UHG - why a separate alternator?

[smgemelos]

Why are manufacturers installing a second alternator into vans as part of the “under hood generator”? Why not use the feed off the existing alternator?

Prior to our current class b, I built my own van conversion based on a Ford Transit. When ordering the transit I opted for the heavy duty alternator for the extra amperage - I think it was 250 amp output. This is more than sufficient to charge the chassis and house batteries and any other loads.

Then there are 5-stage charge managers that will isolate the house batteries from the chassis when the voltage is below 13.5v (meaning the engine isn’t running).

Anyway - seems easier than adding a second alternator.

[booster]

Several reasons are commonly stated.


A lot of modern vehicles have the alternator controlled completely by the vehicle computers and do thing like charging while coasting, shutting down other times, and who know what else. They also measure amps going to the starting battery and probably compare it to the alternator output after figuring in what else is on, so could set codes or give other issues like turning way down and hot charging well.


Factory alternators are often not considered reliable at long, high output, amperages. Most that I have seen will get too hot after about running at 40% output for a while.


Mismatched battery types can mess up the coach charging profile, so a standalone can have a regulator of it's own to take better care of them and charge them more efficiently. Starting batteries are often hit hard for a time at the beginning of the charge and then the charging backs off a bunch.



You can get higher output from the standalone at 280 amps, if you need that much (although you won't net that much over time).


If you do cook the alternator with the heavy charging, at least you can keep driving.


A lot depends on how much battery bank you have and how fast it will charge. If you have bank that will only accept 80 amps, a good sized stock alternator will likely be fine for a long time. If you have a bank of lithiums that max out the stock alternator for hours at a time, I think you would be having durability issues fairly soon. In between could go either way depending on a lot of things.

[wincrasher]

Not to mention, you can go with a 48 volt system at a much lower amperage, eliminating the need for cooling, as well as being much smaller and saving weight and engine load. This is what the Volta system is doing.

[avanti]

For the reasons Booster stated, the OEMs place severe restrictions on the currents that an upfitter is allowed to draw from the vehicle power system. For example, the Sprinter BodyBuilder's manual states that current used for charging additional batteries must be actively limited to 40 amps. You as an individual owner may choose to ignore such guidelines (although this is increasingly a bad idea). But, Mercedes certified upfitters are contractually required to follow the guidelines.

[FrayAdjacent]

Originally Posted by wincrasher

Not to mention, you can go with a 48 volt system at a much lower amperage, eliminating the need for cooling, as well as being much smaller and saving weight and engine load. This is what the Volta system is doing.

That's one of the reasons I like the Volta system... use a 56V alternator and you need much less current. Using 12V alternators for lithium systems baffles me... you'd need giant wires and there would be a lot of heat.

[smgemelos]

Thanks - makes sense.

As far as the 48V or 56V setups - also makes a lot of sense, but the whole system needs to be spdesigned for that voltage. The lithium cells need to be built/grouped to 48 or 56 V, the inverter/charger, and any DC loads (fridge, a/c unit, etc) or just run everything off the inverter 110 (so the inverter runs all the time) or maybe a DC/DC converter to get 12Vdc for all those 12V loads like leds lighting, maxxfans, etc

[gregmchugh]

Originally Posted by smgemelos

Thanks - makes sense.

As far as the 48V or 56V setups - also makes a lot of sense, but the whole system needs to be spdesigned for that voltage. The lithium cells need to be built/grouped to 48 or 56 V, the inverter/charger, and any DC loads (fridge, a/c unit, etc) or just run everything off the inverter 110 (so the inverter runs all the time) or maybe a DC/DC converter to get 12Vdc for all those 12V loads like leds lighting, maxxfans, etc

Yes, the Volta system uses a DC to DC converted to handle 12v loads..

[HarryN]

Originally Posted by FrayAdjacent

That's one of the reasons I like the Volta system... use a 56V alternator and you need much less current. Using 12V alternators for lithium systems baffles me... you'd need giant wires and there would be a lot of heat.

Yes, we do the exact same thing for our larger auxiliary power units as well.

Many advantages.

For smaller systems (1 kW class) , we still use 24 volts internally.

[kite_rider]

If I limit this discussion to Promaster based vans I'd say I've seen more problems with the UGH than benefits. Not worth the trouble.

