Devo 8 battery

I am new to the Devo 8 still waiting for it to be delivered, can i use a 7.4 800 mah 2 cell lipo in this beauty.

Or do you have a better config.
Regards'
Bill.

I believe there are people that do, but let me open that old can of worms, my question would be why?

The Devo 8 has linear regulators taking the 7.4 voltage down to 5 and 3.3 volt respectively, the difference is lost as heat. It has an internal charge circuit and connector to charge NiMH batteries, while
you have to take the LiPo out to charge it.

Get your self low discharge NiMH batteries,4 x 2000 or 2500mAh and you will have no issues.

Hi, thank you all for your reply i have 2700 nimh will these be ok.
Bill.

I put the inner cage out of the battery compartment of my 8S and now there is space enough to put in 5 NiMH cells of 2300 mAh. The Voltage is the same as you use standard batteries = 6 Volt, but the pack lasted ever longer.
Unfortunatly there ist no way to load the pack with the electronics of the Devo.

Greetings, has anyone used a timer to count transmitter on time. I found this feature in my old radio useful to gauge battery life. Using a lipo on that radio... 10 hrs. was time to charge at which time I reset the on timer.

Thanks much for the Lipo warning. I just added one this morning that will be removed. What about life? fully charged the 2 cell is about 6.6 volts.

Hi PB

I don't think that the 5 cells will damage my Devo. The possibility to operate the Devo with 4 x 1, 5V standard cells can be found in the manual.

I agree with your statement about the wasted energy. I have installed a better voltage regulator in my 2801Pro which worked more efficiently than the original from Walkera.

I am considering whether it makes sense to equip the Devo also with a 3,3V voltage regulator and then return to 4-cells.

On my photo of the PCB I can see only the 7806 for recharging the batteries. Do you know where the linear regulator is located and whether it makes sense to change it with a high effective one?

So a 1s 5000 mAh lipo would be enough?

dobosatti wrote: So a 1s 5000 mAh lipo would be enough?

Given that a full charged 1S lipo will start at 4.2V, you should be able to use it down to about 3.6V, below this your guess is as good as mine as to what will happen, especially at higher power levels.

However being a 5000mAh lipo, it should take a while to get down to to 3.6V.

PhracturedBlue wrote: The devo8 runs at 3.3V (even the radio which takes a 5V input, reduces it to 3.3V) but you are providing either 4.8 or 6V to it. Since we're not using a fancy dc-dc converter, the wasted power will be (battery-voltage - 3.3V) * (current used by Tx). the latter is fixed, so you can see that by increasing battery voltage, you increase wasted power.

I have done some measurements on the Devo8s to understand the risk of using a 2S (7.4V) lipo battery. (Personally I use NiMH charged through the 12V external "Power Connector(8-12VDC)".

AS PB explained earlier and quoted here, all the electronics runs of 3.3V regulated by linear LDO regulators. All voltages above that just becomes heat.

The Devo8s design voltage range (battery voltage) seems to be in the range of 3.5-6.5V, based on the support for 4x 1.2V NiHM or 4x 1.5V alkalines. This battery voltage is supplied through a smallish Schottky diode directly to the LDO regulators which drops it down to 3.3V.

There are two risks using a 7.4V Lipo, the dropped voltage x current (= Watts => heat) is more than the LDO can distribute into the PCB or radiate into the air to stay cool. The danger here is that nothing will get damages during a quick test, but for longer use at high RF outputs, it could be just a matter of time before the LDO overheats and you buy a new Devo8.

The second risk is the maximum input voltage the Devo8 components can handle. The RT9167A LDO, generating the 3.3 V for the CPU, can handle only 8.0V maximum. Using a fully changed 2S lipo (8.4V) you are already above the absolute maximum voltage the LDO manufacturer allows, and with repeated use it is a matter of time before the LDO's are stressed beyond it specs and you buy a new Devo8s.

I have not check which LDO is inside the RF module, but I would assume the same, which means you have at least two LDO's that may not survive repeated use of fully charged Lipos.

If you really what to use a 2S lipo, put at least 2 diodes (1N4001 or similar) in series with the red wire going to the Devo battery connector. This will prevent it from being charged if you forget you still have the lipo in there, and secondly it will drop the maximum Lipo voltage to below 8 Volt and dissipate some heat in the two diodes, rather than in the LDO's and PCB.

