is fitting the door mirrors!

Perhaps Mr Dickens has some recent experience of the IVA?

Last modified September 27th, 2013, 19:37:14 by Graham Bichard
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Brian
Posted on: September 27th, 2013, 20:17:28 Quote Report to Moderator
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I was curious and just had a peek, that document is incredibly confusing . Bureaucracy at work!
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jimnaylor
Posted on: September 27th, 2013, 21:20:57 Quote Report to Moderator
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The way I read it is:
With the car in a fixed position, sitting in the rearmost position, for a drivers door mirror you need to see the mark at drivers door mirror height on pole A and at the same time see all the 2.5 m line on the floor.
Similarly with the interior mirror you need to see the mark at interior mirror height on pole B and all of the 20m line. Same with the passenger side mirror, pole C and the 4m line.

The way they have drawn it is confusing. A is how it is drawn, B should be drawn on the centre line of the car, C should be tight against the car as A but on the other side.

I suspect they have these laid out on the floor as drawn, at the test centre and so do move the car about to line up because of different widths of car. For home checking the lines can be laid out to match the car.

You need the drivers mirror but only need one of the other 2 two mirrors

But I'm no expert, only the way I read it.

Last modified September 27th, 2013, 21:28:27 by jimnaylor
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