EEVblog #1172 - TRIAC Testing (WEP Meltdown Part 2) - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: January 24, 2019, 11:51:18 pm
content: A follow-up to the Yihau/WEP SMD Station Meltdown, testing the heater drive TRIAC and looking at the brushless DC fan motor.And how a TRIAC and SCR works.DaveCAD github:https://github.com/EEVblog/DaveCAD

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: January 25, 2019, 01:40:11 am
content: This needs a video link:

author: johnlsenchak
author_rank: Frequent Contributor
timestamp: January 25, 2019, 03:01:45 am
content: I real like the electronic theory we need more of it , instead of the boring debunking videos.

author: ebclr
author_rank: Super Contributor
timestamp: January 25, 2019, 03:06:49 am
content: It's not a thermistor, Is a thermocouple

author: tchicago
author_rank: Regular Contributor
timestamp: January 25, 2019, 03:25:48 am
content: Ahh, you mentioned 6.3V tap coming from your old transformer. There is a long glorious history behind this voltage. It used to be the most standard low voltage in the circuits, similar to the way we have 5V and 3.3V todayI still have a bunch of bulbs rated at 6.3V.

author: orion242
author_rank: Unknown
timestamp: January 25, 2019, 04:22:55 am
content: Still comes back to a sensing problem IMO.The power switching device is fine. The sensing element should have easily seen nuclear meltdown. This POS has some goofy failure that's almost certainly a software bug.Temp short, open should be shutdown. Temp 2X normal..shutdown. There has to be an edge case that isn't properly handled.

author: Andrew McNamara
author_rank: Regular Contributor
timestamp: January 25, 2019, 09:22:01 am
content: Quote from: tchicago on January 25, 2019, 03:25:48 amIt was the most common valve filament voltage. As to why, nobody seems sure - maybe because cars in the early days had 6V electrical systems, so 6V car batteries were handy?

author: TheDane
author_rank: Regular Contributor
timestamp: January 25, 2019, 12:17:59 pm
content: https://youtu.be/4n7iE7pw_WQ?t=835- @13:55The chip looks like IT has melted, or could it be glue holding it in its case?Anyways, the datasheet says device has a 16V maximum operating voltage + it has a 85 degrees C over-temperature protection circuit.In part 1 it was said that the device had been running on/off for 4 hours? Was the handle hot/warm to the touch?- perhaps the chip went into over-temp protection, causing it to stop operating - and the entire handle went 'nuclear melt-down' due to lack of airflowIs it a cap, or resistor in series with the input supply pin, mentioned at the timestamp in the video above?Should not matter, but the fan is rated/powered at 24V, and if it enters over-temp the device current draw should decrease since no current is drawn through the coils - effectively increasing its supply voltage above the maximum operating voltage.- and this is used in a device capable of reaching hundreds of C's, and solely depending on the fan to operate properly.Edit - No direct time stamp linking possible?

author: tchicago
author_rank: Regular Contributor
timestamp: January 25, 2019, 12:34:34 pm
content: Quote from: Andrew McNamara on January 25, 2019, 09:22:01 amThe reason for 6.3 is because the lead acid battery elements are rated at 2.1V. So there were 3 elements in series for the valve filament voltage. So the history goes back to the WW2 military radios.

author: EEVblog
author_rank: Unknown
timestamp: January 25, 2019, 12:55:08 pm
content: Quote from: johnlsenchak on January 25, 2019, 03:01:45 amYeah, all those endless debunking videos I do

author: EEVblog
author_rank: Unknown
timestamp: January 25, 2019, 12:56:35 pm
content: Quote from: tchicago on January 25, 2019, 03:25:48 amIt was a common heater voltage for toobs.

author: drussell
author_rank: Super Contributor
timestamp: January 25, 2019, 03:01:33 pm
content: Quote from: tchicago on January 25, 2019, 12:34:34 pmThere is no mystery there, we are absolutely sure! The reason for tube filament (and later, heater) voltages being multiples like 1.2, 6.3 and 12.6 is indeed because of the nominal voltage of cells and battery chemistry, but it goes back alotfarther than WW2.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 26, 2019, 05:48:04 am
content: Why would a 24V fan fail if you put a 16V Hall sensor in it and remove stuff that mitigates back emf voltage spikes?It's also plausible that Dave found a datasheet of a comparable chip from a different manufacturer but with the same type number.

author: TheDane
author_rank: Regular Contributor
timestamp: January 26, 2019, 08:47:58 am
content: @14:44 - So it's got an onboard driverWhy would the driver fail. Dunno, didn't design or test it

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: January 26, 2019, 04:42:17 pm
content: Be aware that thyristors may work OK on low voltage or when cold but may leak and latch up when hot or under rated voltage. A judicious application of another Yihua unit (non melted down variety) with the triac in series with a mains bulb (no gate drive) might determine if this was the problem.Of course if the second Yihua melts down while you're doing this... (Just kidding)I have the Atten 858D+ and a quick examination shows that:It has a fused IEC socket, and the fuse is in the live. (good)There is a proper mains switch, in the live. (good)The earth wire to the wand is not very substantial, and I wonder if it can pass enough current to blow the fuse. (bad)There might be a thermal cutout in the wand, but it is hard to tell without pulling the insulation to pieces. (?)I'm thinking I will look into improving its safety by fitting a thermal cutout close to the element.The lightweight earth is hard to upgrade without changing the whole flex, but I was wondering about fitting an RCD in the unit. (My bench has one anyway but you have to allow for someone using it elsewhere)Or I could just fork out for a better brand of unit.