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Old 02-10-2020, 02:17 PM   #1
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Default Parallel alternators

Would it be possible to run two alternators in parallel with a balancer like centerfielder to recharge a lithium battery bank? Would this cause electrical problems with a promaster conversion? Doing some preplanning for a future project, where Iím going to want to run a/c at night and charge while driving next day.
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Old 02-10-2020, 02:36 PM   #2
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Would it be possible to run two alternators in parallel with a balancer like centerfielder to recharge a lithium battery bank? Would this cause electrical problems with a promaster conversion? Doing some preplanning for a future project, where Iím going to want to run a/c at night and charge while driving next day.

Two alternators in parallel is not an issue, it is what we have in our 07 Chevy Roadtrek. The best way to do it is to use a single standalone voltage regulator that is rated to run two alternators. That is the best way to get them to share the load more evenly even if the alternators don't match exactly but are close. We have an XP250 and XP280 from DC power/Nations on ours.


As for the Promaster electrical and if it will allow you to do it properly, you will likely need to get with a Promaster forum group or other tech group that is in to Promasters.



Most lithium systems just use a second alternator as a standalone with it's own external regulator. The 280 amp Nations system will net you about 165 amp hours per hour with the heat turndown we usually see in them.


How much charging amps you need will depend on the bank size and how much you use, compared to how much you drive and if you are willing to idle to charge (at a lower rate).


We are hearing more and more about the benefits of charging lithiums a bit slower than had previously been recommended, so that may or may not be a consideration.


IMO, we have seen very few cases where anyone needed more than a single second alternator would give them. I have our system turned down to charge at 180 amps in high rate (which has never been needed while camping) and 120 amps in normal mode. This makes the alternators run cool and charges plenty fast for our use patterns.


If you need super fast charging of a huge bank, you might want to consider getting a unit that has a Volta setup, or see if you can find a place to put one in.
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Old 02-10-2020, 03:14 PM   #3
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Thanks booster for the input, I feel I will need all the alternator help I can get. Because if we stay somewhere for two Nights I’m wanting to charge batteries as fast as possible without driving for half the day. We will definitely be using the a/c living in the south. I’m interested in the Volta setup but couldn’t find a retro Installer in my area and I’m afraid to even ask how much they would want for that system.
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Old 02-10-2020, 03:29 PM   #4
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Do they have to be similar in amps or does that not matter?
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Old 02-10-2020, 03:29 PM   #5
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Thanks booster for the input, I feel I will need all the alternator help I can get. Because if we stay somewhere for two Nights Iím wanting to charge batteries as fast as possible without driving for half the day. We will definitely be using the a/c living in the south. Iím interested in the Volta setup but couldnít find a retro Installer in my area and Iím afraid to even ask how much they would want for that system.

The math starts to get pretty tough when you want to run AC and not drive much as you will probably use 600AH per day, at least air conditioning overnight if it is really hot, plus if you sit the next day, you will either need to run the AC more. Probably the max you will get running continuous out of two alternators would around 320 amps, so at a minimum two hours of running to get 600AH back assuming you aren't using a bunch while charging.


With the limitations you are considering, a Volta may be the only option that could come close to keeping up with little driving.


You may be one that needs to consider the less desirable solution of running a generator, either built in or standalone, as your power needs and low driving requirements might not add up to being adequate.
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Old 02-10-2020, 03:35 PM   #6
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Do they have to be similar in amps or does that not matter?

The closer the better and from the same manufacturer and style so they generate the same voltage from the same excitation you will get from the separate regulator feeding both.
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Old 02-10-2020, 05:36 PM   #7
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I am by no means intelligent when it comes to electrical, so I may be waaaayyy off here, but I spoke to mechman and they can make a custom alternator for the promaster that’s 370 amps max and 200 amps idle. If I had two of them putting out around 575 amps combined (complete guess). With around 200ah from 7 hours of solar and no a/c usage during day because we wouldn’t be inside, could in theory get from a hour of charging from alternators 575 amps from alternator and 200ah from solar = 775 ah total. Please let me know if I’m crazy, I know it would be simpler to run generator. But I really just want to explore a no generator possibility.
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Old 02-10-2020, 07:13 PM   #8
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I am by no means intelligent when it comes to electrical, so I may be waaaayyy off here, but I spoke to mechman and they can make a custom alternator for the promaster thatís 370 amps max and 200 amps idle. If I had two of them putting out around 575 amps combined (complete guess). With around 200ah from 7 hours of solar and no a/c usage during day because we wouldnít be inside, could in theory get from a hour of charging from alternators 575 amps from alternator and 200ah from solar = 775 ah total. Please let me know if Iím crazy, I know it would be simpler to run generator. But I really just want to explore a no generator possibility.

