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3rd May 2017, 08:37 | #21 |
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I like the idea of mounting it elsewhere, especially away from the elements. If it was mounted under the slam panel - with some silicone heatsink paste to aid conductivity, would the lack of air flow be a problem?
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3rd May 2017, 08:45 | #22 | |
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Quote:
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3rd May 2017, 09:26 | #23 |
Doesn't do things by halves
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I think some explanation and caution would be wise here.
KV6 and diesel engines are fitted with a 450 watt motor which, when running at full speed (according to the simple electrical equation) draws about 33 amps. T-Cut, who said he had fitted a 40 amp fuse, has the 1.8 engine with, most likely, a 350 watt motor which draws about 30 amps at full speed. In both cases, should the resistor become open circuit, there will be a considerable surge when the motor starts at full speed. In these circumstances, there isn't much margin for error in the case of the 450 watt motor; the fuse is at risk of blowing when a fault is not present and resulting in overheating of the KV6 engine. Fuses provide only short circuit protection and they work extremely quickly, probably a matter of milliseconds. They are not designed to detect a relatively slow increase in current flow resulting from an under-rated resistor becoming too hot and partially disintegrating. When this happens, the resistor itself behaves like a thermal switch. To put this in perspective, excluding the initial non-resistor design which is not susceptible, we have lived with failing resistors for fifteen years now. I do not remember a single case of a catastrophic fire being caused, or a burned out loom for that matter, but no doubt someone will now come forward with just such a story! As you might have seen from a recent rather passionate debate, I am in favour of improving upon manufacturer's recommendations when justified. In this particular case though, I'd stick with the 80 amp fuse, just for "peace of mind" as they say. Simon
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3rd May 2017, 09:29 | #24 | |
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Quote:
http://www.ebay.co.uk/itm/MIDI-STRIP...9Z8OIsmYstDCmA
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Harry How To's and items I offer for free, or just to cover the cost of my expenses... http://www.the75andztclub.co.uk/foru...40#post1764540 Fix a poor handbrake; DIY ABS diagnostic unit; Loan of the spanner needed to change the CDT belts; free OBD diagnostics +MAF; Correct Bosch MAF cheap; DVB-T install in an ex-hi-line system; DD install with a HK amp; FBH servicing. I've taken a vow of poverty. To annoy me, send money. |
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3rd May 2017, 10:32 | #25 |
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Hi.
There are a few other factors though. Firstly I'd be pulling the fan fuse and check the current with an ammeter where the fuse was. Now it would be a good idea to measure both speeds. At high speed the loading will be higher and it's possible the current drawn could be higher than the rating of the motor would make you believe. The disadvantage of de rating the fuse is it could overheat rather than blow, this could ruin contacts making the problem worse leading to a fire. Let's not forget the 50w original resistor would act more like a fusible resistor than the 100w type.
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Cheers from Trevor MM0KJJ Last edited by murphyv310; 3rd May 2017 at 10:43.. |
3rd May 2017, 10:32 | #26 |
Posted a thing or two
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Harry ... your earlier suggestion of designing a PWM supply is a good one, and should probably have been the original design . . However unfortunately for us normal spanner monkeys its a step too far. .If it would be possible to design a simple plug&play replacement without a T4 involvement , i would think there would be plenty of customers .
This is one area where the original system could be improved .(similar to the sunroof drains /handbrake etc ) . |
3rd May 2017, 10:41 | #27 | |
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Quote:
TC |
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3rd May 2017, 11:26 | #28 | |
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How about for a 450W motor: 1) Use a pair of 100W 1 ohm resistors, connected in parallel, mounted back to back in the normal position 1) Reducing the 80A fuse to say 50A. Keep the 80A fuse in the car as a spare. 2) Putting a lower rated fuse in series with the resistor, say 25A. Then if the 25A fuse blows, the car still has full speed to fall back on, preventing overheating. The resistor is better protected from dramatic failure by the 25A fuse. The 2pcs 100W will operate at half the temperature of a single 100W resistor, which if below 100 degrees C, will stop steam generation, and subsequent explosion. BTW: Is the fan motor a series wound motor ? I seem to remember the current increases dramatically if the motor is jammed. And fans are awfully vunerable in the event of a front end shunt (which aren't exactly unheard of); or jamming on an undertray (as Mike Trident found out!). Last edited by MarkS; 3rd May 2017 at 13:16.. Reason: Added about series wound motor |
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3rd May 2017, 13:18 | #29 |
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I honestly don't see that the current single resister arrangement as a problem worth worrying about. There are umpteen reports of the resistor popping for whatever reason, but there are umpteen thousand resistors in normal trouble-free operation and have been for over a decade. The overheating/explosion issue is out of proportion with the reality.
Of much greater concern in my opinion, is a few reports of overheated or fried wiring with smoke and indications of fire. There should be no possibility of a wiring fire from any system in these cars, including the high ampage fan system. The resistor is as much the victim in this as the wiring. I reckon that's where we need to focus the discussion. My 40 amp fuse is simply a starter for one. TC |
3rd May 2017, 13:20 | #30 |
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Check the scrapyards for unused fire extinguishers in Vauxhall Zafires ? ;-)
Last edited by MarkS; 4th May 2017 at 10:00.. |
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