RC Tank Warfare community hobby forum

Hi Jib, I was thinking about this more and it seems to me the other bottleneck you may have, in addition or perhaps instead of your battery, is the 5 volt regulator on the TCB. If I understand you correctly, you have attached the output of the headlight port to your step-up voltage regulator, which then powers your LEDs. So the 5 volt source that is then stepped up (the output of the light outputs on the TCB is 5 volts), is coming from the 5 volt regulator on the TCB.

As I mentioned before, a step-up regulator must draw additional current in order to transform a lower voltage into a higher voltage. This extra current needs to be supplied by your battery, but in this case since it is coming through the 5 volt regulator on the TCB, that regulator must also be able to pass that current even if your battery can provide it.

The 5 volt regulator on the TCB is doing the opposite of what your step-up regulator is doing - it is converting a higher voltage (your 3S battery), into a lower voltage (5 volts). In this transformation, the difference is manifested as heat, which reduces the efficiency of the 5 volt regulator. First you are providing ~12 volts (3S battery) which is converted to 5 (with heat and loss of efficiency), and then you are converting it back to 12 volts which means drawing more current. It sounds like it often works, but clearly there are certain moments, for example right when the lights turn on and there is an inrush of current, where something is dropping even if only very briefly below some threshold level, and it only takes a brief moment to cause the processor on the TCB to brown-out (reset or shut down).

Since your LEDs need a higher voltage, the process of stepping down the voltage first and then stepping it back up afterwards is not ideal, and I don't know if your battery is being overloaded or the regulator on the TCB, or maybe both. You can increase the size of your battery and see if that helps, but there is no way to change anything about the regulator on the TCB. This regulator can in theory supply up to 3 amps, which I'm sure is enough for your LEDs, but that's in ideal conditions, and as it heats up it is able to supply less and less current. One other thing you could try is to swap out your 3S battery for a 2S battery, that means the TCB regulator has less work to do since it doesn't need to drop ~12 volts to 5, but only ~8 volts to 5.

Or you can just give your LEDs ~12 volts directly without stepping down and then back up, this is the idea of using a 5 volt relay. The TCB will control the 5 volt relay, which is easy, and then the relay will give the higher voltage directly to the LEDs.

I mentioned before that you could try a relay module on one of the general purpose I/O ports, if you have one of those free. If not, you could still control a relay directly from the Headlight output, though if you use one of those off the shelf modules you will have to do some extra wiring, and if you use a standalone relay you will have to add a flyback diode. I can give you more information on how those would be connected if you decide to go that route.

LukeZ wrote: ↑Mon Jan 05, 2026 4:46 pm Hi Jib, I was thinking about this more and it seems to me the other bottleneck you may have, in addition or perhaps instead of your battery, is the 5 volt regulator on the TCB. If I understand you correctly, you have attached the output of the headlight port to your step-up voltage regulator, which then powers your LEDs. So the 5 volt source that is then stepped up (the output of the light outputs on the TCB is 5 volts), is coming from the 5 volt regulator on the TCB.

As I mentioned before, a step-up regulator must draw additional current in order to transform a lower voltage into a higher voltage. This extra current needs to be supplied by your battery, but in this case since it is coming through the 5 volt regulator on the TCB, that regulator must also be able to pass that current even if your battery can provide it.

The 5 volt regulator on the TCB is doing the opposite of what your step-up regulator is doing - it is converting a higher voltage (your 3S battery), into a lower voltage (5 volts). In this transformation, the difference is manifested as heat, which reduces the efficiency of the 5 volt regulator. First you are providing ~12 volts (3S battery) which is converted to 5 (with heat and loss of efficiency), and then you are converting it back to 12 volts which means drawing more current. It sounds like it often works, but clearly there are certain moments, for example right when the lights turn on and there is an inrush of current, where something is dropping even if only very briefly below some threshold level, and it only takes a brief moment to cause the processor on the TCB to brown-out (reset or shut down).

Since your LEDs need a higher voltage, the process of stepping down the voltage first and then stepping it back up afterwards is not ideal, and I don't know if your battery is being overloaded or the regulator on the TCB, or maybe both. You can increase the size of your battery and see if that helps, but there is no way to change anything about the regulator on the TCB.

I tried with the 5200 mah, and it behaved the same as the 1300 mah

LukeZ wrote: ↑Mon Jan 05, 2026 4:46 pm This regulator can in theory supply up to 3 amps, which I'm sure is enough for your LEDs, but that's in ideal conditions, and as it heats up it is able to supply less and less current. One other thing you could try is to swap out your 3S battery for a 2S battery, that means the TCB regulator has less work to do since it doesn't need to drop ~12 volts to 5, but only ~8 volts to 5.

Or you can just give your LEDs ~12 volts directly without stepping down and then back up, this is the idea of using a 5 volt relay. The TCB will control the 5 volt relay, which is easy, and then the relay will give the higher voltage directly to the LEDs.

I mentioned before that you could try a relay module on one of the general purpose I/O ports, if you have one of those free.

