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post #1 of 13 (permalink) Old 06-05-2019, 05:48 AM Thread Starter
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High Output Alternator Questions

Hey guys it’s been awhile since I’ve been on here but had a couple questions about an alternator. I upgraded to a Mean Green alternator a few years back and it never really did create enough amps while at idle. Well it’s time to replace that and I’m looking at a Singer Alternators (they are a local business) it would be a 200 amp alternator.

Question 1: The fuse box has a 120 amp fuse does this need to be upgraded as well due to the high output alternator?

Question 2: Rather than upgrading the 120 amp fuse in the fuse box would this work? Power from alternator to battery, then into a 120 amp circuit breaker, then into the fuse box. This way the fuse box is protected and the 120 amp would not need upgraded because the circuit breaker would blow first.

A little bit of back story on my current setup. I am running dual yellow top agm batteries, but at the moment they are not isolated and wired in parallel - this will soon be changing I’ll be adding a Redarc dual battery isolator system with solar charge controller.

My alternator is not looking good as it’s only putting out 4-6 amps at idle - will be doing further testing on the alternator as well.

Really I wanted to pick you brains and get an idea of what all needs to be upgraded with the high output alternator and if question 2 above makes sense and would work.
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post #2 of 13 (permalink) Old 06-05-2019, 08:16 AM
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Re: High Output Alternator Questions

The 120 amp fuse should be fine if you do get a new alternator always check with them to see what they recommend, I wouldn’t go to the trouble with the fuse box/circuit beaker

It achieve more amps at idle you need a smaller pulley on the alternator which you can do with a Mean Green they should have them if you call

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post #3 of 13 (permalink) Old 06-05-2019, 09:56 AM Thread Starter
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The 120 amp fuse should be fine if you do get a new alternator always check with them to see what they recommend, I wouldn’t go to the trouble with the fuse box/circuit beaker

It achieve more amps at idle you need a smaller pulley on the alternator which you can do with a Mean Green they should have them if you call
I am going to replace the mean green with a Singer Alternator and it will have a smaller puppy to achieve more amps at idle.

Would it make sense to go power from alternator to battery with a 200 amp or breaker in between the alternator and battery then go battery to fuse box with a 120 amp fuse or breaker in between?
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post #4 of 13 (permalink) Old 06-05-2019, 11:36 AM
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Re: High Output Alternator Questions

How many amps are expecting from the new alternator at idle? What are your plans for the green non performing inadequate poor performance used alternator?


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post #5 of 13 (permalink) Old 06-05-2019, 12:52 PM Thread Starter
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Hey Sparky, I’m not exactly sure how many amps I’m expecting at idle but what I’m looking for is to have stability in my voltage meter in the dash. Currently when I come to a stop the voltage is bouncing. I’m only running a 4 channel amp for speakers no subwoofers so it’s not audio related, I do run quite a few accessories while camping such as a fridge / freezer. I have dual batteries and a solar panel but periodically I’ll start the FJ to try and charge the batteries if I’m camping for a few days and not driving. As for the mean green alternator I haven’t really decided I was probably just going to keep it as a spare for an emergency after having it tested.

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post #6 of 13 (permalink) Old 06-05-2019, 02:40 PM
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Re: High Output Alternator Questions

I camp in the FJ and run a fridge and a CPAP overnight, and all I have is a single group 34 Odyssey and stock alt... starts right up strong as ever in the morning.

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post #7 of 13 (permalink) Old 06-05-2019, 03:52 PM Thread Starter
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I camp in the FJ and run a fridge and a CPAP overnight, and all I have is a single group 34 Odyssey and stock alt... starts right up strong as ever in the morning.
Mine was starting right up no problem. Then battery level got so low that believe it was part of the reason why I had to replace the 120 amp fuse in the fuse box because the alternator was not charging the batteries. I was camping for 6 days so I think it finally took its toll.
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post #8 of 13 (permalink) Old 06-05-2019, 04:46 PM
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Re: High Output Alternator Questions

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Currently when I come to a stop the voltage is bouncing.
If you mean it goes down, then back up, and then holds, I think this just what happens while braking.

Mine does that - with a less-than-a-year-old 130A Toyota alternator, a less-than-a-year-old Odyssey 31M-PC2150 battery, and every cable in the alternator/battery/fuse-box system upgraded and with a few extra grounds added.

https://www.google.com/search?&q=bat...+while+braking

Alternators control the current they generate by running more or less current through them as they spin. They can either spin faster or run more current through them, to produce more current. When you brake, the spin decreases, so less current is produced. To make that up, the alternator's got to run more current through it. Combined with incandescent brake lights, if you have 'em, braking is a sudden drop in current output coupled with a sudden jump in current demand - which will manifest as a voltage drop.

It's also possible that the voltmeter on the dash isn't entirely trustworthy. Can you replicate the voltage bounce while parked, just by applying and releasing the brakes? If so, run a multimeter into the cab and see if its voltage reading agrees with the dash gauge.
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post #9 of 13 (permalink) Old 06-05-2019, 06:04 PM
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Re: High Output Alternator Questions

Get an alternator with a pin stator, instant full output.

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post #10 of 13 (permalink) Old 06-05-2019, 06:46 PM Thread Starter
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Quote:
Sigmataun49 previously said: View Post
Currently when I come to a stop the voltage is bouncing.
If you mean it goes down, then back up, and then holds, I think this just what happens while braking.

Mine does that - with a less-than-a-year-old 130A Toyota alternator, a less-than-a-year-old Odyssey 31M-PC2150 battery, and every cable in the alternator/battery/fuse-box system upgraded and with a few extra grounds added.

https://www.google.com/search?&q=bat...+while+braking

Alternators control the current they generate by running more or less current through them as they spin. They can either spin faster or run more current through them, to produce more current. When you brake, the spin decreases, so less current is produced. To make that up, the alternator's got to run more current through it. Combined with incandescent brake lights, if you have 'em, braking is a sudden drop in current output coupled with a sudden jump in current demand - which will manifest as a voltage drop.

It's also possible that the voltmeter on the dash isn't entirely trustworthy. Can you replicate the voltage bounce while parked, just by applying and releasing the brakes? If so, run a multimeter into the cab and see if its voltage reading agrees with the dash gauge.
Firedog,

I can try to replicate the voltage bouncing while driving but my alternator is only putting out 4-6 amps currently at idle. My battery light illuminated on the dash so I’m thinking I’m going to have to replace it. I’m not sure what else could cause the battery light to be on since the battery is charged to 100%.
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