Jumping your battery...

[Midge]

So now even thou ive done this a couple of times i know i shouldnt and guess this maybe one of the reasons my battery has failed but i dont understand it and would like to know if anyone has knowledge into it.

Is jumping a bike off a car battery a bad idea? Why?

Now im sure it is logic to me says i shouldnt because of the battery size difference but WHY and WHAT damage does it do and WHAT is the best method to jump a bike if run flat?

Cheers

[neels]

Can't see why you shouldn't, the battery is probably dead because bike batteries just don't seem to live for very long, it's unlikely that jumping from a bigger battery will kill a smaller battery.

[CookMySock]

You should be fine doing that. Don't start the car though, because the car alternator could put out a higher voltage than the bike regulator is set to, and the bike regulator could just shunt it all hard to ground.

Though thinking about it some more, it seems to me the shunt SCRs are on the stator side of the rectifier diodes, so even if the regulator did close it's SCRs there is no current path from the battery back to the SCRs.

Steve

[Rogue Rider]

Likewise, I have done it heaps in the past, just don't do it whenthe car is running. I use a jump pack too, cuctom made from a mini battery and some hohepa leads I made. It fits where my tool kit goes, just in case. Have save a few bikes on travels too.

[Max Preload]

If you're not using your bike much it's much better for your battery life to get a small charge & maintain battery charger and leave your bike hooked up to it when not in use. Get a fitting put on so you just plug it in.

[pete376403]

Size is irrelevant. Voltage and polarity are the only things to worry about. For safetys sake (ie there is no electrical reason) and assuming negative earth -just about everything these days - attach to positive at both ends first. Reason: if you attach the neg leads first, and then accidentally touch the positive lead to any metal of the car or bike - sparks and damage will occur. Positive on the terminals of both batteries terms first, and if you do accidentally drop the neg lead on car or bike metal - you're still safe.
Other obvious things - positive to positive (and neg to neg), also don't crank the bike for long periods just because the car battery has the capacity to allow it - starter motors get hot

[pete376403]

You should be fine doing that. Don't start the car though, because the car alternator could put out a higher voltage than the bike regulator is set to, and the bike regulator could just shunt it all hard to ground.

Though thinking about it some more, it seems to me the shunt SCRs are on the stator side of the rectifier diodes, so even if the regulator did close it's SCRs there is no current path from the battery back to the SCRs.

Steve

err, if you are connecting to the battery of the car, the voltage has already been regulated to 13 ~ 14v, regardless of what the alternator puts out.

[CookMySock]

err, if you are connecting to the battery of the car, the voltage has already been regulated to 13 ~ 14v, regardless of what the alternator puts out.

Agreed, but it is possible the regulator in the car is set ever so slightly higher than the regulator on the bike. You only need 0.5V difference in a low impedance circuit and huge currents can flow - large enough to fry the bike regulator.

I haven't done it myself, but I was warned of it. As I said in the previous post, it seems that the shunt SCRs are on the stator side of the rectifier diodes, so even if the regulator did close it's SCRs there is no current path from the battery back to the SCRs. So I wonder if the situation is even feasible.

Steve

[Pixie]

So now even thou ive done this a couple of times i know i shouldnt and guess this maybe one of the reasons my battery has failed but i dont understand it and would like to know if anyone has knowledge into it.

Is jumping a bike off a car battery a bad idea? Why?




Now im sure it is logic to me says i shouldnt because of the battery size difference but WHY and WHAT damage does it do and WHAT is the best method to jump a bike if run flat?

Cheers

Jumping your battery...

NEVER EVER DO THIS!!!

An acid disfigured penis is not worth whatever warped fleeting pleasure you may derive from this activity.

get a girl friend

[Midge]

Oh ok thanks guys i was told once i shouldnt do it and that it did reck your battery. I guess i was ok to do it all this time. how long would you suggest a battery would last for? couple years?

[quickbuck]

Oh ok thanks guys i was told once i shouldnt do it and that it did reck your battery. I guess i was ok to do it all this time. how long would you suggest a battery would last for? couple years?

That is a bit of a "How long is a piece of string" question.

A Top of the line battery will last a very long time, like well over 6 years if it is looked after. As in, never allowed to run flat, or sit flat.

A cheap battery will die within a winter if you leave your bike sitting the whole time, and then expect it to start come spring....

So, best idea is if you have a cheap battery and hardly use your bike, then get a battery tender.
If you ride all the time, a cheap battery will do, but for piece of mind, and reliability, buy a top of the line battery.
It will last years, and pay for itself a few times over....

Now, if it was an expensive battery that went flat, and you know the reason (like left your key on too long without engine running), it's performance will be compromised, but I wouldn't worry until the bike becomes a little difficult to start....

Hope this helps.

[davereid]

You should be fine doing that. Don't start the car though, because the car alternator could put out a higher voltage than the bike regulator is set to, and the bike regulator could just shunt it all hard to ground.

Good point Steve. Many motorcycles have a simple shunt regulator, that converts excess alternator output to heat. Some utilise good old fashioned bipolar transistors, and are in circuit all the time, even when the key is off. Thats why putting a big battery charger on your bike without disconnecting the battery from the loom will often cause regulator and / or battery charger failure !

Running the car, will cause the bike to be exposed to the full voltage of the cars electrical system. It may be lower than the bikes regulator, but there is no way of being sure - why risk a regulator finding out ?

As others have pointed out, battery voltage and polarity must be correct, battery size is much less important. Don't crank too long, and once started allows a short period before unhooking the jumper leads. This avoids nasty voltage spikes if the motorcycle battery is deeply discharged.

[CookMySock]

Many motorcycles have a simple shunt regulator, that converts excess alternator output to heat. Some utilise good old fashioned bipolar transistors, and are in circuit all the time, even when the key is off.

The SCR one shouldn't be vulnerable.



Notice with the full-wave bridge rectifier, there is no path for current to flow from the 12V battery back towards the regulator SCRs. The diodes are reverse biased.

Steve

[davereid]

The SCRs in the circuit are safe.

But the control transistor, and zener diode are exposed to the car system voltage.

In normal operation they are protected, as excessive voltage will cause the zener to conduct, switching on the SCRs and reducing system voltage.

But when jump starting, turning on the SCRs will not reduce system voltage - the switching transistor and zener will have to cope with potentially excessive voltage the entire time the car is attached.

They may, or may not be up to the job ! Much easier to leave the car OFF, you will still start your bike just fine.

[CeeBee]

The correct method to jump starting cars / motorbikes is this, Ensure the vehicles are not touching, connect RED to RED (+ve to +ve), now this is the difference to what most of you do and that is connect the BLACK (-ve) on the best battery (In the vehicle doing the jump starting) then the LAST connection is NOT to your battery -ve BUT to a good earth point AWAY from the battery, this safe action prevents two things to which I have seen. An exploding battery and a cooked CPU on EFI bikes / cars. When the engine starts this cable connection is the FIRST to be released.