Smaller Battery - using starter

Hey all !

i'm moving along on my KZ 750 Twin. I don't want to go to kick only, therefore i need to know what is the lowest AH battery i can go to and the bike still run.

Of course i'm looking for a smaller battery to hide under the seat, but i don't want to rid of the starter... I believe the stock is 12V 14Ah ??


HELP?

Yes, stock is 14 A-hr and that is marginal with the stock wiring which leaves all the lights on when the starter turns over. I modified mine with relays to turn off all the lights when the starter is energized and the battery lives a lot longer.

I would highly, HIGHLY recommend dropping the dime one a Shorai battery. Not only do they weight close to nothing, they are very small to boot! The best part is that even in their small form factor they pack a lot of power. There is a multitude of benefits with their batteries, check em out:
www.shoraipower.com/

Note: I dont work for them, I dont know anyone that works for them, I dont sell them, etc. I just really like their battery technology.

RedBullEnema wrote: I would highly, HIGHLY recommend dropping the dime one a Shorai battery. Not only do they weight close to nothing, they are very small to boot! The best part is that even in their small form factor they pack a lot of power. There is a multitude of benefits with their batteries, check em out:
www.shoraipower.com/

Note: I dont work for them, I dont know anyone that works for them, I dont sell them, etc. I just really like their battery technology.

How long have you personally been using a Shorai battery?
What bike are you using it on?
Exactly which model Shorai battery are you using?

Thanks,
Ed

Eight cell Alien LiFePO battery in my 79 KZ750 twin.
Works like a charm, spins over faster than ever before.

650ed wrote:

RedBullEnema wrote: I would highly, HIGHLY recommend dropping the dime one a Shorai battery. Not only do they weight close to nothing, they are very small to boot! The best part is that even in their small form factor they pack a lot of power. There is a multitude of benefits with their batteries, check em out:
www.shoraipower.com/

Note: I dont work for them, I dont know anyone that works for them, I dont sell them, etc. I just really like their battery technology.

How long have you personally been using a Shorai battery?
What bike are you using it on?
Exactly which model Shorai battery are you using?

Thanks,
Ed

I am skeptical about the lifespan of them. The LiFe (lithium iron) chemistry is the exact same battery technology they are trying to shoehorn into electric vehicles. To get decent life, they have to be charged to a VERY accurate voltage (get it full charged but don't overcharge) and the battery stacks require constant monitoring and balancing. Based on that, I would assume the Shorai battery would be light weight and powerful, but the the relatively sloppy voltage tolerance of a bike's charging system (about 4%) and lack of cell balancing capability would spell a short life.

I wait to be proven wrong....

I am just an observer at this point..... :laugh:

I'm using this on my twin, had issues with the 1st one but it was sorted without fuss!

As BH says, i wouldn't go lower than stock, i'd have went higher if the battery case size was the same as this one.

Mine is a 77 & im using a newer reg/rect combo, not the one off a 78/79 but a more modern aftermarket unit.

Speaking of charging an LiFePO4 battery.... here is the charge control IC designed to charge them.

ww1.microchip.com/downloads/en/AppNotes/01276a.pdf

Notice one very important spec:

High Accuracy Preset Voltage Regulation
Through Full Temperature Range (-5°C to +55°C):
-/+ 0.5%

I worked in the IC industry for 30 years. Getting set voltage accuracy better than about 3% requires an expensive operation called "post package trim" because the molding process where the IC is encapsulated in plastic which then hardens, applies a slight mechanical stress to the die which affects accuracy. Getting down to 0.5% requires some added trim circuitry and then zapping the part after it is molded. That's pricey, you would never do it unless it was absolutely necessary.

Which makes me wonder: if the guys building the chargers know the battery charger's final voltage has to be 0.5% accurate, how is that compatible with a bike's charging system where the system voltage is around 14V +/- 0.5V? That's an error tolerance of more than 3%.


ADDITIONAL:

Given the proper final voltage for an LiFEPO4 cell is 3.6V (see app note above), that means if you stack four in series, it adds up to 14.4V. This may be the answer since most car/bike systems charge to about 14V (and would not exceed 14.4V unless something failed) that allows using the LiFE batteries... albeit not fully charging them in most cases.

I recall in the usage of Li-Ion batteries, each 1% below "optimum" for the charge voltage set point corresponded to about 10% less charge returned to the battery..... hence the reason Sony and the rest were beating on us for a 0.5% accuracy (we gave them 1%).

If LiFe is similar:

optimum is 3.6V/cell, then optimum for battery stack s 14.4V.

Charging to 14V is about 3% below nominal, so you are leaving maybe 30% of potential maximum battery capacity unused?

