Rethinking Jumper Cables

[Brad_C]

I have a set I made using 35mm2 double insulated super flexible solar cable. I've started 7L marine diesels with those. They are a whisker bigger than 2 AWG, about 14ft long and *heavy*. I can't imagine carting 4/0awg cables around, let alone using them.

Tinned copper is great in a marine environment. Luckily we don't ever see copper coated aluminium here.

As far as spikes go, the battery is an extremely low impedance sink and automotive electronics is all supposed to be protected against load dump ( immediate disconnection of the battery allowing voltage to rise north of 60V ). I've jumped plenty of cars including latest models and never had an issue. Not saying it's not possible, but I tend to think it is restricted to those early cars that had dicey electronics and little protection ( 80s Japanese cars and some early Delco electronics comes to mind ). A bank of MOVs sounds like a good idea. You'd need some pretty heavy TVS to get similar protection.

 

[Traction]

Originally Posted By: Brad_C
I have a set I made using 35mm2 double insulated super flexible solar cable. I've started 7L marine diesels with those. They are a whisker bigger than 2 AWG, about 14ft long and *heavy*. I can't imagine carting 4/0awg cables around, let alone using them.

Tinned copper is great in a marine environment. Luckily we don't ever see copper coated aluminium here.

As far as spikes go, the battery is an extremely low impedance sink and automotive electronics is all supposed to be protected against load dump ( immediate disconnection of the battery allowing voltage to rise north of 60V ). I've jumped plenty of cars including latest models and never had an issue. Not saying it's not possible, but I tend to think it is restricted to those early cars that had dicey electronics and little protection ( 80s Japanese cars and some early Delco electronics comes to mind ). A bank of MOVs sounds like a good idea. You'd need some pretty heavy TVS to get similar protection.

Still trying to figure out how you get 60 volts, or hundreds of volts previously stated out of a 12 volt battery? The utility companies would love that. Transformers do not work on DC, only AC. Current spikes would be another story. Simply just use good jumper cables, buy a new battery, or park on a hill.

 

[supton]

Originally Posted By: mjoekingz28
What about tinned copper?


What about it? Tinning won't help much, other than to slow copper corrosion. If the crimps (or other connection) to the wire was done with clean copper, and then the wiring is kept from getting wet, I don't see a need to resort to tinning. If anything, tinning then crimping (or bolting) will incur additional resistance, as tin is higher resistance than copper.

 

[supton]

Originally Posted By: Traction
Still trying to figure out how you get 60 volts, or hundreds of volts previously stated out of a 12 volt battery? The utility companies would love that. Transformers do not work on DC, only AC. Current spikes would be another story. Simply just use good jumper cables, buy a new battery, or park on a hill.


Comes from the alternator losing a stability component--the battery acts as a large capacitor, effectively swamping system response. Look up "load dump", that is the test done on auto electronics to ensure that if the battery is disconnected then whatever is being tested can withstand the 100V or so that is generated for (10? 100?) microseconds.

Parking on a hill would only be good if there was enough voltage in the battery to allow the ECU and fuel pump etc to run.

 

[eljefino]

Originally Posted By: supton


Parking on a hill would only be good if there was enough voltage in the battery to allow the ECU and fuel pump etc to run.


You only need enough to light off the field coil in the alternator, then the rest will come to life, on a "classic" 80's injected car.

Moderner stuff with anti-theft key doohickeys may well refuse to start completely. I postulate that turning the key to "start" while, or immediately before, popping the clutch might trick it into allowing the turning-over engine to catch and run.

 

[Shannow]

Originally Posted By: HerrStig
I suggest you read up on square waves. If thee is no inductance in a DC circuit then ignition coils (fed from the battery) would produce NO spark energy. A transformer, which is what a coil is, can work on a DC pulse, in the old days from a set of breaker points.


Yep, Fourier analysis of a square wave shows it's a whole lot of "AC" frequencies superimposed over the top of each other.

That initial spike is capable of strange things (that's mech engineer speak for what I don't understand intimately, but have seen)

Never had an issue with jumping anything. Have a set of leads with a ferrite choke...not saying I'm never going to have a problem, but not so far.

 

[JHZR2]

Originally Posted By: Traction
Originally Posted By: Brad_C
I have a set I made using 35mm2 double insulated super flexible solar cable. I've started 7L marine diesels with those. They are a whisker bigger than 2 AWG, about 14ft long and *heavy*. I can't imagine carting 4/0awg cables around, let alone using them.

Tinned copper is great in a marine environment. Luckily we don't ever see copper coated aluminium here.

As far as spikes go, the battery is an extremely low impedance sink and automotive electronics is all supposed to be protected against load dump ( immediate disconnection of the battery allowing voltage to rise north of 60V ). I've jumped plenty of cars including latest models and never had an issue. Not saying it's not possible, but I tend to think it is restricted to those early cars that had dicey electronics and little protection ( 80s Japanese cars and some early Delco electronics comes to mind ). A bank of MOVs sounds like a good idea. You'd need some pretty heavy TVS to get similar protection.

