Float charge

tonygcan

Hi guys, a quick question. When the xantrex mppt cc goes into float mode does it keep the batteries fully charged even when there is load on the batteries?

From experience, I get more power from the batteries when the mppt cc goes into float late in the afternoon rather than early afternoon. By this I mean that my voltage reading at midnight is higher when the cc went into float at 4 om rather than when it went into float at 1 pm which will mean a lower battery voltage reading at midnight.

Thanks in advance.

BB.

Re: Float charge

It should... Measure the battery bus voltage. If it remains >~13.0 volts even under load--then the batteries are not getting discharged.

Note there is a range of 90%-100% when batteries are "Full"... Getting that last 10% state of charge require more energy (less efficient charging as you are generally gassing the batteries at that point) and harder on the batteries too.

If you can get the battery bank >90% SOC and don't discharge much below the 75% to 50% SOC range regularly--That should be fine.

If you are deeply cycling the batteries on a regular basis (below 50% SOC), then you probably need more batteries and/or less loads (or load shift more loads to day time).

-Bill

NorthGuy

Re: Float charge

When floating, SCC keeps batteries at a fixed voltage. If you add more loads it'll increase production to support loads. Of course, if it's too much loads (or too little sun), batteries will start discharging and the voltage will drop.

The variation could be because:

- loads are exceeding production thus dragging the voltage down

or

- temperature of the batteries is higher, which causes temperature adjusted float voltage to be lower.

zoneblue

Re: Float charge

Like the others said, put differently, theres a difference between being "in float" mode, and holding float.

The midnite will keep its green float light on in both states. If its holding float, the battery voltage will be at float voltage, any less means the sun isnt keeping up with loads.

The controller will only go back to bulk (rebulk) under fairly radical but programmable situations.

Vic

Re: Float charge

Hi Tonygcan,

Well, recall that you are using Surrette Flooded batteries, perhaps S-600 L-16s.

First, if there is any difference in loads on the battery bank, at or before Midnight this will affect the voltage readings. And, as noted before, battery temperature will make a difference.

Also, the voltage SETTING for Float will determine weather the batteries are being maintained at full charge during Float. Your XW SCC needs to have specific voltage values set for Absorption (Bulk) and Float and EQ voltages. Do not use any of the default values.

Be certain that you have had use the Surrette Battery Manual:
https://s3.amazonaws.com/cdn.freshdesk.com/data/helpdesk/attachments/production/1073177/original/Rolls_Battery_Manual.pdf?AWSAccessKeyId=AKIAJWGOEYKNTQ75K5TQ&Expires=1372448723&Signature=GDfKDtCFE6aqGt4j8GIUK8OsFcg%3D

That link may not work, if it does not, and you need the manual, go here, and choose the Flooder & AGM Manual:
http://support.rollsbattery.com/support/solutions/articles/654-battery-user-manual-flooded-agm

AND, if you could possibly add a Signature line, reminding us about the PV Array, batteries and voltage config, inverter/chargers, gensets, etc, it will improve the quality of the answers that you receive, and the time it takes for others to get to the meat of your system. Thanks! Vic