12vdc relay help. - Page 1
Forum section: electronics / beginners

author: wntrhwk
author_rank: Newbie
timestamp: November 09, 2022, 12:30:09 am
content: Hello, hopefully I will be able to describe what I am needing here. I have a 12vdc relay (XHONG XHT78) that will activate the relay side when it reaches a certain temperature. No voltage at relay contacts, just resistance measured when triggered by thermister. What I am looking for is something that will hook up to the relay side of this device and then energize a separate 12vdc device (12vdc snowmobile hand warmers). I am hoping to use this to keep a LIFEPO4 battery warm. Hope this makes sense, thx for the help.Mike

author: chess
author_rank: Newbie
timestamp: November 09, 2022, 06:52:57 am
content: look for KSD301

author: Zero999
author_rank: Super Contributor
timestamp: November 09, 2022, 01:26:37 pm
content: I couldn't find XHONG, but the relay on theZHONGXHT78 board is rated to 10A. How much current do the the hand warmers use? Why not use the relay on the board?

author: wntrhwk
author_rank: Newbie
timestamp: November 10, 2022, 04:11:03 am
content: The relay contacts don't have any voltage to them, that is the issue I am having. I can only measure a continuity change across the 2 contacts.

author: wntrhwk
author_rank: Newbie
timestamp: November 10, 2022, 04:39:44 am
content: This is a picture of the relay. K0 and K1 don't have any voltage.

author: LateLesley
author_rank: Frequent Contributor
timestamp: November 10, 2022, 05:26:42 am
content: That's the way relay's work. It looks like the K0 K1 are just connected to the contacts. Its what they call volts-free contacts. So all you should have to do is feed power into one contact, and when the relay pulls, power should come out the other contact. Just be mindful of the current. It says it can do up to 20A with 14V AC - not DC - it'll need to be much less for a DC supply, because they burn up the contacts more. There is another rating suggesting it's good for 1A, that's the more believable one.http://cba.sakura.ne.jp/parts01/kit_f47.htmIt's because DC switching has a bigger, longer lasting arc than AC, thus it burns up the contacts quicker.https://components.omron.com/us-en/products/basic-knowledge/relays/applications

author: Zero999
author_rank: Super Contributor
timestamp: November 10, 2022, 08:22:08 am
content: Quote from: wntrhwk on November 10, 2022, 04:39:44 amConnect K1 to +12VDC and the load between K0 and GND.The image I found on ebay says 20A at 14VDC, but that's far too optimistic. 5A is more reasonable.

author: BeBuLamar
author_rank: Super Contributor
timestamp: November 10, 2022, 10:46:22 am
content: The relay contacts are just like a switch. You can use it to switch voltage different than the one that operate the coil which is 12V in your case but you can use the K0 and K1 to switch up to 240V power and it can be either DC or AC.

author: Zero999
author_rank: Super Contributor
timestamp: November 10, 2022, 11:20:03 am
content: Quote from: BeBuLamar on November 10, 2022, 10:46:22 amIn theory, yes, but whether it's safe or not, is another matter. It's possible there isn't enough separation between the traces going to the relay's contacts and the control side, for it to safely switch mains. I've seen plenty of cheap relay boards with hardly any separation. I certainly wouldn't recommend this board for switching anything over 60VDC or 25VAC.

author: wntrhwk
author_rank: Newbie
timestamp: November 10, 2022, 02:50:56 pm
content: I appreciate all the reply's, still a little confusing. You you are saying to run a separate 12vdc wire to to K1, then the positive wire from the heater (only pulls 2 amps) to K0, and the ground wire from the heater to ground. If that's not correct would you mind a quick diagram? Thanks for the help, retired Sys Admin, never made it to board level systems.

author: Zero999
author_rank: Super Contributor
timestamp: November 10, 2022, 05:03:21 pm
content: Quote from: wntrhwk on November 10, 2022, 02:50:56 pmYes. It's that simple. The switch will then turn the heater on and off.

author: wntrhwk
author_rank: Newbie
timestamp: November 10, 2022, 08:51:13 pm
content: Thx Zero, appreciate your knowledge and patience, a little out of my element here. Hope you have a good afternoon.