I recently added a 240Ah LiFePO4 battery to my Promaster van in parallel with the camper's 105Ah AGM battery and so far the upgraded 220A stock alternator has been fine. My Lithium battery charges to about 90% in about 30 minutes of driving. So for my electrical needs (24hour Alde furnace, fridge, lighting, microwave for meals and electric kettle for coffee in the morning) this battery setup is fine.

If you are trying to run an A/C off the grid for hours at a time I could see the value of a UGH. Oh, by the way the stock upgraded Promaster alternator had no problem running the rooftop A/C via the 2000W inverter so I don't think my Li battery is putting any more load on the alternator than that was.

As an aside, I just took the A/C unit off this week - I almost never used it and prefer a Maxxfan anyway.

[booster]

Originally Posted by kite_rider

If I limit this discussion to Promaster based vans I'd say I've seen more problems with the UGH than benefits. Not worth the trouble.

I recently added a 240Ah LiFePO4 battery to my Promaster van in parallel with the camper's 105Ah AGM battery and so far the upgraded 220A stock alternator has been fine. My Lithium battery charges to about 90% in about 30 minutes of driving. So for my electrical needs (24hour Alde furnace, fridge, lighting, microwave for meals and electric kettle for coffee in the morning) this battery setup is fine.

If you are trying to run an A/C off the grid for hours at a time I could see the value of a UGH. Oh, by the way the stock upgraded Promaster alternator had no problem running the rooftop A/C via the 2000W inverter so I don't think my Li battery is putting any more load on the alternator than that was.

As an aside, I just took the A/C unit off this week - I almost never used it and prefer a Maxxfan anyway.

You must be starting at something like 50-60% to get to 90% in 1/2 hour?

If you have a battery monitor in the system, it would be interesting to see what the charge amps really are, or put a clamp on meter at the alternator output. Same with using a an infrared temp gun on the alternator case to see where it is running. Balmars, when used turn down at about 220*F for reference. I can't say for a Promaster alternator, but the stock alternators I have had experience with struggled to get above about 50% output for more than maybe 15 minutes without getting too hot.

I think any kind of information and data we can get is good for others who may be thinking of doing the same or similar, so they know what to look for. Did you increase the size of the cable to batteries when you added the lithium?

[kite_rider]

Yea, I don't think the battery was much below 50%. I recall the voltage meter (on the control panel) reading about 13V and it's usually about .1V lower than the actual voltage at the Li battery. Plus, someone on this form was telling me that the real voltage (resting voltage?) is not apparent unless the battery sits for about 10 hours anyway.

I use the Lightwave PowerMon device via a shunt to monitor and control the charge and discharge of the battery - it connects to a 200A automotive relay to connect and disconnect the Li battery. I'm not 100% that I have the shunt calibrated correctly, but peak charging was right after starting the motor and it maybe got up to 80A for a very short time. During most of the charging time I was seeing about 50A of current. Once the Li battery gets to about 13.3V the current drops way down to an amp or two. My algorithm has the battery disconnecting from the alternator when it reads 14.4V for 3 seconds. I might tweak this to 14.2V for a few seconds instead. I recall the battery settling down to about 13.4V to 13.5V with this process.

The cables that go between the battery separator (near the alternator) and my inverter are already very big. They were designed to charge two large banks of EcoTrek batteries as an option. So I think they are fine. Will bring my infrared thermometer next time I do a big charge cycle and see how hot it gets. No camping now, got 2 feet of snow yesterday in an epic storm in Central Oregon!

[B Eventually]

A couple of years ago, we had AM Solar install a Victron Energy based lithium system in our Trend. When we travel the hottest parts of the country, I have been known to idle the engine for AC and running the RV AC off the inverter. I'm sure it's rougher on the stock 220 amp alternator, but that's far preferable than having to step outside and enduring the scorching sunlight and heat.

When I'm idling and not running the Promaster's AC, our Victron display shows roughly 800-1000 watts going back into the batteries. I don't think I've ever paid attention to it after idling for an hour or two in a parking lot. But I imagine the output drops. Also, I believe AM Solar continued from Winnebago's wiring, so it may be that the stock 220 amp alternator has more power to spare?

[InterBlog]

Originally Posted by smgemelos

Why are manufacturers installing a second alternator into vans as part of the “under hood generator”? Why not use the feed off the existing alternator?

