fo r wa rd current of 1 A , and the voltage dro p i s o n l y 0 . 5 V at 1 A! ( B ) T h ere appears to be a smart tex t-book L i Po c h a rg i n g circuit, note the inductivity, diode, a n d ca p a c i to r combinati on along with the nift y I C ( n u m b e rs printed on it don’t make any se n s e ) u s e d i n typical “step-down buck converters”. ( C ) T h ere appears to be a tex t-book pulse w i d t h m o d u l ated (PWM) diver circuit section co n n e c te d on the reverse side of the PCB to th e P F te r m i n a l . W i t h t h i s and the la ck of a bold “10V-DC-in p u tvoltage-required-or-this-device-will-fr y-andT LC - ca n not-be-held- responsible” label nex t to t h e i n p u t jack strongly sug gest that we can u s e a w i d e r range of input charging voltages. He re i s t h e p l a n : Hook up a stabilized adjustable lab o ra to r y D C power supply capable of delivering 5 A ( i f t h e L iPo should die, it won’t suffer) at u p - to 2 4 V to a flat LEGO LiPo. T h e ca b l e required for this experiment is ea s i l y fa b r i cated from the pieces of a $8 “wall wa r t ” t y p e p ower supply and the adaptor plugs t h at t y p i ca l l y come with it, see figure 2.
Figure 2: P h o to g r a p h o f a t y p i ca l “ w a l l w a r t ” t y p e power sup ply and t h e p l u g u s ed fo r t h e c h a r g i n g ex p e r i ments. Such power s u p p l i es o f te n co m e w i t h a v a r i et y o f a daptor plugs. Inse r t : T h e 3 . 5 m m x 1 . 3 5 m m ( x m m l en g t h , n ot im portant) pl u g w o r ks b est w i t h t h e L EG O P F L i Po .
T h e re s ults are shown in figure 3. Below 9 V, n o t h i n g much is happening. At 9 V, the L i Po “c h a rg i n g LED ” started flashing. According to s o m e r u mors, the charging time may be lo n ger t h a n t h e 4 hours time given in Brian’s referen c e d R B a r t i c l e with the original power supply 1 . T h i s
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m a kes s en s e , s i n c e t h e m ax i m u m c h a rg i n g c u rrent at 9 V i s o n l y 3 0 0 m A . At 1 0 V, t h e m ax i m u m c h a rg i n g c u r re nt wa s p ea k i n g at 5 5 0 m A . I n c re a s i n g t h e i n p u t vo l ta ge to 1 9 V wa s co m p l etel y o k w i t h t h e L i Po e l ec t ro n i c s – i t a l ways c h a rge d n i c e l y. At t h e s a m e t i m e , t h e m ax i m u m c h a rg i n g c u r re nt wa s d e c rea s i n g . At 2 0 V i n p u t vo l ta ge “s o m et h i n g ” b a d h a p p e n e d – a l l l i g ht s went o u t a n d t h e L i Po el e c t ro n i c s a p p e a red to b e co m p l ete l y d e a d . O p e n i n g t h e d ev i c e 2 a n d d o i n g s o m e m ea s u rem ent s o n t h e P C B “s o m eh ow ” re a n i m ated t h e L i Po e l e c t ro n i c s , b u t I d o n ’t kn ow exa c t l y h ow . . . I d i d i t a ga i n a n d n ow I ca n ’t re a n i m ate i t a ny m o re . T h e p r i c e I h a d to p ay fo r t h i s res ea rc h … S o w h o ca m e u p w i t h 1 0 V ? M y b est g u e s s i s s o m e s m a r t m a r ket i n g p e o p l e at T LC . Th ere a re o n l y ve r y few ( i f at a l l ) c h e a p 1 0 V D C p owe r s u p p l i es i n t h e sto re s . I d i d n o t f i n d a s i n g l e o n e at F r y ’s o r R a d i o S h a c k. T h e c h e a p o n e s a re u s u a l l y rated 3 - 4 . 5 - 6 - 9 - 1 2 V o r s i m i l a r. Yo u k n ow w h at : W h o ca res ? 1 2 V wo r ks b e a u t i f u l l y wel l . I f re q u ent l y u s e t h e p ower s u p p l y s h ow n i n f i g u re 2 to c h a rge my L i Po “o ff- l i n e ” ; i t ’s a 6 € a n d 5 0 c ent d ev i c e . S u m m a r y : T h e re i s n o n ee d a n d n o a p p a rent re a s o n fo r b u y i n g t h e $ 2 4 . 9 9 L EG O 1 0 V DC s u p p l y f ro m S @ H . T h at t h i n g i s a ( ve r y ) go o d m a r keti n g j o ke . G o to yo u r favo r i te el e c t ro n i c s sto re , p i c k- u p t h e c h e a p e st ( u n reg u l ated ) u n i ve rs a l p ower s u p p l y rated at 8 0 0 m A o r a b ove yo u ca n f i n d a n d yo u a re a l l s et . Even l owe r ( b u t overl o a d p ro te c te d ! ) a m p e ra ge w i l l wo r k – c h a rg i n g t i m e w i l l go u p t h e n t h o u g h . I reco m m e n d go i n g to 1 2 V; eve n i f t h e o u t p u t vo l ta ge i s n o t re g u l ate d a n d yo u ’d go w i t h a “ n o m i n a l ” 1 2 V d ev i c e ( t h es e m ay ge n erate u p - to 1 5 V D C w i t h n o l o a d p re s e nt ) , i t w i l l wo r k f i n e . I t m ay ve r y we l l b e t h at yo u h ave s u c h a p ower s u p p l y a l re a d y s o m e w h e re i n t h e h o u s e. 1 Apparently the LEGO ser vice department claimed that the charging time is roughly 1 ½ hours, which was discussed in the German MBRF forum http://w w w.mbfr.org /smf/index. php?topic=189.0, cf. answer #3 (i n case you understand German ...). In answer #4 user Lithologe calculated that this charging time leads to an average charging current of about 750 mA . However, I doubt the 1 ½ hours. My LiPo charged for about 3 hours before the LED stopped flashing. 2 Just use a sharp drill bit, drive that slowly one or two turns into the plastic plugs in each corner on the base hid ing the screws fastening the lid, pull out the plastic plug , get the screws out and carefully remove the top part.