1977 "garage find"

[gggGary]

Well, no I'm not wrong. Just because you've always done something doesn't mean its right. Wire size, component heat dissipation, component load are all based on amperage calculations. Not Voltage. Car/truck systems are built to handle WAY more amp load than a motorcycle. You wouldn't use 14-2 for a 30amp circuit in your house would you? I don't know maybe you would, I wouldn't. I also wouldn't use 750CCA battery normally used with 00 cables on a motorcycle of unknown condition that was only designed to run a max of roughly 210CCA @1.4A constant load with 8g cables. I only use cable size as an example, but NOTHING in these 37-52 year old motorcycles was designed to handle the amps of a modern car or truck. And yes I realize the guys start their bikes with car batteries occasionally and usually nothing goes wrong, but I would not encourage anyone of unknown skill level to do it bikes of unknown condition as it could cause problems that otherwise could have been avoided. For those of you who seem to be under the impression that amperage is irrelevant, I challenge you to swap the + battery cable in your car/truck with one the same size as the one on your XS (8awg) and see how long it lasts. Or better yet, if amperage doesn't matter go put a 14awg cord on your dryer.

Also, kero is not cheaper option for everyone. Its near impossible to even get NO1 kero in large swaths of the US and where you can get it, it's $13 dollars a gallon at the big box store.

Well maybe but since we are discussing using a battery from a vehical that runs (we'll assume a working charging system) that units battery will be charged And even a stock battery after a bit of cranking will have the XS charging system going as hard as it can for a while. Thing is no matter how big the battery is the XS will only put out it's meager what? 100 watts of net charging. So the small motorcycle cables will deal with that just fine. Lawn tractor or other small equipment battery also good jump candidates. Always good idea to use a battery charger to assure it's in top shape first.
PS I like the old mechanics way of thinking. I've given a near identical speech many times.
IE look a gift horse in the mouth before you start spending lots of dough on it.

 

[Bumblebee]

I've often heard people say that you should never jump a motorcycle with a car but I've never really understood why. Some random rumblings about amperage this and capacity that. Nobody ever seemed sure what horrors would ensue, just that you shouldn't do it.
I can see it would be best to disconnect the jumper cables quickly, no sense in letting the bike charge the car battery for too long. In those few seconds the bike alternator would be putting out its max amperage.
I don't see how that would be catastrophic as, it is designed to put out its max. Just like if the bike had a problem and you cranked a lot before it started. For a few minutes, the alternator is gonna max out until the battery is recharged.
Am I missing something?
The starter will only draw what it needs and the alternator will only output what it can. Where is the harm in jump starting from a car?

 

[DaveO]

A device on the bike (or anywhere) that operates at 36W when attached to a 12V source draws 3amps in current.

Watts = Volts * Amps , 36 = 12 * 4

using Ohms law

or

We can calculate the resistance of the device.

r = 12/4 = 3 ohms.

This is fixed (it varies by temperature, so in a bulb it will change as the bulb starts to operate).

But it means that a device will only draw as much current as it is designed to handle. This is regardless of the potential of the supply to provide higher currents. I don't, for example, worry whether my electric lights are attached to a generator or a nuclear power station.)

The example of swapping battery leads is a red herring. A truck's lead and fuses are designed to handle the total current draw for a truck with air horns, ancillary lights, air conditioning, stereo, CB radio and refrigeration of the cargo. An XS has lights and a starter. The wiring, fuses and battery leads on an XS are designed to handle this current draw. Thats why it has one 20amp fuse.

DaveO

 

[gggGary]

The bad thing is jumping into a badly discharged motorcycle battery. IF that bad battery will accept any charge it could get severely overheated by a big amperage feed. Remove the dead battery from the bike, use only the jumps power. As such things go it gets conflated with using any large battery as a "testing power source".
Use some caution when jumping a from a large battery into an electrical system of unknown condition. A hidden short could make for lots of smoke with a large battery able to dump in some serious amps. If you see big sparks (or wisps of smoke!) when attaching your jumpers, suspect you have some electrical issues, remove jumper and trouble shoot.

 

[Jan_P]

Dont know much about cars but I do know that jump starting a car from another car .there is a procedure how to do it
What to connect first and disconnect first. This I believe is for protecting the electronic in the cars

Now if I was going to use another battery fex a car battery I would disconnect it from the car or other vehicle if possible
And then be careful hooking it up.
Mainly because there can be unknown problems in an old bike .. Should there be a short circuit on he bike the CAR battery can be shorted between + and -
That is not good and you will notice it the hard way.

