The purpose of anti-surge protection on jumper cables

[MikeMl]

I find it hard to believe that the surge protector (connected somewhere down the cable) has a lower impedance/inductance to a spike than the donor car's battery to which the suppressor is connected.

I find it even harder to believe that if a $0.30 surge protector would help protect $2000.00 of car electronics, it wouldn't be installed in every car...

 

[dknguyen]

I find it hard to believe that the surge protector (connected somewhere down the cable) has a lower impedance/inductance to a spike than the donor car's battery to which the suppressor is connected.

The supressor is on both ends of the cable isn't it?

I find it even harder to believe that if a $0.30 surge protector would help protect $2000.00 of car electronics, it wouldn't be installed in every car...

I can. Saves money and you only make money in repairs if someone messes up a boost. Not too many people boost anyways so it never becomes common enough to cause outrage.

 

[crutschow]

The supressor is on both ends of the cable isn't it?

It looks like there's one in the middle of the cable shown in post #4.

 

[dknguyen]

It looks like there's one in the middle of the cable shown in post #4.

Oh yeah, that's less than ideal. These ones have one at both ends:
http://www.omatitalia.com/product-category/surge-protection-booster-cables/?lang=en

But I think it's more likely that the one in #4 is like this one here:
http://www.supercheapauto.com.au/Product/SCA-12V-Jumper-Leads-400Amp-3m/296683

There's only one supressor but it's at one end of the cable, giving the cable an explicit end that must be on the donor car.

 

[crutschow]

There's only one supressor but it's at one end of the cable, giving the cable an explicit end that must be on the donor car.

Still doubt that it will suppress transients better than the donor battery.

 

[dknguyen]

Still doubt that is will suppress transients better than the donor battery.

Maybe, but does anyone here actually know what the internal impedance, not internal resistance, of a lead-acid battery actually is compared to a TVS or MOV?

 

[crutschow]

Here's an article, that discusses some impedance measurements of various lead-acid batteries.
Some of the results are below:

It shows an impedance in the low milliohm region over the tested frequency range, which I expect is much lower than the cheap surge suppressors they likely use in those cables.
Even expensive ones are likely higher than that.

But if you want to pay for those snake oil suppressors, you are welcome to.

 

[dknguyen]

Here's an article, that discusses some impedance measurements of various lead-acid batteries.
Some of the results are below:

View attachment 111250

It shows an impedance in the low milliohm region over the tested frequency range, which I expect is much lower than the cheap surge suppressors they likely use in those cables.
Even expensive ones are likely higher than that.

But if you want to pay for those snake oil suppressors, you are welcome to.

That's the log of the millohms. So it seems to be under 1 mohm up to about 100kHz. However, the graphs do end at 100kHz and the impedance is shown to be continuously rising after that point. A TVS is around 0.5ohms and we know that they are fast enough and low impedance enough to handle ESD strikes which are much faster than 100kHz (but obviously the cable reduces effectiveness). I have no idea what the rise time of an alternator spike might be.

Obviously the battery is providing some protection since a lot of boosts don't seem to cause damage. But then what about those that do? Does it all boil down to being so confident that there is zero chance of a few thousand dollars worth of damage happening that you won't spend an extra $5?

 

[crutschow]

Does it all boil down to being so confident that there is zero chance of a few thousand dollars worth of damage happening that you won't spend an extra $5?

I suppose so. There are a lot of tradeoffs in this world and that's one of them.
But are the jumper cables with this "surge protector" really only $5 more than ones without?

 

[dknguyen]

Here's an article, that discusses some impedance measurements of various lead-acid batteries.
Some of the results are below:

View attachment 111250

It shows an impedance in the low milliohm region over the tested frequency range, which I expect is much lower than the cheap surge suppressors they likely use in those cables.
Even expensive ones are likely higher than that.

But if you want to pay for those snake oil suppressors, you are welcome to.

