[RE-wrenches] 24V Rolls Charging Parameters?

Tue Apr 30 12:31:32 PDT 2013

Wayne,

Sorry about the delay!... I've been in wonderful sunny Nigeria dodging kidnappers and car bombs...

All Rolls batteries require a bit hotter voltage when charging and especially when you are using multiple parallel strings.

With that system I would suggest if you are using the Outback Temp Compensation.

Inverter:
Bulk/Absorb 29.2 (2.45vpc)
Absorb Time 15 Hours.  (I'll explain why below)
Float 26.4 (2.2vpc)
EQ 31.8 (2.65vpc)

Charge Controllers:
Bulk/Absorb 29.4-29.6.
               Normally I set the controller a bit higher than the inverter just so my charge controller don't back off if my inverter is also charging the battery.
Absorb Time 4.5 Hours (Time=.42 * 3280 (C20 Rate) / 320amps (max current of charge controllers) =4.13... Rounded up to 4.5 Hours.   This can be adjusted depending on monthly SG measurements and or water use.
Float 26.4
EQ 31.8

Flexnet DC

End Amps 2% of Battery bank Cap.  65 amps.
Charge Voltage 29.0
Met Time 1-3 min.

Battery Charge Factor 90%
               This means if you take out 100 amps it's going to put back 110% before it determine the batts are full.

The reason for the longer Absorb time is the Flexnet DC determines full charge by three parameters.

1.      Absorb Time Completion

2.      End Amps/Charged Voltage

3.      Battery Charge Factor.

IF ANY ONE OF THESE (OR Statement in the Logic) PARAMETERS ARE MET, AND THE FNDC SEE'S A 60 SECOND DISCHARGE IT WILL RESET THE SOC METER TO 98,99,100%.   It's better to set the Absorb timer longer and force it to use the End Amps or BCF%..

The absolute worst way to charge a battery is by running a timer, all the inverter manufactures do it because it's a cheap (but somewhat effective) method of charging a battery that works as long as you set the absorb timer correctly.  Plus a sulfated battery will rise in voltage too early potentially causing issues with charging.

The best way is measuring the amount of current and shut off the charger when you hit about 2% (New battery) of the battery bank capacity.

Many people make two mistakes when setting up the flexnet dc...

1.      Leaving the absorb timer set at default... this will cause the flexnet dc to think the batts are full and will reset the soc to 100% early.

2.      Not forcing a manual full charge prior to connecting the Flexnet DC... The Flexnet DC when first powered up will assume a full 100% state on the batteries.  Many battery guys know that when they first install them they are usually only at 60-80% SOC.   This will cause incorrect measurements of SOC from day one.

Hope this helps.

Steve Higgins
Technical Services Manager
M: +1.206.790.5840
F: +1.902.597.8447
Surrette Battery Company
Exclusive manufacturer of
[cid:rolls722a0d]<http://www.rollsbattery.com>

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Wayne Irwin
Sent: Monday, April 29, 2013 2:15 PM
To: re-wrenches at lists.re-wrenches.org
Subject: [RE-wrenches] 24V Rolls Charging Parameters?

Hello Wrenches,

Please provide your opinions on the proper charging voltages (e.g. bulk, float, eq,), and recommended durations.

The bank consists of 12 - Rolls 8CS25P (820AH @ 20hr rate) (4 strings of 3). Design based partly on budget limitations.

FYI. The system is off grid and consists of an 8KW array, 2 - OB VFX 3524 Inv's. and 5 - OB MX80 CC's.

I have general parameters programmed based on AH's but would like to have additional opinions/suggestions to compare and/or see if there is something that I have missed.

I have not yet received any feedback from Rolls tech support ..... James?

Thanks in advance for your help,

Wayne Irwin,
President
License #CVC56695
State Licensed Solar Contractor
Pure Energy Solar International Inc.
Wayne at PureEnergySolar.com<mailto:PureEnergySolar at hotmail.com>
http://PureEnergySolar.com<http://pureenergysolar.net/>
352 377-6527 Office
352 336-3299 Fax

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