Electrical engineers and electricians assemble! brew controller question

[Vinylwasp]

any chance of making this post "sticky" at the top of the thread?

Lots of valuable information here. Thanks for taking so much time today to help us muggles (non-wizards) out.

You've really given me a kick up the backside to remediate some of the errors I've made. I don't think I've strayed too far from your guidance so that it's currently unsafe but I very much like the idea of using 'thimbles' for the Neutrik Powercon plugs (is this the term I should search for?), and definitely need to move the high load SSR and heatsink for the elements to outside the enclosures (I have 1 for my HLT and another for the BK, and feed them off different 230v rings in the house). The Fostek SSR only switches the pump on/off so not much load or switching either.

 

[The-Engineer-That-Brews]

Lots of valuable information here. Thanks for taking so much time today to help us muggles (non-wizards) out.

You've really given me a kick up the backside to remediate some of the errors I've made. I don't think I've strayed too far from your guidance so that it's currently unsafe but I very much like the idea of using 'thimbles' for the Neutrik Powercon plugs (is this the term I should search for?), and definitely need to move the high load SSR and heatsink for the elements to outside the enclosures (I have 1 for my HLT and another for the BK, and feed them off different 230v rings in the house). The Fostek SSR only switches the pump on/off so not much load or switching either.

View attachment 99017

Nice work there mate great stuff.

Are those spade connectors I see on the side rocker switch there? You might want to solder those instead, if they are taking any current ...

 

[The-Engineer-That-Brews]

I very much like the idea of using 'thimbles' for the Neutrik Powercon plugs (is this the term I should search for?)

@Vinylwasp I think the proper terminology these days is probably "Ferrules" or sometimes I've heard them called 'bootlaces'

Maybe have a look at these... https://www.amazon.co.uk/dp/B0CNR84K8V ??

 

[The-Engineer-That-Brews]

definitely need to move the high load SSR and heatsink for the elements to outside the enclosures

Hmmm - maybe you could mount a fan on the outside of the box, next to the heatsink, and a few holes on the opposite side of the case so it draws the air all the way through?

 

[MashBag]

Not knowingly.

That is the problem...how you are using it. Best build in the world, would still suffer.

SSRs are very fast switches. They are a digital control. Not analogue.
Using a scale of 1 to 10 (high), they work well 1-6. Above that they get warm. At 10, when you want full power they don't 'close they are switching VF quickly and get VF hot.

So.. Install a bypass for when you want full power.
Or use two elements?
Only use the SSR when you are really turning it down.
Problem solved.

 

[MashBag]

In case it helps, here's a closer look inside one of the TETB power controllers.

First and most importantly, ALL external metalwork (heatsinks, case, control knobs, etc) MUST be properly bonded to earth.

This isn't "elf an safety gorn mad" ... it's just bloody sensible. You're dealing with high power mains in an environment where there's water sloshing around and a lot of bits of earthed metal. Sometimes things go wrong, and this stuff really can kill you.​

Which leads to:

1. Use a plastic box with a rubber sealing strip. External junction boxes (which is what I'm using below) are a good cheap option.
2. Insulate the bare mains connections inside the box too. Water might get in, and sooner or later you'll accidentally leave it plugged in when you take the lid off. Either use electricians tape or (as here) heat-shrink sleeving.
3. Use the correct colours of cables - you might not be the only person who ever uses this box, and someone might assume "it's safe to cut the blue wire because it must be neutral".
4. Use thick enough cable - personally I prefer cable with 2.5mm sq of copper. It's not strictly necessary for the current capacity, but it makes much better connections.
5. Wherever possible use securely crimped ring connectors at the terminal posts - as in the first picture, which shows the connections to the SSR and in the background the safely earth for the heatsink. Avoid like the plague the kind of terminals where a screw terminal pushes down on the conductor (a.k.a 'chocolate block' connector strip). With stranded cable these are a prime source of connections that come loose over time and cause overheating. If you have to use this kind of terminal (e.g. inside the mains plug) then your best bet is to crimp a 'thimble' (thin metal sleeve) over the cable first. Do NOT 'tin' cables going into screw terminals with solder: it makes them even more susceptible to working loose.
6. Use proper 'heater' cable for the mains lead - search for cable meeting specification "3093Y". This is slightly stiffer, but the main point with it is that the outside jacket won't melt if you accidentally leave it lying touching the outside of your kettle...
7. When you need an internal connector, use a proper 'Barrier Block' (the black rectangular thing in the middle of the 2nd photo) and DON'T put too many wires into each strip. The terminals on these must be a flat metal plate that tightens down onto the cable - NOT a screw that digs into it.
8. As mentioned in previous posts above, the heatsink must be big enough, and MUST be in the fresh air - either by it being on the outside of the box, or by forced ventilation of EXTERNAL air with a fan (but in the latter case be very careful to make sure that the air vents can't be blocked or easily sprayed with water...). Note that decent SSR heatsinks are not cheap, and often cost more than the SSR itself. To control a 3kW kettle element over a 1hr boil in a hot brew-shed you want one with a thermal capacity of no more than 2-3 degrees per Watt, to keep the SSR at a sensible temperature (e.g. RS 171-9070 - currently £13.88)
9. As also mentioned above it's highly recommended only to buy SSRs from reputable suppliers (RS, Farnell, DigiKey and so on). I have never had one from tAmazon, eBay, etc that hasn't been falsely re-labelled with the wrong capacity (see here for details of how to spot them: https://www.eevblog.com/forum/reviews/warning-dont-buy-fotek-solid-state-relays/ )

