Re: Building my own equilizer

[Victor Tikhonov <vtikhono@lsil.com>]

I have powerchecks in ACRX. They do work, no one debates that.
Debate is how well and whether worth the price.

After I installed them for the first time (4 month after I got my
well balanced hand picked 28 Optimas), they started blinking away
quite vigorously, but this activity ended in about a week. On the 
rested pack they are like all off - no blinks meaning there is
<60 mV between adjacent batteries.

The only time ALL of them blink, is when the pack voltage reach 
about 405V (14.46V per battery).

What I like about powerchecks compare to Rudman regs (at least 
current ones) - the powercheqs work on partially discharged pack.
If you drive for half hour and don't want to recharge today, the
voltages are near 12.3V per battery. Powerchecks will keep balancing 
regardless, as long as delta is 60mV, regs won't until some voltage
level is reached; i.e. they are useless for partially discharged
and sitting there pack.

What I dislike about powercheqs - each next battery can be 58mV
lower than the previous one (means if the first one is 11.9V, 
the last is 13.52 and the powerchecks think everithing is OK.
They don't compate first to last or best to worst batteries,
only adjacent ones. To be fair, 1.62V first to last battery 
voltage difference for the string of 28, may not be such a big deal.

I talked to the designer of the cheq for about half hour.
They could easily make delta 30mV or 5mV if they wanted to.
This would mean too much DC-DC-ing without real benefit,
so they *chose* 60 mV for their reasons, right or wrong.

Regarding max current and alg - they DON'T reduce the
current from rated 2A to 0A linearly when delta goes
from 120mV to 60mV, they have some patented alg which is
time dependent, some sort of dV/dt thing. He didn't tell me
details on that (I hate that), but it boils down to the
fact that the current they transfer depends on how fast batteries
get equalized, not only absolute delta. If delta is 80 mV,
initially it may be 0.9A. In 20 min it will be 1.3A, they are 
trying harder. If in 1 hour delta is still 80 mV, they give up
and the red light comes on, they don't sit forever doing 1.3A.
(I came up with the numbers to illustrate what I've been told).

BTW, they have 5A version commertially available, just 2A is
by far the most popular for their intended market - stand-by
backup batteries balancing. Those batts do nothing 99% of
the time and don't need more than 2A.

Victor