Prior to our current class b, I built my own van conversion based on a Ford Transit. When ordering the transit I opted for the heavy duty alternator for the extra amperage - I think it was 250 amp output. This is more than sufficient to charge the chassis and house batteries and any other loads.

Then there are 5-stage charge managers that will isolate the house batteries from the chassis when the voltage is below 13.5v (meaning the engine isn’t running).

Anyway - seems easier than adding a second alternator.

Good question. The answer may, in part, be influenced by whether you are thinking about a conventional house battery (AGM) or a lithium cell array.

The short answer is that there may be things happening in the lithium context that the users / the market / the installers etc. do not yet fully understand.

Yesterday's alternator does not necessarily look like today's alternator. This fact bit my husband and me squarely on our patooties when we took at face value the theoretical ability of a 200A Bosch to serve both purposes. We stripped out its clutch pulley and I danged near got stranded in the middle of nowhere as a result, when that Bosch failed at 17 months of age after only occasional use for lithium charging purposes. It is risky to rely on one alternator without special provisions to detect when things might start going horribly wrong because of the atypical demands that have been placed on it.

Rather than re-hash all of that technical stuff here, you might want to check out the Sprinter Forum thread titled Can a lithium pack be charged by alternator alone? It's one of the better threads to come along in this vein recently.

But if you are thinking in AGM terms, that thread might amount to TMI for your situation.

[kite_rider]

Originally Posted by InterBlog

Yesterday's alternator does not necessarily look like today's alternator. This fact bit my husband and me squarely on our patooties when we took at face value the theoretical ability of a 200A Bosch to serve both purposes. We stripped out its clutch pulley and I danged near got stranded in the middle of nowhere as a result, when that Bosch failed at 17 months of age after only occasional use for lithium charging purposes. It is risky to rely on one alternator without special provisions to detect when things might start going horribly wrong because of the atypical demands that have been placed on it.

Interesting note and the link to the sprinter forum was an informative read. Sounds like some sprinters are having trouble charging lithium (specifically yours) and sprinter people seem to frown upon running the rooftop AC from an alternator. I don't know what the root of these issues are since I don't own a sprinter and don't really follow them. But maybe it's capacity, maybe it's the new 'smart' capability, or something else entirely.

What I have noticed on the FB pages, YouTube, and other forums is that the Hymer based class B's have enabled their Promaster builds to run the rooftop AC via the alternator/inverter/battery. This has to be a pretty heavy and unusual load on the alternator. However, I've not heard anybody complain about a failed alternator related to it. OTOH, I've heard about *many* issues related to the second alternator (UGH) for various reasons. Many have had a connections come loose. Others have issues with a coolant line to the UGH that leaks and the worst being the FitRV overheating with James speculating that it may have related to this second alternator install.

I'll be the first to admit that my setup is a DIY install that might lead to some longer term issues with the charging system. But a rebuilt 220A Promaster alternator costs $277 on Rockauto and I can change it out myself. So I'm actually thinking I'm taking the lower risk path to having all the goodness of some additional Lithium power in my camper.

[booster]

Originally Posted by kite_rider

Interesting note and the link to the sprinter forum was an informative read. Sounds like some sprinters are having trouble charging lithium (specifically yours) and sprinter people seem to frown upon running the rooftop AC from an alternator. I don't know what the root of these issues are since I don't own a sprinter and don't really follow them. But maybe it's capacity, maybe it's the new 'smart' capability, or something else entirely.

What I have noticed on the FB pages, YouTube, and other forums is that the Hymer based class B's have enabled their Promaster builds to run the rooftop AC via the alternator/inverter/battery. This has to be a pretty heavy and unusual load on the alternator. However, I've not heard anybody complain about a failed alternator related to it. OTOH, I've heard about *many* issues related to the second alternator (UGH) for various reasons. Many have had a connections come loose. Others have issues with a coolant line to the UGH that leaks and the worst being the FitRV overheating with James speculating that it may have related to this second alternator install.

I'll be the first to admit that my setup is a DIY install that might lead to some longer term issues with the charging system. But a rebuilt 220A Promaster alternator costs $277 on Rockauto and I can change it out myself. So I'm actually thinking I'm taking the lower risk path to having all the goodness of some additional Lithium power in my camper.

