How to incorporate dual alternators

witt

Adventurer
Hi,

I have a ford E-350 build in progress (http://www.expeditionportal.com/forum/threads/72722-Another-E350-build-thread) and am planning on installing a second alternator. There's room for another one in the engine bay, (apparently it came with the ambulance package on these vans.)

I'm planning a year-long trip overseas, and would carry a spare anyway, so I figure I might as well just install it now and have one less thing rattling around inside the van. The main goal of this is redundancy.

So the question I have is, should I:
1. Hook up the second alternator to van's electrical system and then install a split-charge system, or
2. Create a dedicated "house" circuit where the second alternator is only connected to the house batteries, leaving the vehicle's stock electrical system untouched?

The advantage of (1) is that if one of the alternators fails, I don't have to do anything to get things running again. In fact, it seems like I may not even know if one of the alternators has failed unless I install some sort of monitoring system (so that could be a disadvantage).

With option 2, I wouldn't have to purchase and install a split-charge unit, but I probably would have to run some additional wiring to connect the second alternator to the house batteries. In the event that either alternator failed, I'd have to re-wire or jump power to either the house system or the starting system, and without a split charge unit, I'd have to be moving wires around all the time to make sure all of the batteries stayed charged.

Just typing this up is making me think that I should go with option 1 and get some kind of current sensor so that I'd know if one of the alternators had failed.

Anything I'm overlooking here?

Thanks!
 

Fastlane

New member
I would recommend going with invisible option 3.

3. Upgrade stock alternator to high-output unit.

You could purchase a H.O. Large-case conversion kit and just have a single, more reliable alternator. However, if you are stuck on using a stock dual alternator setup (non-large case), I would recommend option 2. - running a "house" alternator directly to the battery(s). I understand the allure of redundancy in the system, unfortunately option 1 (as you have realized) will require a custom harness to run both alternators with the OEM electronics. Frankly, this may not even be possible without the PCM and engine harness from a dual alternator model. In the stock setup, the PCM senses each alternator and sends a DTC when there is a fault. Even on the stock dual-case system, the battery light may not indicate if only one alternator goes down.

Cliff notes:

1. May be impossible without PCM, harness, and possible other proprietary OEM parts
2. Add a second OEM or high-output non-large-case alternator wired only to the battery(s)

3. replace single OEM unit with Large-case 6G High-output unit

If you have any other questions, I will be happy to help.
 
Add a second alternator and run its output to the house battery bank. If your main alternator goes sideways, jump the vehicle batteries over to the second alternator and you're up and running in 10 minutes. Those Ford alternators are for sale pretty much everywhere so getting a broken alternator replaced or repaired should not be problematic. I wouldn't bother with a split charge or battery isolators if you have a provision for a second alternator, nor would I spend a bunch of money on a high output alternator. Just go with good quality Ford 3G units...maybe take a spare regulator to throw in the glove box, and call it good. New, quality, aftermarket 3G at 130 amps should run you under $150.
 

dwh

Tail-End Charlie
Every alternator I can remember having failed was due to worn out bearings. When it happens - you'll know it.

One thing to think about is that normal voltage regulated alternators are pretty poor battery chargers.

I'd rig the second alternator to the house bank using an external 3-stage regulator:

http://sterling-power-usa.com/advancedregulators.aspx

That will insure a tip-top charge to the house battery, which, unlike the engine battery, will benefit greatly from a proper charge routine.


AND I'd rig a split charge relay with a dumb solenoid and a manual switch so I could tie the primary and aux batteries manually in case of alternator failure. Cut the belt off the failed alternator, flip the solenoid switch, keep going.
 

witt

Adventurer
> One thing to think about is that normal voltage regulated alternators are pretty poor battery chargers.

That's good to know.

I found a few threads on installing the second alternator (one here: http://www.powerstroke.org/forum/99-03-7-3l-general-discussion/171363-dual-alternator-setup.html). It sounds like if I'm not going to tie the second alternator into the stock electrical system, I should just need the mounting hardware and a new serpentine belt, but not the Ford wiring harness. Then I'll run my own cabling back to the voltage regulator and house batteries.

I guess I'm assuming that the alternator isn't relying on any signals coming from the car's computer to operate properly. So it's just a matter of connecting the output of the alternator to the voltage regulator?

That sounds like a good way to go as long as I can find the mounting hardware, as it gets me a backup alternator, plus a charging profile that should be more friendly to the house batteries.

Thanks for all the great info!
 

dwh

Tail-End Charlie
So it's just a matter of connecting the output of the alternator to the voltage regulator?
Output of the alternator goes to the battery. Voltage regulator goes to both - senses battery state and engages the alternator clutch (energizes field coil) to control the alternator as needed.
 

dwh

Tail-End Charlie
Serpentine belt? Ouch. If one alternator locks up or starts smoking from a bad bearing...then what? How do you bypass it?
 

witt

Adventurer
Hmm. Was watching a youtube video on how to install the second alternator, and it sounds like you need a different (longer) belt for the dual setup. One could probably keep spare belts for each of the single alternator configurations in case one of them died, assuming that the shorter belt will clear the pulley on the dead alternator.

