Friday, February 24, 2012

More Settings Tinkering

No pictures or video today... Shock, horror!

A bit more tinkering with charging settings, increasing the float Voltage again to 27.00V (3.375Vpc) seems to null out discharging with the long sunny afternoons and water heater running.

I also changed the timers a bit.  If there was not much load on the battery for a few days, even charging for 10 minutes per day to the upper Voltage limit might start to cumulatively over charge the cells.  So I'm now making use of the absorption extension timer.

If the pack Voltage never drops below 26.60V (3.325Vpc) during the night, the next days absorption timer is set for only 1 minute top charge.  This effectively eliminates the possibility of cumulative over charging.  If we went away for a long time, I'd shut the whole system down.

If "normal" amounts of charge are taken from the pack, the Voltage drops to under 26.60V and the next days absorption timer assumes an extended absorption timer setting of 20 minutes.

I had noticed that 10 minutes wasn't resulting in a very large fall-off in input power to the battery during the constant Voltage phase, so extending the time seemed appropriate (with the new safeguard of a much shorter default timer).

The small SunSaver 15 Amp charger has now had its absorption timer defaulted to 1 minute for any condition.

With the clear blue days we've been having, I've seen total charge rates as high as 72 Amps, and at the top of charge, the battery pack doesn't need the assistance of the small charger for long before the Tristar charger can hold the constant Voltage.

3 comments:

  1. Wow, Thanks for your information. I am doing quite the same, and I was wondering the 'equalize' and 'float' settings for the solar charger with about 180AH 24V LiFePO4. The system I cobbled together is actually working quite nicely, as the solar charger (AIMS) has a relay setting for low battery voltage. I have relays that switch from Utility to Solar (unsynced) that seems to operate well.

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  2. Dito... My thanks to you as well! I enjoy studying your approach to designing a lifepo4 offgrid system very much and actually setup my own system basically following your ideas. Your doing some great pioneer work!

    Apart from cost related thoughts, how do you estimate the additional work and monitoring/balancing complexity for going with 48V instead of 12V/24V?

    My best regards from sunny Spain
    Oliver

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    1. That's exactly what I'm working on now - developing the next generation system into a commercial product. We'll have a home energy management system (not just a BMS) that can scale from 4 to 372 cells in series. In practice, we'll do three standard pack schemes, based on 4, 8 or 16 cells, as these fit neatly into the use of existing 12, 24 and 48V loads (mainly inverters).

      The system I've developed has capacity ranges from 2kWh to 40kWh usable energy (based on 80% max discharge).

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