View attachment 99013

View attachment 99011 View attachment 99012

@Chippy_Tea given the safely implications, any chance of making this post "sticky" at the top of the thread?

Excellent post by the way.

 

[MashBag]

Hmmm - maybe you could mount a fan on the outside of the box, next to the heatsink, and a few holes on the opposite side of the case so it draws the air all the way through?

You can, but if used properly and you don't need it.

 

[Vinylwasp]

That is the problem...how you are using it. Best build in the world, would still suffer.

SSRs are very fast switches. They are a digital control. Not analogue.
Using a scale of 1 to 10 (high), they work well 1-6. Above that they get warm. At 10, when you want full power they don't 'close they are switching VF quickly and get VF hot.

So.. Install a bypass for when you want full power.
Or use two elements?
Only use the SSR when you are really turning it down.
Problem solved.

I hear what you're saying here, but if I'm understanding everything correctly, when the PID switches the SSR on, it's on 100% immediately or is there some sort of dwell time while it switches and gets to 100% power, or are you simply saying that when it's cycling (1-6) it's able to remain cool via radiant dissipation of heat?

In the shot below you can see that the PID controlling my HLT element which is heating my HERMS coil is set at 14.3% per 4 second block or 0.572 seconds ON and 3.428 seconds OFF, reflecting the small temp rise of 0.3 C it's trying to achieve from 66.5 to 66.8. I've seen this go as low as 7% per 4 sec PWM block, so I guess it remains quite cool then.

At the same time when the gap is large the PID changes that % until it gets to 100% where the SSR remains closed for a long period like when I'm boiling or heating strike water. Is this when its more likely to get hot?

With respect to managing heat, I think I'm going to attempt to provide some forced ventilation courtesy of a small 30 or 40mm fan, maybe two fixed to the side of the cabinet.

 

[LeeH]

@The-Engineer-That-Brews

No requirement for control switches to be a ground potential. See BSEN60204

Cheers.

 

[LeeH]

I would also look again at your choice of crimps. Selecting them to match the colour of the conductor and not the csa is not a wise choice

Yellow is 4-6mm2, and not to be used because the CPC has yellow on it!

It seems you have managed to squeeze 2 conductors into a red crimp. If those are greater that 0.75 each then I’m not convinced of the integrity of that connection.

Giving electric advice over the tinterweb is difficult especially when it’s not squeaky clean.

 

[RoomWithABrew]

Very interesting thread.
I'll add to this thread from a non electronic engineer level, I melted a fotek SSR, purchased a RS replacement that never worked from first use.
Refitted the melted one but better positioning, thermal paste and a fan has made it cool.
Definitely a user positioning error on my behalf.
My SSR is pid controlled and touch wood all okay.
I do have a spare SSR on the shelf for the inevitable day.
Also now a spare smartPID.

 

[MashBag]

when the PID switches the SSR on, it's on 100% immediately

Yup that's the point where its it switching fastest, working hardest and getting hottest.

gets to 100% where the SSR remains closed for a long period like when I'm boiling or heating strike water. Is this when its more likely to get hot?

Yes. Forced cooling does help MTBF. Bypass fixes. Running a full boil power element and a SSR element could be better still.

Although I agree about crimps & cooling you are fixing the sneeze not the cold.

In another 3 other lives, running SSRs flat out (100%) melted them.
Renewables, FIT diverters and that other subject we don't discuss.
Both had good airflow and were professionally designed & installed.

 

[hoppyscotty]

Yup that's the point where its it switching fastest, working hardest and getting hottest.



