HTech Skis

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holmtech
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HTech Skis

Post by holmtech » Sun Jan 06, 2013 9:09 pm

So I just pressed my 2nd pair of skis. It's about time I started a progress post.

Here are the pics to catch up:

First the press...
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12" beams W12X26, C5X6.7 on the supports. I've got plans to reconfigure the supports so that I can widen the side load area by about 4 inches.

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All sealed up. I tested it the next day. At 75 psi it dropped only 2 psi over night.

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No ramp, but this controller seems to work well. MyPin off of Ebay. I may eventually end up upgrading. For now I'm only heating from the bottom.

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Molds ends ready to cut out.

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Molds and cat track setup. 3/4" steel stock on the cat track.

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Inside of the tool box electrical cabinet.

I'll post the first skis next...

holmtech
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First Skis

Post by holmtech » Sun Jan 06, 2013 10:40 pm

The first set of skis:
188 cm, 142-112-134 20.7 meter turning radius
Bamboo core/sidewall
19oz triax top and bottom
3in strip of 4.5oz carbon top and bottom
bamboo veneer top sheet


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Out of the press

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The main challenge I had was that I ordered my heat blanket from MEC too short for the skis. I was probably thinking that I don't want the blanket burning up if it is sticking out, so better to be a bit short and the skis will still be hot. Not so much. I cut the flash off and immediately saw that both ends of each ski were delaminating. There may have been a couple of causes, lack of heat, and I think there was too much space for the fire hose and the ends had a lot of pressure.

I ramped up 120 degrees for 15 minutes, 140 for 15 minutes, 160 for fifteen minutes, and 180 for twenty. We also heated up the steel cat track ahead of time and had the top cassette right against the cat track. With a flat mold the skis came out with a millimeter or two of weak camber. After skiing them one or two days there is no camber. They're dead flat.

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Cleaned up and a coat of urethane. I'll add a couple more coats later, but I was anxious to mount and ski them and didn't want to wait for multiple coats to dry.

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Photo shoot in the bamboo behind my garage.

holmtech
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Post by holmtech » Mon Jan 07, 2013 12:07 am

So pressing two sets of skis I am 2 for 2 in burning out solid state relays.

Here's my setup:
Heat blanket: 220V, 3000watts
Controller: TA4-SNR, control output 0-10V DC
SSR: 25A, 380V, control 3-32V DC. Mounted on 40A heat sink.
Contactor: 25A, 240V.

I figure that the blanket is only pulling around 13.6 amps (3000 watts/ 220V), so everything should be good here. The trouble is that each time I have pressed, about 15 minutes in the SSR will burn out. Fortunately it burns out in a manner that it is stuck on (stuck closed). I can then just use the switch that I have hooked up with the contactor to turn the blanket on and off, while the controller then is just a thermometer readout, so at least I don't burn my skis up.

This is the relay I am using http://www.ebay.com/itm/SSR-25-DA-Solid ... 337e071b51

I know it's cheap, but I would expect that if it meets the rating (by a factor of two) that it should be OK.

Is anyone else using this relay? And or having similar relay problems? I'm tempted to try the 40A and see if I have better luck.

I'll sketch up a wiring diagram of how i have it setup if anyone is curious. It's pretty basic though.

skidesmond
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Post by skidesmond » Mon Jan 07, 2013 4:41 am

Beautiful skis and a full edge wrap too! Can't help you w/ the electronics.

Jekul
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Post by Jekul » Mon Jan 07, 2013 8:24 am

I use the same relay and have had a similar issue.

My cause was pretty simple: My heating blanket was shorting out when I inflated my air bladder. I did it twice before I figured it out, but since then I've succesfully pressed ~8 pairs since without issue.

holmtech
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Post by holmtech » Mon Jan 07, 2013 9:57 am

Thanks skidesmond. Yeah, I figured with the first pair that I would be happy if they either looked good or skided good. Though there are some obvious adjustments I need to make to the flex (too stiff of a tail and the stiffness tapers off too quickly at the tips) they ski pretty well too.

I'm glad I did the full wrap, but I'm not sure I'll do it again soon. Wow what a pain.

Jekul, thanks. I may have had the same issue. I'm not sure exactly when the first press zapped the relay, but when I pulled the skis from the press I realized that the blanket wires were nicked. I think as we were pulling the cassette out they got hit, but it could have been earlier. So I had a splice, and about 15 minutes into the 2nd press the pressure of the bladder pulled the splice apart. Pop-Zap! And we had to decompress, pull the skis out fix the wire and back into the press. That's probably when the 2nd relay zapped. I think I'm safest to keep the power wire coming out the side below the cat track. There's usually a gap there since the blanket is thick at that point. I wish I had them build the blanket with the wire coming out the side.

