Solved: Humidity / temp / solar kit, bad temp


I was experiencing my temp/humidity/solar board registering elevated temperatures when I supplied it with external power. Withoput external power the temperature readings were fine. But I ended up needing external power to get reliable 1-Wire sensor readings. I did some research/testing and have some additional information that helped me solve the problem (at least for me).

I used a temperature probe and discovered that the C1 electrolytic capacitor on the temp/humidity/solar board was getting warm when I supplied external power. On a cold day it was noticeably warm to the touch, and my temperature probe showed that it was warmer than the rest of the board. I purchased a few new DS18S20 temperature sensors to experiment with. I removed the old DS18S20 from the board and attached some short wires to the bottom of the board (rather than the top) and a new DS18S20 extended an inch or so away from the board. Now all my temperature readings are within a degree or less of each other. And I only destroyed one DS18S20 in the process as well.

I'm going to leave it running and montor it for a while to make sure the readings stay consistent and I don't get a lot of errors. Then I can move on to the rain gauge I just received this week!
That's weird, electrolytic caps do not get hot unless they are installed backwards with positive and negative being reversed or their voltage max is being exceeded.

Was it installed backwards?

Glad you got it figured out.
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I suspected that I had the caps installed backwards (I built the kit myself, so that was always a possibility). I tripled checked, and even emailed Eric to make sure I had them installed correctly. It turned out that they were installed correctly. They don't get really hot, but they are noticeably warm when the surrounding air is cool.

As to the power supply, I purchased the universal AC adapter from Hobby Boards to power my barometer board. The barometer provides the unregulated power from that supply on pin 7 of the RJ-45 connector. I am using that to power my other devices.

I'm not an electronics expert by any means, but I did notice that the caps are rated at 10V. The power supply provides 15V. Could that have anything to do with the problem?
Yes that could be it. A 10 volt rated cap should not have more than 10 volts on it.
Conservative design would say double the running voltage for the caps rating. So if you have 15 volts supply a 25 volt would be ok a 30 or 35 is real conservative.
Yes, exactly.
Measure the voltage on the current cap and then install a new cap with a higher voltage.

Example: If you have 15 volts across the current cap, get a 25volt

I have same problem with my Temp / humidity / solar kit. But for me C1 / C2 are 35v capacitor, not 10v. My board is rev 3.

When i plug external power (~15v) temp grow up to 4°C than other sensors ( DS18B20 standalone).

I don't understand why. I have checked circuit, everything seems OK :blink:
I didn't look at the schematic but if there is a voltage regulator inside, they will regulate the 15 volts down to say 5 volts and the rest is blown off as heat.

Voltage regulators are heat sinked to keep them cool.

You may a component inside heating up and messing with the temp sensor?

Heat rises, I wonder if you can turn the case a different way and get different results?

I run all my HB devices off of a HB 6 channel master hub with a 19 volt external power supply.
I have a HB temp/humidity/solor sensor.
Not sure what voltage the hub sends to my sensor but it's pretty accurate.