Which soil warming cable to get?

[chris2012]

To quote Kev888 "The heat trace cable comes in two types; constant power and self regulating. The latter can be cut to any length and in theory will not overheat (say if covered with insulation), but it can be damaged by very hot temperatures - e.g. if you forget to remove the belt whilst hot cleaning the FV."

So I'm just wondering which type https://www.amazon.co.uk/Parasene-21210 ... B001W7Y286 is?

And if 50W would be enough for UK weather, for a 5 gal plastic bucket fermenter in a shed.

Also does anyone know if that soil warming cable comes with a plug?

Cheers!

[Kev888]

It is almost certainly the constant power type, I'd expect the listing to shout about it if it were self regulating. Not having it looped closer to itself than 5cm is also an indication, since packing it close or crossing itself is usually specified to avoid hot spots. You can get quite similar stuff for vivariums (e.g. here).

The power needed is mostly down to ambient temperature and insulation. 50watts was more than enough for heating beer within a fridge in my outside garage over winter, but I can't say I ever tried it with a naked FV. It could be too much in some situations though, so ideally I'd use it with a thermostat.

BTW warm yeast are much more prone to autolysis-related flavours, and the sediment will also not help heat permeate into the beer. So if/when you position this cable on the FV best to avoid having it too low, where it may directly heat the settled yeast.

[chris2012]

Cheers, that's very interesting wrt autolysis type flavours. Do you have any links to the self-regulating
type wire perchance?

[Kev888]

The stuff I got was sold as heat trace cable but is no longer listed (I chose a low voltage type for safety) but FWIW here is a general example of the type of thing. You can see from the graph that as temperature rises, the power output decreases - the 17w/m stuff is about 12w/m at 20c for example. This particular one won't exceed about 65c, which happily is not higher than its maximum allowable temperature; overheating it can damage it. It can be cut to whatever length you wish, as the heating effect is essentially in parallel.

So, the constant wattage stuff (such as you linked to earlier) is more robust and cheaper; it can overheat but if it isn't in a situation where that will happen then it could be a better bet. Aside from that, its main downside is that it has to be used in specific lengths.

[chris2012]

Awesome, thanks a lot! That looks very interesting.

One last question, with the heat trace cable, do you have to terminate the end in a specific way (I'm assuming probably not?)

[Kev888]

Unlike common flex, it must be remembered that the plastic immediately around the main conductors is NOT an insulator, it allows current to flow and hence heat to be created. So especially for mains termination you would want to insulate any exposed plastic as well as exposed wires. For mains stuff, sealing against splashes would be important too.

You can get two-legged insulation boots to slide over, specifically for terminating this kind of cable, which can be glued in place and sealed with silicone-type glue. TBH I wasn't that concerned with my low voltage stuff so just used silicone sleeve and heat-shrink to insulate, and filled it with silicone sealant to ward off splashes. The electrical connection was made with crimp connectors.

[chris2012]

I just found:

http://www.traceheatingdirect.com/self- ... e-fbt.html

Where they do a termination kit too:

http://www.traceheatingdirect.com/type-fbtt.html

It seems a bit harder than I thought to wire them up now, as I guess you've got to earth them properly somehow with the shielding wire.

I might start just using a heating pad with an Inkbird controller to save some cash and time to start with, as I have one already that's 35W, do you think that could be a mistake though, wrt autolysis flavours.

[Kev888]

Yes, it is more effort and cost so I wouldn't choose the self regulating stuff unless you have a particular reason. Mine was being installed under insulation at the time, but in different circumstances you may just insulate other parts of the FV or put it in an insulated cupboard or fridge etc.

I'm not one to be especially concerned over autolysis under normal circumstances (I think the issue is often over-stated), BUT heat does make a difference and heating the settled yeast is not good practice. Though it would likely be okay if you avoided letting the beer sit on heated sediment for long after fermentation, either racking or just switching off the heat once done.

After a while you could swap to a heat-belt or pre-made warming cable. However there are many choices, from fermentation chambers to aquarium heaters in trugs. Personally I recirculate water through coils, which is either heated or cooled as needed, but that is quite a lot more cost and effort to set up.

