fried circuit question

[penguin]

Hey guys,

After I bought my first MT i was disappointed with its performance. It only ran for like 3 minutes. So i bravely decided to replace the battery with a game boy sp battery. Its a 3.4 600 mAh battery. As soon as I turned my truck on, I noticed smoke and it became super hot. My question is do you know the max voltage and current the ZZ MT can take? What is your battery mod and how long does the MT run for?

thanks,

['Vette Nerd]

Dude, why would you want to waste a 20 dollar battery like that? Micro Rcs are just like that, their charge doesn't last long.(One thing you could do is charge it twice to get 6 min. of life). Although it is strange that the battery would fry it like that though, good question.(I think the ZZMTs max voltage is about 5 volts, anything more means the scrap heap for your monster.) That's all I know. Although if I were you, I would clean that monster up and exchange it for another. Then, if the SP battery ain't fryed, try it again.

[penguin]

The most batteries together I have seen for a ZZ is a 4 battery mod attached in parallel for more current. Which is about 400 mAh. The voltage is not a problem, i think its the current that kills it. I guess the 4 cell mod should make me stop complaining.
I noticed that some people have a 4 gear mod on their MT. Which extra gear do you guys use? The only extra ones I have are the regular zip zap green gear. Would that along with the orange MT gears and motor be strong enough in your opinion or what’s the best combo with speed and torque?

Thanks for your help.

[Azimov]

The MT battery pack is 2.4VDC @ 120mA. The battery you used is 3.4@600mA. 600mA is not a problem at the voltage of the original battery or 2.4VDC. When you add that other volt to the current, you're pushing too much in at once and frying the circuitry. You are going to have to restrict either the current or the voltage in order to use that battery. And, if longer runtimes is your goal, you'll need a voltage regulator between the battery and the PCB that will restrict voltage to 2-2.4VDC.
As to gearing, check out Chili's ZZ site. He has all the info you need there. Sorry, can't provide a link right now, but you can find it all over the forum.

[Michael.mt2k]

That's an interesting idea!
I have an extra GBA SP battery too!
Longer running time would be awesome, given the extra power that multi-gearing and upgrading the steering motors draws.

Seems to me you might be able to get away with just the dropping resistor, but I haven't done the math yet.
I guess I need to see if they have a low voltage regulator for this task as well.

I guess I may have to bite the bullet and buy out my store's remaining stock of ZZMTs just to have "mod fodder"!!
I've destroyed one MT trying to do the articulation mod, but I can do the other engineering mods all day!

[Michael.mt2k]

Waitaminute.

That isn't THAT high a voltage jump!
If people are running quad cells, then that is doubling the voltage.
The GBA battery isn't doubling the voltage, and the MT is only going to draw the amount of current it requires to do what it's doing!!

I am going to go out on a limb here and ask this one simple question:
Did you get the polarity right on the battery connections?

If not, that would explain what happened.
Otherwise I don't see any reason this shouldn't have worked.

I'm guessing you shorted something. I have had 3 quad cell MT's and never fried one. I've made my brother and his friend tri cells too.... we have never had a problem.

I'm guessing you shorted something out when you hooked up the battery. The excessive current is not the problem because, as previously stated, the truck will only draw as much current as it needs. THe fact that I have run 7 trucks with that high or higher voltage with regular motors leads me to believe it was a mistake when hooking up the battery.

Do you remember what color smoke it was? A blueish color usually means a capacitor. Most of the the other components on there can burn up, but none of them should really smoke.

[penguin]

I dont believe that I made a mistake but i guess it possible. So are you telling me that you ran even higher voltage and current and your MT did not burn? If so than I made a mistake hooking up the battery. As for the smoke color, it was dark gray. The diode is completely cracked and the heat around some IC was so intense that the solder began to turn into liquid. The IC and the diode are the only components I noticed damaged. But anyways thanks for your help. Even since that incident though, I will always be afraid the use the GBA battery.

[Azimov]

No, you guys aren't seeing the big picture here. Higher voltages will work at the low 120mA current range. Higher current will work at a lower voltage range. But, you can't increase both at once. Something has to give and it will be the surface mount components on the PCB that are rated at lower specs than you are applying.
Now this "the truck will draw no more than it needs" is nonsense. We're talking about the upper end of the voltage and current limits of the electronic components in the PCB.
You can run an MT at 5-6 VDC or so if the current remains low.
Though you are pushing things. Now increase the current as well, and your electronics are toast. Remember voltage is like pressure and current is like the flow of water. If you increase the pressure (voltage) you can push through more water at once. If you increase current flow, more water moves at a given pressure. If you increase both, you are dumping huge amounts of current very quickly and the components can't take it.

[Michael.mt2k]

Hey I'll buy that. You're right of course!

Now that I've eyed up that battery with an MT chassis I think I'll use them both as two great excuses not to try it! LOL

I don't think you were following what I was saying. If we go back to ohms law, of course more current will flow with a higher voltage becuase I = V/R. What I was saying though is the current is also dependent on the resistance of the circuit, meaning the circuit has to draw the current from the battery. It's not the battery itself.

You can't arbitrarily increase voltage without current. You can limit the current that is hitting the pcb if you put in a resistor before it, but that is only dissipating some of the increased current.

The analagy to water flow only goes so far. Trying to increase the water output of a little hose by increasing pressure will saturate.

"No, you guys aren't seeing the big picture here. Higher voltages will work at the low 120mA current range. Higher current will work at a lower voltage range. But, you can't increase both at once. " --- This is wrong.

Current from a battery has nothing to do with the 120mAh rating. That is simply the capacity of stored charge in the battery. The only way to get higher current with lower voltages is to decrease the resistance of the circuit. Increasing voltage will increase current unless there is something saturating or a limiting component.

The truck will draw what it needs (though that can be too much at times). From it's inherent resistance, it will pull the corresponding current via I = V/R. The curciut determines the current pulled from the battery.


And yes, i've run at least 7 MT's with 3.6 - 5 volts. None of them have fried and it has nothing to do with the mAh rating of the battery.

[Azimov]

You can't arbitrarily increase voltage without current.

That's what I was saying, in a nutshell.
The general point being that putting 5VDC @ close to 1 Amp into a circuit designed to operate at 2.4VDC @120mA, is probably ill advised.

[penguin]

Would a li-ion battery with about 2.4 and 120 mAh work fine with better run time? Or what about AAA rechargable radio shack Xmods batteries (1.2V 700 mah) in parellel or one? What kind of a battery hook up would you recomend.

Thanks again

[Azimov]

Would a li-ion battery with about 2.4 and 120 mAh work fine with better run time?

It would work fine, but you will get no increase in runtime or speed.

Or what about AAA rechargable radio shack Xmods batteries (1.2V 700 mah) in parellel or one?

Two in series will give you stock speeds with unreal runtime. But, you will be carrying alot of added weight, which will shorten that runtime.
I can't recommend any battery configuration for you as I like the MTs as they are. If longer runtimes are mandatory for you, I would suggest buying a peak charger.

[Michael.mt2k]

That would be two in parallel for longer run time, doubling the current.

Series doubles the voltage for zoominess.