HomeRoast Digest


Topic: controlling a 240v roaster heating element with PID and (35 lines)
1) From: Tom & Maria - Sweet Maria's Coffee
I need to indulge you all again with my Sunday roaster project:
Here's my logic, please correct the errors and give advice: I am 
working on a controller for a 240v heating element for a roaster, and 
I was looking into the SCR type unit, but also the PID with the SSR 
as rich suggested. Remember, I only know what wikipedia tells me (so 
clearly I am in trouble), but I can't wrap my brain around how you 
use solid state relays to control a 240v circuit. On a 120v circuit 
you have your hot wire and neutral, and you can simply interupt the 
hot wire with the SSR. But on a 3 wire 240v you have 2 hots and a 
ground, the hot wires pull from the 2 different hot bars in the 
supply box that are slightly out of phase so they form a circuit and 
you don't need a neutral. So you can't install a PID controlled SSR 
on just one of the 2 hot wires, can you? My PID has 2 outputs so I 
suppose it can control 2 SSRs (?) My apologies but google searches 
haven't yeiled much in terms of 220/240 and solid state relay 
controls.
Tom
--
                   "Great coffee comes from tiny roasters"
            Sweet Maria's Home Coffee Roasting  -  Tom & Maria
                      http://www.sweetmarias.com                Thompson Owen george_at_sweetmarias.com
     Sweet Maria's Coffee - 1115 21st Street, Oakland, CA 94607 - USA
             phone/fax: 888 876 5917 - tom_at_sweetmarias.com
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