T105 Specific gravity vs voltmeter.

lesnoy
lesnoy Registered Users Posts: 8 ✭✭
I was doing some testing with my solar system build around Xanterex 6048. As of right now I only have 225 Ah 48 volt battery bank, but considering I only consume around 650W at any given time this should be enough for now.

When I turn grid power off 6048 begins to invert with 18-22Amp going out of the battery bank. Xanterx control panel reads voltage around 49V, which according to Deep Cycle battery FAQ pretty much empty bank. Perhaps when I measure specific gravity in every cell I get anywhere between 1.27 to 1.3 measurements. Just to make sure I went and got another hydrometer and reading are essentially the same.

According to Trojan manual I got from my distributor my specific gravity corresponds to 90% to 100% state of charge. I have Xantrex temperature sensor installed and since I live in S Florida temperature is around 70F.

So my question what do I believe Xantex panel or specific gravity readings and how do I setup voltages as far as charging in bulk, absorb and Low battery cutoff? I tend to believe gravity reading more, since FAQ mentions that voltage reading is just approximate but would like to get a confirmation from more knowledgeable person.

Comments

  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
    Re: T105 Specific gravity vs voltmeter.
    lesnoy wrote: »

    When I turn grid power off 6048 begins to invert with 18-22Amp going out of the battery bank. Xanterx control panel reads voltage around 49V, which according to Deep Cycle battery FAQ pretty much empty bank. Perhaps when I measure specific gravity in every cell I get anywhere between 1.27 to 1.3 measurements. Just to make sure I went and got another hydrometer and reading are essentially the same.

    According to Trojan manual I got from my distributor my specific gravity corresponds to 90% to 100% state of charge. I have Xantrex temperature sensor installed and since I live in S Florida temperature is around 70F.

    I'm confused as to why you would think that 49V would mean a dead battery? Considering the load you've placed on it, roughly a 20amp draw is a big draw on a 225ah battery... in other words that would naturally cause a substantial voltage drop. I'd be more inclined to trust the SG level readings in general, but I think that your voltage reading under this kind of load sounds about right too. One thing worth pointing out however is that this kind of load will drain your battery faster than you think, remember that 225AH is the capacity at a 20hr discharge rate (about 11-12amps) but if you're discharging at a rate that's almost double that your overall capacity will be substantially less.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: T105 Specific gravity vs voltmeter.

    The 49 vdc equates to ~ 12.25 volts for 2 T-105s, or 6.125 for a single T-105. With a ~ 600 watt load that should be no surprise. Remember, battery voltage is only an (semi) accurate) measure of battery condition, and only when the voltage is tested at rest, with no charge or load for a number of hours. Your SG is what will tell you better what SOC you have. That 600 watt draw is ~ 12 amps, and as HB suggests one would expect to see the voltage drop. Turn off the load and measure the voltage.

    Tony

    PS I suggest you re-read these links:

    http://www.batteryfaq.org/

    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: T105 Specific gravity vs voltmeter.

    If you have charging enabled on XW6048, when grid first shows up it will take the battery through an absorb voltage cycle before dropping back to float level.

    This is how the XW establishes the battery full reference for subsequent battery SOC calculations.
  • lesnoy
    lesnoy Registered Users Posts: 8 ✭✭
    Re: T105 Specific gravity vs voltmeter.

    Thank you for answering. Part that I obviously missed is that voltage will drop under heavy load and I was comparing it to a table from FAQ that display no load voltage. My no load voltage looks normal around 51V.

    Now default value of Low Bat Cut off is set to 46V right now on my inverter, is that a good value to keep it at or should I increase it?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: T105 Specific gravity vs voltmeter.

    46 volts is probably a good start... If your inverter cuts out when the battery is low and under heavy loads--you may try 44 volts instead (11.0 volts ref 12 volt battery).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset