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cmrn

Airsoft Micro-fets for Sale In the Near Future

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Hello people of airsoft forums, I build airsoft mosfets and I am thinking of starting a little business with it. For everyone that doesn't know what a mosfet is, it is basically the component that makes your gun "li-po ready". I will be selling them for $20 each and I would install them for you for $40 if you are not confident enough in your soldering/teching skills. The reason I am posting on here is to see if people would buy them. I can ship them with just the parts, a complete mosfet with all of the connectors, or install it for you. All of which will cost $20,$30, and $40 (I specialize in installing them in m4's so sorry for right now I will not be installing them into AK-47's or other non V2 Gearboxes.) Also I am using screws that are a little bit too big but I will be buying smaller ones if people are interested in these little fets. This link is a demonstration video showing the mosfet in action. (the reason it looks so weird is because I made it detachable for testing.) Let me guys know if any of you are interested in buying my mosfets :) Have a good day.

 

Parts list:

International rectifier 3034 mosfet

16 gauge positive and negative wire

22 gauge gate wire

Lonex OEM Motor connectors

 

Link to demonstration:

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I don't wanna be mean, but that mosfet unit is not particularly compact, my own DIY units with the same mosfet chip are more compact as I don't use a screw connector on the drain wire anymore. Now I just solder the wire directly to the heatsink, it won't damage the chip if you're careful, and it makes for a more sleek and compact unit.

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I don't wanna be mean, but that mosfet unit is not particularly compact, my own DIY units with the same mosfet chip are more compact as I don't use a screw connector on the drain wire anymore. Now I just solder the wire directly to the heatsink, it won't damage the chip if you're careful, and it makes for a more sleek and compact unit

I thought you had to use screw and nut so that it doesn't fry the mosfet?

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People are still using a IRL3034? For goodness sakes, there's better parts out there, BTS555 has never failed and if you want the classical MOSFET, here is an example:

 

http://www.digikey.com/product-detail/en/infineon-technologies/IRL40B209/IRL40B209-ND/5683946

 

as compared to the IRL3034

 

http://www.digikey.com/product-detail/en/infineon-technologies/IRLB3034PBF/IRLB3034PBF-ND/2096638

 

(same price, actually slightly cheaper, and otherwise better, lower Rds(on))

 

Don't forget the protective diodes including a TVS diode to protect from Drain-Source and Drain-Gate overvoltage.

 

BTS555 is great if you aren't chasing performance b'cos it has the gate drivers and protection all built into a single package.

Edited by Shutaro

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but wont the negative spike from the motor stopping destroy the mosfet with all that current?

You can of course solder on the external diode together with the drain wire or just skip it and take your chances with the internal diode. I've ditched the external diode on my latest mosfet units, none have failed so far, after at least 2 seasons, looks like the internal diode is holding up fine.

 

People are still using a IRL3034? For goodness sakes, there's better parts out there, BTS555 has never failed and if you want the classical MOSFET, here is an example:

 

http://www.digikey.com/product-detail/en/infineon-technologies/IRL40B209/IRL40B209-ND/5683946

 

as compared to the IRL3034

 

http://www.digikey.com/product-detail/en/infineon-technologies/IRLB3034PBF/IRLB3034PBF-ND/2096638

 

(same price, actually slightly cheaper, and otherwise better, lower Rds(on))

 

Don't forget the protective diodes including a TVS diode to protect from Drain-Source and Drain-Gate overvoltage.

 

BTS555 is great if you aren't chasing performance b'cos it has the gate drivers and protection all built into a single package.

You linked an IRL40B29 with slightly better specs and a tiny bit higher price than the 3034? The 3034 does have an internal TVS diode by the way.

Edited by Lefse

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The 3034 has an internal TVS diode? You are mistaken. Show me where it says this on the datasheet. You sure you aren't confusing it with the body diode (which nearly all power MOSFETS have)? B'cos they protect against completely different things; negative or reverse voltage vs. overvoltage.

 

http://en.wikipedia.org/wiki/Power_MOSFET#Body_diode

 

While the body diode is often enough to supress the negative voltage backlash from an inductive load, a brushed motor is a more complex system that requires additional protection... I know it adds to the size and cost, but don't neglect the importance of the TVS diode or some other form of overvoltage protection!

