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Presto PopLite Roaster Mod Maintenance Tips
ChicagoJohn
Top  #1 Print Post
Posted on 11/03/2015 2:54 PM
After two good roasts today, I decided to do a third with a quarter pound and noticed significantly reduced bean action. No matter what I did, it persisted even with normal or reduced bean loads.

After checking out the voltage and amp draw to the blower motor, I decided to disassemble the motor/heater unit and found a large amount of small chaff had fallen below the air inlet screen and was all over the heating coil assembly.

So while it's somewhat of a pain, at the first sign of any reduction in blower effectiveness, I will be cleaning the inside of this assembly. My guess is that when I went to the larger charge the chaff started collecting more at the bottom of the chamber, circulating and breaking up there, and winding up sifting through the holes in the screen. I don't know, but however it got there it dramatically reduced airflow and bean motion. Everything is back to normal now that it's cleaned out.

Chaff could also potentially get pulled into the air holes in the bottom of the popper housing (not using the chaff collector today), so I may add some sort of screen around there too.

(Since local temperatures in the coil area can easily hit auto ignition temperature, and the surface-area of chaff is huge, that is another reason to periodically clean this.)
Edited by ChicagoJohn on 11/03/2015 3:01 PM
So many beans; so little time....
 
IKR
Top  #2 Print Post
Posted on 11/04/2015 10:07 AM
Good post with good advice. I have had the grey chamber with the heating coils blocked to the point where I thought the motor was on it's last leg. I took everything apart, removed the chaff and the airflow was good to go, small beans were almost flying out the extension. I think quite a bit of chaff if not most is being sucked through the bottom holes if one isn't careful. I've gone to covering the holes with a thin breathable cloth when I roast and have been enjoying good airflow for quite a few roasts. I will have some sort of screen/filter installed for the air holes. I would definitely take everything apart at the first sign of reduced airflow.
Keep the good posts coming
Edited by JackH on 11/04/2015 10:18 AM
 
ChicagoJohn
Top  #3 Print Post
Posted on 11/05/2015 7:00 AM

Quote

IKR wrote:

Good post with good advice. I have had the grey chamber with the heating coils blocked to the point where I thought the motor was on it's last leg. I took everything apart, removed the chaff and the airflow was good to go, small beans were almost flying out the extension. I think quite a bit of chaff if not most is being sucked through the bottom holes if one isn't careful. I've gone to covering the holes with a thin breathable cloth when I roast and have been enjoying good airflow for quite a few roasts. I will have some sort of screen/filter installed for the air holes. I would definitely take everything apart at the first sign of reduced airflow.
Keep the good posts coming


Thanks for sharing your experience. I've come to the same conclusion you did regarding chaff entering the air intake holes at the base. I decided to try something simple; I put a piece of Scotch tape across each of the holes and then cut an X using an exacto knife so that there will be V shaped "flaps" than can flex inward so as not to impede airflow but hopefully prevent entry of chaff flakes, which tend to be pretty large. I found it also works to loosely wrap a tea towel around the base -- chaff falls on that and it doesn't impede airflow.

Of course, using a passive chaff collector virtually eliminates the cause, but while working on optimizing the airflow, I stopped using it so I could see the beans better throughout the roast. That's when this happened -- I disassembled my other unit and found some chaff below the chamber in it also, but only about 1/5 as much or less. I mostly used the chaff collector with operating this unit.

What is clear is that if airflow through the roasting chamber inlet is impeded -- either due to chaff on the other side or too high a bean load or other restriction -- hot air is diverted to areas below the chamber instead -- the bimetallic "thermostat" in mine kept cutting off and on which it never did before. The aluminum thermal fuse, which fails around 250C, would protect against auto ignition of chaff even if the bimetal device fails; assuming that these have not been bypassed. So I will only be using heating assemblies with both of these safety mechanisms intact. Temperature changes can happen very quickly when there is a change in normal airflow.

