adjustment to the battery charging voltage?

[jsyzdek]

Hi fellow riders

GS500F is my first motorcycle. I've been riding it for a year now. Struggled a bit with the clutch for a while but have found this forum (and Haynes manual) very helfpul in fixing it. Now the bike responds to the throttle very nicely.

Now getting to the point - I'm a battery engineer and I have built my own Li-battery pack. It consists of 4x4 (16) A123-26650 cells. The nominal capacity is 11Ah at 13.6V. The cranking current of the battery is somewhere between 600 and 800A. And it weighs only 3 pounds. The best part of it is that it doesn't self discharge quite as quickly as Lead-acid so you can leave it alone for a few months without a battery tender and it will be just fine. Second thing - even when you drain it and then you recharge it - it's like new (exactly what you do to your phone every day). Lead acid - you drain, it's never the same. You leave it discharged for a couple months - you need a new one.

The question I have is about the battery charging voltage. To fully charge my pack I need 13.6V. The alternator seems to put out 13.48V. It doesn't seem like 120mV would make a big difference, right? But because of the battery chemistry (a very flat Voltage vs. capacity profile), 13.48V charges it only to 70% capacity. It still has more than enough juice to start an SUV (have tried that), but I would feel better knowing that I have all 11Ah available when I need them. Any ideas how to adjust the alternator output voltage to 13.6V? (possibly without buying any new parts)

[robfriedenberger]

I'm 100% sure that you are more educated than me on how any thing electrical works, however I think that one battery could start 4 GS500s all al the same time..... You might be able to modify the regulator, and if you screw it up you only in the hole $20


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[Badot]

I was under the impression that you needed a voltage a little higher than nominal to fully charge a battery 

Just curious, how much does one of those packs cost to build?

[The Buddha]

Jsyzdek: If you have much more than that 13.48 you could blow headlight bulbs (of course you can regulate that with a 7812 style regulator) ...

The bike's regulator rectifier basically I think has a schottky diode and some other stuff.
You can change that guy to put out more voltage ... but I dunno how much exact control you would have.

And oh yea, I'm gonna need a dozen or so of em SUV starting 3 lb batteries.

Cool.
Buddha.

[adidasguy]

When running above 3k rpm you should be getting 14 to 14.6 or so volts. Never above 15.
Idling it would be in the mid 13v range.

[jsyzdek]

Well, the higher the difference between the nominal voltage and the charging one - the faster you charge. To start the bike (if it catches immediately) you need 0.1% of your battery capacity. You top it off in a blink.

Lead-acid batteries have the issue of working above the water electrolysis voltage. So as long as battery is not dead, you keep decomposing your electrolyte (water to be exact, that consists about 75% of the electrolyte) into oxygen and hydrogen (and H2 is the explosive gas they warn you about). That's why all non-sealed batteries need to have the water refilled once in a while. So you constantly use some charge to decompose water, hence you need a voltage significantly above nominal to fully charge a lead-acid battery. Li-ion doesn't have that problem (or at least not at the same scale).

I don't need much more than 13.48V. I only need to go to 13.6V to charge it to 98% (not exactly 100, but close enough). I guess everything will be fine. When I fully charged the battery when I put it together it was at 14.4V. I hooked it up and the bulbs did just fine.

I will check what happens at higher RPMs. Thx for the tip!

The cost - I got the cells for free. And I had spare time, sheets of black acrylic, nickel foil and copper rods and some glue/screws. So it costed me virtually no money. Just time. And I really wanted tons of power and energy so this is the largest battery I could squeeze in. You can either buy single Li-ion cells and spend time building your pack and maybe save yourself a buck or two, or buy motorcycle Li-ion batteries off-the-shelf. My friend got one for his Kawasaki 1000 Concours and it cranks it up way easier than the heavy, original battery.

This is what he got:
http://www.amazon.com/gp/product/B00819SWKW/ref=oh_details_o03_s00_i00?ie=UTF8&psc=1 (they have both right and left handed versions)

There are more on the market. You pay 2x the price of Lead acid for 4x the power, less than 1/4 the weight, probably more than 4x the service life and 1000x more peace of mind...

[Zithromax]

It's interesting that you're talking about the exact same topic I was chatting with my uncle about today (who is also an electrical guru). I need 14V to run the gizmos in my tank bag and as you've already found out the bike is cutting us off short of that. He suggested, and the way I'm going to approach it, is pick the voltage coming from the stator BEFORE it gets to the bike regulator and regulate that down with something off the shelf from Radio Shack with maybe a tank cap to smooth it out a bit. I may even look around to see if I can find an adjustable regulator?

[adidasguy]

Many of us use Shorai LiFe batteries. About the same price and stuff as what you bought.
Simple swap out and fill the battery box with the sticky back foam they provide.
All my bikes have them.  Most people that visit the West Seattle Bike Cave end up with them.

Not sure why you need to change anything. The GS500 charges about 14.5 volts so there is no problem.

If you have a bad regulator, then replace it with a MosFet one. More reliable and newer technology than stock.

The first bike I put the Shorai into has had it going on 3 years now.

From the years of GS500's experience and LiFe batteries, I feel you are chasing a non-issue.

[Badot]

Just looked up the specific cells: http://www.batteryspace.com/A123-System-Nanophosphate-LiFePO4-26650-Rechargeable-Cell-3.2V-2500-mAh.aspx

120A max discharge as opposed to ~10A from a standard 26650. Those are some special ones, that's for sure.

I honestly wouldn't be surprised if it would start two SUVs at once.

[jsyzdek]

This is a C/5 discharge and charge test. You can see where 3.37V vs. 3.4V per cell gets you on the charge curve. This is a dynamic test, so I think in static conditions I'm charging my battery a little higher than 70%, but I'd prefer to have 3.4V and not worry about it.

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