Hendrik Ehlers Consult

Hendrik Ehlers Consult



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 power situation.

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 repair (BER).
The four key components of the HEC UPS are:

  1. AC to DC Battery Charger
  2. Battery Bank
  3. DC to AC Inverter
  4. 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 effected.
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.