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My cheap(very cheap! )voltage booster
Lawnmowerman
Hello coffee roaster people. This is Ben. I'm currently using an extension cord to roast because I simply won't use the house wiring. It's aluminum. Shock However, with two elements going at once, I'm getting a voltage drop. With a corresponding power drop. Now short of a dedicated circuit run to my front porch, a variac might just work to restore the line voltage to 120. But that isn't going to happen. My solution: a step down transformer, custom made just for this use. I used a MOT (microwave oven transformer) ,and parts of a twelve guage contractors extension cord. I wound two secondaries, and jammed the space available as many windings as I could,left the end on it and I measured 11.7 volts on either secondary. Perfect! ThumbsUp Now I must stress that I stole this idea from another HRO thread. I wired up the primary and secondary end to end so that the voltages add up. I'm using two separate secondaries in order to drive two separate heating elements and I would need ten gauge to use a single secondary . I will get a schematic up, but I will state that it is the same as a variac. This quick and dirty voltage booster will handle 25 amps! Now to test the safety of this configuration, I took a series current measurement using my smaller unit already in use, testing the current through the primary,did some calculations and I'm getting 333 watts. This primary will easily handle 1000 watts. So all good. A high current only flows through the secondaries. Even though they are In series with the primary. Now a variac of this caliber would require the heavy gauge wire throughout its range making it much more massive than an MOT. With this cheapy version I just use a router controller on one of the secondaries. I can get 109 volts back to about122v with this setup. One more option is to wire both secondaries in series for about 135volts! .!!!!!! At 11.? Amps. I'm good with 25amps 120 for a total cost for parts...nothing.
Lawnmowerman attached the following images:
20140621_101229-1-1_1.jpg 20140720_183218-1-1.jpg

Edited by Lawnmowerman on 07/24/2014 10:15 PM
Bad coffee prevails when good coffee roasters stand by and do nothing.
 
Lawnmowerman
The pic on left is of a fully wired one element booster. To the right is the new 25 amp transformer. It will take some buttoning up before wiring Itin. With both heaters getting the required 120 volts I will be using a lower range on the heat controller. This I've confirmed with just the one element boosted. Hope this help add add someone. Schematic soon.
Bad coffee prevails when good coffee roasters stand by and do nothing.
 
Lawnmowerman
Here are some diagrams. The pic I've labeled "c" is the higher voltage one(just in case someone needs that much)the secondaries are both wired end to end, and in series with the primary, giving enough to restore a voltage drop or even more. It would draw about 1.2 amps or something like that. I'm guessing that figure. But a large enough extension cord is a must. As I previously stated, I will refrain from even attempting this as I have no desire to test the limits of my heating elements. I will be using diagram" d". Both secondaries are wired in parallel and in series with the primary. They aren't shown connected,but the operation is still the same as if they were. Since I made it so redundant, I will be using individual heater connections, just in case I decide to do any current draw tests.
Lawnmowerman attached the following images:
20140802_231234-3.jpg 20140802_231234-2.jpg 20140802_231234-1.jpg 20140802_231650-1.jpg

Bad coffee prevails when good coffee roasters stand by and do nothing.
 
Lawnmowerman
Ok I must also stress that taking apart a microwave oven is something that should only be undertaken be a qualified technical expert! Please believe this. The warnings really need t o be heeded that say don't open it. One can obtain a microwave oven transformer on eBay ,I've heard. But as to the safety of this circuit,I may some specific tests with my assistant Robbie the Robot. The primary of this transformer can handle about 3times the load I will be putting on it. Besides Robbie the Robot, I also consulted a college textbook which describes such a wiring arrangement. It is likened to what is termed an autotransformer. And...a variac is a kind of autotransformer.
Bad coffee prevails when good coffee roasters stand by and do nothing.
 
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