How much wattage can the alternator on a 125cc output roughly?

Just out of interest how much wattage can a standard 125cc engine output without blowing the electrics? I'd like to know as I have a lot of electrical accessories on my motorcycle such as LEDs, heated hand grips and a higher wattage bulb than stock and I'd be interested in knowing how much more my bike could take without damaging the electrical system. Does anyone know the answer or any way to calculate / test it?

It is not possible to give a good answer, if you idle the engine, the output is almost nothing, it drains the battery, if you are running it on a good rev, then it depend on what generates the electricity, and how efficient it is and what capacity it has. It varies with the bike and has nothing with the engine size to do. A good way of testing this is to use an artificial "load", which is a box with variable resistances inside connected to the battery. You increase the load and measure the voltage, normally, to keep a good battery charged, the voltage across the battery should be 13.6 Volt, if it drops below 12.5 you are draining the battery. A recommendation is to install a volt meter on the bike and an amp meter, you can them monitor the voltage and the charge or de-charge of the battery. You can add another larger external generator, or replace the original, but it is a bit messy. Typically a 125 cc engine produces about 25 HP, which is about 18,000 watts, or 18 1,000 watt light bulbs, but then there is no pover to move the bike. Unfortunately, by my own experience, the smaller 125cc does not have much excess electrical capacity but for the ordinary lights, the big cruisers are better. Another trick is to replace all light bulbs with LED lights. then you have more left over for the extras.

Thanks for the advice, I'll have to get me a multimeter and do some testing. Some how I don't think my engine produces 25hp, a 2 stroke 125cc might but mine is a 4 stroke. I'll probably take your advice and replace most of the bulbs with LED equivalents.

Typical spec: http://item.taobao.com/item.htm?id=10187522054

You can change to Δ from the original Y if u know what u're doing. "Cons" is no /low output at low rev.
http://www.procycle.us/info/articles...ta-stator.html
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A guy fitted a used "CBR250 MC19" stator on GN125 :thumbsup: http://www.motorfans.com.cn/bbs/t_16803658.htm

So it can output is roughly 150w? I thought that it would be more than that. So with my 55w headlight ,20w brake and tail lights, 10w indicators, LEDs, heated hand grips, dash lights and what ever the igniton consumes I don't really have a lot of room here.

Will I be able to fit a stator from a CBR250 to my bike without any modifactions to anything then? The translation dosen't really explain much.

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Originally Posted by spencer2004

Will I be able to fit a stator from a CBR250 to my bike without any modifactions to anything then? The translation dosen't really explain much...

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1st CBR250 stator is expensive in UK. 2nd CBR250 uses M6 bolt which means "mod" to fit existing M5 NEED .
Y to Δ (+40% in theory) & higher efficiency rectifier is more common mod in Chinese bike.
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The GN250 Y to Δ
http://translate.google.com/translat...8694486_d.html

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Originally Posted by spencer2004

Thanks for the advice, I'll have to get me a multimeter and do some testing. Some how I don't think my engine produces 25hp, a 2 stroke 125cc might but mine is a 4 stroke. I'll probably take your advice and replace most of the bulbs with LED equivalents.

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No - sorry, the "25" was taken a bit out of the air, it varies a lot. I have had this problem myself when I was running around with a lot of"gadgets" live on the bike, as a ham radio (100W transmission power ;-)). Another solution I have seen is a couple of solar panels, but it looks funny. Usually the flywheel and the generator are combines, but some bikes have a combined electric starter and generator. I have also seen people connect a generator to the back wheel. All kinds of solutions, but none really "elegant".

I'm my Haynes manual it says that the alternator rotor is attached to the left side case cover and it looks fairly simple to remove and replace, the only annoyance is that I'd have to drain the oil and get a new side gasket to do so. I think I've seen the CRB250 rotors on Taobao for around £16 but I would imagine that they are fairly heavy and the postage would be expensive but If I was to get one I suppose I could just tap the original m5 holes with a m6 tap. I thought that solar panels would be a really good idea at first as I could attach them to the top of my luggage box so they wouldn't look too bad but most of the energy goes into lighting which I only use at night so that's a no go :(

A small generator that is separate from the engine could be a better idea now that I think about it; there is some room inside my bike where the air box used to be which is directly above the drive chain so I could connect it to the chain using a small sprocket. If I was to do that would I be better off wiring it directly to the battery, the rectifier or it's own voltage rectifier?

It would be nice to have enough electrical power for a couple of 50w spot lights for unlit roads at night or to upgrade to a 100w headlight bulb just for the sake of it ;)

If buys from taobao, Search "CBR250" "线圈" for the stator, 1st choose is ALWAYS Guangdong seller. GD is the smuggled bike "hub".

