M249 internal upgrading

darkslider

Hi all,
Looking at doing a little internal electrical work on my M249 to toughen it up slightly and prep it for a LiPo battery.
As the switch is reportedly a source of gnashing teeth I thought I'd start there.
So the current switch is meant to be 16A:

and I found this one on Evike.com:

They say it's a reinforced (ahem) 20A switch, but the part code on the switch suggests it's 15A according to the manufacturer: XV-152-1C25.

Or to be more precise:
15A non connection wire (1500Vac)
20A every connection (2000Vac)
more info: Switch Spec

- Not really sure what that means. Perhaps one of you kind people might enlighten me, is this a 20A switch or not?

DeBurca

Fit a basic MosFet and you can get a 12A switch in Maplin for €3.79 and you never have to worry about your switch again

darkslider

I had intended on fitting some type of mosfet unit.
Do you think a complete re-wire is a waste of time then?

ShRT

darkslider wrote: »

Hi all,
Looking at doing a little internal electrical work on my M249 to toughen it up slightly and prep it for a LiPo battery.
As the switch is reportedly a source of gnashing teeth I thought I'd start there.
So the current switch is meant to be 16A:

and I found this one on Evike.com:

They say it's a reinforced (ahem) 20A switch, but the part code on the switch suggests it's 15A according to the manufacturer: XV-152-1C25.

Or to be more precise:
15A non connection wire (1500Vac)
20A every connection (2000Vac)
more info: Switch Spec

- Not really sure what that means. Perhaps one of you kind people might enlighten me, is this a 20A switch or not?

It's a 20A switch alright but only for AC current. It's DC current in a gun however. In this case the rating would be approx 6A at the kind of voltages in use in guns.

The switch lasts though as that would be 6A at a constant draw and aeg's don't draw current constantly. Still not spec'd correctly but get away with it for a while. Not sure what the wiring is like in the gun but if you are going to replace it, go for some silicone coated 16awg wire. Or 14awg if there is lots of space.

Don't bother with the silver wire nonsense that some airsoft places will try and sell you.

darkslider

ShRT wrote: »

It's a 20A switch alright but only for AC current. It's DC current in a gun however. In this case the rating would be approx 6A at the kind of voltages in use in guns.

The switch lasts though as that would be 6A at a constant draw and aeg's don't draw current constantly. Still not spec'd correctly but get away with it for a while. Not sure what the wiring is like in the gun but if you are going to replace it, go for some silicone coated 16awg wire. Or 14awg if there is lots of space.

Don't bother with the silver wire nonsense that some airsoft places will try and sell you.

So it is a 20A switch, Albeit AC. Thanks mate!

See that's the thing, because it's an m249 it's prone to sustained periods of automatic fine - what with the box mag attached. doing this with an 11.1 LiPo could generate a lot of heat during sustained fire and cause the switch to arc. - Hence my trying to replace it. Perhaps the mosfet can regulate this a bit better.

DeBurca

The switch will arc during the make and break of the switch, it does not arc during firing no matter how long you use sustained fire

If you fit a MosFet the fet will be switching the current and the current in the switch will be less then 0.1amp so the contacts will last for ever and a day

darkslider

Fantastic. Thanks.

ShRT

Just make sure to fit a mosfet that connects to the switch. Some times folks will sell a unit that connects at the battery plug and therefore doesn't do anything to protect the contacts.

darkslider

HA! so one way or the other there's a rewire.

I think the FET I was looking at connects to one terminal of the switch as a switch sensor.

ShRT

Yup that sounds about right. In a MOSFET (most common used in airsoft is irlb3034) you have a gate, source and a drain. The gate connects to the switch+battery and the source and drain connect the battery to motor. When the switch closes it connects the gate to source which then triggers the current to flow from drain to source - allowing current to flow from battery to motor.

The amount of current flowing through gate to source is very small so a low amperage switch does the job. 24awg wire will do the job aswell due to low current.

The source to drain can be much higher amperage therefore handles the amps the motor pulls from the battery. Hence the requirement for thicker wire like 16awg (or 14awg if you have room for it in the gearbox. )