Ditch the battery?

[xwhatsit]

Hi, quick question.

I have a kick-start road bike. I want to get rid of the battery (don't ask me why). I know I can do this, technically. Is it difficult? Will it cause running problems at low revs?

Also, will I get grief in terms of the bike being road legal (lights etc)?

[imdying]

As you've guessed, it's a crap idea on a CB.

[xwhatsit]

Lol, crap idea, or not... I've seen plenty of pictures to give me the impression that technically on the CB250RS it won't make it run badly -- however do I need to be able to have lights or anything while the engine is not running? Will the police get the shits?

[imdying]

Lol, crap idea, or not... I've seen plenty of pictures to give me the impression that technically on the CB250RS it won't make it run badly -- however do I need to be able to have lights or anything while the engine is not running? Will the police get the shits?

How do you feel about being rear ended in the dark?

[Ixion]

This used to be pretty common back in the day. From memory what you need to do is wire a 1000mf capacitor across where the battery used to be.

That stops thing frying, and avoids misfire problems.

Without the capacitor , the bike may start and run , but you'll likely get all manner of strange misfires and flat spots. Caused by the "frequency" of the unsmoothed DC falling in and out of alignment with the ignition system demands, I think.

[Flyingpony]

From my experience with Honda's, they won't work with the battery removed/unplugged.

[xwhatsit]

How do you feel about being rear ended in the dark?

Why would I be on the road without the engine running?

But cheers, Ixion. I was thinking about a bloody great capacitor actually, in terms of just smoothing out the peaks, but I'm not really sure about auto electrics yet so I wasn't sure whether that was smart. A battery functions like a capacitor, really, anyway.

Main thing I'm concerned about is WOF and other legal requirements.

[Grub]

From this explanation , I would say that you will fry your electrics

A wee bit of theory :

A bike alternator , in the absence of anything else , will produce some very high voltages . 20 to 30 volts typically.

We only want about 13 and a bit to run things and charge the battery.

Normally the alternator current (after being turned into DC) is fed to the battery. The battery is a big "sink" that "absorbs" the current. To make sure that the battery doesn't get over charged, there is a voltage regulator. This "shunts off" any voltage once the battery is fully charged.

When you run without the battery , all the alternator current is directly fed through to the regulator. Do that for too long , and the regulator gives up the unequal struggle and dies. Now, the whole 30 odd volts is fed into the bikes electrical system. The CDI unit (and other stuff) that is designed to run at 12 volts is suddenly getting hit with 30 volts. So after a bit, it too dies.The DCI unit will usually be the first to go, since it is full of transistors and other delicate whizzy stuff. No CDI unit, no spark. Or feak and weeble ones. Bike, him no go.

(Purists will note that I've simplifed things abit. It's a bit more complex, but that's the general idea)

[xwhatsit]

From this explanation , I would say that you will fry your electrics

Hmm I'm not convinced. Call me stupid (which I am), but isn't that the point of the current sink (bloody big capacitor) that Ixion himself mentioned earlier?

Point is, I know it can be done technically -- I've seen plenty of café CB250RSs minus their battery. How I will accomplish this, I will find out further down the track, probably from those who have already done this conversion. Ixion's capacitor idea sounds like that's the way to do it. What I really want to find out is, is the bike going to be road legal like this?

Alternatively, instead of the cap, I'll just ask my lecturers what the best and most efficient method of sinking a big current is. You'd still need the cap for smoothing out the pulses, and making sure current is still available for spark when the alternator hasn't supplied it. I wouldn't mind replacing the regulator with a switch-mode step-down controller instead of the big inefficient heat-generating (and thus self-frying after extended cooking) linear regulator. But with a big enough current sink, cooking the regulator isn't on the cards. 1000mF is a fairly large value -- that's a 1 farad capacitor -- that should be able to take care of a fair bit of unwanted charge, you could probably do it with a cap a tenth of the size, but a bigger one doesn't hurt.

