Have I blown an element?

[JAMC]

I went to start a batch this morning, but couldn't get the boiling bucket to kick into life. I'm using a 33ltr polypropelene bucket with two 2.2kw kettle elements mounted in the bottom.

The supply is regulated by a PID/SSR combo box, which I've tested and it appears to be working normally. As far as I can tell, power is getting to both elements but neither one is drawing it through and generating heat. The circuit doesn't trip.

What do you think?

 

[JAMC]

OK, to complicate the picture even more...

I just swapped one of the existing elements for a spare that's never been used. Same problem. The chances of that spare element being faulty have got to be pretty small, so I'm looking at the control box again.

SSRs are receiving the signal from the PID, so I'm fairly sure they're not the issue for a couple of reasons. Firstly the two elements are controlled by seperate SSRs and I'd be sceptical of the notion that they've both gone symultaneously (neither element working...) and secondly I believe SSR failure usually results in an "always on" state.

The only common point of failure I can think of is the terminal blocks where all the 240v circuits either draw from or return to the mains supply. I can't remember the connection order, but I suppose a fault there could take out both elements. Those blocks are rated for 30A though, and I shouldn't be pulling more than 20A. Anyone ever had one of those go bang?

 

[chessking]

If I'm reading you correctly, you have replaced the element and have the same problem? Have you put a meter on the element terminals to determine if current is present? If they are live, than the element is shot. If dead than your problem is up stream. You say "always on" and I assume that means a closed circuit. that state actually would be the exception. The SSR usually fails in an "open" position, meaning no juice flow. However, in rare cases, they can fail in a closed position, so don't rely on that as a safeguard. In other words, don't walk away from your system and rely on the PID to shut the element off. I agree that simultaneous SSR failure is unusual, unless they both fail from the same cause. Maybe try new a SSR, they aren't that costly, and you would want a spare around anyway
As far as the terminal blocks, those are normally the last thing you would suspect, without a manufacture error, they are fairly simple and straight forward. Not a lot to go wrong there, but get in there with your meter and look around before you buy anything. In the mean time, you may have to boil on the stove. Cheers.

 

[JAMC]

Good info on the SSR failure, thanks for that. There's a third, (currently) unused SSR in the control box that I could swap out to test this, but as you say, symultaneous failure of two SSRs has got to be pretty unlikely. It's not like the box gets red hot - warm certainly, but not the kind of temp that would cause an SSR to fail after 5 batches.

The other thing I've noticed about the problem is with the elements themselves. They have a small orange LED wired to the outer casing which is normally lit when the element is drawing current. If there was no power reaching the element at all, I'd expect these to be completely dead; however, working the rocker switch on the element causes the LED to flicker on momentarily when switched on, but only for a fraction of a second. Could this be the elements' dry boil cut-out feature conspiring against me? If so, any idea how I dispose of it?

 

[chessking]

First, I assume your SSR's are mounted on an external heat sink. If not, while they may be ok now they will fail w/o some heat dispersion device. The internal temp of the box not a good indicator. The SSR's will heat up and need specific cooling. some guys mount them on a heat sink, but contain the heat sink within the box. For the sink to work effectively, it needs to transfer the heat to cooler air temps. If internal, and the temps rise, the sink looses efficiency of the transfer the heat, and the SSR overheats.
That being said, I guess I'm not familiar with the elements you are using. I just assumed they were a hot water heater element mounted in the kettle. Is the rocker switch and LED part of your control panel, or are they mounted on the element? Also with out a meter on the element Its hard to say. The SSR could be firing enough to light the LED, than fail under the load. Or the element could be screwy. I'm just a shade tree, and know just enough electrical stuff to keep from getting killed. Maybe someone else has a better handle on your problem. It would help to know more about your setup. Some pictures maybe, or a description of the element.

Edit: Also, I dig electric brewing and would enjoy learning about your process.

 

[Altbier bitte]

That diode lighting up is probably just due to capacitance in the circuitry, like an unplugged radio coming on briefly when you switch it on. I hope you can get it going soon. You boil in a plastic bucket?

 

[JAMC]

Thanks for everyone's help on this thread. I've tried a few experiments, and I think excessive heat may have killed the SSRs. They are mounted on heatsinks inside the control box but with vents cut into the sides to allow heat to escape. In retrospect this probably wasn't enought to disperse the heat by itself. The control box is also pretty crowded, which would not have helped airflow. I suppose I didn't realise quite how hot those relays actually get.

I've now got to wait for replacement SSRs to show up, and think about how to disperse heat more effectively while I'm waiting. I've built lots of PCs in my time, so I'm familiar with some of the common cooling techniques and I've got lots of PC fans kicking about. A larger control box might be necessary to make it all line up though.

 

[JAMC]

You boil in a plastic bucket?

Yep. The elements came out of a plastic kettle made from the same material. I've had no problems.

 

[JAMC]

Having spent most of today redesigning and rewiring my control box I'm somewhat annoyed to find that I haven't corrected the problem. I can eliminate the SSRs as I'm now using brand new relays. I think it's either got to be elements or cables. The elements I've used were from a kettle that cost about £5 - I can't imagine they're the most reliable pieces of kit ever to emerge from a Guangzhou sweatshop. I'll track down some replacements and see whether that solves the issue.

Anyone ever experienced fried kettle leads?

Control box now has front and aft PC fans sucking ambient air past heatsinks - SSRs mounted with thermal grease.

 

[JAMC]

Aaaaarrrgghhh!!

Approaching my wits end with this thing now.

Replaced SSRs - still doesn't work
Replaced kettle elements - still doesn't work
Tested kettle leads on another appliance - kettle leads work fine

Don't know what to try next.