Join Date: Feb 2011
Location: San Francisco Bay area
Thanked 64 Times in 64 Posts
Rep Power: 5
Re: House batteries won't start engine - ideas?
I went through this recently on my boat.
Fundamentally the problem is likely to be a high resistance connection somewhere, because it's loose or corroded. At starting currents, even a fraction of an ohm is significant. It's quite possible to have a resistive contact that does not cause much loss at normal house bank currents (I never go over 20A), but when you start pulling 300A you lose several volts at the bad connection.
A starter needs ideally 9V, and the battery voltage might drop to 11V while starting, so that means no more than 2V drop across all your cables and the battery switch. All the connections need to be in tip-top state to achieve this.
There is no substitute for a careful measurement of voltage drops between the starter and the batteries, WHILE engaging the starter.
My main issue was a loose nut on a connection at the starter. However, I also replaced several poorly-made battery cables, and the Perko switch itself. The Blue Sea Systems switches are better. I got the battery cables from Genuinedealz.com, and went a size larger.
It REALLY starts nicely now!
Bristol 31.1, San Francisco Bay
Last edited by MarkSF; 03-12-2014 at 02:15 PM.