7.4 LIPO in place of 8.4 NiMH

[Taiga]

I just got my Marui (High Cycle) Steyr AUG, give it a few test runs. Works perfectly, feels great. No feeding issues, overall I'm very happy with the gun itself.

Now for my question, the gun advises that you run a 8.4V mini NiMH battery, I'm currently running a 7.4V LIPO from hobby king instead. (Linked below)

https://hobbyking.com/en_us/turnigy-nano-tech-1800mah-2s-20-40c-lipo-airsoft-pack.html

I've read in quite a few places that this is reasonably safe and shouldn't damage any internals of the gun, since from what I understand a 7.4V LIPO will give you a power similar or close to a  8.4v or 9.6v NiMH battery pack. Obviously, not being the most well equipped with battery knowledge I'd like some statements on this! (And yes I do know my safety when charging/discharging LIPOS and how to store them)

 

[Adolf Hamster]

it's pretty much a performance equivalent, lipo's are capable of much higher current output then nimh and more importantly they tend to maintain performance until near depletion.

the only thing to consider if running lipo for the long run is consider installing a mosfet, it'll save you having to replace burned out trigger contacts down the line and a decent one will have a lipo cutoff.

otherwise tear away, 7.4 isn't as spicy as say 11.1v where you start hitting issues with the gearbox/motor being hammered too hard.

 

[AK47frizzle]

7.4v lipo gives the performance of a 9.6v NiMH more or less, not an 8.4v.

But yes, people tend to run those batteries in high cycles and seem to be fine.

 

[Iceni]

it's pretty much a performance equivalent, lipo's are capable of much higher current output then nimh and more importantly they tend to maintain performance until near depletion.

the only thing to consider if running lipo for the long run is consider installing a mosfet, it'll save you having to replace burned out trigger contacts down the line and a decent one will have a lipo cutoff.

otherwise tear away, 7.4 isn't as spicy as say 11.1v where you start hitting issues with the gearbox/motor being hammered too hard.

This: But with some modification due to the space constraints of the AUG platform.

You can fit a basic mosfet without a problem behind the gearbox wall. The biggest I've been able to get to fit was a gate nanohard, but that took some serious messing about to get to fit well. You can't really put a fet on the battery side of the gearbox wall, because that eats directly into the space for the battery and there isn't a lot to begin with. The other disadvantage of using a programmable fet is you might not be able to see the LED's that tell you what you are adjusting when in program mode. Again with the nano hard I was able to make it so I can see the glow of this LED but it's a pain to adjust.

A basic non programmable fet put in the correct spot will fit in the void at the back top edge of the motor.

https://www.ak2m4.co.uk/internal-parts/mosfets/acemos

The advantage the aug has over a lot of platforms is you can add a mosfet without needing to open the gearbox. Provided you can solder everything you need to get to is exposed and easy to work on. Personally I solder my motors and use a deans connector to the mosfet, It saves a little space at the bottom of the case and stops the connectors/wires holding the gearbox up. I just use jumper style  (1mm) connectors for the trigger wires. You don't need to worry about adding a wire break between the fet and battery because the loom is so short and you can generally remove the full loom with the gearbox, but you will want the break to the motor and contacts, It helps a lot when you want to remove the motor and work on the gearbox without having wires and a motor getting in the way.

Amp wise that battery should be decent enough 36amp continuous 72amp burst. More than enough for that gun. You could go with a slightly higher mAh rating there are plenty of 2200mAh batteries with 30/60 and 35/70 discharge ratings in the same form factor. It's not something I would worry about.




 

 

[Taiga]

This: But with some modification due to the space constraints of the AUG platform.

You can fit a basic mosfet without a problem behind the gearbox wall. The biggest I've been able to get to fit was a gate nanohard, but that took some serious messing about to get to fit well. You can't really put a fet on the battery side of the gearbox wall, because that eats directly into the space for the battery and there isn't a lot to begin with. The other disadvantage of using a programmable fet is you might not be able to see the LED's that tell you what you are adjusting when in program mode. Again with the nano hard I was able to make it so I can see the glow of this LED but it's a pain to adjust.

