Understanding a power mod

[nonflyingbrick]

I saw a post here of Ed209 getting 39 minutes of flying time at full speed on a Phantom 3 with a power mod. I’m going to buy a P4 (I have a P3A now) and I want to power mod it by connecting the extra batteries’ leads directly to the bird (so as not to have to mod every extra DJI battery). I know that voids the warranty, I’m OK with that.

What are the disadvantages of a power mod?

What can go wrong and how likely is it?

What additional considerations or limitations do you have with a power-modded bird?

I’m good with assuming some some risks, but I’d like to know what they are.

I suppose the guy who got 39 minutes of flying time at full speed was pushing the edge of what’s possible, potentially at the cost of additional downsides. If I put enough extra power to get 39 minutes out of a P4, would I have additional potential problems compared to adding less extra power?


I’d like to pay someone to do the mod for me, I don’t have the skills to do it myself.

Where would you recommend that I go looking for someone who can do it in the US?

If you’ve done a power mod yourself and you’d like to do mine for a fee (in the US), PM me.

 

[AdvRider]

Responding to this older post, I do know several things from my modded P3A. The heavier the battery, the more stress it puts on the aircraft. This stress comes in the form of structural stress, and electrical stresses on the motors and ESC's. It takes a lot more power to sustain flight with the extra weight of the additional batteries. If you get greedy, and all range junkies tend to push towards eventual failure, it's easy to add too much weight. I am running 1800MAH LiHV Hyperion's on my 2nd P3A. This has been the best power to weight ratio I have found that satisfies my range greedy nature. These batteries weigh in about 170g each. IMHO this is the upper end of the weight limit for the P3...some say 200g, but I have only flown this heavy twice....bird was a pig, and when I landed the motors were really hot. I'll bet the ESC's were cooking as well. The second flight ended in failure...fell out of the sky.

 

[nonflyingbrick]

How many of those LiHVs do you add, 2 or 4?

So basically the main downside is that if you're not careful and do your homework (which I probably won't do in as much detail as I should) you don't know when you're going to push too hard, too much weight, maybe too hot a climate and the bird is going to fall off the sky.

Thanks for the post!

 

[AdvRider]

I have a P3A at the bottom of the Intercoastal waterway that I believe failed due to getting "greedy" with weight. Everything has to work much harder to stay airborne.

Also, I am not an electrical engineer, but I see lots of people using regular LiPo 4S add-on battery packs which have individual cell voltages of 4.20v at full charge....that's basically an aggregate full charge starting voltage of 16.8v. The phantoms fully charged battery cells are at about 4.30-4.35v....an aggregate pack voltage of about 17.4v. So....when you hook these packs up in parallel with each other you have the P3/P4 battery dumping charge into the lesser voltage add-on batteries...at how many amps, who knows? Could this cause a fire...maybe, perhaps someone more electrically knowledgeable will comment on this risk? Anyway....this is why I use the Hyperion LiHV batteries....their cells will charge to 4.35v, or an aggregate of 17.4v which more closely matches the P3/P4 full charge voltage. If you use these LiHV batteries, you should make sure your Phantom battery does not go into charging mode after you hook them up...i.e., scrolling LEDs. You can prevent this by not fully topping the LiHV batteries to 4.35 volts....4.30 volts is a better choice. Would love to hear some other more knowledgeable opinions on this.

 

[nonflyingbrick]

Wow that sounds like a dramatic adventure. How much weight did you add to the Phantom that sunk?
How much do you add now, 170g x 2 or 170x4?

Hooking up batteries with different voltages rings a warning bell here too.

 

[AdvRider]

Wow that sounds like a dramatic adventure. How much weight did you add to the Phantom that sunk?
How much do you add now, 170g x 2 or 170x4?

Hooking up batteries with different voltages rings a warning bell here too.

Total weight added on was just over 400g.

 

[nonflyingbrick]

Total weight added on was just over 400g.