You know me, I have zero open ports. Pretty much everything is being used

LukeZ wrote: ↑Mon Jan 05, 2026 4:46 pm If not, you could still control a relay directly from the Headlight output, though if you use one of those off the shelf modules you will have to do some extra wiring, and if you use a standalone relay you will have to add a flyback diode. I can give you more information on how those would be connected if you decide to go that route.

I think I will try this next. If you don’t mind, I will link a relay to here, or if you know of one I could use let me know, and maybe you could guide me through what I need to do to get it running. It would be nice if I could get one where I don’t have to use one of my mini 5v ESC to provide a signal channel, but I can do that if it’s easier than using/finding one that just takes a positive/ground.

So here is something I discovered while using the larger battery today that’s a head scratcher. Everything I’m about to describe also applies to the smaller battery, I tried this with both.

When I plug the battery in, the TCB turns on and locks up (red LED stays on, headlights stay on) every time. If I hit reset, everything starts up normally.

Then I switch the main power on (40v to the motors) and everything is fine.

Then I turn the headlights on, the TCB turns “off” (all LEDs are off) completely.

I press the reset button on the TCB, starts up fine, now I can switch the lights on and off as much as I want. No problem.

Now, if I cut the power by turning off the main power and unplugging the battery from the TCB (I don’t have a switch for this yet), the whole process starts over again (lock up, reset, lights on, TCB turns off, reset, works fine). Same if I switch batteries. Something about unplugging the battery or cutting power to the TCB makes this whole process start over again, every time I tried this.

Alternatively, I have some LED bulbs of the appropriate diameter and color that do not have a resistor on them and are 2.2-2.3V. Could I put these in series with the TCBs headlight circuit and not have them blow (I have a bunch, I could just try it) or would 5V be too much? I guess I could also get an appropriately sized resistor as well and put that upstream of the first headlight. That may end up being a more elegant option than adding another relay. I just don’t know if the LED would be as bright, but I guess if the resistor is being it down to 2.2v anyways, then it would probably be the same?

As always appreciate the detailed response and help!

EDIT: Upon further examination I think I am going to do two LEDS connect in parallel with appropriately sized resistors so they take 5v each. It’s going to be a pain in the butt to get the LEDs out of the headlights, but I think I’ll be happier that I did in the long run

Hi,
This may or may not be related but...check out this thread on the Open Panzer forum where i had a similar issue, not with a genuine TCB but with a diy one i built

https://openpanzer.org/forum/index.php? ... 74#msg3174

I managed to isolate it to the 5v voltage regulator chip on the board, its parameters had gone out of whack over a period of time and was locking up and rebooting as its current / voltage draw was much less than it should have been and was tripping its internal shut down parameters... its quite similar to what you are experiencing.....might be of use.
Worked for me.
Good hunting.
Sub.

Jib wrote: ↑Mon Jan 05, 2026 10:06 pm So here is something I discovered while using the larger battery today that’s a head scratcher. Everything I’m about to describe also applies to the smaller battery, I tried this with both.

When I plug the battery in, the TCB turns on and locks up (red LED stays on, headlights stay on) every time. If I hit reset, everything starts up normally.

Then I switch the main power on (40v to the motors) and everything is fine.

Then I turn the headlights on, the TCB turns “off” (all LEDs are off) completely.

I press the reset button on the TCB, starts up fine, now I can switch the lights on and off as much as I want. No problem.

Now, if I cut the power by turning off the main power and unplugging the battery from the TCB (I don’t have a switch for this yet), the whole process starts over again (lock up, reset, lights on, TCB turns off, reset, works fine). Same if I switch batteries. Something about unplugging the battery or cutting power to the TCB makes this whole process start over again, every time I tried this.

Hi Jib, what you are describing here sounds like the inrush current when things are starting up is too much somewhere, causing source voltage to drop, and the TCB is browning out. When you plug in the battery there is an inrush current to charge the caps on every device that is being turned on, and when you turn on the headlights we have already theorized that the extra load of your step-up converter is too much. So this is not too surprising.

I know you have a lot of circuits in your tank, and taken all into account, the combinations of everything that might contributing to this behavior is so complex it's impossible for me to diagnosis from here. Maybe even there's a ground loop somewhere, who knows.

Jib wrote: ↑Mon Jan 05, 2026 10:06 pm Alternatively, I have some LED bulbs of the appropriate diameter and color that do not have a resistor on them and are 2.2-2.3V. Could I put these in series with the TCBs headlight circuit and not have them blow (I have a bunch, I could just try it) or would 5V be too much? I guess I could also get an appropriately sized resistor as well and put that upstream of the first headlight. That may end up being a more elegant option than adding another relay. I just don’t know if the LED would be as bright, but I guess if the resistor is being it down to 2.2v anyways, then it would probably be the same?

The vast majority of LEDs are rated somewhere in the 2-3 volt range that you describe, and that does not prevent them from being very bright. There are extremely bright LEDs that run at these voltages, they just draw a lot of current. What is surprising to me is that your tank came with LEDs that actually require 9 or 12 volts, I wonder if there isn't some kind of circuitry hidden somewhere in the headlights or something that isn't dropping that down.

