Supercapacitor Battery Replacement

[mechman600]

Originally Posted by Occasionally6

Self discharge? On Maxwell or other manufacturer's site somewhere?

Just something I have always known.
Here's some calculations for self discharge:
http://www.digikey.ca/Web%20Export/S...f?redirected=1

Perhaps a bench test with a variable resistance/load while measuring the current drawn and observe the temp. of the wires?

That's probably the best way. Your concern is melting insulation, so just chart time*current vs melting.

You would be surprised how much current a small wire will handle in short bursts. When I see how small some of the wiring is in my series wound motor in the Electric Booger (2X 2 AWG wires to the brush holder) it amazes me how much current it lives with. 450 amps for minutes at a time.

[redpoint5]

Originally Posted by cptsideways

Are there safety issues with electrocuting yourself out the workshop roof with these things?

Please educate me as I always thought capacitors were potentially dangerous things...... If safe enough then I am onto building a set up for my Lupo 3L

These capacitors are safe, but not all capacitors are safe.

These are safe because they can only be charged to 2.7v each, and strung together in series could only be charged to 16v. This isn't enough voltage to electrocute.

That said, you wouldn't want to touch the positive and negative leads together without a load in between because it will discharge so quickly that it could weld the object touching the leads.

If you are handy with a soldering iron, I would suggest this kit on Ebay. You would spend that much on the capacitors alone if you purchased from Digikey, and it comes with balance components and a PCB.

[redneck]

I'm happy to see that you picked up the ball after I dropped it.

I hope to get started on mine soon. Till then, I'll be watching your progress with much interest.



>

[redpoint5]

I finished building the 6x 400 farad capacitor bank and added the balance diodes. Not knowing what voltage drop I would want for the balance circuit, I performed a test with the following results:

Volts mA Config
2.70 8.55 1 diode 1 red LED
2.65 6.74 1 diode 1 red LED
2.60 5.20 1 diode 1 red LED
2.55 3.54 1 diode 1 red LED
2.50 2.36 1 diode 1 red LED
2.45 1.53 1 diode 1 red LED
2.40 0.88 1 diode 1 red LED
2.35 0.50 1 diode 1 red LED
2.30 0.27 1 diode 1 red LED
2.25 0.14 1 diode 1 red LED
2.20 0.067 1 diode 1 red LED
2.15 0.033 1 diode 1 red LED
2.10 0.017 1 diode 1 red LED
2.05 0.009 1 diode 1 red LED
2.00 0.005 1 diode 1 red LED

2.70 0.100 2 diode 1 red LED
2.65 0.068 2 diode 1 red LED
2.60 0.044 2 diode 1 red LED
2.55 0.029 2 diode 1 red LED
2.50 0.019 2 diode 1 red LED
2.45 0.013 2 diode 1 red LED
2.40 0.008 2 diode 1 red LED
2.35 0.005 2 diode 1 red LED
2.30 0.004 2 diode 1 red LED
2.25 0.002 2 diode 1 red LED
2.20 0.002 2 diode 1 red LED
2.15 0.001 2 diode 1 red LED
2.10 0.001 2 diode 1 red LED
2.05 0.001 2 diode 1 red LED
2.00 0.000 2 diode 1 red LED

I decided to go with just a single diode plus an LED for the balance circuit since 2 diodes increased the fabrication effort and parts count while not providing enough current flow through the LEDs to see the relative state of charge.

After 3 days of no charging, the LEDs are still trimming the voltage while dimly illuminating.


My plan was to replace the supposedly weak battery in the ATV, but it turns out the problem was not with the battery. I opened up the starter motor and found it covered in oil.





I cleaned everything up, including the grooves between the commutator and put it back together. With a dozen tries of the starter and original battery, nothing more than the solenoid clicking happened until finally not even the clicking was heard. I measured the voltage of the battery and found it flat dead at 0v.

I figured I just needed more juice to turn the starter over, so I installed my capacitor bank and gave it a shot. The solenoid clicked and a small puff of smoke came from the the vicinity of the capacitor and solenoid.

I'm pretty sure I assembled the starter motor incorrectly with a short to ground, and that may have in turn flattened the battery and fried the solenoid. I didn't have time to troubleshoot any further, so I still need to figure out what's broken. A solenoid is $10, and a starter rebuild kit is $23, so I might just get both and be done with it.

I gave my dad the battery out of Lafawnda (the Honda motorcycle), to put into the ATV for the purpose of running the onboard computer and powering the electric shifting. This gave me the perfect excuse to put the capacitor bank into the bike. It started right up, went 7 miles to work, and then brought me back home without issue.

I'm fairly confident I can run the capacitor bank alone in my bike as a permanent solution, but I have yet to test in stop and go conditions where my fan kicks on. This could change things since the bike doesn't charge below about 1500rpm (or does it just charge at a voltage below 12v?).

Replacing the battery with a capacitor bank has reduced my bike weight by about 10lbs, and I no longer have to keep it on a Battery Tender over the winter.

Since my capacitor bank is in permanent use, I purchased a replacement from Ebay. I still need to buy a LiFePo4 battery to test how well it works at replacing a full-sized car battery. My hesitation is that LiFePo4 batteries are not to be charged when they are below freezing, or instant and permanent damage will occur. I'd want some way to keep them warm or restrict charging when below freezing.

[redpoint5]

Update:

I've added bold comments to my original post at the top with the answers I have come up with so far. The motorcycle has been running great with just a super capacitor to start and run the bike. However, after about 3 days of letting the bike sit, the charge drops enough that it will not start. Anything below 10v will not start the bike.

