Spektrum DX3r Battery Mod
 

It's nice that the Spektrum DX3r only uses 4 batteries, but the voltage gets a little low when using NiXX vs Alkaline. Maybe on a peaked charge, the NiXX might get to 1.4v/cell, but I don't peak my Tx batteries that high, so maybe 1.3v. At 4 cells, that's only 5.2v. Sooo, I decided to add an extra NiXX cell in there to get the full 6v. Peaked, it might see around 6.5v, but Alkalines aren't exactly 1.5v/cell either...

I opened her up, disconnected the power wires, and took out the battery tray. Nothing magical here, but that block of plastic intrigued me....

http://scriptasylum.com/forumpics/dx3r_mod_1.jpg

So I ripped it out. :smile: And 'lo and behold, two more battery slots! However, there are no actual battery contacts. Poo.

http://scriptasylum.com/forumpics/dx3r_mod_2.jpg

Well, I'm sure we all have at least one or two of these laying around. Makes a good donor for a battery contact terminal!

http://scriptasylum.com/forumpics/dx3r_mod_3.jpg

The battery area without the tray. Looks empty.

http://scriptasylum.com/forumpics/dx3r_mod_4.jpg

It was just a matter of creating another set of battery contacts in the next empty slot and completing the circuit. I did have to extend the wires a bit to give me room to work - Spektrum doesn't give you much wire slack!

I should have taken more pics, but I forgot about the camera and got over excited, so all you get to see is the finished tray with 5 cells. Sorry! :oops:

http://scriptasylum.com/forumpics/dx3r_mod_5.jpg

And of course it works! Note the voltage of 5 freshly charged NiMH Duracell AA's.

http://scriptasylum.com/forumpics/dx3r_mod_6.jpg

Before you go tearing up your $300 radio, let me say getting the switch and power jack back where they needed to go was a PITA. My fingers are too big for such small work. Nevertheless, it IS possible, but don't blame me if you wreck your radio!

Very nice Brian. :great:

So how do you like your DX3R over your old DX3.0? I will soon run out of model space on my DX3.0 and was thinking about upgrading. Is it easy to use? Can you run the same receivers on the DX3R as you do on the DX3.0?

Nice job on installing the 5 cells btw. :yes:

nice to see that the battery tray already has two extra slots. not sure I want to take apart my new radio though.

jnev: I like it a lot. I really only got it for the multiple model memories, but the menu system is pretty cool, it's lighter, and balanced better. Works with the older Spektrum receivers, but they only work in DSM1 mode, not DSM2 (no big deal since I can't tell the difference anyway). One thing I will say: If you reset the parameters, make sure to recalibrate the throttle and steering throws! Failure to do this leads to undesirable operation!

gixxer: Yeah, I can understand that. But I wanted a more stable voltage more than I wanted a warranty. If I needed to do a warranty claim, I can always add a jumper in that last cell spot and put that plastic box back in and no one would be the wiser. But I would only do this if it broke because of something unrelated to what I did.

:lol: I like it and might have someone I know do it to my controller but myself I dont like to soldier stuff that small. In stock form the batteries last pretty good but the extra voltage would make it great. Would probably last as long as the lipo did in my z-1 then.

I toyed with the idea of using lipos on a UBEC with a custom LVC circuit, but didn't like that idea too much. For one, I already had the batteries, so the mod was "free". Two, if out playing and don't want to stop, I can run down NiXXs lower than I would normally without too much adverse affects, but lipos...

Spektrum says the lower overall voltage doesn't affect range, and that makes sense if everythig was designed for 6v. But if the battery goes as low as 4.5-5v, that's gotta affect the range somewhat I would think. This just makes sure I have a solid 6v no matter what. Even at 1.1v/cell "cutoff", I'd still have 5.5v minimum.

I'm sure you are aware that I'm running Lipo/UBEC in my Nomadio React. TBH, I don't think you could really understand all of the benefits of this setup until you actually use it :angel:. No self-discharge, easy charging, super-long runtime (NiMh doesn't always put out what it's rated for...), and the ability to say "my TX runs a Lipo, and yours doesn't!". As for running rechargable AAs too low, my React actually stops functioning at about 4.5v, all the while the vibrate/audible alerts are going haywire. The Lipo is just so much better, with a switch between the Lipo and the UBEC, and an audible low-voltage warning hooked up to the UBEC input.

