More jumping batteries
 

I've thought of a way you might fry your bikes electronics while jumping the bike, and jumping it from a car could increase the chance of it happening. And figured it deserved a separate thread, as opposed to hijacking the other thread again.

There's 2 parts of this, couldn't tell you if effect is actually strong enough, unless you take what zed's seen working on bikes.

So if you take a long cable, it starts looking inductive, batteries look a bit like capacitors. Connecting the last cable up can spark, and that could cause come ringing, and could cause a voltage spike.

The other effect, is if you dump a lot of current through a long cable it'll create a magnetic field, and when the current drops, will collapse, making a voltage spike.

I also know that for instance cmos ic's, when an input or output is pulled to a higher voltage than supply can inject current into a parasitic scr, and if it turns on, will short the supply until power's removed or something burns out.

Now I suspect a fully charged motorcycle battery, would do the same thing, But it is working with 1/2-1/4th the current into a completely dead battery a car battery could provide.

Thank you.

no I am not an EE, have not "worked" in the field as long as some but have seen quite a bit working on everything from Polaris atv's to the big 4.

I did not claim to know the reason it happens, just knew it could.

some others pointed out in that other thread that something must have been wrong before jumping it which is basically what I was getting at. or there were parts used that were on the lower end of the tolerances. we don't know.

I just wanted to point out that there is a chance, no matter how small that you can fry a part of the system jumping it from a car battery. the last I looked at that other thread somone posted that they hooked up a lawnmower (I think) to a car battery and it spun up so fast it sounded like a jet. I thought he was trying to stir the pot some but do remember that happening to 50cc atv's when hooked to like a battery big enough to crank a bigger bike.

The lawn mower was probably 6V, if it was 12v, it'd spin the same, remember 12v's is 12v's. The other effects happen only when you first connect the second battery up and only for a fraction of a second.

That was me,:) 12V rider mower, usually cranked very slow and died in my driveway. I jumped it with my F-250 (not running) and it spun really fast, not literally like a jet, (though I have started those with 12V truck batteries as well).

I've heard some say that if you absolutely have to use your car/truck that you want to stop the motor but have the radio, air, bright lights, brakes, etc going to bring the voltage down.

First, to clear up any confusion, the thread was killed because of something else besides this topic. This topic wasn't what caused it to go away.

I will do some measurements on the inductance of a set of cables and study the electric fields through them, but I doubt I will find much. The standard cable is much too short for any of these to be a real factor. Just a quick guess in my head, the max spikes I could see would be in the milliamp/millivolt range. We are talking a few feet here. If we were running a cable 50 feet, I would might take a closer look into impact of the cable.

oh lord... here we go again :lol:

Cool, And most jumper cables are like 12' or longer, and my "concern" is for current spikes in the few hundred amps+, like you might get connecting an auto battery to a 2 or 3v dead cycle battery.

In cmos, there's a reverse biased diode between in/out pins and pwr/gnd. When I worked on this problem for Harris Semi we'd see problems when injecting 20-100ma into these scr's depending on the specific design. So if you started getting voltage spikes of anywhere between about .4v's and 1 volt you might have a possible cause for what zed's seen.

Oh, and don't forget when getting connected, jumper cables almost always spark, which does funny things with voltage.

BTW, if you consider the last connection as points, the jumpers as the inductor, and the battery as a sort of capacitor, the circuit starts looking a lot like a points ignition system.

Even if the cable were 20', I wouldn't put much hope into the inductance of the line playing a great effect in the circuit of this nature. I would look more to weaknesses in the circuit before I went this route.

An arc flash however, could expose a weakness in the insulation and act as a short.

I jumpez my biketh from mesa truck when its bee deader than dead

Seriously if my bike needs a quick jump because I forgot to pull the key when I left it last a car is easy and it's there. As long as the car isn't running you should be fine.