One other unrelated thing to note: there is a thermistor on a long lead that will kick the cooling fan into high mode if the thermistor tip heats up (NTC). I used silicone RTV and aluminum tape to attach the thermistor to the transformer case instead of the PWM unit. The transformer is by far the potentially hottest area, and I found that when the case measures around 120F, the fan motor speed kicks way up and moves a huge amount of air into the box, and this makes a big difference in cooling the transformer case. So I did this on both my units now.
Edited by ChicagoJohn on 11/05/2015 7:12 AM
So many beans; so little time....
 
HoldTheOnions
Top  #4 Print Post
Posted on 11/05/2015 8:28 PM
You can add small shop vac as blower for around $40 and it solves a multitude of problems, including noise, small batch sizes, bean mass freezing up, better temp control, and this chaff problem. Without question, the single best upgrade I made to popper.
 
ChicagoJohn
Top  #5 Print Post
Posted on 11/06/2015 2:42 PM
Well, the tape didn't work out; too restrictive of air inlet. Outside a tea towel loosely draped works fine.

So I wound up doing my roasts indoors today using the passive chaff collector. My wife and I do not mind the aroma; we actually like it, somewhat like toast or baked bread. As I only do two roasts per week, I'm putting development of the activated carbon odor reduction project on hold. I'll be roasting in the kitchen this winter with the passive chaff collectors.

The most amazing thing to me was that the Hawaiian beans I roasted today had very little chaff when I flushed out the collector in the sink. Maybe that's because they were "Red Catuai Washed", whatever that means. Anyway, I have never before observed this little chaff.

I'm posting my roasting profile below. It shows how closely you can match a target profile using the popcorn popper modification, if you're interested in that sort of thing. I've done much better at this before, but this is what I did today as an "average" example.

I use a profile based upon the recommendations of Scott Rao regarding initial rate of rise and development time after first crack. This seems to have worked well for me so far.
ChicagoJohn attached the following image:
hawaiian_roast_med.jpg
So many beans; so little time....
 
ChicagoJohn
Top  #6 Print Post
Posted on 11/15/2015 2:01 PM
Regarding the issue of chaff entering the air intake and plugging up the opening to the roasting chamber, I did three 91 gm roasts yesterday and another three this morning using the "passive chaff collector" described in a previous thread. Although there is virtually no chaff that escapes, I decided to put a sheet of cheese cloth across the bottom and hold it in place with rubber bands to act as a filter to all possible air intake holes. The combination of these two should completely eliminate this problem. (see attached images)

The cheese cloth does not restrict airflow. I check the bean motion first with the passive chaff collector off and then put assembly in place over the roasting chamber. While it is difficult to see into the chamber with it in place, the sounds of the beans are sufficient indication to me that adequate motion is taking place. The sounds of 1C remain clearly evident.

In addition, I monitored transformer case temperatures at the end of each roast:

Day 1: 112F / 119F / 126F
Day 2: 118F / 132F / 137F

As these transformers are rated for maximum case temperatures in the 180-190F range, this result is fully adequate for my purposes in making a maximum of three batches at once.

Keeping the area below the roasting chamber -- where the blower motor and heating coils are -- free of chaff is critical to maintaining optimal airflow through the roasting chamber and with that optimum bean motion.
ChicagoJohn attached the following images:
cheese-cloth-filter.jpg pcc1.jpg pcc2.jpg
So many beans; so little time....
 
IKR
Top  #7 Print Post
Posted on 11/16/2015 10:04 PM

Quote

ChicagoJohn wrote:

Quote

IKR wrote:

Good post with good advice. I have had the grey chamber with the heating coils blocked to the point where I thought the motor was on it's last leg. I took everything apart, removed the chaff and the airflow was good to go, small beans were almost flying out the extension. I think quite a bit of chaff if not most is being sucked through the bottom holes if one isn't careful. I've gone to covering the holes with a thin breathable cloth when I roast and have been enjoying good airflow for quite a few roasts. I will have some sort of screen/filter installed for the air holes. I would definitely take everything apart at the first sign of reduced airflow.
Keep the good posts coming


Thanks for sharing your experience. I've come to the same conclusion you did regarding chaff entering the air intake holes at the base. I decided to try something simple; I put a piece of Scotch tape across each of the holes and then cut an X using an exacto knife so that there will be V shaped "flaps" than can flex inward so as not to impede airflow but hopefully prevent entry of chaff flakes, which tend to be pretty large. I found it also works to loosely wrap a tea towel around the base -- chaff falls on that and it doesn't impede airflow.

