Mosfet Triggers

http://extreme-fire.com sells a very nice MOSFET trigger kit

One

As someone that is an Electrical Engineer and has built and installed some 20+ of these units, here is the skinny.

First, what the MOSFET isn’t:
- It isn’t a router.
- It isn’t a fuse.
- It doesn’t replace the contacts
- It doesn’t replace anything in the trigger group.
- It isn’t a buffer.

Then we can address what the MOSFET does do for the system:
The MOSFET is a solid state switch, nothing more nothing less. All it does is allow current to pass through it or stop current from passing through it.

Ok, so how does this help with an AEG…?

The contact plates (the little fingers of copper) in the switch is where the power to drive the motor runs though. These fingers have the other component of the switch short across them to make the motor turn. The motor is a high current device and when you release the switch, and the contact is broken, the motor becomes a huge generator for a few microseconds. That causes what is called Back EMF Pulse. This current is huge and wants to make the motor continue, which in essence causes a huge arc of current. This is what is eating the contacts in the normal switch.

What the design of the MOSFET switch does is remove the arcing of the current from the Back EMF Pulse, by cutting the current via electron buildup and not severing a circuit.

Why should I care what the MOSFET does? The current switch mechanism in your AEG will have to remain (or some have done some pretty replacements) because you will still need a physical switch to activate the MOSFET's Gate. When the Gate is un-energized it will have a buildup of electrons on the surface of the semiconductor, which will make it impossible to have nearly any current flow through the device.

When you energize the Gate, it removes the buildup and allows HUGE volumes of current to pass with very little resistance.

How does this help with the carbon deposition on the switch plates…? Well, normally you pass some 30amps of current, and peak spikes that are WAY more than that through those plates with every pull of the trigger. With the MOSFET, you will pass milliamps (0.001 Amps) of current through those same plates. That level of current and the design of the MOSFET which removes ANY Back EMF Pulse from hitting the switch plates and you will never have the same issue with carbon buildup on the plates.

As for any additional benefits…

Well, I have seen a level of ROF increase due to the MOSFETs. But, I will be honest, a ROF of the stock gun at say 300 would move to a 310 RPM. So, it isn’t a big increase as that is only 3%. And that is the best increase that I have seen.

As for the AEG being more responsive… Yes, that does happen, it is the MOSFETs ability to carry the current and that does have some responsive quality. Though I cannot document it, but only anecdotal observation over the installations I have done. I attribute it to the loss of the minute resistance of the physical switch, though that clearly is not much of a resistance in the first place.

Is a MOSFET for everyone? No, because there is additional circuitry in your AEG, if that gets shorted, the system will go full auto with no way to stop it, short of unplugging the battery. If it were to fail in a short circuit mode, and that would be dangerous to the players as you would have no control of the AEG.

Further, it builds up heat quick, so you will need to have some way to get the heat out of the system, which will require a heat sink of some sort. And that will have to placed somewhere in the wiring compartments, which aren’t really all that big in the first place.

Thread 2

Advance Tech II: Solid State Switching with MOSFETs
« on: May 10, 2005, 01:51:16 PM »

Feel free to leave any questions, comments or suggestions regarding this article.
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Advance Tech II: Solid State Switching with MOSFETs
« Reply #1 on: May 10, 2005, 05:20:04 PM »

That is a very detailed and informative article. I just want to mention a few corrections.

On page 3, the site that you linked is actually called "Gunsmith Engineer," and http://gungineer.cande.biz/ is its main page. Also on page 7, the Filipino airsoft community did not come up with the resistor values. They acquired those values from the Japanese sites. Specifically http://www.interq.or.jp/tokyo/akishino/factory/FET%20SWD/fet.htm on a site called "Kiss in the Dark," the original link in the forum thread was broken due to the site owner rearranging the layouts.

Regarding the heat issue with FETs, attaching a small heatsink easily solves the problem. I just cut up a low profile heatsink into the appropriate size for the FET, then used thermal epoxy for attachment.

