lipo possible in a nomadio react

just curious if there is a way to use a lipo battery in a react tx. i cant seem to find confirmation on a way to do it.
thanks

[MetalMan]

It is very possible, but not so simple. The React as you know uses a 4 cell NiMh battery, which is 4.8v nominal. The React is good for a little over 6v, but much more will fry the USB functionality of it (at least 2s Lipo did...). So what you need is a 5v regulator (5v UBEC works great), which will allow you to use any Lipo pack you want, I am using a 2s but 3s would be fine. However, since the Lipo pack wouldn't be connected directly to the React you won't know the voltage it is at, so there is a chance for overdischarge. To solve this I implemented a LVA circuit (audible low-voltage alarm) that kicks in when the 2s Lipo is a bit over 6v. It's a noisy little bugger so I know I have to charge the Lipo as soon as I hear it.

The complexity of this Lipo "conversion" is likely the reason why you haven't seen/heard of too many doing it.

damn ... ok was it worth it? how often do you charge and what pack did you use.
thanks for the detailed answer, much appreciated

[MetalMan]

It was totally worth it to me because I had all the components laying around and didn't have to spend even a single extra penny to do it. I had several older Maxamps 2100mah cells laying around, so I made a 2s pack out of those. It fits perfectly without sliding around.

The UBEC was a XUS Hobby one I stopped using because it caused glitching on an older 75mhz radio setup. The Lipo alarm components I had extra because I bought several sets when I built my first one. In fact I still have enough components to build a 3s LVA.

I don't charge very often at all. But lately I haven't been driving much either. These Maxamps cells are a couple years old, and it seems they don't hold nearly what they used to. However, I would estimate about 4 hours of usage before recharging, when not using any of the telemetry features aside from RX voltage.

OK, but don't some of the ubec's pop, and send full voltage through to the controller; or would it be rather safe due to the low amperage draw, or something to that effect?

[MetalMan]

The CCBEC is known to send full battery voltage when it fails, but under this loading it won't be stressed at all. I think the React pulls something like half an amp, whereas most UBECs are rated at 3+amps. You could use a linear regulator instead, but then you would lose runtime on the React because you would be burning off about 1.35watts [(7.7v - 5v) * 0.5amp].

[BrianG]

Wow, 0.5A??!! That seems high IMO. A typical 2500mAh AA battery set would last about 5 hours, so I guess that seems about right. Unless that linear regulator was heatsinked outside the radio, 1.35w is too high. Doesn't sound like much, but it is.

Or, reconfigure that 5v regulator for 6v operation. Just take a couple resistors. Then the power dissipation becomes (7.7v-6v)*0.5A, or 0.85w. Still a tad high for my taste, but workable.

Or, use a hybrid setup. Run 3s (or more) with the switching BEC of your choice set to 6v along with a LVA. That'll get the efficiency back up. Then, use that 5v regulator at the output of that as a safety net. Power dissipation on the linear reg would be (6v-5v)*0.5A, or 0.5w. If you could get a low-dropout regulator instead, you could set it for 5.5v and reduce power loss to around 0.25w. A little bit of an involved setup, so I guess it depends on how badly you want to run lipos in your radio.

[Unsullied_Spy]

Originally Posted by MetalMan

The CCBEC is known to send full battery voltage when it fails, but under this loading it won't be stressed at all. I think the React pulls something like half an amp, whereas most UBECs are rated at 3+amps. You could use a linear regulator instead, but then you would lose runtime on the React because you would be burning off about 1.35watts [(7.7v - 5v) * 0.5amp].

Would it be possible to put an inline fuse on the positive wire that would blow out instead of wiping out expensive radio electronics?

[lincpimp]

Hard to make a fuse that will blow due to a voltage increase, as that would lower the amp draw as the load is constant. Fuses work on resistance, as the amp draw rises the thickness of the fuse wire becomes incapable of allowing the current to pass thru, it then overheats and melts/pops. Overvoltage would not do that, especially as samm as 1-2v difference.

Now, I would like a lvc that does just that, cuts the voltage off completely... I have a nasy habit of leaving my m8 on at work, and going home, the 2500mah lipo will not usually last the night, unless I just charged it, which never seems to be the case. Does anyone make a lvc that passes thru power and will cut it off at a certain preset level (9v would be fine for me)?

[BrianG]

Nope. By the time the fuse blew, the damage would already be done. There was a discussion about this a while back and one of the options was to use a "crowbar" protection circuit along with a fuse. When the voltage exceeded a certain value, it would short the output to ground and blow the fuse. The other solution was to design a circuit that would interrupt the output if the voltage rose too high. Personally, this is a more elegant solution, but whatever works.

[MetalMan]

0.5A may be more than it really is, but I have never timed how long the radio would go on a full charge. But if it lasts 5 hours (remember, this is a 2s 2100mah), and the UBEC's efficiency is 80%, then the radio itself is drawing about 320mA and the draw on the battery is 400mA.