I suppose so. There are a lot of tradeoffs in this world and that's one of them.
But are the jumper cables with this "surge protector" really only $5 more than ones without?

tbh, booster cables vary so wildly in price sometimes they're cheaper and sometimes not. I think the wire itself plays more role in the price than anything else. It's hard to find a fair comparison. You can even get auto-polarity cables.

 

[Diver300]

Load dump isn't directly caused by the inductance of the power windings. It's caused by the field winding inductance preventing the excitation from being reduced quickly.

Load dump won't happen if there is a battery connected that isn't completely dead, as the battery will accept the current generated by the alternator without there being a big voltage surge. It's only for half a second or so until the field winding current reduces.

All car electrical system are noisy, so a lot of effort goes into suppressing spikes. Some alternators have central load dumps suppression built in, which limits the voltage, but it is still quite big, maybe 30 - 35 V for a 12 V system.

Any well-designed car will have the electronic modules designed to take the alternator's load dump. Without that, a broken battery lead can kill modules.

If you have jump leads with a suppressor, you would need a big suppressor to take the alternator current for half a second or so. Also, you need to know which car has the broken battery, and disconnect the other end first. Personally, I wouldn't bother, and I won't be running out to buy new jump leads. Most jump starting is on a battery that has recently gone flat, so will be able to accept charge perfectly well.

 

[tcmtech]

Maybe, but does anyone here actually know what the internal impedance, not internal resistance, of a lead-acid battery actually is compared to a TVS or MOV?

Low enough to knock things down far enough that the built in individual component/sub systems protection devices of every critical electronic control module has on the vehicle can handle on their own.

Just one of the various standards that automotive electronics systems are built to.

AN2689 Protection of automotive electronics from electrical hazards guidelines https://www.st.com/content/ccc/reso...df/jcr:content/translations/en.CD00181783.pdf

FYI voltage surges taking out components due to jumping are extremely rare. Reversed connected cables between vehicles is what does the most damage the most often by multiple magnitudes of order.

After that its burnt out alternators from overloading due to the too often poor designs of automotive units that literally can't handle being ran at the top end of their rated capacity for more than a few tens of seconds without damaging themselves.

 

[Diver300]

Load dump protection is only really needed to cater for a disconnected battery, so the battery impedance is irrelevant.

For reverse battery protection, low battery impedance makes the problem worse.

The impedance of the wiring is often larger than that of the battery, so high frequency disturbances aren't effectively reduced by the battery.

So for many of the things that are being protected against, the battery impedance isn't important. Good designs will have protection in each module, although I have seen cars where the load-dump is suppressed in the alternator, and then the level of load-dump protection in each module doesn't have to be as effective.

 

[unclejed613]

it would be interesting to see what's in (or not in) the box on those cables... given that in a good set of cables, the bulk of the diameter is in the copper, there's not much that could fit in that box...

 

[Lissajous]

I find it hard to believe that the surge protector (connected somewhere down the cable) has a lower impedance/inductance to a spike than the donor car's battery to which the suppressor is connected.

I don't. Have you looked at the specs for a uni-polar TVS like the one in debe's pic? Response time is measured in pico-seconds (bipolar variants are a lot slower) but these things turn on a whole lot faster than a battery comprising half a bucket full of acid and electrodes. What they cannot do is dissipate huge power for a prolonged period. Fortunately, they don't need to. They are used to clamp the fast transients only. The battery can clamp the slow stuff.

 

[crutschow]

Sorry, but I still don't think there is any significant voltage spike that can damage the electronics (which already have voltage suppression) can get past the battery.
The battery isn't that slow as a 100kHz sinewave corresponds to 5μs pulses.
μs, ns, or ps spikes on the power line are unlikely to have any effect on the electronics.

Still say it's snake oil.

 

[Nigel Goodwin]

Sorry, but I still don't think that is any significant voltage spike that can damage the electronics (which already have voltage suppression) can get past the battery.
The battery isn't that slow as a 100kHz sinewave corresponds to 5μs pulses.
μs, ns, or ps spikes on the power line are unlikely to have any effect on the electronics.