I would be a bit skeptical of those kinds of outputs when actually installed in a hot engine compartment and running full out. The questions to ask are what kind of thermal protection do they have and what is the output at max temperature before they turn down. Also ask what the idle speed rating is at for alternator speed, as they usually rate them at an alternator speed that you will not get in a modern vehicle without a bunch of pulley changes or such. From what I have seen of many of the monster alternators, they are made mainly for the audio or work power customers so aren't really intended to be run for hours at full output. I could be wrong, but I really have never seen anything putting out that much continuously for long periods. DC Power even has a disclaimer on theirs that they aren't intended to be used for charging battery applications at high output. For comparisons, ambulances use a 300 amp continuous Delco alternator (davydd has one in his ARV who is the only one who offers it, and it is huge and heavy, but will do 300 continuous.


200ah per day of solar is going to about 700 watts of solar, and it will only do that on a good sunny day. On average you will be lower by quite a bit, I think, depending on where you camp.


You may be able to do better, but my guess is with two big alternators that also run the van and everything in it, you will probably be able to net out maybe 300 amps to the batteries. I don't know anyone who has tried to it with two running full out, and we are about the only ones around that have two high output alternators in parallel AFAIK. We have 530 amps theoretically, but at idle the heat of no vehicle movement lowers our reliable max rate to about 180 amps continuous/hot. Going down the road we can get more, maybe up to 240 if the AC isn't also on heating the engine compartment, but we really have never needed it.



To put it in perspective, you are talking about nearly 7000 watts of charging, which is about what 2.5 Onan generators would be able to do and they are 8hp engines. That leaves us at 20hp of engine output to charging, which is a huge amount.
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Old 02-10-2020, 08:29 PM   #9
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I would be a bit skeptical of those kinds of outputs when actually installed in a hot engine compartment and running full out. The questions to ask are what kind of thermal protection do they have and what is the output at max temperature before they turn down. Also ask what the idle speed rating is at for alternator speed, as they usually rate them at an alternator speed that you will not get in a modern vehicle without a bunch of pulley changes or such. From what I have seen of many of the monster alternators, they are made mainly for the audio or work power customers so aren't really intended to be run for hours at full output. I could be wrong, but I really have never seen anything putting out that much continuously for long periods. DC Power even has a disclaimer on theirs that they aren't intended to be used for charging battery applications at high output. For comparisons, ambulances use a 300 amp continuous Delco alternator (davydd has one in his ARV who is the only one who offers it, and it is huge and heavy, but will do 300 continuous.


200ah per day of solar is going to about 700 watts of solar, and it will only do that on a good sunny day. On average you will be lower by quite a bit, I think, depending on where you camp.


You may be able to do better, but my guess is with two big alternators that also run the van and everything in it, you will probably be able to net out maybe 300 amps to the batteries. I don't know anyone who has tried to it with two running full out, and we are about the only ones around that have two high output alternators in parallel AFAIK. We have 530 amps theoretically, but at idle the heat of no vehicle movement lowers our reliable max rate to about 180 amps continuous/hot. Going down the road we can get more, maybe up to 240 if the AC isn't also on heating the engine compartment, but we really have never needed it.



To put it in perspective, you are talking about nearly 7000 watts of charging, which is about what 2.5 Onan generators would be able to do and they are 8hp engines. That leaves us at 20hp of engine output to charging, which is a huge amount.

Or very simply: What is the fellow's phone number, link to the website.........

