battery bank inverters lxi

[GregOConnor]

Working thru issues on my lxi Inverter Charger battery. Bank. I can't coordinate both inverters to charge at the same time but shutting one or the other down will allow decent charging. I am assuming some ree or dee engineering took place by rv service techs in the past. My question is how are the house batteries set up. The inverters are not stacked to power the same items but are setup to power different legs of the 120 distribution. I hope to put things back to blue bird specs and then consider changes. I removed both inverters and controllers and dropped them off at a inverter repair shop for bench testing and review. $80 per unit inverter repair service chino ca 909-999-5900 . I used him in the past but he won't work on units while in the bus. Please advise or point me to a document with the battery cabling and charge-use theory.

[davidbrady]

That's right Greg, the inverters aren't paralleled in the Xantrex sense which would result in a 240V system. Instead, Wanderlodge followed the industry standard, and slightly screwed up, installation practice of wiring two independent inverters to all the batteries in the house battery bank. This is good for the case of inverting because each inverter has access to the battery bank's full power; it's bad for the case of charging because one charger will dominate driving the other charger into float mode which means a longer charging time then if the bank were split with each charger charging one half of the bank and each charger operating independently. My Vantare uses the same wiring method with the added disadvantage that my SW4024 inverters are hybrid, and if the voltage exceeds a threshold an inverter may attempt to lower the voltage by switching from charging to inverting and sending power back into the grid. It makes for some interesting outcomes, but mostly it's a corner case with no real serious side-effects except extended charging times. It'd be nice if the chargers would talk to each other and coordinate and synchronize their 3 stage charging switchovers, which I believe is what they do if they're wired in the 240V Xantrex parallel configuration.

There should be an external shunt mounted in the ground path next to your inverters. This is used for the current fuel gauge. BB missed this in some buses. Each inverter has an internal shunt for measuring current into and out of that inverter, but with two inverters wired the way BB did an external current measuring shunt in the ground path is required to get an accurate fuel gauge measurement.

There's a diagram on WaGu that shows the battery wiring config with the engine alternator, voltage and current shunts, and inverter/chargers. It's not that much different than your WB. I'll see if I can find it.

[K Sarich]

Hmmm... I am running (2)-Magnum MS2800 wired into a single battery bank and they will both start charging and continue charging until the programmed end voltage is approached at which time (1)-inverter/charger will spool down followed by the second.

Although we are running Lithium now the charge scenario was the same with the AGM's. When boondocking we'd start the generator, 120v would reach the Magnum's, The first unit would begin charging followed a few seconds later by the second unit. Both units charged at the same amperage until the battery was approaching full and then one of the units would start to lower its amperage. i can't remember if it would drop all the way down before the other unit followed or if they both lowered the amperage with one unit providing more amperage as float was approached.

I believe the wiring is factory and there is no sense wiring between the Magnums that would allow them to communicate. I recently called Magnum with a question as to why one unit would charge at full amperage and the second unit would fluctuate between 100% of and 80% of programmed charging amps. They explained this was normal as each unit, because of slight differences in wiring, would read slightly different voltages. One unit would therefore be dominant and the other would be secondary.

Having both units charging is a huge plus when needing to charge off the generator as it cuts run time way down.

Does Xantrex offer any type of upgrade that would allow dual charging?

[davidbrady]

Hi Kevin,

Great to hear from you. Tell us more about your Li-Ion's. What if any battery management do you use? Do you keep them in a temperature controlled basement bay? I've been reading some real world longevity studies that show temperatures swings can impact life time and number of cycles. One of the big draws of the more expensive Li-Ion's is drastically increased number of cycles but in the real world I'm not so sure.

I believe our dual Trace/Xantrex inverter/chargers have the same behavior that you describe with your Magnum's. If the batteries are deeply discharged then both chargers jump into the constant current bulk phase, as the voltage nears the constant voltage threshold one usually prematurely transitions to the absorption phase. This prolongs the bulk phase. The amount of time that each spends in the absorption phase also varies. At some point the dominant charger becomes apparent and the other prematurely moves to float stage. This is my gripe; they don't move in lock-step thru each stage, but they both definitely charge. With the hybrid nature of mine it can mean that one actually starts to lower the voltage by going into inverting and syncing with the grid!

Exasperating this phenomenon is the lack of a high impedance voltage sense wire. The Xantrex/Trace measures the voltage level of the battery bank using the same 4/0 cable that it uses for charging. The voltage drop, capacitance, inductance, ripple voltage, and impedance of this cable makes it impossible to accurately gauge the true voltage at the bank. If the chargers are to behave in sync then they both need a good independent, clean, high impedance sense line. Does the Magnum have such a line?

[K Sarich]

Hi David,

Good to be here.

