Victor running underwater!
 

Re: Victor running underwater!
 

Fredi,

Tis cool...

Last year I got a pvc union with screw caps, and metal discs and o-rings to seal it up. The plan was to try to put stuff in the tube, fill it with mineral oil and close it up.

the mineral oil would transfer the heat to the endcap discs and it would stay cool.

never got around to finishing the project. but it would be neat to try.

Ed

Re: Victor running underwater!
 

Just wondering if you guys have time for this, but could you possibly put out a white paper for this? A few of our class projects could definitely use some water proofing. The video is great though. :)

Re: Victor running underwater!
 

Sure we could do that!

Re: Victor running underwater!
 

that's neat! It'll be interesting to see what happens when it had to deal with heat....maybe you could wire up the victor to one of your old FRC robot chassis, and do a pushing test....

Although underwater stuff doesn't seem to need nearly so much current

Re: Victor running underwater!
 

You could probably rig up some kind of heat sink mechanism if overheating turns out to be a big issue. It looks good, I also second the "mineral oil" strategy, although I have never tried it, I have heard good things about it and waterproofing electronics. Last time i checked, you could get It by the gallon at mcmaster.

Good Luck and keep us posted as far as any other tests you work on with the waterproofing!!

Re: Victor running underwater!
 

I bet you could run it under DI water without any waterproofing.

Re: Victor running underwater!
 

Clearly 842 is ahead of the GDC curve.;)

Re: Victor running underwater!
 

I remember reading a post by Dave saying that you could run water into the Victor's fan and through the unit without any damage, which he then used to make a cheesy water game hint with. Not something I'd try but interesting.

Nice job on waterproofing a Victor! Seems like you only get one try at that per Victor...

Re: Victor running underwater!
 

The epoxy is glass filled and conducts heat pretty good! We plan on doing the Current test and cause it to trip a breaker, thus proving we have drawn plenty of current.... then of course there is the time factor as well. We will keep you posted

Re: Victor running underwater!
 

We have had experience with mineral oil. Some electronic components degrade over time in oil and stop functioning. You would have to test this with victors. It is not as neat and clean as the glass filled epoxy resin.

Re: Victor running underwater!
 

excuse my asking but what a DI?

Re: Victor running underwater!
 

google says it's deionized water

Re: Victor running underwater!
 

Finally a topic I can post something intelligent on.:D DI water is water that has no dissolved ions in it. It is the presence of positive and negative ions which allow electrons to flow through a solution. Without the ions, there is no attraction for the electrons from the battery, so in theory, you could run a victor under DI water without the need for any waterproofing. Be careful though, it only takes a very little bit of ions to allow electron flow. A simple grain of salt is enough to provide enough ions to conduct electricity in 200 mL of water.

Re: Victor running underwater!
 

Fredi,
At high current, I would be concerned with expansion and contraction coefficients of the material and the electrical components. I think the epoxy can do a great job as a heatsink when exposed to water. What I might suggest is a double dip such that the tabs of the transistors only are embedded in the epoxy while the circuitry remains open. Then encase the assembly as you have shown. This would allow the components on the board to move around with temperature without being broken off as material expands and contracts. I like the dual heatshrink and would recommend it for the entire length of wire. Some wire insulation is made with clay as a filler and therefore it absorbs water. Some wire has a dual coating to prevent this as well. As a test, seal both ends of a short piece of wire and submerge it for a day or two. Then slit the wire open and see if there is any contamination. If you heat the shrinkable tubing and then compress while hot with pliers, the seal should be good enough to keep out water.
As always, I applaud your team. This is a great idea and a wonderful demo. Good Luck this year!

Re: Victor running underwater!
 

Technically, DI water has ions in it. There is a class of purity above that water called reagent grade or nanopure water in which you measure purity in resistance.

Re: Victor running underwater!
 