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Old 02-10-2020, 08:33 PM   #10
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I seriously doubt the Delco alternator I have will fit in a Promaster. The much smaller Nations alternator, let alone two, seems to be perilously exposed. Then don’t you have a limit of wire size to deliver amps to the battery. I have a 4/0 wire that is nearly 1/2” in diameter and that is only good for just a bit over 300 amps.

Seems to me if you want to run an air conditioner, first find the most efficient air conditioner, insulate the hell out of your van, and then have a super huge lithium ion battery bank. The 56 volt Volta system is currently the system of choice if you want to camp off-grid. Solar contributes to necessary other electrical needs and not much more and if you have a humongous battery bank I don’t see much need for solar.

If you feel you need air conditioning you first might consider what people call chasing 70 degrees year round, i.e. south in the winter and north in the summer.

If you have a pet, then the safest choice is to camp where you have shore power.

If no shore power, that’s why gas or propane generators are so popular over running the chassis engine continuously.

Plan your trips. We have been to 49 states, all the Canadian provinces, the Yukon Territory with a cat on board most of the time covering over 210,000 miles, 90% boondocking (off-grid) in 14 years and have never run our generator overnight or idled to charge our second alternator for air conditioning. There is no shame getting caught where you need shore power once in a while. Better than a sound sandwich of air conditioner running along with an engine.
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Old 02-11-2020, 03:11 AM   #11
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Or very simply: What is the fellow's phone number, link to the website.........

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Old 02-11-2020, 03:22 AM   #12
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Found this searching for ideas, APS HPI series alternator seems too good to be true.
https://store-tiunnz3nid.mybigcommer...nators-web.pdf
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Old 02-11-2020, 12:33 PM   #13
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I don't recall if it was that brand or other similar ones, but we have seen those before in some of the discussions about the Volta system, as it has been speculated they probably don't actually build their own alternators.


Higher voltage systems certainly do have an appeal in this kind of thing as the wire sizes and heat generating are much less.



If you are building a ground up system, rather than adapting a existing one, it gets to be mostly a matter of cost and getting the right components in the higher voltage ranges, like an inverter, charger, DC-DC converter, etc. Basically, you would be building a Volta setup but with likely different lithium battery chemistry. 8K+ watts of power is a house use level of power, so making it safe and reliable would certainly take some serious consideration and care. We know it can be done as the Volta system is essentially the same thing.


I just took a closer look at the website for American Power Systems, and the parts they list beyond the alternators look to be essentially the same as Volta is using, but listed like they are individually available. This includes lithium battery packs that appear to be same sizes and chemistry. Also the Sensata (Magnum) hardware. I wonder if they and Volta are one in the same or if Volta has just packaged these parts into a drop in for RVs. There are even what appear to be same diagrams on both sites, so seem to be all the same parts.


