Need some help with this temperature controller

[Andrew Leigh]

Hi,

in the learning phase so a couple of questions if I may on the attached circuit.

1. With 12V a.c. into the bridge, does this equate to (12*1.4)-1.5 = 15.3V at the backend of the bridge?

2. With the LM317 configuration, do the 100R and the 750R resistors give and output of 10.63V?

3. Is there a more elegant way to control a 240V, 180W heater within the current constraints of the circuit? I have searched the forum and the electronic switching I have found is confined to low voltage switching, can a Mosfet device be used to switch 1A at 220V?


Thanks
Andrew

 

[ericgibbs]

Hi,

in the learning phase so a couple of questions if I may on the attached circuit.

1. With 12V a.c. into the bridge, does this equate to (12*1.4)-1.5 = 15.3V at the backend of the bridge?

2. With the LM317 configuration, do the 100R and the 750R resistors give and output of 10.63V?

3. Is there a more elegant way to control a 240V, 180W heater within the current constraints of the circuit? I have searched the forum and the electronic switching I have found is confined to low voltage switching, can a Mosfet device be used to switch 1A at 220V?


Thanks
Andrew

hi,
REF
Q1: there are two diode forward voltage drops for a FWB ie:1.4V................. amended.

Q2: Look at the second posted image for the Vout formula.

Q3: The opto triacs in the first image are suitable.

EDIT: Corrected,
for a full wave bridge there are two diode drops.
For a centre tapped tansformer [CT] , sometimes referred to as a 'bi-phase rectifier', one diode drop.

 

[Andrew Leigh]

Hi Eric,

Q1. I try research a little before and was reading Wikipedia.

"Half-wave rectification and full-wave rectification using two separate secondaries will have a peak voltage loss of one diode drop. Bridge rectification will have a loss of two diode drops. This may represent significant power loss in very low voltage supplies. In addition, the diodes will not conduct below this voltage, so the circuit is only passing current through for a portion of each half-cycle, causing short segments of zero voltage to appear between each "hump".

What did I miss?

Q2. I also found this formula as well I just wanted a cross check to see if I got it right. 1.25 * (1+(R2/R1)).

Q3. Thanks for that.


Cheers
Andrew

PS: Flying in to London on the 10th, zip straight up to Manchester. Back down to Dogmersfield on the 11th, dinner on the 12th back home the following day. Hear you are having a very cold winter?

It was recommended to me, rather than hiring a car at LHR was to take the tube to Euston then the train to Manchester they said it would be quicker?

 

[ericgibbs]

hi Andrew,
You can get connecting flights to Manchester that meet the early morning flight from JHB.
Flight time from LHR to MAN is just over an hour.
If you travel by SAA get the first of the two flights from JHB.
It can be a rush across the terminal, but many go that way.

You could get the tube to London and get the Manchester train but its not cheap on UK trains and that time in the morning its rush hour in London.

Many of our long distance trains only offer a buffet meal service, also in the UK there is no legal limit to how many passengers they can cram into the coach.
If you can reserve a train seat when you buy your ticket I would recommend it.

Dont take a taxi to London, you will most likely get ripped off.

Bon Voyage. Wrap up warm.

EDIT: If you do hire a car, we have 'round abouts' in the UK, at some road junctions.