Mirror heaters, in development

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Post by Phil Bradshaw » Club admin » Mon Jul 11, 2016 12:58 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3818
This started off as a little project: just install some heater film panels inside the Land Rover mirrors fitted on my van.

Take apart a mirror head -

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The rubber outer seal pulls off readily at about 20C but if the glass is stuck in top and bottom then it will be necessary to knife through the adhesive.
Leave intact adhesive where it is on glass and case for re-reassembly

Backing film on the glass requires gentle heat from a hot air gun so that it can be peeled off cleanly.

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Take one handle bar warmer kit -

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Take apart the wiring at the joints so that two wires on each panel are as long as is possible.
Discard everything except the panels.
Now do the same with a second kit.

Secure two heater films to the back of each glass, here using Loctite 598 black silicone RTV -

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A blob of hot glue over heat shrink sleeve retains the wires to prevent strain at the rivet connections.

At this point a question popped up: how to wire the two elements: in series or in parallel?
  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Mirror heaters, in development

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Post by Phil Bradshaw » Club admin » Tue Jul 12, 2016 1:52 am
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3818
The ideal electrical circuit would be one that provides rapid warm-up and an effective steady state temperature without risk of over-heating.

Options 1 and 2: heater elements connected in series in each mirror head, heads connected in series (upper diagrams) or in parallel (lower diagrams).

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Options 3 and 4: heater elements connected in parallel in each mirror head, heads connected in series (upper diagrams) or in parallel (lower diagrams).

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I went for pairs of heater elements connected in parallel in each mirror head.
  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Mirror heaters, in development

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Post by Phil Bradshaw » Club admin » Tue Jul 12, 2016 1:40 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3818
The first prototype (aka lash-up) uses a rocker type fog lights switch to match existing panel switches -

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Switch is made up from bits of broken switches, the harness being cobbled together from headlamps wash/wipe wiring for Facelift/CF2 models.

Wiring for mirrors connected in parallel and using the switch warning lamp -

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For mirrors connected in series, where the warning lamp operates at half battery voltage -

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Give it a go with a 5 Amp fuse, see what happens.

First complete modifications to a pair of mirror arms and heads so that it will be easier than working with bits and wires and tools spread about a desk ...
  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Mirror heaters, in development

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Post by Phil Bradshaw » Club admin » Tue Jul 12, 2016 2:34 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3818
Mirror arm drilled through for cables -

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The drillings must be de-burred and all sharp edges must be removed to prevent damage to cables. Tedious ...

Cable used for wiring the prototype is automotive figure 8 section speaker wire split down the middle to be easier to pass through the mirror arm and head singly.
For 0.5mm² cable this will mean a voltage drop of about 0.27 V/metre at 4 Amp even though the maximum capacity of 0.5mm² cable is well above 4 Amp. This may limit maximum temperature at full power operation (parallel wiring), perhaps more so for the passenger side with longer cable run.

With the arm drilled out as shown 4 x 0.5mm² cables stuffed inside PVC sleeving will fit with an amount of cussing and care in avoiding damage to the relatively soft cable insulation.

Two extra wires can be for a side repeater -

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Which explains the four-way chocolate block connector inside the head -

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LED lamp just needs a supply from the left or right side turn signal wiring, probably behind the dash once installed on the van.

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Bling. :)

Mirror head wiring connections -

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Once a mirror is complete, chuck it in a freezer for a few hours then test by applying 12V once the glass has nicely frosted over -

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This takes between 30 second and 2 minute depending on how cold the mirror is when removed from the freezer. Water mist spray dries off fairly quickly too which is promising.

So far so good. Need to conjure up a way of testing 1 Amp (series) as well as 4 Amp (parallel) operation ...
Last edited by Phil Bradshaw on Tue Jul 12, 2016 4:48 pm, edited 1 time in total.
  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Mirror heaters, in development

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Post by Phil Bradshaw » Club admin » Tue Jul 12, 2016 3:45 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3818
A problem that arose during testing at 4 Amp is the mirror glass becoming rather too hot if left switched on when dry.
At this temperature the rubber seal around the head started to wilt.

