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Changing stock alternator to higher output one

denisegold

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46
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Reno
Not sure if it’s my alternator needing replacing. Had it checked and it shows good but after a four hour drive my voltage only showed 12v during the drive. Wondering if I swap it to a 220a alternator if that might help my batteries? Would the swap cause any issue with any electrical components, glow plugs etc??
Thanks again


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amrg

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I cant see what vehicle you have. But in general, the H3 controls alternator voltage depending on electric load/battery charge for fuel economy. If you want to see if your alternator is maxed out, put a considerable load on it and measure output voltage.

I upgraded to a 250 amp alternator and after 30 mins I would see 12.6 volts. With efans on, the alternator would output a constant 13.2-13.6 volts

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denisegold

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46
Location
Reno
I cant see what vehicle you have. But in general, the H3 controls alternator voltage depending on electric load/battery charge for fuel economy. If you want to see if your alternator is maxed out, put a considerable load on it and measure output voltage.

I upgraded to a 250 amp alternator and after 30 mins I would see 12.6 volts. With efans on, the alternator would output a constant 13.2-13.6 volts

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‘92 HMCO


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amrg

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Well ignore what I said then about pcm control.

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LagunaH1

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Lake Forest, CA
If your alternator is tested and looks good, then O'd start by checking, double checking and triple checking your battery connections. Make sure they are clean and tight.

Couple of questions:

What does your voltage read when you are idling the engine? If it's less than 13.7 volts at idle, does it rise when you rev the engine?
 

denisegold

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Messages
46
Location
Reno
If your alternator is tested and looks good, then O'd start by checking, double checking and triple checking your battery connections. Make sure they are clean and tight.

Couple of questions:

What does your voltage read when you are idling the engine? If it's less than 13.7 volts at idle, does it rise when you rev the engine?

Voltage on dash shows 12 at idle and 13 when driving....


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LagunaH1

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Lake Forest, CA
It should show 13.7 -ish even when idling. If it doesn't, then either the alternator is not right and / or you have something pulling a LOT of current so the alternator can't provide enough at idle.
 

denisegold

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Messages
46
Location
Reno
It should show 13.7 -ish even when idling. If it doesn't, then either the alternator is not right and / or you have something pulling a LOT of current so the alternator can't provide enough at idle.

3272929b9c865b2a2a5e52ac9193760c.jpg




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denisegold

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Messages
46
Location
Reno
Starts up every morning but if I run to the store (10 min drive) it will not start right up upon my return. I have to wait a little bit and then it finally catches. Very strange. No stereo or electronics installed. Stereo will go back in shortly but this issue has me at a loss.


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LagunaH1

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Lake Forest, CA
In that case, check your battery terminals and if they are good, then I think the alternator is the prime suspect despite having been tested.
 

denisegold

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46
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Reno
So then my original question comes back around. Can I use a 200a alternator as a replacement or will it muck up the electronics.


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LagunaH1

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Lake Forest, CA
So then my original question comes back around. Can I use a 200a alternator as a replacement or will it muck up the electronics.


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That’s a good question, one I’m not sure I can answer completely.

I *think* the answer is yes, but I’d be curious what 3Hummers and Hummech have to say on this topic

I do know that you will want to make sure which ever alternator you choose, will produce enough amps at idle speed. The max rating will be at a certain RPM, just like the trucks engine has it’s max torque. And HP at set RPMS


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denisegold

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46
Location
Reno
That’s a good question, one I’m not sure I can answer completely.

I *think* the answer is yes, but I’d be curious what 3Hummers and Hummech have to say on this topic

I do know that you will want to make sure which ever alternator you choose, will produce enough amps at idle speed. The max rating will be at a certain RPM, just like the trucks engine has it’s max torque. And HP at set RPMS


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Used my multimeter on battery 12.5 and when engine at idle ticked up to 14.56. Interesting thing is my gauge still does not show needle above 13? Maybe a bad gauge.


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LagunaH1

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3,703
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Lake Forest, CA
Used my multimeter on battery 12.5 and when engine at idle ticked up to 14.56. Interesting thing is my gauge still does not show needle above 13? Maybe a bad gauge.


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That may be part of the issue right there. If your batteries show 12.5 volts when the truck is off, then that's good.

14.56 volts is a good charge voltage.

It COULD be just a not-so-accurage gauge in the dash, but that doesn't explain why your truck has a hard time starting sometimes....
 

denisegold

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Messages
46
Location
Reno
That may be part of the issue right there. If your batteries show 12.5 volts when the truck is off, then that's good.

14.56 volts is a good charge voltage.

It COULD be just a not-so-accurage gauge in the dash, but that doesn't explain why your truck has a hard time starting sometimes....

I’m thinking it could be glow plug controller. But will be checking battery leads today.


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LagunaH1

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3,703
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Lake Forest, CA
Tell us a bit more about what happens when your truck is having a hard time starting:

Does the engine crank, but not fire?

Does it crank slowly?

What happens when out finally DOES fire? Does it sputter? Does it idle rough?
 
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