I do apologize if this is elsewhere, please could someone clarify specifically lowest safe voltage to fly with on a Devo8 and Devo10, bear in mind the voltage may drop some during that flight. I do realize this depends on the capacity of the battery, but at what voltage does the radio become unstable/unpredicatble is what I am after please, if I can practically use a big mah 1s in my Devo8 I am gonna go that way instead of my 2s life. Big capacity AA nimah are great but I forever forget to charge the damn things ...

Hi Steve

Deviation has the low battery voltage warning to warn the operator, making him responsible for the battery power management. The code also prevents writing to (and possibly corrupting) the Flash memory (File System) when the battery voltage becomes to low. My feeling is there is little more the system or code can enforce or do to protect the operator.

I don't think there is "safe" Voltage Level for a battery - Deviation (can only) measure the Battery voltage as an indication (proxie) for the battery power available and thus "would differs for every battery size, type, age/condition and capacity.

The lower "safe" voltage level of a battery depends on the slope of the voltage drop against power drain - it will obviously be very different for a 1S, 5000mAh battery, 2S 800mAh or 4x NiMH 2000mAh. Using 3.6 V as a alert level (Disclaimer: I don't know if this is safe level) a battery may still give you minutes to fly and land once the "unsafe" 3.6V level is reached, while a set of NiMH batteries may barely give you time to land once the alert triggers at 3.6V. An the of course the condition of your specific battery plays a big role.

TESTS
Having said that, I shall do some tests using a variable power supply at 150mW for the Devo protocol using both the Devention and Deviation Firmware. This should give us a good reference point when the CPU will resets and at what voltage the RF Model transmission starts to become affected. Give me a few days...

The DEWO 12S Tx battery is 1S 3000 mAh.
Much different from the elektronoka DEWO 8S Tx?

Hi Dobosatti

I don't have a DEVO12s, unfortunately I cannot check.

Steve

I have done the tests on the Devo8s with Deviation firmware, I also have a Xl7105 module and a CC2500 module installed, so the readings could be different for Devo8s without any additional modules.

To summarise:

Devo8s, Devo protocol, 8Ch
Input Voltage at battery connector: 6.0Volt

150mW -> 325mA (DSMX -> 375mA; j6Pro-> 387mA)
100mw -> 313mA
10mW -> 302mA
1mW -> 295mA
0.1mW -> 294mA

From 6.0V-3.50V the RF signal is stable and stays the same, below 3.50V the signal patterns on spectrum analyser started changing.

My Conclusions

On the Devo8s any battery with voltage between 6.5V and 3.5V would be ok.\

Above 6.5V I would be careful about running 150mW for long periods, especially on the DMXand J6Pro protocols, which seems draw 10-20% more current through the LDO's. (refer my post above)


Warning

The on-screen voltage display of Deviation is not very accurate, I remember PB had mentioned something about this, but I could not find it in the forum posts.

Deviation cannot read/display below 3.93V and the reading also seems about 200mV to low - so don't use this as an indication of you battery voltage below 4.00 Volt!

Vbat Screen Difference
6.03 5.83 200mV
5.54 5.34 200mV
5.06 4.86 200mV
4.53 4.33 200mV
4.02 3.93 90mV
3.52 3.93 -450mV

I'm now I'm using 4 pieces of NiZn 1.6V 2800mAh battery.
Takes a long time to upload.
It is therefore thought to swap for 1 or 2s 4200 mAh Li-ion battery.
I am now a dilemma of what to do.
I have 2 pieces of 4200 mAh Li-ion cells.
If there is a line, added 8.4 was 4200 mAh.
But more than 8 V is not recommended.
Parallel is filled with 4.2 V 8400 mAh. Safe to use a 1 cell?
If you would like to use 2S battery, then we put it into a 3A diode?
Thus, the reduced voltage 7.6 V

Fantastic thank you for this, a valuable post. This clarified for me personally I think then probably take the time to charge my 4x2700mah NiMh for the long days out at the field, and then for stuffing around in the garden and after work then quick charging & keep my LiFe 2S handy. I don't think I will run a 1S until if it's even possible to get the voltage on the screen more accurate/reliable.

Just a bit offtopic but still related to this thread.

First, thank to RandMental, great work dude!

Second, it should be possible to increase battery life by replacing the linear regulator with a switching dc-dc regulator.

I have this on order for my Devo 10:
uk.farnell.com/jsp/search/productdetail.jsp?SKU=1696320

Inside my 10 there is this 78d05ag linear 5V output regulator that I intend to replace. From what I've read on the net it should double the battery life. I'm looking at ~95% efficiency at 12V input. That's massive compared to what's in currently.

Once I get the switching reg I'll create a separate thread and keep you posted.