Jump starting a car - Page 1
Forum section: electronics / general

author: arildj78
author_rank: Regular Contributor
timestamp: February 04, 2015, 10:07:34 am
content: There are way to many misconceptions on how to jump start a car. People talk about blowing up the battery, ruining the electronics and connecting jumpercables in a certain order.My favorite answers to this is when so-called experts claim that there will be:* An overvoltage so the car short circuits (!!?!)* An overvoltage to quick for the circuitbraker to handle (!!?!)* No possible safe way of performing without special cables* You need to connect a lightbulb to the jumpercables to avoid the spikeWhat is fact and what is voodoo? Will old fashion cables do the trick or do you absolutely need new cables with overvoltage protection? If there is a real problem with plain cables and new cars, what is it and what is the real cause? Are we talking about voltage spikes of thousands of volts or an alternator spike due to a sudden change in load?I hope Dave can make an episode on this, or at least that someone know the facts. My personal belief is that old style jumper cables are more than sufficient and there is no magic order to connect or perform the actions.

author: electr_peter
author_rank: Unknown
timestamp: February 04, 2015, 10:23:23 am
content: Quote from: arildj78 on February 04, 2015, 10:07:34 amThe problem is two folded - on one hand there is high energy source with exposed contacts, on the other hand there are idiots who try to connect these batteries. So no wonder you hear about fires from time to time because somebody shorts out a battery (there were some stories when passer by tried to help to jump start a car and created fire. Fire destroyed broken vehicle.)There is some truth to suggestion to connect jumper cables in a specific order though. Most modern cars have their chassis at negative potential. Thus you can look at battery connections having different sizes - "+" contact is a small size contact, "-" contact is a full car.If you connect external battery with "+" contact first, there is very small risk of shorting external battery.If you connect external battery with "-" contact first, there isvery high riskof shorting external battery.

author: TMM
author_rank: Frequent Contributor
timestamp: February 04, 2015, 10:39:04 am
content: It's not uncommon for there to be a surge of current when you reconnect a battery to a modern car as all the modules power on before entering a sleep state. Just about the worst thing that can happen is that there is a small spark and pop which gives the person connecting the battery a fright.Almost 100% of the problems come from people accidentally shorting out a battery through the chassis, or connecting the external battery with reverse polarity.

author: Psi
author_rank: Super Contributor
timestamp: February 04, 2015, 10:39:21 am
content: If the battery is very stuffed then its internal resistance is usually terrible and it may not accept much charge current. On some cars this can be a real problem because the battery is required to provide some protection from overvoltage (it draws more and more current above its nominal cell voltage).A stuffed battery can be pretty much the same as no battery at all and with nothing to regulate the charging you can suddenly find all your car electronics is getting 18V or more. This was one of the reasons why automotive electronics standards say the device should survive 24V for 1 hour without damage.

author: arildj78
author_rank: Regular Contributor
timestamp: February 04, 2015, 11:05:50 am
content: Reversing polarity is an obvious real issue. As you point out, handling a live positive cable in vicinity of a live negative chassis increases the risk of short circuiting.Another danger I've heard of is the risk of igniting any oxyhydrogen gas present in the vicinity of the receiving battery. This suggests that it would be a good idea to make sure that the last connection to be made is one that is as far from the receiving battery as possible. I've seen it suggested that this should be the negative lead beeing connected to the receiving cars engine block, but in my mind you could get even further away if the last connection is on the suppliers negative battery (or chassis). On the other hand... how real is this issue? Is it a teoretical issue or is it possible that enough gas accumulates to be any danger? Was it a problem with only the classic lead accumulators or is it a problem with new sealed batteries as well?The reason why I started this thread is that I got this advice when I bought a new car i 2012. I had heard it before and accepted the claim without thinking more of it. The other day the same clame resurfaced in a local newspaper citing a national TV broadcaster (http://www.tv2.no/2015/01/31/broom/starthjelp/startkabler/6515853).I googled for a while and found this cliphttps://www.youtube.com/watch?v=ccrBjmoBNL8.Check out the claim made between 10 and 20 seconds out in the video.The internet is certainly not a reliable source of correct information, however I'm struggling to find someone rejecting those claims that old fashion jumper cables are dangerous to your car.