I may go with a 40A relay this next time just to be safe. 3x overkill on the amperage. I'm not sure if there's a down side to this. At least these relays are not too expensive.

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MontuckyMadman
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Post by MontuckyMadman » Mon Jan 07, 2013 5:20 pm

shouldnt you have a fuse in there to prevent burning out the SSR?
sammer wrote: I'm still a tang on top guy.

holmtech
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Post by holmtech » Mon Jan 07, 2013 5:44 pm

Yes, I have got a fuse between the SSR and the blanket. Perhaps since I'm running 220V I should have both leads fused... seems like overkill, but it wouldn't hurt I guess. The fuse that's in there didn't pop. It's either a 15 or 20 amp ceramic fuse.

Jekul
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Post by Jekul » Mon Jan 07, 2013 6:32 pm

I'm certainly no EE, but I think it depends on the breaker/fuse type. Slow blow/ quick blow, time delay...

In either case both lines should be fused/run through a breaker.

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MontuckyMadman
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Post by MontuckyMadman » Mon Jan 07, 2013 7:42 pm

Re: delam?
Looks your useing entropy.
I would cook for 30 min minimum at 180.
Get to temp asap
Let cool a bit maybe to 160 them pull. Post cure for at least a few days before flashing.
sammer wrote: I'm still a tang on top guy.

holmtech
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Post by holmtech » Mon Jan 07, 2013 8:00 pm

Thanks for the tips MM. Yes, using entropy CPM. Which reminds me, I need to bring them back in the house for warm keeping...

I'll try the next ski right to 180. The 3,000 watt blanket seems to get the job done pretty quickly. Hopefully that will give some camber. I cooked a pair this weekend, and ran 120 for 20 minutes and then right to 180 for about 35 min. These don't seem to have much camber either but they're still not flashed. It looks like maybe a millimeter or two. I'll see better after cutting them out tomorrow.

After the next pair, if I don't get decent camber going strait to 180, then I'll just camber the mold.

holmtech
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Post by holmtech » Mon Jan 07, 2013 8:08 pm

MontuckyMadman wrote:Re: delam?
The first ones delamed because my blanket didn't make it to the ends. Stupid me on ordering a short heat blanket. Not the best style, but on this Saturday's cook I cooked it with the blanket running just past the tails of the skis, then decompressed, moved the blanket to the tips and reinflated and turned the heat back on. It was actually closer to 40 minutes total at 180. Kind of a disaster but it worked.

Considering the cost of a new heat blanket, I'm considering ordering a second short blanket at the same wattage per square inch that I could put end to end with my current blanket. Gheto but it will keep me from having to deflate mid press.

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FigmentOriginal
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Post by FigmentOriginal » Tue Jan 08, 2013 8:35 am

Have you looked into making your own heat blanket? You can make your own for about 1/2 the price. Requires some math but its pretty straightforward.

http://www.skibuilders.com/phpBB2/viewt ... c&start=30
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chrismp
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Post by chrismp » Tue Jan 08, 2013 9:29 am

or have one custom built by the user "troublemaker". he seems to build quality blankets at an affordable price.

holmtech
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Post by holmtech » Sun Mar 03, 2013 12:05 am

So a few catch up items. I replaced my last blown 25 amp SSR with a 40 amp SSR. I've pressed two pair of skis since and not only is the SSR going strong, but it seems the better SSR is allowing the PID to keep a more steady temp.

I'm not sure if the 25 amp SSRs were too small (although only pulling around 12.5 amps) or if 25 amp was fine but I just got two bad relays. Fortunately they're not too costly.

The last pair of skis to come out of the press (still bottom heat only) I heated strait to 180 degrees. Full power 3000 watts. These still have negligible camber. I haven't cut them out and put them base to base yet, but they look like they're 2 -3 mm at best. I do use a sheet of hard board between the cassette and the cat track to keep the cat tract from acting as a heat sink. I'm probably going to keep heating from the bottom, but camber the mold to get a bit more camber. No more delams though.

FigmentOriginal, I read through that entire post today. Great stuff. I may end up going with something similar to what MontuckeyMadman built. Side note, I am no fan of the wire that MEI used on my heat blanket. White stuff with thick insulation and some sort of fiber woven reinforcement. The sheath is brittle, and the core is made of just a few strands of brittle wire. Needless to say I've patched it a few times already. A side exit versus end exit for the power leads would have been much better.

Here's a shot of the skis I was working on today. Ladies powder board.

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