If bike's charging system voltage leans a little to the lower side like maybe 13.6V (which could be) then that voltage is about 5.5% below nominal leaving more than half of the potential maximum battery capacity unused.

Since Li batteries have a lot of capacity, running them "low" may be feasible (?)

bountyhunter wrote: Speaking of charging an LiFePO4 battery.... here is the charge control IC designed to charge them.

ww1.microchip.com/downloads/en/AppNotes/01276a.pdf

Notice one very important spec:

High Accuracy Preset Voltage Regulation
Through Full Temperature Range (-5°C to +55°C):
-/+ 0.5%

...Given the proper final voltage for an LiFEPO4 cell is 3.6V (see app note above), that means if you stack four in series, it adds up to 14.4V. This may be the answer since most car/bike systems charge to about 14V (and would not exceed 14.4V unless something failed) that allows using the LiFE batteries... albeit not fully charging them in most cases.

I recall in the usage of Li-Ion batteries, each 1% below "optimum" for the charge voltage set point corresponded to about 10% less charge returned to the battery..... hence the reason Sony and the rest were beating on us for a 0.5% accuracy (we gave them 1%).

If LiFe is similar:

optimum is 3.6V/cell, then optimum for battery stack s 14.4V....

The charging system on the KZ650-C1 (others may vary) produces 14 - 15v. The regulator test described in the FSM has you test the output at 1600 rpm then gradually raise the engine speed (without letting it decrease at any point) to 4,000 rpm. The regulator should keep the voltage between 14 - 15v (anyplace between 14 & 15 is good). I performed this test earlier this year after replacing the rectifier and found that the voltage at 1600 rpm was about 14.5v and when I raised the engine speed to 4,000 rpm the voltage gradually increased to 15.1v at which point the regulator immediately dropped the voltage down to 14.7v as it should to keep it between 14 - 15v. My point is that the voltage definitely varies more than 0.5% from 14.4v, so I don't know if this would affect the battery's performance over time. I have never had charging problems affect a regular lead/acid battery other than when the rectifier had a diode fail. Ed

That's the point. lead acid batteries are the most tolerant to charge voltage change. Anything from about 13.5 - 15V is OK with very little change. Li batteries are very critical for set voltage in terms of how much the battery is charged and whether it is overcharged.

I suspect 15.0V is overcharging. One LiFe battery data sheet stated that 3.6V/cell was the correct voltage but 3.8V/cell was the absolute maximum so maybe they would survive 15V? Don't know how it would affect life.

650ed wrote: The charging system on the KZ650-C1 (others may vary) produces 14 - 15v. The regulator test described in the FSM has you test the output at 1600 rpm then gradually raise the engine speed (without letting it decrease at any point) to 4,000 rpm. The regulator should keep the voltage between 14 - 15v (anyplace between 14 & 15 is good).

That seems a shade high, but not too high. When I was at Fairchild in 1980 we designed the voltage regulator chip used for US automotive apps. At that time Chrysler ran their system at 14.4V and Ford ran theirs at 13.8V (at 25C temp) with a voltage tempco of about -20mV/C so the charge voltage would track the change in battery voltage over temperature.

Running the system at a higher voltage means the battery recharges faster after the "start drain".

This is in line with what I was taught on lead acid:

The correct setting of the charge voltage is critical and
ranges from 2.30 to 2.45V per cell.

Setting the voltage threshold is a compromise, and battery experts refer to this as “dancing on the head of a needle.” On one hand, the battery wants to be fully charged to get maximum capacity and avoid sulfation on the negative plate; on the other hand, an over-saturated condition causes grid corrosion on the positive plate and induces gassing.

To make “dancing on the head of a needle” more difficult, the battery voltage shifts with temperature. Warmer surroundings require slightly lower voltage thresholds and a cold ambient prefers a higher level.

2.30 x 6 = 13.8V

2.45 x 6 = 14.7V

13.8V is the nominal voltage that many automobile systems operate at.
14.7V is higher than you'd usually meet but around 14.4V is common for "topping" mode charging which is used to equalise charge in series connected cells. See the Battery University site for MUCH more information.

Yeah, all of the above is probably true, BH you're an intelligent guy with a hell of a background in this field, infinately more than me! I'm not knocking anything you guys say BUT just sometimes the conventional battery just doesn;t suit the application. If my battery goes prematurely i'll replace it, hopefully it won't but the well laid out explaination you posted seems to indicate a probable shorter lifespan than a lead/acid. That bike i built would just have looked daft (maybe you guys think it does anyway :lol:) with the std size battery hanging out of its arse