What kind of 3,7V 850mAh Li-Po pack is this? 1S or 2S in parallel?

[Fete]

Hi everybody!

Figuring I would try out this hobby, I just purchased a simple (probably below) entry model quadcopter to try out the hobby. Price was around $25. It sure flies and have survived a couple of minor crashes. However, it does not fly long enough

Close examining the battery pack to check for upgrades or future conversion experiments to Li-io didn't make it quite clear to me.

As I understand it, Li-Po packs for RC are usually made up by single cells wired together. So 1S packs have 1 cell with nominal voltage of 3,7V. 2S packs have 2 cells with nominal voltage of 7,4V and so on. I guess that quadcopters that run on higher voltage means higher RPM/altitude more speed and so on.

This pack however seems to contain 2 cells, but the voltage is at 3,7V. Which make me think that the manufacturer wired the cells in parallel instead of in series. Also, there is a cable that surely must be connecting to a balancing chip inside the drone, stabilizing cell voltage. Thing is, I haven't seen this balancing cable on packs with 3,7V and I seem to find just 1 cell packs.. Finding 2S packs with balancing connectors is not so hard, but the ones I find are at 7,4V. I can imagine that this will make the rorors spin faster, giving excessive wear to the motors. So don't want to risk it.

Is this an uncommon type of battery pack? It weighs in at around 25g (making me hopeful that this quadcopter might be supporting a future attempt to mod it, so it will run on Li-ion 18650's instead, that weigh around 20-25g more).

Hoping that someone can help me sort this out a bit. Always fun to learn!

Also, if anyone can tell if if the cable connectors is some sort of a standard, or manufacturer specific, I would appreciate it!

Instruction manual for the quadcopter can be found here: https://www.lidl-service.com/static/2924889016/306200_EN.pdf

Attaching some pictures below:

 

[holtneil]

Hi the biggest problem is will the quad take 7.4v with out going up in flames , you better off finding single call with the highest MAH as possible

 

[Fete]

Hi the biggest problem is will the quad take 7.4v with out going up in flames , you better off finding single call with the highest MAH as possible

Nah, wouldn’t want to risk it, going at 7.4V. Would probably cause too much stress on the quad.

But this battery setup, have you seen it before? Ie what looks like two cells, but “reduced” to 3.7V?

Seems to me that manufacturers usually pair 2+ cells in series, rather then in parallel

 

[holtneil]

Is a strange set up , but they do things like this to make having to buy there spares from them

 

[wafflejock]

Yup could be 2 400mAh to make a 800mAh with them in parallel. Curious thing is with cells in parallel they self balance the one with higher voltage will drain into the one with lower voltage until they are even so no idea why they would have two leads there it's probably the same power out.... Maybe one goes through low voltage cut off circuit or something along those lines but guess if you check voltage out of both pairs it's the same.

 

[wafflejock]

Also a bit weird because why not just use a bigger single cell and avoid the extra packaging and wiring definitely a strange one, guess could be as holtneil presumes just done to make a non standard part they can then sell, but seems like a waste.

 

[Fete]

Is a strange set up , but they do things like this to make having to buy there spares from them

My guess as well.. A shame though, cause I really enjoy flying the quad, loads of fun! This particular manufacturer doesn't offer spare batteries it seems. Making it really strange.. And because it seems very unusal with 2S packs with 3,7V I really have a hard time to find suitable packs. Just found out that the quad won't fly without the balancing cable inserted, meaning that I can't buy standard 1S packs, since they don't have a balancing cable..

Yup could be 2 400mAh to make a 800mAh with them in parallel. Curious thing is with cells in parallel they self balance the one with higher voltage will drain into the one with lower voltage until they are even so no idea why they would have two leads there it's probably the same power out.... Maybe one goes through low voltage cut off circuit or something along those lines but guess if you check voltage out of both pairs it's the same.

No idea here either.. And it complicates it a whole lot, since I can't use 7,4V packs (probably would fry the motors after a while or some other humorous side effects..).

I checked the voltage on the pins, 4,25V from the pack at +/- pins. 3,3V between the blue balancing pin and the positive pin on the power cable. 0,3V between the black balancing pin and the black negative pin on the power cable. No voltage between the two cables on the balancing connector. No idea yet what conclusions to be made from those readings..

I took a pack of Li-Ion just to see if it would handle the extra weight (around 100g, comparing to 25g of the original pack..) and modified the connectors. Turned out that the quad wouldn't start the propellers or even connect to the controller without the balancing connector inserted. Obviously, my Li-Ion pack don't have a balancing connector.. Plugged the original packs balancing connector in, and the propellors started, but when trying to speed them up for lift off, it shut down after just a sec.

My guess is that there is some sort of circuitry inside the quad, monitoring the voltage, and if it detects "movement" but no drop in voltage on the pack (or possibly amp surge) it will shut down the propellors, since something could "be wrong".

Any ideas how I can proceed with a conversion of this unconventional drone to Li-Ion are appreciated. I will go for a single cell, which will weigh around 20-25g more. Must have balancing pins connected, but obviously, it's hard to balance a single cell..

Perhaps the balancing circuit can be bypassed somehow.. My guess is that it also monitors voltage, so I will have to do that manually so I don't over discharge the cell.

Also a bit weird because why not just use a bigger single cell and avoid the extra packaging and wiring definitely a strange one, guess could be as holtneil presumes just done to make a non standard part they can then sell, but seems like a waste.

Two bits weird IMO.. As you are saying, they could avoid the extra packaging and wires. Strangest thing of all is that they don't even offer batteries for sale!

Li-Ion pack connected, would blink LED's, but not connect to remote controller:


Li-Ion pack connected, and original battery's balancing cable connected, will connect and start propellors, but when trying to take off, it just stops when increasing the RPM:

 

[wafflejock]

Ah okay that actually might make some sense. 3.3V is a common voltage for the MCU on an FC to operate with so my guess is there is a 3.3V regulator packed inside with the battery instead of using the one on the FC (perhaps FCs had a QC issue with the regulator and this was a workaround or maybe just distributing components that generate heat... Just guessing). If the 3.3V stays pretty solid 3.3 until the battery is drained to about 3.5V you should see 3.3 output there if it is a regulator.