techbod Posted November 20, 2006 Share Posted November 20, 2006 I'm trying to diagnose why my heated screen doesn't work very well. After being on for 6 or 7 minutes individual element lines appear but it never gets to the point it can clear the screen. I've measure the resistance between the two screen wires and I get 53 ohms. Can anyone tell me if this is correct? thanks. Link to comment Share on other sites More sharing options...
rj Posted November 20, 2006 Share Posted November 20, 2006 53 ohms sounds like a lot to me! It then only draws 3 watts or so. Sounds like the element is broken -> you need a new screen. ☹️ /r Link to comment Share on other sites More sharing options...
techbod Posted November 20, 2006 Author Share Posted November 20, 2006 Thanks. Thats what I hoped it wouldn't mean, but thought it might... ☹️ Link to comment Share on other sites More sharing options...
Beelzebub Posted November 20, 2006 Share Posted November 20, 2006 I would agree that 53 Ohms sounds too high. Have you tried cutting the bullet connectors off & check the resistance again on the bare wires 🤔 If it's still the same I would suggest it's gone pear shaped. Link to comment Share on other sites More sharing options...
rj Posted November 20, 2006 Share Posted November 20, 2006 If it's got clear lines, then it's not an "external" poor connection. It'll be inside the screen. Link to comment Share on other sites More sharing options...
Beelzebub Posted November 20, 2006 Share Posted November 20, 2006 RJ. Techbod fails to state if some or all of the individual lines actually clear. My assumption since he did'nt state otherwise is that all the lines are clear abeit not at full power. [pedant mode] So until he tells us otherwise I stand by my previous post. It would be a pity to remove the screen only to find corrosion between the wire & crimp. It's something else to try before getting the cheque book out. [/pedant mode] Dave. Link to comment Share on other sites More sharing options...
rj Posted November 20, 2006 Share Posted November 20, 2006 [even more pedant mode] OK [/even more pedant mode] Link to comment Share on other sites More sharing options...
Beelzebub Posted November 20, 2006 Share Posted November 20, 2006 Edited to say; I've got my humble pie at the ready 😬 😬 Edited by - Davesport on 20 Nov 2006 12:19:25 Link to comment Share on other sites More sharing options...
techbod Posted November 20, 2006 Author Share Posted November 20, 2006 The first time I turned on the heater (raining cats n dogs in the lakes, screen fogged completely) I only saw a couple of lines clear after about 5 minutes and assumed it was broken internally. Back in the comfort of my garage I fogged up the screen the best I could and left the heater on. Eventually (after a looong time) several more lines faintly appeared. At that point I stopped, so I don't know if they would have all appeared eventually or that was the lot. I'll check the resistance from the other side of the bullet connectors since that is easy to do (and until I do I can still hope that is might not be the screen elements ) How many watts is the heater rated at or what should its resistance be? thanks Link to comment Share on other sites More sharing options...
techbod Posted November 21, 2006 Author Share Posted November 21, 2006 I checked last night and the screen heater resistance, without bullet connectors is 30ohms. That raises a number of issues since the bullet connectors clearly have a fair amount of resistance which needs sorting out, but I imagine that the 30ohm reading for the screen is still to high? I think I'll remove the screen at the weekend and just check that the feed wires are ok. I can feel on one side the hole in the scuttle is heavily burred so I suppose some wire damage is possible (although if its the 12v side I would just expect the fuse to blow of the insulation has been worn through). Link to comment Share on other sites More sharing options...
Sheds Moderator Posted November 21, 2006 Share Posted November 21, 2006 Dunno if 30 ohms is excessive. That will give you *almost* 0.5A, engine running, and the wires are pretty fine. I might be inclined to think that was about right. Link to comment Share on other sites More sharing options...
techbod Posted November 22, 2006 Author Share Posted November 22, 2006 0.5 amp might be a little low maybe. The circuit has a 10 amp fuse if I remember correctly?? So I suppose answering my own question from earlier, if it draws about 6-7 amps, at a nominal 12 volts the resistance has got to be a lot lower than 30 ohms...... So its probably back to new screen time. ☹️ cheers Link to comment Share on other sites More sharing options...
