24V air conditioner Relay board diode question - Page 1
Forum section: electronics / repair

author: MtPockets
author_rank: Newbie
timestamp: August 01, 2017, 02:48:52 am
content: Hello,I'm trying to help a friend out with his Air conditioning issues in his heavy equipment truck. its a 24v relay board that he happened to short out somehow while working on his truck.Upon looking at the board No visual signs of it being burnt, however 1 diodes was bad. 1N5408 3A 1000v. I replaced but wasn't sure if it was supposed to be a Schottky diode or not.Upon reinstalling the unit worked for a short period of time "Intermittent though" he mentioned that one of the relays was warm/hot to touch.I took the board back and removed the suspect relay SCHRACK V23148-A0007-A101 and noticed a bit of corrosion on the through hole "Pretty bad" I removed another and same issue, I was able to clean them up so that it'd have good contact again, but wanted to make sure if I should replace the diode with a Schottky or not.I ordered a few schottky's .thing is is that the other diodes on the board have the same values with DMM as the regular ones and the schottky. " .552 " and the new ones are a big larger. I'm guessing the sizes changed within the past 17yrs.

author: hermit
author_rank: Frequent Contributor
timestamp: August 01, 2017, 03:09:22 am
content: Assuming you pulled the IN5408 from the board, you can't google it?Data sheet says power diode. They seem to be paired up with relays which should indicate what they are used for.

author: MtPockets
author_rank: Newbie
timestamp: August 01, 2017, 03:14:09 am
content: yes pulled, their really isn't any info avail, Yeah I googled and googled several different ways. I was thinking that since it was on a low voltage system that they would use the Schottky's. I replaced all the relays sure was a bear with the conformal coating

author: hermit
author_rank: Frequent Contributor
timestamp: August 01, 2017, 03:38:53 am
content: First hit I got on google for that number was a datasheet.http://lmgtfy.com/?q=IN5408

author: MtPockets
author_rank: Newbie
timestamp: August 01, 2017, 04:18:37 am
content: Thanks for pointing that out Hermit, I was completely lost in your translation. You sure can get a lot of info on that Diode, However not so much on the board and what it calls for standard diode or SchottkySo with that added information, it would be nice if someone with experience with those types of circuits can help out.Much Appreciated.

author: Armadillo
author_rank: Super Contributor
timestamp: August 01, 2017, 05:02:29 am
content: In my view, just any general purpose rated power diode will do.But I think the focus is on the Relay! Rated at 7A foronly6000 cycles. The Relay that your friend said is warm, replace it!Measure all the relays contact resistance.Power up the relay to close & Open, [apply external power to A1 and A2 Pins]Apply by clip on 18v, relay should close [put audible], reduce voltage to 10v, relay should close, slightly knock the relay, it remain closed. Repeat few times. Any failures, replace Relay.then measure the closed contact resistance [Pin 11 and Pin 14]. Change or clean the contacts if any abnormal resistance is observed. Replace the Relay is the best as cycle life may have been exceeded.Also measure the coil resistance A1 and A2, should be between 1100 ohms to 1400 ohms... Deviation out of this window, change the relay.

author: Jeroen3
author_rank: Super Contributor
timestamp: August 01, 2017, 05:40:50 am
content: Just replace all relays. If you're on hourly rate, a new board is ~$200.http://nl.mouser.com/ProductDetail/TE-Connectivity-Axicom/V23148-A0007-A101Spray it with a bit of acrylic (like PLASTIK 70) when done to prevent further corrosion.Or, you know, "You touched it, you own it".

author: MtPockets
author_rank: Newbie
timestamp: August 01, 2017, 04:57:15 pm
content: Thank You very much Armadillo that's what I was looking for.I had changed all the relays, was pretty much looking for diode info.new board is $350 USA from Switzerland

author: Armadillo
author_rank: Super Contributor
timestamp: August 01, 2017, 05:20:54 pm
content: Good to know that you have changed all the Relays.So your friend should be happy now enjoying the aircon?The diode you used, 1N5408 silicon diffused junction diode is too good at 1000V Reverse Voltage.and to answer your question, No you cannot use Schottky diode for reverse freewheeling protection.