Battery Vehicle Society

hi guys - um i run a mobility scooter - OK not the most glamorous EV but essential as i am not allowed to drive gas guzzlers any more - now - i was wondering if there was any way to use large capacitors ( 1 farad @ 12-20 volts ) to stop the batteries getting raked ?? -

probably a really dumb question - but i was thinking if these devices are used to help with power drain in cars from "boom box " use - could not a similar system be used in small ( under 1 kw motor ) EV"s - looking at the wiring from the batteries to the motor and control box - it ain't exactly welding cable - and i will have to run a clamp ( amp ) meter round it to say what peak amp draw is - but any ideas /thoughts appreciated - as some say that we will be able to use some sort of "super capacitor " to power vehicles one day - so why not a little bit of assistance for simple systems - as i think that most draw is when starting stopping - rather than "cruising " ( at 8 mph )

- please correct me if i am wrong on this as i am a newbie to EV tech - but would like to learn a lot more - then do some mods - BUT cant afford to screw my existing system as i need it for day to day transport - fortunately i do have the facility of an old clunker scooter to do any tests on

any thoughts appreciated

Brett ( disabledguy )

The answer is a qualified yes.

Big capacitors (normally referred to as "ultra capacitors") are being developed and used for just this purpose. The snag is that the voltage sags on a capacitor just as it does on a battery, so you actually need some pretty big capacitors to hold up over heavy peak discharge periods.

Those big car stereo ones are pretty poor, as they have a high Equivalent Series Resistance, akin to a battery with a high internal resistance. They work OK for smoothing out the relatively high frequency pulses from a stereo, but won't hold up well for heavy demands over a few seconds. You would also need far more than 1F to do the job, unfortunately

At the moment, ultra capacitors are very expensive, but they are developing very rapidly. They have the overwhelming advantage over batteries of being able to be charged at the same rate that they can be discharged, which makes them well-suited to vehicles with regenerative braking, or power station use to even out demand surges. They also last for ever, at least in theory.................

Jeremy

thanks for that - so sound idea - wrong kit - well i suppose the price on UC's will fall to a reasonable level eventually ( vis - wait till maplin stock em - then wait till they have a sale - then buy some )

Hi Brett,

You may want to investigate the lithium battery option, they don't sag as much as lead under a load. Maybe Lifebatt could provide a solution or have a look at some of the work being done by some of the BVS members, myself included, for a cheaper Lithium option. I have always thought the supercapaciter idea to be a crutch for poor batteries and that the money would be better spent on better batteries, at least for the moment, who knows what the future will bring.

Greg