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Is there a disadvantage to have two alternators ?
Was talking w someone who mentioned an article that spoke that is was not a good option to run two
Dunno, thoughts?
 

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Costs more? Twice as heavy? More points of failure? Originally intended for applications like ambulances and utility vehicles that use PTOs while idling, rather than making megawatts while you drive between campsites?
 
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There might be a few drawbacks, but IMO they are all outweighed by the ability to charge your battery bank faster. Ultimately it depends on what you're doing with your rig. It's probably not needed for weekend trips but it you plan on staying off grid for a long time it would be a worth while upgrade.
 

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Factory installed, all wirely will work with the canbus system. Relatively cheap option to add when ordering new. I did notice my quarter mile times at the dragstrip dropper by .10 😎.
 

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Dual alternators are useful under two circumstances:

1. You have a very large battery bank and you do not drive several hours each day. A 400 amp hour lithium battery would qualify as "very large."

2. You have a large load that you want to run for a period of time while idling (such as running an air conditioner in the evening to cool off the van for sleeping)

For more standard operations, the Transit's stock alternator is quite capable.
 

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  1. If you won't use both alternators (quite possible), the disadvantage is cost.
  2. If you are looking for them to do something they won't (also possible) and want to rectify, the disadvantage is it is difficult to remove the second one and not generate error codes. There is a thread on here from someone who tried and has been unsuccessful. I imagine in time someone will figure out how to correctly "unhook" the second one, but today I have not seen it.
Further comments:
  1. The Ford PCM is designed so that the second alternator does not kick in unless the first alternator is nearing saturation or too hot. I installed a hall effect meter on the wire from the second alternator to see when it kicks in. I have only been able to do limited observations and will have more data next year. But my limited observation is that it will not kick in unless you are idling with significant draw. I had my vehicle AC on full power and was pulling ~2kW/150A charging for my house batteries and the second alternator would not kick in while I was under way. Once I started idling for a little bit, the second alternator kicked in around 25A. This was on a fairly warm day (90F?). I did not idle for an extended period; assume it would progressively contribute more power as the first alternator becomes progressively warmer. So bottom line is if you are planning a system with significant draw for your house batteries, or you live in a very warm climate, or will be idling extensively, the second alternator will be useful; if you are only planning on using a 60A DC-DC charger or something like that, the second alternator may never kick on, even at idle.
  2. The Ford PCM control of the alternators is a black box. You will be subject to the "smart regenerative charging" algorithm of the Ford PCM, unless you override it with high power mode. This SRC charging will reduce voltage to around 12.5V while under way. This obviously reduces power, and it can be an even bigger issue if you are not using a DC-DC charger which will boost voltage to compensate. More generally, you will not be able to fine-tune the second alternator like you can with an aftermarket product. For example, with an aftermarket product you could dedicate the output of the second alternator to your house batteries, and have a completely different charging voltage for your house batteries, while letting the Ford PCM do its thing for the vehicle batteries.
All-in-all, it is a nice system that provides an incredible amount of power for a pretty low price. If you are unsure about your overall system design, not planning to significantly tweak things, and have some budget flexibility, then it's probably worth getting. If you plan on large power draw and want to be able to tweak, then considering using an aftermarket instead, since you will be pretty locked in once the dual configuration is installed.
 