author: VK5RC
author_rank: Unknown
timestamp: February 04, 2015, 11:10:45 am
content: Hydrogen generation if the battery charges very quickly then some fellow either looks into it with a match or disconnects the charger with a small spark, it is one of the more common causes of blindness as sulphuric acid gets blown all over the place.http://www.worksafe.vic.gov.au/__data/assets/pdf_file/0018/44343/Alert-Battery-explosionsv3.pdf

author: bookaboo
author_rank: Frequent Contributor
timestamp: February 04, 2015, 11:11:03 am
content: A big problem can often arise when you have a loose battery connection and the engine running. Without the battery the alternator+regulator spike and dump a huge overvoltage into the 12v circuits, the regulator with quickly adjust but for a short period you have over voltage. Most auto electrics are designed with this in mind but I'm sure it's still an issue.

author: george graves
author_rank: Super Contributor
timestamp: February 04, 2015, 11:24:10 am
content: Quote from: arildj78 on February 04, 2015, 10:07:34 amWho says this? I've never heard anyone suggest that. What kind of people do you hang around? Or was it youtube comments? Cause that's more plausible!

author: sleemanj
author_rank: Super Contributor
timestamp: February 04, 2015, 11:35:48 am
content: A few docs on the subject of the hostile environment that is automotive electrical systems...https://www.digikey.com/document-redirector?doc=https://www.digikey.co.nz/Web%20Export/Supplier%20Content/Tyco_8004/PDF/Tyco_AutoNetwork.pdf#http://www.littelfuse.com/~/media/electronics/application_notes/tvs_diodes/littelfuse_tvs_diode_automotive_circuit_protection_using_automotive_tvs_diodes_application_note.pdf.pdfhttp://www.ti.com/lit/an/snva681/snva681.pdf

author: arildj78
author_rank: Regular Contributor
timestamp: February 04, 2015, 11:58:04 am
content: I'm sorry I didn't include citations. Here they are:* An overvoltage so the car short circuits (!!?!)(http://www.tv2.no/2015/01/31/broom/starthjelp/startkabler/6515853)"Kortslutter bilenI en moderne bil sitter det mange styrebokser og små datamaskiner som kommuniserer med hverandre.Hvis en styreenhet får overspenning og kortslutter, kan det føre til skade på andre dyre komponenter i bilen også."* An overvoltage to quick for the circuitbreaker to handle (!!?!)(http://www.sonnak.com/wp/wp-content/uploads/2009/05/Batteriets-oppbygning-og-virkemaate-2005.page 13)(...) som kan skades, dersom det "kommer" en spenningspeak. Bilens sikringer er såkalte trege, og vil ikke reagere raskt nok.* No possible safe way of performing without special cables()Claim made between 10 seconds and 20 seconds into the video* You need to connect a lightbulb to the jumpercables to avoid the spike(Comment by Bilentusiast onhttp://www.tv2.no/2015/01/31/broom/starthjelp/startkabler/6515853)Den eneste sikre metoden for å unngå skade på elektronikken er å bruke kabler med et eller annet overspenningsvern, faktisk noe så enkelt som en 5w lyspære koblet mellom pluss og minuskabel er nok! Jeg er bilmekaniker, nærmer meg 50 år i faget (...)I included the source material in norwegian, ask google for the translation.

author: dannyf
author_rank: Super Contributor
timestamp: February 04, 2015, 12:03:09 pm
content: QuoteMaybe the misconception is a (mostly?) norwegian problem? I have never heard of the "misconceptions" you cited.

author: arildj78
author_rank: Regular Contributor
timestamp: February 04, 2015, 12:11:16 pm
content: The YouTube clip mentioned is not Norwegian... However, my point is that I don't belive these claims are based on any facts. If none of you have ever heard about this, it can very well be that this is an urban myth that only exists in Norway. Still, quite a few car accessory suppliers sell jumper cables with overvoltage protection. Why? What will cause this destructive overvoltage that new cars need to be protected from?

