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Author Topic: 75mah lipo charging  (Read 1752 times)

Mad_Mike

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75mah lipo charging
« on: May 19, 2012, 11:01:17 AM »

I have salvaged from some toy indoor helicopters 2 75mah single cell lipos, at least i think there lipo anyway, might be life. Anyway these things are tiny about the size of a 5 pence peice.
I currently have a turnigy 2s/3s balance charger very basic which does the job for most of my larger batteries but it has an out put of 800ma and cant be changed. Is there a way i can make up a lead which will charge both cells from the 2s port on the charger but have some circuitry in the lead to reduce the current output?

thanks
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Tug-Kenny

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Re: 75mah lipo charging
« Reply #1 on: May 20, 2012, 11:07:26 AM »

You can reduce the charging current by fitting a resistor in the positive feed to the battery.

What value I wouldn't know. Perhaps there are more knowledgeable people here ?  Also size to accommodate the amps drawn.


ken
 
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Mad_Mike

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Re: 75mah lipo charging
« Reply #2 on: May 20, 2012, 11:24:21 AM »

i thought so but from what i gather that a resitor drops the voltage too. Im not to sharp on electronics, on the other hand i dont want to spend 25 quid on a balance charger when the one i got does the job for the other ones.
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Tug-Kenny

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Re: 75mah lipo charging
« Reply #3 on: May 20, 2012, 11:37:24 AM »


I might add that Lipo charging is unknown to me, but I understand it's a touchy business all around. 

It would be best to get professional advice, that's why I've moved this to the Electrics department

ken
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Mad_Mike

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Re: 75mah lipo charging
« Reply #4 on: May 20, 2012, 12:21:54 PM »

Ive found this:

http://www.ebay.co.uk/itm/150806941202?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2648

from what i gather it has or charge protection, lvc and a circuit breaker combined. I just need to find out how to charge it, maybe a mobile phone charger?
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Tug Fanatic

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Re: 75mah lipo charging
« Reply #5 on: May 20, 2012, 02:37:47 PM »

The ebay board that you have linked prevents over charging by current limiting at 5 amps. This is way way more than a 75mah lipo will take. The charging rate has improved steadily over the last few years but I am guessing that as these came out of a model helicopter they were designed to charge in 15 minutes which gives a maximum charge of 300mah. This likely to be a higher rate than is desirable for long life.

There are so many aircraft models that come with 75mah cells that chargers are really cheap - my Parkzone examples are 70mah but that makes no real difference. Model airshows have boxes of them at 1. They take 4AA cells (I use rechargeables which I have anyway) and give you 20 or so charges. I take 2 chargers, half a dozen batteries & a couple of planes & can fly continuously if I wish. It is good practice to let a LiPo rest before recharging - particularly if it has got warm. At this high charging rate the batteries have a restricted life so are you sure that your are worth saving when new ones with the correct plugs etc are so cheap?

http://www.hobbyking.com/hobbycity/store/__11893__Turnigy_nano_tech_160mah_1S_25_40C_Lipo_Pack_Kyosho_E_flite_Parkzone_Etc_.html

Your charger is designed for 2S & won't get down anywhere near 300mah. I simply wouldn't go there. LiPo chargers are intelligent & I would be concerned about whether they would remain that way if you messed around with them. If you overcharge a LiPo, or let it go completely flat, you have destroyed it. - and if overcharged it might catch fire.


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Mad_Mike

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Re: 75mah lipo charging
« Reply #6 on: May 20, 2012, 03:08:17 PM »

thanks very much for the help. do you mean these things?

http://www.ebay.co.uk/itm/261005688195?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2648

i was looking into buying a small usb charger circuit from the US it was going to cost me 20 quid to get it here.

i was also looking at another battery with a pcm also built in:
http://www.ebay.co.uk/itm/200754560608?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2648

the 75mah battery that i have seems to have a little cicuit board on it and i think that might be a pcm too.

what connectors do i need to plug these batteries into the charger?
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Tug Fanatic

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Re: 75mah lipo charging
« Reply #7 on: May 20, 2012, 03:26:06 PM »

Yes those are the chargers.

If you look at the battery that I linked it has a connector on the end which pushed into the slot that you can see on the front of the charger.

Here you go with the separate plugs:
http://www.indoorflyer.co.uk/miniumparkzone-battery-plugwire-3pk-583-p.asp

I have no experience of the type of battery that you link to but be careful of discharge & charging rates. They can be as low as 1c.  
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