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Other Low Voltage Alarm but full batteries

Jscott27

New Member
Hey guys I am a new flyer and only done a few flight sessions on some Friends planes. I have bought an FMS east trainer 1280 which is RTF - I have set up the plane but ordered some 3 cell batteries at 2200 mah instead of the standard 2 cell 1500 that came with the kit .

I do have an issue now though where I have connected my new batteries and all controls responding well but then the low voltage alarm starts and won’t stop on the in the box transmitter it’s a FMS F4 I think. Anyone had this problem. Or any ideas please.
 

RandyDSok

Well-Known Member
LiPo batteries are more than just their capacity ( 2200 mah ) rating and their number of cells... you also have a C rating which determines how many amps output they can provide. If the C rating for the battery you got was low enough, the motor could have pulled so many amps that it pulled the voltage down and your alarm sensed that and was set off.

Quality of the batteries in question is also another potential cause. There are many cheaply build ones not to mention fake ones that claim to made by reputable manufacturers.

When asking questions of this nature on any product... it's a good idea to provide a link to the specific vendor page that you purchased from. Then guesses, like I've had to make because of a lack of details, about what could be possible can be avoided. As a new user, of course you aren't expected to have learned any of that yet but it is something you should know from this point forward. Reviews of products on their respected webpages are also recommended to be potentially suspect since those can also be faked. Sometimes it's hard to find reviews on other places such as this forum... but you can always ask and we'll never make fun of any such questions.
 

Jscott27

New Member
LiPo batteries are more than just their capacity ( 2200 mah ) rating and their number of cells... you also have a C rating which determines how many amps output they can provide. If the C rating for the battery you got was low enough, the motor could have pulled so many amps that it pulled the voltage down and your alarm sensed that and was set off.

Quality of the batteries in question is also another potential cause. There are many cheaply build ones not to mention fake ones that claim to made by reputable manufacturers.

When asking questions of this nature on any product... it's a good idea to provide a link to the specific vendor page that you purchased from. Then guesses, like I've had to make because of a lack of details, about what could be possible can be avoided. As a new user, of course you aren't expected to have learned any of that yet but it is something you should know from this point forward. Reviews of products on their respected webpages are also recommended to be potentially suspect since those can also be faked. Sometimes it's hard to find reviews on other places such as this forum... but you can always ask and we'll never make fun of any such questions.
Thanks for your advice i’ll certainly do that going forward. I have attached a photo of the battery and the manufacturer detail. The ESC is the FMS-ESC20A https://hobbyking.com/media/file/1016916532X256939X44
The motor is the FMS-Motor-3128 Kv2650image.jpg
 

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RandyDSok

Well-Known Member
Since I haven't used and can't talk about the quality of any of the products you listed directly... I can only talk about the technical specs I found on the motor...

That FMS motor is only rated to take a 2 cell battery. Trying to up the voltage to a 3 cell is unlikely to end well. It lists a max burst amps of 25A... that is only for a few seconds at best at 7.4v. I'd suggest to not exceed 20A for long or be safer something around 15-18A. Since the ESC is rated for up to 20A... I'm leaning more towards not exceeding 15A.

Depending on where the batteries are mounted... you can probably safely increase the capacity as long as you can maintain a good CG on the aircraft... you won't be able to safely ( without burning out the motor ) increase the voltage.
 

Smoggie

Well-Known Member
You cant just swap to a 3S battery. By going from 2S to 3S (and using the same prop) then motor current (amps) will roughly treble which will almost certainly burn out the motor and/or ESC. Add to that the battery will be double the weight which will upset the balance of the plane and make it too heavy.

The voltage alarm is probably because in addition to the low voltage alarm there is a high voltage alarm. You will be over the max voltage due to the 3S battery and thus trigger the alarm.

Fortunately the solution is simple.. just put in a 2S battery of a mAh capacity close to the standard pack. You can probably go for a slightly larger mAh but just watch that the model still balances ok, and weight does not became excessive.
 
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Jscott27

New Member
Thank you for the information guys. If you were going to rip and replace the motor and ESC to match the 3s batteries I have do you have any suggestions for a beginner with this glider. A lot or reviews have suggested upgrading batteries to a 3s as the flight time is so poor on the 2s that come with the RTF option
 

RandyDSok

Well-Known Member
To increase flight time... increase the capacity ( mah ) but as Smoggie and I've said you have to be careful to not add too much weight or throw off the CG balance. Throttle management can also increase how long your batteries last. Often just lowering the throttle some can make a lot of difference without affecting the speed a lot. If this is a glider, the motor is typically just to get the plane up to height and you turn off the motor and glide around. Then using the wind to keep up your altitude or diving a bit to gain speed and bring it back up.
 

Smoggie

Well-Known Member
Randy is spot on. 3S wont necessarily increase flight time (even if you did change the motor/ESC to suit). In fact adding heavier and more powerful electronics could well reduce flight time because the plane being heavier will need more power just to fly.
Just stick to the 2S battery and if you want longer flights use a slightly larger mAh capacity and as Randy said go easy on the throttle.
 

Jscott27

New Member
Randy is spot on. 3S wont necessarily increase flight time (even if you did change the motor/ESC to suit). In fact adding heavier and more powerful electronics could well reduce flight time because the plane being heavier will need more power just to fly.
Just stick to the 2S battery and if you want longer flights use a slightly larger mAh capacity and as Randy said go easy on the throttle.
Thanks for this that’s great advice
 

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