Suggested Mosfets for LiPo 7.4

[Red62]

So yeah, I'm trying to threw together a new mosfet system for my Type 97b. But as it turns out: either i'm doing something horribly wrong or my mosfet I just bought are a load of crap and they burned out very easily. I don't know- doesn't finish turning the motor until it burns out and then starts turning on its own without me pulling the trigger.
I'm using a NTE2975, but should I be using a different one?

[wind_comm]

irlb3034pbf (I think that's the full model name) available off digikey.

make sure you use a TVS as well.

(note: I don't actually know much about building fets, but this is as much as I've gleaned off ASM)

[ThunderCactus]

wait, did you JUST hook up a mosfet switch all on it's own, or did you install the resistors as well?
Looks like the switch you picked out should be able to handle normal current
Either it's installed/built wrong, or your motor could have a bend armature or a short causing the mosfet to burn out. Some motors like the G&P M170 or systema magnum are known to be extremely problematic with mosfets.

[ccyg8774]

I am using this http://www.airsoftcanada.com/showthread.php?t=89097 in my Type 97. Works great.

[Hectic]

Merf 3.2 or for something simple and small the pico (i think thats what its called)
Im not familiar with the fet you posted but i know the two i mention (available at airsoftstore.ca) are easy to use and kick ass.

[Azathoth]

Originally Posted by Hectic

Merf 3.2 or for something simple and small the pico (i think thats what its called)
Im not familiar with the fet you posted but i know the two i mention (available at airsoftstore.ca) are easy to use and kick ass.

The PICO is on my RECOMMENDED DO NOT BUY LIST.

ccyg8774 was kind enough to post DonP old thread
http://www.airsoftcanada.com/showthread.php?t=89097

Originally Posted by DonP

ARE ALL THE PARTS REALLY NEEDED?
Short answer: yes.
You may have seen some other MOSFET switch designs out there with fewer parts, but this design includes safety and protective parts which frankly others should not do without. There are simpler designs but not necessarily more reliable or tougher.

Some other final questions to nip in the bud before we get started:

Q: Do I really need the huge diode?
A: Yes, you should use it. That part eats up the large voltage spikes that are normal in this kind of application. This is not a “theoretical” just-to-be-on-the-safe-side thing, there are some scary voltage spikes that can easily damage and destroy the MOSFET otherwise.

[Stealth]

Originally Posted by Azathoth

The PICO is on my RECOMMENDED DO NOT BUY LIST.

Each to their own opinion, but may I ask why?

John

[Hectic]

Originally Posted by Azathoth

The PICO is on my RECOMMENDED DO NOT BUY LIST.

ccyg8774 was kind enough to post DonP old thread
http://www.airsoftcanada.com/showthread.php?t=89097

I also wonder why. If all you need is something simple for a mild build or space is a factor i think its a good solution if u work within its limits. Tho the merf is my go to fet.

[ccyg8774]

I was thinking about getting a PICO for my VFC SCAR (limited space)...

[lurkingknight]

a pico fet is more than enough for any gun running reasonable discharge rates at 7.4v

A self protecting mosfet is always nice to have... if you're that terribly concerned, pair a pico with a poly fuse setup.

[Azathoth]

Originally Posted by Stealth

Each to their own opinion, but may I ask why?

John

DonP answered that question for me years before. I quoted it already above.

Originally Posted by lurkingknight

a pico fet is more than enough for any gun running reasonable discharge rates at 7.4v

A self protecting mosfet is always nice to have... if you're that terribly concerned, pair a pico with a poly fuse setup.

Depends but that first statement is generally accurate. Putting an inline micro blade fuse or poly fuse is going to cost you about much as putting together a MOSFET with a proper diode. between the wire and the micro fuse, you may as well take the diode instead.

[Stealth]

Originally Posted by Azathoth

DonP answered that question for me years before. I quoted it already above.

