timed auto battery disconnect [Archive]

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applejack

Dec 12, 2007, 12:49 PM

A.T.

Dec 12, 2007, 02:46 PM

Hi, Need a schematic for an auto turn-off ( disconnect from battery ) device that will turn itself off if I fail to turn it off the off switch manually. Need to be able to remain on approximately 45 minutes. The battery pack involved is a 3 cell lipo pack. What I am looking for is a device that will turn off the battery connection if I have one of my senior moments and I forget to turn off the battery and ruin a lipo pack. Thanks Jack

Suggest best method is to use one of the many peak detect charger for Lipo batteries e.g. LN5014 Battery Charger discharger station Lithium, NiCd, NiMH & Pb (http://www.acehobby.co.nz/ossb2/root/OSSBEC1/showitem.asp?PID=54651)
Whilst many are "field chargers" i.e. 12VDC being without a heavy transformer for ease of use where it matters at the flying venue, a 110/230 VAC power supply is readily available or cheap and easy to make your self from an old PC power supply as per the examples under "Battery Chargers & DIY Power Supplies." on my web page.
Regards
Alan T.
Alan's Hobby, Model & RC FAQ Web Links (http://homepages.ihug.co.nz/~atong)

orraman

Dec 13, 2007, 06:22 AM

Is it a timer to work off 3 lipo and to turn off after 45 minutes or is it to turn off after 45 minutes of no activity?

Dave

Dan Baldwin

Dec 13, 2007, 11:09 AM

GiZZeRR

Dec 13, 2007, 06:34 PM

How about a kitchen timer like this
http://www.walmart.com/catalog/product.do?product_id=7755627
You could just set the timer for 45 minutes, and carry it around with you. When it beeps, it reminds you to disconnect the battery.

Dan

I use a kitchen timer set initially for 1 hour then 30min intervals till fully charged. Works for me.

John

applejack

Dec 14, 2007, 02:24 AM

Orraman,

Dave,
The device I have in mind is one that would turn off (disconnect the power ) from a lipo battery. The purpose is to keep from discharging the battery beyond the safe discharge level and ruining a battery pack. This would prevent damage when ( not if ) I have one of my unplanned senior moments.

Thanks for the suggestions everyone.
Jack

Acetronics

Dec 14, 2007, 03:53 AM

Hi, Jack

I already built a 12F675 Pic "LiPo Saver" for the 9C transmitter of a friend ( 3 cells )... but, as is , it just warns, as it just detects the batt level ...

Not so good to switch Tx off when your plane is flying ... :p

It would be simple to drive a Mosfet ( or a couple of ), used as a switch ... ;)

But ... for batt level ... we need to know roughly how much current you draw from your batt, and which is your batt capacity. or tell us which is the device you want to use that switch with ???

Alain

orraman

Dec 14, 2007, 04:28 AM

Jack,
I make a 3 cell lipo saver with an 8pin surface mount picaxe chip for friends that gives low throttle at a preset voltage.
You could make a through hole version on a scrap of stripboard to drive a relay. The flying version uses the transmitter to select the voltage from list but a potentiometer would suffice for your use. The picaxe chip uses 3 wires from 9 pin serial socket (no programmer) and I could send you the programme. They are available from ==

http://www.phanderson.com/picaxe/
------------------------------------
In the time it has taken me to create this masterpiece you have you have a reply from Alain and I started yesterday.

Dyslexic Dave

Ralph Weaver

Dec 14, 2007, 07:36 AM

http://batteryjunction.com/licyba181417.html bottom of the page. There are lots of sources for these types of devices. They disconnect the battery from the load if the voltage gets too low. They monitor the individual cells. Might need to be modified to handle higher loads.

Acetronics

Dec 14, 2007, 08:46 AM

yes,

a processor, a small value resistor for current measuring, may be a thermistor for tempco correction and a pair of parallelled Mosfets as a switch ... that's all !!!

