How to calculate battery size needed?

[gavinnz]

Ok... if a bike had a 14 ah battery and was electric and kick start... and you removed the electric starter....

How can you calculate the minium ah of battery the then needed to run the bikes systems?

Any auto electrical types out their???

Regards
Gavin

[Ixion]

Does bike have indicators ?

[F5 Dave]

Best update for those who aren't familiar with your application.
Race only vs road.
Lights hard wired?
Ignition type.
And another clincher is how long do you expect to sit it without using it. & if so do you (will you) plug in a battery tender.

[bogan]

depends on the bike, EFI? CDI? Points, if its the later, itll run without a battery at all

[gavinnz]

Road use. Led indicators and tail light, headlight hard wired on, electronic ignition but no computers or fuel injection.

I thought you might be able to do something like add all the draw of the parts together... minus the output of the alternator, times it my the length of the piece of string, devided by orange and get an answer :)
Gavin

[F5 Dave]

Have a look at other similar bikes in suggested range.

My 750 had a 12ah battery & I noticed the RF900 used a CTX9BS so I swapped one in & it has been just fine. Saved a kilo on a hardwired sporadically used 4 cyl roadbike.

Must be able to go much smaller, though as I'm finding on my kick only 500 2 stroke the programmable electronic ignition I use has to have good voltage to work & the tiny fist size battery seems to run down if left for even a week or two (cue battery tender).

[Ixion]

Hm. Headlamp hardwired limits things.

Does it start easy, first kick?

problem is if it takes a bit of kicking, that headlamp is pulling the voltage down the whole time. After 2 or 3 minutes the voltage may drop below decent spark point.

Maybe 8 AH ?

[gavinnz]

Hm. Headlamp hardwired limits things.

Does it start easy, first kick?

problem is if it takes a bit of kicking, that headlamp is pulling the voltage down the whole time. After 2 or 3 minutes the voltage may drop below decent spark point.

Maybe 8 AH ?
Good point about the light draining the power down... I will fit a switch so I comtrol the lights.
Nice thanks.
Regards
Gavin

[F5 Dave]

Well you could put a push break in the headlight cct until it starts. If 9 was fine for my electric start 750 (& the RF) left for recently several months with 4 yr old battery then 8 is pretty conservative for a kick only

Hmm 4AH used on DR500. prob min. & would need hardwire interuption.

[kwaka_crasher]

Ok... if a bike had a 14 ah battery and was electric and kick start... and you removed the electric starter....

How can you calculate the minium ah of battery the then needed to run the bikes systems?

The Ah rating is rarely for 1 hour - my deep cycle 85Ah boat battery is based on 20 hours so 4.25A for 20 hours. What you want to know is the RC or reserve capacity.

But removing the electric starter won't make the system total loss which is what everyone is assuming you're wanting to do. Care to clarify?

[jonbuoy]

Have you got an ammeter and do you know how to use one? Can be handy when working out the actual load on the battery -ie is it charging or discharging and at what revs/loads it does this. Its more related to the output of the bikes charging system for a road bike as this is what is supplying the power. With no starter motor the battery is really only for smoothing and supplying power when the charging system output is lower than the power drawn by the ignition and lighting (like sitting in traffic or idling). It doesn't matter how big the battery is - if the charging system can't keep up eventually it will go flat, it will just take longer to do it. Or something like that.

My 750 doesn't charge much at all below 3000 RPM and at idle its quite a drain on the battery hence the need for a big battery (even without using the electric start) to iron out the bumps in the charging cycle. I'm guessing you just want a smaller lighter battery to save weight/space?

[F5 Dave]

. .
But removing the electric starter won't make the system total loss which is what everyone is assuming you're wanting to do. Care to clarify?
Why would anyone assume that? It's a roadbike, he wouldn't want total loss, just to lose weight.

[kwaka_crasher]

Why would anyone assume that? It's a roadbike, he wouldn't want total loss, just to lose weight.

