Imex problems

[simonp]

I've managed to get hold of a used Imex, but am having problems with temperature. I have bypassed the thermostat as I know this has caused problems with some. Initially I had it wired up to my modded dimmer, thinking I could do some good profiled roasts, but I could not get the measured temp (using a thermocouple poked through the exhaust in to the roast chamber just at the top of the beans) above 360C, the roast just stalled here.
Thinking it was an issue with the dimmer, I took this out, but got exactly the same result.
OK, must be a volt drop I thought, so I carfully ran it up with the bottom off, and measured the voltage accross the heating coil, 243V with or without the heater on, so not this.
I've now run out of ideas
I'm roasting inside, the ambient air temp is 19C.
I don't have a chaff collector at the moment, but unless this impedes the exuast airflow usually and helps keep the temp in the chamber up I can't see this affecting it.
The heater coil can only really be OK or open circuit, so the only other thing I can think is that there may be a high resistance joint somewhere on the heater board, one of the rivetted pieces possibly.
Other than this, I understand that some of the exhaust air is recycled, so may be there is some problem here.

All ideas welcome

[Steve]

I heard before of temp's not getting as high as they should, but they have been limited cases. I cant think the chaff collector would make any difference, but its worth a try. :S sorry I cant be any help what so ever

[simonp]

AHA! found the culprit, there is a conical shield that directs the air to the vents to the chamber, it has a spring on the bottom that holds it up, the spring had become compressed so the shield was sitting low and actually blocking part of the vents.
Using the Malabar Gold that I had been using for test roasts which had been taken to 360F on 3 previous occasions, I managed to get it to 460F, and smoking! Boy the cracks are hard to hear with this thing, but then the roast was probably strange due to the previous roastings.
It's a shame that in my probing around for voltages I shorted the dimmer out, and blew it, so I still can't try a profile till I get a new triac, which could be a week or two as I can no longer order components through work, and Farnell have a minimum order of £20

[martinh]

Simon, Let me know what you want from farnell and I can place an order for you.. (welcome to the IMEX gang)

[simonp]

Thanks mate
I did have one lying around on my desk at one point, but let's face it, what's the risk of finding anything on MY desk If I can't find it I'll drop you a line.

[tisri]

I heard before of temp's not getting as high as they should, but they have been limited cases. I cant think the chaff collector would make any difference, but its worth a try. :S sorry I cant be any help what so ever

I had an Imex (except mine was badged Aerolatte) and it was utterly useless. I sent it back for a replacement and the replacement was just as useless.

Obviously the number of people using them indicates that they aren't all useless but when my dodgy one was replaced with another dodgy one I lost faith in the machine and took a refund.

[mnemonix]

Simon,

no experience with the imex, but i would expect the cracks to be greatly diminished if you'd 'pre-roasted' the beans as this would dry them out and it is the heating & expansion of the water in the cell structures that is responsible for the crack. i've found old green often cracks less and more quietly than fresh new stock for the same reason.

chris.

[simonp]

With my first peoper roast after sorting the problems the cracks were quite distinct, even 2nd, although you do have to listen carefully with the Imex. Having a thermocouple in so that you know when abouts to start listening close really helps.

[phil]

Simon - I don't believe you mentioned why you're using the Imex? Because you can? Because your popper blew up?

[simonp]

Simon - I don't believe you mentioned why you're using the Imex? Because you can? Because your popper blew up?

No, the popper is fine, but with winter coming soon and outside roasting being tricky due to cold & dark, it has some issues, the main one being no chaff collection. I could make something to do this, but it would mean that I couldn't see the beans, or stir them at the start of the roast.
Having had a go with martinh's Imex both of these problems are addressed, as the fan is powerfull enough to cope with 150g of beans unaided, and it has a chaff collector and a glass lidm so seeing the beans is much easier.
The roasting chamber of the Imex is much wider than a popcorn machine which should help getting even roasts.

Basically the Imex is the same as a popcorn machine, but beefed up and made more suitable for coffee roasting. It has 2 problems as I see it:
1) On some the thermostat cuts out and makes it difficult to get 2nd crack. I vote to bypass it, but be carefull, and NEVER leave it near the ned of a roast.
2) It roasts too quickly especially at the start of a roast. No problems again, just split the fan and heater circuits, and use the dimmer to control the heat, just like the popper.
Sort both of these things, and hey presto, an industrialised version of a modded popper .

I was fortunate enough to get hold of a broken one that was a fairly simple fix, and so don't have to worry about warranty issues etc, so can mod to my heart's content.

When I fix my dimmer, I'll try profilingthe roast, and post my thoughts.

[quink]

I have bypassed the thermostat as I know this has caused problems with some.

I never knew they had a thermostat in them I've seen pictures of a thermal fuse somewhere on the net that can give problems, but cant remember where. If you come up with a way to get a bit more control over the heat let me know

[simonp]

Quink, follow thiss link for some good info & diagrams on the Imex. Although this relates to the US version, apart from voltgae realated stuff the info is valid. There are good diagrams for the heater bits.

http://www.f11view.net/coffee/caffefr.htm

I re-wired using a wire that is on the heater element side of the thermostat that goes to the on/off switch. I don't really understand its purpose as what happens is when the mains switch is off the live going to the motor & heater now gets connected to the neutral end of the heater coil. I can only assume the idea is to quickly dump any energy into the motor when you turn it off. I couldn't see any good reason to keep it where it was, and it made it easy to bypass the thermostat. I connected this wire on to the switched side of the timer where the wire on the other side of the thermostat had previously connected.

With the thermostat out of circuit there was no problem hitting 460F measrued which corresponded to about 25 seconds of 2nd crack.