Yaatri

I am sorry to dig up an old controversy about current draw of a BMC 1.5 disel engine starter. 50 Amps is in the right ballpark. The engie was rated at 40 bhp (30kW) at 4000 rpm. Assuming cranking rpm to be about 100, we can calculate the power required to start the engine. At 100 rpm you need 30000/40 Watts or750 Watts. With a 12 volt battery, the current would be about 62.5 Amps. Simple sviemve works. Experience is important but experience without science might as well be religion. I don't mean to be insulting, it's simple advice. Purposevof science is to make things simple. It's true that cranking current depends on all various factors rightly pointed out by many here but it does not answer the question posed by Theo. We need not go into detailed calculation using temperature, pressure, compression ratio, engine volume, flywheel, pinion gear and their ratio or frictional losses and other things in order to get a reasonable estimate. It could easily be in 80-100 amp range if cranking rpm is higher, in which case experience rules. Peak current, the current draw when you first crank the engine, will be higherand then drops during cranking before the engine starts. I think my explanation is reasonable and is based on what I know about the engine and the assumption about the cranking rpm, which is always lower than idle no load speed. P.S. I should have introduced myself before posting since I am a brand new member and this is my first post. Hello to all. I arrived here looking for a ball park current draw of a starter during cranking.