Most of the Japanese sites only showed the instructions without any detailed explanations. Your article is probably the first to go through the reasonings in clear and precise language. Keep up the great work. (On a side note, what's next?) lol
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Advance Tech II: Solid State Switching with MOSFETs
« Reply #2 on: May 10, 2005, 06:33:49 PM »

RiotSC is correct. FAS did not come up with the idea. Actually, I found the Japanese site at ASP last year when I asked posters to list links to Japanese airsoft websites. It was like a goldmine of airsoft technical information and DIY projects.

Did the MOSFET mod to all my guns as well as various other mods especially the anti wobble series on TM M16 family AEGS. Then somebody at FAS asked about Systema relay setup for the PSG1 and I mentioned the MOSFET mod and the rest is history.

You did good by soldering the components on to the PCB. My first one suffered a broken leg after a few battery changes in my SD5. Here's another suggestion for those of you with a few guns, try this setup;

AEG=====«====MOSFET====«=====battery pack.

'«' - any type of connector, maybe Deans; all my guns have Deans plug

This way you'll need just one for all your guns.

Landmine used IRF3703 while I used IRL1404. I think he mistyped in that thread and you used IRF3707. IRL 1404 has 4mOhm Rds while IRF3703 has 2.8mOhm. Pd is 200W and 230W respectively. Both of these should be able to handle any modified guns. Try them.

Very nice article!! Keep up the good work.

RiotSC- what's next you ask?…. Cheesy how about burst fire? Cool
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Advance Tech II: Solid State Switching with MOSFETs
« Reply #3 on: May 10, 2005, 07:03:59 PM »

Thanks for the corrections guys, I'll be adding your comments to the main article shortly. As for what's next, Johnyew is correct, I'm working on a burst fire project. Actually it's already done, but needs some fine tuning. The next review will most likely be a tightbore barrel comparison between the Prometheus, KM and Systema barrels, then the .20g Bio BB review, then the burst fire.

Thanks again for all the compliments,
Jay
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battery connectors
« Reply #4 on: May 14, 2005, 03:57:43 AM »

sup jay

i noticed that you were using old style tamiya battery plugs. pulling from my large collection of now useless RC knowledge, sermos power poles are nice low resistance connectors. the deans connectors mentioned earlier are an excellent choice as well. as you pull more amps from the batteries, those tamiya style connectors get hot and eventually "weld" themselves together with enough use. I'm sure mod'd airsoft guns out there will eventually or already have this problem.

this of course means you have to change all the plugs on your batteries, chargers, and guns. expensive, but worth the piece of mind.

since airsoftguns are mostly metal, i wonder if you could use the gun chassis to dissapate the heat of the FET. limitations would vary with each gun design, but it would solve the heat issue easily. of course, then you'll need to weather seal it…

-bum
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Advance Tech II: Solid State Switching with MOSFETs
« Reply #5 on: May 16, 2005, 05:21:47 AM »

love the explanations. thanks again jay! i've been useing the irl1404 for about a month with no failures. setup is 9.6 v 2.3 ahr, sp 140, super torque up gears.
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Advance Tech II: Solid State Switching with MOSFETs
« Reply #6 on: May 19, 2005, 11:24:24 AM »

I'm impressed by the approach you take towards your reviews/guides/articles. My father is a figure head in his science department, which means I'm emersed 24-7 in this type of quandry.

Just a few questions about the type of resistors to use for the solid state switch. The first is when I went to digikey to purchase the hardware, there was a vast selection of 30K Ohm resistors and 100 Ohm resistors. Unknowingly, I ordered the ceramic composite resistors. One of the specs recorded was .25W as the power? I didn't know what to make of it and thought I should order the highest power rating. Does the circuit take in consideration the W?

Second question is how hot does it really get. I was going to put it into my G3SAS and the only place to put it would be where the fuse box is located, which is a tight space. There is really no air movement back there.
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Advance Tech II: Solid State Switching with MOSFETs
« Reply #7 on: May 19, 2005, 11:52:32 AM »

Considering the relatively low current that's going through the gate, you should be fine with those resistors. If you are really worried about it, you can also wire several in parallel to increase the load capacity. I personally used a few of those .25W resistors in some of my setups without any noticeable adverse effects.

