[EVDL] LiFePO4 one cell sagged/balancing, general/universal charging

Mark Hanson wrote:
> Do folk's put a switch on the aux battery to elliminate ghost loads while=
parked for awhile?

I have a smart 12v trickle charger that is powered up any time my car
is plugged in. When I get home, I plug in to charge the traction pack.
After charging I leave the cord connected so the 12v charger stays on.
When driving I have a dc-dc (power supply) augmenting my 12v house
battery.The dc-dc is not powered unless the car is running. I don't
know if the dc-dc has any parasitic affect, but the trickle charger
handles it.

Dave Cover

On Fri, Oct 8, 2010 at 8:43 AM, Mark Hanson <[email protected]> wrot=
e:
>
> Hi Folk's,
>
> On my www.evalbum.com/2749 E-Cat I noticed after two boating seasons (abo=
ut 50 cycles last year and another 50 this year) that battery (buddy pair c=
ell) number 15 out of 16 wasn't coming up to the 3.8V clamp voltage, stuck =
at 3.4V with the final 1 amp charge taper. I put a 8 amp individual char=
ger across that one for an hour and that propped it up. I'm not sure why=
one cell would drift low when they're all clamped (with shunt balancers) t=
o 3.8V on the final two hours of charge dv/dt=3D0 stop.
>
> Also I've been using the same charger algorthm on floodees, STM5-180's Ni=
-Cads (40k miles - 1300 cycles), NiMH batteries and now LiFePO4 Thundersky =
3.3V 200ah (actually 100ah buddy pairs). The algorithm recommended previ=
ously by Trojan's Jim Drizos for a GE charger patent 6,218,812 I did simply=
looks at each hour and compares one hour to the next and when the voltage =
is < than .01V per cell per hour rise (the voltage stops rising or may fall=
slightly on NiMH) the charger stops. It's served me well over the years=
, no fancy temp compensation and seams to work well for all battery types.
>
> BTW, on www.evalbum.com/1273 last night my auxilary 12V motorcycle 12AA b=
attery had dendrites across the plates (stuck at 11V) I tried charging with=
an 8amp charger but it got hot, 120F so replaced and noticed a ghost load =
of 11ma from the radio (which killed it while sitting in the garage over ti=
me - been driving my 70mpg Honda Insight to night windpower teaching classe=
s at www.dslcc.edu). So I pulled the radio and the ghost load dropped to=
1.6ma, pulled all the fuses, still there, probably back-feed into dc-dc co=
nv. Do folk's put a switch on the aux battery to elliminate ghost loads =
while parked for awhile? Or leave the dc-dc converter on, probably relia=
bility converter problems though? Maybe a 13.8V trickle charger plugged =
in all the time?
>
> Have a renewable energy day,
> Mark
> www.reevadiy.org solar home tour tomorrow Oct 9th www.nationalsolartour.o=
rg my place EV rides
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-- =

http://www.evalbum.com/2149

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Mark Hanson wrote:
> On my www.evalbum.com/2749 E-Cat I noticed after two boating seasons (about 50 cycles last year and another 50 this year) that battery (buddy pair cell) number 15 out of 16 wasn't coming up to the 3.8V clamp voltage, stuck at 3.4V with the final 1 amp charge taper. I put a 8 amp individual charger across that one for an hour and that propped it up. I'm not sure why one cell would drift low when they're all clamped (with shunt balancers) to 3.8V on the final two hours of charge dv/dt=0 stop.
>
What's the holding voltage (for the 1A taper) and how precise is it?
If it is 3.8V*16 = 60.8V, then let's see what happens is that voltage
goes 0.65% low to 60.4V

Cells 1-14 & 16 are at 3.8V => total of 57.0V
Cell 15 is still charging at 3.4V => added to 57.0V makes 60.4V => so no
current flows.

Or run the math on those clamp voltages, what is their precision? Maybe
they are all 1% high? 0.6V is enough to cause the above problem.

This is why my BMS has a separate full-charge signal, so you know every
single cell has reached full.

Thanks,
Cory

http://pacificev.com/products.html

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