Battery timer for LiPo + switching V reg in 7E&8S

If you want to use a LiPo or LiFe in a 7E and 8S you should use a switching step down voltage regulator to get a useful increase in battery life and keep the on board voltage regulator from overheating, but then the battery monitor doesn't work because the voltage to the main board is constant and doesn't drop as the battery runs down.

How about having a universal battery timer that would count down constantly whenever the transmitter is turned on? You could then display the time left in place of the battery voltage on the display. It would be even nicer if it could take the transmit power into account. Of course you would have to monitor your battery manually the first couple of uses to determine it's run time and reset the timer to that value every time you charged it.

Do you guys think this might be a workable solution? Any volunteers to do the code?

The battery life will depend heavily on protocol used and on power selected. Do you have a particular mod with switching regulator in mind? May be voltage sensor can be re-purposed as current sensor with minimal modification and then battery measurement can be done by integrating the current.

The Pololu regulator and 4-in-1 looks like it's the best way to go on the 7E because of it's soft shutdown line. The original regulator would only have to handle the main board and no modules then.
Pololu installation: www.deviationtx.com/forum/7-development/...dule?start=780#52623

Edit: Now that I think about it, I'm not sure if the original regulator runs off the Pololu or directly from the battery. Since the stock regulator is only handling the main board, maybe it might be able to handle a LiFe or LiPo without overheating if hooked up directly to the battery and the voltage monitoring would work.

the 4in1 doesn't use the 7e's 3.3v vreg as it has it's own onboard vreg and takes it's power from the higher voltage line that fed the stock rf board

HappyHarry wrote: the 4in1 doesn't use the 7e's 3.3v vreg as it has it's own onboard vreg and takes it's power from the higher voltage line that fed the stock rf board

Is the 4-in-1 regulator switching? I would want to power the 4-in-1 thru a switching regulator when using a LiFe or LiPo for better battery efficiency and not waste the extra voltage as heat. That's why I would use something like the Pololu. But, the main point of the timer is to have at least a crude battery timer for what ever type of 7E batteries or mods you are running that keep the original battery monitor from working.

Switching regulator has it's own problems, especially for radio - it has high frequency noise. You need to carefully filter this noise, otherwise it will modulate your radio output. Admittedly, it's not that bad, but nevertheless, I'd use LDO after switching regulator. Say, battery down to 5v with switching, then LDO from 5v to 3.3v. Radiolink AT9 has one switching regulator and three LDOs serving their own subsystems - MCU, buzzer, and RF.

Almost any modern psu is switching, from any adaptor, computer power supply etc. As switching is high frequency normally 500khz - 1mHz, it is very easy to short the RF noises with relatively small filter and capacitors. I really doubt that argument of RF noise on PSU line is still valid, currently all decent design is based on switching regulators. All our products are stuffed with them and have proven themselves and we will see them more and more.......

Some exceptions indeed wil, stay for very high precision, ultra clean low noise, low current needs, then indeed analog is better.

I'm not saying it wouldn't work - it usually works. I use DC-DC switching regulators myself, but I just recently saw the warning on Adafruit's FONA 3G (actually, in the datasheet of the corresponding 3G module). They proposed using extra ferrite bead to filter out high frequency noise. And better yet to use an active filter - LDO - with good PSRR (Power Supply Rejection Ratio) at the frequency of your switching regulator.

A "global" timer is a nice thing to have so that you can track the usage of the battery in addition to the voltage reading.

On the 7e, if you use lipo, switchers are recommended. Wired properly, you'll get the correct lipo voltage.

In my practice, I used a 3.3v switcher for the 3-in-1, a 5.5v switcher for the built-in module. Both wired to the battery input circuit on the 7e which allows the monitoring of the lipo voltage. Another 3.3v ldo plus load balancing resistor replace the tiny on board 3.3v regulator to support the power down sequence AND to avoid it racing with another 3.3v regulator somewhere on the other side of the main pcb.

@YJ, Interesting,
Could you post add information on what you did modify on the 7e PSU in the corresponding topic?
As I have tried many things still cannot get my finger on the slight fluctuating voltage in my 7e at some protocols. I would like to bypass all the 7e power circuitry, but it must still save setting at switch off Tx, read raw pack voltage at tx display, able to power 1S or 2S liion or 4x nimh (pololu step/updown reg), charge lion/ using small charge module via usb port or external 5v............

@victch On a related topic...

I wonder if you used the parameter saving & power down sequence changes you are working on for the Radiolink AT9 and used them on the 7E if we could change the 7E power switch to a true hard battery switch and avoid some complications on voltage regulator choices & installation due to soft power down.

Then we could just have LiPo -> front switch -> 5V switching regulator -> parallel feeds to main board & 4-in-1

This code is not stable yet, but in theory you can do this.

@Fernandez

Absolutely.

www.deviationtx.com/forum/7-development/...7e-power-supply-mods