How long can you run AC from batteries?

[booster]

Originally Posted by avanti

Well, for awhile we only had 220AH of AGM, and we were able to run for almost an hour. This was with a pretty sophisticated (Outback) inverter, though. 440 is indeed mo betta, though.

What did you have the low voltage cutout set at on the Outback? Having a high end pure sine wave inverter would be a necessity to run on two batteries. I also was able to get out CoolCat to start with two full batteries, but once they got down a to maybe 70% they would trip the low voltage cutout if the compressor cycled. IIRC, I was set at 11.5v. Ours is a Magnum 2000 watt psw inverter.

[InterBlog]

Originally Posted by avanti

I look forward to hearing more of your story. As we have heard numerous times, connecting significant external loads to modern vehicle charging systems can be very dicey--upgraded alternator or not. Don't know if your issue is related to that or not.
....

In response to Avanti, and also in response to Booster's post following it:

It turned out to be a gizmo called an alternator clutch pulley that was damaged by the high demands that the lithium battery placed on it. We've got that damaged unit in the shop getting repaired, so that we can re-adapt it as our van's SECOND alternator. (No more wire hangers?! No more single-alternator off-grid van!!!!)

Here's the first of several blog posts that will describe what happened and what we are doing to ensure that it never happens again. This stuff is dangerous. This type of failure could leave a van owner sitting at a dead stop in the middle of an 80-mph freeway.

PSA: ALTERNATOR CLUTCH PULLEY FAILURES ON LITHIUM SYSTEMS

[booster]

I don't recall what size Sterling you have, but assume the 120 amp one?


The clutches in question are usually just overrunning clutches to smooth out the belt and alternator load and reduce harmonics. It is a bit surprising that it would fail at 120 amps, but the 120 may be output, and with the boosted voltage the Sterling does, it would be higher watts than normal.


There are lots of engine generator systems, both lithium and AGM that are running the Nations alternator with a clutch pulley at much higher outputs than you are running, so it may be that the system was designed to be a "normal" Sprinter power use size and not up to that kind of output.



Of course there are also all the intangibles like the number of poles in the alternator and if the voltage drawdown that the Sterling does is making the MB system do something that could cause some heavy pulsing.


I think it would be prudent to see if a pulley with more capacity if available, even if you do go to two alternators which certainly is a good idea.


As Avanti said, that is a lot to ask from a stock charging system, as they just aren't designed to do that kind of repeated, long term, high output charging.


I would also think you may want to take a look at your damper pulley/tensioner for the timing belt. If the clutch pulley has been pounded hard enough to fail, the tensioner could also have accelerated wear.

[InterBlog]

The big ask is exactly why we upgraded from the OEM 90 A alternator to the Bosch 200 A. Not that it achieved anything in the end.

There's more to this story than meets the eye; I don't have all the details yet. The repair shop had developed a particular fix because they see so many of these clutch pulley failures. But they called back my husband to say that Bosch had changed up something in their design in order to prevent outfits like theirs from applying exactly that fix. WTF?? It's a $450 alternator, and Bosch doesn't want people to repair them so that they are reliable?! Something weird is going on.

[booster]

I just looked at the Nations site and they list a computer compatible large 280 amp alternator for 2007 Sprinters for the stock location and also the well know 280 amp addon kit. The runs on a separate belt.


Of course, if you need to use the computer to run the alternator, you won't be able to parallel the units, but you could wire switchable or as a standalone engine generator. I don't know if anyone has ever figured out what Coachman does to parallel the two alternators, or what MB does when they use two, as the do offer the second alternator mount bracket.


Ditching Bosch might be a good long term idea to consider.

[InterBlog]

Now that we involuntarily own two $450 alternators (one of which is in the shop for repair), I think our path will be to adapt them both if possible.

The replacement 200 A Bosch is oversized for the engine alone, but it is what it is.

As for the being-repaired alternator, there is a space available in our Sprinter for the mounting of a second compressor because some of them (people-movers) have an integrated rear a/c, which ours does not. The repaired alternator might be able to go there.

My husband located a company which does have a T1N Sprinter-compatible alternator bracket. They require a waiver of liability before purchase because they warn that the Sprinter's vibration dynamics can shake its bolts loose. Husband has a workaround identified for that scenario (holed bolts like they use on aircraft - run safety wires through them).

If we can get the second alternator working, it won't be a critical issue if it dies another death by clutch pulley failure, because it will be isolated from the chassis battery.

