Submerged Motor

[NX687]

We all know brushed motors in fuel tanks last 1000 's of hours

Why then with my brushed motor in my Radio Sub is the brush life about 5 minutes ,

Chlorinated pool water ,,,

low power

Suggestions appreciated

 

[MikeHalloran]

Fuel tanks don't have chlorine or other corrosives available to the brushes.

Small brushless motors for computer fans are now down to a couple of bucks.

Why even bother with a brushed motor?

Mike Halloran
Pembroke Pines, FL, USA

 

[NX687]

Thanks mike I am going Brushless , my question is will the speed controller be OK with its 3 wire in the water

The water resistance wont confuse it ? and the back EMF for the motor timing wont get thrown out?, I hope not

Subs for a kids charity have a go meet

 

[NX687]

And what do you mean computer fan , this is an evil big , nuclear sub 700 mm long , about 2.5 kg , it needs power to push that blunt nose

 

[MikeHalloran]

You want POWER?

Read this thread:

http://www.eng-tips.com/viewthread.cfm?qid=337857

Mike Halloran
Pembroke Pines, FL, USA

 

[waross]

Are you using any RTV silicon?? The fumes from RTV silicon are a brush killer.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Generally accepted practice is not to put electrical equipment into water. Are you really immersing this motor in water, or is it encapsulated / enclosed in a watertight compartment with a shaft passing through a gland to drive the prop?

 

[itsmoked]

I agree with Scotty you should avoid any water in the electronics. In a chlorinated pool you're really going to need to follow this rule.
If you just can't hack a waterproof gland you can always go with a magnetic drive that has no penetrations. You can put everything in a single waterproof compartment. Whatever you do, you need to make sure you have a safety pressure release for a compartment. A rubber boot over an opening or something similar. If you short some batteries in a closed compartment you will end up with a bomb. A guy opened the compartment lid on a scuba power tow unit that had a water shorted battery in it. The cover came off like a bullet and hit him in the face killing him. Be safe.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Thanks to electricpete for this thread;
silicon weather sealant around dc motor brushes/commutators Helpful Member!(9)
thread237-343881
See also:

http://eng-tips.com/search.cfm?pid=...s+RTV&t=&h=&searchSite=1&searchArea=1&d=1&s=1

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[NX687]

No

No silicon near the brushes
I did get a good 5 minutes each of performance before both brushed motors died

Fully submerged

Have now a 40A ESC and a Brushless innrunner on with bronze bearings substituting the ballraces, no pool time yet

This has been proven in tap water , dont know about pool water ,

What flush or dunking would you recommend after each running session , WD 40 ---- Innox ,,, Kero ,,,

 

[NX687]

Maybe a demin Water flush ?

 

[NX687]

Ugh ,,,,, Has to be a no oil flush as residue would contaminate my pool with oil film ,

 

[MikeHalloran]

Tap water flush. Demin water is corrosive.

Mike Halloran
Pembroke Pines, FL, USA

 

[NX687]

Thanks Mike
I will report if my ESC or motor dies on operation

 

[ScottyUK]

Demin is a powerful solvent rather than corrosive, it should be fine on most metals and plastics. It's used as a final rinse in the electronics industry. You need to keep it away from anything containing the alkali metals.

 

[mikekilroy]

I have never in 35 yrs of working with dc and ac brushless motors heard of a single successful case of someone taking a standard motor and running it submersed in any kind of water.

This is just not correct application of an electric motor. Brushless is not a solution. Even if it were, do you realize it is controlled totally different than that brush motor? Much more complex driver required - did you plan to replace that too?

If it must run IN THE WATER and you want longer than 5 minute life you may want to consider a rubber band.

Or just spend a few bucks more and buy a sealed motor designed for that use - there are plenty out there - as evidenced by simple google search "waterproof submersible electric motors" - heck there even 12v ones on ebay. For occassional use, one of these in a brush motor design should last nearly forever.

http://www.KilroyWasHere<dot>com

 

[Brad1979]

I would search for IP67 motors rather than "waterproof" or "water tight" motors or any other other key words like that. "Waterproof" means whatever the manufacturer wants it to mean. IP67 means the motor is protected to a depth of 1 meter for at least 30 minutes.

 

[mikekilroy]

I would actually go for IP68 is continuous use submerged; I've heard of mfgrs rating motors IP67 by testing them actually run for 1 sec - or not at all - at 1 meter depth then even if they fail, leave them down for the 30 sec and they passed: the spec does not specifically say they have to run for 30 sec before failure....

http://www.KilroyWasHere<dot>com

 

[Brad1979]

The test condition for IPX8 only says that it is between the manufacturer and the end user but that it is at least severe as IPX7. So IPX8 doesn't guarantee that they have to run underwater, either.

 

[mikekilroy]

Right IP ratings are sorta vague. But at least IP68 usually is better sealed than IP67... We seal to IP65 and on machine tools with motor where it can get sprayed with coolant mist they sometimes don't fill up with coolant for years, sometimes in 2 weeks, depending on severity of spray. We change from IP65 to IP67 on same motor and same application and they usually then take years and seldom less than 6-8 months in worse cases.

http://www.KilroyWasHere<dot>com