cc bec question

[JERRY2KONE]

Originally Posted by slimthelineman

Thought of that but not sure how I would know when I was aproaching the lvc of 9v for the 3s unless the cc bec has a lvc built in. Haven't been home to mess with it been on storm work for the last couple days bit I will mess with it tomorrow. Also the small 3s I have is too long I think to cram inside the tx where the four aa batts went. I'll post a pic or two of the whole setup when I'm done.

Brian G actually did a conversion thread on this a while back and once you open up the radio you can totally remove the 4 AA battery tray and place somthing else in its place if you wish. I am doing the same conversion on my DX3R but using a Hydromax NMH battery pack. I like the idea of using the CC BEC though to protect the radio, but not sure if you need it. Do a search in here for DX3R conversion and you might find that project that BG did. Good luck with that and let us know how it works out for ya.

[JERRY2KONE]

Here is his comments from that thread. I hope this helps to answer your questions.

I wasn't sure what the effects of running just 4.8v (4 X NiMH cells) was, so modded the radio tray to use 5 NiMH cells (6v) to match what 4 alkaline AAs would put out voltage-wise. The voltage of 5 freshly peaked NiMH cells is closer to 6.5v, but hasn't harmed my radio yet.

To use lipo, you could go a couple of routes:

1: Use 2s lipo with a linear voltage regulator. An LM7805 linear regulator would work fine, but only gives 5v. You can easily boost it with the addition of a couple of resistors to get 6v though. And since radio current draw is small, you shouldn't need a heatsink. I figure 400mA worst case current draw (judging by the runtime I get on 2500mAh NiMHs), which equates to 0.96w when the lipo is at 4.2v/cell, and 0.4w when the lipo is at 3/5v/cell. I wouldn't run the lipos down much beyond that because at low current draws, you have much less voltage "rebound" when you remove the load. And at that point, there isn't much runtime left anyhow.

2: Use whatever cell count lipo you want and hook that to a switching BEC. The higher voltage you go, the lower current draw from the lipos. If you use 4s lipo, current draw will be around 200mA if the radio is drawing 400mA @ 6v. The trouble with this setup is that if the BEC fails, it could send full battery voltage to your radio. Not good. So, I would use something like the CCBEC with a programmable output, set it to something like 7.2v, and then use a linear regulator to take it the rest of the way down to 6v. Power loss on the linear regulator will be minimal since the delta voltage is small, yet it provides protection if the BEC should fail. The worst that will happen if the BEC failed is that the linear reg would heat up and thermal, which should be a good indication that something is wrong. Despite the poor efficiency of linear regs, they are pretty bulletproof; you really have to try to break them.

In either case, you'll also need to add some sort of LVC, low voltage alarm, or small voltmeter panel (like this). Otherwise yoou run the risk of discharging the lipos too far.

So, I found it much easier to just stick with NiMHs in this case.