This would make for and interesting DIY, but the integration of the parts would be a challenge. Perhaps the marine folks who appear to be APS customers offer integration for hire, but with these kinds of power levels I bet nearly everyone is going to be very leery of DIY projects.
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Old 02-11-2020, 01:34 PM   #14
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I was thinking the same thing about Volta outsourcing parts and providing more of a complete package. In the pics of the Volta system power pack I’ve seen it’s identical to the system APS also sells. I’ve found the maker of the inverter in both systems (sensata). The battery packs look identical but I haven’t found the maker of it yet. After more research and reading the high amp alternator from mechman would more than likely fail quickly to due load/heat of continuous high load. The Delco alternator has a larger frame and casing is made for heat dispersing. If you look at the Volta and APS alternators they have the same style of housing. So if you find a reputable high quality 48volt alternator, next you gotta mount the sucker. I was at first unsure if it would even fit, but I got to thinking about the Winnebago travato it has the Volta bolted on bottom side of motor. Yes it takes away from ground clearance, but I guarantee they wouldn’t be installing them if it hasn’t been throughly tested and proven to work. Then I would need a Overrunning Alternator Decoupler pulley (OAD). This is exactly what ARV installs on their builds, they just designed their own and call it a “torque converter”, I think if I remember correctly. OAD’s have been used for years, this isn’t a ARV secret product that no one can get. So now I just need a mounting bracket, APS states they have brackets for multiple vehicles they mention Ram trucks and vans. They don’t manufacture them but sell them. I haven’t spoke to them to see if they have the particular one I would need yet. But if they don’t I know a metal fabricator who has CNC machine and he’s a pretty sharp guy I have no doubts he could make something. Then I’ll have to install it making sure it’s perfectly straight with other pulleys, difficult but not impossible. The easy part should be outsourcing electrical components. The point I’m attempting to make is Volta might not be the only option, granted they may be the easier option. But easier is usually way more expensive.
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Old 02-11-2020, 01:47 PM   #15
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Ha, booster we must have been looking at all that at the same time. I do think it will intimidate a lot of people to attempt a DIY project. I’m all on board to attempt, but I’m in the very early planning phase and have a long way to go. I know that much electrical power is over my head, but good thing is I know when to involve the right people.
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Old 02-11-2020, 01:53 PM   #16
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I was thinking the same thing about Volta outsourcing parts and providing more of a complete package. In the pics of the Volta system power pack Iíve seen itís identical to the system APS also sells. Iíve found the maker of the inverter in both systems (sensata). The battery packs look identical but I havenít found the maker of it yet. After more research and reading the high amp alternator from mechman would more than likely fail quickly to due load/heat of continuous high load. The Delco alternator has a larger frame and casing is made for heat dispersing. If you look at the Volta and APS alternators they have the same style of housing. So if you find a reputable high quality 48volt alternator, next you gotta mount the sucker. I was at first unsure if it would even fit, but I got to thinking about the Winnebago travato it has the Volta bolted on bottom side of motor. Yes it takes away from ground clearance, but I guarantee they wouldnít be installing them if it hasnít been throughly tested and proven to work. Then I would need a Overrunning Alternator Decoupler pulley (OAD). This is exactly what ARV installs on their builds, they just designed their own and call it a ďtorque converterĒ, I think if I remember correctly. OADís have been used for years, this isnít a ARV secret product that no one can get. So now I just need a mounting bracket, APS states they have brackets for multiple vehicles they mention Ram trucks and vans. They donít manufacture them but sell them. I havenít spoke to them to see if they have the particular one I would need yet. But if they donít I know a metal fabricator who has CNC machine and heís a pretty sharp guy I have no doubts he could make something. Then Iíll have to install it making sure itís perfectly straight with other pulleys, difficult but not impossible. The easy part should be outsourcing electrical components. The point Iím attempting to make is Volta might not be the only option, granted they may be the easier option. But easier is usually way more expensive.

APS alternators in the smaller frame versions look very similar to the DC Power units, so it is also very possible that APS just has them building them. It looks like they have 12,24, and 48 volt versions and the 12v looked to have similar specs to the DC Power ones, also. APS listed that they had Ford and Chevy brackets for alternators as well as others. If the cases on the alternators are the DC Power ones, Nations likely has a Promaster bracket. I don't know if you could even run 8K watts on a single belt, but Volta may be doing it.


Personally, as DIY, I would rate this an 11 on a scale of 1-10 . The hardware mounting, alternator brackets, wire running are all not too bad, but the integration of the automotive style lithium safely would be pretty daunting, I think. You would also probably need heaters and ventilation cooling with controls. The companies that are doing the boats, work trucks, etc are buying more than one unit (hopefully for them) so they are going get access to much more information on the system controls needed and safety precautions. My understanding is that this battery style is not much safer LiFePo4 that we have seen in most lithium setups in RVs and is of the type that can burn and explode, but others are up more on the various chemistries than I am.
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Old 02-11-2020, 03:09 PM   #17
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The automotive batteries would be overkill anyway, I’m getting further down a rabbit trail. All I am looking for is enough battery to run a/c at night and then a way to quickly charge back up, if I’m not driving to next location. Seems to me I could just get a reasonable size battery pack install a APS high amp alternator and during day I could drive/high idle for a way shorter amount of time. I definitely got way off track than my original goal.
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Old 02-11-2020, 05:45 PM   #18
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Using the safer batteries is a good idea, IMO, although it may complicate some of the other issues if you are using APS 48v nominal alternator.



