Supercapacitor Battery Replacement

[Nautilus]

Took out the dead battery. As I've suspected, it was frozen. As in covered with frozen leaked out electrolyte. 5.64 volts at terminals. Dead as a dinosaur.

Acquired a "virgin" (dry-stored, filled upon purchase) AGM motorcycle battery of 12Ah from Varta. Compared to the defunct 10Ah is a bit heavier (~4kg weight) and potent enough for a 1.8 liter engine by itself, as factory recommended for 1800cc Suzuki Intruder. Got it thoroughly tested and warranty covered as an automotive-systems auxiliary battery, to avoid future hassle. Once filled up, left to settle and charged to specs it holds 13.02 volts.

This should bring the fully assembled hybrid to 6kg in weight. Cutting corners (literally ) means little advantage.



Once fitted, it may bring some minor advantage in mileage, as the supercaps charge very quickly and there is little work to do by the alternator. (Alternators are miserably inefficient, about 40% over most of the rpm band, so they draw pretty kilowatts from the engine while under electrical load.) This is not its purpose, the goal is removal of weight from outside the wheelbase.

Removed the balacing circuit boards and tested the supercaps again. They charge much quicker with a battery charger, hit about 14.25 volts, charger LED lights up and they don't seem to get more charge. Left them to settle down. Dropped to about 14.08 volts and individual voltages in the string are:

+ 2.40 2.27 2.29 2.43 2.21 2.48 -

Charged again to ~14.8 volts and tested the individual voltages in the string. Highest voltage cap closest to - terminal, 2.58 V, lowest 2.38 V (2 caps), the rest in the 2.4x range.

The ratios between individual voltages are similar to what I've got before, with balancing boards fitted. Proof the boards did nothing useful.

[Nautilus]

120 kms (75 miles) of road tests with new capacitor-battery combo (Varta 12Ah AGM, thicker copper strips between supercaps, no balancing boards) over 2 days and 2 nights.

Temperatures: -2 to 5ºC (28-41ºF) day, -6 to -7ºC (19-21ºF) night.

Voltage: 13-13.1 volts just after full charge. Drops to ~12.83 volts after 24 hours. Stays at ~12.6-12.8 volts through the day, multiple starts and drives.

Alternator voltage: 14.6-14.8 volts engine cold just after start. 14.3-14.4 volts engine warm, headlights off. 14.0-14.1 volts engine hot, headlights on, after hours of driving.

Start: 1-2 seconds of cranking. Voltage drops very briefly below 9 volts during cranking.

Rpms climb a little bit faster. Smoother running under load and high rpm.

Effects on roadholding: sharper turn-in on corner entrance, enough to trigger the ESP on dry tarmac with summer tires. (This is due to all bits and pieces moved to change the weight distribution, 36-42 kg overall, not just lighter battery.) Slightly smoother acceleration in gear.

Can be charged by the solar panels over the trunk lid.

[teoman]

I have been pondering on this for a long while. And the only advantage that lithiums have is their ability to deliver a lot of current and their ability to give all their stored energy while in use (and after that they kill themselves).

They already have limited capacity, and with super caps their high amp abilities are not used.

The more i think of it, the more using a very small deep cycle lead acid battery makes sense.

[redpoint5]

Originally Posted by teoman

I have been pondering on this for a long while. And the only advantage that lithiums have is their ability to deliver a lot of current and their ability to give all their stored energy while in use (and after that they kill themselves).

They already have limited capacity, and with super caps their high amp abilities are not used.

The more i think of it, the more using a very small deep cycle lead acid battery makes sense.

You didn't even mention the primary advantages of lithium-ion batteries:

1. Weight savings due to much higher energy density

2. Space (volume) saving due to much higher energy density

That said, most people would likely be better off using a small lead acid battery paired with a supercap.

LiFePO4 is ideal for my Prius since it lives inside the temperature controlled cabin, doesn't get deeply discharged (no starter motor), and the OEM battery is more expensive.

[teoman]

If you have an elderly machine or one that does not suffer from ecu power loss, any battery and a boosy buck converter (2usd) will work beautifully. Even Aa cells.

On a fast motorbike weight savings are also an important factor.

[Nautilus]

AA cells may be a bit overworked unless the vehicle is a motor scooter.

When outside temps fall below the -7 to -9ºC range, at -12 to -14ºC (7-10ºF), the 12Ah+supercaps combo may not start. It holds 12.0-12.3 volts and cranks, but after the first 2 seconds of supercap discharge, it falls below 8 volts and cranks too slowly. This means the battery, which decreases in available amps as the temperature drops, is not strong enough to either replenish the supercaps at the same rate they discharge, or crank the engine by itself.