Still trying to figure out how you get 60 volts, or hundreds of volts previously stated out of a 12 volt battery? The utility companies would love that. Transformers do not work on DC, only AC. Current spikes would be another story. Simply just use good jumper cables, buy a new battery, or park on a hill.


High inductance and very rapid change in current. L*di/dt.

Still, testing batteries at 750 constant Amperes, I only see 3x voltage jump...

 

[supton]

Originally Posted By: Shannow
Have a set of leads with a ferrite choke...not saying I'm never going to have a problem, but not so far.


Where is the ferrite? Around both wires, one big doughnut? Not going to do much, not unless the bumpers were touching. Reason being, equal and opposite currents. Thus the ferrite is along for the ride--magnetic flux is zero in the choke. The fields cancel.

Now if you to put the ferrite around just one wire, or to use two separate ferrites, or a binocular core, then you'd increase the inductance of the wire. Which would IMO be good, as it might isolate the two vehicles from spikes.

However it doesn't do anything for the case presented by the OP: once one cable clamp is removed, the jumper cables are no longer part of the circuit. The donor car alternator could do a voltage jump due to load dump (but IMO the battery is going to absorb that nicely--no, I have no way to test).

 

[JHZR2]

Originally Posted By: supton
Originally Posted By: mjoekingz28
What about tinned copper?


What about it? Tinning won't help much, other than to slow copper corrosion. If the crimps (or other connection) to the wire was done with clean copper, and then the wiring is kept from getting wet, I don't see a need to resort to tinning. If anything, tinning then crimping (or bolting) will incur additional resistance, as tin is higher resistance than copper.


+1. Tin is good to prevent corrosion, but no other real need. Fortunately DC can use most all of the conductor, not just the skin. Tinning is an issue at high frequencies, but for DC, you dont want them (harmonics or otherwise) passing through anyway.

 

[Brad_C]

Originally Posted By: Traction

Still trying to figure out how you get 60 volts, or hundreds of volts previously stated out of a 12 volt battery? The utility companies would love that. Transformers do not work on DC, only AC. Current spikes would be another story. Simply just use good jumper cables, buy a new battery, or park on a hill.


I think you need to go back and re-read what I wrote. "Load dump" is what happens when the battery is *disconnected*. Hugely inductive stator in an alternator, nothing to clamp those inductive pulses because the battery is *gone*.

Now, take that in the context of the rest of what I wrote, in that all automotive electronics is supposed to be protected against load dump, and therefore good for anything that might be generated in a jump start scenario, and see how it fits together. I'm not disagreeing with what you are saying, in fact I agree with it completely. Load dump can be upwards of 60V for upwards of 400ms. That's not a small spike.

 

[George7941]

I don't think there is any issue at all here, for a number of reasons.

The jumper cable inductance is very low.

The battery is a huge sink and will dampen spikes.

Most importantly, modern alternators use avalanche diodes and will dump excess voltage.

 

[Garak]

Originally Posted By: JHZR2
Some examples:

Exactly. And, if the car's battery is depleted to the point it won't start, it's quite likely that the computers and everything else in the electrical system have been exposed to all kinds of maladies over the interim. Sure, "smart" cables might be a better option in some ways, but remember, we're dealing with emergencies. I don't expect to boost my car every day. Eventually, things will get far worse before they get better, if I'm doing something like that. Similarly, I don't try to hook my car to a tow truck daily. Something's going to get damaged. That doesn't make tow trucks obsolete or useless, either.

Of course, one has to be cautious with hybrids, as the article suggests. But, the manual will usually list a procedure, and it's there for a reason. And, as you mention elsewhere, there has to be some kind of failure testing done by OEMs. If this were a giant risk to vehicles, and their own bottom line, they'd say so.

The best defence is to not get in the situation in the first place by vigilance and maintenance. But, batteries can fail unexpectedly, alternators can give up the ghost with little warning, or other components can act up. Goss should spend some time in Saskatoon tonight with it being -30 C, in a car with a dead battery, for a couple hours. When someone shows up with old fashioned booster cables, he'll be writing him up for sainthood, not criticizing him in his next column.

 

[wrcsixeight]

If the jumper cables are thick, and one actually gets more than one clamp tooth making contact on the battery terminals....
I bet one could simply hook the donor vehicle to recipient vehicle, rev the engine to about 1100 rpm for a Minute or 5 sending 40 to 60 amps into recipient vehicle, then shut off donor vehicle.

Leave jumpers connected and crank recipient vehicle with donor vehicle off. It might even start without the cables connected. Depends on how depleted recipient vehicle battery is.

I've jumped A Diesel Bobcat without starting my engine, but the jumper cables were 00 gauge with parrot clamps making excellent connection.

