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Old 07-14-2020, 02:44 AM   #1
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I've seen discussion about adding a 2nd alternator. I've also seen discussion about upgrading the stock alternator to a higher output one. What are the advantages/disadvantages of each?

What are the circumstances that would lead you to doing either?

Is there any rule regarding what output alternator[s] you have vs. battery capacity?

There seems to be some discussion on this list of 2nd alternator in lieu of solar panels. Advantages/disadvantages?

I hope I'm not asking too much but it's an interesting area for someone like myself who is considering upping battery capacity.

thx.glenn
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Old 07-14-2020, 03:32 AM   #2
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From discussions I've read here previously, it's far easier (and far cheaper) to upgrade your 145-160A current alternator to say a 225A model. An upgraded alternator would be plenty to push 60 amps of charge to your coach batteries. But perhaps while at or near the limit of the factory wiring back to your coach batteries (which is probably 4 ga.).

If you add a honking big second generator, you'd need to upgrade your wiring substantially. I currently push 40A from my standard 160A alternator which may be at it's limit. I see voltage drops at idle (only occassionally) when ac is on. No problem once engine speed gets above idle. My alternator has never seemed to get hot, unless that is what's happening at idle when perhaps it cuts back on output.

Adding a DC to DC charger is a cheap way to protect & limit the draw on your engine alternator, isolate the coach & engine batteries, and provide the right charge profile to your coach batteries (especially if they are a different type than your engine battery).
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Old 07-14-2020, 07:01 AM   #3
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We installed a second alternator in connection with our lithium house battery system in our DIY build. We saw two significant advantages. First, the second alternator can be a 'lithium-friendly' alternator specifically intended to charge lithium batteries (the second alternator in our installation has an external programmable regulator which we have set to suitable lithium parameters). The second advantage is that this second alternator can provide substantially higher charge currents than available from even an upgraded first alternator. We regularly charge at 150 amperes or higher (limiting the charge current only to limit alternator temperature during the summer months) - - fast charge rates being one of the advantages of lithium systems. Prior to lithium, we used the first alternator to charge our house battery (at rates of 30 amps or less).
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Old 07-14-2020, 07:11 AM   #4
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PS: We don't understand the concept of "2nd alternator in lieu of solar panels". We use both as they perform completely separate functions. When you're in motion - - use the alternator. When you're not, use solar. It might be argued that solar works both while in motion and stationary. True, but only when the sun is out, and not as 'fast' as an alternator. Go with both, have more flexibility.
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Old 07-14-2020, 01:50 PM   #5
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A second alternator advantages include those that Winston has stated, as in more amps to charge faster and ability to have it on a separate regulator for control. Another advantage is that they provide, mostly, a redundant charging source if the stock alternator dies. You do need to provide a way to connect it to the engine side, though, and it will do no good if the original alternator fails bearings and locks up or explodes.


For smaller battery banks up to the very typical 220ah or so setups in many vans, a single alternator gets more attractive, but IMO should be an improved size and quality one to give lower heat issues and increased reliability. A single 250-280 amp alternator will easily handle a 220ah bank, and last well if you limit the output to about 100 amps or less.


Our van was not computer controlled charging (2007) so I was able to put out second alternator in parallel with the OEM one which had already been replaced with bigger, improved, one. It gave us the ability to run very low % output for reliability and control them off one regulator. We can also just disconnect the coach batteries whenever the batteries get full without worry about damage to the electronics as the starting battery is still connected to alternators.


You likely would need to increase wire size with either a size upgrade or a standalone second alternator.


We have the lots of alternator charging, but also 300 watts of solar, and I would not go without the solar for the way we use the van. The solar is capable of keeping us offgrid, without driving, indefinitely if in good sun. The alternator charging sits in reserve so if we get bad weather or a shady site we can get a days worth of energy back into the batteries in about 20 minutes of driving.


We ran for a couple of years, during our testing of systems, with 260ah of Trojan wet cells, 300 watts of solar, and a single 250 amp alternator, and it did work very well for us, even with a compressor frig. Weak point was that the wet cells had trouble providing enough amps to run the microwave is they were less than full, so we had to idle the engine to run the microwave.
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Old 07-14-2020, 04:01 PM   #6
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Speaking for MB Sprinter owners upgrading your engine alternator probably doesn't give you much because you can only take off 40 amps for house purposes of charging house batteries. I don't know anything about Promasters or Chevys in that regard.