Still say it's snake oil.

I totally agree

 

[unclejed613]

Still say it's snake oil.

somebody exhumed the thread? i agree crutschow, either there's nothing in that box, or whatever is in that box is nothing useful. somewhere a snake is suffering an oil deficiency.

 

[Wirelesscom]

There would be no problem with overshoot (lay people call these events "surges" and "spikes") If the person in the donor car would not rev the ring out of the donor car's engine whilist cranking the stranded vehicles engine.
A slow idle or shut down the donor car's engine will be all that is needed. Unless you are 1000s of Ks into the outback with only ONE battery in the host vehicle, the safest bet is to shut the host vehicle down.
Then connect the jumper leads, and if the leads are in good condition, the stranded vehicle will start.
Load dump and load shed will cause 200+ volt excursions, if the host vehicle's battery is doughy ( higher internal resistance) Magnetic fields take a finite time to change state, the alternator's AVR is fast enough. but when the load is removed, an overshoot does occur.
Tip: Never crank the stranded vehicle with the host vehicle running. A upwards of 2Kw load (Starter motor) on a 12v system is a scary number indeed.
I have always viewed these "surge protected" jumper leads with suspicion. The yellow box is only a MOV device with a breakover voltage of 18 or so volts. Once that disc shaped device goes S/c the pigtails of the component just fuse open cct. much like a piece of 20A fuse wire.

This load dump/shed happens with generator sets too, when a big load is thrown at the genset, it is a sag-out, conversely when a big load is disconnected, an overshoot does occur and is visible particularly with incandecant lights (and cheaper LED lights too).
It takes time for that big hunk of laminated steel to lose its magnetic field after the AVR says 'less' exciter current.

 

[Diver300]

I would agree that a tiny little surge protector won't do much, and that a battery is the main thing that that will prevent load-dump damage.

However, I'm not sure if turning the engine off on the car with the good battery is always an effective way of protecting against load dump.

If a car has a low battery, with not quite enough power to start the engine, but close, then its battery is plenty good enough to prevent load dump damaging anything. Also, in that situation, when only a little bit of help is needed, then jump starting from a car without running the engine is likely to work. But also, running the the engine on the good car won't do any harm. Even if the whole alternator output gets dumped into the battery for half a second, the voltage rise will be 1 volt or less.

The problem comes when a battery is really flat. The internal impedance of the battery will go right up, so it won't be much good at protecting from load dump. Jump starting from a car that isn't running in those conditions has two problems. Firstly, it often won't work. It's difficult to get jump leads and their connections to have a low enough resistance that you can actually crank the engine through them, and 12 V from one battery will not charge even a dead battery at all quickly. You need more like 14 V, which comes from the alternator of the good car. If the jump leads aren't making a really good connection, waiting a few minutes will allow some charge and the car will start after that.

Secondly, if you do get the car with the dead battery to start using jump leads from a good car with the engine off, what happens next? The alternator on the car with the dead battery will produce 14 V, but there is a risk that most of the alternator current is flowing back down the jump leads to the good car's battery. It's a good battery, low impedance, but it's just started an engine so the alternator on the previously dead car will charge it and a lot of current will flow in the jump leads.

Meanwhile, the really flat battery is still really flat. It will take some time before its impedance drops and it starts accepting charge. If the jump leads are disconnected, the current from the alternator will have nowhere to go, as the really flat battery isn't working and that can lead to load dump damage.

If you run the engine on the good car, the battery on the dead car will start charging before the engine starts, so it's going to make starting easier. Also as the battery charges, it's impedance drops, helping to protect against load dump. Then, when the engine starts, the alternators on both cars are producing 14 V, so there will be little voltage difference between the two cars, and little current flowing in the jump leads. If the battery on the previously dead car is still high impedance, the output current of the alternator will have reduced while the jump leads are connected.

With little current flowing in the jump leads, disconnecting them won't cause a load dump.