Alternator/charging questions

kburley · Nov 3, 2017

Hi gents, hopefully I have the right section for this.

Replace my alternator a few days ago after the battery light came on. Replaced the alternator the battery light turned off. 2 days later (last night) I noticed my dash lights getting really dim. withing 5 minutes of that, the truck lost all electrical power and died.

plugged it into a charge pack and it ran fine, but after a few minutes of idling, unplugging from the charge pack killed the engine. I know now that the battery and alternator are both to be replaced (alternator didnt charge the battery and now the battery is pooched as well), so I replace the alternator for the second time as well as a new battery.

What concerns me is that the battery light never came on when the second alternator failed. based on what I have described, was I right to think the first replacement alternator failed? the fact that the light didn't come on makes me wonder if there's a separate issue, like wiring.

also, my multi meter is dead so I have not taken and voltage measurements. any input on this topic would be helpful. if there's anything you guys think I may have overlooked please let me know. It is imperative that this truck runs properly from here on out.

Cheers!

RonD · Nov 3, 2017

You need that volt meter or you will just be guessing

It is very simple to test charging system, but you must have a volt meter
Battery, alternator and wiring are the 3 things that must be OK for charging system to work

You don't have to replace both battery and alternator at the same time, sometimes you do but thats where volt meter can save you money
And if just 1 wire that is loose or fuse is blown then neither battery or alternator needs to be replaced, so you save even more money by testing system with volt meter.

After battery was charged and sitting for a few hours a good vehicle battery will show 12.3v to 12.8v.
A new battery will show 12.8volts
5-6 year old battery 12.3volts

When battery gets down below 12.2v then it won't start engine on a cold morning
If battery voltage is dropping with volt meter connected then it probably has an internal short
Disconnect from vehicle and test again, if still dropping, even very slowly, replace battery, one cell inside has a short so battery is self draining

With battery connected, key off
Test voltage at alternators B+ wire, larger wire back of alternator, on 2005 should be black with orange stripe
It should show battery voltage from first test, i.e. 12.3-12.8volts
If not then it is disconnected or fusible link is blown

If it has battery voltage then move on
Unplug 3 wire connector on alternator
Test yellow wire
Should have battery voltage, if not then fusible link is blown
If OK test Green wire
Should have 0 volts
Turn on the key, engine off
Test Green wire again, should now have battery voltage, this is the ON/OFF switch for alternator
If low or no volts then check fuse #9 in cab fuse box(2005 ranger), 5 amp fuse <<<Battery Light fuse

So pretty simple, test battery then test 3 wires

If battery is OK and 3 wires are OK then alternator is bad

Start engine, battery voltage should now be over 14volts if alternator is working, if you see battery voltage 12.3-12.8volt then alternator is not working

The battery is ONLY used to start the engine.
Once engine starts ALL THE POWER to run the electrics comes from the alternator, voltage in vehicle should now be 13.5 to 14.9volts so the 12volts from battery is not used, higher voltage recharges battery then keeps it charged for the next time it is needed, to start engine again

NEVER disconnect battery while engine is running to "test" if alternator is working, you could do that in the "old days" but it can damage the voltage regulators in the newer, 1985 and up, systems, use a volt meter

kburley · Nov 3, 2017

Thank you my friend. excellent information. I will perform these tests today. I am going to start by testing voltage at the battery while on and off. I didnt initially need to replace the battery, but i ran the truck on battery only for 2 days unknowingly and ruined the battery.

thanks for all the info, I will let you know what I find out later today!

kburley · Nov 3, 2017

RonD said:
You need that volt meter or you will just be guessing

It is very simple to test charging system, but you must have a volt meter
Battery, alternator and wiring are the 3 things that must be OK for charging system to work

You don't have to replace both battery and alternator at the same time, sometimes you do but thats where volt meter can save you money
And if just 1 wire that is loose or fuse is blown then neither battery or alternator needs to be replaced, so you save even more money by testing system with volt meter.

After battery was charged and sitting for a few hours a good vehicle battery will show 12.3v to 12.8v.
A new battery will show 12.8volts
5-6 year old battery 12.3volts

When battery gets down below 12.2v then it won't start engine on a cold morning
If battery voltage is dropping with volt meter connected then it probably has an internal short
Disconnect from vehicle and test again, if still dropping, even very slowly, replace battery, one cell inside has a short so battery is self draining

With battery connected, key off
Test voltage at alternators B+ wire, larger wire back of alternator, on 2005 should be black with orange stripe
It should show battery voltage from first test, i.e. 12.3-12.8volts
If not then it is disconnected or fusible link is blown

If it has battery voltage then move on
Unplug 3 wire connector on alternator
Test yellow wire
Should have battery voltage, if not then fusible link is blown
If OK test Green wire
Should have 0 volts
Turn on the key, engine off
Test Green wire again, should now have battery voltage, this is the ON/OFF switch for alternator
If low or no volts then check fuse #9 in cab fuse box(2005 ranger), 5 amp fuse <<<Battery Light fuse

So pretty simple, test battery then test 3 wires

If battery is OK and 3 wires are OK then alternator is bad

Start engine, battery voltage should now be over 14volts if alternator is working, if you see battery voltage 12.3-12.8volt then alternator is not working

The battery is ONLY used to start the engine.
Once engine starts ALL THE POWER to run the electrics comes from the alternator, voltage in vehicle should now be 13.5 to 14.9volts so the 12volts from battery is not used, higher voltage recharges battery then keeps it charged for the next time it is needed, to start engine again

NEVER disconnect battery while engine is running to "test" if alternator is working, you could do that in the "old days" but it can damage the voltage regulators in the newer, 1985 and up, systems, use a volt meter

I measured before and after turning the truck on. at the battery terminals I get 12.3V off and 14.4 volts on. 12.3 seems a bit low for a brand new battery, but its charging now.

RonD · Nov 3, 2017

New, battery should read 12.8volts, even 13v

After you drive it back from work or after a 20min drive don't shut off the engine, let it idle.
Open the hood and test battery again, should be under 14volts now, 13.5-13.8v

Check volt meter on a 9v battery, or similar to see if it might be reading a bit low
.4 or .5volts off wouldn't be out of line unless volt meter cost over $100

Alternator/charging questions

kburley

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RonD

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kburley

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kburley

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RonD

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