Alternator undercharging?

[donquijote]

I put in a new Delco 21si alternator in one of my 6.2 M998's and it's been running fine for 5 months. Then last night I noticed the headlights were very low, and i looked at the voltage gauge and it was all the way to the left (red). Went straight home and took a reading with my voltmeter. The batteries are new Optima Marine Blue Tops that are 3 weeks old.

Truck Running
Alternator - 14.52v
Both Batteries - 14.35v

Turned Truck Off - I tested both batteries individually
Left Battery = 48v and finally settled to 10.42v after a couple min
Front Battery = 5.25v

Is the alternator causing the problem i imagine? Could it be going bad already?
Thanks.

 

[juanprado]

What voltage are you running? Is everything 24v?

Batteries need to be at least 12.3+ each and alt if 24v, needs to be 28v off the tip of my head.

Need to recharge batteries and make sure they hold load and retest alt output.

 

[orgnal]

What voltage are you running? Is everything 24v?

Batteries need to be at least 12.3+ each and alt if 24v, needs to be 28v off the tip of my head.

Need to recharge batteries and make sure they hold load and retest alt output.

Agree. Check the alternator output voltage - should be 28v. Based on the battery voltages you are reading, your batteries may be done for; better exchange them or get new ones. Alternatively, get the batteries out of the truck, trickle charge each one separately overnight and see if come back to 12.8 volts each.

McReddy

 

[kc5mzd]

Remove all batteries and slow charge each one separately, make sure the all are exactly the same including the MFR date code. When you put them back in make sure all the connections are good and snug. Check the cables and make sure they are working properly - sometimes the ends come loose and make intermittent connections.

 

[donquijote]

Yeah I know what they should be at, and everything is 24v (no 12v accessories). I have them on the trickle charger now, but being brand new batteries and a new alternator. I imagine the alternator is the source of the problem? All my grounds are spotless and good connections, and i routinely check the alternator voltage. Will update the status tomorrow!

 

[Action]

What was the readon for the new alternator?

 

[kzeyus]

Silly question, but it is a 24v alternator isn't it? 14.5V sounds like output of a 12v unit

 

[donquijote]

Right battery after charge is at 7.62v / Left is charging still. But doesn't look promising!

*The new alternator was because the old one that came on the humvee went bad. Yes, the Delco 21si is a 24v unit

 

[juanprado]

deep cycle batteries are supposed to tolerate the continual charge/discharge cycles as that is what they are designed for. I hear more folks with troubles with optima than I hear good things...

You probably have at lease one bad battery(s) Sometimes the chicken and egg dance. Batteries killed alt or vice versa. In my part selling days it was not uncommon to need to replace both. The hmmwv should not need deep cycle batteries as the alt will keep them charged. I would bring them back and exchange for regular batteries. Whomever sold them to you, can also load test the other one if it comes up. The 7v is a paperweight , I suspect.

 

[donquijote]

I am going to take them back to interstate where I picked them up and swap them, since they are only a couple weeks old.

 

[juanprado]

I am going to take them back to interstate where I picked them up and swap them, since they are only a couple weeks old.

Where are you?

Interstate by me in Kenner has refurb group 65 reasonable. O'Reilly also sells the excide military 6TL in their label. Store on Airline in Metairie stocks them.

 

[donquijote]

Its right near me in Baton Rouge on airline, and they give me dealer prices which is nice.

 

[kc5mzd]

Is your battery charger a 12 / 6 volt automatic charger? Before retiring the right battery I would finish charging the left one then connect the two with jumper cables + to + and - to - and charge for about 30 min. Then check the right battery to see if it is venting bulging or getting hot. If not remove the jumper cables and re check the voltage. If it is over 9 volts hook the charger up directly - under 9 but over 8 I would charge them jumped together for another 30 min or so. Be aware if you have a shorted cell in the right battery it will over charge the good cells and could explode - rare but it does happen...

 

[orgnal]

Is your battery charger a 12 / 6 volt automatic charger? Before retiring the right battery I would finish charging the left one then connect the two with jumper cables + to + and - to - and charge for about 30 min. Then check the right battery to see if it is venting bulging or getting hot. If not remove the jumper cables and re check the voltage. If it is over 9 volts hook the charger up directly - under 9 but over 8 I would charge them jumped together for another 30 min or so. Be aware if you have a shorted cell in the right battery it will over charge the good cells and could explode - rare but it does happen...

What's the point? OP already said voltage on one the batteries is 7.2 volts after charging overnight. That battery is toast.

McReddy

 

[orgnal]

I put in a new Delco 21si alternator in one of my 6.2 M998's and it's been running fine for 5 months. Then last night I noticed the headlights were very low, and i looked at the voltage gauge and it was all the way to the left (red). Went straight home and took a reading with my voltmeter. The batteries are new Optima Marine Blue Tops that are 3 weeks old.

Truck Running
Alternator - 14.52v
Both Batteries - 14.35v

Turned Truck Off - I tested both batteries individually
Left Battery = 48v and finally settled to 10.42v after a couple min
Front Battery = 5.25v

Is the alternator causing the problem i imagine? Could it be going bad already?
Thanks.

OP, I did not catch this before - 'Truck running, Alternator voltage - 14.52v'. You need a new alternator. It should be putting out 28v.

McReddy

 

[Action]

OP, I did not catch this before - 'Truck running, Alternator voltage - 14.52v'. You need a new alternator. It should be putting out 28v.

McReddy

No his should not be putting out 28v. In the first post, he said he put in a new Delco 21si alternator. From what i see pn the web, that is a 12v alternator.
Your alternator seems to be working perfectly. It is thd 24v vehicle that is using too much juice.
And, it hasnt benn running fine for 5 months because you had to put new batteries in it three weeks ago...

 

[Action]

I just viewed thd delco remy spec sheet. This model comes in 12v and 24v. Is there any chance you were given the wrong one?
Question for the electricians out there....if i put a 12v alternator in the 24v humvee then start it. Then check the output. Will my tester show roughly 14v output or roughly 28 v that it is hooked up to?

 

[donquijote]

Is your battery charger a 12 / 6 volt automatic charger? Before retiring the right battery I would finish charging the left one then connect the two with jumper cables + to + and - to - and charge for about 30 min. Then check the right battery to see if it is venting bulging or getting hot. If not remove the jumper cables and re check the voltage. If it is over 9 volts hook the charger up directly - under 9 but over 8 I would charge them jumped together for another 30 min or so. Be aware if you have a shorted cell in the right battery it will over charge the good cells and could explode - rare but it does happen...

Yeah it's an automatic 12/6 charger.

Left Battery = 13.52v now and holding
Right is at 9.2v and charging up again.

 

[donquijote]

Not impossible I was sent the wrong one, but if you did put a 12v alternator on a 24v system... would it even start or work at all. I wouldn't think so, right?

 

[orgnal]

Not impossible I was sent the wrong one, but if you did put a 12v alternator on a 24v system... would it even start or work at all. I wouldn't think so, right?

The starter is what cranks the engine. So, the vehicle would start as long as the batteries had enough charge. The 12v alternator would not charge the 24v battery set up.

McReddy