[SouthernDevGirl]

@Richard - based on Joe's schematic, he has the 50DN alternator which should be the oil-cooled unit.

However, being that we're on a forum, it's just as important to provide safe advice for others and the information you've providing is very helpful.  I read quite a bit on RV forums as well and I haven't witnessed the same issues with alternators on the larger diesel pushers (DP).  On other chassis?  Absolutely.

Typically on a DP the belt ratio (from flywheel to alternator) will be somewhere in the range of 1:3 (3 rotations of alternator for every one rotation of crankshaft) keeping the DP alternator running at minimum 2,100 RPM.  IMPORTANT NOTE: I am skilled in electronics, NOT mechanics, therefore, I am out of my element in this statement about the ratio; it could be higher/lower in the DD/Cat/Cummins engine/alternator combos in Newells, please let me know if I'm wrong.

At 2100 RPM a high-quality alternator, particularly the DP alternators that run substantially larger-diameter stators (more room to dissipate heat, multiplied by the higher-pressure airflow) should not overheat unless there were some issue with the fan-blades perhaps? 

Furthermore, a Newell uses an alternator that is designed to run at 24v, producing half the amperage for the same amount of current (watts).  The reason for this is obviously because the gauge of wire and high resistance of running a 12v system which doesn't make as much sense in the context of large diesel engines that require high-current to turn-over, etc.  With a 12v line, you're pushing higher amperage for the same number of watts (heat, the offender in this instance) -- and therefore, the resistance of the wire does help mitigate the drain on the alternator in the situation where you mention charging from a low SoC.

Speaking of charging from a very low SoC, this is not typically something that is done.  In the event someone runs their house-batteries to a very low SoC, typically this is compensated with a separate generator (not primary engine generator/alternator) if it's not the pedestal responsible for the charge.  For that reason, much of this discussion is largely hypothetical or (at least) relatively uncommon in real-world scenarios.

We could go into more detail on the topic, but I think it would be better for me to first understand the issue with people you've witnessed that have suffered from this issue on a large DP with a high-quality alternator.  If you have some in-mind, I'll investigate those and that will help me provide better information.

-- To your second point --

I would not draw a substantial conclusion to the anecdotal "almost all Class A manufacturers use some sort of isolator"; it makes perfect sense that a manufacturer would prefer the isolator; this is not because it's the superior solution for an owner/operator.

I'm here to learn, not debate; however, if I were to debate anecdotes without going deeper into the science, I would mention an analog: that "almost all" Motor Yachts use a VSR of some sort (or in modern times with new chemistries, the more pragmatic, microprocessor based DC-DC chargers).

For now -- if you have some posts you can share that will help me investigate the equipment/situations where people with DP's have burnt-out their alternators due to charging battery banks, please share those and I'll investigate further.

[arcticdude]

I lost my 50DN on my last coach. We were coming back from a rally in central Texas. We’d been plugged in for several days, so all batteries were as topped off as they typically got.

About 100 miles into the trip, I noticed the voltmeters (house and chassis) were both low. Looking at my engine ammeter, it was showing a discharge.

Starting the genny got things back charging and we came on home without further issue.

Since my DN had always leaked oil, I replaced it with an air cooled 330A unit from elreg. No more leaking and it always seemed like the ammeter spike that always occurs after starting was less in duration.

This was in a 12V coach- no 24V on that one.

My current coach has also lost it’s alternators, both with the PO and once with me. It originally had external regulators that were mounted in a high heat location that was not conducive to regulator lifespan.

It’s a split system, running 24V in some areas and 12V in others. It’s now running two 155A air cooled units with internal regulators putting out 24V. So far it’s been happy with this setup.

[SouthernDevGirl]

@articdue, thank you for that detail.

Your experience agrees with my research. I've also read the air-cooled replacement for the 50DN actually runs cooler than the original 50DN oil-cooled unit.

I also agree that it's a horrible idea to place a regulator in an area without forced-air. Perhaps they expect the regulator will be cooled with air during travel; however, this is a recipe-for-failure if running at idle. Your new system with integrated regulators/forced-air make a lot more sense.

Of course in your instance, the alternator was not damaged due to the strain of low SoC house batteries. I hope that we can gain more insight into those that have experienced damaged alternators due to house batteries with low SoC based on @Richard's research.

[Richard]

My research was personal experience. Two penn tex 385 amp alternators in four years charging 6 8d batteries. The alternator would charge at around 200’amps for several hours. We did a bit of dry camping then. My practice was to crank and roll. In addition to replacing alternators, i was frequently replacing ruined alternator belts. When i stopped practice of charging the house batteries with the alternator, and instead charging with the generator/inverter charger, i have not had an alternator failure in the last ten years.