Edited by Shutaro

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I guess I took it for granted that it was simply an internal TVS diode, looks like I was wrong about that. It does say "enhanced body diode" in the datasheet for the other mosfet, so that would probably mean enhanced protection from voltage spikes. I think I'll give the 40B209 chip a try next time I'm ordering mosfet components, it does look like a more robust unit.

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Lefse I would urge you to take some time and study the electronics and theory behind what you are trying to do. Here is an example:

 

http://www.nxp.com/video/driving-inductive-loads-with-mosfets-nxp-quick-learning-44-part-1:MOSFETS-INDUCTIVE-LOADS-1

 

This is the simplest case where he discusses three basic approaches for handling a simple inductive loads. I know people are tempted to do the last in a motor drive situation too (just ignore the problem and depend on the body diode) but you are inviting a failure if you do that.

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I know there's a good reason for having that external TVS diode, and I am taking a chance by not using one. Thing is that space is at a premium in an airsoft gun, and mosfet chips are relatively cheap, so I'm willing to take my chances. Half of my mosfet units does in fact have an external diode, so we're only talking 2 mosfets out 6 without additional protection, so it could be worse. My AK has a MERF 3.2, I presume it has the needed protection against voltage spikes and such.

 

I'm curious, how does IGBT chips handle inductive loads in comparison? They are generally more expensive, but they seem like they're more robust? I did run an IGBT for short time period in my old AUG, but I overlooked that the drain and source pins are swapped compared to a mosfet, so it got extremely hot during use. If I had connected it correctly it probably wouldn't have heated up.

Edited by Lefse

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IGBT is a different beast, its best for much higher voltages than we're using in our guns. With a typical power IGBT, the collector to emitter voltage drop in the on state might be in the 1-2V range. This is insignificant in systems working with hundreds of volts (ie. 1:1 electric cars) but that would be a significant loss for the 7-16V batteries we're using. Same reason MOSFETs are preferred over BJTs. Even if wired correctly, a device driving a motor at 10A and dropping 1V across the collector/emitter path is dissipating significant energy (10W in my example). Whereas to source/drain voltage drop with a power MOSFET is generally insignificant, even at the voltages we use.

Edited by Shutaro

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I see, thanks for the explanation, IGBT is a no-go then. I guess I'll rather try and find more compact TVS diodes, or I might just start buying pre-made units. I'm getting a bit lazy these days, and I have also gotten a taste for more advanced mosfet units. This thread has given me a better understanding of how mosfet chips and such actually work.

 

I took another look at the BTS555 unit, and why we don't just use this is a good question indeed.

Edited by Lefse

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BTS555 is popular in Russia, which turns some Americans off towards it. Also $9 to $10 in small quantities which is a bit more expensive than a $3 MOSFET. And it's installed on the high (+V) side rather than the low side (GND). Which is actually easier the way must guns are wired up from the start, but not what people are used to for MOSFETs.

 

But it really does live up to not needing any external components, I did one airsoft build with it and posted it here years ago, and I've measured the clamping effect on a scope, use it for other weapons (not airsoft) when it makes sense.

 

http://ru.mouser.com/ProductDetail/Infineon-Technologies/BTS555-E3146/?qs=wK%252boHS4yu54MTa%2f39eglNA%3d%3d

 

http://www.digikey.com/product-search/en?keywords=BTS555

Edited by Shutaro

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Yeah, I do apologize, we have pretty much hijacked your thread. If you find a way to make your mosfet units a bit more compact and get a deal with a trusted retailer I'm sure you'll sell a good number of them. Maybe try and find a newly started retailer, that way you can be part of building it up. Maybe add compact PTC fuse units, or make an alternative mosfet unit with the fuse built-in.

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Yeah, I do apologize, we have pretty much hijacked your thread. If you find a way to make your mosfet units a bit more compact and get a deal with a trusted retailer I'm sure you'll sell a good number of them. Maybe try and find a newly started retailer, that way you can be part of building it up. Maybe add compact PTC fuse units, or make an alternative mosfet unit with the fuse built-in.

ok thanks for the advise

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