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  1. If you won't use both alternators (quite possible), the disadvantage is cost.
  2. If you are looking for them to do something they won't (also possible) and want to rectify, the disadvantage is it is difficult to remove the second one and not generate error codes. There is a thread on here from someone who tried and has been unsuccessful. I imagine in time someone will figure out how to correctly "unhook" the second one, but today I have not seen it.
Further comments:
  1. The Ford PCM is designed so that the second alternator does not kick in unless the first alternator is nearing saturation or too hot. I installed a hall effect meter on the wire from the second alternator to see when it kicks in. I have only been able to do limited observations and will have more data next year. But my limited observation is that it will not kick in unless you are idling with significant draw. I had my vehicle AC on full power and was pulling ~2kW/150A charging for my house batteries and the second alternator would not kick in while I was under way. Once I started idling for a little bit, the second alternator kicked in around 25A. This was on a fairly warm day (90F?). I did not idle for an extended period; assume it would progressively contribute more power as the first alternator becomes progressively warmer. So bottom line is if you are planning a system with significant draw for your house batteries, or you live in a very warm climate, or will be idling extensively, the second alternator will be useful; if you are only planning on using a 60A DC-DC charger or something like that, the second alternator may never kick on, even at idle.
  2. The Ford PCM control of the alternators is a black box. You will be subject to the "smart regenerative charging" algorithm of the Ford PCM, unless you override it with high power mode. This SRC charging will reduce voltage to around 12.5V while under way. This obviously reduces power, and it can be an even bigger issue if you are not using a DC-DC charger which will boost voltage to compensate. More generally, you will not be able to fine-tune the second alternator like you can with an aftermarket product. For example, with an aftermarket product you could dedicate the output of the second alternator to your house batteries, and have a completely different charging voltage for your house batteries, while letting the Ford PCM do its thing for the vehicle batteries.
All-in-all, it is a nice system that provides an incredible amount of power for a pretty low price. If you are unsure about your overall system design, not planning to significantly tweak things, and have some budget flexibility, then it's probably worth getting. If you plan on large power draw and want to be able to tweak, then considering using an aftermarket instead, since you will be pretty locked in once the dual configuration is installed.
That is really helpful information - thank you.

In this general area, a typical summer day is over 100 F and 115 F is fairly common. I don't know how accurate these numbers are, but I have seen 119 F on the vehicle outside thermostat.

The behavior that I have been trying to understand is what happens when the vehicle is really stressed, like climbing hills, fairly heavy, on a really hot day. Or idle on a really hot day and pulling a lot of power - in the 1.5 - 2 kW range to run a vehicle rear air conditioner and charge a battery pack.

If you happen to test some conditions like this, would love to hear about them.

Thanks
 

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What I wonder about is what happens when the primary alternator fails. Is it smart enough to fail over to the secondary one?
Easy enough to test. Any takers?
 
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@NealCarney - Great info, thanks for taking the time to do the testing an the write up. This capacity data is very helpful, even for those of us who purchased the single alternator option (and are now having less regrets :)). BTW - what are you using to charge @ 150A?

Now you have got me thinking about if it might be possible to implement an approach for a two level charging set up.
One for idle charging and one for charging at speed. There is square wave vehicle speed signal in the C-33E connector
p. 122-123 BEMM. Perhaps a frequency controlled relay like this to send a voltage signal to current limit assistant on a Victron Multiplus (thanks @gregoryx) that is fed by a vehicle power inverter. Could also be used to switch a second B2B for systems using that approach.

I'd be interested in any input that electrically/control fluent folks might have on this half baked idea.
 

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@NealCarneyI'd be interested in any input that electrically/control fluent folks might have on this half baked idea.
Vehicle speed and RPM are related, but only loosely. I'd be targeting RPM rather than speed because that's directly related to alternator output.

To get this number requires reading the CANBUS or some other external TACH signal, so not as simple as the speed signal you've mentioned. Your idea could work, and I've considered something similar too. I would want more control (always) and the ability to delay turning on/off whatever device when the frequency crosses the activation threshold. Probably a good idea to have some hysteresis too. The device you linked is almost certainly just a low-cost microcontroller with some custom firmware driving a relay. The ability to customize settings would be crucial - for me anyway.
 

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That is really helpful information - thank you.

In this general area, a typical summer day is over 100 F and 115 F is fairly common. I don't know how accurate these numbers are, but I have seen 119 F on the vehicle outside thermostat.