At the time, ten to twelve years ago, i began to monitor class a forums for cause of alternator failures. I personally concluded that many of the failures were cause by the same practice i was using.

[SouthernDevGirl]

@Richard, that's good information, thank you.

I'm sure you're far more mechanically inclined than I -- although in my limited experience, if we were to burn an alternator belt, I'd take that as an indication I might be overdoing it.

Going with an isolator rather than VSR wouldn't alleviate that issue; however, lowering the voltage on the regulator or better yet, using a DC-DC charger, would be best in that scenario.

I hope that most people are aware that charging a low SoC battery bank is best done by the generator (when no pedestal available).  If they do not, I hope they consider added precautions for that unique usage scenario.

Back on the original topic, this application still appears to be a better fit for a VSR than replacing the isolator, in my humble opinion.

One of the most popular models in yachting is the Blue Sea Systems brand.  They are very well proven; the most deployed of any such hardware and it's a superior solution to the original poster's problem.

If it were my coach (and if I were running SLA/AGM in both banks), I would go with something like an Blue Sea VSR over an isolator.
Blue Sea 7620 ML-ACR Automatic Battery Separator for Auxiliary Batteries 12V/500 Amps | Powerwerx

I'm not suggesting this is the only option or the best option; this is merely what I'd use in that scenario (photo included below).

If I went one step further and I was using the alternator to charge low SoC batteries frequently (technically, while important in that scenario, I'd technically go with this solution across-the-board, and this is precisely what we've used in every RV we've owned) -- I would use a DC-DC charger between the chassis/house battery banks.  That is, by far, the safest route.

The newer Renogy's are the best value for the money.  You gain all of the benefits of the VSR (plus added intelligence), solar MPPT charger, reduced current, to lower the load on your alternator, and safer battery charge-rate (extending the life of the batteries).  You also buy yourself a bit of future-proofing if you prefer to change battery chemistries in the future.  All for only $100 (or so) more than a VSR or Isolator.

[arcticdude]

That Blue Sea unit has been working very well in at least one of our 24V/12V Wanderlodges. The owner felt it was a better choice than the Intellitec BigBoy relay. He’s had it for several years without issue.

On the generator or the alternator(s) charging the discharged batteries issue, aren’t both taking a large surge when first started? Neither is going to be at high output for more than a short amount of time. Do you stress the inverter -chargers or the alternator(s)?

I’ve had and heard of alternators failing, and I’ve had and heard of the chargers failing.

What are folks thoughts about those issues?

[SouthernDevGirl]

@arcticdue - Thank you for the feedback. There are also a couple levels of Blue Sea VSR's. The one I mentioned is their 500A version that is the most reliable (I believe the more common version is ~200A and very affordable at just under $100).

Quick question for you -- you wrote "at least one of our Wanderlodges" - do you do conversions? Although we are not in the business of doing conversions, we essentially ripped all of our Class-B's (Leisure Travel's for the most part) down to the metal and rebuilt for our own purposes. Contrary to someone that does this as a business, we lose a lot of money because you'll never get your return on this type of upgrade (too few people appreciate); however, it is a great learning experience .

To answer your question -- the primary issue is with the heat generated by the alternator. Automobile alternators are not intended for maximum-amperage production at long intervals, which is the reason automobile alternators/generators are so much smaller than conventional stand-alone "generators" (the stator/rotor unit mounted to the motor).

In the case of the large alternators used on DP's, the alternator is much larger and should be able to dissipate substantially more heat. Overloading a DP alternator is not as common as a traditional automobile (or non-DP chassis RV).

Consider that the "efficiency" of something is essentially a direct correlation to its heat production. You'll notice your charger is (typically) somewhere over 92% efficient when running at higher amperage. In other words, to use a simple hypothetical: if you're charging at 1000 watts, you are creating 80 watts of heat.

Vehicle alternators are typically around 60% efficient, therefore, at 1000 watts, you're creating about 400 watts of heat (500% more). Fortunately with an alternator you get the intrinsic high-volume fan while a charger typically runs on an electric, relatively lower volume of air-cooling.

While the cooling is not as substantial, the charger is designed for a consistent/long-running duty-cycle and the airflow is adequate. For this reason, typically a charger is not an issue.

As you noted, the alternator's voltage regulator is even more susceptible to issues than the the alternator, in some cases, because it's not properly cooled.

