Replace your car battery with capacitors!

[redpoint5]

Originally Posted by ECONORAM

Or could one of these capacitor banks hold the voltage up at a stoplight...long enough until the engine went off idle?

Yes, but you would need to get a much higher capacity than the 350s I'm running. Perhaps a bank of 1500s. The voltage would still sag over time, just at a slower rate.

Is there something that isn't working correctly when the voltage sags at idle?

[Enki]

Lithium Ion supercaps are out now. They don't go past 270 farad ratings, and have a voltage range of 2.2-3.8 volts but charge in a minute at most. They are essentially fast charge batteries, and in larger sizes, will be a game changer.

Lithium Ion Super Capacitors - Taiyo Yuden | Mouser

Invalid Request

I can't wait for these things to get bigger.

[orange4boy]

So where is the info on the $40 lithium battery you mentioned? Looking for one for my bike. I searched back. Am I blind?

[serialk11r]

Originally Posted by redpoint5

I have been wondering how difficult/expensive it would be to modify the alternator to output 14v. Perhaps it would be as easy as installing a power diode in series with the alternator.

I think my MR2 has a dumb alternator (not controlled by ECU, not engine load dependent), and it puts out 14.4V or something like that, but I noticed the voltage in the other cars in the family varies quite a bit. Perhaps a direct alternator swap would do the trick, or even just the regulator?

[Enki]

You'd want to go to a smaller pulley on the alt (if even available) if it's not putting out proper voltage at idle due to the change in the crank pulley (but that defeats the purpose).

[California98Civic]

Originally Posted by serialk11r

I think my MR2 has a dumb alternator (not controlled by ECU, not engine load dependent), and it puts out 14.4V or something like that, but I noticed the voltage in the other cars in the family varies quite a bit. Perhaps a direct alternator swap would do the trick, or even just the regulator?

It would take more of a swap than that, I think. The Hondas have an "Electric Load Detector" that contributes to the load-dependent voltage changes. The wiring harness also needs lines for the ECU to read the voltage at the alt. Your best mod might be an alt kill switch, greater battery capacity, and grid charging. You could run without the alt for all your shorter trips. MetroMPG saw a 10% FE increase when he tested that setup. It's what I run too. My alt is off most of the time.

[ECONORAM]

Originally Posted by redpoint5

Yes, but you would need to get a much higher capacity than the 350s I'm running. Perhaps a bank of 1500s. The voltage would still sag over time, just at a slower rate.

Is there something that isn't working correctly when the voltage sags at idle?

I put a warm air intake in when I installed my under drive. I know, you should only install one mod at a time. Anyhow, the truck will not idle below 650 now. Prior to this, I could get it to idle at 450. I later pulled the warm air intake, thinking it was the culprit...but nothing changed. So then I noticed the voltage drop when the engine tried to lower to 450 rpm and started speculating that the PCM was watching the voltage to limit the idle rpm. It's a .2 gal/hr difference at idle...

Originally Posted by Enki

Lithium Ion supercaps are out now. They don't go past 270 farad ratings, and have a voltage range of 2.2-3.8 volts but charge in a minute at most. They are essentially fast charge batteries, and in larger sizes, will be a game changer.

Lithium Ion Super Capacitors - Taiyo Yuden | Mouser

Invalid Request

I can't wait for these things to get bigger.

Wow! Thanks for posting that.

[redpoint5]

Originally Posted by Enki

Lithium Ion supercaps are out now. They don't go past 270 farad ratings, and have a voltage range of 2.2-3.8 volts but charge in a minute at most. They are essentially fast charge batteries, and in larger sizes, will be a game changer.

Lithium Ion Super Capacitors - Taiyo Yuden | Mouser

Invalid Request

I can't wait for these things to get bigger.

I couldn't find any more info on the tech besides the link you provided. No info on the allowable charge/discharge rates.

Originally Posted by California98Civic

It would take more of a swap than that, I think. The Hondas have an "Electric Load Detector" that contributes to the load-dependent voltage changes. The wiring harness also needs lines for the ECU to read the voltage at the alt. Your best mod might be an alt kill switch, greater battery capacity, and grid charging. You could run without the alt for all your shorter trips. MetroMPG saw a 10% FE increase when he tested that setup. It's what I run too. My alt is off most of the time.

Although my car is a Honda, I don't believe the TSX has an ELD. The voltage remains constant on my car. I'd like to run LiFePO4 only, and do an alt kill switch, but I need to find out how best to accomplish this without destroying the alternator. I'll also need to figure out how to disable the alternator to determine my average running amps.

Originally Posted by orange4boy

So where is the info on the $40 lithium battery you mentioned? Looking for one for my bike. I searched back. Am I blind?

You talkin' to me?

Here is the battery I'm running. Shipping drives the cost way up.

If you're handy, I'd probably go with the ones Enki linked. They are a little more expensive (you have to buy 4), but have a 10Ah capacity compared to 4.2.

Originally Posted by ECONORAM

So then I noticed the voltage drop when the engine tried to lower to 450 rpm and started speculating that the PCM was watching the voltage to limit the idle rpm. It's a .2 gal/hr difference at idle...

I think you've figured it out. The alternator is no longer spinning fast enough to output the voltage the ECM wants to see. It increases the alternator speed by increasing engine speed at idle.

As Enki says, you need to install a smaller diameter alternator pulley to increase the speed. I'm sure you are wasting more fuel by running a higher idle RPM than the under-driven alternator is saving you.

[Enki]

Originally Posted by redpoint5

I couldn't find any more info on the tech besides the link you provided. No info on the allowable charge/discharge rates.

The sheet listed cycle testing recommends max charge/discharge at 5 amps on the 270s, but that's for testing. I'd have to imagine that since these are actually capacitors (and really high capacity ones at that) that they would be fine for normal extreme dump/charge rates that a regular capacitor would be good for.

[PaulB2]

Back in 1969 I bought a Norton N15 mortorcycle, a 750 cc bike. It had a 4700 microfarad, 63V capacitor across the battery terminals. With that one could kickstart this bike even without a battery. I did something like that with a Honda XR250L recently (putting in a cap and removing the battery), but it always needed three kicks to charge up the capacitor enough to run the ignition electronics. Also I needed to turn up the idle a bit as at low rpm generators don't put much out and the headlight has to be on.

Anyway a couple of things worry me about this supercap business. Having your capacitance cut down to 1/6 or 1/5 by using caps in series seems a huge waste. And I worry about the voltage spikes in the system. I wonder why Norton-Villiers put a 63V cap across the battery...