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Capacitor Drainage Vs Plug In Appliances In Cars

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  • nmfire
    replied
    Well that explains it. I had a feeling something would click sooner or later because it sounds like you know what your talking about with cars.

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  • Rescue101
    replied
    My original post was put up after a 80hr work week and I was thinking more of power interruption rather than accessory backfeed even though that was the original post.Forgetting completely that many vehicles today have redundant grounds.Unlike your thinking,I DEPEND on our databases when working on vehicles because no two vehicles today are wired the same over a time period.We print out the info we need for each repair we do on that EXACT vehicle and system.Obviously this is impractical for vehicle rescue operations.So the nutshell version will be the most workable although no entirely foolproof. T.C.

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  • nmfire
    replied
    Yes. As I stated earlier, that is exactly what I teach. Just like we don't build a camp fire next to a tanker crash just because it isn't leaking, we don't play around airbags just because the battery has been removed.

    I'm not arguing that. I'm arguing your misconception that somehow removing a battery from a parallel circuit will inhibit any other parallel power source from functioning. If you've been doing automotive electrical work for 30yrs, you should know this by now. Whatever you are reading, you're reading it wrong. I don't need a CD of schematics to know this.

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  • Rescue101
    replied
    NM,obviously you're much well versed in these things than I. We've only been doing auto electrics for about thirty years.We use a program ondisc called "mitchell information services"perhaps you've heard of it"?At risk of being blunt let me reword my answer.SECURE ALL power and grounds including ANY acessory sources.Maintain a safe distance from any airbags during operations.I believe this "nutshells" the process without confusing anyone,yes?T.C.

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  • nmfire
    replied
    Originally posted by Rescue101
    Flawed? GM,Ford,Chrysler cigarette lighter are dedicated power circuits.Remove the GROUND you DO NOT have a circuit.And most of these are not fed into or from the ign side of the switch.Perhaps you work on vehicles everyday and are more knowledgeable than myself.I do make mistakes but according to my schematics on the above vehicles I stand by my original post.Can you backfeed and keep the airbag circuit live?Not saying you can't but I AM saying not every vehicle WILL.As was mentioned,short of removing every SRS device,it would be wise to remove any potential power sources AND maintain your distance from the bag. T.C.
    Sir, you're misinterpreting whatever it is you are reading. None of what you are saying makes any sense at all. First of all, yes, I do work on vehicles (specifically electrical systems) frequently on a personal, employment, and fire dept equipment basis. So yes, I do probably have more knowledge of this than you do. And even if I didn't, this is basic parallel circuit electrical theory that I learned when I was 10yrs old playing with one of those experiment kits. Whatever schematic you are reading, you are reading it wrong. I'm not trying to be an *** here, but you are really very very wrong here.

    Disconnecting the battery ground is doing nothing more than removing the battery from the circuit. It is not interrupting any other part of the electrical system. If power is applied elsewhere in the electrical system, it will energize whatever part of the system it can reach. If you can not understand this, I can't think of any more simplistic way to stating it over and over. You're just going to have to trust me.

    Lighter plugs and big car stereo components are usually on a constant power circuit meaning they are not switched off with the ignition. Therefore, any of these devices that are backfeeding power into the electrical system will energize anything that can function without the key being turned on, including the airbag system.

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  • Rescue101
    replied
    Flawed? GM,Ford,Chrysler cigarette lighter are dedicated power circuits.Remove the GROUND you DO NOT have a circuit.And most of these are not fed into or from the ign side of the switch.Perhaps you work on vehicles everyday and are more knowledgeable than myself.I do make mistakes but according to my schematics on the above vehicles I stand by my original post.Can you backfeed and keep the airbag circuit live?Not saying you can't but I AM saying not every vehicle WILL.As was mentioned,short of removing every SRS device,it would be wise to remove any potential power sources AND maintain your distance from the bag. T.C.

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  • nmfire
    replied
    Originally posted by Rescue101
    Yep, you're right.GENERALLY,if you disconnect the ground you interrupt ALL flow of power thru the system.And on some vehicles this will apply even with backfeeds.It depends on where your accessory grounds terminate.Best bet is pull every plug and accessory feed AND disconnect the battery/batteries grounds.Thanks for the refresher. T.C.
    I'm not sure where you are getting this information from but it is quite flawed. A power source is a power source is a power source. The battery is one power source and it has it's own positive and ground connection. Disconnecting either or both of those will have NO EFFECT on other power sources. All you are doing is removing that power source from the circuit. The rest of the electrical system is still perfectly intact and that includes other sources of power. This is not "in general", it is rock solid and basic electrical functionality of a parallel circuit.

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  • Rescue101
    replied
    Yep, you're right.GENERALLY,if you disconnect the ground you interrupt ALL flow of power thru the system.And on some vehicles this will apply even with backfeeds.It depends on where your accessory grounds terminate.Best bet is pull every plug and accessory feed AND disconnect the battery/batteries grounds.Thanks for the refresher. T.C.