Yes. Forced cooling does help MTBF. Bypass fixes. Running a full boil power element and a SSR element could be better still.

Although I agree about crimps & cooling you are fixing the sneeze not the cold.

In another 3 other lives, running SSRs flat out (100%) melted them.
Renewables, FIT diverters and that other subject we don't discuss.
Both had good airflow and were professionally designed & installed.

Sorry,but for the benefit of the slow ones at the back (probably just me), the bypass just applies full power to the element directly until such time you approach your set temperature then it hands over control to the SSR? Makes perfect sense in principle of course, however in my case my SSR was rated at 75a vs a 24amp load...not accounting for any spiking, so though the SSR is bound to get hot surely these components are appropriately designed for some level of heat tolerance...especially in high current circuits? My logic was that by over-speccing the SSR then it should have more than sufficient margin for coping with the task at hand...poor quality of the cheap Chinese made SSR aside....

I like the idea of having a bypass but not sure how to achieve it.

 

[LeeH]

Controllers (even the eBay ones) have a manual/hand mode, flick through the manual and enable it, set to 100%. No ‘bypass’ needed.

In respect to over sizing the relay, the logic is sound but as all components are not built equally, some with have tight tolerances, some will not. Only experience with that specific component will tell you.

Industrial brands like Croydon/Siemens will run flat out all day every day….until it doesn’t. Then you’ll find it fail closed and running balls out which is no major drama in this process really.

 

[hoppyscotty]

Ah yes the controller does have a 'manual'mode where you set the output as a percentage, so could set to 100% upto close to the boil then either remain in manual mode and ramp back the power or switch to PID mode. But I didn't bother because I thought the SSR will be fully on until the temp approaches target temp anyway and it is not that convenient to adjust the percentage power output in the PID as you have to navigate through a menu system so just let the PID take the strain. Could give it a go next brew and see what's what.

 

[The-Engineer-That-Brews]

Perhaps I’ve misunderstood, but I think of a “bypass” as a hard, physical conduction path that connects the heating element directly to the mains supply (see below).
The reason you might want to do this is that all SSRs even when manually set to “100%”, have a voltage drop across their ‘contacts’ of about 1.5V. So at full load this corresponds to a small amount of power (20 watts at 13A, double that at 32A) that is dissipated as heat in the SSR instead of reaching the element.
Personally I’m not usually fussed about losing 20W on 3kW; and on the odd occasions that I am, I just unplug my boiler from the controller and plug it straight into the wall socket.
I’m unaware whether commercial controllers have a separate physical relay to bypass an SSR like this when they are set to 100%.

 

[The-Engineer-That-Brews]

when the gap is large the PID changes that % until it gets to 100% where the SSR remains closed for a long period like when I'm boiling or heating strike water. Is this when its more likely to get hot?

Yes that's right.
You can think of the voltage dropped across the SSR in it's "ON" state as being a pretty-much constant voltage of about 1.5 to 2V (you can find the exact value on the manufacturers datasheet).

So the working temperature your SSR will stabilise to after a while (e.g. during a long boil) will be approx:

Room temperature PLUS ( Load current in Amps x SSR on-state voltage drop (about 1.7v) x thermal capacity of heatsink in deg C per Watt )​

Just for reference a good heatsink with the fins vertical in free air, typically has a thermal capacity of from 2 to 5 deg C per Watt.

 

[The-Engineer-That-Brews]

Here's an example of where to find the ON state voltage drop in an SSR datasheet.

This is for the following, fairly typical device (RS stock no. 903-2970): a single pole SSR from I-Autoc

The datasheet for it is here: https://docs.rs-online.com/3083/0900766b81457292.pdf

The bit we are looking for is on the second page:

The datasheet also gives you a lot of other useful and important info such as the thermal de-rating curves on page 4.
These show that for the 25Amp version of the device, at an ambient temperature of 25 deg C and under continuous load, with a good (2 deg C / Watt) heatsink you should get about 22A out of it without overheating; whereas with no heatsink you'd be lucky to get 7A.

 

[Vinylwasp]

a good heatsink with the fins vertical in free air, typically has a thermal capacity of from 2 to 5 deg C per Watt.

Good to know. That heatsink I'm using is a bridge so has a long run of fins below the SSR and shorter runs either side of it so has plenty of surface area to dissipate heat. I'm thinking that when I mount it next time I'll use some adhesive mounting material that I've used in the past to mount it.

 

[MashBag]

Manual mode? Does this not just send 100% through the SSR?