The Stovebolt Site Forums The Shop Area The Electrical Bay Cranking Voltage - what's normal

I think its cranking ok but not sure.

Starter has new brushes, newer 600 CCA battery, cleaned all connections including frame where attached. New brass nuts and bolts for connecting. Cables look pretty good.

I get 4.8 volts measured from starter frame to copper stud on starter while cranking. Temperature: 60 degrees, fresh engine - cold. Cranking is definitely not fast but seems ok.

What do you all think???

What gauge are your battery cables? 4.8 is not bad, but It could probably be improved with bigger cables and clean connections.

Connections are fresh, cables are 1 ga. Next time I need a battery, NAPA has an 800 CCA for $80, I may get it. Don

That's good cranking voltage for the battery you're using. If you have access to a high-load battery tester, pull a 300 amp load (1/2 the CCA) for 15 seconds, and check the voltage while the load is still on. You should get 4.5 volts or more. The battery should be able to do at least 3 load tests in a row 5 minutes apart without seriously dropping the test voltage.
Jerry

Use 2/0 cable on a six volt system. Regardless of how many battery amps you got the motor only operates on teh voltage at its terminals. 4.8 volts on battery sounds like you are dropping voltage on starter cable and or ground cable. Check each cable for voltage drop while you have someone crank it when cold - DISABLE ignition you do not want it starting.

Dan Bentler

Check the voltage on the battery terminals (right on the posts) while cranking. This will tell you if the drop is internal to the battery or connectors or cables. The voltage at starter will be lower voltage on posts. Use same technique to determine if cables or connectors have resistance.
note:
On a 12v system, a drop to 9v on the posts while cranking indicate a battery with high internal resistance. A good battery should read 10.5-11 v.on the posts.

Hank, I'd love to buy my batteries wherever you're getting yours! If an engine is very low on compression those voltage numbers might be correct, I guess! I haven't seen battery terminal cranking voltages that high on a 12 volt system in 50 years of working on, and teaching automotive electrical systems.

On a 6-volt system, series resistance, which is the voltage drop from one end of a cable to the other, should be 1/10 volt per cable. Each connection should have an allowable drop of 1/10 volt, with NO voltage drop on the ground side of the circuit except for connections like the ground cable's attachment to the frame or engine block, and the battery terminal connection. For 12 volt systems, those measurements can double due to the higher voltage available to push current through the resistance. All these measurements should be made while the engine is cranking with the ignition disabled.
Jerry

Thanks for the great info. I checked again, looks like all is good except the positive cable to the starter, it measures .28v. The battery is not the best but I think it will do for now. What's the best supplier for the 2/0 ga positive cable? Don

Often, you can find 00(2/0) cables at Tractor Supply Store. A welding supply shop might make them but they might not have 2/0 terminals. A good large-truck repair shop might be able to make them correctly.

Welding cable is made up of hundreds of strands of hair-fine wire, which will carry current much more efficiently than the relatively coarse strands of a battery cable. I've had very good luck using #1 or #0 welder cable for battery leads, and soldering the terminals on to minimize voltage drop.
Jerry

I'll try Tractor Supply first. Years ago I made a pair of jumper cables out of Welding cable, best thing I ever did. They work great, never stiff in the cold. Don

A good method to check the voltage drop in a circuit is to span it with your volt meter while it is operating. Like on your starter system put one lead on the batt. POST and the other on the starter bolt then have someone operate the starter. The only thing you cant get with this is the starter switch on the old stomp types.Do the same with the ground circuit.

Maybe I was not clear where to measure the battery voltage drop. The test leads are directly across the battery posts(very good connection). With a fully charged battery this voltage drop will be a good indication of the internal resistance of the battery under load.This is the voltage you are delivering to the wire,starter, connectors,etc. High internal resistance in the battery is an indication of decreased plate area internal to the battery and less current available to the starter. Try the measurement with the engine cranking let me know the voltage you read. I respect your years of experince,mine was 36 years EE

Hank, the last two letters of your post explain the problem precisely- - - - -EE!

Try doing it in the real world for a while, where theory runs head-on into actual facts and figures! My brother has those same letters after his name, plus PHd. He has the added advantage of being an ASE certified Master Technician with real, hands-on-the-wrench experience to go with his theoretical pipe dreams! All I've done is troubleshoot and repair cars, trucks, buses, construction equipment, airplanes, boats, and industrial equipment since the mid-1950's, with a specialty in DC electrical systems.

The SAE (Society of Automotive Engineers) specification for acceptable 12 volt battery testing results is 9.6 volts or above, measured at the battery posts, after a load test of 15 seconds at 1/2 the Cold Cranking Amps figure. Load a 500 CCA battery to 250 amps for 15 seconds, measure the terminal voltage with the load still applied, and the voltaqe should be at, or above 9.6. The electrolyte specific gravity should be 1.250 or above to assure an accurate test.
Jerry

Enough said lets get back to work. I always enjoy a friendly discussion.Lets always keep it fun.
thanks hank