I think you will be best to have a single battery module, at it will need to be in the range above 10KWH if you want reliable AC and other uses. Bigger might be even better to perhaps 15-20KWH. The old "warp core" that Roadtrek had as it's biggest offering, IIRC, was about 20KWH.



You will need to find a shore charger to charge at the approx 56v with the right profile for the safer batteries, as well as a regulator for the big alternator that has the correct charge profile for the different batteries than APS uses. The solar will also need to be high voltage or have a step up converter.



You may get lucky and have the battery profiles line up OK with APS parts, which would be good for simplicity and sourcing. I don't know if anyone makes a monitoring system that can handle that voltage, but maybe someone like Victron can do it.


I would recommend getting the battery bank at a known USA supplier, even though going direct to China would be a lot cheaper. You are wandering into uncharted territory with the whole project, so adding questionable batteries or even misrepresented ones, is not something you want in the mix.


I really don't know how much, if anything, you would save in cost by changing battery chemistry, as you will still need almost all of the same parts to make it work at 48v.


Any way you look at it, this is going to be a very expensive endeavor.
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Old 02-18-2020, 08:22 AM   #19
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Would it be possible to run two alternators in parallel with a balancer like centerfielder to recharge a lithium battery bank? Would this cause electrical problems with a promaster conversion? Doing some preplanning for a future project, where Iím going to want to run a/c at night and charge while driving next day.
SWLA, to get back to your original question and your reason for asking it, check out the description of my ProMaster conversion's electrical system and the way I use it to air condition my van while boondocking, which is here:

https://www.classbforum.com/forums/f...tml#post101222

A few general thoughts:

You probably don't really need a system that runs your AC all day. Not many Class B owners sit around inside their van for long periods of time at camp sites. If you plan to do that, you should probably get a fifth wheel or a class A or C, which will provide the elbow room you'll want for long term interior comfort. Most Class B owners spend most of our time outside enjoying whatever it was that attracted us to an area in the first place. But as a Texan, I do understand your desire to run the AC when you're sleeping, which is what I described at the link.

Also, other than the satisfaction of designing the system as an intellectual exercise, to me it makes no sense to spend tens of thousands of extra dollars on a system that can generate and store 500 or 600 amps in one hour (if that's even possible with two alternators, which I doubt). The ProMaster gas engine burns about $1.25 worth of gas per hour at idle speed, and it does no harm to idle the engine, so why not just do that for as long as it takes to top off the battery? Five hours of charge time at that rate costs $5 more than one hour. At that rate your payback period on a Volta system is probably about fifty years. Again, see the link for a real world description of running an air conditioner with batteries during the summer in Texas.

Finally, somewhere above you asked whether the alternators have to put out identical charges / amps. The short answer is no. One amp is the same as another as far as your battery is concerned. You can have 80 amps coming from one source, and 300 from another, and the battery will happily accept it all. You just need to make sure not to overcharge the battery, which is where the lithium battery management system (BMS) comes in. And you need to make sure your alternators' diodes aren't fried by the spike when the BMS disconnects the charging circuit, which is where the voltage regulator comes in.
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Old 02-18-2020, 11:22 AM   #20
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Finally, somewhere above you asked whether the alternators have to put out identical charges / amps. The short answer is no. One amp is the same as another as far as your battery is concerned. You can have 80 amps coming from one source, and 300 from another, and the battery will happily accept it all. You just need to make sure not to overcharge the battery, which is where the lithium battery management system (BMS) comes in. And you need to make sure your alternators' diodes aren't fried by the spike when the BMS disconnects the charging circuit, which is where the voltage regulator comes in.

IMO, the issue is not that the batteries care where the amps are coming from, it is in the output control for the alternators themselves so they don't get damaged or not give the output they should.



If they are not matched close enough to share the load one can max out and the other not put out much at all. A lot of the difference can be from mismatched internal regulators in different styles or types of alternators, but windings, diodes, heat rise from output etc all influence the output of the alternators. In a perfect world you would like to see them with the same output % of their rated output as each other (doesn't need to be same amps) and running at the same temperature. That would give you the highest output potential and longest alternator life, IMO.
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