Steve K-B 51 Report post Posted July 28, 2013 Ive relocated my battery on my project car and need to run some new battery cables. I have access to an OE cable but its bloody huge and weighs a ton. For me, smaller, lighter and something flexable is what im looking for. Id like it flexable because the way ive mounted my kill switch as its not in a really ideal location cable wise... Any idea what a Starter motor will draw? 100, 120 amps? Its running an m52b28 with an m20 starter motor. What size cable have some of you guys run with six cylinder engines? Ive been told BMW cable is good quality stuff and im sure it is but as I said before.... Its too big and heavy for me. Any good brands in the automotive cable industry? Quote Share this post Link to post Share on other sites
BM WORLD 1280 Report post Posted July 28, 2013 isnt it more like 500-800amps?? for a starter motor Quote Share this post Link to post Share on other sites
Allanw 1068 Report post Posted July 28, 2013 In THEORY about 200 amps would probably cover it... BUT try it on a cold day, with cold oil/engine, and it could possibly increase a lot, as the slower it turns with more load, the longer each winding is a "short" for. The current will peak at each compression stroke. 200 Amps at 12V is about 2400W, which is about the rating of a M54 starter motor (dunno what the others would have), but thats not taking into account how in-efficient the motor is - And I don't think they are very efficient - my electric assist bike only gets up to about 85% and it's electronically controlled DC brushless motor). Just because the starter is rated at 2.5KW, doesn't mean that power is always required either - the engines compression/tightness determines the required load. The wire resistance also goes up as it heats up, so if you are too close to the limit, a long cranking time could result in less and less power to the starter, and the wire getting hotter and hotter, making EVERYTHING worse A geared starter should have less peak draw, as they spin faster and smoother., but it's average will still be quite high It could still get up pretty high in the right situation. Quote Share this post Link to post Share on other sites
polley 916 Report post Posted July 28, 2013 (edited) Some 35mm weldflex would prob do the trick, a lot lighter and more flexible than the OE stuff. You would prob even get away using some 25mm weldflex. Edited July 28, 2013 by polley Quote Share this post Link to post Share on other sites
hotwire 352 Report post Posted July 29, 2013 25mm cable will cover it in this application. I assume you are running the later reduction drive M20 starter & battery mounted in the boot? Starter current would initially peak @ 300 -350 ish & drop from there during crank. Make sure you put a good chassis earth at the battery & another engine - chassis up front. Quote Share this post Link to post Share on other sites