As this relates to the original poster's question --

In my humble opinion, the VSR (or similar) is a simpler, more effective, more suitable option. However, if he intends to use the chassis-engine as a generator to charge batteries from low SoC (not as intended/recommended), the best approach will be decoupling the alternator and limiting current to a degree. For example, a DC-DC charger because this will intrinsically limit the current (based on the capability of the charger, which uses non-transformer based voltage adjustment; essentially mosfets, schottky rectifiers, caps).

[arcticdude]

SDG,

I was not even aware Blue Sea had other versions than the 500A version.  That's the version that was used when the Wanderlodge owner changed out his OEM relay.

There are only slightly more than 50 450LXi's out and about and much fewer are "active" owners.  So we tend to be a fairly tight family and seem to all take a little ownership in each other's coaches.  Especially since we do not have a factory available to offer assistance anymore.

While I do not do retail conversions, I have done similar in my current coach.  Here's what I started with:
   


and here is where I am now:
   

I've still got to finish installing the shower, as it was completely removed, as you can see by the curved hole in the floor behind the refrigerator.  I've got the shower pan and walls in, I'm working on installing the surround.  I removed all the corian and installed granite in it's place.  MUCH nicer!

The biggest issue I've run into with this renovation has been sourcing folks to provide the materials.  Since everything has been custom, I had to go to Florida for the granite (of all places) and Pennsylvania for the shower materials.  Fortunately, everything else is mostly elbow grease!

I was aware of the heat issues, as that's what typically gets the OEM installed regulators on these rigs.  I was thinking about the inverter/chargers only being in the 140A range, so they're taking as big a strain as the alternators are when first started.  Having had 2 chargers go out in my previous rig, I was curious to see what the collective thought about that.

Good stuff!

[kaptain]

@SouthernDevGirl @jumpshowhigh @bestgenman @richard

Thanks to all of you shared your valuable insights. A few things I'd like to clarify:

Furthermore, a Newell uses an alternator that is designed to run at 24v, producing half the amperage for the same amount of current (watts).

 I have a DN50 alternator (part#  1117860), it is oil-cooled. It's a 12v version, not a 24v version.

 What kind of alternator is on your coach? a 24V alternator running at half power or half output voltage? 

I really can't see a scenario where a VSR isn't better for your situation; none of the issues you're concerned with should be an issue with a quality VSR.

 The "Blue Sea 7620 ML-ACR Automatic Battery Separator for Auxiliary Batteries 12V/500 Amps" does look attractive. 
 I had browsed their product line, and I was looking for similar or identical products at different product pages, https://www.bluesea.com/products/7622/ML...2V_DC_500A

 These were the thoughts that made me choose Victron ArgoFET over an electronic-driven but mechanically energized switch:

1) While BlueSea Automatic Charging Switches (ACR) show low operating amperage (low power consumption), but when activated, it consumes ~7 amp electricity to keep energized, that's nearly 100 watts of power consumption at 14v. That's nearly the same power consumption compared to a traditional diode-based isolator at 150 amp, assuming diode voltage drop 0.7v x 150 amp = 105 watt.

2) BlueSea ACRs are dual-sensing, which means it activates whichever side of the battery reaches the triggering value. This could potentially overload the inverter/charger when the coach is on shore power without the alternator is not running because the original design was to let the inverter/charger connected to the house battery only and let an Echo Charger draw a small amp when the house battery voltage reaches 13v or more. Using the ACR will make the Echo Charge redundant.

   

To reach TRUE isolation between two battery groups, you'll have to use more than just one such switch:

   
   

Amazon's review on the BlueSea switch is pretty good, although most feedback seems to be with boats/marine applications.
https://www.amazon.com/Blue-Sea-Systems-...001VIXLRO/

 You'll never drain your chassis-batteries into your house-batteries, or overload your alternator.....

BlueSea 7620 ACR, being a dual-sensing switch, whenever one side voltage is over 13.1, the relay will close, and one side will charge the other side when the alternator is off, provided that you go with the 3-relay setup.
 
   

...if you have some posts you can share that will help me investigate the equipment/situations where people with DP's have burnt-out their alternators due to charging battery banks, please share those and I'll investigate further.

Dead Battery burns alternator. I believe this can happen. See what someone who has been in the selling alternator business for 15 years has to say on the topic, "Can a weak battery destroy an alternator?":

Absolutely yes. I sell alternators all day every day - and a poor battery is often the root cause of alternator failure.

A battery with a short in it will cause the alternator to run at full output for extended periods of time, if not continuously - and they are not built to do this. Alternators the world over are built to supply an initial high current, tapering back as the current used to start the vehicle is replenished. Constant running at full output simply overheats them and the rectifiers fail. *See edit below

If your battery is 'Open Circuit' the alternator will either not start charging at all or will erratically bounce from low to high voltage. This causes the regulator to fail prematurely (or immediately!)


