Voltage Drop

[Kpar]

Looking for some advice. My 33 is 6volt pos/earth with a battery isolator on the firewall. How much voltage drop at the isolator should i expect when cranking the engine. At the moment with a fully charged batt voltage drops to 4-5 volts. All cables sizes are above specs and have good connections.
Do I need to check the starter motor if so how to test if it is drawing too much current ?.
Kpar

[Kurt in NJ]

You take a volt meter and connect 1 lead to tyhe starter post, the other to the battery post, crank engine---the volt reading should by 1/2 volt or less (the higher the voltage the more that is getting "lost" in the wire, switch and connections

another way to test is simple---crank engine with ignition OFF for 15 seconds, feel all the wire and connections, anything that gets too hot to hold without burning is a problem

starter test specs---
locked (not turning) 3.2V@ 500amps ---14 ft lbs torque
normal cranking --100 eng rpm,225amp @ 4.75Volts
spinning free---2700 rpm,@50amps

[Kpar]

Originally Posted by Kurt in NJ

You take a volt meter and connect 1 lead to tyhe starter post, the other to the battery post, crank engine---the volt reading should by 1/2 volt or less (the higher the voltage the more that is getting "lost" in the wire, switch and connections

another way to test is simple---crank engine with ignition OFF for 15 seconds, feel all the wire and connections, anything that gets too hot to hold without burning is a problem

starter test specs---
locked (not turning) 3.2V@ 500amps ---14 ft lbs torque
normal cranking --100 eng rpm,225amp @ 4.75Volts
spinning free---2700 rpm,@50amps

Thanks Kurt, I'll follow your instructions and see how things pan out.
As far as Auto Electrics go "I know enough to be dangerous"
Kpar

[koates]

Keith, Your cranking voltages are in the OK or good range. Why do you ask, are you having a cranking speed problem ? Another thing to be wary of are cheep shit plastic body battery isolator switches which are good for only 200 amps or less. These need to be metal heavy duty (truck type) switches capable of handling 500 amps or more for your 6 volt system so as to avoid too much voltage drop. Regards, Kevin.

[Kpar]

Originally Posted by koates

Keith, Your cranking voltages are in the OK or good range. Why do you ask, are you having a cranking speed problem ? Another thing to be wary of are cheep shit plastic body battery isolator switches which are good for only 200 amps or less. These need to be metal heavy duty (truck type) switches capable of handling 500 amps or more for your 6 volt system so as to avoid too much voltage drop. Regards, Kevin.

Thanks Kevin, The reason I asked is that it is very slow to crank over for the first revolution almost like too much advance. It has me worried sometimes that its not going to crank up. But it does this with ignition off. Good point on the battery isolator though.
I think Lawrie had some issues with his so I'll have a chat with him.
Kpar

[Kurt in NJ]

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Could there be oil or grease on the commutator or brushes-----sometimes this will give a starter a slow start, then pick up as it heats it up some