limiting output on power supli

[landries]

hello
i want to charge lithium batteri's whit mi power supli
i have battery's whit a capacity off 60AH (60000mah)
i own a power suply 1to15 volt 25amp
i can not regulate the output amperage
how can i limit the current to 15 ampere
thanks for any help
ps:sorry for my englisch
greetings from belgium
luc

[chipmonk]

without more info on the batteries i would caution against what you are proposing
here is a helpfull link giving the pro`s and con`s of charging lithium cells
http://www.batteryuniversity.com/partone-12.htm

[landries]

batterys made whit cells of 3,7 volt 1400 mah
each battery 1/S50/P so 3,7 volt 70 AH
each cell has a protection against overcharge and overdischarge
i want to charge tru my power suply i can regulate the voltage but not the amperage
i want to regulate the voltage on 4,15 volt so no risks
how to regulate the amperage to 15 ampere knowing that my power suply can handle 25 amp continu and 30 amp peak
any help is welcome
greetings luc

[tve]

Have you looked at this thread yet?

http://www.rcgroups.com/forums/showthread.php?t=304448

[landries]

this tread speeks about chargers whit 3 amp output i have chargers of 5 amp and it takes me to long to charge i have 8 off these batterys to charge each one off 70 AH
this takes me 2 days whit 5 amp that's why i want a 15 amp charger

[tve]

[edit] wont work either.... :) maybe I should give up.

[tve]

OK,

How about this part? I think it will do what you want with the appropriate FETS, inductor, etc.

http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1037,C1078, C1089,P2279,D3249

[edit]

Actually looking closer at the data sheet, it might be kind of hard to get rsense down to the value you would need for 15 amps. Anyway, hope this gives you some ideas anyway...

[edit again]
The more I look at this part, the more I think it would work for you. I think it would be a really fun project. I might work on it when I get some more time...

[Warske]

i want to regulate the voltage on 4,15 volt so no risks
how to regulate the amperage to 15 ampere knowing that my power suply can handle 25 amp continu and 30 amp peak
any help is welcome
Take a look at N Channel Hex Fet Power MOSFET IRL3705N $2.60 at Digikey http://www.digikey.com

datasheet http://www.irf.com/product-info/datasheets/data/irl3705n.pdf

See fig 1 & 2 below. At Vgs = 3 v, current is about 20 Amps. For lower current, use lower Vgs. Use 2 resistors to bias the gate. Note that current goes up some with temperature. Use a heat sink.

Below 1 volt, current starts to drop, but at 0.1 volt across the FET, you still get about 4 amps. Not perfect, but simple fast and inexpensive.

For better current regulation, sense the current and use electronics to feedback and control Vgs, but that turns into a project.

For safety, suggest using a 20 Amp fuse in the charging circuit. Charge it in a fire proof box. Add over temperature alarm and shutdown.

The gate of the FET is static sensitive. That is, you can burn it out by touching it.

Charging LiPos is like playing with gasoline and matches. Please be careful.

Warske

[landries]

thanks for reactions but i dont know much about electronics is there someone ho could build something for me against payement?
i already use these batterys but can only charge them whit a charger that gives only 5amp
thanks again for all the fast reactions
luc