Could Vehicles Be Started on Smaller Batteries Combined with Large Capacitors?

A standard capacitor is an excellent device for storing a charge with high voltage and low current, but it is unsuitable for storing a charge that is low voltage and high current. The capacitor would discharge in the first few milliseconds into the low resistance starter windings and would do nothing for the remainder of the 1 to 3 seconds it requires to start an engine. Unless there are new types of capacitors that I am unaware of.

There is at least one such capacitor-cranking product already on the market. The company I found is in Canada (and I'll leave finding it to savvy googlers rather than give the company link). I also found an essay on cranking a car using a homebrew cap stack using some off-the-shelf parts.

I have no idea how much such a thing would cost, but I'll bet it's more than just having a larger, more powerful battery to begin with.

Not my field at all, but very interesting to read up on. I think I stumbled on it in relation to an automotive search.

Try googling supercapacitor, ultracapacitor or EDLC.

This blog may be of some interest to you.

Certainly this can be done but I'm not sure it will help from a strictly electrical point of view. The DC motor used for a starter generate the most torque from rest. It is the back EMF that happens once the motor gets up to speed that limits the rotational velocity by limiting the current draw and torque. But this happens once the motor is already moving. I can see some scenarios though that having two current paths that follow different cabling paths (one from the battery and one from a capacitor) will reduce the effective wiring resistance for the starting instance of current drawn.

Now when one considers the Chemistry and Physics of the battery, there you might get some help. The energy dumped into a discharged capacitor will self heat a cold battery thus raising the battery's output voltage. Naturally the capacitor and battery will have roughly this identical voltage (minus the voltage drop across the capacitor battery wire drop) so a slightly and possibly significantly higher voltage will be applied to the starter.

No. IMO
(not reliably without a load of additional stuff, to recharge the Cap at a rate supported by the battery)
It could be done but would prob cost more than getting a decent sized/quality battery.
Del

and you would have to so carefull about servicing etc cos if you touched the capacitor you would be very dead very quickly.

Why would it be more deadly than the battery itself?

Surely it does not matter if you get your 12volts out of your battery or that super-cap or does it? Of course if you directly lean on the battery terminals, especially with oily hands, you will get the message just as much as you would from those caps.

These super-caps store high currents at the nominal voltage of the battery.

I remember at question time during the webcast a Tesla engineer asked them about high voltage application and they said, it is possible as long as they get the details they need.

I have personally contacted them and they told me there are criterias and they need some details. I believe the starter issue would not be a problem any more as that is one of the most commonly addressed one by now.

It is (relatively) common to have a super capacitor (or similar high capacity low voltage capacitor or capacitor array) connected across a car battery, but not for the reasons you may suspect.

http://en.wikipedia.org/wiki/Electric_double-layer_capacitor

Put simply in places like Canada and Russia it is very cold. Cold temperatures lower the batteries ability to provide current, which in turn makes it difficult to provide enough current to the starter motor to start the car. Adding a super capacitor helps.

I'm thinking of being able to double a car battery's cold starting current by waiting a second whilst the cap charges, then fire the starter.

Yes that would work, however the capacitor would need to have a substantial storage capacity (in Farads - F) to provide the high currents needed for the relatively long time (few seconds) it needs to provide current. This is further compounded (and this is the big problem) by the fact that the capacitor voltage drops as it discharges and so it will stop supplying current when the capacitor voltage drops to or below the battery voltage. There are ways around this (like step-up voltage inverters) but this further increases the cost.

The simple answer is it just isn't economically practical. The best advise I would give is to just do what everyone else does - either replace the battery with a new one (as batteries age their capacity drops and as such so does their ability to provide the power needed to the car motor starter), increase the battery size (capacity), or switch to a battery with a larger cold cranking amp capacity. All these solutions are far cheaper and economical than adding a super capacitor array to assist or replace entirely the battery.

I have even heard of people removing the car battery from the car entirely and storing it inside to keep it warm, but this solution would only really be needed if the weather was exceptionally cold and your vehicle was stored outside.

or if its cold thats causing the problem a heating sheet or blanket for the battery to sit on.

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GA. The idea works, but its implementation is currently quite expensive, and ads complexity that is not warranted for the vast majority of cars.

Hi Gents,

Review this link -

http://www.csiro.au/science/Ultra-Battery.html

What is the UltraBattery?

The UltraBattery is a hybrid energy storage device that integrates a supercapacitor with a lead acid battery in one unit cell.

This unique design harnesses the best of both technologies to produce a battery that can provide high power discharge and charge with a long, low-cost life.