The solution: two KDS9700 thermal cut-out switches, one for each mirror head.

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45C was chosen as the limit temperature for no more reason than somewhere to start experimenting.

Each switch is stuck to the back of the upper heater element using Loctite 598 black silicone RTV. No photo of this, or the 5-way chocolate block connector replacing the 4-way one to provide connection points for the thermal switch. Maybe catch up when a mirror has to come apart.

So, with the thermal switches providing an upper limit the heaters could be used in 4 Amp mode without overheating. However, not all conditions will require full power operation.

During testing of 1 Amp operation it was found that this was sufficient to clear list water mist spray once the glasses had warmed up, or sooner with a pre-heat at 4 Amp for a minute or two.

This is asking for a double pole switch to provide switching between parallel and series operation.

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Double pole switches with illumination tend to be for mains use only with having a neon bulb so a plain switch with a separate warning lamp was envisaged as easier than modifying switches -

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In series mode, the heater elements and warning lamp operating at half supply voltage -

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NOTE. Diagram of switch is unrepresentative of contacts layout, usually with centre 'Common'.

After a number of sessions outdoors in British Standard Wet testing this arrangement with the mirrors clamped in a Workmate it has been found that, from cold (about 18C ambient), a warm-up time of about 90 second in parallel (4 Amp) mode is about right, after which series (1 Amp) mode is enough to cope with drizzle and light rain.

I was going to install this set-up to try it on the road ... but something else presented itself: a timer relay, H3Y-2 type for 12V with time adjustable over 3 minute and bought with base for a rack frame -

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Automating the warm-up sequence is attractive as is retaining the matching fog lights rocker switch.

A quick re-design required ...
  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Mirror heaters, in development

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Post by Phil Bradshaw » Club admin » Tue Jul 12, 2016 4:18 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3818
Timer relay circuit, switch position 0 -

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Switch position 1, parallel operation -

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Switch position 2, timer circuit energised (PW LED lit), parallel operation -

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Switch position 2, time end, relay energised (UP LED also lit), series operation -

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Rocker switch, fuse, relay and harnesses -

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Relay in this photo is a 4-pole version (H3Y-4) using just 2 of the poles: H3Y-2 relays hadn't arrived at this point.

This lot now is installed and working.

Findings so far -
  • Being able to reset the relay timer or over-ride to parallel (full power) mode as desired is turning out very useful, especially in Motorway traffic in wet weather.

    The heaters won't cope with very wet conditions of course but the rocker switch can be left in position 1 (parallel mode) until conditions improve and the mirrors start to clear then switched to position 2 (timer mode) or position 0 (off) as appropriate.

    The only problem now is having to clean off dried mud and crud every now and then but that usually coincides with a break.

    The rocker switch is showing its age by sometimes refusing to work unless stabbed on and off a few times, or the warning lamp bulb works loose and won't light.

    Some of the speaker wiring used has had to have damaged insulation repaired where it has caught against panel edges behind the dash; re-wire using automotive thinwall cable required methinks.
  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Mirror heaters, in development

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Post by Phil Bradshaw » Club admin » Tue Jul 12, 2016 6:29 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3818
Prototype 2.

A change prompted by finding a 19mm diameter rotary switch that ostensibly is double pole double throw -

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The switch is double pole but it's a sequential type - it comprises two changeover switches that operate separately - and the LED is for 24V.

Changing the switching isn't a problem and the 24V LED is VERY BRIGHT but it will light with less intensity at lower voltage down to below 6V so will be usable.

The proposed circuit -

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22-47kΩ resistor is to reduce the intensity of the LED so that the change from parallel to series operation is more apparent. Actual value to be determined according to annoyance factor if the LED is too bright once the system is installed.

Otherwise the circuit does the same job as when using the fog lights rocker switch.

There's a round hole vacant in the lower part of the dash where the switch could go which then would free up the rocker switch position for another project that I have in mind.