As for heat, my IRF3703 can beomce burning to the touch during prolonged automatic fire. Then again, I don't think most of you would use 14.4V (12 cell) packs. As long as you do short bursts, you should be fine. Do note that FET decreases in efficiency as it becomes hotter. You can find the temperature ratings in the spec sheets. To improve the situation, you can either attach a heatsink or use multiple FETs to spread the load. Check the bottom pics of the page http://takamiyama.com/fet.htm They should give you some ideas.
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Advance Tech II: Solid State Switching with MOSFETs
« Reply #8 on: May 19, 2005, 01:46:06 PM »

Thanks for the compliments Rickets.

RiotSC is correct. There is very little current running through the resistors in the circuit, so the wattage rating of the resistors does not come much into play. After prolonged bursts, my resistors were barely hot to the touch. The MOSFET however was a different matter. It became much too hot to touch with bare skin. Due to the lack of space in the rear of the G3SAS, you may want to investigate a different approach, such as attaching the MOSFET to the rear sling screw of the the SAS rear cap, from the inside. This effectively turns the entire metal rear cap into a heatsink, which should easily dissipate the excess heat.

On the subject of using multiple MOSFETs, it's interesting to note that Systema's 300% kit for the PSG1 uses precisely this approach, wiring 2 MOSFETs in parallel in an aluminum holding tube which serves as a heatsink. This arrangement doubles the current and power handling capacity of a single MOSFET, allowing them to employ cheaper components.

-Jay
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Re: battery connectors
« Reply #9 on: May 19, 2005, 01:52:42 PM »

Quote from: "Anonymous"
sup jay

i noticed that you were using old style tamiya battery plugs. pulling from my large collection of now useless RC knowledge, sermos power poles are nice low resistance connectors. the deans connectors mentioned earlier are an excellent choice as well. as you pull more amps from the batteries, those tamiya style connectors get hot and eventually "weld" themselves together with enough use. I'm sure mod'd airsoft guns out there will eventually or already have this problem.

this of course means you have to change all the plugs on your batteries, chargers, and guns. expensive, but worth the piece of mind.

since airsoftguns are mostly metal, i wonder if you could use the gun chassis to dissapate the heat of the FET. limitations would vary with each gun design, but it would solve the heat issue easily. of course, then you'll need to weather seal it…

-bum
non-airsoft poster
car and camera junky

Danny-

Yes the tamiya style connectors do have their drawbacks, and many people do switch to Dean's plugs when appropriate. For my custom wired VLTOR stock battery M4RIS, I switched to Dean's plugs just because there was no sense soldering back on the inferior tamiya plugs. As for using the gun itself as a heatsink, unfortunately most guns are made of plastic, although the mechbox itself is metal. I did consider using the metal mechbox as a heatsink, but there is some danger there as the mosfet metal heatsink attachment "tab" is also connected to the drain pin. This creates the potential for a short to occur with the rest of the wires that run inside the mechbox, if a break should occur.

PS. So when are you going to join the dark side and pick up an airsoft rifle? Trust me it's loads more fun than pink ball.

-Jay
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Advance Tech II: Solid State Switching with MOSFETs
« Reply #10 on: May 19, 2005, 03:47:11 PM »

Riot SC-
In that bottom picture, what's up w/ the bottom three setups? It almost seems that there's a computer in those wire looms! What other options are there interms of this circuit (I don't know lick about building electronic circuits and the such). Lastly, the way that system is layed out, the two dean connectors go straight from motor to battery and is there a small connector that goes to the switch (is that the white objects on the motor side of the harness).

Jay-
I have the slither stock on my g3sas and I'm running a LiPoly Battery from thunder power, so at full charge my voltage is around 12.5. There is only plastic back there, so if I run two mosfets then I will cut down on the heat. Is that right?
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Advance Tech II: Solid State Switching with MOSFETs
« Reply #11 on: May 19, 2005, 04:34:24 PM »

The bottom 3 are with speed controllers. The one with the toggle switch has the burst mode added. Regarding the wiring, the owner made such layout so he could share the units with different setups . Plus it would be easier to do any modifications to the circuits.

