Lithium-ion 12v Battery Replacement

[teoman]

You can bump the voltage higher for the start.

[Ecky]

Originally Posted by teoman

You can bump the voltage higher for the start.

Bump the voltage of what higher for the start?

[teoman]

Somehow charge the capacitors higher for the startup. They can go up to 16V. You gain quite a bit of energy which should get you to start the car. (If the other systems are not negatively affected by the higher voltage). That will result in a higher voltage once the engine has started.

[teoman]

Now i am pondering the battery configuration of my arrangement.
With 6S configuration:
MAX: 24.9V
NOM: 22.2V
MIN: 18V

with a 4S configuration:
MAX: 16.6V
NOM: 14.8V
MIN: 12V


From what I have logged the car keeps the battery voltage at 14.2V.

Now if the components of the car (VW passat 1.8 TSI 2010) is unhappy with voltages above 14.7 V then I have to use a capacitor and voltage regulator. Because if not then I can not fully utilize the battery. Even if it is OK at nominal voltage, I will not be able to charge it without upsetting various ECUs in the car.

PS apparently the cells I am getting are the same ones in the hyundai iconiq (except it has 192 of them)

[Ecky]

I can't see charging the caps higher as being realistic.

Due to the size of the capacitors, I think a decent sized battery in parallel is absolutely necessary: one that can potentially even take a starting load, even if it's not a full sized car battery. Hop in the car, turn the radio and lights on, fiddle with your phone for a minute before leaving, the car doesn't start and you're stranded - that's just not acceptable. Starting at the voltage an alternator charges, you can't have the key in the ignition without starting the car for more than a minute or two.

Given my experience with these, I feel like a set of caps in the range of 1000F+ is more appropriate for starting a car on their own. There's some forgiveness there.

[teoman]

Any battery and a 3 dollar boost converter should get your caps up to any desired voltage.

You will only be limited by the capacity of the battery (not its instantaneous output power). And time ofcourse.

[redpoint5]

Originally Posted by Ecky

Correction: Might not be workable, at least with my DC-DC converter supplying 12v. After starting the car, the DC-DC kicks on, then its overcurrent protection trips and it shuts back off, car runs for about 15 seconds then dies when the caps get too low. I'll need to think about this.

So the Insight uses a DC-DC converter rather than an alternator?

Is it possible to put a current limiting resistor in series with your supercaps from the DC-DC converter, or better yet, have the converter charge your battery, and then have your supercaps in parallel with a current limiting resistor so it doesn't pose such a drain as it builds charge.

[RedDevil]

A row of diodes and a resistor all parallel. The diodes allow the starter to draw current, but block recharging so the charge current has to pass the resistor.

A DC-DC converter would efficiently and safely recharge the caps, but most cheap DC-DC converters have a significant parasitic draw on either end - even if the other end is not connected.

[Ecky]

One bad capacitor?



Will see if I have time to pull it out tomorrow and measure.

[redpoint5]

You suspect because of a bright LED?

I don't think that indicates a bad cap. LEDs can be brighter or dimmer with slight differences in voltages.

I'd still test it all though. As I said, it's a good idea to charge them to the same voltage and let them sit a while and see if they discharge at similar rates.