More bling too: switch looks good to me when it lights up. :)

So it's back to bits and wires and tools spread about a desk while prototype 2 takes shape.
  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Mirror heaters, in development

Post by philbut » Fri Jul 15, 2016 10:32 am
Joined: Thu Oct 03, 2013 11:30 am
Posts: 247
Nice. I love a good electronics project Phil.

I have to admit that I don't tend to drive mine when it's cold enough to want the mirror heaters, but I do find they work wonders on the car (well on the side that they work anyway!). I've been toying with the idea of fitting some to my winter bike, as you really need the mirrors on a motorbike in London traffic. I'll be interested to see the final evolution of this.

Re: Mirror heaters, in development

Post by entwistlecymru » Fri Jul 15, 2016 10:59 am
Joined: Tue Apr 07, 2015 9:52 pm
Posts: 57
This looks like a very useful upgrade Phil, especially for those of us who use our vans all year.
1978 Manta SR, 1980 Rekord van, 1984 Carlton 1.8S estate, 1985 Carlton 2.2 GL estate, 1985 Carlton 2.2 CD, 1985 Manta GT, 1984 CF FF LWB minibus, 1985 CF 350, 1986 CF SWB minibus, 1987 CF 250, 2006 Triumph Tiger 1050, 2016 Triumph Thruxton R

Re: Mirror heaters, in development

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Post by Phil Bradshaw » Club admin » Fri Jul 15, 2016 12:21 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3818
The weather doesn't need to be cold for mirror heaters to be worth having, just British Standard Wet. :)

Practicalities in using the rotary switch have influenced the dash wiring harnesses: everything connected to the switch must pass through its securing nut (19mm thread) because I've not found an 8-pin connector to fit.

This means splitting the dash wiring into two main harnesses -

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The relay harness splits the mirror heater and repeater wiring left/right, i.e. long and short runs to the two 4-way connectors which are wired so that door harnesses to the mirrors can be identical. All being well the 4-way connectors should land near the top of each A post (door hinge post), maybe with some excess harness to cable tie out of the way but that will be better than too little.

The switch harness connections can be made at the relay base once the switch is installed. The bared conductors could be just stuffed under the screw clamps (provided more for single strand cabling used in rack systems) but they should be twisted and soldered first to prevent fraying. One step further is to shape the twisted strands of each cable into an eyelet before soldering. This means a fiddle with each screw connection but the eyelets guard against cables coming off if screws vibrate loose, a possible outcome with using kit designed for static installation.

The switch harness carries the ground connection common to the relay timer, heaters and repeaters as well as the supply line fuse. The line fuse isn't a type that I favour because of the tendency for plastic bodies to melt and separate when fuses run hot without blowing. Suck it and see: if the fuse holder does wilt, possible with a 5 A fuse operating at 4A, then something else will need to be conjured up.

Also included in the switch harness is the link for the switch LED ballast resistor (pink wires, shown with resistor assembly connected) which I'm not too happy about. However, once I've decided what the resistance should be it can be made permanent within the harness because I've found that with the 22kΩ 0.25 Watt carbon resistor used for testing there's no heat loss to worry about. Makes some sort of sense too: switch LED 5mA current draw measured at 12V shakes out as 0.06Watt.

Using thinwall 0.35mm² and 0.5mm² cable is great for applications where standard automotive cable is too bulky but the ultimate connections to standard cable of original wiring can present a challenge. Fuse link connection is catered for by using a line fuse with 1.5mm² cables and the two cables for common ground fit neatly in a 6mm eyelet terminal for 1.0mm² cable. For the repeater dash connections the solution is to add a 2-way connector with standard 1.0mm² tails for connection to left and right side turn signal wiring.

Incidentally, weatherproof connectors ('Superseal') accommodate 0.35mm² to 1.0mm² cable equally well although for smaller cables the crimp tabs need clipping down to avoid mis-shapen crimps with sharp edges.

There's a handy Howto on Superseal connectors on youtube -

[youtube]OgrA_6zFqqY[/youtube]

Mirrors next ...
  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

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