Heated Rear Window Current Consumption
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The fuse is to protect against short circuit and is usually much higher than the current actually drawn.
I would be amazed if the HRW uses anything like that Apart from anything else, the long cable wouldn't support such a high current and the 35A alternator would struggle too, let alone the cars with dynamos. My guess is that it's more like 10A.
I would be amazed if the HRW uses anything like that Apart from anything else, the long cable wouldn't support such a high current and the 35A alternator would struggle too, let alone the cars with dynamos. My guess is that it's more like 10A.
- mikealdren
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The generaic reply to this question is: 10-20A, depending on screen.
More precisely, for a +2 screen, I'd say the current draw is 15A when cold, reducing to 12A when hot. These are the figures I used when re-wiring my car. I used 2mm2 thinwall, ( but think I could easily have used 1mm2) with a 20A, 10 mins relay protected by a 25A fuse.
More precisely, for a +2 screen, I'd say the current draw is 15A when cold, reducing to 12A when hot. These are the figures I used when re-wiring my car. I used 2mm2 thinwall, ( but think I could easily have used 1mm2) with a 20A, 10 mins relay protected by a 25A fuse.
Hal Adams
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Evora S
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Here is the one I used, and tested a few times, works a treat!
https://www.autoelectricsupplies.co.uk/ ... tegory/210
Having said that, of course I am using new switches and for the HRW, I am using the modern method with a non latching switch. If you are using the standard Lotus switch, then a bog standard relay at three quid is more than adequate:
https://www.autoelectricsupplies.co.uk/ ... ategory/36
https://www.autoelectricsupplies.co.uk/ ... tegory/210
Having said that, of course I am using new switches and for the HRW, I am using the modern method with a non latching switch. If you are using the standard Lotus switch, then a bog standard relay at three quid is more than adequate:
https://www.autoelectricsupplies.co.uk/ ... ategory/36
Hal Adams
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Evora S
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I've previously measured the current draw on my Sprint at 0.3 Amps.
Don't be fooled into thinking it's the same as one of those old electric fires where the coils glow red
Don't be fooled into thinking it's the same as one of those old electric fires where the coils glow red
- persiflage
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persiflage wrote:I've previously measured the current draw on my Sprint at 0.3 Amps.
Don't be fooled into thinking it's the same as one of those old electric fires where the coils glow red
This seems far too low, 4W wouldn't warm up much.
- mikealdren
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Get more heat by blowing on it ...... I'm trying to remember
It's long time since it was used in anger and I would not describe it as being anything like the efficient modern hrw in my daily drive.
The original afterthought toggle switch located by the drivers knee was replaced by a relay and proper Sprint rocker switch in the dash years ago (before I measured current.)
Picture shows the current measured today at the window tag, following a recent rear harness remake. What was previously about 0.3 Amp has reduced somewhat.
It's long time since it was used in anger and I would not describe it as being anything like the efficient modern hrw in my daily drive.
The original afterthought toggle switch located by the drivers knee was replaced by a relay and proper Sprint rocker switch in the dash years ago (before I measured current.)
Picture shows the current measured today at the window tag, following a recent rear harness remake. What was previously about 0.3 Amp has reduced somewhat.
- persiflage
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You have something wrong - the multimeter is shot, it is incorrectly connected or your HRW is shot. There is no way this item draws less than an amp! Physically impossible!
The catch-all for a 12V HRW is 120 - 240W dependant on size and efficiency. Maybe a small one 100W but not less. Look up any car spec.
The catch-all for a 12V HRW is 120 - 240W dependant on size and efficiency. Maybe a small one 100W but not less. Look up any car spec.
Hal Adams
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As I say, I don't recall it being the most efficient demister, just that this is what my one draws.
2 different meters tried, both agree .... And they were connected correctly
2 different meters tried, both agree .... And they were connected correctly
- persiflage
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