So the guy who flew 39 minutes on a P3A, who probably added around 500-600g, was absolutely pushing the limits, probably in a cold climate to help cool the motors and ESCs, and still facing significant chances that the bird wouldn't make it back.
It makes sense that the Phantoms aren't tested or designed to withstand any extra weight, so you're on your own adding batteries.
The P3 in particular has pretty crappy plastic arms that get stress cracks even without extra weight.

 

[AdvRider]

Yep...39 minutes is quite the feat. Surprised it would lift off. Smarter people than me (like the engineering guys and the guy who achieved 39min) could probably offer some color and weights lifted. There is a video on YouTube of a guy lifting a 5 gallon bucket....not sure what it weighed?

 

[John Locke]

This is good info. I was just getting ready to order a battery mod from Horizon for my P3p. I'll check out the total weight increase.

 

[AdvRider]

This is good info. I was just getting ready to order a battery mod from Horizon for my P3p. I'll check out the total weight increase.

If you plan on using the higher capacity LiHV batteries, consider an issue I ran into. Specifically, I topped up a pair of Hyperion 1800mah 4S LiHV batteries to 4.35v per cell (17.4v in total). When I went to fire up the main P3 battery, immediately after connecting the Hyperions, my P3A battery thought it was getting charged and the LED display started scrolling as it normally would during a charge cycle. And...since the main P3 battery was already full, it turned itself off just seconds before I was going to lift off. Needless to say if I had of been airborne this could have been a disaster. So, if you are going to use these light weight LIHV batteries, consider charging them to 4.3 volts per cell or a little less. It's better to be at a very slightly lower voltage than the Phantom's battery so as not to make the Phantom battery computer think it's being charged. DO NOT TAKE OFF IF THE PHANTOM BATTERY LEDS ARE SCROLLING LIKE IT's BEING CHARGED....THE LOGIC CIRCUITS IN THE BATTERY COULD TURN OFF THE BATTERY UNEXPECTEDLY ONCE IT THINKS IT'S TOPPED UP.

 

[Sim597]

The one thing I been wanting to do is add one of those Sunhans amps to the video downlink antenna. (Bird side mod)
The reason we haven't seen as many P4s modded is the way they now connect the batteries, the P3/P-A-S all have just the easy to mod power and negative where the P4 has the 20 slot or whatever connector, I'm sure eventually someone will start to mod these, but it's been a slow start off the gates for sure

 

[AdvRider]

The battery bus on the P4 must have more than one pair of +/- contacts for the main battery power feeds.....or at least I hope so. Those little contactor blades on my P4 look a little small to me, especially if only two of the contactor blades are feeding the mains to the bird. The fact that the charging cable is not polarized leads one to believe that they are using at least two positive and two negative contractors. Anybody got a Pinout diagram on the P4 battery bus?

 

[nonflyingbrick]

If you plan on using the higher capacity LiHV batteries, consider an issue I ran into.

Thanks for the tip Adv. There's a lot to juggle with a power mod it seems.

 

[John Locke]

The battery bus on the P4 must have more than one pair of +/- contacts for the main battery power feeds.....or at least I hope so. Those little contactor blades on my P4 look a little small to me, especially if only two of the contactor blades are feeding the mains to the bird. The fact that the charging cable is not polarized leads one to believe that they are using at least two positive and two negative contractors. Anybody got a Pinout diagram on the P4 battery bus?

I've seen a pinout on the battery connector somewhere in this forum, but can't find it. But you're right, there are multiple power and ground pins. That's the only way to conduct that much current using those smaller pins.

 

[suck it up]

I've seen a pinout on the battery connector somewhere in this forum, but can't find it. But you're right, there are multiple power and ground pins. That's the only way to conduct that much current using those smaller pins.

I agree, I thought I saw the same thing. Those are too small to handle all the power needs.

 

[AdvRider]

Some of the other guys on the forum suggested using Deoxit on my P3A contacts....which I do. After looking a little closer at my P4, it looks like the power blades in the P4 can be swabbed with some Deoxit, albeit not as easily as the P3. It's probably more important to prevent oxidation on the P4 than the P3 due to the tiny size of those P4 contacts.