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$$$$ Chargers - 7/7/2003 8:25:12 AM   
e-bird


 

Posts: 204
Joined: 4/20/2003
From: Sacramento,ca
Status: offline 		There are many chargers that Cost $$ But you can build
your own Cheap The people that make IC's that the hobby
Buy chips from Why Not You. CU
http://www.national.com/catalog/AnalogRegulators.html
       Post #: 1

$$$$ Chargers - 7/7/2003 11:15:57 PM   
Steve Neu


 

Posts: 70
Joined: 6/19/2003
From: San Diego, CA, USA
Status: offline 		Sure you can build your own charger--but there is a lot more to it than a couple of chips. Most of the better chargers have a DC-DC converter to boost the 12 volt car battery voltage to a level high enough to charge 20 or 30 Nicad cells. Power electronics is not cheap to make. Most chargers have a micro controller computer and a LCD display--again not cheap.To that add a few hundred hours to write the software to control everything--then add a box and switches with cables and connectors and soon the chargers that are offered for sale don't seem so expensive.

Steve

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       Post #: 2

$$$$ Chargers - 7/19/2003 8:16:03 PM   
tailheavy



Posts: 132
Joined: 5/12/2003
From: Virginia Beach, VA, USA
Status: offline 		Depends on what the application is. If you just want to do li-po's you may be able to make a home made charger just for doing li-po's. I seen a thread on rcgroups that mentioned some one doing that successfully but I believe it was to allow him to charge up the li-po to ~90% only (too dangerous to go to 100%). He then used the expensive commercial charger to charge it the rest of the way. That's a good way to charge multiple packs with just one expensive charger to top off all your packs. I will eventually look in to it myself. Since I am very knowledgeable about electronics this sort of thing doesn't scare me, just be sure you know what you are doing and why. It also helps to have good test equipent too.

As far as making your own full featured charger, good luck. I agree with the previous poster. Better off buying a good quality commercial charger.

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       Post #: 3

$$$$ Chargers - 7/23/2003 11:51:11 PM   
HappyHobit



Posts: 8
Joined: 7/23/2003
From: Allen Park, MI, ALBANIA
Status: offline 		I have to agree with the statements that it's better off buying a good quality commercial charger for NiCd and NiMh batteries.

But it’s really not hard, or dangerous, to build a charger for LiPoly batteries.

It can be done with 2-LM317 adjustable regulators, with heatsinks, a current limit power resister and a voltage reg pot. Total cost for a 1 or 2 cell, 1.5 amp charger is $8.00. The only thing you need to make it safe is an accurate voltmeter.

You will need a power source. You can use a car battery, a computer power supply or a wall wart AC to DC power supply. Anything that will supply 12 to 20 volts DC at the current you want.

This charger will charge a cell to “100%” safely. All it takes is time.

Here’s one I built for 145ma cells.

Jay

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$$$$ Chargers - 7/24/2003 2:37:30 AM   
tailheavy



Posts: 132
Joined: 5/12/2003
From: Virginia Beach, VA, USA
Status: offline 		Did you design that circuit yourself or did you just copy someone else's schematic? Also are you saying that it can only charge batteries that are 145ma in capacity. If this truly does safely charge lipos to 100% I would be very interested in getting more info on it.

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       Post #: 5

$$$$ Chargers - 7/24/2003 4:42:28 AM   
HappyHobit



Posts: 8
Joined: 7/23/2003
From: Allen Park, MI, ALBANIA
Status: offline 		I “designed” the circuit myself. I combined a current limiter and voltage regulator, as designed in the LM317 datasheets. (pg. 16) http://www.national.com/ds.cgi/LM/LM117.pdf

There are 3 rules for charging the LiPoly cells.

IF the battery is ‘Less Than 3 volts / cell’ charge at .1C until voltage greater than 3 volts / cell.
Limit the voltage to 4.2 volts per cell.
Limit the current to 1C.

An LM317 X 2 charger can be used to charge LiPoly batteries up to 1.5 amps and 3 or 4 cells, limited only by heatsink size and power source.

The picture I included in my origional post was for a dedicated 4.2 volt, 145 ma charger. It cost me about $7. If you wanted to add other current limit resisters and switches it could be used for other size calls. Just make sure you have it ‘programmed’ correctly before you plug the battery in. Mine is a ‘No Brainer’.

This thread in RC Groups is based on this charger design

http://www.rcgroups.com/forums/showthread.php?s=&threadid=130567&perpage=15&pagenumber=1

I had built my charger before this thread started but the design is the same.

Jay

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       Post #: 6

$$$$ Chargers - 7/24/2003 8:20:32 PM   
tailheavy



Posts: 132
Joined: 5/12/2003
From: Virginia Beach, VA, USA
Status: offline 		Wow that's some great info I need to make something for my 1200ma 3 cell Lipo's. I'll have to figure out how to do the programming though.

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       Post #: 7

$$$$ Chargers - 7/25/2003 1:48:20 AM   
HappyHobit



Posts: 8
Joined: 7/23/2003
From: Allen Park, MI, ALBANIA
Status: offline 		The math for sizing the components is fairly simple. Well sort of.

You are going to need a power source of 18 or 20 volts and two good size heatsinks.

Each LM317 will ‘lose’ 2.5 volts. So for a 12.6 volt output you’ll need at least 17.6 volts input.

With a 20 volt supply you’ll have to dissipate 9.6 watts in the voltage reg. LM317 and 5.2 watts in the current limiter LM317. Each would be a couple watts less with an 18 volt supply.


Now for sizing the Current limiting resister. First you'll need a 2 watt or larger resister.

