Li-ion Discharge Rates: Answers to DIY Battery Jump Starter Questions

[gideon0223]

More of a general question but thought I'd post it here.

Motorcycles are notorious for losing battery charge and not starting requiring a jump or rolling start.
Was looking to get one of these new Li-ion battery / jump start modules capable of starting a car (and charging a phone or tablet). Something like this one: http://junopower.com/collections/automobile/products/junojumpr-black-most-portable-jump-starter

My question is how do you think they are achieving this high amperage out of these batteries without damaging them? I am totally guessing its something like 6 Li-ion cells in there 3 in series and 2 parallel sets of 3 or something to get around 300 amps (6600mah) and 12+ Volts- I assume something like a 30C discharge rate for short bursts or is there some type of circuit you can design with capacitors to get you the amps you need without lowering the voltage?

How hard would it be to build one of these as a DIY project?

I ask purely out of curiosity. Thanks in advance guys...

 

[zoki85]

It isn't hard to make circuit with inductors and capacitors charged slowly by batteries, and then quickly discharged through low impedance nework. But start modules designed to perform specific tasks you describe are not so trivial.

 

[gideon0223]

Yeah, I guess I was asking more along the lines of:
Do you think this is a bunch of caps doing this? (Seems really thin for that)
Or do you think this is just some high discharge li-ion cells wired together to get the 300amps?

 

[zoki85]

I highly doubt you'll find just battery cells inside

 

[alphy]

I cannot provide an opinion on a specific product. However, I can explain the general principles behind Li-ion discharge rates and how they may relate to jump starters.

Li-ion batteries are known for their high energy density and relatively low self-discharge rate. However, their discharge rate, or the rate at which they can release energy, is limited. This is because the chemical reactions within the battery that produce electricity have a certain speed limit. Going beyond this limit can cause damage to the battery and potentially lead to overheating or even fire.

To achieve a high amperage output, as in the case of jump starters, manufacturers may use a combination of techniques. One approach is to use multiple cells in parallel, as you mentioned, to increase the overall current output. Additionally, they may use specialized circuitry to regulate the discharge rate and prevent the battery from being damaged. This could include using capacitors or other components to temporarily store and release energy in bursts, as you suggested.

Building a DIY Li-ion jump starter would require a great deal of knowledge and expertise in battery chemistry, electrical engineering, and safety protocols. It is not recommended to attempt this without proper training and understanding of the potential risks involved. It is always best to purchase a product from a reputable manufacturer that has undergone rigorous testing and safety certifications.