slakwhere

Recipes 

wonder what the life expectancy of that resistor is tho...

-TH-

Recipes 

Well I'm not an electrical guy so I have no idea. But what I do know is that a 7.5 Kohm 8W resistor will draw 32mA @240V and that equates to 7.7 Watts (just under the 8W rating). So I would think with just a few hours a month use it should last a while. But like I said I really don't know for sure.

__________________
TH

Builds, etc: E-Brewery | Fermentation Chamber | Concrete-Roller Mill | Stirplate | Bottle Cabinet | Pneumatic Bottle Capper
Resources: www.EZWaterCalculator.com

mrstevenund

Recipes 

Life depends on several things including wattage, how much use, and temperature. The resistors we use at work have a wattage de-rating down to 50% at our normal operating temperature according to the datasheet.

-TH-

Recipes 

How long would you guess mine will last?

__________________
TH

Builds, etc: E-Brewery | Fermentation Chamber | Concrete-Roller Mill | Stirplate | Bottle Cabinet | Pneumatic Bottle Capper
Resources: www.EZWaterCalculator.com

ajdelange

Recipes 

But it's not going to have 240 across it as it is in series with the leakage resistance of the SSR. Measure the voltage across it, then use V*V/R to calculate the power dissipated. It will probably last a long time.

[Edit]

Cancel that thought as it will have 240 across it when the SSR is on.

Have you thought about sensing element current i.e. with a current transformer?

passedpawn

Recipes 

Nobody liked the varistor in series with the LED? A 120V varistor, then the resistor, then the LED would probably work.

Not sure what's available at Radio Shack, but they probably have them. You could also scrounge one out of an old 120V power strip with surge suppression. Or, just buy from Digikey.

__________________
Now there's some take delight in the carriages a rolling
and others take delight in the hurling and the bowling
but I take delight in the juice of the barley
and courting pretty fair maids in the morning bright and early

BetterSense

Recipes 

Um, no. If the control side was operating properly, WHY would it ever command the SSR on, if the SSR was 'failed closed'?

passedpawn

Recipes 

OK, you're right if the PID is in auto mode, where the temp sensor is the feedback channel.

However, in manual mode, where the PID ignores the feedback, I'm right.

I'll split the difference with you.

__________________
Now there's some take delight in the carriages a rolling
and others take delight in the hurling and the bowling
but I take delight in the juice of the barley
and courting pretty fair maids in the morning bright and early

-TH-

Recipes 

Since I know nothing about varistors you would have to explain to me how/why it would work, and then also why it would be better than a single resistor in parallel with the LED that I've already got working.

__________________
TH

Builds, etc: E-Brewery | Fermentation Chamber | Concrete-Roller Mill | Stirplate | Bottle Cabinet | Pneumatic Bottle Capper
Resources: www.EZWaterCalculator.com