Replace your car battery with capacitors!

[PaulB2]

Check the voltage before starting. If your battery is bad you won't be charging the capacitor bank to the desired level.

In the case of the BCAP350, the max discharge rating is 170 Amps

That's a lot. Depending on the voltage, the battery and the capacitor are each either a source of current, or a sink of alternator current. I've had a lot of starting problems caused by dodgy batteries or by poor connections to battery posts (unfortunately the latter won't show up until you are actually cranking).

I guess I'm losing the point of this exercise. Removing 20 or 30 pounds at substantial expense, in dollars and time, it is worth it? And that's assuming no backup battery! To me this is interesting in a motorcycle, where every pound counts and the backup is an easy bump start, but in a car?

[Blue Angel]

I didn't have time to read through the whole thread so forgive me if this has already been posted. I dropped 20 lbs out of the nose of my Corvette by switching to an Odyssey PC680 motorcycle battery. Lots of cranking power for that big V8, right down to below freezing temps. In a 4 cyl car it might be a viable option even in winter.

Not much reserve capacity, though, so no sitting with the key on and the radio playing. Still, a much more "risk free" weight reduction than a batch of capacitors.

[redpoint5]

Originally Posted by Blue Angel

I dropped 20 lbs out of the nose of my Corvette by switching to an Odyssey PC680 motorcycle battery. Lots of cranking power for that big V8, right down to below freezing temps. In a 4 cyl car it might be a viable option even in winter.

Not much reserve capacity, though, so no sitting with the key on and the radio playing. Still, a much more "risk free" weight reduction than a batch of capacitors.

Agreed, but as you say, not much reserve capacity. For those occasions where a door wasn't shut all the way, or the radio was on while the car was parked, the battery runs down and is damaged.

With a capacitor, deep discharging doesn't harm them. They should last the life of the vehicle and then some. For applications such as my diesel truck, a small lead-acid battery just won't supply the necessary cranking amps.

I maintain that capacitors are a better option for vehicles that are parked in the sun and can be topped up by a small solar panel. However, I'd sure want to bring a small emergency battery along if I were headed into the wilderness or anywhere that a failure to start would be disastrous.

[ECONORAM]

Originally Posted by Blue Angel

I didn't have time to read through the whole thread so forgive me if this has already been posted. I dropped 20 lbs out of the nose of my Corvette by switching to an Odyssey PC680 motorcycle battery. Lots of cranking power for that big V8, right down to below freezing temps. In a 4 cyl car it might be a viable option even in winter.

Not much reserve capacity, though, so no sitting with the key on and the radio playing. Still, a much more "risk free" weight reduction than a batch of capacitors.

I am a bit surprised that battery turns the 'vette's V8 over. Sounds tempting, maybe I could combine that with a capacitor pack after this Diehard decides to quit (only a year old).

[redpoint5]

Originally Posted by ECONORAM

I am a bit surprised that battery turns the 'vette's V8 over. Sounds tempting, maybe I could combine that with a capacitor pack after this Diehard decides to quit (only a year old).

If your battery is just a year old and is dying, you likely have a large parasitic drain causing premature wear. Have you measured the parasitic drain with your vehicle turned off and all doors closed?

Aftermarket parts are often a culprit of excessive drain. I've got an aftermarket car alarm on the Camry and it pulls 50mA, which is more than twice as much as any other vehicle I have.

Determining parasitic draw is the first step in sizing a small battery or capacitor. You have to know how many days the vehicle can sit without causing damage to the battery or failing to start.

[ECONORAM]

That came out the wrong way. I only replaced my battery a year ago; it's doing quite well. once it finally starts falling off, then maybe I'll do a capacitor pack...is what I meant.

[oldtamiyaphile]

OK, so here's what's happening with my paralleled 350F supercap bank.

The car's CANBUS only switches the alternator on a few seconds after the engine is started.

So with the battery sitting at ~12.6v, the car starts and stumbles as apparently the supercap is drawing so much power that the coils are being starved. The voltage will typically sit at 11.x volts until the alt comes on line.

Interestingly, if I EOC and bump start, much the same thing happens, the battery voltage sags to about 11.6v until the alt fires.

I fitted the supercap to prolong battery life, now it seems like it might be having the opposite effect? I suppose some sort of charging limitation has to be implemented on the cap but the car's under warranty so I think my options might be limited?

I'm adding a 100w solar panel next week so I wonder if that could be arranged as the supercap's only charge source?

Any input appreciated.

[Enki]

You'd need some pretty big diodes to prevent it from charging from the alt I think. I wouldn't run them in parallel, as they don't work right that way.

[redpoint5]

I too was thinking diodes, perhaps with a limiting resistor to keep charge rates at a modest level.

You could have a diode in one circuit that allows full discharge of the supercap, and a diode on another circuit that allows charging through a current limiting resistor.

It should work, but seems like a hassle. The best bet is probably to get a higher farad rated capacitor bank, or just replace the failing battery.

Perhaps there are other charging issues at play here?

My Acura can start and run without issue using just the 350 farad (58 series farads) capacitor bank, and it has large electrical demands and many computers.

[oldtamiyaphile]

Both the car and battery are six months old, no issues with either other than the slightly excessive time between the engine firing and the alt being enabled, which is just part of the Canbus programing.

I wonder if adding a bigger bank is the right way to go as I worry that it will still deplete and just put an even bigger load on the battery for a longer duration. I'm just wondering if I'm doing the battery more harm than good.

FWIW, the 350 farad bank can't start my 875cc Fiat. Modern European cars apparently draw too much power. I charged the cap bank with an R/C charger and it accepted around 200mah from zero to 14V. Does that sound correct?

I first tried the Cap bank on the Jeep which still has it's original battery, and I also go a slight stumble.