11 replies to this topic

[ThatBritishGuy]

So I replaced the 6 D cells with 4 trustfire 14500 batteries in a 4 AA battery holder. When i connect the pack to the battery tray in normal bias and try to fire the gun (all the other locks are still in place) the bolt advances about 1/2 an inch and then stops. When i then turn the circuit off it doesn't retract. When i then replace the trustfires with the original D cells, the bolt automatically fires and then resets to normal.

I'm not sure what i'm doing wrong. In this thread (http://nerfhaven.com...=1)SpectreX said connecting it in reverse bias solved his problem but that hasn't worked for me.

Thanks in advance.

[Exo]

Did you charge the batteries?

[ThatBritishGuy]

Yes.

I forgot to mention, i did a continuity test on the 4 AA pack with the trustfires and they run fine.

I'm confused because SgNerf has put over 20 Volts through the stampede's motors without any problems.

[Epic Pie]

I believe that your discharge ratio is to low. When you have less batteries, their current can be reduce, while voltages remain the same. Try to add a few more AA's.

[Ivan S]

4 14500s should be enough for a stampede. Check the voltage of each battery to make sure they're fully charged/working properly. Also, are you sure you're using the unprotected variety? If they're trustfire, they should be the gray kind.

[Aeromech]

When the you fire the Stampede, the bolt advances and presses down on the switch leading to the main motor. This is why you can tap the trigger and release it before the dart has left the chamber; it's a means of preventing double feeding and boosting reliability in it's stock form. It is also the main reason for runaways when the voltage is increased.

In your case, the trustfires only have enough strength to advance the bolt/plunger assembly partway forward. The switch to the motor is still depressed by this assembly, and will fire once adequate power is supplied, (in this case from the original batteries.) That's what's happening mechanically.

I don't have a terrible amount of experience with rechargeables, but on a more general level, compare the voltages and curent output of the two battery types, and some simple calculations can get you an approximate value for the power output from the trustfires vs the original batteries. Check that you have wired them correctly, and remember that "voltage" is only part of the equation.

Edited by Aeromech, 19 February 2012 - 07:20 PM.

[SgNerf]

ThatBritishGuy,

Are you using protected or unprotected TrustFire Li-Ion batteries? Some sellers may not indicate the characteristics clearly on their product info, so you have to check with them directly to make sure.

Protected batteries have limited discharge rates so once the motor is under load and the amp draw increases above the discharge limits, the battery's protection circuit will cut off the power... hence resulting in a similar effect you encountered with the plunger only moving abit then stalling.

Thats why we use unprotected versions instead, as they can supply the motor with enough amp current to pull the spring load properly.

Edited by SgNerf, 20 February 2012 - 02:37 AM.

[ThatBritishGuy]

ThatBritishGuy,

Are you using protected or unprotected TrustFire Li-Ion batteries? Some sellers may not indicate the characteristics clearly on their product info, so you have to check with them directly to make sure.

I'm not sure, but from your description of grey batteries and the problem i am guessing mine are protected (they are black with flames on the sides).

Do you know of any way to unprotect the batteries? If circuitry is required thats fine, i have PCB production facilities at school.

[Hammy]

I recommend that you do not open the batteries. They should be considered as sealed units and left alone.

These batteries are capable of outputting high currents and can get hot in the process and maybe explode.
So if you try and open up one of these guys, And short circuit it in the process, you could have bits of batteries implanted in your face.

You say you have PCB equipment at your school, so that means there should also be bench power supplies.
You could definitely use a bench power supply to test that your mod worked, whilst waiting for your next unprotected trust fires to arrive.

You could also try a 12-V compact lead-acid battery. Try the bench power supply at 12 V, if this works, then try it with
A 12 V car battery, then if this works, proceed to Maplin or RS and buy a compact 12V lead acid battery. these devices are also sealed,
Lead acid batteries are capable of delivering high currents, this is why they are used in vehicles to turn the starter motor.

Edited by Hammy, 21 February 2012 - 03:41 AM.

[Demon Lord]

Please do NOT use a car battery for testing anything or modding anything. The average car battery runs at over 500 amps and is enough to melt steel in seconds if short circuited. If you need 12 V anything to test with use a lantern battery as they are much safer for applications like this.

[Hammy]

500 Amps should certainly be enough to pull back the stronger spring, but that kind of current is dangerous and can kill, so
Please forget the lead acid battery concept.

Just use the bench power supply to make sure the mod works, and await delivery of your unprotected Trustfire's.

[ThatBritishGuy]

Ok thanks, ive ordered the unprotected version. I already did the test to make sure it worked with 16-18V and it did so there is no problem with the stampede.

Thanks for all the help in this thread feel free to close it now.