Starting circuits

[Hitch]

Had a few issues with a forklift starting and rapid battery drain.

Putting a tester across a new battery, 12.6v.
Engine starts no problem at all. No change in voltage after running, I'd expect to see 13-14v...no difference at any rpm. Put tester across alternator wire and body, all I get is battery voltage. Points me to a dead alternator.

Ran a tester between live terminal and starter connection, when cranking, get about 0.3v.

Ran a tester between negative terminal and clean point on engine block, I can get about 6/7v. When cranking.... nothing otherwise. I shouldn't have hardly anything should I?

Is that voltage a likely symptom of the dead alternator?

 

[anto44]

Ran a tester between negative terminal and clean point on engine block, I can get about 6/7v. When cranking.... nothing otherwise. I shouldn't have hardly anything should I?

That's a definite bad earth between the block and the battery, that would cause the alternator to charge at a much lower rate but not stop it completely. I'd fix the earth problem first and then retest the alternator then and see if its charging.

 

[AKN]

Is there an ignition warning light? If so does it come on when the ignition is turned on? If the bulb is blown it will stop the alternator starting to charge through lack of excitation.

 

[zzr1200]

What forklift make/model???

 

[Hitch]

What forklift make/model???

Heli. Need we say more.

I'll run through the earth side and check the warning light next week.
Anything much more, and they can get a forklift man out.

 

[anto44]

A jump lead from the battery negative terminal to a clean spot on the block will temporarily fix the bad earth problem and allow you to test the alternator and see if the earth is going to fix it or if further repair will be required. I would definitely fix the earth issue as even if it's not the cause of the charging problem, having that much drop during cranking isn't going to be good for your starter motor.

 

[mtt.tr]

Assuming the starter is pulling possibly 200amps under cranking equates to 0.03ohms though at 6v loss must be snail speeds and bloody hot though I'm not 100% sure where you are measuring to and from

I would rather see the voltage from the starter negative to ground

But it doesn't add up, I would rather take a current reading that will disprove the bizarre measurement given, equally disprove it by taking a resistance reading.

Just sound like the alternator has packed up.

 

[m_c]

If the voltage drop is really 6V, I'd be surprised it was actually managing to crank fast enough to start.

 

[Hitch]

I

If the voltage drop is really 6V, I'd be surprised it was actually managing to crank fast enough to start.

Well, it's very slow cranking after a few goes on a freshly charged battery.

 

[mtt.tr]

I

Well, it's very slow cranking after a few goes on a freshly charged battery.

What's the battery voltage at this point, and what's the voltage whilst cranking

 

[Hitch]

12.6v, new battery put on this morning.
I didn't check the voltage across it when cranking tbh.

 

[mtt.tr]

12.6v, new battery put on this morning.
I didn't check the voltage across it when cranking tbh.

That would rule out the battery being tired.

 

[brightspark]

might be the solenoid contacts burnt and starter not getting full power

 

[500e]

Negative terminal to clean spot on engine block should be 1v ideally max cranking really
Check the cable for broken strands, if ok remove, clean both cable eye and block re fit, you did check battery terminal for cleanliness /corrosion
Check voltage on starter to ground when cranking 10 volt min with good battery. Alt warning bulb will stop charge on some
Check alt wires for good connection did one last week pulled main feed wire it came out of connector was as crisp as a good digestive ! it must h ave been running with a poor connection for months about 50mm wire was damaged.
People run FL into the ground

 

[not done it yet]

If the alternator is getting an excitation current, it should be charging at up to 14.4V. They are very much self-contained as far as that goes. However, the current supplied might be naff-all if it is not connected to the battery and the machine circuits are not using much.

 

[frank horton]

also depends on how it's been looked after.....
mine had a few dubias add on wiring extras.....dash removed etc.....
it will get a full rewire quite soon....
same with old tractors, they always get cobbled up....

 

[Morrisman]

Ran a tester between negative terminal and clean point on engine block, I can get about 6/7v. When cranking.... nothing otherwise. I shouldn't have hardly anything should I?

Is that voltage a likely symptom of the dead alternator?

If it’s a negative earth vehicle you should not read any voltage between battery negative and the engine block.

 

[Matrixx]

Cranking voltage is irrelevant, battery negative and the engine block should be solidly connected, just measure ( with the battery disconnected) the resistance earth from the alternator B- to the block & battery negative they should all be the same.
the next point is excitation, as mentioned the Charge fail bulb is sometimes used as the charge excitation current, or sometimes it could be a resistor.
If the diodes have failed then the charge fail light will stay illuminated.

All the connection points need to be cleaned, I have seen battery clamps with no voltage while mounted on the lead battery terminal, because there was corrosion between the clamp and the stud.