[booster]

Be aware that overrunning clutches don't always fail like yours did and keep working, kind of. Sometimes the lock up, which would be OK, but sometimes they also come apart, which would put you by the side of the road. We have the clutches on both alternators on our Chevy, and I do worry about them, but from what we have seen here and other places they seem to hold up well. Our tensioner does not move at all now, even at 280 amps of output and low idle, so the pulley are doing their job.

[cruising7388]

Originally Posted by booster

I don't know if anyone has ever figured out what Coachman does to parallel the two alternators, or what MB does when they use two, as the do offer the second alternator mount bracket.

This is still somewhat of a mystery. It'is part of the package Xantrex provides on the Galleria and presumably provides additional charging from the OEM alternator somewhere in the whereabouts of 40 amps. Parallel operation is triggered only if the Nations Balmar regulator puts the Nations alternator into a bulk/constant current mode. What puzzles me is how the batteries recognize both alternators since the Nations alternator is bulk charging while the OEM alternator is absorption charging.

[booster]

Originally Posted by cruising7388

This is still somewhat of a mystery. It'is part of the package Xantrex provides on the Galleria and presumably provides additional charging from the OEM alternator somewhere in the whereabouts of 40 amps. Parallel operation is triggered only if the Nations Balmar regulator puts the Nations alternator into a bulk/constant current mode. What puzzles me is how the batteries recognize both alternators since the Nations alternator is bulk charging while the OEM alternator is absorption charging.

Bulk and absorption are the same voltage setpoint and the only difference is how much current the batteries are accepting. Bulk is the first stage and runs at constant until it hits the voltage setpoint for absorption as the batteries fill. At that point, nothing really changes as the voltage is held constant at the end bulk, run absorption voltage, and not allowed to climb any more by limiting current.


The two alternators, if tied together, cannot have on in absorption and one in bulk, because the voltage is being set by the battery acceptance. If the voltage is running below the setpoint for absorption, both will be in bulk/constant current. If the voltage has reached absorption setpoint, both would be in absorption, but the controller would disconnect them if that is how it is setup.

[cruising7388]

Originally Posted by booster

The two alternators, if tied together, cannot have on in absorption and one in bulk, because the voltage is being set by the battery acceptance. If the voltage is running below the setpoint for absorption, both will be in bulk/constant current. If the voltage has reached absorption setpoint, both would be in absorption, but the controller would disconnect them if that is how it is setup.

The Nations alternator is controlled by the Balmar regualtor which determines whether charging is in the bulk or absorption mode. I think you're indicating that the factory alternator behaves identically. That I don't get unless the factory alternator regulator replicates the Balmar charging protocol. Does it? Without a bulk charging instruction, isn't the factory alternator always going to provide absorption charging? Has the Canbus network changed this?

[booster]

In general, the alternator isn't going to care if the computer thinks it is bulk or absorption when it is first turned on. The computer will let it do charge at whatever rate it can until it gets to the absorption setting and then it will just start tapering the current. As long as the Xantrex software takes the connection between the two alternators apart before either get to their absorption settings, neither will really know the other is there, I think.


What I do wonder is how the Xantrex limits the MB alternator to 40 amps without messing with the computer.

[Reed]

Have noted on other threads that we have 2002 -19’ Roadtrek which has
415 W solar
4.5 kW-hrs LFP
2.5 kW PSWI

We have run it for about 1 hour in evening to cool down the compartment. We have run it for 2 hours in mid day sun to see what we could do. This was in Xelac, Quintana Roo(Yucatan).

We sleep with a couple of 110 V DC fans. Breeze from Caribbean was generally sufficient.

We do use awning plus three sections of Aluminet to cut down solar loading. This works quite well.
Reed and Elaine

[Gemlake]

Graham Smith of the Travato Facebook group is one of the early adopters of Winnebago's Pure3 (Volta) lithium system. He recently wrote a detailed FAQ about the system, in which he addressed, among other things, the question raised by the title of this thread:

"[T]he [Coleman] Mach 10 spec sheet indicates that it will draw somewhere between 1350W to 1625W. . . . If you assume the worst-case then the math would tell you that 8700W / 1625W would give you 5.3 hr of run time. But in one rather unscientific test I did, I ran the A/C on Low speed for roughly 5 hrs and the SOC went from 90% down to 40% or about 10% per hr. So clearly there are a lot of variables at work."

[Sid]

Yes, AC and DC is apples and oranges, but the conversions to get from one to another are well known. She says 120V for the AC voltage. This the RMS vale. If you connect a scope to the AC outlet, it will be about 350V peak to peak. This will be 175V peak, which is 120V RMS. So, she left out the RMS, but it's implied by it being 120V. With AC voltage, the RMS value is the value that will produce the same power dissipation in the same load as a DC voltage. So, 120V AC RMS delivers the same as 120V DC.