[Sutripta]

^^^
Bait??

OK. So now we know which side of the discussion you stand. But initial question was on battery capacity. So something a bit more detailed, laying out the thought process, into which we can plug in numbers. Like 'If ... then the battery rating should be ... .

Regards
Sutripta

[ashwinprakas]

Irrespective of the self start feature the importance of a battery is predominant in a DC ignition system as it draws current directly from the Battery which is charged by the Stator.





As for determining draw, I've been doing it the amateurs way by using a multimeter after the fact by seeing if the battery drops below charging voltage at maximum draw.

Which is not ideal as you'd already be investing in the accessory at hand.

As for calculating draw on paper it would be best to do so by estimating stator output at idle and battery capacity by ensuring that the maximum draw doesn't exceed stator output at idle.

Which is my understanding after going through the detailed posts by Motard_Blr.

Regards,
A.P.

[srini1785]

"Bait"?.

Probably a wrong word choice. But having clearly laid out two schools of thought Viz A and B weren't we entering a debate?. What i was stating were the opening arguments for my side of the debate i.e Alternator remains the primary source of power. But, yes, i did miss your first sentence question i.e where do we stand on battery capacity?. My reply is given below.

Figures for ref only:

If:
Battery terminal voltage : 12V.

Connected loads : 50W ( Lights ), 120 W ( Starter motor - Momentary ), Horn 20W. Total connected load : 190W ( peak).

Current drawn from battery : 190 / 12 : Approx : 16A ( peak ).

Then :

A 12Ah battery should be sufficient.

This is due to the fact that it is capable of giving 12 A for 1 hour. When starting the bike , the starter motor would draw a max of 10A even then 2 A is available for other peripherals. In fact, even a 9AH battery would be sufficient since its only a momentary load.

Here i am assuming that the firing circuit is fed from the alternator directly. if not then it also becomes a connected load to the battery. Needless to say that as the connected load increases, the AH capacity of the battery should also increase.

[Motard_Blr]

Originally Posted by Sutripta

^^^
Bait??

OK. So now we know which side of the discussion you stand. But initial question was on battery capacity. So something a bit more detailed, laying out the thought process, into which we can plug in numbers. Like 'If ... then the battery rating should be ... .

Regards
Sutripta

For a single cylinder engine of about 300 to 400 cc, like the bullet, g310 or a KTM, the starter motor tends to be rated about 400 W to 500 W. At a battery voltage of 12 V, the continuous current draw would be about 30 A to 40 A. But the initial current draw is probably about double that. Also, each subsequent starting attempt will be at a slightly lower battery voltage so the current drawn will increase with each subsequent attempt. This means that the battery has to be rated for enough cranking amps for starting. This means that starting current could be as high as 100 A. This means that the required CCA rating of the battery should be at least 100 A . So the 8 Ah VRLA battery worth 120 CCA, that are fitted on these bikes, except the Bullet, is the right size.

Ok most bikes the electrical load doesn't vary much from the maximum as there are few accessories. In cars this is the opposite since they have a lot more accessories such as AC blowers, music systems, electric power steering, amt gearboxes, etc. Some of these run continuously (AC blower) and some run intermittently (power steering motor). Powering that sort of demand requires both large battery capacity and a large alternator. Before someone says "That's because cars have such big engines.", bikes with equally large or larger engines still have small batteries.

[Sutripta]

Originally Posted by srini1785

A 12Ah battery should be sufficient.
...
In fact, even a 9AH battery would be sufficient since its only a momentary load.

Hedging?

And while we wait for AP's observations, how do we size/ rate the alternator?

Regards
Sutripta

[ashwinprakas]

Originally Posted by Sutripta

Hedging?

And while we wait for AP's observations, how do we size/ rate the alternator?

Regards
Sutripta

I've already replied, guess my reply got missed in the mix.

https://www.team-bhp.com/forum/motor...ml#post4684563 (Understanding & troubleshooting Motorcycle Charging Systems)

In the linked post I've also shared the ignition wiring diagram from my service manual along with a footnote from the same that advises against running the motorcycle without a battery.

I'm currently on a 1k run within the state on the CT100B(Read: Posting from a crappy phone), hence the abrupt and delayed responses.

As for estimating output and draw in watts from the Stator and Battery lines, i belive the procedure is done with the Multimeter passing through(being part of) the circuit, though I'm not knowledgeable about the specifics, maybe someone more knowledgeable can guide us.

Regards,
A.P.

[Sutripta]

^^^
The question was one of battery capacity/ rating. And your post referred to makes no mention of that beyond stating that the battery in a DC system is important.

Guess one will have to wait till you are back from your ride for a detailed explanation.

Regards
Sutripta

[ashwinprakas]

Originally Posted by Sutripta

^^^
The question was one of battery capacity/ rating. And your post referred to makes no mention of that beyond stating that the battery in a DC system is important.

Guess one will have to wait till you are back from your ride for a detailed explanation.

Regards
Sutripta

Sorry for the ambiguity, what I meant was that since the battery is the source of current for everything including ignition on a motorcycle with a DC CDI/EFI then it would only make sense to keep the draw at par with battery wattage.

Regards,
A.P.

[Sutripta]

^^^
Too many ambiguities here too. 'Draw' - how does one calculate it? Battery rating has a time component to it (and a discharge rate if one gets into slightly more details). How does that figure with the 'draw'?

And what about MotardBlrs view that the primary value to keep in mind is the ability to deliver the required CCA?