Sheds Moderator Posted November 22, 2006 Share Posted November 22, 2006 Hmm, you are probably right Techbod. 6 or 7A from 13.5V (approx) implies as you say something with a resistance of about 2 ohms. The reason I was thinking in terms of 0.5A was the extremely fine wires in the glass which are never ever going to take 6A. However if you wire all those very fine wires in parallel then the current divides up between them - 50 wires sharing 6A means 120mA each, which should be easy. i suspect (as you have no doubt already worked out) that your high resistance is the result of a number of broken wires in your screen. Link to comment Share on other sites More sharing options...
Paul Deslandes Posted November 22, 2006 Share Posted November 22, 2006 I've just measured the resistance of mine and its 42 Ohms including the wiring so your 30 Ohms is about right, assuming my screens ok which it was the last time I used it. I would replace all the bullet connectors and solder them on everywhere. Get the decent solder-on brass ones from a proper motorfactor. The plated crimp ones are crap! Also check that the bullet inter connection sleeves, chassis connection and the switch connectors and contacts are clean and sound. Spray some switch cleaner into the switch and operate it a few times to clean the contacts. As you've obviously got a digital meter check the voltage across the screen on the screen side of the bullets when its on and the engine's running. Remember that power is proportional to the square of the voltage so any voltage drop in the wiring will cause a huge drop in heat in the screen. Doesn't sound as though you need a new screen although 5 or 6 Watts doesn't intuitively seem enough to do the job. Link to comment Share on other sites More sharing options...
techbod Posted November 22, 2006 Author Share Posted November 22, 2006 Thanks for all that - you've given me hope I've just been grabbing 5 minutes here and there on the problem so far, but at the weekend I'll have time to try and sort it out properly. Link to comment Share on other sites More sharing options...
rj Posted November 22, 2006 Share Posted November 22, 2006 I'll see if I can get around measuring the resistance of mine tonight as 5-6W seems by far too little to me, but of course it could be me who is going to eat pie... /r Link to comment Share on other sites More sharing options...
rj Posted November 23, 2006 Share Posted November 23, 2006 Have just measured the resistance: 2.0 ohms! Draws 6.7 amps when engine is not running! Therefore the power is some 80 Watts ! Not me who's eating pie /r Link to comment Share on other sites More sharing options...
Paul Deslandes Posted November 23, 2006 Share Posted November 23, 2006 Oh BH! Looks as though mine's knackered as well. I thought the power was a bit low to be effective. Sorry techbod. Maybe we can do a bulk buy with CC!! Or maybe just do without. Link to comment Share on other sites More sharing options...
Roadsport06 Posted November 23, 2006 Share Posted November 23, 2006 I think as stated that if a number of elements have broken then the total resistance will increase. This fits in with your resistance readings and only a few lines starting to demist. It might mean a new screen, although it would be a shame if it got chiped in the meantime and it needing replacement by the insurance company . Do Caterham have the screens at the moment though BRG and Yellow nose VU06 XZX Link to comment Share on other sites More sharing options...
millsn Posted November 23, 2006 Share Posted November 23, 2006 I take it you've looked for the universal dodgy earth and checked your battery before getting all technical? Nigel Mills - 2.0 Zetec TB's + cams. I like my engine Link to comment Share on other sites More sharing options...
rj Posted November 23, 2006 Share Posted November 23, 2006 A dodgy battery wouldn't cause the screen not to demist. If the battery caused this, then it'd also cause the engine not to run as it would be a short circuit. Link to comment Share on other sites More sharing options...
Beelzebub Posted November 23, 2006 Share Posted November 23, 2006 I'm saving my pie for later. IMO saved by 23 ohms across the dodgy crimps. However I have to concede it sounds like it's not well Link to comment Share on other sites More sharing options...
rj Posted November 23, 2006 Share Posted November 23, 2006 Davesport, Couldn't 23 ohms in fact be 2.3 because you need to remove the pie from your glases? /r Link to comment Share on other sites More sharing options...
techbod Posted November 24, 2006 Author Share Posted November 24, 2006 Thanks to everyone who grabbed a multimeter and went out and checked. I'll have a good go at mine tomorrow ("you're a rubbish heater, is that the best you can do? pah etc" ) and see if I can find anything obvious. If not I expect its some kind of antifog stuff on my christmas list. cheers Link to comment Share on other sites More sharing options...
Paul Deslandes Posted November 24, 2006 Share Posted November 24, 2006 Let us know what you find, there could be a common cause. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now