Devo 7e USB charge mod

Haven’t seen this mod anywhere yet so I figured I’d make a thread for it. Nothing incredible but it’s a very cheap and easy mod that makes life a little bit easier. All you need is a 12v step up. My original intention was to just add a usb charger, specifically a variable DC step up that has a micro usb charger on it. After spending a couple minute trying to find a good place to mount it I couldn’t and the idea came up to just use the existing one. Turns out the voltage in on the miniusb on the 7e isn’t even used, which explains why you need the battery to even turn it on for USB. So using the existing miniusb port has the added benefit of now being able to power the tx. No more battery needed for flashing and .ini edits. Now batteries go in and you charge it via USB for a year or two until the batteries go bad, no lipos, no balance charges, no moving or touching batteries, just plug it in to a USB port.

All you need is a 12v step up. You’re going to tap into the power coming off the miniusb on the main board. Positive will be the top pin that isn’t being used and it can be grounded with any of the joints to the main shell. 12v power will go into the charging port, the tabs are easy to solder to, positive voltage will go on the tab that connects to the white wire.

(Orange is positive and white is ground)

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Very cool! Having not had a Devo I like watching the hacks.

Nice project there @KewlbasaDawg

I use a Devo 7E running NIMH batteries and I would love as many details as you would like to share. With those rechargeable batteries in the stock batter carrier, it is very hard to get the battery pack out so that I can recharge them in a wall charger setup. They are marginally bigger than the lead acid batteries and that bows the carrier just enough to make it hard to get in and out of the TX

Yeah this is definitely the mod for you. Doesn’t get simpler than this. I think I explained pretty well in the first post but I’ll do a step by step:

  1. solder a wire to the little pin coming off the miniusb port that isn’t going to anything, this is ~5v from usb (check with a multimeter)
  2. solder a wire to any of the joints that hold the main metal shell to the board
  3. solder these wire to a 12v step up, doesn’t need to handle much current at all, mine is 1A.
  4. solder some wire to the v out on the 12 step up
  5. solder these wire to the tabs on the inside of the stock circle charger(or a resistor on the main board but I wouldn’t recommend that unless you need the back case separate from the front often) positive will go on the tab on the left that connects to the white wire, ground goes on the other.
  6. insulate and close everything up, that’s it

I’ll start opening it up to take pictures and work on a little schematic, I’ll update the first post with those.

Very cool indeed, I like it. @KewlbasaDawg you might be able to plug it into your Laptop or an external cellphone battery to power it to using that mod.

Thanks yes some photos and a link to a suitable step up would be great if possible :slight_smile: So you are using NIMH batteries the same as me?

@MasterRC_sTudenT Yup, any USB you can find is going to be able to charge it. In fact any 2v-12v source can charge it with the step up.

@pedro147 Just updated the first post with some decent pictures of the internals. I use adjustable step ups because they’re a buck each and adjustable. They’re a little bigger and heavier but I use them in so many different things it’s all good. Just search “adjustable dc dc” or “adjustable step up” and you can find tons of different kinds and sizes. I’m also using NiMH batteries, rated at 2200mah but they’re from horrible freight so I doubt that.

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Thanks for that @KewlbasaDawg I might draw up a quick schematic when I open it up in a few weeks to wire in the NRF24LO1 just to make sure I an not misunderstanding anything :slightly_smiling:

No problem. Pretty straight forward so it might be a good test before you try adding the module. I added a a7105 first but that was pretty easy, and I used all the same color wires as you can see in the corner of one pic. Just do one at a time and double check and it’ll be fine.

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I will be following this schematic that a guy helped me with after I did the A7105 some time ago

A7105 module wiring

Yeah I did a pencil sketch but honestly didn’t even look at it and just used this picture

when I was doing it. Just doing one wire at a time, brown goes there and there… yellow goes there and there… and loop this around…and 5 minutes and I was done. Great schematic though and the same as how I wired mine, I’ll probably need it when I go to add a nrf24.

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Great idea. However, I wanted to check something. Is there a risk of overcharging batteries when charging this way? I guess if left plugged in this system would never stop charging as there is no circuit to deal with that. Is that even something worth worrying about when it comes to AA batteries?

I, and the few others I found while googling, aren’t really sure. It’s regulating any charge voltage down to 6v so even if it doesn’t have a fancy charge circuit it doesn’t really get too high for NiMH. Going to true 1.5v per cell for NiMH is pushing it a little bit and starting to overcharge them, but NiMH cells are supposed to function in the 1.5-1v range. They charge so slow I don’t think it’d be a serious issue. I just watch the voltage on the devo and when it drops below 5v I plug it in for 4-5 hours and that only brings it up to ~5.5v. I’d say if you are unable to remember to not leave it charging for >7 hours to continue to just use normal AAs.

I’ve also had an issue where I can’t charge it and access it as a mass storage device. My computer would see it but wouldn’t be able to mount it. I had to unplug the battery and just use usb power to power it and then it was able to mount it. Kinda weird, it may have been because the battery pack was so low.