My Magnums use the same method as theTrace/Xantrex to measure voltage. No sense line is utilized. I recently installed Magnum's Battery Management Kit, which uses a shunt to measure voltage and amps in/out as well as battery SOC. Although the BMK does provide more precise readings than the Magnum's remote control displays show that information is not used by the Inverter/chargers.

Our Magnums do behave a bit differently in that bulk and absorb is matched to within 2 or 3 amps while charging at 100 amps per unit and one unit does not wind down until the end of charge. With the Lithiums this means that they are working together for all but the last 10-15 minutes of the charge "cycle". Additionally the battery does not need to be deeply discharged for the units to work together from the start.

That's just wild to think your system charges and inverts at the same time. I understand the why, but is this normal for dual hybrids?

As to the Lithiums: We are running a 1250amp battery comprised of (4)-1250amp cells(3.2v ea.) in series. Each cell is monitored for under/over charge and is passively balanced thru the included Battery Management System. The battery is installed in the exposed factory battery bay behind the tag axle.

After 4 1/2 months of boon docking, including a continuous 2 1/2 months at Quartzsite, charging by generator and/or solar only we have come to love this technology. Batteries are always discussed in quantitative terms, but it is the qualitative improvements to our rving experience that are the most important to us.

As to longevity: I'll check the battery out after a year and see where we stand, but so far I have found no reason to doubt the manufacturers claims.

[davidbrady]

Kevin,

Who's Li-Ion batteries are you using? What does passive balancing mean? Do you run a shunt at each cell to bypass excess charging current and to clamp the cell at a specific charging voltage. That's a good setup for a lot of applications, but in an RV I'm thinking that using the batteries as in the middle 80% of their capacity (in all practical sense) might provide us with the best performance/longevity tradeoff. What are your thoughts?

I probably shouldn't have said "deeply discharged". In fact, anytime my coach is disconnected from an AC source upon reconnection the inverters both go into bulk charging. The issue of sending power back into the grid is disabled on my inverters. What happens is when the chargers are near the bulk setpoint voltage (28.8) one will likely continue on into absorption while the other transitions to Float. This isn't really an issue because one charger is more than capable of supplying the necessary absorption current, so no time lost in overall charging. The inverter that transitioned to float will actually try to lower the battery voltage to the float setting (26.6V) by inverting. The AC power it produces is used by AC loads in the coach up to the maximum 33A rating of the inverter. Only when the 33A draw is exceeded does the inverter augment with shore power. This all takes place while the other inverter finishes up the absorption phase. So, in essence the inverters are "fighting" each other during absorption. Welcome to the world of hybrid inverters! LOL

I believe the above can be cured by using the Xantrex Parallel Stacking cable, but then we have a 240VAC house system and I'm told that the stacking cable has its own set of issues like shutting off both inverters for problems only seen by one inverter, so few converters use this approach.

[K Sarich]

Greg, sorry if we've hijacked your thread.
Please do give us an update when you get your Inverters back.

David,
I bought a the assembled package from Balqon.com. Not sure of the definition of passive balancing as I am just repeating what I read. After 8 months the cells are in balance, so whatever it is it is working fine.

As for longevity: Yes, I believe we will benefit from not taking the battery to either end, in fact for storage they suggest storing at middle charge. That, to me is one of the ultimate beauties of these things. You do not need to charge to the top. This translates in the real world to - seeing your battery needs a charge, realizing your heading to dinner in an hour, so you crank up the generator, pump in a hundred amps or whatever, turn the generator off and head to dinner. The next day or the next month you can put some more juice in and you have done no harm to the battery.

It takes a bit of adjusting the brain to realize many of the lead acid conventions no longer apply. A typical pre-solar install day for us at Q would be to go to sleep with the battery at 13.2v or 13.3v and wake up at 13.0v or 13.1v then sometime during the day charge for a couple of hours. On occasion we would charge to the top( 13.38v) or so and occasionally if we didn't want to run the generator I'd let them drop to 12.8v. Prior to the Lithiums we were charging a couple of hours TWICE a day.

I spent a lot of time trying to get the charging voltages just right, it turned out in hindsight that I was both mis-understanding and receiving conflicting info from Balqon and Magnum. In the end the best advice I received was from Samra at Balqon who said, "Just go play with the battery, if the charge voltage becomes too high the battery will shut down". I did, it did. I then realized we should stop babying these things and just enjoy using them.

[GregOConnor]

I got the inverters back today. One motherboard needed work. I am fortunate that this guy can repair the boards and not just r and r them. the repair tech seems to think the genset put out greater than 60 htz at some point. He doesn't think it was shore power related because the damage is typical of off grid systems. 400.00 for the repair and 80.00 for service and checkup to the other unit and the two controllers. 909-999-5900. I may drop by a generator dealer and have them run the genset or research on the best way to test output. I was curious as to why the PO put in a complete new genset 5 years ago with such low use