Blown fuse after adding SHS Highspeed Motor

[brooxy]

Hi all, just another quick question. I've just fitted an SHS highspeed motor to my MP5 and it blew the fuse after a 10round burst. I've bypassed it for now as I want to keep it to shorter bursts anyway, but I wouldn't mind getting the issue resolved for peace of mind.

- Shimming is spot on with no mechanical lockups at all from what I can tell
- Wiring is the standard Marui wiring with deans connectors added to the battery
- Battery is a 3700mAh 8.4 brick - also running deans
- Spring is a Guarder SP110
- No fuse issues ever had with this gun under the old motor (EG1000)

Before shelling out the monies for wiring / connectors ETC, anyone know what the obvious issue might be? At the moment I suspect it's either the large tamiya connector between the gearbox and stock, or the wiring needs upgraded to help the added power draw. If this sounds right, I'll be ordering some extra wire this week when I go and order a few more components. Anyone able to confirm whether this sounds like a good shout or not?

EDIT: Also just had another thought - as it's the stock marui fuse, I think it only supports upto 15A - would it be worth sticking a 20A fuse in there, or would that be too high to prevent any potential damage to the gun? should SHTF? Obviously electrics isn't my strong point...

[jonny lovegrove]

Re: Blown fuse after adding SHS Highspeed Motor

The high speeds have a MASSIVE current draw. It may also be shorting out... The fuse shouldnt blow at all if the circuit is fine...

[Mickydoos]

Re: Blown fuse after adding SHS Highspeed Motor

If I remember correctly the draw on a SHS is about 35A. Would explain the fuse popping.

Solutions:

Bypass and hope the wiring holds up.

Uprate the fuse and hope the wiring holds up.

Re wire with a lower gauge wire and uprate the fuse.

I run a SHS high torque on standard wiring and my rifle is unfused and seems fine. I'd say uprate if you spam the trigger constantly.

[sj_asc]

Re: Blown fuse after adding SHS Highspeed Motor

Guarder's SP110 is a tough spring anyway, at least in comparison to stock TM, it's pretty lucky you didn't pop the 15a fuse with just the spring alone - But that's a good thing

As said, High speed motors draw more current than the equivalent high torque's because of the lower wind count, factor in that that high speed arms will also struggle more (demand more current)to pull the load more than the high torque and also that SHS motor cans use neodymium magnets which will mean the initial current draw will be higher also.
I think 35amps would be on the greedy side, but a 25a replacement would be reasonable.
I would also highly advise swapping your connectors out to Deans (or at least equivalent for the non conformists!)

If you are using stock TM wiring (18AWG/16amp) id suggest re-wiring with 16AWG/22amp) for better efficiency.
Also it's often forgotten by many, but bare in mind that the wiring capacity is only as good as the rest of the circuit. Many people fly at swapping the connectors out, and forget the other factors that bottleneck the circuit. Connectors alone will do very little to boost performance.

In addition to replacing the wiring and connectors, I would strongly advise;
*MOSFET (IRL3034 based would be ideal) - The SHS motors additional current draw is being switched by the mechanical trigger switch, the arcing the previously occurred would be much greater than before as would the heat created and subsequently the switch block lifespan. The FET would switch all of the power solid state, cold and eliminate any arcing from the main switch as well as boost efficiency (3034's can sustain 60 amps!)

*Soldering the motor connectors - The common connectors (2.8x0.5mm Spades) have a maximum rating of 16 amps which is poor and this number will drop along with connection reliability (wear and tear) and fall into wasted energy in the form of heat. Even in an ideal world where they remain tight, at 16 amps, they would still be the bottleneck of the circuit.

[dadio]

Re: Blown fuse after adding SHS Highspeed Motor

check the insulation around the plug's that go to the motor , if that's all you'v changed it's the first place to look , then try upping the fuse in 5 amp increments until it does not blow , over 30 amp's and i'd say there's another fault or the wiring isn't up to it .

[brooxy]

Re: Blown fuse after adding SHS Highspeed Motor

Thanks all.

In the short term I'll procure an uprated fuse and change the tamiya connector between the stock and gearbox out with a deans connector (which will also match the battery connection). Why Marui couldn't have used one set of cables from gearbox to battery is beyond me...

Long term I'll be building a mosfet for Project M4 - once I've done that, I'll set about redoing all the wiring on the MP5, with mosfet (I expect to break my M4 many times before it's done).

One thing I'm not sure about is sniperjesus' comment about soldering the battery connectors - as there is no cage like a V3, the motor has to be disconnected ETC when the gearbox comes out, meaning that work on the gun could be a bit more complicated. Is there a non-soldering method that I could use to decrease resistance at the motor terminals, or a method that would be soldered, but easily detachable (for example, soldering the motor, but running bullet connectors down the side of the motor for ease of gearbox access)

Again, all appreciated chaps - thanks again

[sj_asc]

Re: Blown fuse after adding SHS Highspeed Motor

Yes as with m4's the grip its self is the cage and soldering is a little more tricky, but it depends on how often you plan on having it apart - hopefully not that often! In such case, the lack of ease with dis-assembly is worth the trade off for low resistance and a more reliable connection (no crimps to work their way loose). If you have space, you could get some small gold bullet connectors in there, but IMO if you have a soldering iron then its not that much of a fuss.