FET problem in my MR02

[HACHI-RYOKU]

Hey all. Long time no see. I’ve been around though. Just been a ghost. Anyway,

I’ve had some problems trying to get a 3 X 2 stack of 7317 fets in the MR02. That stupid black block box is right in the way, so it?s hard to see, much less solder. I think I’m not getting good connection on the fet next to the black box.

I may have shorted something out to begin with. The first time I turned it on, I was using a metal clamp to hold the PCB. That’s one of the dumber things I’ve done, but I did it. I think it was touching Vcc and Grnd at the same time. Everything got pretty warm before I realized what I did, but I unclamped it and turned it off quickly. I think I still managed to fry something, because now I have this problem.

When I put the batteries in that fet stack heats up. It actually blew the fets the first time. But, a single stack of fets works just fine. I resoldered some new fet stacks and it started doing it again. I just put the last battery in for a second or so and felt the fets. The fets closest to the black box are still getting warm with the batteries in. Mind you, the car is turned off during this.

Is this a problem with the PCB or do I just need to get better connection with the fets to the board?

[rcs2die4]

Hey 86,

Only a better connection is needed…..

Make sure that the rows of pins that are closest to the black box are the pins closest to the dot that marks pin 1 on top of the fet !! The dot should be above the top left row of pins

Make sure that the 4 rows of pins (top to bottom) in each stack arenot sorted between each other (left to right) .. make sure that all the pins in each row are connected to each other properly so it makes a continuousline top to bottom… I test each row top to bottomwith my multi meter (I build the stack out of the car then solder it to the board !!!)

Thepins that have to remain in rowsare the pins closest to the black box…

All of the pins on the rear(closest to the connectors where the motor wires go) of each stack canbe soldered together,ie: solder every single pin on the rear oftheleft stack to each other then solder every pin on the rear of theright stack to each other…. then solder each stack to the board…

Make sure all of the bottom 8 pins are connected to the pads on PCB correctly in both stacks… If you have the connections dont right, it will not get hot!!If just one pin is not done right the fets will ! get hot ….

Hope that makes sense!!! let us know how you go….

Edited by – rcs2die4 on 04 January 2006 05:37:06

Edited by – rcs2die4 on 04 January 2006 05:40:35

[HACHI-RYOKU]

Thanx RC. The input is very much appreciated and makes sence. Been kinda busy with work and the wife. I will get this hooked up soon and let you know.

[HACHI-RYOKU]

Got it all worked out……..I think.

I’m running a plasma-atomic with neo mags in it. The speed of this thing is rediculous. This is my first mini-z. I was already impressed by it’s performance stock. Now with the 2X3 stack of 7317’s and the plasma-atomic, I’m floored. I use to be so proud of being able to get my gen 1 Xmod to keep pace with my near stock Xmod EVO. Now I don’t know if I’ll ever buy another Xmod.

Anyway, I did have a bit of a problem. While I was running it (for about 5 minutes), it seemed to get a mind of it’s own and ran into a curb. After that it wouldn’t respond. So, I shut it all off and pulled out the batteries. Checked everything inside, but it was all OK. I put the batteries back in and the motor started going while the car was turned off but the fets weren’t getting warm. So, I checked it all again, but everything was fine. Fets and all. I took a break, came back after a bit, put some fresh batteries in and it returned to normal. No problems. I suspect some radio interference, but am not certain as that would not explain the motor running while the car was turned off. I’m kinda clueless to what happened, but I am still enjoying the car. Nothing else has gone wrong.

Anyhow, here’s some pics of the PCB and the car;

[ph2t]

Hey Hachi, good to see you’re still around bud. Just some tips with mini-zs.

Always turn on the TX first.

Never leave batts in the mini-z, even with it off. Technically the fets are not swtiched off. whilst this ain’t a huige issue, it’s good to play it safe.

IF you’re runing this baby primarily on concrete then you need better tyres, especially with the setup you have. Get a set of 11mm Gandini racing foams from the ausmicro shop. Aaron is the only one that stocks the FULL LINE of Gandini pre-mounted foams. Trust me, get them and a set of 30-40 deg 8mm slicks for the front end and your handling on concrete will be excellent. Trust me, betty and I did this and have not looked back ever since!

Get a good ball diff. This will help you control that bugger in corners.

I would keep the gearing on the low side with the plasmatomic. Seems to work best in that setup for tight tracks.

Striaghten that antenna! lol. A good antenna is always right angled to the ground. Put some heatshrink tubing around the firs 6-8cm of it to ensure it doesn’t short out against the motor wires / motor.

Get an oil shock. A must for concrete racing. You don’t need a tricky sway bar / shock setup. Just an oil shock and a good CF h-plate. 3 racing make some of the best cf hplates.

cheers, good to see you’ve finally taken the pluge and got a *cough* real *cough* 1:28 scale racer, lol….

ph2t.

