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Transformer help
BetterCoffee
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Posted on 04/04/2018 10:53 PM
Hi,
I'm in the process of gathering parts to mod a poppery 2. I am following the instructions on Jim's west bend poppery 2 coffee roaster site here:

http://popperyii....i-mod.html

However he recommends a 25.2v transformer and the specific one he references is from radio shack which no longer sells them. I'm a complete beginner when it comes to electrical stuff.Can anybody point me in the right direction for a suitable replacement transformer? Thanks for any help!
 
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AMRoberts
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Posted on 04/05/2018 12:25 AM
Obligatory safety statement: There are comments in other posts that address safety practices, please take note. Seek out local, in-person help with part selection, wiring, and testing your mods unless you are certain you understand what you've read on the internet. You are working with voltages which can kill you, and a thermal environment which can burn you, or worse.

https://www.digikey.com/product-detail/en/triad-magnetics/F-107Z/237-1897-ND/5032218

(slightly lower secondary voltage, your motor might need more current than this one can supply)

https://www.digikey.com/product-detail/en/triad-magnetics/VPS24-3300/237-1276-ND/666162

(can supply more current)

https://www.digikey.com/product-detail/en/signal-transformer/A41-80-28/595-1295-ND/953165

(voltage slightly above the Radio Shack recommendation, probably enough current)


For less than the cost of those transformers you can have 5A of 24VDC with a switching power supply -

https://www.amazon.com/gp/product/B019OMDP9C/

But you aren't going to be able to vary the output (to get fan speed control) by using a common lighting dimmer on the line voltage input to the supply. You'll need to accomplish that with a DC fan speed control. I'll be trying this one -

https://www.amazon.com/gp/product/B073Z7PB5G/

On the popper I'm hot-rodding tomorrow, pricey but: 1) gives me a voltage out display, and 2) it will handle a higher-voltage DC motor in the future (possibly for the next roaster). You can cut the cost if you don't want a display -

https://www.amazon.com/RioRand-Controller-Waterproof-Modulator-Regulator/dp/B077K3B8WZ/

and cut it further if you don't care about being able to re-use the part for a higher DC voltage -

https://www.amazon.com/Control-Controller-Regulator-12V-24V-One-way/dp/B012A8QQWU/


FWIW, someone local with experience may also have the test equipment needed to measure the voltage driving your fan motor and the current consumed (doing this will probably require some wiring changes). This can inform your parts/cost decisions. As an example, if it turns out that 24VDC and <= 2A is enough, a $12 "adjustable brick" -

https://www.amazon.com/Adjustable-Converter-100-240V-Electric-Controller/dp/B078S6BBH7/

might be your entire fan speed solution.


Good luck, be safe!
Alan
 
BetterCoffee
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Posted on 04/05/2018 9:05 AM
Wow, thank you for the detailed response Alan! I really appreciate it, this helps me out quite a bit.

One more newb question, If I get one of the Dc fan speed controllers do I still need a transformer?

Oh, and all safety advice is being followed, I claim all responsibility for my own safety! Grin
 
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AMRoberts
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Posted on 04/05/2018 10:20 AM

Quote

BetterCoffee wrote:
...
One more newb question, If I get one of the Dc fan speed controllers do I still need a transformer?
...


Sorry for the confusion, there are (at least) two different strategies to achieving fan control on a popper and my reply crossed both of them ...

If you want to keep the diode bridge on the base of the motor, but feed it with an external source of controllable low-voltage AC, the transformer is the piece that does this without generating (much) heat. You don't have any easy way to use DC fan control with this strategy (since the diodes are soldered directly to the motor terminals). That is why the modding article you referenced varied the average voltage to the primary of the transformer, with the hardware-store light dimmer.

If you are removing the AC wiring and diodes and just adding wires directly to the motor terminals, then you need a controllable source of DC. You could get that DC via an external transformer and diode bridge of your own construction (search on "unregulated linear power supply design" will get you far more than you want to read), buying a switching power supply (what I did), or using a discarded laptop/other device's "power brick" (these are also switching power supplies) as long as it can supply high enough voltage and enough current.

When you have your low-voltage DC from a separate device, you can use a DC speed control device. I believe all of the Amazon DC controller links I put in my post expect an input source of low-voltage DC, except the last link, which is an adjustable AC-to-DC supply all in one unit.

Does that help?

Cheers,
Alan
 
BetterCoffee
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Posted on 04/10/2018 10:44 AM
Alan, sorry for the delayed response. But, yes your answers have been great, so helpful and I really appreciate it. After i finish this bad boy I'll take a few pics to let you know how it went! thanks again!
 
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AMRoberts
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Posted on 04/23/2018 9:26 AM
No worries, my spare time has been spent trying to roast with my modded Nostalgia APH200, I haven't been reading the forum. Glad it was helpful.

Good luck with your modifications, and one thing to watch out for based on my experience. The fan motor on my APH200 had a "faceplate" (face sticker?) rating of 18VDC. When I adjust my DC PWM control to provide 18V, the popper is loud ... As in 82-85dB, makes me want to wear ear protection loud. I can hear some of the louder pops of first crack when they happen, but I'm not sure I can hear the entire event in a start/builds up/finishes sense. I haven't tried to roast dark yet, but I have doubts about being able to hear second crack at all.

I hope your popper has a quieter motor/fan. I'm pondering how I can impose some sort of baffle to block some of the popper sound while still being able to hear what is happening inside the roasting chamber. I now have an appreciation for why many of the fluid-bed designs in that forum put blower inside some sort of enclosure.

Cheers,
Alan
 
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