dual alternators...advantages...failures...replacements

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Sep 29, 2014 | 02:13 PM

busflyer

Thread Starter

Mountain Pass

Joined: May 2007

Posts: 108

Likes: 1

From: KY

dual alternators...advantages...failures...replacements

Just received my rebuilt FICM from FICMrepair and wanted to comply with the warranty so went to have one of my two alternators bench tested. It comes back as basically a boat anchor only putting out 50 amps at best. I've got the other one off now and will be taking it in to have it tested as well. I would like to upgrade to a higher output unit but wanted to ask for thoughts on how to go about it with a dual alternator system. Would I need to be upgrade both at the same time? Do I even need to upgrade if I replace them both with properly functioning stock units? Its a bit hard to swallow having to buy two of them, why would I need 500 amps of capacity. What advantage do I have being equipped with dual alternators. Do they provide me with extra capacity or does one sit in reserve? I guess my big question is can I just replace one or will they have some type of "phase" problem or will one overpower the other and cause some other type of issue.
Thanks for the help,
Eric

Sep 29, 2014 | 09:46 PM

waumpuscat

Senior User

Joined: Aug 2004

Posts: 152

Likes: 0

watching this one myself, I have dual alternators and am eager to hear the replys

Sep 30, 2014 | 12:49 AM

Coronado

Mountain Pass

Joined: Jun 2006

Posts: 187

Likes: 8

From: Texas

Dual Alts are typically for Fleet applications, snow plowing, ambulances, or any instance where you need a lot of juice on a regular basis.

You can get two stocker alternators from DC power which provides a fantastic aftermarket product. Be wary of their wait times though. I bought a 190 stock alt and it took them over 3 1/2 weeks to ship it.

Sep 30, 2014 | 01:23 AM

Yahiko

Fleet Owner

Joined: Apr 2012

Posts: 27,307

Likes: 549

From: Spanaway

You may want to do a little research on DC Power
and there customer service. From what I have
been reading they leave something to be desired.

Sean

Sep 30, 2014 | 02:54 AM

HT32BSX115

Logistics Pro

Joined: Feb 2005

Posts: 3,952

Likes: 117

From: Upper Left Coast

Quote:

Originally Posted by busflyer

why would I need 500 amps of capacity. What advantage do I have being equipped with dual alternators.
Thanks for the help,
Eric

Howdy,

The only reason you'd need 2 alternators is because 1 doesn't provide the current to run all your accessories.

You have batteries for essentially 1 purpose.

To provide starting current at a minimum voltage for the starter, ECM, FICM and other accessories that might operate during start.

Once the engine is running the alternator(s) provide current to recharge the batteries and current for all accessories.

It should (ideally) have enough current capacity to power everything and provide MAX charging current simultaneously.

Most designers would want a "pad" of extra current capability so the alternator never operates at max rated current.

Any additional over and above the "PAD" is unnecessary.

If I was designing a multi-alternator (2 or more) set up, I would provide current sensing with the regulators so alternators would all deliver approx the same current (load sharing)

Unless you're running one of these:

8000 Watt Modified 12 Volt Power Inverter

Quote:

Continuous output power: 8000 Watts
Surge power capability (peak power): 16,000 Watts
dc input / operating voltage: 10 to 15 Volts · Output voltage: 120 Volts ac +/- 10%
Output wave form: modified sine wave with phase correction
Output frequency: 60 Hz +/- 1 Hz
Battery low voltage alarm: 10.5 +/- 0.5 Volts
Battery low voltage shutdown: 10.0 +/- 0.5 Volts
No load current: < 1.3 DC amps
Full load efficiency: 90%
1/3 load efficiency: 95%
No load minimum operating temperature: 30ºF
Full load maximum operating temperature: 150ºF
AC Output Socket Type: quadruple Type 2 -3 prong
High input voltage protection: 15V-17V
Low input voltage shutdown: 10V
Internal fuse protection
Product size: 19” X 7” X 6.5”

You probably don't need dual 250A alternators!

Sep 30, 2014 | 04:08 AM

WatsonR

Lead Driver

Joined: May 2014

Posts: 6,545

Likes: 13

From: Virginia Beach VA

What was the warranty requirement for the FICM? I would think that dual functioning alts at the level they should operate is sufficient to meet requirements. Stock is 140 and if one's putting out only 50, time for a new one.

You could run the 95-97 3G alt with an adapter for a 170 output each. I even think they are cheaper than the 6G we use. Spend the saved money on a better cable for less impedance and call it done.

In the dual configuration, I think only one gives max output mainly, the second unit only picks up the slack when commanded. Not both outputing max all the time, it would blow up batteries I would think, or cook them.

Sep 30, 2014 | 07:58 AM

busflyer

Thread Starter

Mountain Pass

Joined: May 2007

Posts: 108

Likes: 1

From: KY

Thanks for the replies folks. i was able to get the secondary alt off the truck and run it out for testing and it came back good. Despite that I was hearing a bit of bearing noise and felt a bit of the "pepper grinder" as a spun it freehand so it is being replaced as well just so I don't have to get into it again when the weather gets cold. I think the DC power alt would be a good investment but I just don't have the time to be without my truck any longer. I picked up two reman units from NAPA and will install them this morning. Lesson learned is to take the advice on FICMRepair.com's website and do the testing while waiting on your repaired unit rather than after it shows up. As an aside, their turnaround on my repaired FICM was really incredible. Tracking indicated it showed at their place on Friday and it was back in the mail Saturday at 11 AM. At my door Monday by lunch. Looking forward to putting it all back together. I'll do some more research in hopes of upgrading at a later date.
E