\


From what you mentioned earlier, it sounds like your are pulling only 80 amps for a short time and then even less that that. Even throwing in 20 amps to run the van (our Chevy is a bit lower than that unless the heater fan is on high and/or headlights on) you are not even at 50% of rated. I would expect that the stock alternator would not have much heat issue at that output periodically. As comparison, our 440ah AGM bank will pull 180 amps for well over and hour if we are way down to 10% SOC, and that will heat cycle the Balmar at over 220*F.

I think you will have little trouble with your setup at those low amperages. It would be different if you were running the AC off the inverter and pulling over 100 amps for hours on end, repeatedly, I think.

[InterBlog]

Originally Posted by kite_rider

Interesting note and the link to the sprinter forum was an informative read. Sounds like some sprinters are having trouble charging lithium (specifically yours) ....

We don't think it's a Sprinter thing - we think it's an alternator thing, and specifically, a lithium thing. We just happen to have installed our example in a Sprinter. I think if we'd taken the same lithium design and put it in a Promaster, odds are high we would have gotten a similar outcome.

As I noted on other threads, this is an issue that would be greatly helped by hard statistics. We have anecdotal reports only of other alternators failing, sometimes repeatedly. But there is no centralized source in which to amass information. Lithium hasn't been around long enough, and the people who are charging lithium batteries from alternators are not pooling their experiences in a centralized place, or in an organized manner.

Plus the people who are charging big bucks for lithium retrofits don't necessarily want the rest of the world to know when one of their systems has an ooopsie. I've tried to warn a few of them that this might be a risk, and they didn't want to hear about it. To them, a 200A alternator on paper will be able to perform. If the specs work on paper and in theory, then there's nothing that needs to be said about real life.

[avanti]

Originally Posted by InterBlog

It is risky to rely on one alternator without special provisions to detect when things might start going horribly wrong because of the atypical demands that have been placed on it.

I think that this little bit of wisdom is the heart of the matter.

Modern OEM alternators are part of highly-engineered systems that protect themselves very well, but only within the performance envelope defined by their engineering specs. For example, Mercedes limits the permissible current takeoff for external battery charging to 40amps. The rest of the system assumes that you are following this spec. If you don't, then there are almost certainly failure modes that may or may not occur, but are not guaranteed not to happen.

Second alternators have their own, independent protections (or not). For example, the Balmar regulator will modulate current production as a function of alternator temperature. If it is a good system, it will take care of itself. The important thing is that it makes few assumptions about the behavior of the rest of the engine.

[Davydd]

I have a Delco 330 second alternator in my Sprinter and I’ve had it now for more than 4 years. It consistently slams 270-280 amps ito the battery and has done so for an hour of testing when it ended with the battery at 100% driving 50 mph on the Natchez Trace. High idle will charge about 230 amps per hour but I rarely need to do so and even rarer have never used Autogen (a much more sophisticated Voltstart) much except for demonstration, testing and accidental “butt” starting from the key fob. Generally in an overnight boondock situation driving less than 30 minutes can recharge my 800ah lithium battery bank. I am a heavy user of our batteries in that the inverter is on all the time, we have two electric articulating beds with vibration that operate on 120v, the Kuerig coffee pot brews 4-6 cups in a boondocking stay, the Instant Pot and induction burner gets used for an evening meal and the induction burner gets used for breakfast. We have even baked in our microwave/convection oven, We are also charging 2 iPads and two iPhones in leaving them plugged in and I have a WiFi network always on. Refrigerator/Freezer is a 6.8 cf compressor 12v. Simply put, I don’t have to monitor my energy use much and I have the same electrical in boondocking as if plugged into shore power going on 4-1/2 years.

It has been trouble free except an original Nations alternator failure (replaced by a better performing Delco) and an electrical short from water penetrating our supposedly sealed battery box caused by a pressure differential in rainstorms. A nickel sized retrofitted Gortex plug solved that. That was all in the first half year of use in 2015.

It is here now if you want to pay for it. I don’t believe in next year or 5 years to wait for better or cheaper as I might not even be RVing then. My next Class B will have a better lithium battery system but I am not getting the 48v Volta system.

[booster]

It has been discussed many times about the ability to overwork either the van generator or and UHG with big battery banks, not even just with lithium.


