Merging a Xantrex SW2024 to a Tesla Lithium battery

[howardwheeler]

I have a Xantrex SW2024 that states in its manual that under a custom battery setting that the bulk charge can be set anywhere from 3v to 32v. It also states that when the voltage rises to the absorption voltage that it will switch to absorption from bulk. Well, unless we are really missing something, it appears neither is the case. Multiple calls to Xantrex have been fruitless. Problem? I have installed a 24 v Tesla in the place of four size 31 FLA batteries. Everything is working great on my solar charging system, and we were able to program it perfectly to the Tesla parameters. Not so the Xantrex in spite of its clear statements in its manuals. We cannot get it to be set below a bulk rate of 27.2 v which will fry the Tesla. We caught it before catastrophe. But I need to occasionally be able to charge from shore power via generator or plug in. But I'd have to sit there watching the charger to make sure the voltage does not rise above 25.2 We have an automatic shutoff solenoid attached to our BMS in case we overlook it sometime, but that shuts everything off. So two questions: Does anyone know how to set the bulk limit to 25.2, or second, does anyone know why it does not shift to absorption when the absorption voltage threshold is reached, which would effectively limit bulk voltage to safe levels even if we couldn't actually set the upper limit to bulk voltage? Does anyone understand Xantrex inverter chargers well enough to give us some clue as to why you cannot harness the bulk voltage to a 25.2 volt limit? The battery works great by the way, and I've shaved 479 lbs of my pin weight by removal of the FLA batteries and generator. I'm happy with the battery but perplexed by Xantrex.

[shastagary]

wonderful you got it all worked out i find it very satisfying when i don't give up trying to figure out a problem and i learn and get it resolved in the process. sometimes i have to walk away and come back with a fresh mind it may take some time but in the end it's worth it. and you actually made your system better with the tablet access congratulations great work.

[howardwheeler]

And thanks to everyone for the great advice. I have to say that this setup does seem just right for my needs. It had to be dialed in just right and had a learning curve, but now that it’s done, it seems looking back that it would be a simple changeover from FLA. There were a few perplexities encountered (like the Xantrex needing reprogramming), but as insurmountable as they all initially seemed, all were really in the end simple fixes. When you don’t know what you’re doing, every obstacle can seem enormous. Again thanks for the help.

[BFL13]

Thanks for the update. Got to admire getting it all working as reward for sticking to it like that. "Where there is a will, there is a way."

[MrWizard]

That's Good News
Congratulation on job will done

[howardwheeler]

Update and report: First, we finally found someone—Wendy—at Xantrex who took an interest in my problem. It turns out there was an available firmware update that would allow the programming of the bulk voltage down to acceptable levels. Problem? I had to send the unit—already installed—back to Xantrex! No good. But Wendy comes through and says that the Xantrex Combox allows user programming and firmware updates. So I found a good deal at Hodges Marine on a ComBox and got everything hooked up. I’m actually glad I got this because the Combox allows for a wireless router (my son had an unused Apple Airport Express) to be hooked up and I can now with a $39 Android tablet from Walmart monitor all Xantrex devices and reset them from anywhere in the fifth wheel. No more bending over. So we reset everything and all works great now. So let’s go on a trip. We went into the Colorado high country with one of my sons and his family and were six days completely off grid. A good test. We had good Colorado sun most of the time and my three solar panels that total 945 watts had no trouble filling my battery to 24.8 volts. Having the residential fridge and furnace running (every night was near freezing) we would every day drop down to around 21.6 volts. So the average cycle was 24.8 down to 21.6 volts. With anything close to this, which is keeping things between 90 and 40% of my Tesla’s capacity, the battery will last longer than myself or the trailer. Also because there’s no need for ventilating the battery I can have it in my heated basement so I don’t have to worry about the Tesla going to 32 degrees and charging, which would ruin the battery. Another very nice attribute of the Tesla is how fast it charges. Just to try it, I hooked up my Honda 2000 (rejetted for high altitude) and it rapidly charged the battery at a rate of around 40 amps at 24 volts. No more dropping off of amps as it nears full. I can reprogram the battery to be used from 25.2 volts down to 18 volts, giving me much more useable power but to cycle it that far will wear it out much faster. I might only have 700 cycles or so charging at that rate as opposed to probably ten times that doing it the way I am. Anyway, I’m extremely pleased. I’ve shaved 479 lbs off my pin weight, which, for the first time ever, actually puts my Alpenlite below the official rear axle rating of my truck. I took out all four heavy FLA batteries and the Onan generator. So I’m lighter. I can seemingly run forever in the Colorado high country and have a virtually maintenance free battery.