author: arildj78
author_rank: Regular Contributor
timestamp: February 04, 2015, 12:11:47 pm
content: There is no doubt that oxyhydrogen gas is dangerous, that voltage spikes can occur if you have a loose connection, that running the alternator without any load can give interesting voltages in your system and that booting your car draws more current than when it is in standby.But if we go back to the original question: Will oldfashion jumpercables with no electronics or overvoltage protection ruin any of the cars involved in a jump-start? If so, how? What is the destructive force behind this damage?

author: george graves
author_rank: Super Contributor
timestamp: February 04, 2015, 12:29:40 pm
content: Quote from: arildj78 on February 04, 2015, 11:58:04 amYou had to search high and low for those! Congrats on proving me wrong! But really, the *average* person knows you connect red to red, and black to black. (ok if your smart, you connect the car needing the jump to ground lug) "You ground the bad car" As in pushish it.

author: arildj78
author_rank: Regular Contributor
timestamp: February 04, 2015, 01:02:46 pm
content: Didn't feel the need to prove anybody wrong. Scary thing however is that one of those references (the pdf) is a fact sheet from a battery supplier. When they start talking about fuses that are to slow to protect from overvoltage, they've lost me.

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 04, 2015, 02:08:36 pm
content: Quote from: arildj78 on February 04, 2015, 01:02:46 pmFuses are not made to protect from overvoltage.

author: Towger
author_rank: Super Contributor
timestamp: February 04, 2015, 02:17:48 pm
content: Jump starting the Phontonicinduction wayFor once he does not blow anything up, but the comments make interesting reading on the dangers of destroying his merc.

author: N2IXK
author_rank: Frequent Contributor
timestamp: February 04, 2015, 02:37:03 pm
content: The main precaution I was always taught was to make the negative connection on the dead vehicle LAST, and make it to the frame/engine block well away from the battery itself. This is to prevent the spark that is created when completing the circuit from igniting any gases present around the dead battery.

author: rollatorwieltje
author_rank: Unknown
timestamp: February 04, 2015, 03:28:02 pm
content: Quote from: N2IXK on February 04, 2015, 02:37:03 pmSomewhat related, when you connect the negative first you can short out the positive lead anywhere on the car by accident, as usually metal parts are connected to the negative battery terminal.

author: dannyf
author_rank: Super Contributor
timestamp: February 04, 2015, 04:28:31 pm
content: QuoteTo make money off people foolish enough?QuoteAny jumpercable is a tool. Like any other tools, if mis-used, they can cause damages.So to answer your question:No. Tools by themselves are not capable of causing damages;Yes. Tools can cause damages if mis-used (by people).

author: electr_peter
author_rank: Unknown
timestamp: February 04, 2015, 04:38:58 pm
content: Quote from: arildj78 on February 04, 2015, 11:05:50 amThat video advertises (thus all the FUD in a video) Michelin 5100 Smart Jumper Cables - it is supposed to be idiot proof. It is polarity insensitive, but only operates when both ends have enough voltage (cannot jump start dead or missing battery).I guess they use few MOSFETs in H-bridge configuration with MCU. I would prefer to have high gage simple cables instead.

author: G7PSK
author_rank: Super Contributor
timestamp: February 04, 2015, 04:41:56 pm
content: I once had a Nissan Patrol that was 24 volts, my father wanted to jump start his car, so I tossed him the keys. Ten minutes later there was a very loud bang, I went outside to see what happened although I could guess, He had done every thing right, connected up + to + and - to - but forgot to use the ground side batter for the + connection so he put 24 volts into a very much smaller 12 volt battery and within seconds it had boiled and blown the side out of itself. My two heavy duty batteries were totally unharmed.

