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MYHELIGUY

LIPO ONBOARD HELI MONITOR

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HI, I am new here,need some advice.Looking to build a onboard monitor for lipo 2 cell and 3 cell packs.need it to alarm at the low limit safe discharge,which is 3.2 each cell. need to monitor my lipo battery while flying my rc helicopter. need a good schematic drawing with manufacturers name and part numbers. it has to be as small as can be and weight lite as possible,i want to build it possibly on pb .anyone have ?

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:unsure: Hi, Mr Cam

I've noticed the LiPos have a not negligible tempco ( - 20 mv/cell/°C from KoKam datasheets ) what make me strongly think a voltage limiter has to be temp corrected.

Summer : 25 °C ... Winter 5°C ...

for a TX (3 cells ) that make : 20*20*3 = 1.2 volts difference at the same discharge level... ( say just before voltage falls quickly )

Overall ... limiter will "ring" as soon as powering up for cold weather conditions ...

Some thoughts about that ??? :(

Thanks for all of us.

Alain

Edited by Acetronics

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Whatever coefficient there can be, what counts is still that each cell must not be discharged under 3V. That will mean you can draw less on the battery before it reaches that level in the winter (fewer mAh drawn in the end), but the voltage at which the warning needs to tell you you're low is pretty much the same...

The goal there is not to give a precise fuel gauge, but to tell when you're close to the low voltage limit. As Heliguy said, 3.2V/cell is a good figure.

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Hi, Kilrah

3v or 3.2v @ testing temp !!! ( generally 20- 23°C )

The problem is the voltage limit is also temp. dependant !!! figure the curves are translated down per - 20 mv/cell/°C ...

What is funny is @ 0 °C ... the limiter will tell you to stop, and you only have drawn 10% or less of your batt capacity ...

the goal is just to fly ... say 70 or 80 % of the batt capacity ...

Alain

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The standard cutoff voltage is what I have been using. I'm a fair weather flyer -- if it's cold outside, I stay inside. :)

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I've been flying in -8°C conditions.

There's one more thing you have to consider. Ever taken your main battery in your hands after a flight? Yep, it's warm, usually in the 30-50°C range depending on how you draw on it. The same happens if it's cold outside, the battery will keep itself warm due to its own power losses. It's of course dependent on the cooling as well, so a battery in a fuselage won't see the cold that much. When I flew my motor glider for 30min in -8°C, my pack was still at ~20°C at the end of the flight. So unless you cold soak your pack before the flight it will never reach the 5°C you mention. If I have multiple packs I keep them in a warm place (jacket, car...) before using them.

The problem is the voltage limit is also temp. dependant !!!

Nope!

figure the curves are translated down per - 20 mv/cell

Yes the curve would be translated down, BUT in any case you still stop discharge at 3V/cell not to damage the battery. The only difference is that in a lower temp, as the curve is lower you will reach that voltage sooner, and thus be able to draw less capacity out of the battery. Check below graph (taken from a Panasonic battery datasheet).

temp.jpg

Edited by Kilrah

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Hi, Kilrah

Some exerpt of KoKam datas :

Cell voltage: 3.7V, nominal; 4.2V maximum

Nominal capacity, weight and dimensions per Exhibit 1B for all cells

Discharge condition: 2.5V absolute; 3V nominal

Cycle life: 600 cycles at discharge rate of 2C while maintaining >80% capacity

Operating temperature: charge, 0° to 45°C.; discharge. -20° to 60°C

If you have a 3v limit @ 20°C ... ( whether the batt. origin ...)

you just end your flight by a superb " autorotation" ... cause there's nothing more in your batteries.

just suppose you were using a BEC ... ( moto glider i.e. )

FUN

Just understand here you have no more "security capacity" to land quietly :rolleyes: . and ,as the voltage drop is weak, it's rather difficult to keep that security without reducing seriously the overall disposable capacity.

