SteveP Posted April 4, 2005 Share Posted April 4, 2005 Just looking in the Owner's Manual and I notice that it says that you should attach the negative jump lead to a good earth (e.g. engine mount or similar) and not the battery's negative terminal when jump starting from another vehicle. Can anyone offer a reason why this should be? Cheers SteveP The Caterham Pages here Link to comment Share on other sites More sharing options...
Myles Posted April 4, 2005 Share Posted April 4, 2005 Well, it's true for all jump-start instructions I've ever seen - not just the Caterham - but I universally ignore it because it can be quite hard to find somewhere suitable to make a decent connection. I'd like to know the reasoning too - so I can ignore it in safety rather than in perilous ignorance as at the moment... Project Scope-Creep is underway... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Frying Pan Posted April 4, 2005 Share Posted April 4, 2005 I think it's to do with the (small) risk of sparks. We provide remote battery connection points on most of our vehicles (Land Rover) for this purpose, and becasue the batteries are not easy to get to. Guy See some pictures of the build here. 5000 miles completed! Link to comment Share on other sites More sharing options...
SteveP Posted April 4, 2005 Author Share Posted April 4, 2005 Thanks Guy, I did wonder if it was to do with the increased risk of a short or something like that. I was getting kind of worried that it might do some irreversible damage to a sub system or something (I had to jump start my Seven the other day and just attached the leads to the battery terminals) Cheers SteveP The Caterham Pages here Edited by - SteveP on 4 Apr 2005 11:33:14 Link to comment Share on other sites More sharing options...
elise_s1 Posted April 4, 2005 Share Posted April 4, 2005 I think it's because of the high load (Ampere) running through those connections when cranking. Connecting to a good earth (ideally the engine block) helps to keep the lowest resistence in the circuit: it bypasses any possible resistance from the original battery negative to the engine, giving the highest crank power. BTW, if the battery is properly earthed, the resistance difference is minimal. cheers Carlo Link to comment Share on other sites More sharing options...
Frying Pan Posted April 4, 2005 Share Posted April 4, 2005 No, should be no problem. On Range Rover, we have an explosive device that blows the +ve attery lead off the battery if a crash is detected . Direct connection to the battery is not recommended.... Nothing similar on the Seven (inertia switch only does fuel pump). Guy See some pictures of the build here. 5000 miles completed! Link to comment Share on other sites More sharing options...
robert heywood Posted April 5, 2005 Share Posted April 5, 2005 if you connect the jump leads on to a dead or dodgy battery you are then putting the charge through the dodgy item, putting the earth jump lead to another place on the car (7) you are bypassing the problemb Link to comment Share on other sites More sharing options...
owelly Posted April 5, 2005 Share Posted April 5, 2005 You should always connect the earth lead LAST (and remove it first) and to another part of the vehicle that has a good earth. The reason is to take the spark away from the top of the battery and its' explosive gasses. You will make a spark, however small. I very rarly do even after having my best shirt blow to bits by an exploding battery. Lazyness I spose its only a game......... http://daftlardycars.mysite.wanadoo-members.co.uk/ Edited by - owelly on 5 Apr 2005 23:34:45 Link to comment Share on other sites More sharing options...
Chris W Posted April 7, 2005 Share Posted April 7, 2005 The reason is the risk of a spark close to possible battery gases that a couple of people have already mentioned. "Bypassing a dodgy battery" and "resistance" reasons are nothing to do with it whatsoever. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
elise_s1 Posted April 7, 2005 Share Posted April 7, 2005 not 100% convinced about it. if the main reason is to prevent sparks, the same should apply when trickle charging (maybe smaller sparks, but just as good for igniting gases...) or am I missing something? Carlo Edited by - elise_s1 on 7 Apr 2005 08:17:39 Link to comment Share on other sites More sharing options...
thinfourth Posted April 7, 2005 Share Posted April 7, 2005 when trickle charging you get very little gassing when you are using a jump start you can put loads and loads of amps into the battery. I speak from experience the amps get a bit silly after melting all the insulation off a set of jump leads when jump starting a fishing boat. If you are wandering how or why i used to work in marine electrics and had a wonderful van with or 4 fishing boat batterys in the back all wired in so they were charged off the alternator and you could get it close enough to the boats you could start anything. The alternator finally died one day and we just removed it and ran around with a total loose system just recharging the car when you needed it. It was a bizarre car as you opened the glovebox and the battery warning light cam on and the fuel gauge started to work Sod the heater wheres my shades Link to comment Share on other sites More sharing options...
elise_s1 Posted April 7, 2005 Share Posted April 7, 2005 ahem... when jump starting the high load is not towards the faulty battery, but towards the starter motor. Melting the insulation off a set of leads is a very good example of high resistance through the leads. edited to add: I think the "good earth instead of negative of battery" subject is related to the car that receive the jump start, not the donor. In fact, the donor should connect both leads to the battery (no risk of spark there?) Edited by - elise_s1 on 7 Apr 2005 08:43:52 Link to comment Share on other sites More sharing options...
Johnty Lyons Posted April 7, 2005 Share Posted April 7, 2005 I regularly jump start Big Boats I use 40mm 30ft long jump leads and NEVER connect to the Batery bank Far To Risky jj N.I. L7C AO. Membership No.3927. Se7en Services.N.I. Caterham Service Agents. www.onthelimiter.com Link to comment Share on other sites More sharing options...
owelly Posted April 7, 2005 Share Posted April 7, 2005 Triclke charging will not make sparks if you do it properly!Don't switch the charger on until after you have connected it to the battery its only a game......... http://daftlardycars.mysite.wanadoo-members.co.uk/ Link to comment Share on other sites More sharing options...
Chris W Posted April 7, 2005 Share Posted April 7, 2005 If you run the maths, the initial current surge between the two batteries may be of the order of 100 amps. Thus big sparks possible. The current is only limited by the batteries' internal resistance and the resistance of the leads and croc clips. Whereas, with a trickle charger, the current is limited to around 4 to 8 amps typically. Still enough to produce some sparking though and I agree with Owelly that the charger should be switched on after connecting the charger to the battery. Interestingly the handbook to my Jag warns (in bold print) never to connect the donor negative lead directly to the Jag battery but rather to a remote earth point. It also states (contrary to popular belief) NOT to run the donor battery's engine while jump starting for fear of damaging the Jag's electronic systems. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
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