Smuggled? You mean that everything he sells is nicked (stolen)?

Nicked / NOT road worthy (accidents/ emission ... ) that sold to "exporter" are the majority. Tax "FREE" NEW bike ordered from Hong Kong.
EVERYthing u can imagine that a "religious" guy won't touch are there :mwink:
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NOT only bike are smuggled in, these "monster" TOO. Keep left is the "correct" manner in some site.
http://www.tudou.com/programs/view/HnCVmSIk78w/

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Originally Posted by spencer2004

I'm my Haynes manual it says that the alternator rotor is attached to the left side case cover and it looks fairly simple to remove and replace, the only annoyance is that I'd have to drain the oil and get a new side gasket to do so. I think I've seen the CRB250 rotors on Taobao for around £16 but I would imagine that they are fairly heavy and the postage would be expensive but If I was to get one I suppose I could just tap the original m5 holes with a m6 tap. I thought that solar panels would be a really good idea at first as I could attach them to the top of my luggage box so they wouldn't look too bad but most of the energy goes into lighting which I only use at night so that's a no go :(

A small generator that is separate from the engine could be a better idea now that I think about it; there is some room inside my bike where the air box used to be which is directly above the drive chain so I could connect it to the chain using a small sprocket. If I was to do that would I be better off wiring it directly to the battery, the rectifier or it's own voltage rectifier?

It would be nice to have enough electrical power for a couple of 50w spot lights for unlit roads at night or to upgrade to a 100w headlight bulb just for the sake of it ;)

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If you attach a separate generator connected to the drive chain, you may need some gears, a planet gear for instance, in-between to get the right revolutions on the generator so it produces. The chain is pretty slow moving. Make sure you place a regulator between the generator and the battery, the battery should have 13.6 volt, and you can carefully increase that to 14, but at 14.5 about, the battery starts "boiling" and if it is a sealed gel battery it can explode. Not so nice.

Most bikes of that size, you may not have to drain the oil, there is often just a dry cover to expose the flywheel and generator, and you can adjust the contact breakers, unless the bike has electronic ignition.

I have a question:
Suppose the engine is 250cc, and i have the following extras:
1. Two HID kit 35wx2
2. 8pcs LED strip light Kit
3. Alarm
4. Two 3Amps Horns

Stock:
1. Two headlight but only one light per selected beam (55W)
2. Normal flat horns.
3. Battery 9AH

Will this affect battery and charging when running?

Nah that's fine; you're only slightly increasing the wattage drawn by the headlights, LEDs don't really use much power, the horn is going to be barely used and the alarm is only on when the engine is turned off. The battery acts as kind of a buffer so if you do start to draw more power then your alternator can generate (which you shouldn't with your current config) the battery will supply the extra power for as long as it holds charge.

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Originally Posted by Deom2i

I have a question:
Suppose the engine is 250cc, and i have the following extras:
1. Two HID kit 35wx2
2. 8pcs LED strip light Kit
3. Alarm
4. Two 3Amps Horns

Stock:
1. Two headlight but only one light per selected beam (55W)
2. Normal flat horns.
3. Battery 9AH

Will this affect battery and charging when running?

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It definitely will have some effect, but it depends how you are using all that, and how you drive the bike. Road use at higher speeds and revs give more charging. Usually an alarm does not use much, but of course, you are not using it when driving, the HID headlight is only used at night maybe (it is good safety thinking to use it always though), The use of the LED's are probably negligible (Each three LED's usually use 0.020 A), The HID lights use about 7 A, horns 6A, which means that if you stop the engine, leave the lights on and the horn blaring (don't try this in your neighborhood) your battery is flat after 40 minutes about, providing it is in best condition and fully charged at the beginning. It has nothing to do with your engine size at all, but with the amperage output from your generator at different revolutions. The manufacturer may have some info there, otherwise you can easily teat it out yourself. Remember too that the charging efficiency of a Lead acid battery is about 60% to 80%, that means that if your generator produces 10 Amp during one hour, only 60% of that ends up in the battery. Usually cruising bikes get larger generator capacity, as it is expected that people mount more electrical gear on them. Again, mounting a volt meter and ampereage meter vill give a lot of useful information.

Thanks guys for the information.
The added voltage will be around 20w extra from HID and for the LED strips which have total of around 86LED (86x0.02A)= approx 2Amps.
wattage is calculated by multiplying 12V or 13.4v?

As per your info it means the bike charging motor can supply enough power. :icon10:

I have another question, sorry it not based on the thread title but still deals with bike electricity.