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  • nmfire
    replied
    Originally posted by Rescue101
    One way to eliminate it is remove the ground/grounds from the battery/batteries.This will also allow any capacitors to dissipate their energy.
    You might want to re-think that one. Think about what you are saying. The battery grounds are just that... the battery grounds. The grounds for that one power source. Cutting or removing the battery's main negative cable(s) right at the battery will do the exact same thing is undoing each of the individual battery grounds spread out under the hood if there are multiple negative cables leaving the battery. Cutting them right at the battery is the by far the best way since you know you got them all in one shot.

    Doing this will however have ABSOLUTELY NO EFFECT on other power sources that might be backfeeding into the main electrical system.

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  • fdsq10
    replied
    First let me apologize to you MFDSSIM and to my Brother Firefighters,& Officers for the way I answered your question. My intent was not strut my stuff or to show off in any way. Your right I should have just answered the question straight up and offered to you what I knew about your question, I did not do that and it was wrong. This forum is a great way of sharing information, had I ask the same question and you replied back as I did in a disrespectful tone it would not have set well with me. STAY SAFE!!!

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  • rmoore
    replied
    Received this same type of question, just like the original post in this thread, from a Canadian firefighter.

    Question:
    I've recently come across some conflicting information with regards to the effects of having portable appliances (laptop, DVD player, CD player, etc...)plugged into an automobile's cigarette lighter electrical source, as having an effect on battery drainage time with regards to its capacitors? Is this true? The argument brought forth is that since these various appliances all apparently have their own capacitors, the claim is that it could be possible for these independent capacitors to trigger airbags if the car they are in is involved in a crash, EVEN IF THE CAR BATTERY IS NEUTRALIZED! Can you please calrify this for me.

    My Reply:
    The answer to your question about power appliances at a crash scene is "Yes". Here's the scenario. You arrive at a crash and cut battery cables or disconnect them as per your protocol. You think the airbag system is now draining down and that the airbag capacitor will be empty in a few moments. From that point on, you think you have a higher degree of safety. After all, the battery is shutdown and the capacitor is draining. That's where or thinking may actually be wrong.

    My engineering contacts tell me that a portable device within the crashed vehicle, something that has it's own battery power supply, which remains plugged into the cigarette lighter port of an automobile, canor may "power backfeed". It's own battery power supply can feed current in reverse back into the cigarette lighter outlet. The engineers tell me that this is a designed system. Auto mechanics buy these power backfeeding devices for use in repair shops. I bought one for $9 just to see it. They plug the device into the cigarette lighter and connect a 9v transistor radio battery to it. That 9-volts keeps the car's black box computer brain charged if they have to disconnect the real battery to work on the car. When finished, they do not have to re-program the computer of the car. The power backfeeding device kept the computer energized the whole time.

    Unfortunately for us, one of the circuits that this power backfeeding system also can keep energized is the airbag electrical system. In other words, the airbag capacitor will never drain like we thought it was! We cut the battery and really, nothing got better as far as the airbag electrical system is concerned. It could be just as energized with the car's battery connected as it is without the battery hooked up. Power backfeeding is the reason.

    Kill the power and then pull the plugs; all devices connected into all plugs or power ports throughout the vehicle. That's power shut down, 2007 version!

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  • bkmcse
    replied
    Here is a link to the video I was talking about
    http://www.autodesignextrication.com/videostreams.htm
    look at the video "Power Feedback"

    Leave a comment:


  • Rescue101
    replied
    This question was posed to us and kicked around by our staff.Almost without exception a FACTORY installed cigarette lighter(or power source in modern terms)will have twelve volts,dedicated power ALWAYS live(as long as you have battery).Hence it IS theoretically possible to have a backfeed thru this circuit.One way to eliminate it is remove the ground/grounds from the battery/batteries.This will also allow any capacitors to dissipate their energy.The trick to this is make sure you've located ALL the batteries,some vehicles have more than one.Short of carrying a voltmeter around with you, I know of no way to be certain when a circuit is totally dead.And unless you're working on vehicles everyday where are you going to make those tests?Crashes have a nasty habit of putting something you know in a spot it doesn't belong or maybe a bit inacessable.No matter what you do use the "live" airbag distance rule just to be safe. T.C.

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  • nmfire
    replied
    That is pretty much what I teach. Avoid the deployment zones at ALL times, even after you *think* it has been rendered safe or if there are no airbags at all. If you do it all the time, you are less likely to forget "that one time".

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  • GFD615
    replied
    Many instructors offer secondary suggestions that add to the safety of a firefighter during a rescue situation. But to be quite honest, I believe every instructor will agree that no firefighter should ever feel completely safe anytime they are in the presence of a damgaed vehicle. Ideally, keep yourself out of the airbag deployment zones, and don't cut the gas.

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