The behavior that I have been trying to understand is what happens when the vehicle is really stressed, like climbing hills, fairly heavy, on a really hot day. Or idle on a really hot day and pulling a lot of power - in the 1.5 - 2 kW range to run a vehicle rear air conditioner and charge a battery pack.

If you happen to test some conditions like this, would love to hear about them.

Thanks
We typically top out around 100-105F in DC, so I expect to have some data for those conditions next summer. I did not realize Livermore got that warm; my myopia had me assuming it was like SF.

What I wonder about is what happens when the primary alternator fails. Is it smart enough to fail over to the secondary one?
Good question. As suggested by @Sparky961, the only way to really know is disconnect and test. The issue is not directly addressed in the Transit service manual. But from reading it I would guess that some kind of failure in the primary alternator (multiple types of failure could occur) would cause it to switch both alternator to self-excite in default mode at 13.5 volts. The first snippet below is from a general description of the charging system and mentions the default mode. The second snippet talks about diagnosing a problem with second alternator (the "B" alternator controlled/monitored by GENCOM2 and GENMON2) and it mentions that the secondary alternator will go into default mode in case of a failure with the primary alternator sense circuit.

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Vehicle speed and RPM are related, but only loosely. I'd be targeting RPM rather than speed because that's directly related to alternator output.

To get this number requires reading the CANBUS or some other external TACH signal, so not as simple as the speed signal you've mentioned. Your idea could work, and I've considered something similar too. I would want more control (always) and the ability to delay turning on/off whatever device when the frequency crosses the activation threshold. Probably a good idea to have some hysteresis too. The device you linked is almost certainly just a low-cost microcontroller with some custom firmware driving a relay. The ability to customize settings would be crucial - for me anyway.
Thanks for the input
Yea, I am aware of the disconnect between speed and RPM ... something to do with a transmission I think ;).

I would not be looking for such a refined approach or trying to eke out every last higher amp opportunity. I am thinking that for my use speed might actually be a preferable control. My thought was setting the relay on at something like 50mph which would put the engine at about 1500+ rpm/ alternator at 4000 rpm, which is where the output curve starts to flatten out. > 50mph would (mostly?). This would generally mean that the vehicle would be on open road and so there should be good airflow and frequent/rapid changes in speed would not be common.

With RPM as as the control input there might be frequent cycling of the charging cycle, which may or may not be an issue depending on the device. A greater possible concern might be conditions where the van is above the RPM trigger point in lower gears while in traffic where airflow might be restricted. Admittedly, summer traffic/temps in NJ might be a greater concern than in BC.

Not quite sure about you comment that is would be a good idea to have hysteresis. Is to avoid frequent cycling if the input signal (RPM or speed) is bouncing around near the trigger point. FWIW - the device I posted has a hysteresis pot. Did not know what that would be for. Thanks for the education on that!
 

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BTW - what are you using to charge @ 150A?
I have what I would call an experimental setup consisting of two Victron Smart BMS CL 12-100 using direct alternator output, in conjunction with SRC inhibit (aka third party high power mode). Each device can provide up to 100A output. The Smart BMS CL 12-100 is in concept a neat device. Only costs $200, performs BMS function (only for Victron batteries), and is a current limiting device to protect you from overdrawing current due to the low resistance of LiFePO batteries. You can select the max amount of current you want to draw on each device, from 9A up to 100A. I'll have to do a separate write-up sometime; the dual/parallel devices are not officially supported. Not 100% happy with the results, but so far a pretty reasonable solution for getting robust charging at relatively low level of cost and complexity.

I have the upfitter switches control relays to remotely turn each device on/off, so I can have either no charging, 100A charging or 200A charging. Sort of the dumb version of what you are after with speed-based control.
 

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We typically top out around 100-105F in DC, so I expect to have some data for those conditions next summer. I did not realize Livermore got that warm; my myopia had me assuming it was like SF.
Yes - it is really surprising just how different it is - really in every possible way. Might as well be two different planets.

Another 50 miles inland and it is even hotter.

