Originally Posted by noelex 77
Maine Sail I am puzzled why you are not measuring the much larger inrush currents reported by others. The inrush current is always going to be much larger than the steady state starting current by a factor of at least 5X. If I accept the conclusion that
The steady state starting current would be less than 26 to 36A.
As you are not convinced by the Blue Seas data here is another link
This link shows an inrush current of 1295 A measured on Isuzu C240PW
It should be remembered that these inrush currents are very short duration. They are not to be confused with CCA ratings or the current carrying capacity of conductors. These specifications are for durations a couple of orders of magnitude higher.
I have to agree with David
Again, I measured it with a meter capable of capturing in-rush to 1/1000th of a second and those test show that the times are longer than my meter captures so unless it is broken I should be capturing good data. I bought this meter specifically to capture in-rush loads because I purchased one that claimed in-rush but that was not fast enough on DC.. Those engines referenced are all significantly larger than my small Mitsubishi and significantly larger than anything on most small sailboats. I never doubted Blue Seas data as I have seen it but that data can't be applied to all engines.
I still don't understand the point? Are you insinuating that deep cycle house banks can't start a motor
because of a few milliseconds of in-rush current? On BIG engines you'll need BIG cranking amps but on small diesels you can still get BIG cranking amps compared to what the motor
My whole point in this was that I had seen about my fourth set of fried diodes because boaters believe they NEED to start on the start battery then switch back to the house bank. They do not, in most cases and with most boats out there wired with a factory installed 1/2/BOTH/OFF switch the less switching you do the less chance you have of HEF (human error factor). I always prefer to re-wire the vessel so that fried diodes can't happen but some owners just don't want to spend the money
These in-rush currents are insignificant to starting a small diesel
off a sufficient house bank. Even if you did or do have a 1200 A peak, bigger engines certainly can, your cable and a 200 amp ANL fuse would still sustain this just fine as would your battery bank deep or starting.
I have measured in-rush currents over 1000 amps just not on small motors like mine. I measured over 1300A on a big John Deer marine
engine in a lobster boat. The fisherman was using some old 6V batts from a floor polisher cause he got them for free. Motor started fine and the batts were 3 years old when he installed them. Lobstermen are tight with the buck. The biggest I have seen on small motors are the old Perkins
engines but still not an issue for starting off a good house bank.
In the spring, when my boat un-thaws, I will again measure in-rush. I will use both the Extech and a Fluke to make sure they are in agreement. I still suspect it will be where it was a few years ago but either way it still does not matter to the original point.
BTW here is a pic of the bank of two T-105's and the big Cummins engine in our old power boat
. Even in the icy cold temps, we left her in over the winter, the T-105's started that rather large beast of a motor without issue...