Waterproofing leads

I received an aquarium for Christmas, and of course, building an aquarium monitor immediately jumped to mind. One critical feature of that is temperature monitoring, so I wish to immerse a thermistor in the aquarium, perhaps 6 inches down.

Now a thermistor is in effect a resistor, so I don't want spare parallel resistance coming back at me from leakage through the water. If I can solder up the leads on the thermistor, then dip it into some waterproofing compound far enough to protect the underwater portion, I should avoid problems.

My question is, has anyone had experience with this, and can you recommend a good, long-lasting waterproofer that works?

Hot melt glue

LarryD:
Hot melt glue

I didn’t think hot glue was water proof?

I’ve used Polymorph to waterproof a few things. I think it would likely work in this application.

I’m sure there are lots of glues designed for this sort of thing. If you use silicone, make sure it’s the right kind. I think the stuff that smells like vinegar will corrode wires.

Fish can be delicate creatures. Stainless steel tube would be the way to go for various reasons, including it wouldn't be too hard to look at. Solder the bottom end and use some sealer at the top even though it shouldn't be immersed.

DuaneDegn: I didn't think hot glue was water proof?

I've used Polymorph to waterproof a few things. I think it would likely work in this application.

I'm sure there are lots of glues designed for this sort of thing. If you use silicone, make sure it's the right kind. I think the stuff that smells like vinegar will corrode wires.

I used it for water proofing a sensor for years in a 45 gallon aquarium.

hot melt glue covered with a heat-shrink sleeve is quite effective I believe - the shrinking of the sleeve
forces out the glue from both ends and thus guarantees no gaps for the water to get in.

You could use a plastic dip coating like this: Liquid tape

Russell.

Your bigger problem will be electrolytic corrosion of the junctions unless you get them properly waterproofed. You can of course buy ready made waterproof RTDs designed specifically for aquarium monitoring.

Get a DS18B20-sensor and put it into a glass or stainless tube - fill up with silicone if you are unsure about the hot-melt glue. If you get the hot melt glue properly hot (as in gas torch directly on the gluestick) it will stick extremely good and won’t fail.

// Per.

I commonly work with these setups, the easiest and cheapest way is to cover it with heatshrink and inject with sillicone

In my line of work I often have to repair metal that has corroded because it was in contact with silicon.

In particular there was a 68 Chevy Impala that a gentleman had restored himself at home. He had used silicone instead of the usual seam sealer. It had rusted out everywhere there was silicone even though the metal had been painted first. It was a very expensive lesson for him.

Go with the hot glue.

Hutkikz: In my line of work I often have to repair metal that has corroded because it was in contact with silicon. Go with the hot glue.

Of course you don't use acid-curing silicone on metals! - only platinum-curing silicone (alcohol-based)

// Per.

The acid-curing stuff smells like vinegar as its acetic acid it generates when curing.

http://www.ebay.co.uk/itm/Digital-LCD-Fish-Tank-Aquarium-Marine-Water-Terrarium-Thermometer-Temperature/301762874895?_trksid=p2141725.c100338.m3726&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20150313114020%26meid%3D60923a822c2b4da9bad55462d9fdf63a%26pid%3D100338%26rk%3D7%26rkt%3D26%26sd%3D262079926204

Cheaper than a tube of silicone , just cut off the sensor

Put the probe in a glass test tube.

Zapro: Get a DS18B20-sensor and put it into a glass or stainless tube

At least in the U.S., I believe such things can be purchased for a few dollars.

Done the same with a small capilliary tube and a blowtorch to make a mini test tube.

Gives a better response time than a test tube if its needed.

So - what is wrong with the obvious - just using one of these?

1.Brand New High Quality 2.The probe the temperature sensor DS18B20 original chip 3.High quality stainless steel tube encapsulation waterproof moistureproof prevent rust 4.Stainless steel shell 6*50mm 5.Power supply range: 3.0V to 5.5V 6.Operating temperature range: -55°C to +125°C (-67°F to +257°F) 7.Storage temperature range: -55°C to +125°C (-67°F to +257°F) 8.Accuracy over the range of -10°C to +85°C: ±0.5°C. 9.No other components, unique single bus interface 10.Output lead: red (VCC), yellow(DATA) , black(GND) 11.Cable length: 100 cm

Paul__B: So - what is wrong with the obvious - just using one of these?

I have seen some people using these in water, and after some weeks it stops working because it's not really water tight under the shrink wrap!

// Per.

they are not designed for immersion but suitable for exterior use generally