I live on top of a hill that seems to attract a considerable amount of lightning during a storm. Over the course of many years there have been numerous near misses and one direct lightning hit to my house. Even the near misses have caused damage to some of my sensitive electronic devices. For example, I’ve had to replace my A/V receivers twice due to lightning strikes no closer than a couple of hundred feet. I’ve learned to put lightning arrestors on any devices inside my home that seem to be vulnerable and connect them to a good earth ground.

Interestingly, I’ve never had an instance where a near lightning strike has had any effect on the electronics of any car I’ve owned. I suppose the metallic body of the car acts as a fairly good Faraday shield in protecting its delicate electronics.

But what changes when I attach the wire leads of a maintainer to the car’s battery?

The wire between my car and the maintainer is about 12 feet long and not shielded. And the maintainer itself is indirectly connected to the house wiring which is also not shielded. The horrendous electromagnetic field generated by a near lightning strike will induce a high voltage on that wire which is connected directly to the car’s battery.

Since I never know when I’ll be driving the XJ, I try to connect it to my CTEC whenever the car isn’t being used. But am I being overly cautious in disconnecting the maintainer whenever a lightning storm is near? If I don’t disconnect, is the car battery capable of absorbing the energy of a near lightning strike and hopefully protecting the car’s electronics? Is anyone aware of any device that could be placed between the maintainer and the battery that would protect the car without the need to disconnect? And finally, has anyone ever experienced damage to their car’s electronics because their maintainer was connected during a lightning storm?

Vince

 

Other than disconnecting the CTEK and car from your house power, I'd recommend a surge protector just before the CTEK. Have you considered a whole house surge protector connected at the service entrance to your electrical panel? The safest thing to do is unplug the CTEK, though.

 

Vince, what you need is 2 large zener diodes that are rated for say 20 VDC You will then wire the zener anodes together and then cathodes to the wiring. What this is going to do is any time the voltage gets above 20V, the zeners are going to conduct and only allow the car to go up to 20VDC (which the battery is going to absorb). You can even take this one step further and add say a 0.5 ohm 10 watt resistor between the zeners and the car to help minimize the voltage seen at the car. This should not affect the CTEK all that much as it will have a slight voltage drop due to the resistor, but hte amount should be minimal unless you start getting into a decent charging condtion (ie, trying to charge at say 4+ amps).

If you want to know more, please let me know.

 

Many thanks to both Freddy J and Thermo for your excellent suggestions. The whole house surge protector should handle any lightning surge coming into the house through the mains. On the other hand, I hadn’t thought of using parallel Zener diodes in the line from the maintainer to the car battery. I just checked to see if there was such a thing as a high current Zener and indeed there is. Again, thanks Gents!

Vince

 

A big enough strike will overwhelm just about anything (& definitely zeners/transorbs/etc) so if you're really worried then yes disconnect.

The above kind of electronic devices will cope with charged atmosphere.

 

Vince, if you use the zeners, they need to be wired in series with each other and in parallel to the battery. One way the zeners hold back a finite amount of voltage. The other way they act just like a diode and let the voltage flow with very little resistance. So, you need one to flow forward into the other one that is backwards and resisting the flow.

 

JagV8,
I totally agree that if a lightning strike is too close then all bets are off! I've had one direct hit to my house that popped sheetrock nails out of the wall and scorched the wall studs behind. (Lucky there was no fire). Scary! I suppose lightning rods on the roof might have helped a bit, but there's no assurance that it would.

Vince

 

Thermo,

Thanks for the additional info. I've been working on an idiot-proof way to prevent tearing the maintainer off the wall whenever I forget to disconnect it before driving off (with me being the idiot). I'll incorporate your Zener diode concept into the design. Many thanks!

Vince

 

VinceCh, I've had the almost tear it off the wall experience myself! Now, whenever I use the CTEK, I put a giant piece of cardboard on my drivers side windshield with the word Connected on it. Believe me, when I jump in the car and can't see out of the windshield, I remember to unplug the pigtail. That piece of cardboard has saved the maintainer from this idiot more than a few times.

 

Vince, something you may want to ponder is taking say a tennis ball and attaching a string to it and then attaching the ball to a support post. Then, you put your connection in the tennis ball and this pulls the ball back to say over the driver's door (ie, CTEK on the wall, connection in the middle of a 15 foot run of cable, tennis ball at the connection, the far end of the wiring attached to the battery. You go to get into your car, the tennis ball is going to be in your way. You then pinch the tennis ball, expose the connector, undo it, let the tennis ball fall back to the CTEK unit and you tuck the rest of the cable into the trunk. Granted, cardboard trick does the same thing. I like the tennis ball trick as it is self installing and you can't forget to put up your warning device.

 

This thread made me curious to look at it, since I've had some near hits in the past with nothing serious.
Vince, I would strongly suggest you NOT install a lightening rod on your house or anywhere near it. A direct hit could take out everything. (I'm sure Thermo will be alone to correct me which is perfectly good with me)
If you can, find a spot a 50 --100 feet (or so) away from your house and make it taller than your house.
Remember that lightening can travel a long way underground perhaps many hundreds of feet or more.

