HL Tiger 1 Turret LED resistor

[westwick]

Hi folks, new to the forums but have been thoroughly reading through many posts here already to get to grips with my recent purchase.

It's just the basic Heng Long 3818-1, 1/16th Tiger 1, all plastic features model (even though advertised with metal drive wheels by nitrotek...).

Although it's very much an entry level model I have greatly enjoyed stripping it down and learning the ins and outs of the circuitry and modules. And spotting the obvious weakpoints of plastic construction.

When trying to fix a jammed BB pellet in the barrel I noticed the resistor that goes to the firing warning LED on the turret had come apart from the solder.

In a rather amateurish fashion, the resistor only had one leg and the other side had been directly soldered onto the LED wire, giving a very weak connection that had come apart at a feather touch . So it's impossible to resolder back together securely without melting the resistor.


I reckon it's a 68ohm one - blue grey black - and it comes out at roughly that on the multi-meter but I wanted to check with you learned experts if this is the right value before I order a few.


Thanks again for being here it's been a great resource to get the most out of a tempermental machine.


My next projects are:

Realigning the drive wheels,
straightening out the road wheels by tensioning the suspension
adding another link to the tracks to stop it skipping on the sprockets.


Cheers

[Tankbear]

Hi westwick

Welcome to the forum. From memory 68ohms sounds about right but should still work with 100-200ohm resistor. Just be slightly dimmer but you probably wont notice.

Regarding track links on the tiger the inside edge has the textured end to the pin to hold in place so basically you need to push pin in from outside edge of the track.

Ian.

[jarndice]

Westwick welcome to the forum, I hope before you order more parts for your Tiger you have a close look at the vendors site because there have been a number of complaints about NITROTEK and as you will see we advise members to give them a miss if you have any doubts, of course if you get on well with them that is good news, a lot of people have issues with TANKZONE but my dealings have always been positive so I will continue to buy from him. Just beware you could have a problem. shaun

[MichaelC]

Welcome Westwick ! Just a related question, when do you need resistors for LEDs ? I am always confused about this one. For example, there is never a resistor for the MG or the headlight, but then some aftermarket LED does ask for resistor as well. Is there a general rule of thumb ? I don't know enough about it to know you need it in some places and no in others........If anyone can enlighten me on the finer points of resistors that would be great !

[Tankbear]

Michael yes you always need a resistor with LED. You don't see one for the headlights or machine gun because it is already taken care of in the RX18 or Taigen control board.

The airsoft warning light is powered off the airsoft motor supply. Which needs a moderate amount of power to work the motor the LED doesn't therefore the need for a resistor to stop to much current going through the LED and damaging it. (note a LED can only handle about 30milli amps max)

To work out resistor size for an LED

Supply votlage i.e. battery - LED voltage (normally 2-5v)

divide by the current of LED (normally 20-25mA)

Example

BAttery 7.2v
LED 3v @ 25mA

7.2v - 5v = 2.2v

2.2v/0.02A = 88 ohms

[MichaelC]

Thanks again Ian. It is safe to say that anything that runs off the RX-18 directly (i.e. Headlights, MGs and IR LEDs) are probably okay without the resistors ? Really the Airsoft warning light is more the exception then the norm I suppose.

[Tankbear]

Yeah your correct just the airsoft LED warning light is the exception.

Also forgot to mention different colour LED have different operating voltages and consumption. I think red use less power but white most. So if you add a red LED to your tank for tail light you find the headlights stop working, well basically the red is using all the power so you need to add a resistor to the red LED to stop all the power been used by the red LED and the white headlights will start working again.

Ian.

[Saracen]

The maths has gone a bit awry in that example:

Battery 7.2V
LED 3V @ 25mA

7.2V - 3V = 4.2V

4.2V/0.025A = 168 ohms

Adrian.

[Tankbear]

The maths has gone a bit awry in that example:

Battery 7.2V
LED 3V @ 25mA

7.2V - 3V = 4.2V

4.2V/0.025A = 168 ohms

Adrian.

sorry typo I was using 5v LED

[westwick]

Thanks for the responses chaps!


I knew what I was buying wouldn't be precision engineered, the service from nitrotek was great in terms of packaging and shipping, but yes I have seen a few less than pleasant reports. I quite like it's imperfections as it gives me something to work on. In future I would probably go down more consistently trusted routes for purchases but nitrotek was alright to start with.


I'll fire in a 68ohm to start with to see if that matches the existing resistor then swap in a few larger values to see what brightness I prefer. I could run without the turret LED but after modding the airsoft gun I should really have some sort of safety warning so my brother doesn't look down the barrel and blind himself.



I'm fairly handy with the electronics but I wanted to double check here because I did think it was wierd that this LED was drawing power from the airsoft motor instead of the board.


For anyone still curious about the resistore calculations. You use ohms law as above which is just Voltage =Current x Resistance

So if you have a total of 7.2V supply and need 3V over the 25mA LED that means there needs to be 4.2V over the resistor. To work out what size resistor you need you use the easy ohms law to find it. So like before, we rearrange it to find the resistance as Voltage / Current, so 4.2/0.025 = 168.


If I was to stick with a 68 ohm resistor it would give a current of (again rearranging ohms law) 4.2v / 68 = about 62mA, which seems a bit high to me. So I wonder why this was in the tank to start with. I can't really say for sure without seeing the circuit diagrams but I reckon the motor will be taking a chunk of the voltage in this section hence the seemingly low resistance value.

Any thoughts on this?