This makes me wonder - the React runs 4 rechargable AAs stock. Granted, it's not "DSM", but still. And the React is supposed to have a 10x greater output power than the Spektrum radios. Ideas?

Brian i just did this to my DX3R and it was really easy. Thanks for the great directions. Now you or somebody needs to figure out how to install a backlight. :mdr:

Well done, that is a top mod

Great mod Brian!

Quick question.... With the tray removed did it look like there would be anough room to fit 2 a123 cells in there? I have been toying with the idea for a while, but havent gotten around to tearing up the radio to check out feasability. I'm sick of buying AA cells and I agree I didnt like the lower voltage of the NiMH when it was only 4 of them. Now that I see its not that hard I may get to it. I would love to make a couple 2s a123 packs that would fit with an normal JST plug or something like that. What are your thoughts on fitting it in there?

Well, the tray (with the "box" removed) fits 6 AA cells. The thickness of the cells may give you some trouble though. There is a little room above the tray, but not sure how much, or enough for the A123 cells.

Then, what about the voltage? Peaked, 2s A123 cells are 7.2v (a bit high), nominal at 6.6v (probably ok, but still a teeny bit high), and LVC at ~5v. A UBEC (or even a linear regulator) has too much drop-out voltage to use it effectively (esp at LVC), and besides, a switching BEC would be wasted here due to the low differential voltage and relatively low current. If I were to use 2s A123s or lipos, I'd probably use a diode in series with the + line to drop a consitent ~0.7v. True, at LVC, that will be quite low, but A123's drop fast though. Just set the radio voltage alert for ~5.6-5.8v.

Just thinking about this again. If you are using 5 NiMH cells they are 1.4 to 1.5v peaked so 5 of them is 7.0 to 7.5v and 2 x a123 cells are only 7.3v peaked (3.65 x 2) I might try hooking upa 2s a123 pack to the radio just using aligator clips on the inputs just to make sure I dont toast the thing before I tear it apart and make any modifications.

I guess that a 2s2p pack of the 1100 a123 cells would fit in there? Just an observation...

i just bought a dx3r and am anxious to try this out.

brian if i wanted to get a lipo in there are there any options that i could look at?

There is a thread over at nitrokillers where someone (Jason IIRC) used lipos instead. The problem is that the DX3r wants 6v, and lipos are too low in 1s (3v min and 4.2v max) and too high at anything above LVC in 2s (6v min and 8.4v max) to get the right voltage. Normal radios that take 8 X AAs function just fine on 3s since the voltage of 3s is ~9v min and 12.6v max.

He used a BEC and a low-voltage cutoff/alarm, but that's getting a bit pricey just for a radio battery solution IMO. Not to mention what would happen if the BEC went bad and outputted the full 2s (or higher) battery voltage. Not sure how sensitive these radios are to overvoltage, but 8.4v (2s @ 4.2v/cell) is quite a bit higher than 6v...40% higher to be exact.

oh your right.

AAs are not a big deal i was just wondering if it would be a simple plugin.

guess not!

thanks

Here we go again :lol:. The cost isn't that much - $10 cheap switching BEC, maybe $5 for the components to make your own dead-bug style audible low voltage alarm (schematics are at RC Groups).
The chance of the BEC failing in the TX is MUCH less than if used to power a RX at a higher input voltage. So, you are much more likely to have a fried RX than TX due to switching BEC failure.

well is it really worth it to buy the materials when you have 5 rechargeable AA's sitting around the house?

i think that is what Brian meant.

Yeah. I already had the cells from my DX3.0, so it was essentially a "free" mod in my case.

And, I don't think anyone knows for sure exactly what causes the BEC to go bad. We are assuming overcurrent can do it (which is probably true), but there could be other issues as well like a weak/faulty component, heat (it is enclosed inside a radio box after all), voltage spike, or any number of circumstances. Personally, it's not worth risking a $300 radio just to be able to say "I have lipos in my radio". Is it cool? Sure. Is it practical? hmmm.

