Cheap Lithium Charger for Electronics Tinkerers - Page 11 - RC Groups
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Aug 20, 2003, 02:47 PM
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SMjett's Avatar

Re: Over Discharged Cells


Quote:
Originally posted by electron_head

...
Also remember that this charger will still charge your cells at 1C even if they have been over discharged and need charging at 0.1C!!!!
How about a using a cheap 78Lxx regulator across the output to drive an LED?
This will give you the few milliamps required to maintain regulation on a fully charged battery and use the dropout of the regulator for a quick status check on the pack before you turn on the supply voltage.

For example, on a 3-cell charger use a 78L08 across the output feeding an LED. Connect the battery to the charger before turning on the power. If the LED glows brightly you are good to go. If it does not glow brightly then either the pack is over discharged or you're hooking a 2-cell pack to a 3-cell charger

SMJ
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Aug 20, 2003, 07:21 PM
Registered User
I am not an electrician or electrical guru but would like to build the simple Lipoly charger. can someone actually write down the instructions on how to build this thing. This would be an awesome post for us electrical neophytes. You guys do amaze me with ingenuity.
Aug 20, 2003, 09:09 PM
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SMjett's Avatar

Re: Over Discharged Cells


Quote:
Originally posted by SMjett
How about a using a cheap 78Lxx regulator across the output to drive an LED?
I suppose a zener diode would probably do this a lot better

Coop: This design is about as simple as it ever gets. Read the whole thread through then read the first 3 pages once more. Just calculate the required resistor values as explained in the first post and then build it like it shows in electron_head's excellent diagrams.

SMJ
Aug 20, 2003, 09:27 PM
Registered User
SMJ I mean ok you solder this to this. That is what I mean. I am not good with schematics.
Aug 20, 2003, 11:37 PM
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SMjett's Avatar
Quote:
Originally posted by Coop
SMJ I mean ok you solder this to this. That is what I mean. I am not good with schematics.
The diagram on page 1 of this thread isn't a schematic. Its a picture of the pieces soldered together. Its almost impossible to go wrong. If you need help with the resistor values post the type of packs you want to charge and I'll tell you which ones you need. But first read this whole thread, then read the first few pages again.

SMJ
Aug 23, 2003, 08:19 PM
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gtstubbs's Avatar
Meet the latest twins, would have been Quads but could only get 4 samples of the LM 1084 at a time. Total cost $AUS15 for 2

Otherwise to be set up to charge 3S1P ETec 1200.

I was thinking of ripping the guts out of a cheap multimeter ($AUS 9) to use the meter for measuring amps and volts but for now just rigged a harness to do the same.

Pic of the twins.
Aug 23, 2003, 08:30 PM
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Twins in a crib
Aug 23, 2003, 08:31 PM
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Twin in a crib
Aug 23, 2003, 08:36 PM
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gtstubbs's Avatar
The harness
Aug 24, 2003, 09:18 AM
veni,vidi, roto volubilis
Happy|Harry's Avatar
Right here we go. I'm about to try and build 2 of these, 1 for
2s1200's e-techs and 1 for 2s1600's from batteries america,
after reading (and re-reading-and re-reading) i have came up with this
i will need

4 x LM317
4 x heatsinks for above
4 x 1uf Ceramic resistor
2 x 5W wirewound resistor 1ohm

here's where i want to be sure
for the voltage regulator resistor both chargers will need 686ohms(96 x 8.4v - 120)

for the current regulator resistor the 1200mAh needs 1.0416667ohms(1.25/1.2)
" ------ " ------ " ------- " ---- " -- 1600mAh needs 0.75ohms(1.25/1.6)
all resistors need to be 1/4 watt mf 1%

is this correct, and how can i get these values for the resistors(eg 2x*ohm resistors
and 1 x*ohm resistor in series/parallel) or are there resistors in the
values i need?
thanks in advance

phil
Aug 24, 2003, 12:03 PM
Registered User
SMjett's Avatar
Quote:
Originally posted by Happy|Harry
Right here we go. I'm about to try and build 2 of these....

phil
Phil,

Your calculations are all correct. You can use a 680ohm resistor for Vr. (686ohms is within the 1% tolerance range).
The 1 ohm resistor can be 5% tolerance.