author: SeanB
author_rank: Super Contributor
timestamp: February 04, 2015, 04:46:07 pm
content: Donor vehicle, connect positive lead of jump lead to battery positive. Drecipient vehicle connect positive lead to battery positive. Make sure you have the positive lead of each vehicle, and that the vehicles are not touching. Donor vehicle connect negative lead to battery negative. Recipient vehicle connect negative lead to engine block, using a place where it will not be hit by belts, and well clear of the moving parts.Start recipient vehicle, and do not rev engine for at least a minute, so that the alternator does not burn out from the overcurrent of full power operation. Disconnect negative lead from engine block of recipient vehicle. Disconnect negative lead from donor vehicle. Disconnect positive lead from recipient vehicle. disconnect from donor vehicle and place the leads neatly back in the bag or rolled up in the storage space you keep them. That way you have little risk of blowing up batteries, alternators or vehicle electronics.As a side note cheap jump leads with little copper inside are worse than useless, they will either burn out or catch fire.

author: G7PSK
author_rank: Super Contributor
timestamp: February 04, 2015, 05:19:53 pm
content: And remember to check vehicle voltage before you start.

author: IanB
author_rank: Super Contributor
timestamp: February 04, 2015, 05:26:11 pm
content: Quote from: N2IXK on February 04, 2015, 02:37:03 pm^^^^This.You want to make sure the last connection is far from the battery so there there is no chance of a spark igniting any flammable gases in the battery when the connection is made.

author: IanB
author_rank: Super Contributor
timestamp: February 04, 2015, 05:28:19 pm
content: I have usually found it is sufficient to run the donor engine for a few minutes to charge the receiving battery, after which the receiving battery typically has enough charge to start the engine by itself. There is no need for the jump cables to actually carry the starter motor current.

author: Stonent
author_rank: Super Contributor
timestamp: February 04, 2015, 05:44:59 pm
content: Quote from: IanB on February 04, 2015, 05:28:19 pmIf done that way, you have the minimum chance of the fire and minimize any load on either side's circuitry.The battery in effect becomes a bypass cap. I've also seen sometimes if you attempt to start the dead car before there's any sort of charge in its battery, there can be sparks at the connection point of the jumper cables on either car if the connections are not tight.

author: Unknown
author_rank: Unknown
timestamp: February 04, 2015, 06:07:16 pm
content: Reminds me of the myth that storing car batteries on concrete will deplete the charge

author: Yago
author_rank: Frequent Contributor
timestamp: February 04, 2015, 06:46:09 pm
content: I'll add a couple that happened at place I used to work at.Guy was working on a car, and he dropped a crimp that fell behind the battery.He reached in to get the crimp and his steel bracelet sports watch shorted between battery and chassis.Sparks, the watch welded in place and immediately started to glow red.Luckily for the guy(he was certainly due some at this point!), an engineer was cropping a PMR antenna and cut the watch off in seconds.I myself dropped a small spanner that clipped the live terminal and an air con braided hose.The flash ruptured the pipe and vented the entire air con and set the car alarms off.Looked a bit like a certain Delorian returning from temporal jaunt.My ears felt like they needed a new time zone from the bollocking I got.Yep, as Dave says "trap for young plays", and as it was decades ago, even I was young then!

author: arildj78
author_rank: Regular Contributor
timestamp: February 04, 2015, 09:56:30 pm
content: If we remove all the factors related to possible mishandling of the jumper wires (such as shorting out or reversing polarity). What can actually go wrong when using old fashion cables on new cars as compared to new fancy ones?Quote from: SeanB on February 04, 2015, 04:46:07 pmI'm reluctant to believe that reving the engine on the receiving vehicle can cause alternator failure due to overcurrent while charging the empty battery. Are there any documented cases of this happening?Quote from: PA0PBZ on February 04, 2015, 02:08:36 pmThis was my point exactly. The statement is from a supplier of car batteries which instantly ruined all their credibility.Quote from: N2IXK on February 04, 2015, 02:37:03 pmHave anyone ever been able to produce enough gas while jumpstarting a car to blow up anything? In a closed environment, while charging for a period of time, sure, but while jumpstarting with an open hood?

author: SL4P
author_rank: Super Contributor
timestamp: February 04, 2015, 10:18:23 pm
content: And I thought we were going to discuss 'popping' the clutch in second gear to turn the engine over when the battery is flat.