I guess there are those who like a challenge, and those who prefer against it.



JK :lol:

lol, hardly a challenge. I've never been a betting man, and it's worked well for me thus far. :tongue:

Mod fight! :yipi::lol: You boys need to get along.:mdr:

Who's not getting along? I stated my opinion, he stated his (even though it was wrong), my opinion means more to me. End of story. :lol:

J/K. I'm sure using the lipo is his is cool and all, I just don't think it has the "bang for the buck" factor.

Well, different circumstances, different results. ALL of the Lipo-related stuff in my TX was stuff I had laying around. The switching BEC was one from an old project (caused glitching in my FM equipment), the LV alarm components I had left over from a prior order, and the 2s 2100mah Lipo was salvaged from a 4s2p Maxamps pack that had a couple puffed cells.

Brian mate, EXCELLENT mod! Nice and quick/easy to do, but you weren't kidding about those short cables lol.

I've been having serious issues with my DX3R's range with my HPI Baja and a modded Pico fail safe with a whole bunch of different receivers so I'm hoping this will fix the issues :D

Again, thanks a lot mate, much appreciated!

Hello.
Is making my Dx3R with LiPo.
Anybody know how many volts it can handle the highest!
Can you possibly put 2s LiPo in Without the bec.
Have a bec that can provide either 5 or 6v.
It might just be better if I could escape bec while using spectrum voltage alert!

Well, I've run mine off 5 freshly peaked NiMH cells, which is 6.5v and it works fine. However 2s lipo is 7.4v nominal and 8.4v "peaked", which I wouldn't try. I think it would be best to use a BEC, use 5 NiMHs, or 4 Alkalines.

I was contemplating switching over to 2s lipo, but was concerned that the nominal and peak voltage of 2s would be too high. So, I contacted Spektrum and listed my mod and asked about using 2s lipo.

And their response:

So, it seems that 2s is a no-go, unless regulated. But if regulated, the voltage meter won't show the true battery voltage which risks discharging them too low. Regardless, I've found that the Spektrum voltmeter is not accurate anyway, it seems to be always ~0.4v lower than what the batteries really are. But, it looks like 5 NiMH cells is fine.

Despite the system being designed for 4 rechargeable cells, the cutoff voltage of ~4v (~1v/cell) is a bit low and range has to suffer. So, I think I'll stick to using 5 NiMH cells...

To bring up an old thread once again, I thought I would mention an alternative to lipo for the DX3r. Really, the only reasons for going lipo in a transmitter is flatter discharge curve and lower self-discharge. Well, how about using some LSD (low self-discharge) NiMHs? Doesn't really solve the flat discharge curve, but the high LSD of regular NiMHs can be a PITA if your radio is sitting on a shelf for a couple/few weeks. So, I've been doing a little reading and found this: http://www.stefanv.com/electronics/l...discharge.html. The cells tested here dropped only 0.04-0.07v after 7 weeks sitting on a shelf. That's a heck of a lot better than the Duracell NiMHs I'm using now. I'd probably opt for the cells that dropped the least, which is around 0.04v after 7 weeks, but even the worst ones would be better than nothing. Sanyo would most likely easiest to find, and I think I remember my LHS saying something about some LSD batteries they had. I might have to check them out.

I have my Eneloops in for a few weeks (charged only when I got them) and voltage is still 4.8V. :intello:

Too bad I didn't see these before:

http://www.hobbycity.com/hobbyking/s...dProduct=10456

Awesome mod and info.

I stumbled upon this thread while googling the reason my 2nd hand dx3r keeps beeping a few minutes after being on. I will definitely being doing this MOD asap.

Before you do that, why not lower the alarm voltage point? It's in the system menu option.

After all the reading, it appears 6v is the voltage the the electronics were meant to operate on.

I just wanted to offer a suggestion before voiding the warranty, not to mention taking the risk of damaging it.

No problem, thanks for the tip. This unit is 2nd hand, no receipt, no warranty.

Alright, got mine done. Overall easy, but annoying. 35% of the time was spent bending a single battery bar to act as a spring/connector for connecting two batteries. 50% of the time was spent putting the battery tray back into the radio. Other 15% was dis-assembly and soldering.

Great mod. :)