Because he doesn't say why he wants to remove the starter and if you're not using the battery for starting you can go almost as small as you want.

Why the fuck would anyone want to remove a starter and fit a smaller battery to 'save weight' on a road bike? It's a negligible difference.

I honestly can't fathom why anyone would want to do this.

[AllanB]

Batteries - I want to know why a expensive factory Honda battery only lasted just over 2 years (like a month out of warranty!). I know another guy who had exactly the same happened to his CB1300 a few months ago. :blink:


Anyway - If you have not yet signed up to Bits4bikes.co.nz you can do so and get a $25 discount on purchases over $100. My new battery was discounted from $126 to $106 less my $25 discount to $81.

A new Motobatt - some fancy fiberglass gel thingy all sealed and maintenance free. One good design is the dual poss/negative mounts.

[gavinnz]

Because he doesn't say why he wants to remove the starter and if you're not using the battery for starting you can go almost as small as you want.

Why the fuck would anyone want to remove a starter and fit a smaller battery to 'save weight' on a road bike? It's a negligible difference.

I honestly can't fathom why anyone would want to do this.
In answer the to the why here it is....

Gilera Saturno Bialbero Superleggera 558 project outline.

My aim is to make my Gilera Saturno as light as possible while having all road equipment and still being instantly recognizable as a Saturno.

Why am I doing it? For a fun intellectual and practical creative exercise in trying to think outside the box. Taking an already light bike and making it even lighter but I not only want it to BE light but to LOOK light. I am not trying to make the bike more powerful. I want it to be a torquey bike that it best on tight twisty roads with great brakes and "torque to weight ratio" and gearing to make it really pull out of corners.

Weight to be measured with bike ready to go with just petrol added. Starting weight of 153.05kg with pod filter and no airbox, otherwise standard 350.
I am confident I can get 20kg off the bike, but I am aiming for 33kg and a final weight of around 120kg.
This is the thought process I run on each part, however small.

1. Focus on one part.
2. What function does the part perform?
3. Can it be done without?
4. Can it be replaced with a lighter component?
5. Can it be made smaller?
6. Can it be made from a different material?
7. Can it be incorporated with other parts to do more than one job?

Removing the electric starter has a lot of flow on effects...
You can lose say 2.5kg of battery, 3kg or starter, 1kg of starter clutch and gear train, 500g of starter relay and heavy duty wiring.
So all up about 7kg off a 154kg bike or 4.5% of the start weight.
That is going to be a noticable amount.

If anyone is interested I have the mods I have done and intend to do in a list here I could post...

Later
Gavin

[kwaka_crasher]

In answer the to the why here it is....

Gilera Saturno Bialbero Superleggera 558 project outline.

Seems like a pointless waste of time for a road bike to me, but whatever floats your boat.

But back to the question: Like I said, unless you're planning on spending lots of time putting around town at low rpm you don't need much of a battery at all - the alternator will provide all the power you need - the battery is just for starting and as a buffer.

[gavinnz]

Seems like a pointless waste of time for a road bike to me, but whatever floats your boat.

But back to the question: Like I said, unless you're planning on spending lots of time putting around town at low rpm you don't need much of a battery at all - the alternator will provide all the power you need - the battery is just for starting and as a buffer.
I have the time and the point is I enjoy the creative process of doing it.
And I will enjoy the lighter more responsive and unique bike.
A lot of the best things in live are pointless... :)

Later
G

[AllanB]

Sounds like a cool project to me.

Now don't forget to put the rider on a diet too :sweatdrop

PS - batteries are surprisingly heavy!

[CookMySock]

Hm. Headlamp hardwired limits things.He needs some diodes and a relay so the headlight comes on when the stator starts producing output.

I'd try a bunch of AA penlight cells in a 12V holder and see if it would allow you to start the bike. If it did, then try some NiHM cells.

http://jaycar.co.nz/productView.asp?ID=PH9209

Don't run the carbon penlight cells for very long coz charging them will pop them.

Steve