author: calexanian
author_rank: Super Contributor
timestamp: February 04, 2015, 10:38:05 pm
content: Push starting cars is much more fun!

author: IanB
author_rank: Super Contributor
timestamp: February 04, 2015, 10:41:49 pm
content: When 99% of cars in America are automatic, is it even possible to push start a car any more?

author: DarrylB
author_rank: Newbie
timestamp: February 05, 2015, 02:17:24 am
content: I don't think you can bump start an automatic. If the vehicle is petrol, beware of jump starting because excess burnt fuel that hasn't been burnt can get into the catalytic converter (assuming it has one) - this is bad for the catalyst - at your next MOT (or whatever emissions test you need to do in the country you live in) you'll need to buy a new one. They are not cheap.

author: N2IXK
author_rank: Frequent Contributor
timestamp: February 05, 2015, 03:34:20 am
content: No, you can't push start an automatic, because there is no hydraulic pressure to make the transmission work unless the engine is running. The hydraulic pump is driven off the engine side of the torque converter.I've wondered the same about the actual likelihood of creating a flammable gas cloud around a battery with the hood open as well. After all, the gas in question is H2, and that flies away very well given any opportunity. But I guess its one of those better safe than sorry kind of things.Have seen a few cars where the positive battery post isn't even accessible to clamp onto, and you are supposed to jumpstart to a terminal provided on the main power distribution box that connects to the battery cable.

author: cimmo
author_rank: Frequent Contributor
timestamp: February 05, 2015, 03:58:13 am
content: My personal method (based on some paranoia and maybe a bit of Dunning-Kruger) is thus:1: Both cars switched off.2: Connect cables3: Start donor car, fast idle for several minutes.4: Switch off donor car - leave cables connected.5: Start recipient car (donor car NOT running, but donor battery in circuit), fast idle for several minutes or until warmed up a bit (especially if very cold weather).6: Switch off recipient car, disconnect cables.7: The recipient car should now be warmed up and will crank easier and with some charge put in to the battery it should start OK.I think this procedure (whilst a little time consuming) can rule out any possibility of load dumping spikes/alternator overvoltage. Unless the recipient battery is actually faulty, ie, merely discharged beyond the ability to crank, then this will work.IF the recipient battery is so faulty that it won't start the car after this procedure, then it is not likely to act as a suitable load for the alternator anyway and the recipient car's electrics could be damaged by alternator spikes.If this is the case and the owner of the recipient car wants to take the risk, then use this for step 6:6: Leave recipient car running, disconnect cables.

author: sleemanj
author_rank: Super Contributor
timestamp: February 05, 2015, 03:59:55 am
content: Quote from: calexanian on February 04, 2015, 10:38:05 pmAs long as you are the one in the driver's seat!

author: arildj78
author_rank: Regular Contributor
timestamp: February 05, 2015, 03:51:38 pm
content: This is how I sum up the discussion so far:Apart from the fear of shorting out or reversing polarity, there are absolutely nothing that can be damaged from using standard jumper cables on a new car. All the voodo is to either minimize the risk of shorting out the battery or because of myths about things that can go wrong, none of which can be documented.

author: SeanB
author_rank: Super Contributor
timestamp: February 05, 2015, 04:05:22 pm
content: Modern alternators are cost cutted severely, using a whinner wire to keep the cost of copper down, along with diodes on poor heatsinks. Trying to get the full 60/80/100/120A out of the standard unit for more than 30 seconds is very likely to result in it failing. The only saving grace is that the wiring to the battery is also thinner so the resistance does limit the current somewhat.Cars with dual batteries and stock alternators 9 the car sound guys) will regularly blow up the alternator until they put in an upgraded unit that can handle charging at the full current for long periods, as they run the one battery down during engine off. Same with outdoor vehicles, because the auxillary battery often is left till it is flat then the starter battery can easily start the engine, but then it is run at high RPM to charge the flat one at a very high current.

