going batteryless - capacitor size and voltage

[robocog]

I really want to ditch the battery on a bike I'm working on (CG125 with CDI ignition)

I have realised you can't just ditch the battery as it seems it causes havoc with the reg/rectifier and seemingly the worst case is bulbs blowing, a wonky sounding horn and indicators that don't

I know all is OK with the rest of the wiring as it all works flawlessly with a battery in place

Bike is kick start only so no need for a battery

Looked into fitting a capacitor but keep umming and ahing about size and safety margin voltage wise

I almost bid on a 1 farad DC cap designed for fitting into a car for audio amps - it went for £5 in the end, which would be a cheap solution...however
I have also read that when bought new these usually come with a resistor ~ to limit its initial charge as far as I can tell? (giving the impression that it may be unsafe to just plonk one uncharged across the bikes battery terminals?)

There must be some chaps on here that have used a capacitor in place of a battery on a bike?

What values did you use?
Was it sucesfull?
Do I need to be using a resistor to limit things (or is my reg/rectifier already doing this?)

Regards
Rob

[The Artist]

Why would you want rid of the battery?

I don't think a capacitor is the right thing for the job. If you really want to, something out of a windup torch or something albeit larger would do.

[baldy]

my xr has no battery and has a capacitor. It is no where near as big as one for a car. It's only about 2cm across and 4cm long.

I thought that capacitors were meant to store a large charge for a short time then dump it all at once?
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One day i will rule the world, just not today.

[Raffles]

Is your battery knackered and are you trying to save some pennies by not replacing it? Other than that I can't think of any reason to dispense with your battery. Please enlighten us.
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A good loser will always be a loser.

[temeluchus]

Provided the capacitor is enough to hold charge for the lighting and ignition whilst the engine (and alternator) runs, there is no real reason to have a battery on a kick start only bike.
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Some shite cruiser. Now with guns and FREEDOM!

[EnergyInducti...]

[robocog]

No reason to have a battery other than to keep the reg/rectifier happy as far as I can tell
Bike does run without a battery, its just not very good at taming the AC from the genny

I have a good battery for it, but really don't want to have it strapped to the bike and CBA to remake the seat in an attempt at hiding it up high in the pod

weight is the main reason, and nowhere out of sight to put one is a second
(doing a bit of a Colin Chapman excercise on it ...to add speed, add lightness etc)

Have lost a fair chunk of weight off it so far, and looking at the cheap or even free end of weight reduction if poss as its only being done for a laugh so not trying to break or set any records ..ok maybe I am trying to break through the 100 mpg gallon mark and still have a reliable bike that makes me giggle

battery was the next heaviest deadweight on the list and I know that some of the elder folk on here would possibly know what values and wiring requirements are - I believe they were quite common at one time
(though not sure if modern reg/rectifiers are more or less suitable these days?)

Do I need a 'zener and heat sink' to keep the cap at a safe voltage?
(or is this something the reg/rectifier does anyway? I would have thought the name regulator covers this? or am I jumping to unsafe conclusions?)

Do I need a resistor to limit current in and out- again is this something the reg/rectifier does? or does the original system rely on a battery's internal resistance?

Regards
Rob

[finpos]

It's possIble, but don't expect your IndIcators, horn etc to work at low revs. Battery Is just a bIg capacator, and mr. Honda wIll have chosen the smallest possIble functIonIng battery to fIt purely on cost.

F.

[sickpup]

[baldy]

I thought they did that to remove the load of the alternator from the engine as well as save weight?
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One day i will rule the world, just not today.

[Alexio]

[Robby]

From my GCSE and A level (shaky) understanding of capacitors, they take a while to charge and then discharge it all very quickly. I'm not sure if you can partially discharge one without clever electrics.

It seems that your reasoning for a capacitor is to protect the reg/rec and therefore protect the rest of your bike electrics, by having something in the circuit to soak up any spikes and give you some buffer. A resistor may do this.

However, have you ever ridden a bike with no battery on a dark night and braked for a corner? Your headlights go extremely dim. Your battery stops that happening.

Have a look for a very small, rechargeable 12v battery if you really want to save every last gram. I assume you have already fitted a light single seat and cut the frame back, removed the centre stand, ditched rear footpegs, ditched bodywork, drilled holes in things, fitted lightweight indicators, chopped down the front mudguard, ditched the mirrors and cut down the chain guard.

