Turbocharger Posted June 5, 2011 Share Posted June 5, 2011 Quite a lot of our modifying, tweaking and bodging suffers from guesswork because we don't know the real numbers involved. Since I've borrowed a posh multimeter with data logging etc, I thought I'd post up the starting current I found, in case anyone's doing any sums. You can see 373A starting current, and then 48A charging current falling quickly to 16A within 30 secs when I took the photo (the battery had just been on charge). I also measured various voltages and found a peak 2V drop between the starter motor body and the gearbox earth stud during cranking, which explains the poor starting I've been suffering recently (and was why I'd borrowed this posh machine). 2V at 373A is 0.005 ohms, so not a big resistance - it shows how good the heavy current paths have to be! Hopefully the ballpark starting current will be of use to someone. Quote Link to comment Share on other sites More sharing options...
stuck Posted June 5, 2011 Share Posted June 5, 2011 What vehicle / engine was it? Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted June 5, 2011 Author Share Posted June 5, 2011 Sorry, 300Tdi engine, standard starter, probably an undersized battery and a torturous earth path. Quote Link to comment Share on other sites More sharing options...
stuck Posted June 5, 2011 Share Posted June 5, 2011 Sorry, 300Tdi engine, standard starter, probably an undersized battery and a torturous earth path. Cheers for posting, handy to know. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted June 6, 2011 Share Posted June 6, 2011 Excellent, this belongs in the tech archive I think! Quote Link to comment Share on other sites More sharing options...
simonr Posted June 7, 2011 Share Posted June 7, 2011 My 'top starter tip' is to run the battery -ve directly to one of the starter mounting bolts then from there to the chassis stud. It gives the thing with the biggest draw the best connection. For me and others it has cured a multitude of starting woes! It also helps the return path from the Alternator. It's surprising how much drop there can be even on an apparently good connection. On a winch at 500A I was seeing 0.5v drop on each of the ring terminals along the path and about 1v on the contactor. All in that gave about 4v drop at full load. By re-crimping then soldering the rings and making sure the studs and nuts were scrupulously clean - I got that down to about 2v. It was a big problem with my Electric Freelander which has many more connections and can draw 1000A for short durations. In this case it manifests itself as the connections getting very hot and melting the battery plastic casing! After the winter and a bit of terminal corrosion, it was dropping 10v on the interconnections. It doesn't sound much - but that's 10kw of heat being generated! When I build the next EV I'm going to use big solid copper bars to connect the batteries with the tapered receivers for the terminal posts machined into the ends. Si Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted June 8, 2011 Share Posted June 8, 2011 <..> 2V at 373A is 0.005 ohms, so not a big resistance - <..> Not a big resistance, but 2V at 373A equates to three quarters of a kilowatt thrown away that could have been helping to turn the engine... An excellent and thought provoking post - I for one will be out there at the weekend with the emery cloth and Vaseline, even though I have no problems in that area.. Quote Link to comment Share on other sites More sharing options...
Roverbo Posted June 9, 2011 Share Posted June 9, 2011 ... By re-crimping then soldering the rings and making sure the studs and nuts were scrupulously clean - I got that down to about 2v. I soldered my negative battery cable at two points directly to the chassis on my old RRC (Takes some heat and rosin). Really cured the "will not start in damp conditions unless you attach a starter cable to the block" ... There is, however, a reason for not soldering the cables on automotive cables: They get stiff where the solder is absorbed, giving a risk of breaking after prolonged vibrations. Thats the explanition i´m told, anyway... But hey, then you know what to look for .. Regards Bo Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted June 9, 2011 Share Posted June 9, 2011 ... There is, however, a reason for not soldering the cables on automotive cables: They get stiff where the solder is absorbed, giving a risk of breaking after prolonged vibrations. Thats the explanition i´m told, anyway... There won't be any prolonged vibration if the bugger won't start Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted June 9, 2011 Share Posted June 9, 2011 Glue lined heatshrink over the joint, cable ties & mountings / P-clips keep it neat and stop it vibrating any more than it should. Neat = reliable. They knew how to do it in the old days: Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted June 9, 2011 Share Posted June 9, 2011 Ooo that looks like telephone cabling with the old waxed cotton lacing, it's a long time since I did that but it does look neat when finished :-) Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted June 9, 2011 Share Posted June 9, 2011 Ten points Mr Wabbit, it is indeed, a very small part of a wall of Type 62 test panels. Back nearer the original topic, if you use busbars then neatness is also a factor: Don't drop yer spanner across it Quote Link to comment Share on other sites More sharing options...
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