[jaroporter]

Unlike common flex, it must be remembered that the plastic immediately around the main conductors is NOT an insulator, it allows current to flow and hence heat to be created.

which cable are you talking about here? certainly it is with all heat trace cable i've worked with. thermal conductor sure, but not electrical.

the heat trace cable chris linked to last is good. i use their economy constant wattage cable. it's cheap enough and has the advantage of being cut to any length required. the 10w/m is absolutely fine for direct contact on plastic FVs when on constantly. termination using the kit is also very easy. i wrapped an FV in it then through crimped the end onto some flex/13A plug before insulating over, though there are more elegant solutions

you may be able to see the shadow/ripples where the cable wraps around under the green stuff..

[Kev888]

Unlike common flex, it must be remembered that the plastic immediately around the main conductors is NOT an insulator, it allows current to flow and hence heat to be created.

which cable are you talking about here? certainly it is with all heat trace cable i've worked with. thermal conductor sure, but not electrical.

I was talking about self-regulating heat trace cable; in this, the stuff moulded immediately around the conductors/wires is electrically semiconducting. This is what bridges the two conductors, and heats up when current is passed through it. So although there is apparently plastic-like material covering the conductors, it isn't true insulation - the insulation is in the outer layers, there is non per conductor. So ideally when you break out the two conductors individually for termination, IMO they should be covered with an insulation sheath.

Your setup looks ideal for this self regulating stuff, very much how I used it for mine with insulation covering it. It is really good stuff, the only reason I reluctantly moved on from it was the relatively low temperature limit; for a permanently attached installation I'd be worried about damaging it when steam cleaning the fermenter, especially metal-walled ones.

[jaroporter]

ah i see kev, i checked out the self-regulating and see it mentioned as semiconductor. never really thought about it but makes sense as the method of self-regulating. the SR termination kits do make account for heatshrink sleeving. i've only ever used the constant wattage cables so hadn't come across it.

EDIT: just looking back at this thread and my last post, just thought i should clarify that when i suggest that the constant wattage cable can be cut to any length, i mean in multiples of 1m (which is close enough for many applications here) rather than buying a prefabricated heat cable. i didn't mean it can be cut at any point like the self regulating.

if you wanted cable to withstand steamcleaning, i'd have thought the constant wattage (say 8w) comercial/industrial would be a good option (up to 200C)

[Kev888]

Yes the constant wattage stuff is different. It is essentially a series resistance so current flows out along one resistive conductor and back down the other, not between the two, so they can be insulated.

The constant wattage cable can, as you say, work under insulation if both its power and watt-density are cautiously rated. It needs to be low enough that heat transfer to the wort and environment (via any insulation) is sufficient to prevent local hot spots developing around the cable, and ideally for overall losses (or thermostatic control) to prevent excessive temperature rise.

But it is a balancing act, balanced against potentially changing situations - such as rising ambient temperatures or the FV being empty with the cable accidentally on. The cable would still continue to deliver about the same amounts of energy even if there was nowhere for it to really go, so temperature would rise as a consequence. I have seen pictures of melted insulation due to a heat belt which wasn't intended to be covered for example, but these belts can have a much higher watt-density so are a worse case than your heat cable. There is a lot to be said for larger areas of gentler heating over smaller (often cheaper) more intense heating for the same power.

[Kev888]

EDIT: just looking back at this thread and my last post, just thought i should clarify that when i suggest that the constant wattage cable can be cut to any length, i mean in multiples of 1m (which is close enough for many applications here) rather than buying a prefabricated heat cable. i didn't mean it can be cut at any point like the self regulating

If you shorten simple series resistance heat cable, then (for a given voltage) it will actually increase current, power and watt density. Go too far and you will exceed the rating of the cable (even if the things it is stuck to can take the heat). So if yours can be adjusted by the meter, i wonder if you actually do have self regulating cable, or else something else a bit more sophisticated than the bog standard cheapo stuff.

[chris2012]

I ended up going for Parasene 75W cable for ease, I'm just wondering is it safe to wrap a sleeping bag matt around that, at the mo' I just have a towel around it. Or do I risk burning the shed down? 75W doesn't seem that powerful though?