A basic non programmable fet put in the correct spot will fit in the void at the back top edge of the motor.

https://www.ak2m4.co.uk/internal-parts/mosfets/acemos

The advantage the aug has over a lot of platforms is you can add a mosfet without needing to open the gearbox. Provided you can solder everything you need to get to is exposed and easy to work on. Personally I solder my motors and use a deans connector to the mosfet, It saves a little space at the bottom of the case and stops the connectors/wires holding the gearbox up. I just use jumper style  (1mm) connectors for the trigger wires. You don't need to worry about adding a wire break between the fet and battery because the loom is so short and you can generally remove the full loom with the gearbox, but you will want the break to the motor and contacts, It helps a lot when you want to remove the motor and work on the gearbox without having wires and a motor getting in the way.

Amp wise that battery should be decent enough 36amp continuous 72amp burst. More than enough for that gun. You could go with a slightly higher mAh rating there are plenty of 2200mAh batteries with 30/60 and 35/70 discharge ratings in the same form factor. It's not something I would worry about.




 

Thanks for the tips, I'm not the most experienced in this sort of thing, but I do know a few tech people, one who works on aircraft/Helis, cars and real guns. The other is an airsoft tech at my local shop, so I'll definitely look into it.

Also I picked up 2 of the 1800 mah batteries because for one, they fit well, for two, there cheap and three, they have decent reviews everywhere I looked. I don't mind swapping the batteries out at lunch, that way I know for a fact I wont drain one.

 

[Rogerborg]

It looks like your AUG has a V3 gearbox, which means you should be able to wire in a MOSFET without even opening the gearbox.

With a bag of small spade connectors and some wire, you can replace the entire wiring (outside the gearbox) while keeping the original wiring aside and intact in case you make any errors.

That said, if you have a techie to hand who can do it, there's no shame in getting it done right first time, especially if you can watch the process and get some confidence to get stuck in yourself next time.

I fully agree on running two batteries and swapping them over to spread the load around, that's a smart idea.

 

[Taiga]

On 21/09/2018 at 07:41, Rogerborg said:

It looks like your AUG has a V3 gearbox, which means you should be able to wire in a MOSFET without even opening the gearbox.

So, from what I understand, is I'm basically just removing the end to the old connector, adding the mosfet in and fitting my required connector to the end of said mosfet cable. Then the mosfet will act somewhat like a voltage switch in the circuit? 

 

[Iceni]

It's knowing where to cut the wire. Aug's are different to a regular v3 gearbox because of the 2 sets of contacts.

Give me 20 minutes and I'll edit this with the pictures of where to cut and what to do.


The first part is the cuts.

You need to cut the wire on the red X's. You can make the green tails longer if you want, but do not cut above the solder points. Sometimes the wires both come out looking up so make sure you cut the wires that go to the motor and battery.... NOT the ones that go to the front contacts.

This gives you 2 tails on the green area that are going to be for the trigger wires.

And the 2 in blue become the motor wires (these have polarity +/-) don't mix them up.

If you are doing a solder in type like the Xcoretech xet304u or the AK2M4 one then the loom is the same, but you have to solder both sides of the fet rather than just using spade connectors.

It's still the same number of wires cut in exactly the same place.

Polarity on the trigger doesn't matter, But polarity on both the motor and the battery side is very important to get right. And you have to look on the PCB of the Fet to know the way round they go... My diagram might not be correct to the fet you pick up so pay attention.

Provided those 2 initial cuts are in the right spot you can't go wrong with the AUG rewire. It's a very easy gearbox to do a fet on.



If you want it easier to work on the gearbox in the future then you also want to add some connectors on the circuits.

Doing this will allow you to remove the motor and the mosfet so it's not in the way when you have to replace internal parts.

 

 

[Taiga]

It's knowing where to cut the wire. Aug's are different to a regular v3 gearbox because of the 2 sets of contacts.

Give me 20 minutes and I'll edit this with the pictures of where to cut and what to do.

Alright mate, thanks!