HALL HORROR: best heat resistant glue to lock them down?

[voicecoils]

I was experiencing a weird 'pulsing' at the end of my last two rides. I thought it was my CA going haywire but after fixing it, it still happend at the end of my second ride. I think I found the reason: My hall sensors are not hel, when d in place. Perhaps the glue has come off in the heat of operation, I'm not sure. They're just loosely sitting in place; when I opened it up 2 of the 3 were hanging out of their slots.

(with the halls placed in their slots, the motor runs fine, so they must not be toast)



Anyone know the best thermally resistant glue to lock them back in place?

 

[HAL9000v2.0]

I am using pure epoxy resin.

 

[voicecoils]

I am using pure epoxy resin.

Cool. Can you tell me why it's best and secondly, where I can find it?

 

[HAL9000v2.0]

I am not sure that is the best but it holds and I get up to 150°C in coils. Still holds.
In any hobby store you can buy small bottles or double syringe.
When I fried my halls I was the first thing that I found in my garage, that's why it's best for me...

 

[voicecoils]

I am not sure that is the best but it holds and I get up to 150°C in coils. Still holds.

Sounds good. I think I know what you mean, the double syringe stuff.

My only fear is that if the halls fry, will I ever be able to dig them back out then?

 

[HAL9000v2.0]

You will with a sharp knife and patience.

 

[fechter]

The slower setting (2 hour) stuff is gernerally more heat resistant than the 5 min stuff.
Either one will become soft enough to dig out with a pick if you heat them to 100C.

RTV silicone glue is the ultimate in heat resistance (over 500F), but it is not rigid.

 

[John in CR]

Different epoxies have different thermal limits. I think vinyl ester resin has a higher thermal limit than epoxy, and is typically used in motor rewinds. Nastier stuff though, so use it in well ventilated are.

John

 

[voicecoils]

The slower setting (2 hour) stuff is gernerally more heat resistant than the 5 min stuff.
Either one will become soft enough to dig out with a pick if you heat them to 100C.

RTV silicone glue is the ultimate in heat resistance (over 500F), but it is not rigid.

Thanks.

Well, RTV silicone glue might be good then. Is rigidity actually something necessary? As long as it's held in position, having a bit of a 'cushion' might not be a bad thing...

 

[fechter]

I think silicone will be good in your application. There won't be much stress on the wires. Silicone is pretty easy to tear off if need to replace them. You should probably clamp the sensors while gluing so they are as low in the slot as possible. You can wedge toothpicks on top of them or something. I used scotch tape on over the top of the slot when gluing to form kind of a mold. This keeps excess glue from sticking up where it might rub on the magnets. You can trim the glue later too.

 

[Mark_A_W]

Abraham

Araldite is the local brand of epoxy - comes in 5 minute and 3 day cure.


But I agree that RTV silicone would work too. $13 at Bunnings - but make sure it says RTV. I know they sell it because I bought some for my CRT projector HV leads (we have another common hobby).


Mark

 

[voicecoils]

Abraham

Araldite is the local brand of epoxy - comes in 5 minute and 3 day cure.


But I agree that RTV silicone would work too. $13 at Bunnings - but make sure it says RTV. I know they sell it because I bought some for my CRT projector HV leads (we have another common hobby).


Mark

Cheers. Will try to get to bunnings this week then for some RTV silicone.

I can send you the rest of the tube for your bafang :wink:

 

[Mark_A_W]

I already have some.

And my Bafang is a paperweight until I find another metal gear.


I might sell it, let someone use it at 36v 20A, not 66v 30A like me

 

[voicecoils]

I already have some.

And my Bafang is a paperweight until I find another metal gear.


I might sell it, let someone use it at 36v 20A, not 66v 30A like me

Have you worked out what the gear type is in it? # of teeth, overall diameter & thickness would be a start. It should be a reasonably standard metric size. If we can find a metal gear for you a few others might be interested too in grabbing some too...

If you get the chance, take some pics of the internals. You only showed it to me briefly and perhaps others are interested too.

 

[Mark_A_W]

Have you worked out what the gear type is in it? # of teeth, overall diameter & thickness would be a start. It should be a reasonably standard metric size. If we can find a metal gear for you a few others might be interested too in grabbing some too...

If you get the chance, take some pics of the internals. You only showed it to me briefly and perhaps others are interested too.

Nuh, I done jack so far.

Too much on my plate...

 

[voicecoils]

Bunnings had one tube of RTV Silicone left. Good to 205 deg C sustained and 265 deg C short term 8)

I've siliconed them in place and put a liberal amount underneath and over the 3 wires coming into them for each.

I also bought the longer curing Araldite just in case I need to revisit this area of the motor.

You can see in the first pic that there is string holding the wiring in place. It's gone totally brittle and just crumbles off when touched. Same for the bits of coated paper that were under the hall wires. The first stage worked well so I went back and slathered the silicone on a big chunk of the back side.

