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Possible battery problem!

#1
Hi flitetest community!

I just bought a 3s 850mah 45c battery for my FT mini Guinea. I charged it up and went out to fly. I put on a voltage alarm and throttled up to about 2/3 throttle to make sure the ESC's were working. As I did I saw that the on the voltage alarm that the battery voltage would drop from 4.2 volts to 3.3 - 3.6 volts, then when I throttled back, I would go back up to 4.0 - 4.2 volts. I was just wondering if that is what it is suppose to do or if there is a problem with the battery.

The battery was completely new.

Thank for any help!
 
#4
Grifflyer:
One of my oldest batteries does that. It charges normally, and tests normally, but under a load I cannot get the same thrust as a comparable battery. In my case I believe one of the cells is failing. You could have an intermittent balance wire or you need to calibrate the ESC or a cold solder joint in your battery plug.
 

Hai-Lee

Old and Bold RC PILOT
#5
You have only supplied half of the picture!

What current is being drawn by the motor/s?
What Props, Motors, and ESCs are you using?

The symptoms you mention are those of a battery suffering from excessive discharge current or a battery with high internal resistance but without knowing the load it is impossible to state which it is!

Have fun!
 

FDS

Well-known member
#6
2x 1806 2300kv motors, 20A esc’s, from OP’s build thread.
Props are 5x4 ish.
I make that a peak load of about 16-20A with props on, just on the motors. That shouldn’t cause that level of voltage sag. Maybe on a trashy 25C 850, given it will hit only 21A continuous. Shouldn’t trouble a 45c provided all the cells are good. OP, your battery will dip below 4v under load when fully charged, but only momentarily, it shouldn’t go straight down and stay down, Lipo is supposed to give a higher continuous discharge with less voltage sag.
Are you sure you correctly fully charged it before use?
 
#8
Grifflyer:
One of my oldest batteries does that. It charges normally, and tests normally, but under a load I cannot get the same thrust as a comparable battery. In my case I believe one of the cells is failing. You could have an intermittent balance wire or you need to calibrate the ESC or a cold solder joint in your battery plug.
My battery is completely new though.
 
#9
You have only supplied half of the picture!

What current is being drawn by the motor/s?
What Props, Motors, and ESCs are you using?

The symptoms you mention are those of a battery suffering from excessive discharge current or a battery with high internal resistance but without knowing the load it is impossible to state which it is!

Have fun!
I am using what @FDS said, 2x 1806 motors, 2x 20a ESC's, and 5x4x3 props. The plane is the Mini Guinea.
 
#10
2x 1806 2300kv motors, 20A esc’s, from OP’s build thread.
Props are 5x4 ish.
I make that a peak load of about 16-20A with props on, just on the motors. That shouldn’t cause that level of voltage sag. Maybe on a trashy 25C 850, given it will hit only 21A continuous. Shouldn’t trouble a 45c provided all the cells are good. OP, your battery will dip below 4v under load when fully charged, but only momentarily, it shouldn’t go straight down and stay down, Lipo is supposed to give a higher continuous discharge with less voltage sag.
Are you sure you correctly fully charged it before use?
I try it without props and the voltage just dropped a little bit, then I tried with 5x4x3 props and the voltage went down to 3.3v and then I throttled back and it went back up to 11.7, then I tried 5x4.5 props and it did the same thing the 5x4x3 props did. It's a new battery so no cell's should be bad. The voltage doesn't stay down, it goes back up to around 11.8v - 4.0v when I throttle back.

I plugged it in to the plane for just a second before I charged it for the first time, I didn't have a charger yet but I wanted to see if my everything on my plane worked.
 

DamoRC

Well-known member
Mentor
#11
Do you have a watt meter or a way of checking the current? Sag to 3.3-3.6V at 2/3 throttle seems excessive.

Is the battery 45C continuous or burst. (Link to the battery and motor could help)
 
#13
Do you have a watt meter or a way of checking the current? Sag to 3.3-3.6V at 2/3 throttle seems excessive.

