Charging a battery with a supercap

[Hero999]

Oh sorry Diver, I thought you were replying to my post, you're right.

 

[James1986]

Hey Blueroom,

Could you explain a little more about the ESR point you made, I'm not very savvy on that particular part. From the website the ultracap has an ESR of 19mOhms; is that milli or mega?

Also here is a link to the paper I read...

**broken link removed**

Thanks!

 

[Hero999]

My general understanding of super capacitors is that they tend to either have a very high ESR or a very high leakage current. I think he was confusing them with the type of super capacitors used as a backup for CMOS memory ICs.

The types of super capacitor used in automotive applications have a very low ESR but tend to have a high leakage current which is even worse in this application because it will flatten the battery.

I suppose you might be able to get low ESR low leakage super capacitors but they would be very expensive.

EDIT:
I notice you've linked an article which you have to pay for.

Have you bought it?

Could you please post a small part of it which would be classed as fair dealing under copyright law?

I'm very skeptical, if there is a way of reducing sulphation then I would think it would be more complicated than just connecting a super capacitor in parallel with the battery.

 

[charlie_r]

A quick search revealed that the article in question appears to be a dissertation by one Adam W. Stienecker at the University of Toledo.

The article in it's entirety is available here: OhioLINK ETD: Stienecker, Adam

 

[James1986]

The supercap in question has a current leakage of 1 mA after 72hours at 25deg c. Check it out here

Maxwell Technologies: Ultracapacitors - BPAK0058-15V

Anyways, thank you all for your constructive criticism; its given me good points to critically analyse; however the topic is to get some help on how to quantify the decisions I have made.

Hero, one of the benefits of being at university is that I get a free Athens login!

Back to the calculus!

Anyone know by anychance how much voltage and current a typical brushless dynamo will give off compared to its RPM? I'm assuming it corresponds to its windings?

 

[blueroomelectronics]

Your dynamo will also have to be the primary brake. Do you plan on having two dynamos? One on each wheel?

 

[Hero999]

I think I can understand how this works now, the capacitor can charge and discharge faster, more efficiently and has a longer life than the battery so it takes some of the strain off it.

1mA is quite high for a capacitor, it's probably a good idea to disconnect it when it isn't being used.

 

[James1986]

Blueroom, I don't plan on having conventional dynamos, just a hub motor which fits into the wheel; so yes this will act as a brake, much like engine braking in a car. Check out the current E-bikes on the market to see! Some incoroprate a freewheel planetary gear system, but this eliminates the possibility of regen =( There are ways around this too of course =)

That is correct hero! Although current leakage shouldnt be too bad considering most people will use their bike twice 5 days a week (commuters). Also, with the circuit design, once the controller is switched off, the capacitor will be isolated (as standard).