> > Philip asked: > > > > Is it normal for a hot engine to require 5 times more current > > through the starter?
> Peter wrote: > > The windings aquire high resistance with age, compounded by > further resistance increase when they are hot, with the result > that the starter will be pulling something like 2000A and not > spinning the engine! > Peter then added: > Normal starter draw is around 900A cold, less hot as the > engine spins easier. Higher draw hot indicates heat related > resistance increase in the starter windings. If the resistance goes up, the current draw will have to go _down_! If we are to believe Ohm's law. > > Philip commented: > > Maybe it's time to build a shunt or a coil. I have 12, 14, > > 18, 22, and 24 AWG wire. A few inches of one of them should > > get me a shunt of suitable resistance. > Jim replied: > That would work. I think 24ga wire would be a nice emulation > of an undersized fuse! The trick is getting it nicely > calibrated, 1 mV/A would be ideal. 24 AWG was a joke. *smile* I too was thinking 1 mV/A would be nice. To achieve that, the shunt would have to be 0.001 ohms. (I=E/R; E/I=R; 0.001 V/1 A = 0.001 ohm). I dug out a wire resistance table. 13 AWG has a resistance of 2 ohm/1000 ft. So 6 inches (0.5 ft) of 13 AWG should have a resistance of 0.001 ohm. But where to get 13 AWG wire? Well, it so happens that if two identical wires are run in parallel, the result is an effective wire size that is 3 sizes larger. So a pair of 16 AWG is the equivalent of 13 AWG. So I took two lengths of 16 AWG, soldered the ends together, was about to cut it to exactly 6 inches when I realize I should have made it longer so I could make the distance between attachment points 6 inches. Oh well. I was only after a general number. If this worked, I would refine it. I rigged my shunt between the positive terminal on the battery (using a spare battery post clamp) and the positive cable (I just tucked the end of the shunt wire under the clamp's nut). I cranked the engine from the glowplug relay so I could see the shunt and the meter. And the result?? SMOKE!!!! It took less than 0.1 seconds to melt all the insulation from the two wires _and_ vaporise a 1 inch section of the copper out of the middle!! That was more than 300 A!!!! I wonder how much heat it takes to vaporise a copper wire.... Anyway, the started had deteriorated to the point it acted this way even when it was cold. So I am confident the starter is "bad". But it was now after 21:00 on a Saturday night and I needed the car. This is the reason for parts cars!! I pulled a starter off of one of them. While I had the two starters sitting on the garage floor, I used jumper cables to test them. The bad one would not even spin! I will have to open it up just to satisfy my curiosity. -- Philip _______________________________________ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