 

[fechter]

If you can seal the area right where the wires come out of the hall sensors adequately, then the entire thing should be very resistant to water. Many motors don't have a good coating right there and will malfunction with the slightest drop of water on that spot.

The same thing goes for hall effect throttles.

You look like you should be good for fully submerged operation.

 

[MidniteTweeker]

I've heard that you need to be careful using RTV around electronics. Something to do with the acetic acid outgassing and causing corrosion. A special grade of RTV is made for use with electronics. Since you're already done, all I can suggest is to be sure everything is fully cured before you close it back up. Probably would not be good to trap any residual fumes.

MT

 

[fechter]

I've heard that you need to be careful using RTV around electronics. Something to do with the acetic acid outgassing and causing corrosion. A special grade of RTV is made for use with electronics. Since you're already done, all I can suggest is to be sure everything is fully cured before you close it back up. Probably would not be good to trap any residual fumes.

MT

Quite correct.

The acetic acid (stinky smell) from curing silicone is very corrosive to metal.
As long as the glue is fully cured before enclosing it, corrosion is not a problem.
It is a real problem if you apply some to a part inside a box and put the cover on while it's still wet. Only the vapor seems to be corrosive, not the glue itself.

In applications where you don't want to wait for outgassing, you can use the non-corrosive "electronic grade" variety (RTV 162 for example). Not nearly as stinky, but it is not as strong when cured and takes longer to cure.

 

[Mark_A_W]

It's RTV silicone. No vinegar smell.

Not acetic cure.

They are different.

 

[voicecoils]

It's RTV silicone. No vinegar smell.

Not acetic cure.

They are different.

It seems there are different types:
http://www.logwell.com/tech/servtips/RTV.html

"Never use acetic acid cure room temperature vulcanizing (RTV) silicones in your well logging tools, or on any electronics for that matter."

"RTV silicone made for non-corrosive electronics applications uses an alcohol curing system rather than an acetic acid curing system. The alcohol cure products have a slightly sweet to ethereal odor as opposed to the distinctive vinegar odor of the common acetic acid cure products. Both are one part curing systems that depend on air moisture to cure into silicone rubber. Examples of non-corrosive RTV silicone pastes are: clear or gray Dow Corning 3145; white General Electric RTV 162 or gray high strength RTV 167; and clear Loctite 5140."

 

[voicecoils]

This is the stuff I used:

http://www.selleystrade.com.au/Silicone-401-RTV794/default.aspx

 

[MidniteTweeker]

Yup. The "acid cure" is the tip off. In my experience, most of the RTV you find in typical hardware or building supply stores is the acetic acid cure variety. Usually need a specialty shop that carries the non-acid stuff.

But let it cure completely while the motor is still open and you should be OK.

The fact that it remains soft should be very helpful if you have to disassemble.

Another good use for RTV (believe it or not) is to retain bearings when the fitup isn't quite right. Usually it's just a matter of something being a few thousandths of an inch out of spec and you don't want the bearing to spin in the bore or on the shaft. Smear on a small dab of RTV and assemble normally. The excess squeezes out and leaves a very thin film in place that "floats" the bearing nicely centered. Of course the various Loctite products work also, but I never seem to have the right stuff on hand, and I definitely *do not* want to use the permanent stuff (red, I think) out of desperation.

MT

 

[Mark_A_W]

It's RTV silicone. No vinegar smell.

Not acetic cure.

They are different.

It seems there are different types:
http://www.logwell.com/tech/servtips/RTV.html

"Never use acetic acid cure room temperature vulcanizing (RTV) silicones in your well logging tools, or on any electronics for that matter."

"RTV silicone made for non-corrosive electronics applications uses an alcohol curing system rather than an acetic acid curing system. The alcohol cure products have a slightly sweet to ethereal odor as opposed to the distinctive vinegar odor of the common acetic acid cure products. Both are one part curing systems that depend on air moisture to cure into silicone rubber. Examples of non-corrosive RTV silicone pastes are: clear or gray Dow Corning 3145; white General Electric RTV 162 or gray high strength RTV 167; and clear Loctite 5140."

Well, did it smell of vinegar?


Even if it did, I wouldn't be worried. It will be fine.


But it does sound like you are going to cook your goose at 72v 20A...

 

[voicecoils]

Well, did it smell of vinegar?
Even if it did, I wouldn't be worried. It will be fine.
But it does sound like you are going to cook your goose at 72v 20A...

I think it did. I'll stick my nose in it tonight to double check. Your stuff didn't? Mine was just under $13

I'm not too worried. It's open and will have been sitting fully ventilated for 24hr before I close it up. The bafang is poorly sealed anyways so it will probably continue to ventilate.

I don't eat fauna. However, are you suggesting that I might char-grill this butternut pumpkin even if the nylon gear weak link has been fixed?

The motor really is tiny, especially from a copper mass perspective. I'm looking into a temperature monitoring solution. My options are 72v20A or 48v30A (battery side limited), I don't know which is worse temperature-wise. I'd think the later since it's more current through the same windings...

Anyone want to walk me through the calculations to figure out the current seen on the motor side?