This resister must drop 1.25 volts at 1C. R = E / I = 1.25 / 1.20 = 1.042 ohms. Not easy to find.

A 1.0 ohm resister would limit the current to 1.250 amps or 4% over. A 1.1 ohm would be 1.14 amps. or about 9% under


The volt regulating Lm317 requires a minimum of 4ma to regulate properly. With a 12.6 volt output a 2k pot would produce 6.3 mili-amps.

That’s it. Nothing to it.

Jay

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       Post #: 8

$$$$ Chargers - 7/25/2003 5:17:09 AM   
shenion



Posts: 263
Joined: 3/19/2002
From: Stone Mountain, GA, USA
Status: offline 		There's always mine at: http://shdesigns.org/lionchg.html

It is the first discussed in the posts.

I don't see and advantage to the dual LM-317 version. Mine needs only about 2.5 volts more in than out, and has a charge LED. It will work better on 2-cell Li-Ion batts with 12v input.

Apparantly hundreds of these chargers have been built. I get emails from users that once they built one, they need to build more for their friends. The schematics have been downloaded literally thousands of times. Web page has close to 8000 hits over the last 6 months.

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Scott Henion
My Planes page:[color=red] [link]http://shdesigns.org/planes.html[/link][/color]

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       Post #: 9

$$$$ Chargers - 7/26/2003 2:37:22 AM   
tailheavy



Posts: 132
Joined: 5/12/2003
From: Virginia Beach, VA, USA
Status: offline 		That brings up a very important point. I cannot use my computer power supply since it only puts out 12.5 volts. So would need to get a different power supply right?

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       Post #: 10

$$$$ Chargers - 7/26/2003 2:47:36 AM   
tailheavy



Posts: 132
Joined: 5/12/2003
From: Virginia Beach, VA, USA
Status: offline 		shenion, your circuit is for lithium Ion batteries. Aren't Li po's different?

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       Post #: 11

$$$$ Chargers - 7/26/2003 4:39:29 AM   
HappyHobit



Posts: 8
Joined: 7/23/2003
From: Allen Park, MI, ALBANIA
Status: offline 		TailHeavy,

Unless the –12 volt supply has enough capacity you will. Try not to get a power source any larger than necessary. Any voltage you don’t need has to be disposed of as heat.

The same Lithium charger can be used for LiIon and LiPoly (but NOT LiMetal). Lithium Ion has liquid electrolyte that tends to boil and produce explosive quantities of gas if mishandled while the Lithium Poly has a polymer electrolyte which, when mishandled will expand but not explosively.

Have you been able to access the URL SHenion provided?


Jay

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       Post #: 12

$$$$ Chargers - 7/27/2003 1:35:01 PM   
shenion



Posts: 263
Joined: 3/19/2002
From: Stone Mountain, GA, USA
Status: offline 		[QUOTE]Originally posted by tailheavy
shenion, your circuit is for lithium Ion batteries. Aren't Li po's different? [/QUOTE] Not for charging.

My charger is used more for LiPolys than LiIon as I get more feedback from LiPoly users.

_____________________________

Scott Henion
My Planes page:[color=red] [link]http://shdesigns.org/planes.html[/link][/color]

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       Post #: 13

$$$$ Chargers - 7/27/2003 7:16:14 PM   
Mike Taylor



Posts: 464
Joined: 5/23/2003
From: Camarillo, CA, USA
Status: offline 		Are you guys POSITIVE the same charger can be used for all type of lithium batteries, or just making a guess???

The LiPolys have different voltages and charging profiles from the other types of litium cells. Chargers made for LiPolys say not to use them with other types of cells, and the literature with the cells says not to use chargers made for other types of cells (including LiIon cells).

If what the manufactures says is true, and my guess is that they know what they are saying, then any money you save by building a cheap charger will be wasted on ruined LiPolys. At ~$9 a pop for single cell, it won't take ruining many packs to have bought the best charger there is out there...

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       Post #: 14

$$$$ Chargers - 7/27/2003 8:18:11 PM   
HappyHobit



Posts: 8
Joined: 7/23/2003
From: Allen Park, MI, ALBANIA
Status: offline 		Hi Mike,

I was just talking about Lithium-Ion and Lithium-Poly batteries

Check out this website for more info on Lithium Ion/Poly batteries. The last paragraph compares Lithium Ion/Poly batteries.

http://www.batteryuniversity.com/partone-12.htm


Jay

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       Post #: 15

$$$$ Chargers - 7/28/2003 7:11:36 AM   
shenion



Posts: 263
Joined: 3/19/2002
From: Stone Mountain, GA, USA
Status: offline 		[QUOTE]Originally posted by Mike Taylor
Are you guys POSITIVE the same charger can be used for all type of lithium batteries, or just making a guess???

The LiPolys have different voltages and charging profiles from the other types of litium cells. Chargers made for LiPolys say not to use them with other types of cells, and the literature with the cells says not to use chargers made for other types of cells (including LiIon cells).

If what the manufactures says is true, and my guess is that they know what they are saying, then any money you save by building a cheap charger will be wasted on ruined LiPolys. At ~$9 a pop for single cell, it won't take ruining many packs to have bought the best charger there is out there... [/QUOTE]

The data sheets I have for Li-Ion and Li-Poly show the same charge voltage.

The only difference was the charge rate, but that varies from cell to cell anyway.

Some Li_ions say 0.7C others say more. Some Lipoly's say 0.5c but I have seen some say 1.0C.

Basically you need to determine the current required for the particular type you are using.

Now Li-Metal (Duralites) are different. Basically the same algorithm, but different voltage thresholds.

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