Alain

orraman

Dec 14, 2007, 09:42 AM

Ralph Weaver,
Your link is to a good product at a fine price and I was tempted as each cell is tested individually but the Overdischarge Protection is stated to be 2.4v +/- 0.08v per cell.
I searched for similar products but some of these go as low as 2.3v per cell.

3v per cell seems common for individual cells now with perhaps 3.2v for series discharge, all dependant one's personal risk assessment as hard info is scarce.

dd, Late again

applejack

Dec 14, 2007, 10:19 AM

Hi Ralph, Thanks

The 'over-discharge protection' circuit shown on the battery junction site would do nicely if I understand the application. The price is certainly right but I would rather have the battery shut off at no lower that 2.8v per cell.

Hi Alain,

The application for the 'timed auto-shut off' device is for a transmitter. I fly indoor electrics only and I rarely fly more than a few minutes at a time. My concern is that I will fail to turn off my transmitter, put my transmitter in my field box, take it home and fail to hear the soft low voltage alarm built in the transmitter. I have Futaba 4 and 6 channel transmitters. The battery pack involved is a 2000 mAH 11.1v lipo.

Jack

Ralph Weaver

Dec 14, 2007, 10:26 AM

There is a difference between monitoring your battery while flying and cutting off the load in case you forgot to turn off. 2.4V is fine for the latter - it's the industry standard and is in use on millions of cell phone and laptop LiPo cells.

There is some advantage to a timer and an alarm, but how do you power the alarm? What do you do if the alarm discharges the battery too far?

applejack

Dec 14, 2007, 02:06 PM

Thanks Ralph,

If 2.4v is an industry standard then I shall quit being concerned. Thank you for the information.

Thank each of you for your response and your efforts to help me.

Jack

Acetronics

Dec 14, 2007, 02:41 PM

Hi Alain,

The application for the 'timed auto-shut off' device is for a transmitter. I fly indoor electrics only and I rarely fly more than a few minutes at a time. My concern is that I will fail to turn off my transmitter, put my transmitter in my field box, take it home and fail to hear the soft low voltage alarm built in the transmitter. I have Futaba 4 and 6 channel transmitters. The battery pack involved is a 2000 mAH 11.1v lipo.

Jack

Hi, Jack

What we could do is :

1) beep ( or blink a led ) once a while when batt Ok and tx ON ... tells you it is still ON ... especially when putting it in your case !!! :rolleyes:

2) beep quicker and quicker as the batt level falls :o
( I had an option with a level bargraph - PSoC processor ) ... but the display ( std 2x16 LCD ) is a bit huge to enter the transmitter ... LOL !

3) cut the Power when the security level of 7.2 volts is reached. :censored:

That could both avoid Tx power reduction/ and or Tx µP resetting problems ... and batt damaging. ;)

What about ???

Alain

Tomapowa

Dec 14, 2007, 02:45 PM

edited...
Sorry I thought you were charging your Tx battery... :confused:

pilotpete2

Dec 14, 2007, 04:11 PM

Here's a good solution, fuggedaboud the lipos in your transmitter and switch to the new low self discharge Eneloop NIMH cells from Sanyo ;)
Pete

applejack

Dec 17, 2007, 05:01 AM

Thank you pilotpete2 and all.

Using the lower self discharge NiMH cells would be an improvement. However, I still like the way the lipol pack performs.

I just ordered 2 of the circuit protection PCB's from BatterJunction.com and another 3 cell 2000mAH budget pack from CommonsenseRC.com. My main concern is to protect the pack from being ruined in the event I left a transmitter on and the pack could be fully discharged. As an added bonus, this circuit board also protects against over charge as well. If any one cell drops below ~2.5v then the pack stops conducting. That will do what I need to have happen WHEN and not IF I leave a transmitter on. Yes, I am a certified antique and do have a senior moment now and then.

Merry Christmas to all.
Jack