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howardwheeler's avatar
howardwheeler
Explorer
Aug 10, 2020

Merging a Xantrex SW2024 to a Tesla Lithium battery

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.

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  • BFL13's avatar
    BFL13
    Explorer II
    Aug 11, 2020
    Strange terminology with "bulk voltage". In Bulk, battery voltage rises until it gets near the Absorption voltage setting. (typical 14.6v for a 12 and 29.2v for a 24.) Then amps start to taper while the charger holds the voltage at the Absorption voltage.

    Anyway, this is for a 24v system? So 25v would be like 12.5v for a 12v system. That would not charge a 12v battery, so 25v will not charge a 24v battery.

    The charger thinks it has a 24v battery there (as set?), so keeps on going to something more like 29v. 27 is the lowest it will do in 24v mode as stated in the OP, which makes sense.

    You need an adjustable voltage charger that you can set the voltage and it stays at that no matter what the battery system is. PowerMax has such a thing. Some others might too but don't know.

    EDIT--Oops their 12v only goes up to 16.5v and their 24v starts at 26v.

    https://powermaxconverters.com/product/pm3-12v-series/

    Maybe you can use the 24v job and add a resistor so it does under the 26v. I am not a tech so can't say. If you can do that, maybe you can tame the Xantrex the same way to stop it going above 25.
  • shastagary's avatar
    shastagary
    Explorer
    Aug 11, 2020
    You may need to view the firmware revision number (F/W Rev.) of the Freedom SW when troubleshooting the unit with authorized service personnel.


    there may be a firmware update for the inverter

    is this the manual you have? it describes the settings better than some of the manuals i have seen.
    Freedom SW manual
  • howardwheeler's avatar
    howardwheeler
    Explorer
    Aug 11, 2020
    Yes, we do have a BMS, and it keeps all the cells well balanced, but it can only trigger an alarm or solenoid when voltage overall gets too high. That’s what we now have set up, so that, should I forget and don’t watch the Xantrex as it’s charging, it will shut down all charging if the voltage reaches 25.2. This is a new Xantrex. I’ve owned five Xantrex inverter chargers over the years, but I’ve never had to do a custom setting as I’ve always had FLA batteries. It just gets me that their specs clearly say I can do what would make this whole setup work great, and yet it does not allow you to do what it says it can do. We cannot limit the bulk voltage to 25.2 or lower. And it does not shift to absorption as soon as it reaches the absorption voltage. I’m going to hassle Xantrex some more. In the meantime I was hoping someone had experience on setting up the custom battery profile.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Aug 11, 2020
    Howard,

    WAG that the Tesla present too little resistance to the Xantrex, so it tries to hammer in as many amps as possible, raising the voltage in the process.

    Is there a battery management system on the Tesla pack? If not, adding one may get the results you wish to have.

    The solution may be to replace the Xantrex.

    I really wish I had gone to a 24 or 48 volt battery bank.
  • howardwheeler's avatar
    howardwheeler
    Explorer
    Aug 11, 2020
    My problem is not the transition from absorption to float, but the transition (or lack thereof) between bulk and absorption or any other way to limit the upper end voltage out of the charger while in bulk mode. And my problem is strictly with the Xantrex. Solar works great with a programmable Morningstar MPPT controller and can easily be shut off. It never goes over voltage. But according to the Xantrex manual (which we went by in buying the Xantrex) there should be two ways the voltage output in bulk can be limited. First, the bulk mode itself should be able to be programmed to anything between 3 volts and 32 volts. We tried over and over to set it no higher than 25.2 volts, but it would not take that setting. Second, even if the bulk voltage limit is set too high, it should never go above the absorption setting, which we can set at 25.2 or lower with no problem. We seem to be able to set both absorption and float exactly as the manual indicates. But the manual states that the charger will dump as many amps as possible during bulk UNTIL the voltage rises to the set absorption level, and then it will charge at the set absorption voltage with the amps slowly ramping down as the battery fills. It does not, however, switch to absorption when it reaches the set absorption voltage but allows the voltage to continue to climb. We don't know how far it will climb, but it came dangerously close to 25.5 before we caught it. A little more and my Tesla battery would have been toast. Any help would be greatly appreciated.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Aug 11, 2020
    I've owned a Trace 4024 since 1988

    When starting out charging the unit like any other may charge to it"s limit of 60 amps. It does not have the canines at 60 amps to reach it's set voltage. That is sales speak as BULK. When the charger reaches voltage limit that is saled speak as absorbsion.

    When more chargers are added boosting amps to the point where voltage limit is instantly reached I have given it a name. Saturated Charging
    In my case saturated charging occurs at 590+ amps.
  • shastagary's avatar
    shastagary
    Explorer
    Aug 11, 2020
    there are a lot of settings with the inverter the manual says
    NOTE:The battery voltage can increase above the float voltage when using an external charging device such as PV arrays, wind turbines, and micro-hydro generators. Be sure to include appropriate charge management equipment with all external DC sources

    are you shutting down the solar charging when using the xantrex to do the charging.

    these settings will change the charging also
    The Freedom SW transitions to the float stage if either one of the following two conditions are met:1.The charge current allowed by the batteries falls below the exit current threshold, which is equal to 2% of the programmed battery capacity (for a 500 amp-hour battery bank, this would be 10 amps), for three minutes.2.The Freedom SW has been in absorption for the programmed maximum absorption time limit. The default is 3 hours, but the time limit is programmable from 1 minute to 8 hours

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