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Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1667

Posted: 09:46pm 19 Jan 2019

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Just wondering is my DS18B20's are self heating themselves a bit.

Not so much the sensor it's self, but the SMD Led & 1k resistor on the board.

This is them....

What has got me thinking, apart from the possible 1�C or so value I question is the heat I'm seeing in my solar blocking diodes.

When carrying 8 amps they get to about 62�C, & I'm guessing that is coming from about 5 Watts.

The LED & resistor would consume 25mW? Is that a significant amount for the size of the PCB & module?

These are the solar diodes...

Cheers

Phil.

Edit:-

My modules have the 10k resistor, D1, removed.
It's between 5V & the data pin.
Mine are connected as a string of 10.Edited by Phil23 2019-01-21

Chopperp

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Joined: 03/01/2018
Location: Australia
Posts: 1106

Posted: 01:40am 20 Jan 2019

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Hi Phil

I would like to see the DS18B20 mounted off the board a bit to thermally isolate its case from the board itself & move it away from the LED etc. (I assume by the look of the photo it is sitting on the board).

BTW, on some of my open air sensors, I use a female spade connector as a bit of a heatsink.
I cut any plastic insulation off them & open the spade part up just enough so they slide over the sensors. Having a heatsink will even out temperature fluctuations & reduce any self heating effects. It does slow down the response time a bit though.

Not sure what you are on about with the solar blocking diodes.

. They will dissipate heat with current going through them when operating.

What temperatures are you actually measuring?

Brian

ChopperP

Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1667

Posted: 03:28am 20 Jan 2019

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Chopperp said Not sure what you are on about with the solar blocking diodes.[/quote]

I mentioned them as I was a bit surprised by the temperature they reached with only about 5 Watts being dissipated.

[Quote]What temperatures are you actually measuring?[/quote]

I've got 1 in the lounge room, bedroom & two offices.
1 at ceiling height in the lounge, one in the roof space & an outside one.

They are all read & used to control the dampers & blowers that move air around the place.

As per this previous thread.

Note the hardware has changed since back then...

Phil.

PS.

Not trying to pull down the 55�C air I have there at this time of year during the day; more interested in the 20�C overnight stuff that is present in the early hours.

Chopperp

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Location: Australia
Posts: 1106

Posted: 04:59am 20 Jan 2019

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Thanks Phil

They do get hot. A 5W soldering iron gets very hot as does a 5W resistor at full power.

Somehow I missed your earlier 2016 thread.

Brian

ChopperP

Phil23
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Joined: 27/03/2016
Location: Australia
Posts: 1667

Posted: 12:19am 22 Jan 2019

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Quick & dirty analysis this morning.

Cut the track to the LED on 2 of the sensors hanging easily accessible...

My office down from 29.4 to 28.1.
Bedroom down from 27.75 to 26.5.

Not much scientific control of the comparison, but it looks like at least as full degree of variation.

Should win immediate brownie points for the lower temp readings with MrsC I suspect????

Phil.

Chopperp

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Posts: 1106

Posted: 08:10am 22 Jan 2019

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Phil,

Have you tried blowing a gentle stream of air across your (unmodified) boards to see what happens?

Should reduce effects of the heating elements etc.

(Not much good if you are just measuring still air though).

Brian

ChopperP

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