[Motu]

XR250's run without a battery,no reason why a CB 250RS can't.The battery is just a storage device,so a capacitor can handle that.You may need a battery for indicators,stop light and horn...remember,you can use a bulb horn legally.Worst case is the engine stalls when you brake with the lights on....but engine should be seperate from lighting anyway.Get an XR wiring diagram and check it out.

[imdying]

Why would I be on the road without the engine running?

Main thing I'm concerned about is WOF and other legal requirements.

You know how if your battery is weak, your lights dim when you're idling and brighten when you rev it? I'd hate to see you squashed flat at the lights because of a dim taillight. As far as the WOF goes, so long as your lights go you're fine... you would have to check the manual on the LTSA website as to whether they need to operate without the motor running though. You don't want a stalled motor to get you run over! Imagine if all that work on the motor went to waste due to being totalled!!

I guess we should mull over what you want to accomplish... a 1 farad cap would take a little reengineering and a little bit of room... maybe just using a physically smaller battery (perhaps of a better quality with similar CCA?) would suit what you're trying to achieve better?

You could always attach a battery somehow for warrants of course... maybe a combo approach? Maybe a small 12v power pack stashed somewhere to run the taillight for 5/10 minutes if the motor dies, and a cap for general running with the motor on?

[imdying]

Worst case is the engine stalls when you brake with the lights on.

Wot he said

[vifferman]

It's doable.
I used to run my MT250 without a battery, because the headlight ran straight from one of the coils on the stator/magneto or whatever the hell it had. The only problem I had was that it used to blow the tail-light bulb because I didn't have a battery eliminator or capacitor.
I took everything off that wasn't essential, and the only thing I ran afoul of Mr Plod with was the regulations changed regarding mirrors. Blardy silly, because the mirrors were used to useless so even when it did have one on I didn't use it.

[Ixion]

There is no issue with WoF. Many older bikes (famously, the BSA Bantam) had no provision for a battery and none could be fitted. You are entitled to have the motor running for the WoF check (though you'll have to go somewhere where you can stay with the bike, trying to explain that to a typical tester could be hard). Rev the motor for light and indicator checks.

Indicators will be the trickiest, sometimes the pulsating voltage upsets them But I had a T500 running just fine without a battery,everything working. Horn can be a bit feak and weeble, but as mr Motu says, if the tester baulks, just fit a bulb horn , from your local bicycle shop. Quite legal. Mates had all sorts of other bikes running too. It works. BTW, pre 1978 you don't legally need indicators or stop lights.

Only downside is (obviously) you need a kickstarter. And you will blow bulbs rather more often.

EDIT 1000mf cap is about 1 inch diameter, about 1.5 inch long. Try the electronic surplus place at the top of Queen St.

[xwhatsit]

XR250's run without a battery,no reason why a CB 250RS can't.The battery is just a storage device,so a capacitor can handle that.You may need a battery for indicators,stop light and horn...remember,you can use a bulb horn legally.Worst case is the engine stalls when you brake with the lights on....but engine should be seperate from lighting anyway.Get an XR wiring diagram and check it out.

Mr Motu sir! You're a genius! Now why didn't I think of the XR250? Same engine, even!

@Imdying: I see your point now. I wasn't thinking about the engine stalling -- that is a situation that I'd be on the road and the engine running. That's a good point.

@Vifferman: Yeah I'd love to lose the mirrors too -- both the originals and the borrowed spare ones I'm borrowing from GiJoe1313 (he won't take them back yet, lol) you can't see shite; and the vibrations from the thumper tend to make them pretty blurry at most RPMs.

@Ixion: Ah, thank-you -- I wondered about older bikes, but then I thought they might have some exception, like the 1978 indicator thing you mentioned (EDIT: I'm not pre-'78, just a little bit later than that). A squeezy-bulb horn would be a crackup! I'm having retro-café thoughts but I'm not sure I'd go that far back in time unless I had to...

As a side note, I love that shop -- Surplustronics it's called. Every time I walk past it I have to go in there, and end up walking out with so much useless crap. I got a couple of $5 barcode scanners once... lots of cool bits to scavenge. For the electronically-uninitiated, that shop is like walking into a bike wreckers -- so much cool decrepit stuff you want to buy but don't really need, lol.