"She canny take it captain!"  This is the most dodgy thing I've done in a while. - Page 1
Forum section: electronics / beginners

author: paulca
author_rank: Super Contributor
timestamp: December 12, 2017, 08:06:52 pm
content: So my 40A 240V mains PWM dimmer is failing. But I really, really, really need it to last just one more hour.It controls the power going to a 30 litre boiler for home brew. The 3kw boiler made it rain beer in my kitchen the first time I did a 1 hour boil. Literally rained beer.So the PWM "dimmer" works a charm to lower the power to the boiler. It smells a bit from time to time and gets a bit toasty, but it usually behaves.Tonight however I noticed it making a interesting buzz. Had it on for about 30 minutes at a very low setting and no issues. I did notice the green mains terminal blocks on the PCB where showing signs of heat wear and were miss-shaped.But... when I cranked it up to bring the wort to a boil I noticed a smell. I brought the torch down to look in the little hole that used to be occupied with an ammeter and noticed smoke. "Oh shit!"Looks like the mains connector block is melting around the live wire. The nuetral and earth are fine.The wort was up to the boil and the dimmer just needs to run on about 45% power for an hour without going up in flames.Getting nervous...Also, I'll need to come up with a new one.Should I DIY it or should I get another dodgy Chinese PCB?

author: paulca
author_rank: Super Contributor
timestamp: December 12, 2017, 09:14:41 pm
content: Well, it survived it's last boil with only a little more smoke. Took apart and the PCB connector blocks disintegrated.Look at it, it doesn't seem to be much more than a large pot two caps, a resistor and a big mosfet like thing on a heatsink. Unless that mosfet looking thing (which is still too hot to touch or I'd try and get a part number off it) is a PWM IC.I'll try and work it out and get a part number tomorrow.I'm going to need a new way to limit the power to the boiler.

author: james_s
author_rank: Super Contributor
timestamp: December 12, 2017, 10:47:23 pm
content: That "mosfet like thing" is very likely a triac, that sounds like a typical light dimmer circuit, assuming this is AC mains powered.

author: rmacintosh
author_rank: Regular Contributor
timestamp: December 12, 2017, 10:57:48 pm
content: I have seen a lot of people use an SSVR for the same application you are using your dimmer with.https://www.auberins.com/index.php?main_page=product_info&products_id=332Still pretty DIY solution, and you could go all out and build a PID contoller to control your boil with a temperature feedback system.

author: james_s
author_rank: Super Contributor
timestamp: December 13, 2017, 12:12:31 am
content: While I'm a fan of DIY, there's hardly any sense in building a PID controller when you can get dirt cheap Chinese industrial controllers for peanuts. I've used several types that actually work very well.

author: paulca
author_rank: Super Contributor
timestamp: December 13, 2017, 07:48:45 am
content: So I think the issue was caused by the green connector block for live on the PCB melting out of shape slightly which caused a partial connection. The buzzing I was hearing would have been a tiny amount of arc'ing. That caused heat build up which caused more melting and some smoking.I could repair it. Just need to put a proper set of mains rated high temp plastic terminals soldered onto the board again.As to a temperature controller. It wouldn't work. The boil is always 100*C. 99.9 is not boiling. 101*C will never be reached. (Actually it is, but that just because it's not just water I'm boiling). What I am limiting is the amount of heat used in the worts latent heat of evapouration. 3kw is enough to convert an awful lot of beer to steam. I estimate I need about 1.2kw to maintain the "rolling" boil.I think I will go for the repair option and at the same time re-instate an volt/amp/power meter since I blew the first one up.

author: Terry01
author_rank: Frequent Contributor
timestamp: December 13, 2017, 08:52:39 am
content: Ha Ha! Funny story to tell the grand kids!

author: paulca
author_rank: Super Contributor
timestamp: December 13, 2017, 10:39:10 am
content: Pretty sure what I have is one of these, but it was sold as "PWM".https://www.ebay.co.uk/p/4000w-AC-220v-SCR-Voltage-Regulator-Speed-Controller-Dimmer-Thermostat-BS/934320155?iid=272594352350&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D49569%26meid%3Ddc014e62427a4c1499fa296c7393d599%26pid%3D100005%26rk%3D6%26rkt%3D6%26sd%3D192129954375&_trksid=p2047675.c100005.m1851

author: Mr. Scram
author_rank: Super Contributor
timestamp: December 13, 2017, 10:47:01 am
content: This thread is worthless without pics!

author: paulca
author_rank: Super Contributor
timestamp: December 13, 2017, 11:00:12 am
content: Quote from: Mr. Scram on December 13, 2017, 10:47:01 amI have a video of smoke wisps coming out of the box and a few photos of the aftermath. I'll try and upload them later

author: Mr. Scram
author_rank: Super Contributor
timestamp: December 13, 2017, 11:00:45 am
content: Quote from: paulca on December 13, 2017, 11:00:12 amSeeing the aftermath should be good!

