Starter motor current

[colinwcolclough]

Hi Guys,

Am rewiring an outboard powered boat and need to know how much current my starter motor is expected to draw in order to decide battery cable size. Engine is a 1987 70hp. I know it will vary due to instantaneous current and depending on things like how good compression is and oil viscosity etc, but a ball park figure would be good.

Many thanks,

Colin

 

[roger]

You're in motor car territory here so car battery cables are probably near enough. You do have a noticable problem with the terminations. You need terminations that fit the cable and a very good crimper to make sure they don't come apart.

 

[Phoenix of Hamble]

My last engine, with an elderly 21hp inboard diesel drew approaching 200A...

Assuming your outboard is petrol, then the compression will be lower, but its a biggish engine at 70HP....

So agree with the above.... something in the same order as a decent car battery cable...

 

[tangofour]

Cold morning, sticky oil. 200A would be the minimum rated cable you should go for.

 

[andy_wilson]

The important bit of the battery cable is usually part of the outboard power loom, has it failed? If so, get some the same diameter, but it will need to be stranded to allow the flexing that occurs on turning and tilting the engine. Might end up being engine manufacturers original stuff you need to buy.

The make of engine might have been useful in your posting. Not many 4 stroke 70hp engines around in 1987, are you sure it has oil to be viscous? or is is a 2 stroke, in which case commpression is effectively lower and therefore the cranking current and cable requirement will be less.