De-ionized water (sometimes referred to as "distilled" by users) is used for cooling water in some high power transmitters. Water flows over high voltage and low voltage parts and current probes are used to determine the conductivity of the water. High voltage power supply trips at a few milliamps are common with poorly maintained equipment. In some cases, designers actually use china pipes to keep the water insulated from sensitive (read 'human') objects just in case some contamination enters the system and causes conduction to skyrocket. The UHF transmitter I worked on in Peoria many years ago had 25,000 volts across the output tubes and the cooling water. As I remember it had both a ceramic filter and a de-ionizer in the circulating water. The collector (plate/anode) was vapor cooled. This means that cold water is just poured onto the structure and cools while turning to steam vapor. The steam is carried off to a heat exchanger where it is turned back into water. Regular maintenance includes scheduled water changes.

Re: Victor running underwater!
 

I was lucky Al, I got to work on installing satellite ground stations after the cryogenic cooled receivers and water cooled transmitters had run their course....

Re: Victor running underwater!
 

The Victor is sealed in Max GFE A/B epoxy from Polymer Composites, Inc. It has a thermal conductivity of 0.682 W/mK, which is about the same as a thermal grease like Wakefield 120 (0.735 W/mK).

Here's the closest thing I can find to an online datasheet for this product:

http://cgi.cafr.ebay.ca/EPOXY-RESIN-...7 C240%3A1318

It also provides information on their recommended mixing and casting procedures.

Re: Victor running underwater!
 

Thanks Karen!

Re: Victor running underwater!
 

*sigh* I thought I sounded intelligent...*sigh*

Re: Victor running underwater!
 

That's hard to do in a thread where Al says something :)

Re: Victor running underwater!
 

*sigh* I thought I sounded intelligent...*sigh*

A few years back when they made me a manager and the radar guys said they needed some deionized water for the transmitter tube, I had never heard of the stuff. They said to make sure it was reagent grade.
Boy did I have a hard time finding that stuff! Now I know why.

Re: Victor running underwater!
 

You are!!!! People like you are my heros.

Re: Victor running underwater!
 

If you find the expansion / contraction to be an issue, another option is to pot the power devices with a layer of a thermally conductive RTV to provide a "cushion" layer between the packages and the epoxy. We use a material from NuSil at work that has a thermal conductivity of 0.81 W/mK to bond high power RF terminations to mounting surfaces. This is for a vacuum application where there is no other way to get the heat out besides conduction. The part number we use is CV-2960. I doubt it is cheap, but you could probably talk to them and get them to sample you enough to coat several units.

Re: Victor running underwater!
 

I think it would be to your advantage to reduce the amount of potting material you use, for both cost and thermal reasons. Perhaps place a few inserts in your mold?


As a point of reference, Aluminum is about 250 W/mK and stationary water is about 0.58W/mK.

Re: Victor running underwater!
 

It's been a few years since I opened up a victor, but I recall that they have an optical isolation on the PWM input from the controller.

Is it safe to assume that thats accomplished with a 'closed' unit, and there are no concerns about getting something opaque in there?

Re: Victor running underwater!
 

Andy,
Yes, that is a sealed opto-isolator, one of the 4N series as I remember.

Re: Victor running underwater!
 

The optical isolation is accomplished within the confines of a single component on the board. There is no risk of getting something opaque in the way unless they break open that chip.

If you do break a victor open and take a look, it is the tall-ish 4 or 6 pin* device near the connector.


* (I can't remember: Only 4 pins are used, but often these devices are in a 6-er to match the 5-pin devices in the family.)

Re: Victor running underwater!
 

If you want to go with high current, you will need some sort of heatsink. Probably the easiest is to solder some copper tubes coming off the metal transistor tabs on the Victor that poke out of the compound. Why use a 40A speed controller if you're never going to pull it? I think this is eluding to a new possible design from these guys ;)

Re: Victor running underwater!
 

Jesse,
Everyone needs to remember that the tabs on the FETs in any controller are at different potentials depending on the operation of the controller. Any heatsink needs to be insulated from the FETs.

Re: Victor running underwater!
 

I was going under the assumption that the copper tubes wouldn't touch each other, though I also didn't realize the tabs actually carry current. Good spot.