[HACHI-RYOKU]

Gandini soft foams, ball diff, bearings and oil shock already ordered. That, and some fets for the Xmod Evo. All from Ausmicro.

A9 tooth pinion is considered low right? It’s the largest stock, but I’ve seen larger.

Antenna straightened. I was enjoying the sweapt look.

You’re not kidding about the ‘real 1:28 scale racer’. I had planned on getting a mini-z first, but a sale on Gen1 Xmods ($25) made me get one of them first. Then I had to wait cause I knew my wife was gonna get me one for Xmas. She also picked me up a Xmod EVO. So now I’ve got one of each. The mini-z blows the Xmods away in speed and control. It’s on a completely different level.

Thanx for the tips. I’ll be doing most of my racing on a waxed clinic floor. Pretty smooth surface. I’m hoping the gandini soft foams will work well on that. I picked up some GPM rubber tires because they were easily attainable. The GPM tires blow nuts. Their 8 degs areabout as stickyas the stock mini-z tires. In fact, I picked up some 8, 15 and 35 degs. They were all pretty much the same. I’ll be using this a little on the road. Mostly for testing purposes. And I would like to take it down to the LHS were they race on Sat. The track there is carpet with a huge straight away. Not a small track. It was made for 1/10. Requires foams though.

[HACHI-RYOKU]

Blew those damn fets today after running it pretty hard for about 1 1/2 hours. The forward fets are crispy critters now. I think the fets are in a bad position. They are too close to the batteries and closed in. They can’t be getting good airflow or anything there. Heat probably builds up easily. Anybody have their PCB’s positioned differently to offer a better position for the fets. Probably should have given them a rest.

Thankfully, it looks like everything else is ok.

Oh, on a side note. The gandinis are awesome. The iwaver ball diff and the oil shocks are very good too.

[rcs2die4]

Hey 86,

I have a stack in my 02 andit’s all sweet !! mine is 3×2 as well but you have better fets..

my fets donteven get remotely hot !! but,I have cut the hole where they sit a little bigger and

I also stacked my fets on a little bit of an angle towards the middle of the PCB…

Maybe the fetsare touching the batteries !!!!

[HACHI-RYOKU]

They”re a few mm away from the batts. Maybe I”ll wire it or just get an external board.

I’m also kinda wondering if there is a different problem. Most of the wires close to the fets melted a little. I’m wondering if some wires melted together and shorted. I still need to give it a thorough inspection.

Edited by – HACHI-RYOKU on 12 January 2006 14:37:23

[HACHI-RYOKU]

Well, got some new fets in there. Running good again. I took a good look at my blown fets and it looks like the top fet’s pin # 2 on the fets next to the black box wasn’t touching the pin below it very well. I guess it was just sloppy soldering on my part. I picked up an $8, 15 watt iron from rat-shack, which was alot easier to work with than my 30~80 watt butane iron. I took my sweet time and made sure to get them all connected correctly. I put one on at a time and tested it with a volts meter after each one. Now it’s back in the game.

Allready broke of a little bit of the body on the front. Oh-well, what’s a good car without some battle scars, right? This is actually my beat-up body. I picked up a green Takata Dome with the set originally, but I couldn’t bring myself to beat the piss out of that one. I’ll probably do some body work to this one and give it a fresh coat of paint soon to spiff it up some.

Can’t comment enough on those Gandini foams though. Those things rock and there not even getting worn down yet. I don’t like blowing that much dough on tires, but they are worth every penny. I would recomend the soft foams in the back and the medium or hard foams in the front. It makes a little understeer, but it’s better than flipping. This setup is still better than the other tires I’ve tried. You were right PH2T, I’ll never look back. The oil shock is also a must in my opinion.

[Aaron]

Glad to hear the Gandini Foams are doing the trick. And that the FETs are back in and running good 🙂

A.

--
Site Owner Guy.

[betty.k]

and we have another conversion! praise da lord!!:D :8ball:

[HACHI-RYOKU]

You guys are gonna laugh at me.

I put some fets in a Xmod evo. A stack of 2X3. I’m running a plasma-atomic with neo mags in it. The fets get hot. It doesn’t blow the fets, but at one point it melted the solder on some of the fet’s pins and it shorted out with the pin next to it when I slammed into a table leg. This was all on the output side of the 9910’s. The fets didn’t blow. They wanted to but the batteries were running out of juice and I caught the problem early. I fixed it and it’s running like it was before. It still gets hot around that area though, so I lifted the metal motor contacts that touch the top of the fets. I figured that if they are getting hot, then they’re just contributing to the problem. I also replaced the motor wire with longer and thicker wire. The area is still getting hot though. Otherwise the car is fast as hell. It’s AWD and it has the highest stock gear set.

Anybody have any essay on this? I was thinking I might need to reduce the gear ratio……maybe? Anybody else getting this problem?

I’m starting to grow tires of fet stacks. The only ones I haven’t had any problems with in a 1:28 scale car are the ones in my Gen 1. Sad, but true.

[Author]

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