Electrolight

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Hello All, I have a unique situation.

Long story short...
I want to charge a 4s lipo with ease. I want to walk up to my device and then plug it in and have it instantly begin charging then shutoff when full. No button pressing should be required. Also, I do not want the device to allow the batteries to over discharge... Ideas?



Long story Long...
I have a great wonderful little black and Decker vacuum.

Problem 1: is its powered with Ni-cds.
Solution 1: I opened it up and there is precisely enough space for two 4s 2150mah li-po packs. (idk what those ni-cds are rated but this should at least double the amp/hr rating.)

Problem 2: I want my girlfriend to be able to charge it by walking up to it and plugging one simple little cord into it. She doesn't know how to operate my hobby chargers nor do I want her to have to know how to use it because I'm sure she'll probably avoid the vacuum do to lack of "user friendlyness".
Solution 2: That means a smart pcb that can cutoff at full and cutoff at low in the vacuum. Or it means smart charger with a 7 pin plug (4s balancing and positive and negative). NOTE this smart charger needs to not require button pressing. I'm talking plug and play responsiveness.

Safety...
Don't worry I already cut out my kevlar to wrap the lipos for safety. Besides they will be discharged at like 2-4C which is way less than their 20C rating.

Ideas?



The vacuum is a great little beast and if I can manage this project it will be truly a work of art.
Thanks for all of your help!
Electrolight


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startazz

Not sure if you can find one out there that would do that but there is a couple out there that come close,you will have to tap a button at least twice but other than that it will do what you want,plus there are only two buttons on it so it's not like the rest of them out there that have minimum of four buttons.

So your girl friend should be able to use this one,all she has to do is tap the button twice i think and then when the charging is done she just has to unplug the lipo,job done.

http://www.hobbyking.com/hobbyking/s...e_Charger.html

tacx

My Feedback: (1)

I hope your girlfriend doesn't find out about how much trouble you are going through to make sure she always has a charged up VACUUM !!!!! LOL You might find it plugged in somewhere else !!!!

t9dragon

My Feedback: (11)

You are asking for problems.. Lipos should never be left unattended when charging.

bgosselin

I agree! If you want a more hassle-free setup, I'd use properly-sized Li-Ion's (or A123 cells) that aren't as prone to issues, similar to what power tools use.

Really, all Lixx cells need is constant-current charge up to the termination voltage (4.2v for lipo, 3.6v for A123). After that, it should switch to constant-voltage - but because you don't get much charge at this stage, you could simply stop the charge. You should also use a BMS circuit so the cells are balanced, and so the voltage on any single cell will dip too low or rise too high; similar to what laptops use. Something like this: http://www.all-battery.com/pcb4SLi-ion15-20A-32128.aspx

Electrolight

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Thank you for all the replies. So I think I found the perfect board to squeeze in there so the cells are always balanced and its a pcm circuit. [link=http://www.batteryspace.com/Protection-Circuit-Module-PCM-with-Equilibrium-Function-and-Fuel-Gauge-for.aspx]here[/link]

This simplifies my charger requirements but it also brings up two issues... I still need a Low voltage cutoff and either a charger that knows when to cutoff or at least another pcb that could cut off.

Also, regarding lipo vs li-ion... The reason I leaned toward the lipo is because If I used the lipo I could fit them into the available battery space and use it all up completely giving me 4300 mah (2150X2) VS having a bunch of empty space but still only able to fit exactly 4 18650s with 3000 mah. (here are my [link=http://www.ebay.com/itm/2pcs-New-Samsung-18650-Rechargeable-Li-ion-battery-3000mah-Free-Shipping-/270939404192?pt=US_Rechargeable_Batteries&hash=item3f153f37a0]18650's[/link]. I have about 12 of them that are brand new (although their rated capacity is about 3000 mah on my tester I average about 2910 mah))

Anyways, If ya'll think it would be that much safer then I think I will go with the 18650 lions. Wish I could fit 8 in there...


Anyhow. Thank ya'll for your help and if anyone has ideas on how to get a pcb that cutsoff at full or low I would really appreciate it. Have a good day.
Electrolight


PS startazz thanks for the link, I think I may end up having to make my own cable that connects to that charger and then put it all in a wooden box that has one button on top that says "START". That would be easy enough for her ^^



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