Total heat generation with 2 FETs will still be the same as that of 1 unit. Well, maybe slightly lower due to less energy wasted from heat build-up with the spread out load. The main difference is that you would have double the surface area to dissipate the heat. So the individual units would be cooler.
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Advance Tech II: Solid State Switching with MOSFETs
« Reply #12 on: May 19, 2005, 05:32:14 PM »

Oh, the burst mode would be w/ a capacitor in the gate side leaving the mosfet turned on for a period of time even though the trigger switch is open.

What's the purpose of a speed controller?
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Advance Tech II: Solid State Switching with MOSFETs
« Reply #13 on: May 19, 2005, 06:21:09 PM »

A speed controller does exactly what its name implies. Most ESCs (electronic speed controllers) use PWM (pulse-width modulation) to control the voltage to, in turn control the speed of, the motor. By using an ESC, you can adjust your system's rate of fire anywhere at or below the maximum achievable with a direct power feed. The main benefit is the overall system energy efficiency. Not only does the unit smooth out any ripples, it also removes the initial surge from motor start-up. You would end up with cooler motor and battery, similar effect to that of installing direct inline capacitor(s). The difference is that the pulses are now adjustable to suit different motors and to further improve efficiency.
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Advance Tech II: Solid State Switching with MOSFETs
« Reply #14 on: May 19, 2005, 07:32:41 PM »

I guess this question is just inevitable. Is there any way to get the schematics/ drawings for those speed controllers? If not, is there a source which I could get the specs?

Just by looking at the pictures, I can't desypher what is what.

If there are any other questions please feel free to comment or ask.

Thread 2

Hi,

I was wondering if there would be any interest in a Systema MOSFET Repair Kit sold by Extreme-Fire. It would fix these:

http://www.black-wolf.ru/makenotes/makenotes014.bwc It's the left button…

BTW - The black, red, and blue wiring diagram (second from the top) is all totally messed up there!! Forget you ever saw it!

The kit would have:
Two IRL1404ZPDF MOSFETs to replace the crappy RFP50N06 FETs.
Metric Allen wrench - I don't know the size?
2 feet of no-clean solder
Tooth picks
Instructions
New (30 Amp) fuse?
Anything else?
Maybe a big flashy EXTREME-FIRE sticker to put on the gun so all your friends will know that you have a "good" gun now Cheesy - Just joking Cyclops

With two of the mighty 1404Z FETs in it it would be a pretty good MOSFET switch again and would be vastly more resistant to failure. Of course you could replace it with the fabulous SW-AB-LONG Grin But a little repair kit would fix the Systema gun MOSFET up pretty easily with minimum effort. I think it would cost about $15. Soldering iron, wire cutter, and pliers would do it:

http://www.radioshack.com/product/index.jsp?productId=2062759

I have never actually seen on of these Systema switches, so if any one has an extra (or a broken one you want fixed) let me make you a deal Grin I need one to make the instruction pictures/video.

I am very interested in any comments!

BTW - Never run these with a low battery. - That is what kills them. If the gun does not fire when you pull the trigger, let go of the trigger right away! - The FET is frying if the motor is not turning.

BBTW - The fuse could go to 30 amps with the new FETs if that would help anything.

I am hoping the new Systema Revolution will not need this kit Cheesy

Gandolf
« Last Edit: March 29, 2008, 09:32:16 PM by Gandolf » Report to moderator Logged
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Re: Systema MOSFET Repair Kit
« Reply #1 on: March 30, 2008, 04:05:50 AM »
Reply with quoteQuote
Its been a while since I looked thru a Russian website, normally they are in English or German to me, thanks for the variety

and yes good idea there, my only question is that with the minimal cost difference, why use the crappy FET's?
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Re: Systema MOSFET Repair Kit
« Reply #2 on: March 30, 2008, 04:09:36 PM »
Reply with quoteQuote
Quote
my only question is that with the minimal cost difference, why use the crappy FET's?
The super low RDSon automotive style HEXFETs were introduced in late 2004. At the time, Systema used a reasonable FET. However in modern times we have a far better selection of FETs now that are vastly better. What is cool is that with modern FETs, that old Systema unit would really rock! It a shame not to just fix them for the usual PTW use that does not need anything more fancy. Systema's switch was bleeding edge and they just bleed a little extra Wink We know a whole lot more 'now' about FETs in AEGs Cyclops I trust the new Revolution has gone to the far better FETs too.