As Gary says above.

 

[RustiePyles]

I've often heard people say that you should never jump a motorcycle with a car but I've never really understood why. Some random rumblings about amperage this and capacity that. Nobody ever seemed sure what horrors would ensue, just that you shouldn't do it.
I can see it would be best to disconnect the jumper cables quickly, no sense in letting the bike charge the car battery for too long. In those few seconds the bike alternator would be putting out its max amperage.
I don't see how that would be catastrophic as, it is designed to put out its max. Just like if the bike had a problem and you cranked a lot before it started. For a few minutes, the alternator is gonna max out until the battery is recharged.
Am I missing something?
The starter will only draw what it needs and the alternator will only output what it can. Where is the harm in jump starting from a car?

No, the starter does not "only draw what it needs" thats why it turns the motor faster the more amps you push to it. All the systems will use the amperage they are supplied with and if that amperage exceeds what the system was designed to handle it manifests in heat. When you exceed the amount of heat a system was designed to dissipate the components fail. In modern motorcycles with electronic and digital components this can result in immediate failure. In motorcycles with all solid state components its a roll of the dice where failure will be based on the state of the component. When I worked as a full time motorcycle mechanic at HD I lost count of the number of ignition modules I had to replace due to over amping from jump starting with car batteries. While points XS's are far less susceptible to failure from a brief amp spike from a large battery. TCI XS's with old all ready degrading TCI boxes are VERY susceptible to failure by heat a from huge amp spike from a car/truck battery. And lets not forget some of the aftermarket iggys used on XS that are made from super cheap Chinese components that can barley handle the amperage/heat produced by the bikes all ready weak battery, a blast from your Duramax's battery will fry those instantly.

Will a car battery start your bike? Yes
Is there a 100% chance it will damage it? No, not on an older bike.
But I mean its not like XS's are known for buggy charging and ignition systems. So by all means slam a bunch of amps through a bunch of 30+ year old components that you are completely unaware of the condition.

 

[Bumblebee]

No, the starter does not "only draw what it needs" thats why it runs faster the more amps you push to it. All the systems will use the amperage they are supplied with and if that amperage exceeds what the system was designed to handle it manifests in heat. When you exceed the amount heat a system was designed to dissipate the components fail. In modern motorcycles with electronic and digital components this can result in immediate failure. In motorcycles with all solid state components its a roll of the dice where failure will be based on the state of the component. When I worked as a full time motorcycle mechanic at HD I lost count of the number of ignition modules I had to replace due to over amping from jump starting with car batteries. While points XS's are far less susceptible to failure from a brief amp spike from a large battery. TCI XS's with old all ready degrading TCI boxes are VERY susceptible to failure by heat from huge amp spike from a car/truck battery. And lets not forget some of the aftermarket iggys used on XS that are made from super cheap Chinese components that can barley handle the amperage/heat produced by the bikes all ready weak battery, a blast from your Duramax's battery will fry those instantly.

Will a car battery start your bike? Yes
Is there a 100% chance it will damage it? No, not on an older bike.
But I mean its not like XS's are known for buggy charging and ignition systems. So by all means slam a bunch of amps through a bunch of 30+ year old components that you are completely unaware of the condition.

It seems to be annoying you that I'm asking questions about your thoughts on this. I'm not gonna discuss it with you any further.

 

[RustiePyles]

It seems to be annoying you that I'm asking questions about your thoughts on this. I'm not gonna discuss it with you any further.

Not at all annoyed, If I offended you I apologize. That was not my intention.

 

[Bumblebee]

Some of what you said is correct, some of it is not quite correct. When you defend all of what you said with a sarcastic, "By all means, slam a bunch of amps through 30+ year old components..." that's not helpful.

 

[Old RT3 Guy]

No, the starter does not "only draw what it needs" thats why it turns the motor faster the more amps you push to it. All the systems will use the amperage they are supplied with and if that amperage exceeds what the system was designed to handle it manifests in heat. When you exceed the amount heat a system was designed to dissipate the components fail. In modern motorcycles with electronic and digital components this can result in immediate failure. In motorcycles with all solid state components its a roll of the dice where failure will be based on the state of the component. When I worked as a full time motorcycle mechanic at HD I lost count of the number of ignition modules I had to replace due to over amping from jump starting with car batteries. While points XS's are far less susceptible to failure from a brief amp spike from a large battery. TCI XS's with old all ready degrading TCI boxes are VERY susceptible to failure by heat from huge amp spike from a car/truck battery. And lets not forget some of the aftermarket iggys used on XS that are made from super cheap Chinese components that can barley handle the amperage/heat produced by the bikes all ready weak battery, a blast from your Duramax's battery will fry those instantly.