On a typical summer day, there can be a 40 F difference in temperature between the west side of San Francisco and Sacramento.
 

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I have what I would call an experimental setup consisting of two Victron Smart BMS CL 12-100 using direct alternator output, in conjunction with SRC inhibit (aka third party high power mode). Each device can provide up to 100A output. The Smart BMS CL 12-100 is in concept a neat device. Only costs $200, performs BMS function (only for Victron batteries), and is a current limiting device to protect you from overdrawing current due to the low resistance of LiFePO batteries. You can select the max amount of current you want to draw on each device, from 9A up to 100A. I'll have to do a separate write-up sometime; the dual/parallel devices are not officially supported. Not 100% happy with the results, but so far a pretty reasonable solution for getting robust charging at relatively low level of cost and complexity.

I have the upfitter switches control relays to remotely turn each device on/off, so I can have either no charging, 100A charging or 200A charging. Sort of the dumb version of what you are after with speed-based control.
This I find very interesting Neal and I'd love to know how you fair with this. I had been looking into the CL 12-100's myself, while toying with how best to get the most reasonable/reliable power potential out of the Ford's Dual Alternator set-up and had thought I may have found the solution or at least a solution when coming across these Smart BMS units from Victron myself.
While on the surface the CL 12-100's seems, well "smart" based on their own description and just how they are marketed by them. But in reality, after having probed a bit further I came to find out mysef that Victron may have actually left quite a bit of the smarts out of these Smart BMS units, which appear to act more like charge feed limiters then actual BMS battery charging profiler's, which any typical LiFePO battery on the market would normally want or need to thrive or even survive. This was effectively confirmed for me when reaching out to one of Victron's approved reps here in the states, who pointed out that despite the Smart BMS talk, nowhere in the products description is Victron actually offering to properly profile the charge rate needed for your otherwise very expensive set of batteries.

This left me going back to the drawing board so to speak, but also puzzled about why Victron would leave out one of the most important parts of what in effect is marketed by them as a battery BMS Smart charging unit, dedicated to their LiFePO batteries, like the ability to properly profile the charging rate for such batteries Victron themselves makes, markets, sales and knows firsthand these battery's actually need?

PK
 

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Reading these posts makes me ask how much alternator charging is needed for your application? Does one need that much amperage? Have your loads been listed to show that the single alternator will not be adequate?

I understand that there are some applications that do require two alternators. Does your use need two?

With my application I seldom ever need to charge from my single alternator. Solar keeps the house battery charged. I do not have a need for high alternator output.

I use a vehicle powered inverter to supply120 volt AC power to the shore power charger. I was able to install the 1000 watt inverter so it does not load the electrical system when engine is starting. Used one of the user defined dash switches to provide a signal to the inverter remote for starting the inverter. The user defined switches are powered in the accessory key position so that signal would start the inverter before the engine started. Added a time delay relay between the user defined switch and the inverter remote. Bought a solid state time delay but that did not work. There is enough leakage through the solid state time delay that the remote was triggered from the leakage power so time delay did not occur. Had to change to a time delay with mechanical contacts.
 

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This I find very interesting Neal and I'd love to know how you fair with this.
I've created a new thread to describe this in more detail. See it here.

Reading these posts makes me ask how much alternator charging is needed for your application? Does one need that much amperage? Have your loads been listed to show that the single alternator will not be adequate?

I understand that there are some applications that do require two alternators. Does your use need two?
Answering how much amperage is required is relatively straightforward. Prior to starting my build and electric system design I did a load table to determine my electric needs. Our biggest consumer is recharging two electric bicycles, which takes a lot of power. Each bike has 1kWh of battery capacity, so if we fully deplete the bikes (easy to do with 70 mile daily ride) we need 2kWh daily just for that one portion of our usage.

Answering whether dual alternators are required was sort of the question of the OP, and the answer is not as straightforward, due to number of variables involved.
 
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