The BobCat owner told me to start my engine, I said try it first without.

 

[Brad_C]

Originally Posted By: wrcsixeight
If the jumper cables are thick, and one actually gets more than one clamp tooth making contact on the battery terminals....
I bet one could simply hook the donor vehicle to recipient vehicle, rev the engine to about 1100 rpm for a Minute or 5 sending 40 to 60 amps into recipient vehicle, then shut off donor vehicle.

Leave jumpers connected and crank recipient vehicle with donor vehicle off. It might even start without the cables connected. Depends on how depleted recipient vehicle battery is.


This is the thing. If it's flat then a surface charge is usually enough. If it shagged then you need real jumper cables. If you have decent cables and the donor battery is big enough then you don't need the donor running at all.

The whole "have your car running" thing is to get the donor voltage up to compensate for [censored] cables while putting a surface charge on the dead unit. If the battery is sufficiently toast then you won't jump it ever with cheap thin cables.

 

[440Magnum]

Originally Posted By: Traction

Still trying to figure out how you get 60 volts, or hundreds of volts previously stated out of a 12 volt battery? The utility companies would love that. Transformers do not work on DC, only AC. Current spikes would be another story. Simply just use good jumper cables, buy a new battery, or park on a hill.



Same way you get 10s of thousands of volts out of a 12 volt ignition coil.

When you *interrupt* the flow of a current that has established a magnetic field due to the inductance of the conductor, you WILL get a higher voltage spike.

Now the issue I see is that a pair of jumper cables has just pico-henrys of inductance, no where near enough to produce a substantial voltage spike. That's why there's a coil in an ignition coil... to raise the inductance to a practical level so that when you interrupt it, you get a voltage spike. Plus the coil is wound as an auto-transformer, which multiplies the voltage spike on the primary by the turns ratio.

 

[JHZR2]

Originally Posted By: supton

Now if you to put the ferrite around just one wire, or to use two separate ferrites, or a binocular core, then you'd increase the inductance of the wire. Which would IMO be good, as it might isolate the two vehicles from spikes.

However it doesn't do anything for the case presented by the OP: once one cable clamp is removed, the jumper cables are no longer part of the circuit. The donor car alternator could do a voltage jump due to load dump (but IMO the battery is going to absorb that nicely--no, I have no way to test).


Why would more cable inductance be good? Its not, IMO. Ive observed this in testing high power cells at high current - short cable runs still produce 3x the nominal voltage... 20' cables would be even more...

Keeping inductance low is key, IMO/IMT.

Originally Posted By: 440Magnum


Now the issue I see is that a pair of jumper cables has just pico-henrys of inductance, no where near enough to produce a substantial voltage spike. That's why there's a coil in an ignition coil... to raise the inductance to a practical level so that when you interrupt it, you get a voltage spike. Plus the coil is wound as an auto-transformer, which multiplies the voltage spike on the primary by the turns ratio.



You sure? IIRC, the value provided by the reference I linked to in this thread (cable manufacturer) indicated ~0.8uH/ft. A 20' set of cables would be 40' of cable length... So more like 32 uH.

 

[rustypigeon]

Originally Posted By: bioburner

I just seen cable set 4 gauge copper, 20ft for $20 at Walmart


At that price I can guarantee that they were copper clad aluminum.

 

[rustypigeon]

I recently made a couple sets of jumper cables out of welding cable. I made a 15ft set with 4AWG cable and a 20ft set with 2AWG cable.

With the heavier 100% copper cables, it gives you the ability to start most cars with the donor vehicle off. This should eliminate any chance that the donor vehicle will be damaged during the jump start. There is a possibility of draining the donor vehicle to the point that it won't start, but if you keep them hooked together for only a short amount of time, you should be ok.

I tested my 15ft 4AWG welding cable jumpers by starting my truck with all current from the battery going through the cables. I disconnected the battery cables from the truck, and used the welding cables to connect the battery posts to the vehicles battery connectors. The cables allowed enough current to start my 4 cylinder truck on a cool 35F winter morning.

-If I am home and have the time, I will use my battery charger to charge the battery.
-If I am home and in a hurry, I will use my JNC660 jump pack to start the car.
-If I am away from home, I will use my jumper cables. I keep a set in each car.

Here are the cables I recently made out of welding cable. The #4 15ft set cost me $51 ($31 for wire $20 for 4 clamps). The #2 20ft set cost me $65 ($45 for wire, $20 for 4 clamps). If you were to try to buy a commercially produced 20ft #2 all copper wire set, you would spend about $130.

 

[JHZR2]

The best all copper parrot clamps cost nearly $70 for all four by themselves!!

 

[BalticBob]

Once I was helping jump start a vehicle, the owner had small gauge cables, they were not working. I also had small diameter cables, but we paralled them, and it worked quite well.
After that event, I purchased some large gauge cables.