author: SeanB
author_rank: Super Contributor
timestamp: February 05, 2015, 04:41:38 pm
content: Quote from: sleemanj on February 05, 2015, 03:59:55 amI was with a friend one day at a garage buying some lamps and there there was a couple of guys who came in, with the one towing the other to the garage so he could put fuel in the pulled car. Battery there was flat, so he simply pulled the battery out of the towing car ( engine running) and put the battery in the towed vehicle, then started it. Then disconnected battery and put the flat battery back in the tray ( loose, without tightening the terminals either) while the first car got it's battery back. Towing vehicle was an Isuzu KB, towed vehicles was a Ford Escort. I tok a bet with my friend that the Ford would need a new distributor module soon, knowing just how sensitive they are, and driving at that time a Ford with the same engine. I kept a module in the car, along with the 7mm spanner and a capsule of grease, as just in case spares, having had a few of those module fail, especially when hot. Ford ones were 10x the price of the aftermarket ones, and often came in the same box with the same batch codes on them.

author: VK5RC
author_rank: Unknown
timestamp: February 05, 2015, 08:37:33 pm
content: An observation, when the roadside service guys jump start your car (way too much experience as a young fella) they NEVER use the car/vans battery, they always use a second free battery.There is at least one automatic that can be push started, we had an old Humber Hawk automatic that had a dry plate clutch for top gear and I think a rear pump as well! I think with anything after 1970 you would be in a hard place because of the electronics.

author: Zero999
author_rank: Super Contributor
timestamp: February 05, 2015, 09:51:12 pm
content: Lots of those myths started by people who don't know what they're doing.I remember my brother and his friend trying to jump start a motorcycle by connecting a spare battery to it via a skinny piece of 0.5mm2mains cable and wondered why it wouldn't work. He thought the fact it's mains cable meant it should be able to take 12V. I had to explain to him it the cable is only rated to 3A and the starter motor needs much more than that which is why the cable got hot and started to melt. Fortunately I had some properly rated cable handy.

author: SeanB
author_rank: Super Contributor
timestamp: February 06, 2015, 04:59:43 pm
content: Quote from: VK5RC on February 05, 2015, 08:37:33 pmSimple, as they often have to jump start having a spare battery in a carry case with the leads attached makes it easy, without having to first align the 2 vehicles ( hard on a freeway with 65 ton trucks coming past about an inch from your behind) head to head. Plus it is easy to lug into the garage without having to drive the van up the steep drive and figure out if your leads are long enough. Plus often the battery is on a small 2 wheel trolley with a wooden board on the back frame that the cables are wound around and then the clamps are held by the board. Makes it easy to lug out of the van, and as it is a large battery, often from a wrecked vehicle, the battery is free to them, and is simply charged at the end of shift for the next day. Same used in car dealerships and workshops to jump start the stock or vehicles in for repair.

author: gregallenwarner
author_rank: Regular Contributor
timestamp: February 06, 2015, 05:40:29 pm
content: Just a personal story of my experience jumping cars. I'm usually very careful. I always double and triple check my polarities, connect the + first, etc. But once I was jumping a friend, and after I had connected the leads to my battery terminals, and was about to connect the other end to his dead battery, heinsistedthat he be the one to connect his own battery. I agreed, because I didn't doubt his capability. I just reminded him to make sure of the correct polarity.I start my car with no problem, however, when he goes to start his car, the engine turns over once and is followed by smoke billowing out of his battery. I rip the cables off my battery in a hurry and then run over to see what's going on with his.He had connected his side backwards, even after my warning.One of the terminals shot right out from the battery housing. He then needed to buy a whole new battery. Miraculously, my battery was unharmed, but I was pretty worried because for a moment, both batteries were hooked up in series with each other.Anyway, the lesson I've taken from this is my new personal policy. If you want a jump from me,Iconnect both sides of the leads. If you don't agree to that, you can get a jump from somebody else.

author: IanB
author_rank: Super Contributor
timestamp: February 06, 2015, 06:04:00 pm
content: Quote from: gregallenwarner on February 06, 2015, 05:40:29 pmI see the point, but it is safer still if two people consider a situation together and both agree to the next action before taking it. For instance, "We are going to connect this red clip to this battery terminal here, right? Agreed. Agreed." You may believe you are reliable and won't make mistakes, but one day you may have a brain fart and someone else will save you.