But anyway, if you want to run multiple LEDs it's best to put them in parallel with a single upstream current limiting resistor. Yes, it is possible to take two 2.3v LEDs and put them in series and then give them 5 volts, but it's not usually recommended, unless you're using a LED driver chip. Just do them in parallel and add the correct resistor.

Jib wrote: ↑Mon Jan 05, 2026 10:06 pm EDIT: Upon further examination I think I am going to do two LEDS connect in parallel with appropriately sized resistors so they take 5v each. It’s going to be a pain in the butt to get the LEDs out of the headlights, but I think I’ll be happier that I did in the long run

I think this is the best approach.

LukeZ wrote: ↑Tue Jan 06, 2026 9:30 pm

Jib wrote: ↑Mon Jan 05, 2026 10:06 pm So here is something I discovered while using the larger battery today that’s a head scratcher. Everything I’m about to describe also applies to the smaller battery, I tried this with both.

When I plug the battery in, the TCB turns on and locks up (red LED stays on, headlights stay on) every time. If I hit reset, everything starts up normally.

Then I switch the main power on (40v to the motors) and everything is fine.

Then I turn the headlights on, the TCB turns “off” (all LEDs are off) completely.

I press the reset button on the TCB, starts up fine, now I can switch the lights on and off as much as I want. No problem.

Now, if I cut the power by turning off the main power and unplugging the battery from the TCB (I don’t have a switch for this yet), the whole process starts over again (lock up, reset, lights on, TCB turns off, reset, works fine). Same if I switch batteries. Something about unplugging the battery or cutting power to the TCB makes this whole process start over again, every time I tried this.

Hi Jib, what you are describing here sounds like the inrush current when things are starting up is too much somewhere, causing source voltage to drop, and the TCB is browning out. When you plug in the battery there is an inrush current to charge the caps on every device that is being turned on, and when you turn on the headlights we have already theorized that the extra load of your step-up converter is too much. So this is not too surprising.

I know you have a lot of circuits in your tank, and taken all into account, the combinations of everything that might contributing to this behavior is so complex it's impossible for me to diagnosis from here. Maybe even there's a ground loop somewhere, who knows.

Yes but most everything is off when the TCB is started. Power to all of the FPV stuff is off (via a physical switch), power to the smokers is off (via the relay being in the off position). The only things I can think of that get power at start up are the two RX’s, the DasMikro, a 12v to 8.4v step down, a 8.4v servo (recoil), a 5v step down, and the LED’s (headlights, tail lights, coax MG, aux MG that all flash in start up, maybe the LED’s with the 12v-5v->12v are causing this). Maybe that’s a lot, I dunno.

LukeZ wrote: ↑Tue Jan 06, 2026 9:30 pm

Jib wrote: ↑Mon Jan 05, 2026 10:06 pm Alternatively, I have some LED bulbs of the appropriate diameter and color that do not have a resistor on them and are 2.2-2.3V. Could I put these in series with the TCBs headlight circuit and not have them blow (I have a bunch, I could just try it) or would 5V be too much? I guess I could also get an appropriately sized resistor as well and put that upstream of the first headlight. That may end up being a more elegant option than adding another relay. I just don’t know if the LED would be as bright, but I guess if the resistor is being it down to 2.2v anyways, then it would probably be the same?

The vast majority of LEDs are rated somewhere in the 2-3 volt range that you describe, and that does not prevent them from being very bright. There are extremely bright LEDs that run at these voltages, they just draw a lot of current. What is surprising to me is that your tank came with LEDs that actually require 9 or 12 volts, I wonder if there isn't some kind of circuitry hidden somewhere in the headlights or something that isn't dropping that down.

They didn’t, the model originally came with something else that got burned out when I was upgrading everything… my bad.

I stupidly thought more volts meant more brightness…

Thanks for the information on LEDs, I’m still learning.

LukeZ wrote: ↑Tue Jan 06, 2026 9:30 pm
But anyway, if you want to run multiple LEDs it's best to put them in parallel with a single upstream current limiting resistor. Yes, it is possible to take two 2.3v LEDs and put them in series and then give them 5 volts, but it's not usually recommended, unless you're using a LED driver chip. Just do them in parallel and add the correct resistor.

Jib wrote: ↑Mon Jan 05, 2026 10:06 pm EDIT: Upon further examination I think I am going to do two LEDS connect in parallel with appropriately sized resistors so they take 5v each. It’s going to be a pain in the butt to get the LEDs out of the headlights, but I think I’ll be happier that I did in the long run

I think this is the best approach.

I will start by converting the 12v LEDs to 5v LEDs in parallel via a single resistor and then get back here with the results from that. Probably going to be a bit, I’m in the middle of taking down/putting away Christmas stuff and retrieving/putting up Carnival/Mardi Gras stuff.

Thanks for everyone’s help and suggestions!