IRF7317 mosfets from the shop, a little review….

[ph2t]

I got some of those new IRF7317 mosfets from the ausmicro.com shop and I decided to try them out. I hadn t done a mosfet stack in a while and I wanted to get back to my roots, lol….

They come in a pack of ten, I decided to test them as I did each layer to see how they stood up to the attention of my beast motor, the ATOMIC/Plasma dash hybrid with neo magnets and running at 15t MRS4 alloy pinion.

So I soldered on one layer and tested it, the car is off the ground with the rear end afloat, I call this my no load test, :). Punching full throttle, after about 0.3 of a second the mosfets would get way too hot and scorch my fingers! ouch! Clearly I need to stack another layer to be able to just handle the no load current.

With a 2×2 stack now happening I tested again. Now the mosfets handle full throttle under no load quite well. They wouldn t get warmer than room temperature when running at full speed. The transient times though when I was going from full fwd to full rev (or full throttle ) from a stop would cause the mosfets to get hot quickly and then cool down slowly. This I noted. I then put the chassis on the tamiya speed checker and slightly forced down on the chassis to increase the load. Now the mosfets got quite warm to hot and would stay like that. I think under this situation a few good runs on some really punchy batteries would possibly blow the 2×2 stack.

So in the end I added another stack of mosfets, now it s a 3×2 stack and due to this the temperature of the mosfets on average is lower. I still get “heat peaks” when going from full throttle fwd to full throttle reverse but now it s contained better and the mosfets cool down faster after going through this transistion… I tested it again in the tamiya speed checker and now the mosfets stayed at a more stable temperature and wouldn t increase in temperature greatly when I applied a load onto the chassis.

It s with the 3×2 stack that I felt confident enough to take the chassis for an actual spin. She didn t dissapoint! Throttle response is strong and solid. I could coast into corners yet still have enough torque to power out of the corners (yes, even with a 15t pinion! gotta love this motor combo! 🙂 )

Top speed is insane!!! On the speed checker I m getting 62kph!!!! (yes, that s with the SLOWER neo magnets and only 4 cells too!!!)

These are great mosfets!! You can rest assured that a 3×2 stack of these mosfets will take any hot 130 sized motor out there, period. Hell if it can handle a plasma dash armature (27t), then it can handle anything…..

Here s how they look installed on my IW-02 chassis….

I placed some glue in between each stack as I did them to hold the upper mosfet in place. I also used some long nose pliers to bend the pins on the mosfets SO-8 package inward to make a better connection onto the pins of the mosfet below it.

For the 3×2 stack you need to cut out a hole in the PCB cover.

Fit s like a charm. 🙂

Note: You CAN go higher in the mosfet stack. The pack of 10 I got from ausmicro is enough to do a kick butt 5×2 stack!! But then the mosfets will protrude even higher fromt the chassis.

If you want to put in a roll shock set (and what racer doesn t!!) then your limited to a 3×2 stack since it mounts flush to the top surface, see below.

So if nelly ain t your cup of tea then seriously go these mosfets from http://shop.ausmicro.net The pricing is excellent and they are performance wise on par with the Si4562 mosfets….

Cheers,

ph2t.

Edited by – ph2t on 20 December 2004 21:54:27

[icebreaka]

Great review..! Very helpful to me!

It’s about time I change the fets on my Z.. Problem is, I’ve been looking around for a tutorial on FET upgrades with no success… Anyone got a link or tutorial with pics? 😀

The ebay ad for these fets says to look in tinyrc.com or ausmicro.com .. haha and thats where i’ve looked and i can’t find nothing! hehe sorry Aaron!

Some help please 😀

[icebreaka]

Can i get a pic of the other side of the fets please? So i can see how to solder the other side..

Thanks

[snailpace]

icebreaka, i’ve done a similar setup to ph2t on my iWaver02 with 7389’s with the same 3×2 stake configuration. Sorry i can’t pictures but on the other side of the FET stack you can just solder all the pins together (on each vertical stack). If you look carefully at the solder tracks on the PCB, they are common rail.

