[Archived]

I think Gil’s advice to run the generator prior to quiet time is good advice no matter what kind of battery is used because the same issue with a generator start in the middle of the night can apply. It is just not an Li issue.

[Chas]

All of this very good discussion has caused me to dive into the manuals and understand how the auto gen function works on my coach. There is a Schneider Electric Xantrex XW Automative Generator Start box that controls the interface between the batteries, generator, and inverters. There’s a 100 page manual just for this box, and I am just beginning to understand it. The generator can be automatically started in response to low voltage, AC loads on the inverter, thermostat triggers, and a scheduled time to exercise the generator. The low voltage triggers can be set according to periods of 30 seconds, 15 minutes, 2 hours and/or 24 hours. Thermostat triggers would be associated with a temperature that would fire up an air conditioning unit (for example). Load triggers would fire up the generator anticipating the draw on the batteries. A quiet time mode exists similar to the one discussed in the posts above. Quiet time trumps all triggers to run the generator, so it needs to used judiciously.

I haven’t delved into the actual setting of the triggers on my coach. That’s for another day when I am more familiar with the menus, etc.

The rest of the system includes two Schneider Xantrex XW inverters, a Kohler 20kva generator, and three Mastervolt MLi Ultra 24 volt batteries. Some of the house systems run on 24 volt and some 12 volt.

I am still learning, having owned the coach for 4 months.

[Ken]

Ed,

You realize of course that now we are going to expect you to be our Li battery systems expert.

[Peter]

Ed,

It looks like the AGS is the Xanbus AGS unit designed for
the SW family of inverter/chargers.
Given this and the MV batteries communicate over a network, it’s
possible that some message delivery and possibly protocol translation occurs between the
MV and Xantrex. If not, then the AGS is
set to trigger on a given voltage. You
can scroll through the current settings on the AGS unit and see what it’s set for. BTW, most of the pages in the AGS manual deal with the ways of wiring and controlling the many generators that are supported. You can skip these pages.

My bet is that if they don’t have the AGS and batteries
communicating over the network, then they may be faking one of the temperature
triggers. Sure, they could use the voltage for the trigger. If given the choice, I would opt for the State of Charge being the trigger. The battery voltage will drop pretty quickly once it begins to drop. I can see them putting in a
relay that is triggered by the battery’s state of charge and using that relay
to trigger the AGS temperature trigger.

I’d be interested in how they have this set-up once you figure it out.

After spending some time in the MV battery and control manuals, it appears they have a pretty well thought out product.

Given the complexity of Li-ion batteries, I’m a bit
surprised they didn’t use the MV Combi inverter/chargers that could have communicated
with the batteries to ensure the charge only when required. Also MV has a multitude of network conversion
boxes to talk to other network protocols and even support for relay contacts.

[Corey]

Jon, I’d worry about anyone who is listening to me for expertise.

Gil, I’m afraid you’re ahead of me on these issues. I will work to get more informed and weigh in after a bit more study. Thank you for your input!

[Archived]

I checked out how Marathon set the autogen presets to trigger the generator autostart. Here’s what I found on the trigger settings:

30 second low voltage: 23.5 volts. This seems to make sense given the discharge profile of Lithium batteries.

Autostop: Absorb

Start Load: 30 amps

Stop Load: 10 amps

I was surprised to see that the Autostop is set to Aborb, which stops the generator before the batteries are fully charged. The manual states that this should only be used if alternative charging sources of power are available. While the shore power and engine alternators provide charging sources, this setting will shut the generator down prematurely if you’re dry camping. The manual says this is not the recommended setting, and it can cause the batteries to fail prematurely. However, this may not be written with Lithium batteries in mind.

The alternative setting is Autostop: Float where the generator shuts down when the batteries are fully charged. Float is the manufacturers recommended setting. I’ll check with Marathon on this.

[Mike]

Float would be the answer Ed or a timed amount of gen run time to assure full batteries before the stop.

[Edward]

Hi Ed and Sharon,

It is so good to see a new coach owner posting. We are just two steps behind you as ours is being built now.