author: gregallenwarner
author_rank: Regular Contributor
timestamp: February 06, 2015, 07:01:23 pm
content: Quote from: IanB on February 06, 2015, 06:04:00 pmOh, absolutely. The other person is welcomed and encouraged to look over my shoulder as I'm connecting the leads to the terminals and grounding point on the engine. But it's still gonna be my hands performing all the steps, as my vehicle is connected to the system and I'm not putting my vehicle into the hands of somebody else. I've bothered to take the time and learn proper jumping procedures; I don't trust the other person's done the same.

author: Artlav
author_rank: Frequent Contributor
timestamp: February 06, 2015, 07:51:38 pm
content: I suspect the myths arise from lack of understanding.Consider a regular carburetor car, that have no electronics in it more complex than a radio tuner.Turning the key switches the starter motor on and pulls it's gear link into contact with the engine.Anyone can visualise that, and so it is obvious what to do and not do.And if it's not, there is a full set of blueprints in the user manual.Now, take a look at the modern car.Stuffed full of electronics few people have any idea of how they work internally.No schematics in the manual.Does it need 12V, or will 14V do?Wouldn't all these computers go crazy from seeing a lack of a battery?Won't some spike fry everything?Won't there be interference from the other car's electronics over the cable?Just a jumper cable is no longer seem safe, so you go charge the battery at home and come back the other day.Complexity of the cars overtook the people's ability to understand them.Therefore, myths.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 07, 2015, 02:55:36 am
content: Ihaveused normal jumper cables to start reasonably modern cars,but the last few sets of jumpers I've bought do have a "spike protector,or whatever it is,just to be on the safe side.The "protected"one usually costs about $10 more than a basic one,which raises the question:If spike protection can be provided on a cheap jumper lead,why isn't it hardwired into cars which cost tens of thousands of dollars?Auto Electricians have always kept an undeserved aura of mystery over car electrics.Most of the "high tech" stuff uses circuitry which was in common use in other fields 20 or more years ago.

author: David_AVD
author_rank: Super Contributor
timestamp: February 07, 2015, 03:26:55 am
content: Quote from: vk6zgo on February 07, 2015, 02:55:36 amI suspect that's partly because often they don't really understand how a lot of things work. They know the procedures to troubleshoot, but they don't understand the underlying principles.

author: SeanB
author_rank: Super Contributor
timestamp: February 07, 2015, 04:47:32 am
content: Auto electricians have a vague understanding of the parts, and how they are connected, but the internals are true black boxes. Most ECU units returned to the manufacturer under warranty are tested, and no fault is found, as the ECU is changed to see if it is the fault, and doing so corrects the intermittent connection fault that actually was the issue, or they also changed all the sensors as well where one was faulty.Most ECU units are pretty reliable, aside from the usual designed in faults, like Hyundai using cheap capacitors that failed after 6 years, or Bosch where they used a steel leaded power resistor that developed dry joints on the leads after 5 years in service.Older vehicles had a 5A fuse in the main fuse box to feed the ECU, and next to it was a transient suppression block that was designed to protect the ECU from damage by over voltage by blowing the fuse, and it was also designed to fail as a short circuit from prolonged over voltage. Only problem was auto electricians would pull the module ( looks like a plug in Bosch relay) and jumper it out if the fuse kept blowing, and leave it jumped out with a 20A fuse. Thus the next time you would blow the ECU, through no fault of the manufacturer other than the protection box being an expensive spare part.

author: calexanian
author_rank: Super Contributor
timestamp: February 07, 2015, 08:21:31 am
content: You can get an old style automatic transmission car running by pulling it. Depending on the torque converter anyways. use a tow strap and begin pulling the car. Most will fire at around 20 to 30 MPH, but make sure you have along tow strap cause when the car starts its going to be all out of whack and you don't know what gear its going to try and put itself in. I would not try it an any vehicle with an ECU or electronic controlled anything. You will probably fry everything. Obviously if you have another running vehicle you could just go get another battery anyways. Only experienced rednecks and hillbillies need apply.

