Strange battery problem

[Distracted]

Hi all,

 

Got some new batteries today, VP Airsoft 7.4lipos with 30c and 1600mAh to run my PDR-C. The old battery is a Nuprol 7.4 with 20c and 1100mAh.

 

The problem is that none of the (5!) new batteries will fire the PDR-C, but they all work fine with a different AEG. The old battery works fine with both guns.

 

Any ideas?

[adox]

I would guess the fuse in your gun (in the mosfet) will not allow the higher coulomb charge of 30c so it does not allow the use to possibly protect your gun getting fried...???

[Iceni]

7 hours ago, adox said:

Clearly the fuse in your gun will not allow the higher coulomb charge of 30c

That makes very little sense as a statement.

A coulomb is a measure of static (stationary) charge (potential). You can raise the potential of any object to high level, but without flow that charge does nothing.

The unit you are interested in is coulombs per second flow. Or amps as most people call them.

Fuses don't care about coulombs, a static charge without flow will just sit as a potential. Fuses care about Amps.



To add into this the SI metric symbol for Coulombs is C (<- capital). And in equations Q. I think you have confused the SI C as having the same meaning in battery explanation as it does in electronic physics. It doesn't.

Batteries use a C symbol in 2 ways

30/60c this represents the discharge characteristics of the battery.

Multiply the Ah by that number and you get the amp discharge potential.

Example.

2200mAh 30/60c

Gives 2.2x30= 66amps continuous and 2.2x60= 132amps burst.

The second use of the C number is in reference to charge ampage.

Sometimes a battery will be labelled as 2c or 5c. This should never be confused with 2s and 3s, as they link to the number of cells in the battery. 1s (1cell) 3.7v, 2s (2cell) 7.4v, 3s (3cell) 11.1v

In this instance it's a charge ampage multiplier.

So the same 2200mAh 30/60c 7.4v battery.

It's standard charge ampage is 2.2 amps. For a 1 hour charge. 1c

A 2c version is safe at 2.2x2= 4.4amps (30 minute charge) 2c
A 5c version is safe at 2.2x5= 11 amps. (12 minute charge) 5c

Capitals with the battery numbers are interchangeable depending on who wrote the label.



Now lets go back to the problem and what you are suggesting.

7.4v 20/40c 1100mAh works.
7.4v 30/60c 1600mAh doesn't.

Well lets look at the working battery.

It's got an amp discharge of 22 amps continuous and 44 amps burst. Pretty low by airsoft standards.

The other battery is capable of 48 amps continuous and 96amps burst. Pretty average by airsoft standards.

A typical gun will draw 15-20 amps. So both are capable of driving the motor. The higher ampage model will have less stress placed on the chemistry in continuous use, and be slightly safer but otherwise they will both do the same thing.

What i suspect is this is a case of either:

Slow burn fuse, It'll be glowing red hot but not blowing. It should still try to drive the motor.

Or more probably an incorrect polarity on the connectors. RC car batteries can often have the polarity swapped on the connector block. If this is the case the red lead will be plugging into the black on the gun. Easy to spot unless you have a gun with single colour wires.

In airsoft round is red (+) on a tamiya connector.

In RC cars square is red (+) on a tamiya connector.

Deans are normally done the correct way in both systems.



 

[adox]

I see, I am still new to airsoft and appreciate the knowledge. No-one had replied to him for quite a while so I'd thought to give it a go.

[Iceni]

1 hour ago, adox said:

I see, I am still new to airsoft and appreciate the knowledge. No-one had replied to him for quite a while so I'd thought to give it a go

 
It's not a problem.

The lack of response to the thread is probably due to not enough information given.

We knew the gun, and the batteries, but not the connector type

 

On 29/08/2018 at 18:20, Distracted said:

The problem is that none of the (5!) new batteries will fire the PDR-C, but they all work fine with a different AEG. The old battery works fine with both guns.

This is also a problem. You see he claims they work with another AEG. And the older battery works with both AEG's.

So there is something wrong somewhere, and not enough information to troubleshoot it. Might be a fuse, might be a mosfet, might be a dodgy connector or trigger. There's just not enough information, and the OP doesn't seem to have the technical knowledge to offer a troubleshooting route. So it's one of those threads you just don't touch. It's better they send the gun out to someone that can do the basic troubleshooting.

[Distracted]

Been out of comms for a few days, but this have been resolved. 

 

The trigger switch and motor were both partially fried, meaning they could handle lower C ratings, but was unable to draw on a higher