Posted by John Beardmore on September 17, 2005, 4:27 pm
I don't know. Any future 'surplus' inverter is likely to be smaller,
cheaper and more powerful than its predecessor, and it's easy enough to
rewire to another battery voltage.
But not to a single obvious choice of voltage I fear.
Posted by nospam.clare.nce on September 17, 2005, 5:17 pm
On Sat, 17 Sep 2005 17:27:35 +0100, John Beardmore
Well, with 8 6 volt batteries, the obvious alternatives are 12, 16
(not common at all), 24,32 or 48 volts.36 volts doesn't work out too
well, and 72 and 96 are out of the question. The most common voltages
for low cost inverters and UPS systems are 12 and 24 - with 48 being
used on several large units.
Problem with 48 volt systems is they are generally larger capacity -
and should really have a larger battery pack than you have.
I'd suspect 24 volts is the most likely scenario in your position. (or
wire it as 2 12 volt packs that you can easily switch s/p for 12 or
Posted by John Beardmore on September 17, 2005, 6:57 pm
You mean 18 ?
Don't know that they are, though these and higher voltages tend to be
used with wild inputs from wind turbines etc.
Not a bad strategy.
Posted by nospam.clare.nce on September 18, 2005, 4:34 pm
On Sat, 17 Sep 2005 19:57:25 +0100, John Beardmore
Yes, you caught me- 36 works fine
How will you get either 72 or 96 volts with only 8 X 6 volt batteries
- Maximum voltage POSSIBLE with this battery pack is 48.
Posted by Marc F Hult on September 17, 2005, 4:32 pm
FWIW, here's what I do (use fixed-spacing font to view ASCII diagram):
Home Automation Control System
28vdc NG Genset -->| Switch over------+
AC line --+--60amp charger/converter -+-- 14vdc batteries ---o 28vdc
| | | |
+--80amp charger/converter -+-- 14vdc batteries ---o 14vdc
| | |
+-------+--------+-------------o vdc 'grnd'
A bank of deep-cycle lead batteries is series connected to provide 14vdc
(nominal 12vdc) and 28vdc (nominal 24vdc).
Most loads including home automation computers, UPS, and low-voltage light
dimmers are connected to the 28vdc output.
Home control and other devices that can run off 12vdc (security panel, home
automation controllers, video modulators multiplexors, cameras, audio
equipment) are connected to the 14vdc rail.
Devices that need other voltages are supplied via DC-DC converters (eg 5vdv
for microcontrollers, router, switches and so on) or DC-AC inverters (eg
24VAC for HVAC)
The 'lower' (0-14vdc) bank of batteries is recharged and powered by a
UL-listed 80 amp Inteli-power (one "l") charger/supply
The 'upper bank' (14-28vdc) is recharged and powered by an 60 amp
Together they provide nominal 60 amps at 28vdc and 20 amps 14vdc =~2000 watts.
A Baldor natural gas 28vdc genset has been purchased (not yet installed) to
kick in during power outages that has additional capacity for additional 28vdc
and 120VAC UPS needs. Controller is a Bouchette A120
The choice of 28vdc was driven in large part because this the highest nominal
voltage that meets the requirements of the under-30-volt sections of the
National Electrical code (NEC). A 14vdc system would require conductors
(wires) with twice the cross-sectional area to have the same distribution IR
This provides isolated, UL-listed, NEC-compliant single-conversion power for
the most/all of critically needed devices including lighting. There is no
interruption whatever if line power goes down because the system is connected
directly to batteries at all times. A power outage simply changes the charging
source from line AC to genset.
The system can be expanded to higher voltages or currents with additional
batteries and chargers. and additional charging sources (eg photovoltaic)
DC Grounding and maintaining isolation of subsystems that need to have
separate "grounds" is _very_ important and a whole 'nuther topic.
HTH ... Marc