A second alternator like Nations or Delta (I've had both) charge your house batteries at up to 330 amps. Of course you need a wire coming off the second alternator to handle that. Mine is nearly 1/2" in diameter! With that kind of charging I can replenish my 800ah lithium battery bank in about 30 minutes of driving or idling for a day's stay in place boondocking with my all electric (no propane) van. I have 420 watts of solar but will not have any on my next van. Look at it this way. I am a profligate user of battery power at up to 200ah per day. My solar panels can charge my batteries at probably a maximum 120ah on a good sunny day. That is a losing situation. My second alternator can put that back in 30 minutes. Even if I stay in place at a boondocking campground for several days, I usually drive somewhere every day. Solar can never replenish my batteries. I store under cover when not in use, so solar in that regard is useless. I can think of other things to utilize on my roof like extra storage, skylights, decks, kayaks, etc.

I think if you have more than a 400ah battery bank solar contribution is negligible for the return and you probably should have a second alternator. If you have under 200ah as most Class B RVs do it can make a significant contribution but then a second alternator is a waste of money.

BTW, this is what 420 watts of solar looks like in 3 panel on an extended van Sprinter of 24 foot. If I had less, my comparison numbers would be worse. That's why I am going no solar on my next van.

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Old 07-15-2020, 12:14 AM   #7
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I am a profligate user of battery power at up to 200ah per day. My solar panels can charge my batteries at probably a maximum 120ah on a good sunny day.
We, too, are a "profligate user of battery power" and would love to use our roof space for kayaks etc. But we like the diversity of having multiple charging sources. While we designed our system to allow 'idling' to charge our batteries, we aren't a fan of this approach and would rather have solar do that job when parked for several days.

This summer has been interesting for solar. We spent more time, further south, than usual. Couple that with higher altitude, cooler temperatures and bracketing the summer solstice and we 'smashed' our prior solar 'collection' records. Our max was, two days in a row, 5.3 kwhs with many days over 5 kwh/day (which equates to 408ah/day). And this just about met our "profligate" electrical energy consumption!

So guess we'll have to consider 'blow-up' kayaks - - as we're gonna keep the solar.
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Old 07-15-2020, 12:27 AM   #8
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First define how many/much battery you are going to add. With one additional battery even an upgraded primary alternator is not necessary. If it is lithium then a DC to DC charger is needed.

Install the battery or batteries then decide on charging options.
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Old 07-15-2020, 12:38 AM   #9
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I understand the desire to have multiple means. But I do have a question relating to solar. If you are parked, say, in the shade of trees, how much solar is harvested? Being from the SouthWest and camping almost exclusively in the SW we would never camp in the sun unless there was no other choice. So I am curious about the advantage to having solar but camping always in the shade.
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Old 07-15-2020, 12:43 AM   #10
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I understand the desire to have multiple means. But I do have a question relating to solar. If you are parked, say, in the shade of trees, how much solar is harvested? Being from the SouthWest and camping almost exclusively in the SW we would never camp in the sun unless there was no other choice. So I am curious about the advantage to having solar but camping always in the shade.

It has a lot to do with how deep the shade is and if it is all day or partial, plus is you are series or parallel wired.


It is very easy to have ours go to 1/2 or considerably less in deep shade. In cloudly, drizzly foggy weather seen in do only 10-20% of our good sun harvesting.
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Old 08-12-2020, 11:13 PM   #11
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My first post here. Working on designing a full-timing RV on a 144 HR Sprinter chassis. I have been reading about the advantages of a second alternator with ARV's automatic implementation, and would like to go that route and not opt for solar panels for what I think would probably be close to a 800Ah battery system. However, I have also read about significant problems with idling the MB diesel engine and how MB cautions against it. Not sure if this problem has been resolved with later models, but I am also not sure if we are going to get a new van or look for a used one. Any advice would be greatly appreciated. Thx.
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Old 08-13-2020, 04:41 AM   #12
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It would appear that what you need is based on what you typically use.......as others have pointed out to me in this forum. For example:

My electrical draw is for the ceiling vent fan (c. 1a), furnace fan (c.1.5a), plus the water pump and the lights, which are all LEDs. Oh, and the propane and CO detectors. I don't imagine that I use more than 10-15AH/day on that usage. I have a single 100AH Lifeline.