However, it's very easy to jump start. Just after connection to a fresh battery or running alternator, it starts just fine, as quickly as it does at positive temps. This happens because it needs only to replenish the supercaps, not the battery. Lead acid batteries which are too weak to crank charge slowly when jump started and need multiple attempts to give a strong cranking by themselves.

So it needs either a pocket sized lithium jump-starter, or an auxiliary lithium battery in the trunk. Or to be parked in some place where temps do not fall below -9ºC.

PS Laserhacker's experiment worked with a much smaller battery because he used a RC-car type lithium pack. These are made to give quickly a lot of amps for acceleration, almost like supercaps do.

[Stubby79]

Originally Posted by teoman

If you have an elderly machine or one that does not suffer from ecu power loss, any battery and a boosy buck converter (2usd) will work beautifully. Even Aa cells.

On a fast motorbike weight savings are also an important factor.

You could feed the ECU separately, so it never sees less than an acceptable voltage.

[Nautilus]

Until now, the AGM+supercaps combo performed reasonably.

Reliability: survived -11 to -16ºC (3-12ºF) nights without discharging or freezing. Cranked at -6 to -9ºC (16-21ºF) and above. Supercaps still leak over time, but the combo can hold 12.0-12.3 volts and crank. Connecting the solar panels (which include a pair or small 2.4Ah AGMs) when weather is bright compensates for the leakage, allows it to hold 12.6-12.7 volts over time and 13.0 volts under the winter sun.

Problems: cranked too slowly at -12ºC and couldn't start engine without a jump from a pocket lithium jump starter. Next weekend, after starting flawlessly from cold and running for some time, cranked slowly once in a gas station, when warmed up, for no apparent reason. Saved again by the pocket jump starter. Afterwards it ran properly.

For some weird reasons, the more exercise (start-run-stop-start again warm) is given to the supercaps, the better they perform. If the car is daily driven, they couldn't be happier.

Added a small cooling duct: 3/4" wire-wound rubber duct, from battery box to air filter box, and another from cold air intake tube to battery box. This way, engine draws cool air through battery box. Compared to yesterday (1-5ºC outside temps), today (6-7ºC outside temps) the inside of the battery box (after a similar run of some tens of miles) can be felt much colder.

Total weight moved from front to rear, toolboxes included, is around 42 kg / 92 lbs. Best roadholding is when gas tank (placed amidships, well inside the wheelbase) is half full, not full to the brim. This is not due to fuel weight itself, but to fuel sloshing left-right in tight turns; when tank is full, it can be felt and it's annoying. With half tank it's not.

Side note: all front wheel driven GTI cars are flawed from using small family car chassis and bodywork. Which had been designed for best weight balance when fully loaded. This is the reason for all efforts to balance the weight distribution.

Judging by cost, labor, reliability problems, a hybrid battery with supercaps is more or less a gimmick. Its only visible advantage is light weight. Even giant 2000-3000F caps are not great in this matter, since they approach in weight a small lead-acid battery anyway.

For people who seek a reliable car and they're not too much interested in brisk handling, the 150+ year old lead-acid is far more profitable.

[Nautilus]

Originally Posted by redpoint5

I'm running 6x 400 farad caps alone on my CBR600, and it starts every time. You have very little time to waste in starting the bike once you turn the ignition on, and only 1 shot to start. I have no problem with this in daily use, but if the bike sits for more than 3 days, I have to put it on the trickle charger or else it won't start on the 4th day. I'm willing to put up with these limitations since bump starting is always an option if the caps ever did fail to start the bike.

Most supercaps will leak. The difference between high-grade brands like Maxwell, poorer brands like Samwha or Nippon, or no-name copies, is the rate of leakage. (Samwha even quotes, for a fully assembled 66.6F pack, a leakage rate of up to 50% after 15 hours.)

It holds 12.0-12.3 volts (and crank) for the next 48 hours if the engine is not started or no trickle charging is applied. In my case, if there is not enough sunlight to feed the solar charger. But after 48 hours with no engine run, things get murky. If outside temps are too low, even quicker than 48 hours. Available battery power may fall too low and crank too slowly.

For this reason, a supercap pack is a gimmick. Most people do not care having to jump start during some freezing weather, they value reliability above a few pounds shaved from the vehicle. Or they may use a smaller, lighter lead-acid battery from Varley or Odyssey in place of a standard one.

[teoman]

How about one 2v lead acid in parallel with every supercap. Should bleed of the excess voltage.

I do not know if there are 12 lead acid batteries with a connection for each cell.