This DC submersible motor safe?

[ahsrabrifat]

This is a DC submersible motor. I used it couple of times years ago and it had been unused since then. I need to use it again for a sprinkler project. When I took it out of my almirah today, I discovered this long crack on the motor's body. Do you think it is safe to use this motor anymore?

 

[Nigel Goodwin]

It's only low voltage, so not a safety issue - but presumably the crack means water will get inside, where it's not supposed to, and the motor will probably die after a while.

 

[Grossel]

In short term, the motor may be water cooled - but that is not of any advantage unless it's feed with more than rated power.
In longer term - even if the housing isn't submerged, it seems to be open for dust getting in to the motor itself - that of course being depended on the environment where you plan to put it to use.

[edit]
Wait a minute! You said "sprinkler project" - as in fire extinguisher system ??

Well, in that case - no f... way I'd agreed to use components holding that low of a standard. You need a system that you can actually trust, this motor at the picture can fail at any moment.

 

[Externet]

After well dried, wrap in many turns of tight vinyl insulating tape and test. It is broken, cannot break it more. If works for a while, great.

 

[MaxHeadRoom78]

Wrap if gkass cloth, and then coat with fibreglass resin as used in covering water craft etc.

 

[ZipZapOuch]

You can sacrifice a soldering iron tip or wood burner tip or, if you have an iron nail and a candle or torch, you can thermal stake it. Just drag (poke) your soldering iron or nail across good area and into the crack. Poke into the crack first, (blue arrows) if the resin melts reasonably well - then do the crisis-cross as in second photo.

 

[schmitt trigger]

An interesting question would be: “how come did it crack in the first place?”

If it had an impact or was it crushed I could understand it. But if it was caused by chemical degradation of the plastic body, that could be a sign that it will continue to disintegrate.

Many years ago I purchased a Micronta FETVOM. I understood the reason for a high-impedance input but as an electrical student I couldn’t afford something from the big manufacturers.

The meter was reasonably accurate and I took utmost care of it. After using it I would carefully store it back in its original box.

Then one day the handle cracked. I repaired it. The enclosure then started cracking. I still repaired it. Then the banana posts cracked, then the rotary switch and all the plastic pieces simply crumbled. I had to throw it away.

To date, I haven’t found out what happened. My theory is defective or low grade plastic stock. Perhaps the resin stock had too much recycled material.

 

[ZipZapOuch]

An interesting question would be: “how come did it crack in the first place?”

Plastics like nylon and polypropylene are considered "semi-crystalline" and continue to crystallize as they age. As the volume fraction of "crystallized" polymer increases the volume decreases and the material gets more brittle and cracks - especially likely if there's a metal core of some mechanical valve or other imbedded inside (that the resin was molded over). Since the inner metal piece doesn't change size over time, the part will likely crack over time.

 

[rjenkinsgb]

Nylon also contains a percentage of water as part of its structure. If it's kept in dry surroundings, that can also cause shrinkage and brittleness. eg. Nylon 6 holds up to around 3.5% water.

(I learned that decades ago, for nylon propellers for radio control aircraft - they are supposed to be taken off and kept in a zip bag with some damp cloth when not in use, or boiled for a while every so often to rehydrate the material. If they dry out too much, they can shatter in use.)

 

[ahsrabrifat]

Thank you, everyone. I have not tossed it away but I have ordered a new one. I may try the troubleshooting tips later.