author: Artlav
author_rank: Frequent Contributor
timestamp: February 07, 2015, 12:53:45 pm
content: Quote from: calexanian on February 07, 2015, 08:21:31 amOr someone stuck 20km away from anywhere with a broken drive pinion on the starter motor.

author: VK5RC
author_rank: Unknown
timestamp: February 08, 2015, 05:51:53 am
content: Quote from: calexanian on February 07, 2015, 08:21:31 amThat makes me one, dang, or whatever I am supposed to say. HiHiReminds me of an excellent Australian series about Australian Aborigines who are legendary for being able to get a pile of rust moving,As a uni student I spent 3 months with the Warlpiri people, they are a pretty interesting lot. Lajamanu is one of the major settlementshttp://en.wikipedia.org/wiki/Lajamanu,_Northern_Territory"Bush Mechanics"

author: richard.cs
author_rank: Super Contributor
timestamp: February 08, 2015, 09:25:20 am
content: Two things that haven't been covered much:1) Cheap jump leads, those nice fat looking cables are not a good deal when they're a couple of stands of copper up the middle of a mass of plastic. They might be described as "20 mm cable" in the hope you think it means "20 mm^2" but it's really the diameter of the insulation. Those with an actual cable size specified are often aluminium so aren't quite as good as you first think either. Even those with real cable often have poor terminations with the core folded back over the jacket and the whole lot crimped. Any of those are probably best considered "charging cables", given time you can dump enough energy into a flat battery to start a car but if you try to crank it with the donor battery they just get very hot.2) All the "connect the negative last to the engine block" stuff assumes both cars are negative earth. Positive earth cars are pretty rare now but they do still exist so if starting or jumping from an unfamiliar car it's probably worth a sanity check, you're working next to the battery anyway so it should be pretty obvious. We're mostly talking cars from the early '70s or before but some military vehicles were positive earth later than that (and some are floating chassis).

author: Rerouter
author_rank: Super Contributor
timestamp: February 08, 2015, 09:40:31 am
content: There is also the reverse situation, if your using a fancy car to jump start another, and pulls the voltage low enough while its running can corrupt something... e.g. you short out, or the battery in the fancy is tiny (which is common),if you have ever seen an audi showing ------, its either because some idiot tried to change the mileage, or someone kept on trying to turn over with a near open circuit battery and cheap thin jumper leads, the inductive spikes screw with the clusters more than it should... ford AU falcon is a similar case but not for jump starting, it seems to be more of a problem with European, than US or asia region, which is the reverse of what most might think...I myself follow the rule of negative to chassis rather than terminal, as at the power levels would like some limitation, let it trickle across until it starts drawing decent current, wait another 2 minutes, then try and crack the dead car with the donor still connected, as i mainly drive a work ute i have a clamp ammeter and a good set of leads on me at all times, but most might not have this luxury,

author: calexanian
author_rank: Super Contributor
timestamp: February 09, 2015, 02:49:38 am
content: When I take by truck into the bush or desert I always take along a topped up deep cycle battery and some jumper cables I made from end cuts of 2/0 welding cable and some arc welding ground clamps. The cables are only about 6 feet long or so and I have never had any trouble getting a car going with that setup. You have to be careful with some modern setups. Primarily Mercedes and BMW because the battery is in the trunk and hard to get to in some vehicles. There is typically a couple of jump start lugs under the hood but some have proprietary connectors. that tow companies sometimes have. Some of the hidden battery compartments require special tools as well. I have (And do not recommend because you can fry the cars brains) connected jumpers right to the terminal on the back of the starting solenoid because there was no other spot to get at a guaranteed positive low impedance terminal that did not go through some other sort of part of the system. That was out in the desert and I was nervous as hell that I was going to fry the cars electrics. It worked like a champ though. Everybody should make a set of those cables. They make it so easy. No waiting to charge. Just clamp her on and go.