[robocog]

Robby - yup, its as if you have seen the bike by the description you just gave..lol
(apart from it not yet having a front mudguard and not drilled the chain side of the engine casings yet as I am unsure of what pattern to mill/drill)

Ref lights going dim at low RPM and using brakes -don't all CG's do that anyway?
(my other one does and would have thought a cap would improve matters as they are not "soaking up charge as well")

Can just pick the bike up off the floor with 1/2 a tank of fuel in and I'm an aged weakling, so its pretty light so far
I did collect a lot of the bits that got chopped off into a box and the weight of acumulated shards of metal and trim was quite impressive
I had to remake the bolt that holds the rear brake pedal in place, and forgot to drill a hole through it, bit late to stick it in the lathe now its welded in place...doh!

Theres still a few bits to bolt up to it yet namely
headlight
front mudguard- or the bare minimum that counts as one
and some method of attaching a number plate and rear lights
Hoping to have it done for the return of better weather
Most likely wont really get much use at night anyway, will only be a fun dry weather toy

I have a much smaller 12v alarm type sealed battery (7ah) that may fit under the seat pod out of sight without too much hassles, but again it does weigh quite a lot and unsure if these things are safe to use on their sides, which it may well have to be
(esp if the only mounting option is only seperated by a thin layer of fiberglass and my arse, the potential of picking shards of glass strand out of delicate parts is making me cautious about just hooking it up to see if its safe)

Still willing to just stick a big cap on it to see what happens if no one has the answer
I guess the worst that will happen is a big bang and shards of alloy case and paper get spewed out...must get an air filter before trying...lol

Regards
Rob

[smegballs]

[finpos]

Try again...

The battery is acts to both as a smooth the voltage in the charging circuit and as an energy store for when the bike is running at low or no revs. It is in fact just a huge capacitor with a very slow discharge time. If you put a proper capacitor there, you'll get the smoothing but very little of the storage.

You have two separate electrical circuits (in addition to the ignition...) on your CG. One is called direct lighting - not to be confused with DC current, which is the head and tail light running straight off the alternator and that's why it goes dim and brightens with revs. The other one runs off the battery and probably operates the horn, indicators and brake light.

If you replace the battery with a capacitor, you'll get the smoothing for the regulator but no appreciable storage. So when the bike is at low revs, the brake light, indicators and horn probably won't work well, much like the headlight. The reason these things run off the battery instead of direct lighting is because it's probably a good idea they should work while you are sat in the middle of the road on a dark night waiting to turn right.

No reason you can't use a maintenance free (i.e. sealed) battery upside down or any way you like.

f.

[finpos]

Stoopid double post.

[smegballs]

[Alexio]

[finpos]

PossIbly - the headlIght wIll run fIne off the larger battery that's fItted to power the starter motor on the newer ones. The battery on a kIckstart model won't be man enough for the job.

F.

[smegballs]

Did the older CG's come in 6V flavour?

If they were 6V models then I'm assuming they came with silly and gay half wave electrics!

[Raffles]

[The Shaggy D.A.]

Not sure where it came from, I think it was one of the Royal Enfield sites I'd visited, but here's the contents of a text file I had squirrelled away :-

[finpos]

[.]

Robocog,
If you have 12volt electrics, then speak to someone like boyer bransden about their powerbox. They probably have something suitable for your needs.
I have one and don't require a battery. The only downside is my bike stays running after switching off the engine as mine is connected directly to the coil. Either an ignition cut out switch, or a decompressor (which is what I have on my engine) is advisory.

[robocog]

Managed to scrouge some sealed 12v batteries from a mate who I mentioned my idea to.... and they are bigger and heavier that the CG's original

so back to the original plan...

Just ordered a 33,000uF 40v DC cap and will report back when it arrives

I guess it may not be as effective as the 50,000-mfd mentioned in The Shaggy D.A.'s post, but has a safer voltage safety margin?

Not sunk too much money into it and cost less that a good firework, so if it does go bang hopefully it will at least get captured on video and will make a good "how NOT to do it" for youtube

Looked at the Boyer units, bit too pricey for this project as it costs roughly what the bike has cost me in total so far!

Regards
Rob