Replace your car battery with capacitors!

[oldtamiyaphile]

The same set up failed to start my 0.875L Fiat By the time the fuel pumps spooled up, the ECUs have initialised etc , there's nothing left for the starter.

[jray3]

Caps won't prop up a failing battery because the battery will drain down the caps to a matching, low voltage, and a tired battery will only put extra load on the capacitors if the battery's voltage sags faster than the caps when under load (in parallel). Plus, capacitors won't recover any voltage when resting off of charge, unlike a battery. This means that you'll get one good crank out of a reasonably sized capacitor bank, maybe two, but if the engine fails to start you're out of luck. A solar trickle charger would be no help in that situation. Anybody carry a 12V hand crank generator?

For this reason, I think caps pair better with deep cycle batteries (which normally wouldn't have the cold cranking amps for reliable starting).

Ongoing balancing loads on the caps should be minimal between cycles.

One benefit of a bank of caps is fast boosting via jumper cables. Depleted caps will draw tremendous current, but not for long enough to damage the cables unless you've got a bad connection. Likewise, connecting your caps to a dead car means instant starting for them!

[Enki]

You could always upsize the bank.

[jray3]

But don't forget that voltage on a capacitor bank falls linearly as energy is pulled out. You only have a tiny fraction of the total energy content available in the useful range between 14.4 and 12 Volts. If the cap is in parallel with a lead acid battery at rest, it is only helping between approx 12.4V and 12.0V, a miniscule fraction of the total capacitor capacity. Plus, capacitance drops in a series string.

[Enki]

That's all been covered in the thread, jray3. I've even posted videos of my power hungry Mazda starting with power to spare on the 500 farad bank. He can make it work pretty easily, imo.

[jray3]

Originally Posted by Enki

That's all been covered in the thread, jray3. I've even posted videos of my power hungry Mazda starting with power to spare on the 500 farad bank. He can make it work pretty easily, imo.

I agree with you I just think it's risky for a daily driver that's not completely dependable. Do you want to be stranded after one missed start? I use caps to crank my 6.9 L diesel, but with a battery backup and some stout jumper cables!

[Enki]

It's not nearly as much of a risk if you know how much power the car bleeds off when not running. The bank would work just fine in my dad's 1972 Chevy truck, since it uses zero power when off.

My car can't use it at all because it would bleed it to the point of failing to start in a couple hours, but if I did do it, I could easily use a small rechargeable battery to counteract that drain, or just let it roll down the driveway and pop the clutch.

sreeve212 just needs to do some testing similar to what I've done; on a similar note, for all we know oldtamiyaphile just needs to use a bank of 650s instead of the 350s to be good to go.

Just need some research and proper planning to be able to say what can and can not be done.

[sreeve212]

Thank you all for the tips! I will consider trying it. Should I decide to go forward with buying the module and testing it, I will post the results here.

Thanks again! (and feel free to keep leaving feedback )

[cptsideways]

Have you guys thought about using these mini car jump packs, tiny things that appear to work quite well, to go with the caps.

[redpoint5]

Originally Posted by sreeve212

Thank you all for the tips! I will consider trying it. Should I decide to go forward with buying the module and testing it, I will post the results here.

Thanks again! (and feel free to keep leaving feedback )

The 350 Farad series capacitor bank will fail to start your vehicle. My 400 Farad bank is just enough to start my 600cc motorcycle, which draws a paltry 80 cranking amps.

Here is the proper order of steps to take when considering replacing your battery with ultracapacitors:

1. Determine the amount of Ah it takes to start your vehicle
2. Determine the vehicles rate of parasitic draw in mA.
3. Decide how long you want the vehicle to be able to sit parked (assume no sun), slowly draining the reserve on the capacitor while still being able to start.
This post has the formula and I'm happy to help with the math.
4. Size your capacitor bank to meet the demands above, keeping in mind that you only get to use a fraction of the capacity before the voltage sags too low to be useful. In the case of my motorcycle, the minimum voltage required to start is 10v, and it probably sags to 8v when cranking.

Balancing is probably unnecessary since the capacitors bleed rate correlates to the voltage; that is, a capacitor at a higher voltage should bleed off charge at a faster rate than their lower voltage counterpart and approach a similar state of charge.

The balance circuit on the 350 Farad kit on Ebay is insufficient to bleed off the excess energy provided by a solar panel that outputs more than about 1 watt. Solar panels of any output would totally fry a non-balanced capacitor bank.

You could add higher output LEDs, or wire more diodes/LEDs in parallel to increase their ability to burn off the excess charge. The balance boards sold on Ebay for the higher rated capacitors would likely handle a modest overcharge from a solar panel.

If I were building for a car that lives outside in the sun, I'd probably get the 1500 Farad kit and balance boards and pair it with a 2.5 watt solar panel. I haven't run any numbers to see if the balance boards can cope with the excess energy, so don't take my estimation as gospel.

Here is my thread on the subject.