I think it was Avanti that posted a trace of his system with 440ah of AGM batteries charging at high rate off his Balmar regulator, that was regularly turning the output down due to high alternator temp. With the Balmar this a 50% reduction in field current, the relates roughly to a 50% decrease in amps. Our best guess from the current curve was that with the cycling it was netting about 165 amps on average from the 280 amp alternator (maybe a 270 amp). While cycling like this definitely protects against overtemping the alternator, I have never been a fan of thermal cycling equipment like this as it generates a lot of thermal stress on the units, but it is mostly the only option currently available. The Balmar can also be reduced in output by a % field that is something like 40-99% output, but it isn't switchable so you would lose the ability for short fast charging or running a high amp accessory. I think for some people it might be no problem to turn it down to net maybe 120 amps without cycling as it would be better for the system parts. If you don't need a very fast recharge or sudden burst of full output, I think it would be a good thing to do,



It would be very nice if there were a switchbox system that could be used to limit the current to the batteries, independently of the regulator, or even better, built into the regulator for standalone systems, to be able to chose the output you want from the alternator based on conditions and use at the time. For instance, there is no reason to run the alternator full out if you are going to be driving six hours, so you could turn it down to keep the alternator cooler and still get charged fine, or turn it up full if you want to run the microwave for a bit of time.


We are "lucky" as our 07 Chevy did not come with a computer controlled alternator, so we can parallel two alternators to lower the amperage on each under all conditions and run both off a remote regulator. We currently have a 280amp and a 250amp DC Power units on an Amplepower regulator that allows two turndown points that are switchable. It does not have alternator temp control, though, so we have to be set right. Right now we are set at about 280amps and 180amps which gives us a very rapid charge for a short time with the 280amps or long term charging without overheating the alternators with the 180amps. We have found we never have used the 280amp setting except for testing it, so I am thinking about turning it down to about 120 amps and keeping the 180amp as is. The 120 amp would cover, I think, at least 95% of our recharges with no penalty at all, based on our past use. I think it would be a good overall idea as it would be easier on the alternators and belt, and would also help keep the batteries cooler, I think. Ours are underbody, behind the rear axle, and even though shielded, they tend to get pretty hot in very warm weather or at the 180amp charge rate for long periods. We are temp corrected for the alternators, but turning down the voltage to still charge hot batteries is not as good as just keeping the cooler if you are looking for less battery wear. Of course, lithium systems would not have the hot battery issues, but all the other stuff would likely apply to them, plus the fact that some of the lithium batteries have a current limit that could be very easy to exceed. This is true of many of the "drop in" style lithium batteries especially.

[kite_rider]

Originally Posted by InterBlog

As I noted on other threads, this is an issue that would be greatly helped by hard statistics. We have anecdotal reports only of other alternators failing, sometimes repeatedly. But there is no centralized source in which to amass information. Lithium hasn't been around long enough, and the people who are charging lithium batteries from alternators are not pooling their experiences in a centralized place, or in an organized manner.
.

+1! The sharing of experience, research, and ideas are what make these forums great. On a practical note, you're and engineering type and I'm an engineering type so we can talk somewhat intelligently about this subject. You don't have to veer very far on the interwebs to see these discussions just become emotional with a lot of angst. For example, I post frequently on a FB page dedicated to the Carado Axion. They are a very nice group of people for the most part, but the content is not very analytical or deep from an engineering perspective. It's great for simple DIY enhancements and clever accessories. Plus, you get to hear where others have had problems - even if those problems are not presented with the level of detail that you or I may prefer. As an aside - that platform is much easier to post pictures on. Something I struggle with on this forum!

Anyway, to the original point of this thread. All I'm trying to say is that adding a second alternator is expensive, complicated, and opens the potential for other failures. I back that up with the anecdotal evidence I've observed (for Promasters primarily) on the forums and FB pages. So I'm suggesting, if your additional loading is not all that high - which seems to be the situation for my camper - then you might want to just invest in a factory certified upgraded alternator rather than add a second one.

By the way, if you building a 52V (or 48V) system, then having a second alternator makes a TON of sense to me. I floated this idea with pretty minimal response when I was thinking about building a sprinter 4x4 based camper rather than buying one. At the time Volta was not out with their system so there didn't seem to be much thought around this idea. Plus, I was recommending a different chemistry for Li than the 12V friendly LiFePO4 chemistry that many are using for their campers.
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