Jay Summet wrote: > I'm wondering how much capacity the capacitors are adding to the system, > as the voltage of the capacitors can never go below the sag voltage of > the LiIon cells under load, and can never go above the LiIon cells > voltage during regen. > > I'd love to see a comparison graph of the voltage of the system battery > bank during a hard acceleration and a hard regen event both with and > without the capacitors installed to see the voltage regulation effect.
Victor Tikhonov (of MetricMind) used a string of 2.7kF Maxwell supercaps (17F total) in parallel with the lithium pack in his CRX conversion, back in 2004. Something Victor mentioned on the site for his conversion is the need to disconnect the string of caps from the battery during charge. Unfortunately, the links in Victor's original message (quoted below) appear dead, however, his comments describing the results of his measurements are still informative. > -----Original Message----- > From: Victor Tikhonov [mailto:vtikh...@lsil.com] > Sent: October-07-04 4:53 PM > To: e...@listproc.sjsu.edu > Subject: Does the passive balancing of uptracaps stack really works? > > I've made a few measurements on the most easily accessible > caps (last 10 caps in the series string) after couple of > driving/charging cycles. Objective was to see if they are > drifting apart far enough that the passive resistor based > balancing cannot keep up with bringing them all back to order. > > Looks like whatever initial voltages are settling at, they all > go up and down at the same rate, so at the end of the day > while overall average SOC is different, deltas between the same > caps are still identical. Which tells me that for my circumstances > making active balancing would be waste of effort. > > Will see how well this keeps repeating in the long run. > > http://www.metricmind.com/misc/ultracap.gif > > In case you missed the link showing about 10x stiffness > improvement using ultracaps, captured data screens are here: > > http://www.metricmind.com/misc/test1.gif > Left half - with caps, right half - without. > (did few hard regens in the middle - to separate data points) > > Zoomed in version: > http://www.metricmind.com/misc/compare.gif > > I'm noticing a side benefit I didn't think of before: > no matter what the SOC of the battery is, combined > with ultracaps it feels just as stiff at the end of > discharge as full. This is because ultracaps have fixed > internal resistance no matter how discharged they are. > > When the pack getting tired, recharging caps from LiIons > after accelerations getting slower, but by the time it is > completed, the pack is as stiff for the next acceleration > as the fresh one. > > From here (bottom plot) you can see how efficient > my system happen to be (motor power out / batt power in): > > http://www.metricmind.com/misc/eff.gif > This is actually unrelated to the presence of the capacitors. > > So far I'm very pleased with outcome of my setup. LiIons > don't get much chance to see more than 30A out of them > during quick accelerations, the same absorbing regen. > The caps do all the work :-) > > -- > Victor > '91 ACRX - something different > _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)