10 volts with key on

[sendo70]

hi i have a 1987 Ski Centurion Tru Trac II with a 351 inboard, i am having a problem with hard starting so when i check the electric choke i only getting 9 volts. so trying to chase it down i start at the battery, and i have 12.15 volts, same at starter, but when i get to the dash the main wire is 12 and when i turn the key to on it drops to 10 volts, also my batt gauge reads 10 volts. sorry for the long post, what can it be?
thanks, sendo

 

[achris]

Re: 10 volts with key on

Does the battery voltage drop when you turn the key to ON also? If it does, replace (or recharge) the battery. If the battery voltage doesn't drop, start looking for a resistive (bad) connection somewhere.

 

[sendo70]

Re: 10 volts with key on

no the battery stays at 12.15 so does the starter
thanks, I will go check connections

 

[sendo70]

Re: 10 volts with key on

just came in from trying to find where the voltage drop is, I cleaned the connection at the engine ground and starter solenoid, so now with the key off at the starter solenoid i have 12.37 volts, turn key on i have 12.15 and the red wire that goes to the front of the boat from the solenoid has 12.15. when i go to the front the red wire has 12.03 and goes to 11.45 with key on. this is not normal or is it?

 

[Silvertip]

Re: 10 volts with key on

When you turn the key on, the ignition system begins drawing power as do any accessories that are switched on. Some voltage drop (source to destination) due to the resistance of the wire and connections varies by wire size is not a big deal. You just found out that dirty/corroded terminals adds resistance as you cleaned and tightened one end and gained some lost voltage. Now do the other ends as well as the battery terminals and you may pick up additional "lost" voltage. Every connection on the boat represents "resistance". They need to be clean and tight.

 

[sendo70]

Re: 10 volts with key on

thanks i will do that, now this red wire that i tested from the starter solenoid to the front of the boat is about 8ft and got the different reading is the same wire no connection between it, how much drop is normal for that wire?

 

[achris]

Re: 10 volts with key on

thanks i will do that, now this red wire that i tested from the starter solenoid to the front of the boat is about 8ft and got the different reading is the same wire no connection between it, how much drop is normal for that wire?

Depends on the size (diameter), exact composition and the temperature of the wire (mostly the size), and the current being drawn.

for example, 12 gauge wire has a resistance of 1.588 ohms/1000ft (@35*C), and 37 gauge wire has a resistance of 224.3 ohms/1000ft (@35*C).

Using Ohm's law (E=I.R) and knowing the current being drawing you can work out the voltage drop.

Chris..........