According the the Russian site. They were using the RFP50N06.

http://www.fairchildsemi.com/ds/RF/RFP50N06.pdf

At 5V that thing can only push 20 amps before it folds up. They used two for 40A at 5V. But that was the problem, with a low battery, the FETs become space heaters and fry. Fairchild's MegaFETs where just never made for a low VGSon situation. I suppose the battery was weak but the gun still managed to turn the motor. But the FETs where cooking off heat like crazy.

At 5V, two of the IRL1404Zs can push over 500 amps!! At say 100 amps the old 50N06 FETs would dissipate 110 watts as pure heat on a good day. But the IRL1404Z only dissipates 12.5 watts!! So the difference the new FETs would make is gigantic!! In fact, If "I" had a PTW with the old FETs in it, I would just change them out anyway. It would make the failure prone old FET unit practically bullet proof.

Maybe I should charge more Cheesy Of course, anybody can get the replacement FETs

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=IRL1404ZPBF-ND

$7.34 for two FETs plus $5 handling plus $7 shipping…. $19, and you still don't have the Allen wrench Cheesy Since I order stuff from DigiKey at like $700 a pop now, I can do the QTY and such for free…

A kit would provide everything you need and instructions at a very competitive cost for those that need some help with the repair.

Gandolf

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Re: Systema MOSFET Repair Kit
« Reply #3 on: March 30, 2008, 10:22:31 PM »
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Quote from: Gandolf on March 29, 2008, 08:40:23 PM
Metric Allen wrench - I don't know the size?
As far as I remember, Systema switches uses an M5 screw.

Quote
I trust the new Revolution has gone to the far better FETs too.
They use 2 mosfets there, I don't think they've changed the model for the revolution mechbox.
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Re: Systema MOSFET Repair Kit
« Reply #4 on: March 31, 2008, 04:26:29 PM »
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Quote from: Gandolf on March 29, 2008, 08:40:23 PM
Hi,

I have never actually seen on of these Systema switches, so if any one has an extra (or a broken one you want fixed) let me make you a deal Grin I need one to make the instruction pictures/video.

Gandolf

Do you mean the ones that fit in the PSG-1?

If so you can have mine once I replace with a decent one which I've ordered from yourself.
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Re: Systema MOSFET Repair Kit
« Reply #5 on: April 05, 2008, 09:52:51 PM »
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Hi,

I got my paws on a blown Systema MOSFET switch today Cyclops (and I have since cleaned the yucky off the center of the camera lens Cheesy)

This is very easy to fix! The kit will be simple and effective.

Funny how they self thread the screw through the MOSFET mounting hole. Roll Eyes Of course, the other bare FET (the hot one) is the one that is blown. You can actually just cut out the FET 'without' the screw and it will work again.

The Allen wrench is a M2.5 (2.5mm) which is the same one I use for the magnet mounting screws in the mag sensor thing Smiley

So the repair kit is a go! Grin Parts will get here next week and I'll get it up on my site. It is sort of a shame just to waste these things if they work alright normally and they can be fixed and made so much better with a little kit. Very easy to fix with little tear down of the gun too!

I wonder if it only needs "one" FET?? The IRL1404Z is equivalent to like ten of these original FETs… FETs "DON'T" load share!!! The hot FET takes all the load away from the cold FET… As I think about it now…. The second FET it totally useless!!!! Probably far worse in fact with it in there!!!…. I am thinking the kit will be $10 now Cyclops

BTW - The metal case is electrically LIVE on these things!! Tongue The metal case is connected directly to the motor negative wire. I will send some heat shrink in the kit to isolate it in case something else shorts in the gun.

The kit should be cool! Cool

Always remember with these things!

1 - Don't use a run down battery! The low battery voltage is what kills these things!

2 - If you pull the trigger and the gun does not fire, let go of the trigger right away!!! It won't get better, but it will catch fire!! Cheesy

Gandolf

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