Of course, using a passive chaff collector virtually eliminates the cause, but while working on optimizing the airflow, I stopped using it so I could see the beans better throughout the roast. That's when this happened -- I disassembled my other unit and found some chaff below the chamber in it also, but only about 1/5 as much or less. I mostly used the chaff collector with operating this unit.

What is clear is that if airflow through the roasting chamber inlet is impeded -- either due to chaff on the other side or too high a bean load or other restriction -- hot air is diverted to areas below the chamber instead -- the bimetallic "thermostat" in mine kept cutting off and on which it never did before. The aluminum thermal fuse, which fails around 250C, would protect against auto ignition of chaff even if the bimetal device fails; assuming that these have not been bypassed. So I will only be using heating assemblies with both of these safety mechanisms intact. Temperature changes can happen very quickly when there is a change in normal airflow.

One other unrelated thing to note: there is a thermistor on a long lead that will kick the cooling fan into high mode if the thermistor tip heats up (NTC). I used silicone RTV and aluminum tape to attach the thermistor to the transformer case instead of the PWM unit. The transformer is by far the potentially hottest area, and I found that when the case measures around 120F, the fan motor speed kicks way up and moves a huge amount of air into the box, and this makes a big difference in cooling the transformer case. So I did this on both my units now.


Funny you note how important airflow is in keeping temperatures low enough to not trigger either of the 2 safety switches/fuses. Once I kept the airflow solid I can roast into nasty territory (past 2nd crack) without triggering the bimetallic switch. I like your latest filter solution for the bottom intake.
Happy roasting
 
ChicagoJohn
Top  #8 Print Post
Posted on 11/29/2015 2:49 PM
After four different roasting sessions now with three roasts per session, I'm finding that the 50 VA Honeywell 24VAC transformer used for the blower motor is topping out at around 67C / 150F, well below maximum rated case temperature. Average amperage to the motor is 2.5. The cooling fan is kicking into high gear after the first batch of the three, and it appears to be effective in helping to remove heat from the transformer.

Also, the combination of the positive chaff collectors (described in a previous thread) and the cheese cloth wrapping around the base have eliminated problem of chaff entering the air intake to the blower motor and plugging up the works, as it were.

Looks like this is a final solution for my with a typical maximum campaign of three 91 gm roasts at any one time.
So many beans; so little time....
 
IKR
Top  #9 Print Post
Posted on 11/29/2015 9:57 PM
Your final build is so nice! I still have a few upgrades planned but I think my reliability is fairly good having done e few 6x105g back to back charges without a hitch. Thanks for posting so much good information about your roasters.
Happy roastingBBQ grill
Edited by JackH on 11/30/2015 3:52 AM
 
ChicagoJohn
Top  #10 Print Post
Posted on 11/30/2015 7:45 AM
Thanks, man. I've learned from you and so many others too. Kind of a pioneering adventure of discovery. Not that there is anything wrong with buying coffee at the supermarket either. My wife, for instance, buys a pound of CharBucks ground espresso at a time and it lasts her two months. Some people are just in it for the caffeine buzz.

People like you and me, we love to mess with appliances someone spent a lot of time and engineering designing for some other purpose than we want to use it. And we're not alone on these forums where many seem to agree, "If it gets hot, there must be a way to roast coffee with it."
Edited by JackH on 11/30/2015 8:54 AM
So many beans; so little time....
 
ChicagoJohn
Top  #11 Print Post
Posted on 01/23/2016 4:27 PM
As an update to this, after installing the cheese cloth, I've done 20-30 batches with no issues in loss of bean motion. Also, due to inclement weather here in Chicago, I've taken advantage of warmer days and done six consecutive roasts at a time on three different occasions and the transformer case temperature registered less than 60C each time. I have been using the positive chaff collector throughout this and emptying it every 3 or 4 roasts.

