Making my drum roaster spin faster? - Page 2

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
Capuchin Monk

#11: Post by Capuchin Monk »

Culainn wrote:However, I've found that on max with the PWM my motor only goes as fast as 64RPM (I counted). How did you manage to make the motor spin faster? I can only make it spin slower.
That's odd. Mine can be controlled from 0 rpm to about 100 rpm. Which PWM board did you get and how is it set up?

Culainn (original poster)

#12: Post by Culainn (original poster) »

Capuchin Monk wrote:You don't have to change the motor. Install PWM board like I did with my Kaldi 400. There are other versions available. You can put something like this in a simple plastic box and have the wire hook up to your roaster DC power input so that it's away from the heat source.
I bought this PWM board - https://www.amazon.co.uk/gp/product/B07 ... UTF8&psc=1

the inputs and outputs for the power and motor are labeled on the board so that's how I wired it. Red in and black out.

Any idea's what might be going wrong?

Thank you again for the support.

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Culainn (original poster)

#13: Post by Culainn (original poster) »

civ wrote:Hello:

Making the drum spin faster will increase the centrifugal force (which is not a force but a concept) the beans are subjected to.
The result is that the beans will be pushed harder against the hot wall of the drum.
This seems to be the opposite of what you want to achieve.

I expect that your roaster's OEM has already found the right speed for your drum which is directly related to the drum's length and diameter as well as vane design and optimum batch size.

Check this site, it was very useful to me:
http://coffeenavigated.net/roasting-coffee/

image
Image/text courtesy of coffeenavigated.net

And these other ones:

https://paradoxroasters.com/news/heat-t ... n-balance/
https://paradoxroasters.com/news/heat-t ... lance-pt2/
https://shopcoffeeroasters.com/learn-to ... rum-speed/

You can also look for mods other roasters have made to this same roaster.

Bear in mind that two same model roasters from the same OEM may not necessarily behave in the same manner.

Best,

CIV

Thanks for the reply CIV. I'd not heard of centrifugal force before. It's something I will take into account from now.

'Capuchin Monk' has actually already made a similar alteration to their Kaldi 400 Wide so I am using that as a starting point. I believe my drum speed is too slow based on feedback from an online course I'm currently doing with Scott Rao, so I want to speed it up and be able to control it. From there I should be able to lower it if the centrifugal force is too great (I think I'm saying this right).

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LBIespresso
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#14: Post by LBIespresso »

My understanding (limited to internet research on a similar problem is that PWM will pulse the full voltage on and off to average the voltage that you need. This may kill your motor immediately or vastly shorten the life of it if it is not rated to what you are sending to it on the on part of the pulse.

I bet if you list all specs on your equipment there are people here that will set you in the right direction.

Good luck.
LMWDP #580

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civ

#15: Post by civ »

Hello:
Culainn wrote: Thanks ...
... not heard of centrifugal force before.
You're welcome.
Should you be interested: https://www.livescience.com/52488-centr ... orces.html

You may want to consider that what you are indirectly attempting to achieve ie: reduce the transfer of heat to the beans by conduction is not just a question of drum speed.

Like I mentioned previously, there are other important aspects eg: besides drum geometry, vane design and air flow which are to be considered.
These are all balanced together and that balance will eventually define the optimum load size for a roaster.

Best,

CIV

Capuchin Monk

#16: Post by Capuchin Monk »

Culainn, sorry, my mistake. PWM board can only make it slower because the motor will spin at its max rpm when DC voltage is fed so it won't spin any faster with PWM. It's been almost 3 years since I modified it and my memory wasn't fresh on what I observed.

In short, you need either a faster motor or different gearbox that will allow the shaft to spin faster. In my case, it was easier to find the motor that came with the gearbox and the price was reasonable so I opted to replace the whole thing. Hope this helps.

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Randy G.

#17: Post by Randy G. »

I have had this chart for ages. I do not remember the source, so all fwiw.

Speed Chart for Coffee Roasting Drums
-----------------------------------------
quieter<- - - - ->noisier
less even<- - - >more even
- - - - - - - - - - - - - - - - - - - - -
COLUMN A = Drum diameter in inches
COLUMN B = 'sticking speed' RPM
COLUMN C = Minimum speed RPM
COLUMN D = Maximum speed RPM
A - - B - -C - - D
- - - - - - - - - - -
2, 187, 11.2, 165,
3, 153, 9.2, 135,
4, 133, 8.0, 117,
5, 119, 7.1, 104,
6, 108, 6.5, 95,
7, 100, 5.0, 88,
8, 94, 5.6, 82,
9, 88, 5.3, 78,
10, 84, 5.0, 74,
11, 80, 4.8, 70,
12, 76, 4.6, 67,
13, 73, 4.4, 65,
14, 71, 4.2, 62,
15, 68, 4.1, 60,
16, 66, 4.0, 58,
17, 64, 3.9, 57,
18, 62, 3.7, 55,
19, 61, 3.6, 53,
20, 59, 3.6, 52,
21, 58, 3.5, 51,
22, 56, 3.4, 50,
23, 55, 3.3, 49,
24, 54, 3.2, 48,
25, 53, 3.2, 47,
26, 52, 3.1, 46,
27, 51, 3.1, 45,
28, 50, 3.0, 44,
29, 49, 3.0, 43,
30, 48, 2.9, 43,
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LBIespresso
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#18: Post by LBIespresso »

Wow. Thanks Randy. That's a bit more thorough than the Rao post that I read that inspired me to look into increasing drum speed on my roaster.

But I still think Rao's post was interesting so here it is:

https://www.scottrao.com/blog/2018/9/13 ... ter-issues
LMWDP #580

Culainn (original poster)

#19: Post by Culainn (original poster) »

Capuchin Monk wrote:Culainn, sorry, my mistake. PWM board can only make it slower because the motor will spin at its max rpm when DC voltage is fed so it won't spin any faster with PWM. It's been almost 3 years since I modified it and my memory wasn't fresh on what I observed.

In short, you need either a faster motor or different gearbox that will allow the shaft to spin faster. In my case, it was easier to find the motor that came with the gearbox and the price was reasonable so I opted to replace the whole thing. Hope this helps.
Phew, that's good to know at least that I wasn't wiring it wrong. I've gone for the new gearbox motor idea. Only downside it is needs to come from China so might take a couple of weeks or so.

I was wondering if you'd ever taken the chance to upgrade your gas input? I'm using a portable indoor gas hob with a control that's not great as it's non-digital and has a bit of give in it before the gas actually changes. I'd heard that hooking up a manometer is a good idea to have a measure of gas pressure but I'm not very convinced. Any thoughts?

Capuchin Monk

#20: Post by Capuchin Monk »

I just go by the sight. After many roasts, I know what position of dial it should be at and I've marked it on the surface. So for me, no need to upgrade the gas input.