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Originally Posted by Cobb
I think you need to check your starter with a V-O-M meter and make sure the armature isnt shorting to ground.  |
I've heard that several times on here. I assure you that 290 peak amps isn't unusual. The Camry draws 255A, and the Cummins 5.9L peaks at over 400A, which is higher than my gauge can go. The motorcycle peaks at 80A, and it only has a 0.6L engine.
A motor at dead standstill IS basically shorted to ground. The copper windings in the armature have very low resistance, so when it's connected to the battery, a huge spike in current flows through them until it gets spinning. Once spinning, the reverse EMF induces a resistance and the amps quickly drop down. The faster the motor spins, the more resistance is induced and amperage is reduced.
The battery only has to sustain the ~300 amps for the fraction of a second it takes for the motor to begin spinning. After that, it might fall to 1/4 of that.
There is a reason batteries need to be rated at 400+ CCA. The initial surge is tremendous.
That said, I have a pretty sweet SuperCap/LiFePO4 setup that I'm going to install right now. I'll update my thread with my findings.
EDIT: Some comments from
another forum:
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A starter motor from a normal 2 Litre petrol car draws between 60 and 200 Amps when turning over the engine when the oil is warm and thin.
Under winter conditions, this current can easily double when the oil is thick.
Diesel engines have a very high compression ratio e.g. 22:1 and require more powerfull starter motors. On average they draw between 300 and 500 Amps for average sized car engines 2 to 3 litre while on truck engines the current could easily reach 1000 Amps at initial turn over... The resistance in these circuits are between 0.1 and 0.01 Ohms.
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I think that 300 amps is a better estimate for that car.
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I've heard 70A @ no load and 400A locked rotor @ 4v across the motor. Maybe 250A amps while cranking?
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FYI- A stopped motor that has not yet begun to spin IS a locked motor.
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The 12 V starter motor for a V8 4 litre diesel takes a peak of around 1000 A.
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