Roasts are uniform, profiles easily controlled. The caveat is that I am consuming about 25 grams of roasted beans per day. Obviously not a solution for those who consume a lot more.
So many beans; so little time....
 
IKR
Top  #12 Print Post
Posted on 01/29/2016 10:32 PM
As another data point, I looked at my roast logs, and I've done 51 batches since I last posted in this thread. Last Saturday it was 8 105g charges back to back without a hitch. Since implementing filtration, keeping chaff from entering the bottom of the roaster, my airflow has been fine. I actually had problems with a few light beans coming out the roaster with my 6" extension. Anyone using a Poplite Roaster should take your maintenance tips to heart. Wishing you continued good roasting with your Poplite.
IKR
Edited by JackH on 01/30/2016 3:32 AM
 
ChicagoJohn
Top  #13 Print Post
Posted on 03/09/2016 12:07 PM

Quote

IKR wrote:

As another data point, I looked at my roast logs, and I've done 51 batches since I last posted in this thread. Last Saturday it was 8 105g charges back to back without a hitch. Since implementing filtration, keeping chaff from entering the bottom of the roaster, my airflow has been fine. I actually had problems with a few light beans coming out the roaster with my 6" extension. Anyone using a Poplite Roaster should take your maintenance tips to heart. Wishing you continued good roasting with your Poplite.
IKR


Fair dinkum, mate. I've been goin' full bore all Winter here without a hitch, eh?

Except my main power switch busted itself. But I bought a dozen of 'em so that wasn't no problem to replace. But other than that, I'm roastin' right along.

Thanks for sharin' your experience!
So many beans; so little time....
 
Dann-Oh
Top  #14 Print Post
Posted on 05/11/2016 10:21 AM
Awesome tips. I just started roasting with a Poplite, I have 2 batches under my belt and tonight I will be roasting my third batch. My unit is currently un-modded.
 
ChicagoJohn
Top  #15 Print Post
Posted on 05/19/2016 1:14 PM

Quote

Dann-Oh wrote:

Awesome tips. I just started roasting with a Poplite, I have 2 batches under my belt and tonight I will be roasting my third batch. My unit is currently un-modded.


Cool beans, Dann-Oh. When you get a chance, I'd be interested to know your process -- quantity, times, first crack time and anything else you can share. How are you making your beverage from the roast? I use an Aeropress and hand cranked burr grinder.
So many beans; so little time....
 
Dann-Oh
Top  #16 Print Post
Posted on 05/25/2016 6:14 PM
ChicagoJohn,

I roasted 2 batches that day, it was my first time roasting back to back batches.

Quote

Cool beans, Dann-Oh. When you get a chance, I'd be interested to know your process...

I am using my un-modded poplite, in order to keep the beans moving AND stay in the roasting chamber I am using oil-lamp chimney under the original plastic hood. This allows me to tilt the roaster to about 30-35deg and not have to touch the hot glass. I am also shaking the beans about every 15-20 sec while they are still "wet and heavy" once they start to brown the fan keeps them moving pretty well. These batches were the first time I used BOTH the thermocouple and timer app (Coffee Roaster app on android) So the time and temps may be a little off.

Quote

...quantity...

1/2 cup green beans per batch

Quote

...times, first crack time...

First Batch
7:25 finish @ 430deg F
first crack at about 1:51 @400deg F

Second Batch
9:45 finish @ 445deg F
5:12 first crack @ 391deg F

*NOTE this was the first time I used BOTH a thermocouple and a timer app (Coffee Roaster on Android) so the times and temps may be off

Quote

...anything else you can share.

It was definitely a more hands on experience with both the thermocouple and the app. I would really like a more automated way of recording the time and temp data but this will get easier with more roasting. I tried to slide the unprotected thermocouple tip between the glass tube and the popper wall, this made the glass tube a bit more unstable which is why I added the plastic housing back onto the roaster. The first batch (my third batch) came out the best so far, I still have some coffee that the lady got me from my favorite micro roaster I'm finishing before I try the second batch (my fourth batch). I'm looking forward to getting to roast more coffee.

Quote

How are you making your beverage from the roast? I use an Aeropress and hand cranked burr grinder.

