Replacing the 3 wire power cord from old Heathkit Weather Station? - Page 1
Forum section: electronics / repair

author: dentaku
author_rank: Frequent Contributor
timestamp: May 11, 2015, 12:53:18 am
content: I found an old Heathkit ID-4001 Weather Station this afternoon but the power cord is cut off. I don't really care if it works because I don't have all the extra hardware that goes outside, I just want to know if it will light up before salvaging the useful parts from it.It has three wires so it used a three pronged plug but I'm wondering exactly how to rewire this so I don't fry anything. I have a wire I want to use, I checked and the green is the center prong as I expected.Which wire goes where?

author: kwass
author_rank: Frequent Contributor
timestamp: May 11, 2015, 01:05:46 am
content: The ribbed lead is the neutral, the smooth lead is the hot. Color coded: the white lead is the neutral and the black lead is the hot and the green is the ground. so:White = RibbedBlack = SmoothGreen = Ground (also green)

author: IanB
author_rank: Super Contributor
timestamp: May 11, 2015, 01:17:03 am
content: Pretty poor instructions when they don't label the terminals as "hot", "neutral" and "ground". Presumably Heathkit products were not sold as educational kits?

author: dentaku
author_rank: Frequent Contributor
timestamp: May 11, 2015, 01:34:36 am
content: Quote from: IanB on May 11, 2015, 01:17:03 amI was thinking the same thing too.

author: dentaku
author_rank: Frequent Contributor
timestamp: May 11, 2015, 01:44:52 am
content: Quote from: kwass on May 11, 2015, 01:05:46 amOK.I just checked on the device then the schematics and the smooth lead is the one that has a fuse (funny looking glass fuse with a spring and a resistor inside) so it seems logical that it's the hot.Here's the schematic I probably should have posted earlier.

author: SL4P
author_rank: Super Contributor
timestamp: May 11, 2015, 01:57:04 am
content: I'm sure we all appreciate your interest in learning, and recovering some bits from the device, but in all honesty, if you have to ask "how to wire up a mains power cable" in a forum - I'd seriously take a step back before you doanything.Do you have kids, pets... the chances of an accident are small, but very real.When you pass the box on to a relative - will it have a warning sticker that the case may be 'hot'?You can buy an off-the-shelf power supply, and connect to the secondary side of the transformer - or something less dangerous until you have a better grasp of the fundamentals.

author: Farley
author_rank: Regular Contributor
timestamp: May 11, 2015, 04:06:55 am
content: What is the purpose of R301, the 2.2M resistor between the neutral (ribbed) lead and ground? I've not seen that before.

author: dentaku
author_rank: Frequent Contributor
timestamp: May 11, 2015, 10:22:14 am
content: Quote from: SL4P on May 11, 2015, 01:57:04 amI'm more interested in the electronic stuff and was just making extra sure when it came to the 120V ACelectricalpart so I didn't ruin any interesting parts.If the instructions and schematic would have used better terminology than just the "smooth" and "ribbed" wire it would have been easier.I'm never going to use this thing, just salvage the fun parts.

author: dentaku
author_rank: Frequent Contributor
timestamp: May 11, 2015, 03:03:25 pm
content: I found this image this morning explaining how these old style three wire power cords work.

author: IanB
author_rank: Super Contributor
timestamp: May 11, 2015, 04:22:16 pm
content: Quote from: dentaku on May 11, 2015, 03:03:25 pmThey are not old style. Three wire "figure 8" power cords still seem very common in the USA. Do you not see them in Canada?

author: TimFox
author_rank: Super Contributor
timestamp: May 11, 2015, 07:22:00 pm
content: Sometimes the easiest three-prong replacement cords to find are cheap "IEC" computer-style power cords. Just cut off the international-style female connector. The cable is usually European color-coded:green/yellow = groundblue = neutralbrown = line

author: dentaku
author_rank: Frequent Contributor
timestamp: May 11, 2015, 07:44:19 pm
content: Quote from: IanB on May 11, 2015, 04:22:16 pmI see one on my old Weller WTCPS soldering iron but mostly I see round cords in this room.Hmmm. I see a few in the kitchen now that I checked. I've never looked at appliances much. I guess I'm more interested in lower power DC stuff and haven't had to mess with power cords other than when I built my power supply but that's 2 wires and the transformer came with the power switch and fuse already attached.By the way, the weather station seems to work. I think I might send some BCD to the wind direction sensor terminals and see if I can get it to read something other than SE.

author: dom0
author_rank: Super Contributor
timestamp: May 11, 2015, 07:54:34 pm
content: Quote from: Farley on May 11, 2015, 04:06:55 amOh, but you did. It's the bleeder resistor for the three capacitors, just wired from hot/phase to ground, because cold/neutral is bridged to ground somewhere in the mains installation. It's just uncommon because large parts of the world use non-polarized plugs for mains power, which means that the bleeder must always be connected across neutral and phase, since you don't know which one is which.

author: dentaku
author_rank: Frequent Contributor
timestamp: May 12, 2015, 02:20:54 am
content: Just to drag the thread on even longerI just connected 4 toggle switches to the wind direction connectors and it turns out that they wired the 16 LEDs the show N, NNW, WNW, etc. in such a way that if you just use regular binary to count up it doesn't work as you expect but if you use 4 bit gray code it lights each LED in sequence around the circle perfectly.Of course the wind direction sensor has an optical encoder disk inside it that puts out gray code.Tomorrow I'll see if I can make the windspeed display show something other than 0.

author: Stonent
author_rank: Super Contributor
timestamp: May 14, 2015, 02:05:44 am
content: When in doubt insert a 15 watt light bulb in series. If you feel it is ok, move up to a 40 or a 60.