 

Freddy J and Thermo,

I'm so happy that you picked up on my comments about not ripping the maintainer off the wall! I'm in the process of starting a thread that will show my solution to the problem. Both your ideas are incorporated to a degree, plus a couple more that may interest you. Watch this space for more info. BTW, I found that the cardboard on the windshield works only if you put it there in the first place. We've got to remember who we're working with!

Vince

 

Thank you, jayt2, for your comments. It's my understanding that lightning rods don't attract lightning, but rather dispel static electricity buildup that would otherwise be the precursor of a direct strike. I may be corrected on this.

Vince

 

Been there, done that! (Ripping the CTEK off the wall). I now run the cable from the maintainer and loop it around a nail in the wall that is positioned at neck height, and is festooned in orange flags!

As, agreeing with my wife for once, I am stupid, I work on the principle that if I'm dumb enough to ignore the flags, being strangled by the lead should get my attention!

wombat

 

Wombat,

It's good to know that someone else has a self-image similar to mine! However, my present solution to ripping the maintainer off the wall is somewhat different than yours and a lot less dramatic. Hold off a while as I assemble a new thread on the topic.

Vince

 

The secret to the cardboard success is to put it there before you plug in the CTEK. I made that as step #1 the second time I became aware of the idiot I was working with.

 

Getting back to the original topic of protecting the car/battery from a lightning induced surge, My CTEK has a 15 amp fuse in the pigtail connector going to the battery. Doesn't that provide protection?

 

Freddy J,

Probably not. A fuse needs two things to protect a circuit: First, an amount of current greater than the ampere rating of the fuse and, second, a certain amount of time for the fuse element itself to heat up and melt. Lots of things to ponder here, but I think the most realistic consideration is in the nature of the induced voltage/current on that 12 foot section of wire running from the CTEK to the battery.

Most likely, the indirect lightning hit will create a whopping bit of current and some very high voltages, possibly in the thousands of volts. While the current requirement will certainly be met, it will still take a finite amount of time for the fuse element to vaporize, most likely in nanoseconds. And even if the fuse element does open, the voltage will be so high as to bridge the gap of the open fuse and wreak havoc with the car’s electronics.

I’ll run all this by my Thursday morning breakfast gang which is mostly old retired geezers who have some experience with electronics and electricity.

Great question, and thanks for getting us back onto the original topic!

Vince

 

Freddy, if you look on fuses, you will normally see 2 numbers, an amperage number and a voltage number. So, like fuses in your car are normally 12 VDC and say 20 amp. The amp number is pretty obvious in that this is the number that above which, the fuse is going to open. Now, keep in mind, as the fuse is opening, it is going to draw an arc (hence why you sometimes see a flash of light coming from the fuse when you subject it to too much current). The voltage is the maximum voltage that it can quench the arc. Above that voltage and the fuse may just become an arc welder (well, you get the idea). The arc may start, but the posts are too close to get the arc to stop. So, the power continues to flow. This is where some fuses have sand inside them to make the path for the arc to flow much more torturous and therefore they can block the arc for a higher voltage.

So, in the case of lightning, the strike itself is in the millions of volts. But, now it has to travel through some very resistive materials and also cross wiring insulation and whatnot, so the voltage that gets into your house is normally much less. But, it is still more than the normal line voltage. So, most fuses are going to provide some protection, but you cannot guarantee 100% protection. That is why I like the zener diodes. They are going to take the brunt of the initial surge (yes, they may fail, but they knocked the surge down) and then when you mix it with say a fuse, you stand a better chance of protecting your investment.

I know some of you are going to say "my car runs at 13.7 VDC, so my 12 VDC fuse is not going to stop the arc because 13.7 is more than 12". I hear what you are saying, but no, the fuse is going to do its job. 12 VDC standard in the electrical world is a median voltage. The easiest way I can prove it to you is to have you take any 12 VDC power supply in your house that you have plugged in to your wireless headsets, your TV boxes, etc and measure the voltage coming out. I bet you will find that it is up at around 15.0 VDC with no load on it. I've seen some as high as 20 VDC. Now, once you put a load on them, they tend to come down. So, your 12 VDC power supply may be feeding your device 13.0, 11.0, or possibly up around 14.0 VDC. Only very high end power supplies are a true 12.0 VDC at all currents. MOst are designed to operate over a range. Hence why the associated fuses actually have a bit more range to them than what is stated. Kinda like the 115 VAC in your house actually goes up to around 160 volts at its peak because of how they assign the voltage number to AC voltage (the number is based on the DC equivalent in power output throughout the whole AC cycle). So, a 115 VAC fuse actually needs to be able to kill an arc up to around 200 volts. (160 volts plus a bit of a fudge factor).

If you want to know more about this, please, let me know. If I am going above your head, say so, I can break it down further and explain it a different way. I know not everyone is electrically knowledgeable and some just don't get the concept.

 

Vince, Thermo, thank you for the tutorials. I have to admit that I anticipated your thinking re the fuse. I would expect the entire CTEK device may become a fuse with a lightning strike. What prompted me to throw out the fuse question was the response I got from CTEK. I was interested in knowing what the CTEK manufacturer had to say about the their product providing lightning protection for the car and they came back with the 15 amp fuse answer in their email. Obviously, not well thought out on their part regarding lightning.
Thermo, thank you for the sensitivity....I'm retired from Westinghouse and have a bit of background.