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ssassen

Lawmate 100mW Tx modifications

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Okay, so I ordered a 200mW Lawmate a while ago, decided to test it out today. So I shrinkwrapped it like I normally would and put in on the test bench to see how it would fare. I normally do this with any electronics I use for RC, so I can find any faults, issues, or problems on the ground, prior to taking off, rather than in air.

To my surprise the 200mW gave up on me after running continuesly for about 45-mins being fed an image from my backyard using a KX-131. At first sight it was a thermal overload (runaway) that killed it, and after opening it up that was clearly what has happended. In the air you normally would have an airflow over it, so it'll get better cooling, but still.

Modified Lawmate 100mW Tx with SMA connector installed

12116.jpg

12117.jpg

So I decided to just junk it, as I opened it up anyway, but first use some of the parts for a new 100mW Lawmate Tx I had laying around who's antenna didn't really impress me that much anyway. So I took the SMA connector from the 200mW module and mounted it on the 100mW. After a quick checkup and installing a 3dBi whip antenna it has now been running for the past four hours without a hitch, excellent!

Cheers,

Sander

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Wrapping it in shrink wrap is a bad idea, it acts as insulation and traps the heat in the case. I am not suprised that it burnt up on you...

Running a Transmitter without a heatsink is bad enough, running it wrapped up with no airflow is almost assured to destroy it. Airflow makes all the difference, if it were on an airplane, and not very badly abused, it would have probably lasted you for years.

JetPilot

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Jetpilot,

I'm going to respectfully disagree. These modules are not meant for FPV excusively, they are marketed and sold as a solution for wireless A/V transmission. Normally these would be built into equipment having no airflow whatsoever, for example in tightly packed baby monitors and such.

Furthermore, the Lawmate modules seem to be the only ones having these thermal problems, I'm currently using Airwave and even their 500mW module doesn't even get warm to the touch when shrinkwrapped and tested on the bench with no airflow.

As an MSEE I can only conclude that there's a impedance mismatch somewhere, or the output stage of the Lawmate modules is not performing as efficient as you'd like, hence a lot of power is wasted simply as heat.

Saying that airflow is a requirement is simply encouraging the existence of products that apparantly have a few kinks to be ironed out still to remain on the market. As an engineer I frown upon that, that's just silly, other products from a different manufacturer do not have these drawbacks.

Cheers,

Sander.

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Well I agree with JP that heatshrink is not always a good thing, its a good idea to see how hot something runs at before putting it in heatshrink. I also found that the Airwave 500 did run very hot when I tested it.

But I also agree with Sander that any of these modules should run ok just in free air. At the end of the day it was wise to bench test before flight !

Terry

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I'd put a bet for a faulty unit. Mine is also shrinkwrapped, but even worse it has a 5V Vreg soldered on the case, that I power off a 3s lipo, as an extra heat source.

Works fine on the bench, running at ~50-60°C.

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I'd put a bet for a faulty unit.

Yeah, very likely, I'm not going to order another though to find out B)

Cheers,

Sander.

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Well, I'd have returned it in the first place ;)

With heatshrink:

post-2-1197154688_thumb.jpg

Edited by Kilrah

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Sorry, I was talking about your 10mW lightweight setup you use on the zoomzoom, where you have the transmitter and regulator attached to the back of the camera. I didn't make it clear which one I was talking about.

I think it's similar to ssassen's setup here: http://www.rc-cam.com/forum/index.php?showtopic=2389 Except that you also use a regulator so you can run it off of a 2 cell lipo.

Edited by twinturbostang

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Oh, nothing special then. Everything just holds with a bit of shrink tubing.

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Everything's just connected by wires. Everything can move, and is held together by the shrink tubing.

The wires from the TX, camera and power cable all join on the reg, if you wish.

Edited by Kilrah

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