# Lithium battery charger

Discussion in 'Power Electronics' started by BlinkingLeds, Mar 31, 2013.

180
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Feb 23, 2013
Hi I want to change the dead Ni-Cd batteries on my rechargeable drill with Lithium batteries.
It's 18v so i will need 5x 3.7v. The most cost effective way is to use 18650 batteries.
This requires a new charger for them. I have 2 options:
1. Make one

The problem i face is that i can't find a charger with the money i want to spend (under 10\$) that will charge them fast enough. If i use a charger like THIS one, it will take 5000mAh (my batteries) x5 / 5A (charger rating) = 5hours?. I need it to charge within one hour. I could get smaller batteries but i would like to avoid that if possible.
Another problem is that i don't know the max charge rate of the 18650 batteries but i hope that all Lithium based batteries have more than 5C.
Is there a way to modify a charge like the one in the link to be able to output 25A or i will have to make one (I have no idea how) .
Thanks

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,412
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Jan 21, 2010
Wouldn't you only need a 1C charge rate?

I believe the general recommendation is to keep the charge current below 1C, but could be wrong.

In any case, 1C gives you an approximate 1 hour charger (longer because the current will drop off near the end of charge)

edit: if the batteries are in series, 5000mAh batteries require 50000mA = 5A for a 1C charge.

180
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Feb 23, 2013
that's a good idea but i can't find a charger that will charge 5cells in series.

4. ### donkey

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56
Feb 26, 2011
you are looking at this wrong, if it were me I would go to the local tip(rubbish dump) and check their tool section.
find an old cordless drill 18v lipo and rework it. you don't need the drill just its charger.
someone on here might be able to tell you if any modifications are needed but I figure that's a start.

all batteries are individual cells combined together. grab a lantern battery (6volt one) and in some of them all you find is AA batteries combined.
if you hook up your batteries in series then what you are in fact doing is making a battery with 15 cells as the lipo pack will most likely have 3 cells in it already

Last edited: Mar 31, 2013
5. ### Harald KappModeratorModerator

10,346
2,250
Nov 17, 2011
Donkey's idea is a good one.
Note that for charging bat´teries in series some kind of balancer is recommended. Balancing batttery charge prolongs the lifetime. Chances are that a battery pack (a from a tool) has a simple type of battery balancer built into it.

6. ### donkey

1,289
56
Feb 26, 2011
ok..ok..ok can someone frame haralds comment for me.... I came up with a good idea yay me

180
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Feb 23, 2013
I can't find an charger for a cordless drill without actually buying the whole drill set which is expensive.
How about the link i posted? will this work? can i enhance it somehow for more output current?

8. ### CDRIVEHauling 10' pipe on a Trek Shift3

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May 8, 2012
Here ya go.

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• ###### Frame.JPG
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Last edited: Apr 2, 2013

180
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Feb 23, 2013
Ok how about a constant current/voltage source connected to the pcb from my link that will switch off charging when 4.2v. will that work buy charging individual cells in parallel, not in seiries?

10. ### CocaCola

3,635
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Apr 7, 2012
Ebay? Probably hundreds of them, like this...

http://www.ebay.com/itm/Ryobi-P113-..._Tools_Batteries_Chargers&hash=item3f23c17870

Get a Ryobi lithium battery pack and you will also get the balance and overcharge circuit that matches the charger and even the cells, all done in one package...

Sorry it's not \$10 but things cost what they cost sometimes...

FYI: If someone is claiming 5000mAH out of a 18650 they are pulling your leg with false claims, 3000mAh is about all the chemistry will allow in that sized cell for name brand high quality cells, and that is measured at a LOW drain rate, not a cordless tool drain rate.. If you are getting generic from Asia, you are likely to find with a 1A drain you are really getting close to 1500-1800mAH as that is about the norm for cheap knock off cells from Asia...

180
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Feb 23, 2013
They don't meet my requirements most of them don't specify max output current and some of them that do have fairly low ratings.

Perhaps DIY is the only way to go.

12. ### CocaCola

3,635
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Apr 7, 2012
Your requirements are 1 hour charge, are they not? Using the paired battery to the charger I linked get you just what you requested, a one hour or less charge...