I think that booster had tested out a 100W solar panel at 30AH/day in optimal sunlight and as low as 9AH/day in cloudy rainy weather. So it makes sense to me that in the bright sunlight of AZ, my 100W solar suitcase would top off the battery in less than 1/2 day........which it does.

So here's my thinking and please jump in and comment/correct.

If I were to add a compressor fridge to the equation which was 3-3.5cf, it appears that the daily draw would be between 25+30AH/day. Is that a correct assumption?

My thinking would be to up my battery capacity to 200AH and add 200W of solar to the roof. Does this seem like appropriate resizing?

As you noticed from one of my unanswered posts, I can't figure out the size of my current alternator. I do know that there is a 40A circuit breaker between the alternator and the battery. How do I determine if my alternator will handle 200AH vs the current 100AH?

My current convertor/charger is rated at 35A. Should it be 40A? If left at 35A would that mean that the batteries would never get fully charged or that it would just take longer?

I suppose my greatest question has to do with sizing. I don't have and never will have an inverter. We don't use the microwave. We make coffee with a pour-over cone. We don't have a TV. So this boils down to taking a very simple, minimal draw system and augmenting it with a small compressor fridge.

Thoughts appreciated.

cheers.glenn
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Old 08-13-2020, 04:56 AM   #13
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[QUOTE=GallenH;114444
As you noticed from one of my unanswered posts, I can't figure out the size of my current alternator. I do know that there is a 40A circuit breaker between the alternator and the battery. How do I determine if my alternator will handle 200AH vs the current 100AH?

cheers.glenn[/QUOTE]

Sorry! Winston, rowiebowie and booster give some insight for me in the posts above.
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Old 08-13-2020, 12:25 PM   #14
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I think for a 3.0-3.5 compressor frig I would widen the power use range a bit to something like 25-50ah per day as conditions and use patterns can vary a lot.


If you have a single 40 amp breaker from the alternator to the coach (be sure it is not two 40 amp ones permanently hooked together to make 80 amps, which was done on a lot of vans), you probably only have a #6 wire to the coach. You can't really increase charging amps from the alternator to the coach batteries unless you increase that wire size and if you go up to 200ah of AGM, a 40 amp breaker will tripping on and off a lot. We even hear of a lot of the 80 amp ones tripping a lot on 220ah of AGMS.


200ag range of AGMs really should have at least an 80 amp circuit from the alternator, but also so current limiting, I think to help save the breakers and the alternator. A bigger, higher quality, stock location, alternator is usually plenty to run such a system.



Most of the users have found that the typical 200-240ah battery setups work well with a compressor frig unless there are other high power uses going on a lot.


If you are getting by on a single 100 watt panel now, adding at least one more for the frig would be a good thing to do. The typical 30ah per day of a 100 watt panel would leave you a bit short to cover all the use, though, so 200 watts would give more chance of longer term offgrid times. If you drive every couple of days a single panel would be fine, I think, or even just an added battery.
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Old 08-13-2020, 02:02 PM   #15
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My first post here. Working on designing a full-timing RV on a 144 HR Sprinter chassis. I have been reading about the advantages of a second alternator with ARV's automatic implementation, and would like to go that route and not opt for solar panels for what I think would probably be close to a 800Ah battery system. However, I have also read about significant problems with idling the MB diesel engine and how MB cautions against it. Not sure if this problem has been resolved with later models, but I am also not sure if we are going to get a new van or look for a used one. Any advice would be greatly appreciated. Thx.
I have an 800ah lithium ion battery system from ARV with a second alternator. I am having built another ARV on a 144 WB chassis with as much as 864ah of 6 group 27 drop in Valence lithium batteries (undetermined at this point as I am considering reducing it with my experience.) Maybe 576ah can achieve my historical use and travel with no apparent change with a 3 day non-traveling stay. We seldom use air conditioning. I've owned my current ARV almost 5 years and 92,000 miles on the road. So, with that, all electric, no propane, I can tell with 800ah or less of batteries and a second alternator you will not need to idle your engine and not need solar when traveling. I'm dropping solar entirely with my next Class B. Solar could be useful if you store longterm outdoors.
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Old 08-13-2020, 04:25 PM   #16
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Davydd, I would like to replicate the ARV's 2nd alternator design since I am expecting my battery needs to be as high as yours. Would it be possible for you to share the design details? - Components and schematic? Also, as I asked in my post above, how do they address MB's advice to not idle the diesel engine for long periods? Would appreciate a reponse. Thx.
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Old 08-13-2020, 05:23 PM   #17
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470W solar panels allow me to run fan, compressor fridge, lights and other light duty items pretty much indefinitely if reasonably sunny outside. But, since I use microwave, induction, occasional AC, etc. the solar really isn't enough to keep up. As Davyyd points out, driving for a bit, which we typically do most days, fully charges the batteries, making the solar redundant in most situations.
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Old 08-13-2020, 11:51 PM   #18
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Davydd, I would like to replicate the ARV's 2nd alternator design since I am expecting my battery needs to be as high as yours. Would it be possible for you to share the design details? - Components and schematic? Also, as I asked in my post above, how do they address MB's advice to not idle the diesel engine for long periods? Would appreciate a reponse. Thx.
MB recommendations are not to idle with an auto start not anymore than two hours at a stretch without driving 30-40 minutes at highway speeds before you idle again. MB has a five start limit before you have to drive again or really just start the engine up with a key. ARV's Silverleaf monitor can set the SOC percent when you get down to it to auto start. They recommend 30%. I've got it set at 40% and never invoked it other than testing to see how it works. As I mentioned I never idled other than testing and demonstration. They also have an automatic cutoff after 1 hour 55 minutes. Then of course you must have a certain amount of intelligence as to why the cutoff and drive. At 800ah it is nearly impossible to get down to where you need it unless you are extremely careless or try to use your air conditioner for several hours. I've never ran an air conditioner more than 3 hours (deliberately to dry the van out and only once) so have no practical experience in the holy grail of running it all night.