Regards
Sutripta

[ashwinprakas]

Originally Posted by Sutripta

^^^
Too many ambiguities here too. 'Draw' - how does one calculate it?

I've done it by calculating everything on the motorcycle that consumes electricity turned on at the same time.



Indicator means 2 Bulbs ON at the same time.

I do understand that I have calculated even momentary draw but I believe its the right way to do so just to avoid any surprises when least expected.

Battery rating has a time component to it (and a discharge rate if one gets into slightly more details). How does that figure with the 'draw'?

I believe rate of charge is insignificant here as a bit of Googling as led to be understand that a motorcycles alternator generates about 25Ah at peak output which I'm assuming at idle would be around 12.5Ah or more going by the assumption that Volts and Amps are RPM dependent.

So there would be enough power to take on all electrical load and some left over to charge the battery as well.

The problem arises when the draw exceeds power output at idle which would result in the battery depleting steadily as a result of which the electricals would start to suffer.

And what about MotardBlrs view that the primary value to keep in mind is the ability to deliver the required CCA?

As for CCA, since its an estimation for periods measured in seconds, I'm skeptical about keeping it in mind when it comes to adding more draw by adding accessories i.e unless for some reason we're contemplating going down on battery capacity or powering a kettle from the motorcycles battery at the time of cranking.

Regards,
A.P.

[Sutripta]

^^^
Lots of additional questions and observations (like understanding of CCA, or the value for brake lights), but if I've understood you properly you want the battery to power all electrical systems of a mobike (other than self starter) for one hour. Have I understood it right?

Regards
Sutripta

[ashwinprakas]

Originally Posted by Sutripta

^^^
like understanding of CCA,

Google would help with that.

My understanding is that back in the day batteries weren't as reliable as the ones we have today hence CCA was computed to ensure that a battery can crank a motor for the first time without failing.

The reason I do not give much importance to it is cause I have jump started by F10D Zen Estilo using the 2.5Ah battery on my CT100B using jumper cables. Not a recommended move but had no other option at the time.

or the value for brake lights),

The value of brake light consumption wasn't provided in the manual so I just made an assumption, draw is negligible since its LED unlike the indicators and other lights.

but if I've understood you properly you want the battery to power all electrical systems of a mobike (other than self starter) for one hour. Have I understood it right?

I expect the alternator to power everything(battery included) on the motorcycle indefinitely as the roads are full of surprises.

It is not a good sign for the battery to drain when the motor is running.

Because if so its only a matter of limited time, in which case a bigger battery would serve most cases, but that is not what we want.

For an individual who doesn't take his motorcycle past Panchayat borders there is no need to fret as however small the battery might be it would still have enough charge to handle periodic drain, but its a whole different ball game for someone who travels interstate hence why the worst case scenario is accounted for.

Regards,
A.P.

[srini1785]

My 2 paise before we close this thread.

1. CCA / AH : Cold current ampere is a important parameter of a battery. However, the thing to understand is that the CCA is available @ near short circuit conditions ( i.e volts being near zero ) while Ah is available @ terminal voltage ( 12V ). A battery rated @ 100A ( CCA ) and 12Ah has a stored VA rating of 12x12 = 144 VA now if you draw say 100A from it at start, then the available voltage would be

Volts = 144/100 = 1.44 V.

So for all load calculations, only Ah rating is considered since its available at terminal voltage.

2.

Originally Posted by ashwinprakas

Sorry for the ambiguity, what I meant was that since the battery is the source of current for everything including ignition on a motorcycle with a DC CDI/EFI then it would only make sense to keep the draw at par with battery wattage.

From the circuit that is posted by you ( Post #17) and also by me in earlier posts , it would be clear that even for a DC CDi , the supply is taken from the alternator ( diode rectified DC ) and not the battery. AC / DC CDi is defined based on whether the charging capacitor uses is a AC or DC.

Originally Posted by Sutripta

And what about MotardBlrs view that the primary value to keep in mind is the ability to deliver the required CCA?

See my reply in point 1.

[Motard_Blr]

Originally Posted by srini1785

My 2 paise before we close this thread.

1. CCA / AH : Cold current ampere is a important parameter of a battery. However, the thing to understand is that the CCA is available @ near short circuit conditions ( i.e volts being near zero ) while Ah is available @ terminal voltage ( 12V ). A battery rated @ 100A ( CCA ) and 12Ah has a stored VA rating of 12x12 = 144 VA now if you draw say 100A from it at start, then the available voltage would be

Volts = 144/100 = 1.44 V.

So for all load calculations, only Ah rating is considered since its available at terminal voltage.

...

CCA measurement requires a charged 12 V battery to be discharged at the rated cold cranking amps while retaining between 7.2 V to 9.0 V, depending on the test method.

Refer:
https://batteryuniversity.com/learn/...d_cranking_amp

[ashwinprakas]

Originally Posted by srini1785

2.


From the circuit that is posted by you ( Post #17) and also by me in earlier posts , it would be clear that even for a DC CDi , the supply is taken from the alternator ( diode rectified DC ) and not the battery. AC / DC CDi is defined based on whether the charging capacitor uses is a AC or DC.

If it's not much trouble could you edit the image that I've shared and mark where the Alternator feeds the CDI on a DC CDI system?

The only input from that area in general is from the Pulser/Pick-Up coil which is also shown on the diagram I've shared.

Reason for me asking for a confirmation is because a motorcycle with a DC CDI simply fails to fire right without the battery present and I say this from experience, the Bulleteers would concur to this.

Regards,
A.P.