As usual, the more I look into the details of this the more complicated it gets! :)
 

dwh

Tail-End Charlie
Hmm. Was watching a youtube video on how to install the second alternator, and it sounds like you need a different (longer) belt for the dual setup. One could probably keep spare belts for each of the single alternator configurations in case one of them died, assuming that the shorter belt will clear the pulley on the dead alternator.

As usual, the more I look into the details of this the more complicated it gets! :)


Or, if the alternators are the same, if one failed you could move the good one to the location for which you have a spare, shorter belt.
 

mhiscox

Expedition Leader
I also vote for a second alternator dedicated to the house batteries, which was the setup I ran on my Unimog camper. However, my second alternator was run off a separate short belt driven by a separate crank pulley mounted in front of the main pulley. I've no idea whether this is practical in your truck, but it is worth investigating as I believe this would be considered "best practice" when possible.

A second point worth noting is that most automotive alternators do indeed do poorly at deep-cycle battery charging, but it is possible to buy a marine-quality second alternator (Balmar is perhaps the most widely cited brand) that will do very well at charging the house battery bank. These alternators can be sized to match the battery bank size, which means they'll routinely be more like 70 amps than 150+, and they are very well built. Sadly, though, that's reflected in the pricing.

A setup that had a dedicated, properly sized, high quality alternator driven of a separate belt would be tough to beat if it was practical for your truck.
 

witt

Adventurer
Yeah, a separate belt/pulley would be ideal, but that would definitely require some non-standard modifications to the engine.

I'm running into two issues here:

If I install a Ford alternator (or an aftermarket alternator designed for the engine), the physical installation should be straightforward. However, the smart regulators (from Balmar and Sterling power) require a connection to the field terminal of the alternator. Do all alternators have that externally accessible? I found a wiring diagram for the Ford dual alternator setup conveniently posted online: http://www.powerstroke.org/forum/99...er-install-any-wiring-diagrams-out-there.html. Any idea which of the terminals on the alternator in that diagram is the field terminal?

Or if I go with a Balmar alternator and regulator, the wiring connections should be straightforward since they're designed to work together, but the physical installation would probably be harder since the alternator isn't designed for my engine.

I'm thinking that if I can figure out how to wire the regulator to an alternator that is designed for my truck, that would be the easier and cheaper way to go.

Thanks very much for everyone's input on this!
 

dwh

Tail-End Charlie
In that schematic, the field is controlled by the "sensing and switching circuits" (the (presumably internal) regulator).

The connections are A, B+ and I. The diagram has those labeled inside the border of the unit. But at the lower right, it looks like the wiring of the field coil connects to something that is outside the border and not labeled. Looks like an "O". [EDIT: I see they have the same dealy for the B+ connection...so yea...it might be...]

No idea what that is supposed to mean in that diagram. Could be an external field connection but no way to know without seeing the alternator itself.


Even if your alternator doesn't have an external field connection, it probably wouldn't be a big deal to have an alternator shop add a connector for you.

I'd call up or drop by a local alternator rebuild shop. In Denver...dunno. Maybe these guys?

http://www.yellowpages.com/denver-co/mip/generator-exchange-co-5957771?lid=5957771
 
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witt

Adventurer
dwh,

Thanks for taking a look at that! I also sent the question to Belmar tech support and got a confirmation:

"Automotive alternators are internally regulated. You will need to take the Ford alternator to a shop and have them disconnect the internal regulator and bring the field wire out. The field wire can then be connected to the field output of the MC-614. The 614 would be just fine for your application. As to pricing, it would be best to contact one of our dealers in your area or find them on line."
 

Ozrockrat

Expedition Leader
OK I will play the devil's advocate here! Stick with a completely standard ford installation. You get the system monitoring of both alternators. Carry a spare "Short" belt in case of failure (although I have never seen an alternator catastrophically fail without plenty of warning. The only thing that will cause you to stop running is a failed bearing/seized alternator). You get to hear about that long before it goes to a seized state. If it happens put the short belt on (maybe move the 2nd alternator into the primary position).

Then do not run house batteries, parallel up the whole bank but install low voltage cutout master for all house equipment (I use mine to isolate all power when leaving the van parked for any length of time, Thieves would need to know how to turn the isolator on to get the van running). Ford also has a high idle option so that if you need a lot of power you can be running the engine at a ramped up idle as required for the current draw. (winching, battery charging, run the espresso machine for everyone :coffeedrink:)

Benefits
  1. Quicker replenishment of all batteries.
  2. Larger capacity for winching, engine starting.
  3. Spreads load across all batteries evenly.
  4. Less time in the critical discharge state resulting in longer battery life.
  5. Any ford guy will know what he is looking at if you ever have problems.
  6. Lowest cost solution gets you more fuel and miles traveled.
  7. System monitoring of both alternators (can read the ford codes to see if there are problems)
  8. Standard parts available from anywhere.
 

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