Supercapacitor Jump Starters

The Project Farm youtube channel has several jump pack comparos. Good Medicine. (Plus Todd is a fun guy. )

Cheers

Phil Hobbs

A lead acid battery at 9-10V is without any meaningful charge and won't be able to supply any energy to a supercap.

A lead acid battery will have some residual charge after the point it cannot supply the power to turn over a starter. However the terminal voltage after a short recovery will be more than 12V.

Supercaps have an incredibly low internal resistance. I don't know enough about their internals but I am aware a bank of them, or two, can supply megajoules to a magnetic coil-gun:

I have one containing about a 15Ah lead-acid, so still easily liftable with one hand without being an explosion risk. Lithium is smaller and lighter with less self-discharge but as you say, a bit risky.

Lithium iron phosphate PP3 cells have been offering 10-year life for some twenty years now. I used to have to buy them from Farnell/Newark.

They weren't cheap - about as much as the smoke alarm - but they were handy.

I have discharged the gel battery of my Ford Mondeo Ghia several times to approximately 5 volts. I charge with a current of mA till the battery recovers to 10 Volt than increase slowly the current. The garage advises to change the battery, but I can till start the motor with it. It is from 2000, so if an interior light is left on, or the parking lights, it is severely discharged. It makes no sense to replace the battery, I make this mistake at least once a year. Conclusion the battery is not ruined, at least not totally.

Groetjes Albert

Ok, that's the key to it. But there must be some kind of DC-DC up converter at the front end to bump the voltage from the ailing battery up to 12V before it's passed to the supercaps? It wouldn't make sense to attempt such a convertion at the output, immediately after the capacitors.

These "smart" chargers are just awful (just like most other stuff marketed as "smart" - it's only smart for the company selling it, not the customer). You're better of with an old fashioned trickle charger at a couple of amps. Yes, it takes an age, but it never fails and doesn't stress the battery.

Careful with the bench power supplies: They do not like if there is a storage battery with some life in the output and the input goes off.

In cold winters we had more than enough of bench power supplies to repair. It begins to be cold enough now (around -18 C or 0 F).

That is actually a very smart way to charge: a sulfated battery can easily need 40V or more to break down sulfate films and get charging started. Line voltage is cheap!

piglet

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That sounds like a very bad design, linear or switching.

That happened in the 1970's, when we had a couple of pretty cold winters, down to -30C. The power supplies were off-the-shelf lab power supplies common at that time, no switchers at all.

I do not use a charger. I use a power supply with regulated voltage and a current limiter. In the beginning I charge with 10 mA or such. I only charge with a less than 1 Volt over the current battery voltage.

Still bad design. A power suppy could be powering something with big input caps, when the AC power was switched off.

I do that, turn off the supply with a load connected.

I have had one for a few years now. I got it early in the pandemic when my Golf R would lose charge whilst not being used. It could only tolerate ~3 weeks of non use. It has served me quite well.

How can you charge at 1 volt over the current voltage? Won't that end the universe or something?

I charge a car battery that is supposedly dead < 5V.

Groetjes Albert

I charge 10 mA if the current voltage is 5 V. Slowly the voltage creeps up. For example at 8 V I risk charging with 100 mA. At the end the battery is functional, i.e. I can start the car with it.

Groetjes Albert

It wouldn't shock me if a battery had over 10 mA of self discharge.

But why not charge at an amp or two and be on your way? Where's the risk?