A battery that simply will not accept charge won't necessarily cause premature failure of the alternator unless it is permanently at a low voltage, in which case see the 'shorted' section above.

Hope that helps?

*EDIT: Some bigger commercial and marine alternators are designed to run at full output constantly, but I don't get the feeling you're talking about those :) In 16 years of selling parts for alternators I've never heard of the brushes and slipring wearing and the grease in the bearings overheating from high charge current at idle. These issues are caused by other problems not in scope of this question.





source: https://mechanics.stackexchange.com/ques...alternator

[SouthernDevGirl]

@arcticdude - that is awesome! I hope you post photos as you go through the stages.

There is some confusion about the alternator. I'm not suggesting that they run at 24v. That was my entire point -- that they are running at 12v, HOWEVER, they are intended to run at 24v. Therefore, at the same gauge wire, running at 12v as Newell does, you're effectively increasing resistance and reducing the effective current, which is a substantial help on the alternator's load.

Keep in mind that the 50DN which Joe has -- it's rated for 75% output at *idle*, according to their specs. That's a very high-end alternator.

I'm seeing comments made about traditional alternators as if they are similar to one that outputs 75% at idle and runs a 9" stator -- those are worlds apart, lol.

--

Joe,

Just to put things in context... You quoted a StackExchange comment re:Open Circuit batteries. Of course an "open circuit" battery would kill just about anything/everything. That's the anomaly that one would become alerted to before doing damage -- much like a reliable engine that will also go bad without oil.

If we're going to look for exceptions-to-the-rule, I could brainstorm dozens of different situations that could kill your alternator.

Of course none of this is (not in any way) related to intelligent VSR's and DC-DC chargers --vs-- isolators. In fact, it's more reason that VSR's and DC-DC chargers are a superior alternative to isolators.

Keep in mind -- in an "open circuit" battery, an isolator will still connect because the voltage will be high enough for an SLA-threshold isolator and therefore, the exception-to-the-rule that you mention is worse in a situation with a simple / non-intelligent isolator versus a more intelligent option, such as programmable voltage cutoff.

Based on your reply, there is substantial confusion on the Blue Sea product. It may be that I linked the wrong product or that there is a miscommunication somewhere.

Yes, they are very popular in Yachts. Yes, Yachts use better quality equipment than RV's in almost every situation that I'm aware (relative to their quality level, of course). No, there is not some reason why using a solution that is popular with yachts is somehow less ideal on an RV. In your case specifically, you have an issue with corrosion; gear that is designed to tolerate a marine environment is ideal in that instance.

For starters, the VSR that I included is a magnetic *latching* unit, meaning that it shouldn't require more than the 40ma current draw, which is substantially less than self-discharge on a 6x8D battery bank (for relative perspective).

Second, every one we've used has a 30-second and 120-second requirement before switching over, they also have BOTH high/low voltage cutoffs, which add additional protection over an isolator. You'd have to review the user manual; however, there is no scenario where they flap/oscillate.

Third, there is no situation where paralleling more batteries should cause the inverter-charger to burn out. Your inverter-charger is set for 24x7 duty-cycle. If it's not, dump it and find another -- I've never had an issue under any amount of load for any amount of time, when properly cooled. Adding more parallel batteries does not require more current in your unique situation; a 6x 8D battery bank is already utilizing the full load, you merely have a longer cycle if for some reason both sets of banks were low SoC (again, that's a very strange situation and in the majority of real-world cases, this is a major feature, not a drawback).

These esoteric scenarios appear to be strange to me. It's a bit like saying that someone doesn't want to use the the best/highest-speed tires, because it will allow you to go faster and if you took advantage of that, it might over-rev the engine or some such secondary/tertiary side-effect of the added feature/capability. The idea that a positive/added-feature allows you to do something impractical that can be viewed as a negative, to me that's a bit counter-intuitive.

Regarding the Blue See offering to connect from either side -- it's just one option, of dozens. If you prefer a one-way model, by all means, there are plenty of others. I was merely recommending one that we had used effectively, one where we have first-hand experience, back before new battery chemistries became affordable.

By all means, for your application -- definitely go with the isolator.

For others that stumble on this post, I think it's doing them a disservice to suggest that VSR's are a sub-par or questionable alternative to isolators. Or far worse -- that somehow isolators will save your alternator but a VSR or DC-DC will not, when the opposite is true.

That's just my opinion/experience. I certainly could be wrong. Good luck to you.