We will also have lithium batteries so I will be watching your responses. If your Marathon was at the MCC in Indio a couple of months ago, we looked at that coach which was beautiful. The glass sinks were awesome.

Safe travels,

Mark

[Peter]

Tom, that makes sense to me. I have a question into Marathon.

Mark, that wasn’t ours as we bought it as it was approaching 99% completion in the factory. Once complete, they shipped it to us here in Ohio. Our coach does have the glass sinks you mentioned.

I’ll post the answer I get from Marathon regarding the appropriate trigger for shutting down the generator after a charge.

[Peter]

I think you are doing the right thing Ed. As coaches become more sophisticated it becomes very important to understand, as an owner, not only how the systems are set up, but also why they have been set up that way.

A story has been circulating about a new owner of an Li equipped coach that was of the opinion because he had Li batteries their “10 year life” meant he never had to worry about, much less provide for recharging. Apparently things got a little tense between him and his converter.

All coach owners, especially those who have never owned a Prevost conversion really need to allow a significant amount of time for formal training, plus do a lot of independent reading of owner’s manuals for the coach, conversion, and the devices that have been installed.

[Archived]

Jon, thank you for those thoughts.

I heard back from Marathon. Apparently, Li batteries have a unique charging pattern, and during the Bulk charging phase, reach 85-90% of full charge. During the Absorption phase of the Xantrex charger, charging voltage is maintained at the same level as during the Bulk Phase for 1 hour, and then it switches to a variable current phase. Current is supplied at whatever level is needed to maintain constant voltage. The charger shifts to the Float stage when this current falls below a preset level, or when a selectable time limit has been reached. Because Li batteries are only 15 minutes or so away from full charge when exiting the Bulk phase, the Absorbtion logic would result in the generator running unnecessarilly long. Thus, the logic of generator shutdown being set at reaching the Absorbtion phase,

This logic seems sound, although I wonder about the ramifications of not charging to the full 100% when relying on generator charging. I need to learn more about Li batteries, their needs and limitations.

[Archived]

I sounds like you have to get a new inverter/charger if you go with Li batteries.

[Archived]

Ed,

The Li technology as applies to our coaches with 12 and 24V circuits, the need to deep discharge and then recharge is nothing like the AGM or gel systems we are all used to.

The systems are complex, have a lot of safety features, and have been set up by the converter to do all that is required. It might be such that Marathon set up your system in a fashion which differs from how another converter set up their system so the best and only advice you should heed is that of Marathon in your case.

What you say makes sense and I think you will be pleased with how your Li batteries perform.

[Ron]

When I read the first question in this posting, I started to respond, then in further reading to see if anyone had covered the points I was going to make, noticed that someone opened the “can of worms” about Lithium Iron Phosphate battery charging….I decided to not touch that one based on the book of information that would be required to adequately cover the subject of charging, autostarting, and lithium cell power management.

I will mention this: Everything you understood about lead-acid batteries goes in the trash for the characteristics of Lithium Iron Phosphate battery construction and chemistry.

As for the regular, either flooded or AGM lead-acid type battery, any autostart system that just looks at battery voltage alone is seldom accurate in starting based on actual battery capacity left. Because of internal resistances and electrolyte stratification, an autostart MUST know what the discharge RATE is to be accurate. The voltage that would represent 50% of battery capacity could be 21.8vdc or 23vdc, depending on if the current flow out of the battery is 1 amp to run a clock only, or 200amps running air conditioners, microwave, refrigerator, etc all at the same time. Some autostart systems utilize an ammeter shunt PLUS voltage to calculate amp-hours out of the battery bank, others use different voltage values held for certain periods of time to account for the current coming out of the battery bank.

An autostart that looks at only one voltage to start the generator to recharge is only accurate for ONE discharge rate/load current value.

Anyone having an autostart that only starts on one set voltage are better off to err on the side of “worst-case” to prevent over-discharge of the bank. The drawback to that is they may not seem to get much dry-camping time.

Hope this helps.

[Ron]

Thanks Ben. As usual excellent advice.