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Heated front screens, series. 6 volts for longer periods


Gazzar
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I'm thinking of fitting heated screens to the 109, as I've mostly stripped the dash and the instrument cluster.

So, the easy thing to do is fit the two screens in parallel, using the various relays and timers, defender style.

But, it occurred to me that having the screens on at a low power setting might be advantageous in humid conditions, to keep the screen clear.

If I powered the screens in series, not parallel, they'd be getting 6 volts each, would running them at this voltage for extended periods cause the elements an issue?

Would it generate any heat?

 

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My Citroen BX DTR Turbo had 2 electric fans and switching which connected them in series for low speed and parallel for fast. So why not switch them so you've got the choice - low - in series, high - in parallel.

Since the elements are embedded in glass I can't see that running them under voltage will hurt.

 

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It's what I did on my heated screen - but after the re-wire I measured the current and it's so low anyway (<10A) that I just run them on the full 12v now.

BTW the Freelander dual-fan relay box has the necessary 4 relays to do series/parallel switching for engine cooling fans or heated screens, I've got one running the fans in the 109 and will be doing the same on the ambulance.

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That was the plan, a low and a momentary high position, linked to a timer.

The elements burn out if on for more than 20 minutes, apparently.

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2 hours ago, Gazzar said:

The elements burn out if on for more than 20 minutes, apparently.

I never found ANY info with mine (bought from Devon 4x4, made by Uroglas) no-one could say if it needed a timer, how much current it drew... mine's just on a switch & relay at the mo.

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Snagger has a different opinion. He thinks they burn out if abused. That price? Not taking chances.

And EVERY mainstream manufacturer has a timer on their front screens, I think. Ford do, for sure.

So, I'm going with really simple, for now. Momentary switch, standard defender timer, fused relay.

 

That is:

Until I can figure how to get the "engine on" part of the timer to work on the low power setting, and find a Lucas off-on-momentary toggle switch.

What's best for sealing these screens into the series frame? Not Dum Dum, surely.

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Thanks for the link. The switch isn't exactly what I'm after, subtle, but it's missing the half dome of the Lucas switch. Too small for the hole, too.

I'll stick with simple.

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On 4/7/2020 at 5:18 PM, Gazzar said:

...   What's best for sealing these screens into the series frame? Not Dum Dum, surely.

I haven't done the job myself, but reading the S2C forum I've become almost bored with the multiple posts asking virtually the same questions - 'the best way of mounting the glass'.
The two points that have stuck in my mind are:

The glasses are really too small for the frames, and to ensure the glass fits centrally the base of the frame needs 'filling'. A lot of flexible filler could be used, but what gives more consistant results over time is to use small bits of plastic, cut off whatever you have to hand. I've seen similar to centralise infill uPVC panels on double glazed house doors. I've seen tapered wedges, which can obviously be cut down, used to level floor standing kitchen cupboards, and the get wall hanging cupboards to hang straight on imperfect walls.
Secondly, don't overtighten the frame clamping screws, which sort of points towards a soft filler, phyisically evenly spread before the frame is tightened.
Thin butyl tape off eBay may be recommended, as it is for sealing between floorplates etc, without gluing them together.

Really, if you don't get clearer replies here, my best advice is to search the S2C Forum. Nowadays, as an anti-spam feature, you may have to register. It wasn't that long ago that a Group Purchase was made, so the same old questions went round again.

Regards.

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