My bike has two projector headlamps. Left for Low beam and Right for High beam, Bulb type H4 single. Each lights independently.
I want to add HID kit but i need two head light to be on when Low and High beam. If i use H4 H/L bulb it can work?

Now if i want only one to light on Low beam and two on high beam is this possible?
Im thinking on using H4 h/L for Low beam and single H4 H for high beam. Can i fool the system both both to work because low bulb has high bulb too?

H6m is also used in bikes and has same socket connection with H4 H/L, should i go with H6m?

Quote:

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Originally Posted by Deom2i

Thanks guys for the information.
The added voltage will be around 20w extra from HID and for the LED strips which have total of around 86LED (86x0.02A)= approx 2Amps.
wattage is calculated by multiplying 12V or 13.4v?

As per your info it means the bike charging motor can supply enough power. :icon10:

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The LED's work on about 3.5 Volt. so in the strips the use 3 in series and a resistor to pick up the difference, so the actual use is probably a third of what you mention. Watch too, sometimes one of those light "dots" that look like one LED can contain tree LED's, that means four "connectors" at the end of the strip, and sometimes those are of three different colors. The nominal wattage on most light bulbs are, or should be, measured at 12 V, so if you run them at 13.6 volt, usually the maximum for the battery, the electricity use increases, but it is not linear as the filament is hotter with less resistance as a result. The easy way to find out is by measuring. There is a +- 10% variation usually, Japanese light bulbs are more accurate while Chinese is the opposite.

Quote:

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Originally Posted by Deom2i

I have another question, sorry it not based on the thread title but still deals with bike electricity.

My bike has two projector headlamps. Left for Low beam and Right for High beam, Bulb type H4 single. Each lights independently.
I want to add HID kit but i need two head light to be on when Low and High beam. If i use H4 H/L bulb it can work?

Now if i want only one to light on Low beam and two on high beam is this possible?
Im thinking on using H4 h/L for Low beam and single H4 H for high beam. Can i fool the system both both to work because low bulb has high bulb too?

H6m is also used in bikes and has same socket connection with H4 H/L, should i go with H6m?

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That should not be a problem. Best is to leave all switches on the bike as they are, and use relays to achieve what you want. This is completely independent on what system you use, or combination of systems. It may need some clever physical re engineering of how the light bulbs are fitted though. You could also add manual extra switches to change the "behavior" of the bike lights.

I have a questions that isn't entirely related to this thread but I couldn't be bothered to make a new one; I'd like to wire a set of LEDs and some heated grips to the main relay so that they can only be turned on with the key in, will it be able to handle the extra load or will I need a seperate relay?

Quote:

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Originally Posted by spencer2004

I have a questions that isn't entirely related to this thread but I couldn't be bothered to make a new one; I'd like to wire a set of LEDs and some heated grips to the main relay so that they can only be turned on with the key in, will it be able to handle the extra load or will I need a seperate relay?

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I was thinking on doing the same...All device to turn on when key is position to on, except the remote which will be on all the time.
Its a nice question lets hear how expert will answer.

Are the relay universal or each is manufactured per specific function?
Thanks again for all your tips?

Quote:

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Originally Posted by Deom2i

I was thinking on doing the same...All device to turn on when key is position to on, except the remote which will be on all the time.
Its a nice question lets hear how expert will answer.

Are the relay universal or each is manufactured per specific function?
Thanks again for all your tips?

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The relays are universal and not specific to each bike, but can be of different quality and different electrical data. On a good quality bike it is significantly over dimensioned, so you can add various electrical stuff. The LED's is what you call a resistive load, like a light bulb. Capacitive loads (rarely exists on bikes) or inductive loads, as a coil, for instance in a horn or a starter motor, put significantly more load on the relay contacts.

I just thought of something; can't I just test this by using a multimeter on the battery terminals, reading the amps and volts then multiplying them together to get the wattage output?

Quote:

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Originally Posted by spencer2004

I just thought of something; can't I just test this by using a multimeter on the battery terminals, reading the amps and volts then multiplying them together to get the wattage output?

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Yes - but what you will be measuring is the actual wattage, effect, from the generator at just that moment, not the capacity of the generator. If you have a well charged battery, that will be less than the maximum. What you need is an artificial load, which is a variable resistor, you disconnect the bikes electrical system, give it a good rev, adjust the load/resistor so you have 12 volts, read the amps, and there you should have the max generator power. Repeat that by adjusting the resistor so you have 13.6 volt, that means the battery would be charged, and you have a practical max power if you want the battery charged.