[howardwheeler]

That’s what I’ll do because at least I know that would work. Does anyone know how to get hold of a Xantrex schematic?

[MrWizard]

I understand what you are saying
I would err on the side of caution
And install the second contactor
I don't know what the Xantrex would do with line power at the out put terminals
Less expensive than letting all the magic smoke out

[howardwheeler]

Okay, we are installing a normally closed contactor on the AC wire coming into the Xantrex inverter charger, following the very good idea from MrWizard. My question arises because the Xantrex usually passes the AC right through the Xantrex when no inverter is needed. If the contactor we are installing opens up because of high temp sensed by the BMS (which controls that contactor) then the Xantrex will go into inverter mode and the output wire is no longer simply shore power being passed through but is now battery power being inverted to 120v ac. This isn’t terrible because that’s what it is for. But our contactor is a DPDT, and I’d like it to open the power line to the Xantrex but close a circuit to the output wire from the Xantrex, which would normally be the AC being bypassed through the Xantrex anyway, but, with the contactor switched, the ac would be bypassing the Xantrex completely. In effect all that is powered by the 30 amp bypass current through the Xantrex would now just completely circumvent the Xantrex and continue to power everything vis shore power rather than the inverter. I know (at least I think I know) that I can safely do this with two DPDT contractors, with the second in line on the bypass wire coming out of the Xantrex, being NC letting the unit operate exactly as it does when all is well, but, when energized by the first solenoid because of overvoltage, it would open the line BACK to the Xantrex and close the ac current coming from the first contactor, thereby not only bypassing the Xantrex but also preventing any voltage from “back flowing” into the Xantrex through the output side. Does anyone know if I should be worried about power going back into the Xantrex via the output wire? If I don’t need to worry about that then the single DPDT will do the trick. Can anyone possibly follow what I’m attempting to explain? I’m not at all worried about all of you and your capacity to comprehend, but I’m totally convinced of my inability to explain with clarity what I’m doing. If anyone does understand please comment. Thanks.

[BFL13]

It's hard to be humble when you are a genius in every way! 🙂

Meanwhile the big Chinooks are starting up-river (Big Qualicum) already, but it is mostly still the little Pinks. This indicates our ideal off-grid summer is nearing an end. Only way to deal with that is eat more blackberries (now peaking), and BBQ more steaks!

Be there or be square! 🙂

[howardwheeler]

I have not done that. I have merely assumed it was reading battery voltage.

[MrWizard]

There is still the problem of

Will the Xantrex output a charge current
When it can't do voltage read of the batteries

This might be the basis of the "current" situation
Can the Xantrex actually read the battery voltage or is reading the BMS
Have you tested this, have you connected (2) 12v in series and connected them to the Xantrex to see if it obeys the 25.?v absorb command

[MrWizard]

Barry
You might be on to something
Another dpdt contactor with 110v coil

N.O. contacts Xantrex terminals are connected at the solar controller input

N.C. contacts Xantrex terminals are connected to battery

When on generator or Shore power the contacts close and the Xantrex is connected to solar controller input, solar controller outputs correct charging profile

When no 110vac is available (normal situation) ,
The Xantrex is connected to the battery and operating in inverter mode

This contactor activation coil wires to the 110v terminals coming from the safety cutout over voltage contactor powering the Xantrex

So no 110v is default inverter mode connection
110v available is charge controller mode connection

It's a work around kludge , but it should do the job
I would set the voltage to something less than nominal solar input
In charge mode the Xantrex will be paralleled to solar panels, they are solid state devices a higher voltage can produce a current flow thru the solar panels
Consider a second duplicate solar controller to use with the Xantrex connected to the battery, the Xantrex will be it's solar power,
It's only duty will be to control the Xantrex input when 110v is available

[howardwheeler]

This is interesting. Let me talk over this suggestion and try to work out some possibilities. The Morningstar MPPT controller works exactly as it says it should. If only the Xantrex would do likewise..... Thanks.

[BFL13]

You do have the MPPT controller that works now doing 25v, so you just need to get the Xantrex to charge at say 28v into the MPPT and leave the MPPT set at 25.

It would involve some kind of switching so you are on inverter but not charging from the inverter/charger when on solar (charger off/ disabled/whatever they call it).

You can have the input to the controller be either panel or inverter/charger (one of those 1-2- except not both! switches? or just use parrot clamps to one or the other) and the controller is already on the- battery so that stays there so no issue like Mr Wiz mentioned with disconnected battery from controller.

Be a wiring job to where the controller is, or move the controller too, but no new equipment. Just new procedure.