Heating Element Controlled By A Pid - Current Draw Once At Temp

[matho]

I've seen divided opinions on that. Some say yes, some say no. Some say just make sure it's bolted to something metal. I bought a heatsink originaly for the first ssr I bought, but I didnt this time round. I will be bolting it to the metal box I'm builing my panel out of. if it gets hot, I'll get a heatsink for it. the last one was only $5....

a box would probably dissipate the heat well.

 

[matho]

here is a PDF about sizing heatsinks for SSR's

View attachment HS_WP_HS.pdf

sorry to the OP for the off topic

 

[QldKev]

I started reading the doco on heat sinks, but ouch!

Will this heatsink do?
http://www.ebay.com.au/itm/270934403144?ss...984.m1497.l2649

 

[matho]

I started reading the doco on heat sinks, but ouch!

Will this heatsink do?
http://www.ebay.com.au/itm/270934403144?ss...984.m1497.l2649

hehehe yeah it can get a bit confusing, that one should be fine and it is drilled and all. I'm using THIS for the SSR I have but thats because it fits the build better

cheers steve

 

[mILLrAT]

I dont use a heat sink for the SSR. Mine are screwed onto the wood sides of my homemade scrap timber box.

Even though your fridge is connected up to a 10 amp socket it doesnt draw 10 amps. A typical fridge draws about 600 watts while the compressor is running, current=watts/volts, so the fridge draws about 2.5 amps. Every time the compressor starts you will get a higher startup current draw but that is over quickly. I dont know at what continuous current draw a heat sink would be required, but 2.5 amps seems fine.

 

[kjparker]

here is a PDF about sizing heatsinks for SSR's

View attachment 54588

sorry to the OP for the off topic

It's all good, all good useful information!

 

[QldKev]

I dont use a heat sink for the SSR. Mine are screwed onto the wood sides of my homemade scrap timber box.

Even though your fridge is connected up to a 10 amp socket it doesnt draw 10 amps. A typical fridge draws about 600 watts while the compressor is running, current=watts/volts, so the fridge draws about 2.5 amps. Every time the compressor starts you will get a higher startup current draw but that is over quickly. I dont know at what continuous current draw a heat sink would be required, but 2.5 amps seems fine.

The topic title is "Heating Element Controlled By A Pid - Current Draw Once At Temp" Most are 1800 to 2400w.


QldKev

 

[Maheel]

I started reading the doco on heat sinks, but ouch!

Will this heatsink do?
http://www.ebay.com.au/itm/270934403144?ss...984.m1497.l2649

if you see any old PC desktops laying around there are often big ally heatsinks on the old processor motherboard chips
easy to drill and fit SSR's to

i collected a few for the scrap parts box

 

[Parks]

The topic title is "Heating Element Controlled By A Pid - Current Draw Once At Temp" Most are 1800 to 2400w.


QldKev

That would be peak though. I think OP was hoping that the PID throttled the element, or somehow ran it at 500W or whatever to hold temp when it actually turns the element on full for a second, then off for a second (or whatever the actual timing is) so the average might be 500W but it's not a constant wattage.

 

[Parks]

if you see any old PC desktops laying around there are often big ally heatsinks on the old processor motherboard chips
easy to drill and fit SSR's to

i collected a few for the scrap parts box

:icon_offtopic:
I was just about to throw out 2 old power supplies when it hit me that the IEC socket in the back would be perfect for my next control box... One even had a power switch and and output IEC - double bargain!

 

[JPAT]

That would be peak though. I think OP was hoping that the PID throttled the element, or somehow ran it at 500W or whatever to hold temp when it actually turns the element on full for a second, then off for a second (or whatever the actual timing is) so the average might be 500W but it's not a constant wattage.

What type/model PID controller are you using?

 

[Parks]

What type/model PID controller are you using?

I'm not yet, just my understanding of PWM.

Feel free to correct me if I'm wrong.

(I will be using an Arduino once I've finished building it)

 

[JPAT]

I'm not yet, just my understanding of PWM.

Feel free to correct me if I'm wrong.

(I will be using an Arduino once I've finished building it)
[/quote

PWM will throttle back current but it would probably be a good idea to use a relay so both elements are never on together

 

[Parks]

PWM will throttle back current but it would probably be a good idea to use a relay so both elements are never on together

PWM doesn't actually throttle or reduce the current. It turns the signal on and off repeatedly so the average appears to be throttled.

I am coming from the point of view that this will be going through an SSR.

eg, if it's a 2400W element, 240V @ 10 amps and your PID wants to run it at 1200W then it will constantly turn the SSR on and off (how ever many times per second) to achieve this. The element still draws 2400W when it's on, but it also draws 0W when it's off.

 

[MastersBrewery]

It's this one. Works a treat :icon_cheers:

you could always use a dimmer switch as above to limit max power and PID to control temp by switching on off. would take a bit of trial and error to find the best setting on the dimmer for mashing, but for boil just max it, or switch so the dimmer is no longer in circuit. I've now prolly confused everyone..... including me :blink:

 

[Parks]

you could always use a dimmer switch as above to limit max power and PID to control temp by switching on off. would take a bit of trial and error to find the best setting on the dimmer for mashing, but for boil just max it, or switch so the dimmer is no longer in circuit. I've now prolly confused everyone..... including me :blink:

That makes sense to me.

The dimmer will reduce the voltage to the element and thus wattage.

-- assuming that elements will be OK with it, I don't see why they wouldn't be --

 

[JPAT]

PWM doesn't actually throttle or reduce the current. It turns the signal on and off repeatedly so the average appears to be throttled.

I am coming from the point of view that this will be going through an SSR.

eg, if it's a 2400W element, 240V @ 10 amps and your PID wants to run it at 1200W then it will constantly turn the SSR on and off (how ever many times per second) to achieve this. The element still draws 2400W when it's on, but it also draws 0W when it's off.

When the PWM turns on and off faster than one cycle it cuts the wave meaning it reduces the voltage which reduces the watts which reduces the current. One cycle is 20mS long.

 

[kjparker]

you could always use a dimmer switch as above to limit max power and PID to control temp by switching on off. would take a bit of trial and error to find the best setting on the dimmer for mashing, but for boil just max it, or switch so the dimmer is no longer in circuit. I've now prolly confused everyone..... including me :blink:

Except that would probably muck up any self tuning the pid has done....

 

[Parks]

When the PWM turns on and off faster than one cycle it cuts the wave meaning it reduces the voltage which reduces the watts which reduces the current. One cycle is 20mS long.

That doesn't sound right - got any info sources?

 

[MastersBrewery]

Except that would probably muck up any self tuning the pid has done....

yes it would.


perhaps using the dimmer directly in line and removing pid control from the boil, thus the pid would self tune to always switching the lower (dimmed) wattage.