This is what i’ve done and it works fine, good also in a structural way, keeps the stack nice and strong.

Definitely need to cut out the chassic, i didn’t do this originally, having to really push the chassis cover down tight. After a few runs the plastic started to warp and melt. Suppose in a way makes the cooling of the FETs more effective.

[snailpace]

Sorry about the poor grammar guys, too many Christmas parties and drinking! :dead:

[kitsune]

Great … now I need to do even more work on frankie :smiley2: … 62 on 4 cells I wonder what I’ll get, Thanks for a great review, unfortunately it sounds like they won’t be suitable for F1’s 3×2 may be a bit big … I might need to look into some sort of heat sink arrangement.

[Aaron]

A couple of tips too:

On the drain side (motor terminal) of the stack use solder to ‘bridge’ the 4 legs, into two thicker more solid legs! This has two benefits, it’s a bit physically stronger and it does have a reasonable amount of heat-sinking improvement.

Also if you’re really keen like ph2t is you could possibly mount a heatsink (using a non-conductive glue) to the top of the stack, just don’t bridge the legs, it does wonders for heat management.

Lastly, The stock of IRF7317s we just sold out of was the last reasonably priced supply in Australia. We’re chasing more but there may be a slight price rise, up to the IRF7389 pack ($25) level to counter this.

A.

--
Site Owner Guy.

[kitsune]

Now I’m reallu regretting only asking for one lot 🙁 Ahh well It’ll give me time to experiment

[mocky]

u should as some thermal paste like ARCTIC SILVER 5 THERMAL COMPOUND auspcmarket.com.au or thermal expoxy. like the stuff they use on cpus and then at the top buy a small heatsink voila effective coolin.

[kitsune]

frankie’s rebuilt 🙂 tho going quite a bit slower now, though that may be due to nearly flat batteries, I’ve realised I’ve replaced so much of frankie that I have enough bits to do a whole new Iwaver, minus pcb + controller,

once I charge up the batts it’ll be interesting to see how it performs. at the mo it has a 3×2 stack of 7317’s, before it was a pair of 7839’s stacked on top of the original Iwaver fets.

the 7317’s are cold to the touch at the mo, I’ll let you guys know how things stand once I use a fully charged batt.

[jamiekulhanek]

Heres my tips,

1). Build the FET stacks first, use a poly cement to hold them together.

2). Carefully clamp them in a vice, but GENTLY, you only want them just being held.

3). On the output side, carefully bend each pin down flat on the side of the stack, then tin all the output pins

4). useing a couple of pieces of solder wick, lay them over the output pins and solder them on, this makes a nice big thick layer of metal which will have some heatsinking abilities.
BE VERY CAREFUL YOU DO NOT OVERHEAT THE FETS, make sure you do not apply the iron for more than about 6 seconds when the fets are at room temperature.

5). Flip the FET stack around, and bend all the input pins back as in step 3. Strip some copper wire at least 10cm long. Take one strand and lay it over each vertical row of input pins (top to bottom) and wrap it around the FET stack to hold. This will make it very hard to make a dry (non conductive) joint and will make the whole row of pins thicker and less resistive. Cut the excess wire wrapped around the stack off, check for bridged tracks…

6). Finally, snip off the excess overhang of solder wick from the output side of the fets..

It’s a good idea to lay 2 pieces of wire strand on the Vcc and GND pins, this will make them thicker and have less resistance again.

[icebreaka]

damn i wish i understood that :S

i got lost afta step 3… any pics? blackeye:

[jamiekulhanek]

I can install FETs for a small charge if you would like…

[Aaron]

After exhausting opportunities to get more IRF7317 in stick within Australia through Australian distributers (meaning 6+ weeks) We’ve bitten bullet and ordered direct from IRF (Manufacturer) Stock should arrive in 7-10 days.

A.

--
Site Owner Guy.

[icebreaka]

hmm .. i might take up that offer if i get desperate.. I’m just lost with the solderwick bit.. whats solderwick?

[Author]

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