nStor NexStor 4700S Series, Руководство пользователя

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Chapter 1 - Getting Started
Battery Backup Unit
13
Battery Backup Unit
The main board of the SCSI-SATA RAID Controller includes battery control
circuitry for a single cell Lithium Ion battery along with a battery pack mating
connector. The main purpose of battery backup is to maintain the cache memory
during brief power interruptions, but is capable of maintaining the memory
content for several hours, depending on the type and size of the memory.
The battery control circuitry has constant current using a constant voltage (CCCV)
charger. The battery charger provides a maximum 250mA charge current. When
the charge current falls below 16mA, the charger determines that the end of charge
has been reached, generates an end of charge indication and shuts itself off. If the
battery voltage drops below 3.0V, a complete battery discharge is indicated.
The battery control circuitry includes a battery safety circuit. The safety circuit
protects the battery by limiting the over-voltage to 4.3V, the maximum discharge
current to 3A for catastrophic events, and the minimum battery voltage to 2.35V. If
any of these conditions exist, the safety circuit disconnects the battery. These
conditions will only exist if there is a hardware fault present, and would never be
seen under normal operating conditions. In addition, the battery pack utilized
includes a resettable polyfuse that trips when the current exceeds 700mA at room
temperature. This protects the internal circuitry when, for example, a partial short
exists caused by a component failure.
Lithium Ion batteries have no requirement for conditioning, even after partial
discharges. The current battery pack utilizes a Renata ICP883448A-SC cell, with a
nominal capacity of 1150mAh. For a completely discharged battery, the charge time
is approximately 5 hours. Under lab conditions, current draw was measured for
different configurations of memory. The table below shows the results of those
tests, and the expected backup time is indicated for the specified memory
configuration. The table shows the absolute maximum backup time calculated from
the current draw measurements. The “Expected Safe Backup Time” is the absolute
maximum de-rated by 50% to account for different operating temperatures and
capacity reduction due to battery charge/discharge cycles. This is the time that
should be used when developing a system level power backup plan.
BBU Battery Hold-Up Times
Configuration Memory Vendor and
Part Number
Measured
Current Draw
Absolute Maximum
Backup Time
Expected Safe
Backup Time
NexStor 4711S w/512 MB Kingston
KVR266X72C25/512 27.9mA 41.2 hours 20.6 hours
NexStor 4712S w/1 GB Kingston
KVR266X72C25/1 48.3mA 23.8 hours 11.9 hours
4700S.book Page 13 Wednesday, April 6, 2005 2:14 PM