Sorry but I'm not reading in between your lines. You'll have to excuse me for being bone-headed. What exactly are you referring to?

The reason I ask is because Gate is one of those companies who actually listen to retailers. If I asked them to investigate something, they will do it.

I'm not an Electrical Engineer (I am an Engineer but in a different field...) and so I look towards customers like you to tell me what can be improved upon.

So please tell me - what happened with your experience of the PicoSSR?

Terry, whose Extreme-fire mosfets are the benchmark of mosfets for airsoft, has commented on the PicoSSR before on ASM. He didn't seem concerned at all.

John

Originally Posted by Gandolf on ASM

It looks really look cool and fine!

I think they are using this FET:

http://www.mouser.com/ds/1/302/PSMN1R2-25YLC-55487.pdf

Good power and current and very low Vgs(on)! They have light TVSs too that should do well.

For a light to moderate powered AEG I think they will be fine. The very close big wires make nice heatsinks too!

They make a lot of AEG FETS and they know what they are doing. I would not worry. If You have some 18.1V 60 RPS 700FPS monster gun you will probably bust them, but they should drop into 98% of the AEGS out there just fine!


With units like this just keep the battery well charged. If the gun does not fire or something goes wrong, get your finger off the trigger ASAP! If you remember to do those two rules, you will not bust these FETs.

With a low battery voltage, the FET will lose gate drive voltage and will become resistive and turn into a space heater. If say your motor is jammed and you hold the trigger down for a few minutes hoping it will get better... It will just get far worse... But if you avoid those two perils, even little units like this do very well!!

[Azathoth]

You have a huge post to quote.

Either their are some really bad installs on the PICOSSR, or they were "defective".

Three cases of the SSR heating up and melting the plastic on a glass 9a fuse holder. Half a dozen 'failures' in a 6 week span is generally a sign of QC issues or a defective product, damage from shipping etc. After that, the people who ran the PICO switched to Terry's basic mosfet.

[Stealth]

That's really unfortunate that these individuals did not contact me and let me know of such issues and I'm hearing it from you. Please tell them to email me.

This is an open invitation to ASC: if you had a PicoSSR burn out on you while operating within the design parameters, let us know.

"Half a dozen in 6 week span" seems like a large number. Sifting through my old records we didn't even make that many sales to Alberta prior to June. I wonder if they had gotten them from another source which had some old stock.

The first batch of PicoSSRs were indeed defective. Upon learning of failure Gate redesigned things and we quickly pulled them off our site. This was well documented publicly here:
http://www.airsoftcanada.com/showpos...9&postcount=30
and here:
http://www.airsoftcanada.com/showpos...9&postcount=38

Customers who got the old "Gen1" defective ones we promptly issued refunds or sent them a replacement "beefed up" "Gen2" version free of charge.

Here's how to tell if your PicoSSR is from the old batch vs the new batch:
Old batch: Resistor values are "102" and "101" - throw these out!
New batch: Resistor values are "363" and "101"

John

[ThunderCactus]

Could be a different retailer had the gen1 units and didn't issue any sort of recall.
However, from my own experience, I know that mosfets in general are sensitive to what kind of motor you're running.
For example, if you're motor had some kind of defect that makes it draw too much amperage (systema magnum comes to mind), then your mosfet is extremely likely to overheat very quickly and either trip it's resettable fuse, blow it's slow blow fuse, or melt.
And it's not just restricted to after market motors, I've seen a few G&P M120s develop internal shorts. One was destroying LiPo batteries by over-current draw. And another had actually melted the solder of it's motor connectors causing it to disconnect.
So, it could be a batch of gen1s, it could be they were installed incorrectly or the wiring arced through the body (I've fixed at least a dozen of those), or the problem may not have been the mosfet at all.
More details would be needed to determine the actual point of failure.
Like one could say the systema hop adjusters are crap because they keep breaking, when after investigation you find people are just tightening the shit out of them and breaking them lol