I am making my beverage in a french press (I cant remember the brand), 3 min "soak" time and then I pour into my coffee cup for enjoyment. I'm using some brand of blade grinder, it works great for my unsophisticated pallet.
 
ChicagoJohn
Top  #17 Print Post
Posted on 05/28/2016 9:43 AM
Thanks for sharing that information. If you're interested, here are a few observations. (1) with a half cup, you're using about 80 gm of beans. I use 91 gm and get very good motion / mixing without moving or tilting the popper. A couple of factors might be that I installed a funnel which gives a 60 degree wall angle as compared with the 45 degree angle the popper comes with. Another possibility is that if you take your assembly apart, you may find (as I did) that chaff has been drawn into the base air intake and is impeding flow into the chamber from the fan. After cleaning it out, I wrapped a single layer of cheese cloth around the air intake area and have had no problems since.

(2) Your process is reaching 1C very rapidly. One of the advantages of a modification is that you can run the blower at high speed while reducing the heat from the coils to slow down the heating process. I am hitting the first first crack at about 7 minutes and reaching final temperature and cooling two minutes thereafter. My target profile for each minute in degrees C is 0, 90, 118, 139. 157, 174, 183, 191 usually 1st 1C at around here), 196, 204 (9 minutes), heater off, blower still on for 2 minutes until temp = 50C.

In my novice opinion, there is no right or wrong profile; it just depends upon what you like in the end. It sounds like you're having fun, and that's what I like about it too: It's fun to play around with and try different things to see how they affect the results.

Thanks again for sharing your experience and I look forward to hearing more about it as you go along. BBQ grill[
So many beans; so little time....
 
IKR
Top  #18 Print Post
Posted on 05/28/2016 8:25 PM
Chicago John, Good to hear things are still going well for your roaster. I will second the importance of keeping chaff from being sucked into the bottom of the Presto Poplite (actually I think I stated this before so this is just confirming it an additional time). I usually hit first crack 7:30 or so for my typical roast profile so my experience is similar to yours. Too quick to first crack with an air popper gives me an underdeveloped roast for my tastes so the ability to control heat and air to allow a slower ramp up is a big benefit for my tastes. Still going strong and my usual roast is 105+g with stirring at the beginning (still need to do the funnel mod).
IKR
Edited by JackH on 05/29/2016 3:21 AM
 
Dann-Oh
Top  #19 Print Post
Posted on 06/03/2016 11:36 AM
Well it turns out I need to go to Harbor freight anyways for some other items I'm guess the lady of the house wont even notice if I slip in the router speed control. Woot Woot It looks like I have some modding to be done.
 
IKR
Top  #20 Print Post
Posted on 06/03/2016 10:05 PM

Quote

Dann-Oh wrote:

Well it turns out I need to go to Harbor freight anyways for some other items I'm guess the lady of the house wont even notice if I slip in the router speed control. Woot Woot It looks like I have some modding to be done.

There's worst things you can spend your money on! Be careful, modding the Poplite as a roaster is a slippery slope Grin
 
Dann-Oh
Top  #21 Print Post
Posted on 06/22/2016 10:28 AM
After looking at the mods a bit more Im not sure modding the unit is the best use of money. I mean I can buy a Fresh Roaster SR500 for about the same cost and it is in a nice clean package. My biggest issue with modding is I am horrible with electrical work, it might as well be written in latin.
 
JSA Coffee
Top  #22 Print Post
Posted on 06/22/2016 11:51 AM
If you aren't comfortable doing the electric work, then don't do it. Consider adding a drum to your BBQ or even using a whirly pop. If you are an occasional roaster, or roast in small batches has, you could get by without a motor on the BBQ and crank it by hand.
 
Dann-Oh
Top  #23 Print Post
Posted on 06/22/2016 1:11 PM
Instead of trying to wire up a transformer could I simply use a 19.5 VDC output laptop power supply? I understand I will need to remove the Rectifier Circuit from the fan motor but this seems much simpler and a little cleaner of a build.

My question/concern would be can the fan provide enough airflow at 19.5 VDC?
 
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