Will a car battery start your bike? Yes
Is there a 100% chance it will damage it? No, not on an older bike.
But I mean its not like XS's are known for buggy charging and ignition systems. So by all means slam a bunch of amps through a bunch of 30+ year old components that you are completely unaware of the condition.

Excellent explanation of a normally confusing topic.

 

[gggGary]

No, the starter does not "only draw what it needs" thats why it turns the motor faster the more amps you push to it. All the systems will use the amperage they are supplied with and if that amperage exceeds what the system was designed to handle it manifests in heat. When you exceed the amount heat a system was designed to dissipate the components fail. In modern motorcycles with electronic and digital components this can result in immediate failure. In motorcycles with all solid state components its a roll of the dice where failure will be based on the state of the component. When I worked as a full time motorcycle mechanic at HD I lost count of the number of ignition modules I had to replace due to over amping from jump starting with car batteries. While points XS's are far less susceptible to failure from a brief amp spike from a large battery. TCI XS's with old all ready degrading TCI boxes are VERY susceptible to failure by heat from huge amp spike from a car/truck battery. And lets not forget some of the aftermarket iggys used on XS that are made from super cheap Chinese components that can barley handle the amperage/heat produced by the bikes all ready weak battery, a blast from your Duramax's battery will fry those instantly.

Will a car battery start your bike? Yes
Is there a 100% chance it will damage it? No, not on an older bike.
But I mean its not like XS's are known for buggy charging and ignition systems. So by all means slam a bunch of amps through a bunch of 30+ year old components that you are completely unaware of the condition.

Yes it does? BUT it may "need" more than the motorycle system can provide. IE under heavy draw through thin cables voltage will drop, the starter will not be at optimum performance. But supplied by a big 12 volt battery and cables it will operate at design speed, NO MORE.

A device on the bike (or anywhere) that operates at 36W when attached to a 12V source draws 3amps in current.

Watts = Volts * Amps , 36 = 12 * 4

using Ohms law

View attachment 210268
or

View attachment 210267

We can calculate the resistance of the device.

r = 12/4 = 3 ohms.

This is fixed (it varies by temperature, so in a bulb it will change as the bulb starts to operate).

But it means that a device will only draw as much current as it is designed to handle. This is regardless of the potential of the supply to provide higher currents. I don't, for example, worry whether my electric lights are attached to a generator or a nuclear power station.)

The example of swapping battery leads is a red herring. A truck's lead and fuses are designed to handle the total current draw for a truck with air horns, ancillary lights, air conditioning, stereo, CB radio and refrigeration of the cargo. An XS has lights and a starter. The wiring, fuses and battery leads on an XS are designed to handle this current draw. Thats why it has one 20amp fuse.

DaveO

Exactly.
An old mechanics "trick" when approaching a bike with a discharged battery with jumpers is to use a current limiter in the circuit to get the bike battery up to at least 12 volts before using straight on jumper cables. an easy "current limiter" is a 12 volt light bulb in series. conveniently it will show the relative current flow by it's brightness.
Any experiences based on a bunch of Harley riders attempting emergency road side repairs may be a bit, ahem, biased, ;^).

 

[DaveO]

No, the starter does not "only draw what it needs" thats why it turns the motor faster the more amps you push to it.

The "push" is provided by the voltage, which 12V in both cases. The same push into the same component the same current.

"Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential between two points, which (in a static electric field) is defined as the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage (potential difference) is named volt. In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule (of work) per 1 coulomb (of charge)."

It may be that in your experience, @RustiePyles , bikes came into shop with damaged components after being jump started from a car. I can only surmise that a running car's charging system provides a range of voltage. I honestly don't know but I've said in my original post that I would use only the battery, not a running car. I would defer to someone who knows.

It could also be that the faults are unrelated to the attempts to start it from a car. Correlation is not causation. Here are some other things that correlate.

http://www.tylervigen.com/spurious-correlations

Dave

 

[RustiePyles]

Yes it does? BUT it may "need" more than the motorcycle system can provide.