Given time, I think this path for electrical energy storage will solve most of the current problems ............ !!! ...............

Thanks for some very interesting info, Amit.

The issues and solutions that you have mentioned using supercapacitors seem to give credence (to me at least) to the half-ideas I had when posting this thread.

I had wondered what the actual difference between caps & super-caps were and now I'm getting a better picture I suppose super-caps are what I had in mind all along.

I would be interested in hearing more about your firm's case studies, for one.

The concept is interesting. However, I understand that both capacitors and batteries can bleed off charge over time. In that respect, how do ultracaps compare with batteries?

It seems as if the field is promising for ultra caps in auto applic- but concern has to be raised of longevity of caps in the hot environement of an eng bay(most failures in electronic equip is electro caps drying out). However there is a solution- simply carry a sla batt- these small units are found in comm jump starter packs- they can put out 100,s of amps for a short time(as in starting). I personally used one for a situation where car would start perfectly cold, but after say 10 mins running, after being stopped, would not restart until say 30 mins later. After much change of equip incl batt, start motor, ading extra solenoid to starter circuit, adding extra earthing cable etc, a clue was found after reading official factory workshop manual where it said upon starting, batt volts must not drop below 11.6 while cranking- fitted a higher rated batt(cca) than orig-no more trouble. When the engine heated up, extra power was needed to crank it(more comp I guess)- anyway while having these troubles, simply lift hood , clip on sla(about 15AH) -instant start-everytime!. Remove sla, recharge later using dedicated sla charger. Actually made a unit so could be charged from alternator car circuit if needed(main diff is car batt charges at 14v &sla at 13v8.

Quote, !It seems as if the field is promising for ultra caps in auto applic'.

Yes - sure is just check up on Eestor and the electric auto out of Canada they were involved with (can't think of the name).

Both will go down as one of the great scams!

In years to come - maybe. Today - no.

Thanks to everyone for great ideas and insights on this subject. I had no idea it'd be so popular!

Additional thoughts to throw into the melting pot:

What's the likelyhood of using an AC starter motor (this might already be common place, but my auto-electric experience is well out of date)? I think maybe some modern engine stop-start systems use a combined dynamo/starter so this must be an AC machine I assume. Also there is, I read, a move to higher voltages in car electrics - from my understanding this can only be a good thing for efficient elec systems and would also make non-traditional configurations of battery and power conversion electronics a more attractive option.

Returning to the question of cost of capacitor-enhanced systems - The advantages would only be worthwhile if the added cap-bank and associated electronics were designed to last at 4 or 5 times as long as the lead-acid.

An AC induction motor will not be a good choice for a starter. First, you will have to have an inverter to generate the AC. Second, getting an AC motor to start rotating is difficult. This is why there are starter circuits, shaded poles and centrifugal switches on various AC induction motors. AC motors are designed to be most efficient once the shaft is rotating. By definition a motor starter one wants the highest efficiency to be at start.

Well, the monster car stereos use big multi-farad caps to handle the bass peaks. They aren't expensive.

And I've been pondering an electric car with big caps to handle the need for sudden acceleration, like getting on the freeway.

Your idea seems worth investigating.

http://www.tavrima.com/pdf/alternato.pdf

this looks like it could answer your question

http://www.tavrima.com/pdf/alternato.pdf

taken from above link

Our existing technology allows us to produce super-capacitors with voltages

from 6-V to 300-V capable of discharging high power pulses of energy whilst

reliably withstanding hundreds of thousands of cycles. European and

American engineers, just like their Japanese counterparts, are interested in exploiting the advantages

presented by the super-capacitors, especially the ones operating at 42-V, because this is the prevalent

voltage of most ISA systems. The energy rating of such super-capacitor does not have to be high since it

can be quickly recharged from its fellow battery. For instance, to meet peak power requirements of the

starting system of the previously mentioned GM truck the capacitor must be rated at 10-kJ, 42-V. Energy

stored in such super-capacitor is sufficient for two consecutive engine starts. Due to the high velocity of

cranking the engine would start in 0.3 to 0.5 sec.

We are developing a relatively inexpensive 42-V automotive super-capacitor feasible due to limited use of

special materials and an efficient manufacturing. Our basic technology is proven to be one of the most costefficient

and reliable high voltage super-capacitor technologies on the market today. Considering rapid

development of the ISA automotive systems we look forward to meet anticipated demand with our 42-V

super-capacitors.

Thanks for the info, peterg7lyq.

Maybe this type of tech will be the final piece in the puzzle that spells the end for the ol' Lead-acid.