our applications were a bit different, as I dealt with a LiPo supply for a Fut. 9C Tx ... no "automatic heating" to hope !!! ( a glider had been totally destroyed before my belgian friend understands the genuine voltage alert is "not so good" for the LiPos ... :blink:

Alain

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Hi, Kilrah

Some exerpt of KoKam datas :

􀂄 Cell voltage: 3.7V, nominal; 4.2V maximum

􀂄 Nominal capacity, weight and dimensions per Exhibit 1B for all cells

􀂄 Discharge condition: 2.5V absolute; 3V nominal

􀂄 Cycle life: 600 cycles at discharge rate of 2C while maintaining >80% capacity

􀂄 Operating temperature: charge, 0° to 45°C.; discharge. -20° to 60°C

If you have a 3v limit @ 20°C ... ( whether the batt. origin ...)

you just end your flight by a superb " autorotation" ... cause there's nothing more in your batteries.

just suppose you were using a BEC ... ( moto glider i.e. )

FUN

I don't get what you're trying to say with that one :unsure:

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MR.RC-CAM, YES,I have read and went over that link, problem is, the parts needed are obsolute unless ordered from two or three different places with no guarantee,is what i found. unless someone can update those parts numbers. plus i wanted a comparison ideas of someone else. i appreciate your replies .

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... the parts needed are obsolute unless ordered from two or three different places with no guarantee,

I looked over the schematic and didn't notice any obsolete parts. Digikey.com stocks them; They are a very good source for those folks that are located in the USA.

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I don't get what you're trying to say with that one :unsure:

Hi,

I'm just saying :

if you want to save the LiPos only 3.2 v or 3.0 v is Ok for the limit.

if you want to save the liPos AND the heli or plane ... the limit has to be set to a bit more : just before the curve bends downwards ( say 3.6 v i.e.)

that's quite simple !!!

Alain

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OK.

Personally on my MikroKopter I have a 3s/2200 battery, and draw about 7A when hovering. There is a sound alert on the mainboard that I've set at 9.5V (a bit less than 3.2V/cell).

The thing is that the current draw varies continuously, and the voltage changes all the time anyway, so you won't wait until the alarm sounds continuously when hovering to land. But you will soon enough notice that it will start sounding more and more early when you put some pitch and draw a bit more power. That's when you will know it's time to land. The time to come back it will start sounding more often, but you get used to the timing after no more than 2-3 flights and can work out pretty precisely how much time you have left when it starts kicking in at relatively low draws.

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Hi, Myheliguy

Here you can find scheme + Hex program for 3 LiPos

Was intended for a Futaba 9C Tx ... with nominal current draw of ~ 200 mA

Voltage on GP1 has to be set the closest to 4.096v ...

Alain

VoliPo_Tx.pdf

Edited by Acetronics

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Link not working for some reason. the AlmVoltTX.HEX i appreciate your input, can you post the exact part numbers to order from www.digi-key.com, so i don't get the wrong items,thanks

Edited by MYHELIGUY

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Hi,

Save as "AlmVoltTX.HEX" ...that's all !!! :)

For the parts numbers ... I just can give you the drawer they come from !

Seriously, there are no specific components ... just take a 25T trimpot for R6.

Alain

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Hi,

Save as "AlmVoltTX.HEX" ...that's all !!! :)

For the parts numbers ... I just can give you the drawer they come from !

Seriously, there are no specific components ... just take a 25T trimpot for R6.

Alain

the link in the folder that a internet explorer link,no work.

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i have tried that download ,which is a internet link, its blank, except for a line of numbers across the top. also, i am wondering on the possible weight and size of this project when completed.

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The link seems to be working. The file is the hex code for his PIC microcontroller project. Hex code is a list of numbers in a format that your PIC programming system can read.

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Hi, Mr Cam

I get the same "trouble" here ...

the file is automatically given a .PDF suffix ( Why is THE good question ... :rolleyes: ) , just needed to use "save as" and choose "all" in the file Type window at bottom of download window ...

Alain

Program Hex reloaded here !!!

AlmVoltTX.zip

Edited by Acetronics

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