As I mentioned the Silverleaf monitor touch screen is a mini-computer that controls just about every function in the van so you don't have any other readout, toggles, etc., just a 5 inch screen with a whole lot of back up hidden behind a flip up cabinet. As for my electrical system that too resides in the Silverleaf monitor to me and I think ARV said at one time they had about two dozen outside partners programming it. So I don't know the schematics our know what the many control boxes do in the cabinet behind other than I've seen it opened up and it is amazingly complex.

They have three different second alternators, the Volta 48v, the Delco-Remy 330 and the Nations 280. I don't know if they offer the Nations anymore since the Delco is vastly superior. I had both. Balmer is regulator. The Volta is a complete system Winnebago also installs.

The battery systems are the Elite Power Solutions made up of 16 200ah 3.4v cells which I currently have. They have their own BMS which communicates with the Silverleaf. Then they offer Lithiumwerks Valence batteries which are in a Group 27 drop in profile with its own BMS, and the self-contained Volta system.

I think currently they are using the Xantrex Freedom 3012 3,000 watt pure sine wave inverter/charger other than again, the complete Volta system. That is pretty much what I know. I have an Outback 3000 which is a beast and looks indestructible. They said they switched to Xantrex because it communicated better with the Silverleaf.

I'm getting the Valence system which will be inside under my bed.
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Old 08-14-2020, 02:36 AM   #19
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Davydd, It's very kind of you to give me all this detail. Much appreciated. At this point, a lot of it is Greek to me but I hope to catch up. I was fairly certain that ARV would not install something that wasn't recommended. I am also trying to figure out if it would be worthwhile adding the under-hood and under passenger seat auxiliary batteries, wire them for some circuits and mainly have them available as backup. Some people have used them with an inverter to charge house batteries but that only makes sense if the system is based on a single alternator that cannot charge house batteries.
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Old 08-14-2020, 03:25 PM   #20
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If this is Greek to you, then you have a long way to go if you want to do a DIY lithium ion battery attempt. There are several turnkey companies with complete systems that can help you. I have no specific names as I have not paid all that much attention. On Sprinter-Source.com there are several members that have described their own DIY setups. Again, I can't judge whether they are good or not.

To describe what ARV offers maybe in better detail, this White Paper may help. However, it is a couple of years old now so could be fast getting out of date.

https://advanced-rv.com/wp-content/u...hite-Paper.pdf

ARV has a fest every year in May and has their whole staff there to answer questions and displays of all their systems including what is in the works. It is open to owners, potential owners and anyone simply interested. For instance, the FitRV and Humble Road have been there and clearly have picked up pointers and ideas you can trace from ARV and have gone on from there with their own advancements.
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