Yes any DC motor will run at the same speed at a given voltage regardless of the amperage applied... Under zero load. No starter runs under zero load, therefor the starter will turn the motor faster the more amperage applied until it reaches its max operating rpm at that specified Vdc, which it was not designed to under a load . My whole point was that its unwise try and operate a system of unknow condition under parameters that exceed its normal operating amperage. As capacitors degrade they can increase in impedance, as resistors degrade they can increase impedance, as coils degrade they can increase impedance, dirty contacts and switches have increased impedance. If you don't know the condition of all of the components in a system it's not a great idea to double or tripple the amperage that the system was deigned to operate at especially if you don't even own the bike.

 

[BluzPlayer]

Hmmm.
Just a little out of my element on this question.
However I have an enquiring mind and unfortunately did not stay at a Holiday inn last night soo...
I most definitely understand what @RustiePyles is saying in regards to current. However my understanding is that you need a component to draw those amps. The dryer doesn't draw the entire 30 amps even though it is available. The draw of amperage is dependent upon the component(s) in the circuit, not the amperage that is available.
There are no components on the xs650 that will make those kinds of demands from a large cca battery. It is the voltage that is the critical aspect.
In each example Rustie gave as a dare to try; the suggestion involved placing a wire smaller than the demanding component required. That is the issue. That would indeed be a problem. The wiring must be suitable or GREATER than required for the demand. The supply (amperage) must be suitable or GREATER than the demand requires. That is my understanding. I'm not an electrician but my brother is. I did have years of training in electronics in the Air Force not that any of that matters. So if anybody can put my enquiring mind to rest please do so.

 

[Raymond]

We seem to have moved away from helping TomMead resurrect his garage find 1977 XS? I think the main points so far are, take a good look at what you have, have a good think about what you want to do with it, do some prep such as bunging some oil down the bores, turn the motor over slowly ie using the kickstart, possibly squirt additional oil in at the valve gear, and see if the bike will run before spending money on it.

 

[5twins]

I may hook a battery up and turn the key on just to see if power is flowing on a new-to-me bike, but I like to go through ALL the wiring before attempting a start. I'll inspect and clean/rebuild the carbs as well (usually needed). On my '83, I found the two big plugs next to the battery box for the ignition unit and reg/rec badly corroded. I'm guessing battery acid or acid fumes had gotten to them. I actually had to replace a few of the crimps in the plugs as they were practically rotted away. After doing all that, I was rewarded with a bike that started right up with 2 or 3 kicks after sitting like a dozen years.

 

[Bumblebee]

I think it's important to consider the difference between electrical and electronic components.
Motors, incandescent light bulbs and old school mechanical switches are electrical.
Resistors, capacitors, diodes and generally solid state circuits are electronic. Some electronic circuits are sensitive to voltage and amperage variations. To many amps and poof, the smoke is released.
Light bulbs and motors will use only the amperage they need. If unlimited amps are available, the bulb doesn't get brighter, the motor doesn't spin faster.
The problem then becomes the load. With increased load (on a motor, for example) the amperage demand gets higher. With unlimited availability, the motor can overheat, if the load is high enough.

When jump starting a motorcycle from a car battery, effectively we are applying unlimited amperage. If there are short circuits, bad electronics, bad wiring or the engine is frozen (causing high amperage draw) then things can be damaged.
On the other hand, if the problem is just a low battery (the most common reason for a jump start) then only the low battery is a concern. It can draw high amperage and possibly overheat.

If while attaching the jumper cables there are large sparks and crackling noises, then jump starting is a bad idea from ANY source.
Bottom line is, amps don't get pushed in electrical circuits, they are drawn by components in the circuit. The quantity of supply isn't an issue, unless other things are wrong with the system.

 

[Bumblebee]

+1 on getting back to topic.
Be sparing on oil in the cylinders. Too much could cause a liquid lock and bend connecting rods.

 

[DaveO]

We seem to have moved away from helping TomMead resurrect his garage find 1977 XS? I think the main points so far are, take a good look at what you have, have a good think about what you want to do with it, do some prep such as bunging some oil down the bores, turn the motor over slowly ie using the kickstart, possibly squirt additional oil in at the valve gear, and see if the bike will run before spending money on it.

Sorry @RustiePyles. Sorry @Raymond Sorry @TomMead.

 

[RustiePyles]

Sorry @RustiePyles. Sorry @Raymond Sorry @TomMead.


View attachment 210292

@DaveO no need to apologize for being technically right.