author: vealmike
author_rank: Regular Contributor
timestamp: December 13, 2017, 11:06:18 am
content: I found the biggest problem to be that the wort would burn on a 3KW kettle element, especially as any trub would settle to the bottom of the copper, where, coincidentally the element needed to be. To solve, I attached an anodised heatsink to the element, spreading the heat generated over a larger area of wort.Well that, and the fact that my kettle element leaked at the join to the copper -cough brewbin cough- the mains plug got wet and the RCD tripped every five minutes, a sort of built in power limiter.Boiling used to take ages and was always conducted outdoors.Don't try this at home kids.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: December 13, 2017, 11:21:36 am
content: Sounds like a loose connection rather than an electronic fault.

author: paulca
author_rank: Super Contributor
timestamp: December 13, 2017, 11:23:25 am
content: Quote from: vealmike on December 13, 2017, 11:06:18 amhttps://www.cnmonline.co.uk/cygnet-electric-water-boiler-with-thermostat-30-litres.html?gclid=EAIaIQobChMIruyyr--G2AIVgQvTCh1Y6wTBEAQYBSABEgISbfD_BwEThough I found my cheaper for around £45.The other option, if you are using a 30 litre plastic bucket and kettle elements, is to use 3 individually switched 1kw elements. Then you can control the boil by switching one or two of the elements off. I think yo might need a little more than 1kw to keep the rolling boil. (If I hadn't of blown up my ammeter I could tell you how much mine requires, but it had the wrong instructions and made a few lovely burn marks in my carpet as a result!)EDIT: The boiler above is NOT suitable. You must check that it will maintain a boil and the highest temp setting is above 100*C so you can then control it separately. The one above cuts out at 96*C so will not maintain a rolling boil unless you hack it.

author: paulca
author_rank: Super Contributor
timestamp: December 13, 2017, 11:27:44 am
content: Quote from: IanMacdonald on December 13, 2017, 11:21:36 amYep, that's what I'm thinking. I believe the cheap PCB terminal connectors have slowly melted, miss shaped and caused an intermittent connection which has caused heat build up, melting the 13A connector block, which is what caused the smoke and the smell.I think I can just replace the PCB terminals and the connector block and be back in operation.Can anyone recommend a reputable source for PCB mount mains terminals rated for 13A+?These might do? I suppose I should measure the PCB holes and try and match them. Alternatively I could solder the mains directly in.https://uk.rs-online.com/web/p/pcb-terminal-blocks/8966696/

author: oldway
author_rank: Super Contributor
timestamp: December 13, 2017, 11:53:55 am
content: For this kind of application (boiler), the solution of phase control is not recommanded because of low power factor.Far better to use the full wave switch.Adjusting the ratio Ts/To, you can control the power in your resistive element.

author: amyk
author_rank: Super Contributor
timestamp: December 13, 2017, 11:59:01 am
content: Quote from: IanMacdonald on December 13, 2017, 11:21:36 amThis.Even expensive terminal blocks won't help if you don't clean and tighten them enough.Also, this is a good excuse to get a thermal camera

author: Gyro
author_rank: Super Contributor
timestamp: December 13, 2017, 12:02:11 pm
content: Quote from: paulca on December 13, 2017, 11:27:44 amMost likely the other way round, the intermittent live connection caused the heat which melted the block, otherwise the Neutral would have been equally affected. If you'd stopped briefly to re-make the connection when you first noticed it you would hav got away with it.

author: vealmike
author_rank: Regular Contributor
timestamp: December 13, 2017, 12:17:02 pm
content: Quote from: paulca on December 13, 2017, 11:23:25 amThanks, but I've not brewed (beer) for 30 years. It was a long time ago, when I was a student and couldn't afford proper equipment.Incidentally I found some old bottles in a crate a couple of months ago. One of the stronger brews was still perfectly drinkable. Not bad for 30 years old! It had definitely dried out and was extremely strong. Just like drinking a pint of fortified wine. I always used a top fermenting wine yeast, as beer yeasts tended to get stuck before they hit the 8ish percent I was invariably targeting.From memory the beer that was still drinkable was an ale, targeted at around 10%. It had definitely "matured". Hic.

author: paulca
author_rank: Super Contributor
timestamp: December 13, 2017, 12:33:51 pm
content: Quote from: Gyro on December 13, 2017, 12:02:11 pmAww well. The PCB board survives to be repaired and the most important thing of all is that the Christmas brew got made. A little late, but 10 days fermenting and 3 days clearing and it will be grand!

author: Gyro
author_rank: Super Contributor
timestamp: December 13, 2017, 12:35:40 pm
content: Haha, true.

author: paulca
author_rank: Super Contributor
timestamp: December 13, 2017, 12:41:50 pm
content: Quote from: amyk on December 13, 2017, 11:59:01 amI looked at those, but they are very expensive. Too much money to justify for limited use case. Although my fingers have several burns already trying to work out if a 100R resistor or a PNP is being overloaded. The usual process is:"Is that NPN .... OUCH! yes."

author: Mr. Scram
author_rank: Super Contributor
timestamp: December 13, 2017, 01:00:10 pm
content: Quote from: paulca on December 13, 2017, 12:41:50 pmNature gave you those wonderful nerves for a reason.Plus we shouldn't pretend that we aren't going to touch it anyway. We always have to touch the wet paint.

author: alanb
author_rank: Frequent Contributor
timestamp: December 13, 2017, 01:35:21 pm
content: Reminds me of thishttps://youtu.be/7grLpxx61eYat 1:20:12