Is the battery 45C continuous or burst. (Link to the battery and motor could help)
Unfortunately, I don't have a watt meter. What other ways would I check the current?

45C is continuous.
 

Hai-Lee

Old and Bold RC PILOT
#15
According to the little internet search on 1806 motors and applicable propellers the 5x4x3 can be pushing the motor slightly beyond its rating at full throttle. At this rating the battery is almost at max current handling capacity or "C" rating. when using 2 motors. Luckily the battery is protecting the motors by folding down its cell voltage so the motors are fine.

I always try to have at least a minimum of 25% excess current capacity or "C: rating in all of my builds so if you wish to use the 5x4x3 props I would recommend either a 850mA 65C battery or a 1000mA 45C battery.

As for the battery itself I would charge the battery fully using a balanced charger before repeating any further tests, and in addition I would ensure that the battery is at room temperature before proceeding.

I have had a similar battery issue a long time ago when I found a local model shop BUT the batteries he had where rather old and had been sitting on the shelf for many many months. Most came good after a few cycles but a couple never recovered!

Just a few thoughts!

have fun!
 
#16
According to the little internet search on 1806 motors and applicable propellers the 5x4x3 can be pushing the motor slightly beyond its rating at full throttle. At this rating the battery is almost at max current handling capacity or "C" rating. when using 2 motors. Luckily the battery is protecting the motors by folding down its cell voltage so the motors are fine.

I always try to have at least a minimum of 25% excess current capacity or "C: rating in all of my builds so if you wish to use the 5x4x3 props I would recommend either a 850mA 65C battery or a 1000mA 45C battery.

As for the battery itself I would charge the battery fully using a balanced charger before repeating any further tests, and in addition I would ensure that the battery is at room temperature before proceeding.

I have had a similar battery issue a long time ago when I found a local model shop BUT the batteries he had where rather old and had been sitting on the shelf for many many months. Most came good after a few cycles but a couple never recovered!

Just a few thoughts!

have fun!
Thanks for the information!

I don't really want to buy another battery, so what props should I use instead of 5x4x3's? I already tried 5x4.5 and it did the same thing.

I haven a few charges through it already. I use the OCDAY DP6 180W 16A charger.
 
#17
Also, I tried with a 3s 2200mah 25c with 5x4x3 props and the voltage only dropped to 11.6 and stayed there. Why would it work with a 25C battery and not work with a 45C battery?
 

PsyBorg

Wake up! Time to fly!
Mentor
#19
What brand battery is it? When I first started I used Floureon batteries. They were not hapoy at all until broken in.

The cell voltages were pretty far apart for the first 4 - 8 uses. Then like magic they woke up and I abused the snot outta them. I still have two I use for goggle / dvr batteries. They also supply power for my Ft Edge 540 nicely.

Basically when I boyght new ones I woukd charge them full, hover for 1 minute, then recharge them. Once the cells were coming down within .02 - .03 v between cells I ripped the snot outta them and they were fine until I smooshed em up in crashes. The two I have left are about 3.5 years old at this point.
 

Hai-Lee

Old and Bold RC PILOT
#20
Thanks for the information!

I don't really want to buy another battery, so what props should I use instead of 5x4x3's? I already tried 5x4.5 and it did the same thing.

I haven a few charges through it already. I use the OCDAY DP6 180W 16A charger.
You have a number of options. If you can accept less thrust/motor power then go for a 5x3x3 prop or similar. Alternately you could get a second 850 3S and run one battery for each ESC/Motor. Finally you could use the 2200 3S to power the bird.

Or of course any combination of the options!

When charging a highly stressed battery charge it slow and only when cool/cold. If you stress it or fast charge it whilst it is hot it will fail in short time and you WILL be buying new batteries and quite often! Make sure that the battery and ESCs have plenty of cooling air in flight!

Have fun!