Here's a video showing how low the voltage can go on the bike before the computer stops functioning and the memory resets.

http://www.youtube.com/watch?v=k_FQnZQZzSE

I was concerned that no power is generated from the alternator on the bike below 2000 RPM, but was surprised to find that it maintains 12v at 1000 RPM idle with a single 55w headlight on. Here is a video of that experiment.

http://www.youtube.com/watch?v=MlMdeyt5yWA

Here's a general video with me explaining my setup, and showing the bike starting, the peak amp draw at start (about 80 amps), and subsequent charging.

http://www.youtube.com/watch?v=qweEl8Wypzg

As an aside, I fixed the ATV starter by installing a new brush plate, brushes, and o-rings. The other brushes were badly worn, oil was infiltrating the motor, and I had accidentally shorted the positive post of the motor to ground. No testing has been done with replacing the battery with a super capacitor since my dad seems to be happy with the battery from my motorcycle. When I get more time I'll swap the capacitor in and test it.

EDIT: After 1 week of sitting, the bike voltage dropped to 7.5v. I coasted down my driveway and easily bump started. The computer retained all memory.

[redpoint5]

A battery and charger has finally arrived from Hobbyking.


The LiFePo4 battery is rated at 4.2Ah at 13.2v, with a max charged voltage of 14.4v. It has a sustained discharge rating of 30c (126 amps) and a 40c max (168 amps). The recharge rating is 2c (8.4 amps).

I used this balance charger to discharge the pack to 12v, and then balance charge it to full capacity. I was happy to see that even though I didn't fully discharge the battery, it still took 4.3Ah charge.

Next up, I need to find a power resistor that will limit the charge rate to 8.4 amps. I'll assume my battery will not drop below 10v, and the alternator will not put out more than 14.5v, for a 4.5v difference. Ohms law R = V/I says that I need a 0.5 ohm resistor to limit the charge current.

I'm just wondering if this is the right way to go about doing this, and I also wonder if limiting the charge rate is even necessary. I'll do some testing to find out what some real world charging rates look like with, and without a limiting resistor.

It's a shame that the battery is limited to a 2c charge because the 30c discharge capability is not utilized. Perhaps I could make separate charge and discharge circuits using power diodes.

I wonder if I could use this diode for the charge circuit, and this diode for the discharge.

[redpoint5]

The Anderson Power Pole connectors just arrived, and I will use these for all connections except for the connection to the positive and negative terminals on the vehicle. I also got two watt meters so I can track and compare the charge/discharge efficiency of lead-acid, LiFePO4, and capacitors.

I worked on my truck yesterday and found that the parasitic drain was 45mA. The backlit thermometer that was wired directly to the battery was responsible for 39mA of that!

After removing the thermometer, the truck had a parasitic drain of only 5.89mA. This drain is likely entirely due to the aftermarket radio since the truck doesn't have any power features. I removed the faceplate of the radio to see if drain further reduced, which it did by a measly 0.3mA. Interestingly, I noticed periodic spikes to 11mA after removing the faceplate, and found this was due to an anti-theft LED that blinks with the faceplate removed.

I'm fairly certain that I can remove the 2 huge and failing batteries and replace them with just a bank of six 3000F capacitors. I would keep the system charged using a 1 watt solar battery maintainer. Unfortunately, I cannot determine the starting amps because my meter only goes to 400A, and the truck consistently exceeds this, although I don't believe it exceeds it by much.

I found that my 2.5W solar battery maintainer is totally inappropriate for maintaining the charge of my 350F (58F series) capacitors. With overcast sky, the panel put out 40mA of charge, and in direct sun late in the evening (6pm) I managed 140mA. It could probably peak at 200mA in direct noon sun. When I checked on the state of charge, my bank of 6 series 350F capacitors were charged to 16.02v and rising. The balance LEDs were beaming brightly trying to dissipate the extra charge, but were being over-run by the solar panel.

A 1W panel like this is probably more appropriate. At 85mA peak output, it would likely not over-run the balance LEDs on the capacitor bank.

[mechman600]

You could always make up a simple voltage regulator on your solar panel to avoid overcharging. Motorcycle style regulators basically shunt power directly to ground when the voltage exceeds 14.5V or so. All you would need is an appropriate zener array that adds up to the voltage you want, all secured to a heat sink, of course. Inefficient, but that doesn't matter in your case - wasted solar energy. It would be much better to have a larger voltage regulated solar panel that is capable of maintaining on cloudy days.

[Enki]

(Moved from other thread...derp)

You could easily double up on the LEDs for cheap, vs purchasing a new solar panel. Also, diodes are usually a couple pennies and can be purchased in the same voltage ranges as LEDs (or with better ranging) and at different wattages of dissipation. You could also opt to set up an array of LEDs/diodes/resistors to target your peak bank voltage and then that will also help bleed off power as well.

My spreadsheet calculations (which may be incorrect) suggest a single 1.4 watt 140 ohm resistor should do the trick to keep your bank at 14 volts @ 100 mA. If anyone out there has better math, please correct me.

[redpoint5]

Originally Posted by mechman600

You could always make up a simple voltage regulator on your solar panel to avoid overcharging. Motorcycle style regulators basically shunt power directly to ground when the voltage exceeds 14.5V or so. All you would need is an appropriate zener array that adds up to the voltage you want, all secured to a heat sink, of course. Inefficient, but that doesn't matter in your case - wasted solar energy. It would be much better to have a larger voltage regulated solar panel that is capable of maintaining on cloudy days.

Agreed. The only vehicle I have that lives outside is the truck. I'll have to come up with battery supplements to my supercaps for the other vehicles.

At this point, I don't think I'll ever run a battery in the motorcycle. I've had zero issues with running just the 400F bank of supercaps and using the Battery Tender to keep it topped up. The headlights no longer dim when the revs fall off like they did when running on a lead-acid battery.