Relay replacement desoldering issues - Page 1
Forum section: electronics / repair

author: jerryk
author_rank: Regular Contributor
timestamp: December 26, 2022, 08:08:23 pm
content: I have a "simple" repair that consist of replacing two relays. The problems is heat transfer. The last two contacts are in the solid copper bar that goes to the ground of a lithium ion battery pack. The heat I apply to free the last relay contact transfers up the contact into the battery almost instantly. I'm trying to keep the battery at a reasonable temp yet get the two remaining contacts free. Any attempt so far to keep the battery cool and the contact hot enough to melt free is failing. I have tried chip quick, low temp solder paste, and just tried to apply mass heat quickly. I finally cut the relays free of the last contact and still no success in melting the contacts out without the heat transferring into the battery.Any suggestions on desoldering the last two contacts would be greatly appreciated.Jerry

author: coromonadalix
author_rank: Super Contributor
timestamp: December 26, 2022, 08:12:30 pm
content: mm i would use an very powerful iron at 840 degree, to be fast and precise without taking too long to avoid the overheating

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: December 26, 2022, 08:34:01 pm
content: Put everthing that dont have to be heated in a dielectric coolant and take all your time to prform a nice solder.https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjGitXLkJj8AhXhRaQEHUz7Dx8QFnoECBAQAQ&url=https%3A%2F%2Fwww.shell-livedocs.com%2Fdata%2Fpublished%2Fen%2F615128f8-db18-4709-bb03-10bf668eb6eb.pdf&usg=AOvVaw1ZoaBovdeGyO3_i5yC8MeP

author: jonpaul
author_rank: Super Contributor
timestamp: December 26, 2022, 11:10:34 pm
content: Metcal SP-200 smart heat iron, blunt large chizel tip63/37 Eutectic leaded solder, like Kester 44Jon

author: Martin72
author_rank: Super Contributor
timestamp: December 27, 2022, 12:01:59 am
content: QuoteWhat you need is power and patience..At work I got a Weller station (WX2) with 120W soldering iron.In a case like yours I would take the biggest tip for it, set the temperature to 400°C and using a solder with more flux.Important is the power of the iron, not the temperature.

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: December 27, 2022, 09:54:43 am
content: Quote from: Martin72 on December 27, 2022, 12:01:59 ampower of the ironthermal inertia.A large tip will give you a resevoir of calorific energy that is avaliable in few milliseconds, the heating element is too slow for that, at the exception of the very expensive soldering stations that come with lightning strike speed control of the tip temperature.

author: Martin72
author_rank: Super Contributor
timestamp: December 27, 2022, 10:10:58 am
content: Like mine.......Only at work...

author: jerryk
author_rank: Regular Contributor
timestamp: December 27, 2022, 06:18:09 pm
content: Thanks for the suggestions above. I have a large block of solid copper in the freezer that I'm going to try to fix to the copper bar above the two relay terminal connections. I'm not sure if this will be an effective thermal block or if I'm just fighting myself by increasing the need for heat at the relay terminal solder joints.I do have a Hakko FX-888D along with a Hakko FR-300 that I used in tandem to free the other side of the relay terminals. They would work on this side however the heat that travels up the copper bar into the battery I suspect will melt the PVC sleeve and possibly damage the battery. Like you all have said, it's about power and time with regards to the heat transfer and I'm doing this too slow. I'm not going to purchase another solder station over this repair so I'm trying to accomplish this with the tools that I have.I do have a small butane torch I may give a try if I can protect the surrounding area from flame damage and then use a blast of compressed air to knock the terminal out. Otherwise I may try to just use a dremel and small bit to cut the remaining terminal from the slot in the copper. I think soldering the new relays will be easier to to do by flood soldering the joint.Jerry

author: floobydust
author_rank: Super Contributor
timestamp: December 27, 2022, 06:51:27 pm
content: I think high heat, in and out fast is preferred to low heat and a long contact time. Forget the use of small soldering irons like an 888.So I would put a heat shield over the battery, either a thermal (plumber's) blanket or metal plate (that can't short the battery) and use a blow torch. If the flame exhaust is contained to the bus bar, it should go well.A soldering iron for stained glass window work is also excellent for high heat, you could maybe find a shop and use one there.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: December 27, 2022, 07:52:06 pm
content: Can't the battery be removed?

author: jerryk
author_rank: Regular Contributor
timestamp: December 27, 2022, 08:40:45 pm
content: Well progress has been made. The old terminals are out and new relays ready to be installed.@flobbydust tipped me over my lack of courage ledge and I used the butane torch in the picture. It still took more time than I wanted but using the frozen copper block and some freeze spray along the battery connection of the copper bar it seems to have went well. I also used some heat insulating tape, a ceramic tile, and various cutouts of exhaust manifold gasket material for a heat shield around the surrounding area. I did blast it clean with an air hose but I'm not sure that was a great idea because it undermined the solder joint between the two copper bars which is not really what I wanted and may make cost me time in re-soldering the new relays.The copper bar is integral to the battery and is under the PVC (expansion protection) sleeving which is something I did not want to violate. I also assume that the cell tabs are spot welded to the copper bar and the order of initial assembly would be to solder relays to copper and then spot weld to the battery tabs. Bottom line is you cannot remove the copper from the battery as far as I know so I was stuck with this heat transfer dilemma.Now on to re-soldering things and I suspect the butane torch may get used again to finish things off so I have a real solid connection on the relay terminals.Thanks for the help.Jerry

author: floobydust
author_rank: Super Contributor
timestamp: December 28, 2022, 05:04:29 am
content: That worked out well. What product is this to have such hefty copper bus bars and 70A relays?I do autopsies on old relays, cut them open, you might want to see what went wrong with them.

author: jerryk
author_rank: Regular Contributor
timestamp: December 28, 2022, 06:38:37 pm
content: I cut them open before I went tried soldering the replacement relays on. Here is what the relays looked like on the inside. The device is a NOCOGB70 jump pack. Notice the rating on the cover. I'm not sure how NOCO calculates these amperage claims but they sure seem far fetched to me.This same relay is ubiquitous in the jump pack industry. A lot of companies use one of these relays in the dongle that has the battery leads. The last photo is what you will typically see in a jump pack dongle. The one shown is off an MicroStart XP-10 HD which claims 650 amps peak current.Jerry

author: Swake
author_rank: Frequent Contributor
timestamp: December 31, 2022, 11:09:04 pm
content: Who told you that the A stands for AmpèreAnd if it was, why would you think that current is coming out of the leads?yeah, I would have expected the same....My preferred farmed has just made a video about these things: