The HEC UPS was developed to meet an
urgent need of MgM Demining NGO in Mozambique.
The MgM Mozambique (MgM Moz) field operations
were having great difficulties in maintaining
reliable 220 VAC power supply for the
camp which resulted in much higher expenses
in detector batteries as they could not
use rechargeable batteries due to the
The UPS is a package which receives mains
power when available and uses this to
charge a bank of high capacity batteries
(24 VDC in this case) which store this
power for use when the mains (generator
in this case) power is not available.
Another section of the UPS converts this
stored battery power back into a very
clean, mains type power output (220 VAC).
This power output is always present as
long as there is a stored charge in the
battery bank. This type of power is called
Inverter Power and is available 24/7 (pending
battery state) for use on critical appliances
connected by the user. In the case of
MgM Moz, this is the essential detector
battery rechargers, satellite telephone,
radio communications equipment, and the
main office computer.
The HEC UPS is an "On-Line"
type which means that the attached appliances
only "see" the clean and stable
power output of the Inverter section.
This is essential for sensitive and inexpensive
consumer equipment which does not tolerate
low voltage, brown outs, black outs, and
excessive noise. These will usually destroy
sensitive appliances beyond effective
The four key components of the HEC UPS
- AC to DC Battery Charger
- Battery Bank
- DC to AC Inverter
- Robust Simplicity
The first three items are Commercial
Off The Shelf (COTS) items and the fourth
item is a little bit harder to come by.
The electronic components are Industrial/Marine
products of very high reputation and reliability
(www.victronenergie.nl). The batteries
are locally produced, deep cycle, tubular
batteries as used in larger electric forklifts,
electric mine trains, and larger UPS applications
(www.willard.co.za). These are normally
2 VDC cells which must be combined to
achieve the required battery bank voltage.
These batteries are usually a very high
capacity and require very low maintenance
as they are designed for a 15 to 20 year
service life. Robust Simplicity is arguably,
the most important component of a field
deployed UPS. There are a few robust products
on the market and a few simple products,
but very few Robust AND Simple products.
The end product must be able to be handled
in the field with improvised devices (Robust)
and have as few interconnects and external
feature circuits as possible (Simple)
to minimize points of failure and facilitate
long distance, field repairs where the
support person has little control of repairs
The initial high cost of a large UPS of
this type is recovered very quickly in
field conditions by the highly diminished
cost of appliance repair and replacement
and in the MgM example, by the cost savings
of using rechargeable batteries rather
than disposable batteries and their associated
logistics costs. The HEC UPS installed
at MgM Moz will pay for itself in 9 months
on disposable battery costs alone.