I would recommend that you go with the LM1085 LDO regulators. They will cost about an extra $1.00 each but are rated for 3A and they will happily charge a 2s pack from a 12V source at full current. All the components are the same but you can use 47uF aluminum electrolytic capacitors on the input and output instead of 1uF ceramic.

I'm about 2 weeks away from releasing a simple kit version of this charger. I'm just finalizing the design for the safety and charge status indicators and getting parts ordered.

SMJ
Aug 24, 2003, 02:26 PM
Registered User
Well I will buy the kit SMJ. Put me down for it.
Aug 24, 2003, 03:48 PM
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electron_head's Avatar
Happy|Harry,

You are certainly on the right track by reading the whole thread.

One thing. The minimium value for the current resistor should be 0.8 ohm as if you go lower you will be exceding the 1.5 amp rating for the IC. A 0.75 ohm may work but if your after more the LM350 might be a better option.

Adding a 5 amp ampmeter to the circuit is a must in my opinion as then you can see at a glance the state of packs by plugging and unplugging them and also how far charged they are when charging.

Regards Garry
Aug 25, 2003, 08:34 AM
veni,vidi, roto volubilis
Happy|Harry's Avatar
Thanks for the replys guys
i think i better let you all know that i'm a complete noob at electronics
and this is my first project (apart from making up 2 GWS350C's
from just bare motors eg: no pinion, capacitors or wires)

Ok i'm going to go with the LM350's, but the LM350 comes in different forms

LM350T TO-220
LM350AT TO-220
LM350KSTEEL TO-3 [edit]<< i know from looking at the data sheet that this one isn't correct>>[/edit]

which is the correct one T or AT? also with what i've read the LM350 has
a smaller voltage drop than the LM317 which is always a good thing
(less waste ) but does that mean any of my calculations need to be changed
for the resistors etc? if not what size resistors can i use for my
needs? I now know i can use a 680ohm for the voltage reg,
will a 1ohm resistor work for the current reg for the 2S1200?

So as i have it now my list is

4 x LM350
4 x heatsinks for above
4 x 1uf Ceramic resistor (are these 1uf or 0.1uf? AND do i really need them?)
the following resistors need to be 1/4watt 1% metal filament
1 x 1ohm resistor for current (for 2s1200)
1 x 0.75ohm resistor for current (for 2s1600)
2 x 680ohm resistors for voltage resistor

correct me if i'm wrong (if i'm wrong i'll just wait for the kits from SMJet)

thanks again

phil
Aug 25, 2003, 09:51 AM
Registered User
Happy Hobit's Avatar
Hi Harry,

Quote:
Originally posted by Happy|Harry
Thanks for the replys guys
i think i better let you all know that i'm a complete noob at electronics
and this is my first project (apart from making up 2 GWS350C's
from just bare motors eg: no pinion, capacitors or wires)

Ok i'm going to go with the LM350's, but the LM350 comes in different forms

LM350T TO-220
LM350AT TO-220
LM350KSTEEL TO-3 [edit]<< i know from looking at the data sheet that this one isn't correct>>[/edit]

which is the correct one T or AT?

The LM350T is fine. Check the top of page 2 of the National Semiconductor LM350 datasheets.

Quote:
also with what i've read the LM350 has
a smaller voltage drop than the LM317 which is always a good thing (less waste ) but does that mean any of my calculations need to be changed for the resistors etc?
NO

Quote:
So as i have it now my list is

4 x LM350
4 x heatsinks for above
4 x 1uf Ceramic resistor (are these 1uf or 0.1uf? AND do i really need them?)
Ceramic capacitors not resisters. .1 ufd input, 1 ufd output. They're optional.

Quote:
the following resistors need to be 1/4watt 1% metal filament
NO. All resisters need to be 1%

These should be a minimum of 2 watt.

Quote:
1 x 1ohm resistor for current (for 2s1200)
1 x 0.75ohm resistor for current (for 2s1600)
These are 1/4 Watt

Quote:
2 x 680ohm resistors for voltage resistor
You'll need 2 x 680-ohm and 2 x 120-ohm resisters.


Jay


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