Maddog Kevin decided it was time to get a decent multi pack charger with the flexibility to charge multiple 4 and 5 cell receiver packs from 600mAh to 2400mAh capacity. After much investigation he came out with just one choice.

S.M. Services (UK) Ltd was formed in 1988 by a partnership between an electronic production engineer and an electronic design engineer with a combined experience of over sixty years in the electronics industry. The object of the partnership was to design and manufacture electronic units for r/c aircraft. The initial range of ten products was developed using our knowledge of flying model aircraft since the mid 1950s and the range has continued to expand to its current size. "Our overriding objective is to supply technically advanced and reliable products at an affordable price, this is achieved by using advanced components and manufacturing methods and selling direct".

The Multi Charger Mk2 has been designed to charge a wide selection of Ni-Cad and lead acid (Gel) batteries in normal use by model builders. The Ni-Cad section comprises six independent outputs, each programmable by the user to eleven different charging currents (11,25,50,60,70,85,100,120,140,180,200,220 mA ) All Ni-Cad outputs feature automatic voltage selection for 1 to 10 cells per pack, individual 14 hour charge timers and pulsed maintenance charge on completion of the timed charge. The pulse charge allows a battery to be connected to the charger without overcharging but at the same time replacing any capacity lost due to self-discharge. All outputs are short circuit and reverse polarity protected. Connections are via 2.5mm power plugs (supplied). The lead acid section is switched to cater for 2v, 6v and 12v batteries. The charger is supplied with a 220/240v AC power pack. An optional 12v DC converter is also available. Also supplied are a pack of 7 cable headers for making charge leads. Size width 175 mm height 58 mm depth 130 mm.

Having read the supplied manual and ingested the method for changing the charge capacity on the various Ni-Cad outputs I set about the unit with a screwdriver to get inside. One of Kevin's first comments was how much lighter the unit was in comparison to the Mainlink Delta 6 charger he had borrowed from me recently. I pointed out most of the weight for this unit was housed in the external power supply and that is is made of plastic. When combined it was still lighter than the Mainlink unit which has an internal power supply but also has pressed steel case. Once open the intricacy of the charger is apparent with a vast number of electronic components used in the construction of the unit. Most prominent are the large transistor heat sinks ~ one for each output and the rows of matching resistors used to vary and regulate the charge current. Each charge output is regulated by the pin grid shown above. The blue jumper (or shorting link) is moved to set the required charge. This varies from 11mAh to 220 mAh depending on the capacity of the pack to be charged. Each output is timed to deliver a 14 hour charge and when charging is complete it switches to pulse trickle charge to keep the battery pack at peak charge. When this happens the charge licks flashes to indicate the main charge is complete and the pulse charge is working. With the charge rates set accordingly I used a selection of packs with various capacities to test the unit. Two receiver packs of 4 cells 600mAh and 1500mAh, one 7 cell pack of 2000mAh and two 8 cell packs of 1250mAh and 2400mAh. One thing this charger is capable of is restoring a pack which is completely flat, this is something the Mainlink unit will not do. Three of the packs shown in the picture above where completely discharged, the SMS charger returned all the packs to working order.

Since initial testing Kevin has used the charger a number of times for his large model receiver packs and reports he is very happy with the performance of the charger itself and the packs charged with it. A valuable addition to any workshop where multiple Ni-Cad battery packs of 1 to 10 cells require charging together. Very well constructed with good instructions and easy to see charge indicator LED lights. The power supply unit does get quite hot so needs to be situated carefully but no more so than any other type of mains adapter. The charge output selection using the pin and jumper method may be a little tricky at first for anyone not used to it. The table below outlines the charge capacities and typical cell type in that range. Charge Rate Cell Type Cell Capacity 11mA PP3 110mA Hrs 25mA Half AA 240mA Hrs 50mA AA 500mA Hrs 60mA AA High Capacity 600mA Hrs 70mA AA High Capacity 700mA Hrs 85mA AA High Capacity 850mA Hrs 100mA AF 1000mA Hrs 120mA Sub C 1200mA Hrs 140mA Sub C High Capacity 1400mA Hrs 180mA Sub C High Capacity 1800mA Hrs 200mA Sub C High Capacity 2000mA Hrs 220mA C 2200mA Hrs This unit is just one in a large range of chargers and other electronic accessories produced by S.M. Services. Other units include micro-processor controlled combined battery charger /discharger /cycle and charge capacity meter, battery cyclers, battery monitors, servo testers, retract sequencing units, crystal checkers and transmitter frequency scanners. To see the full range visit the S.M. Services web site listed below. S.M. Services (UK) Ltd, 18 Orchard Way Cranfield Beds MK43 0HU Phone 01234 751095 Fax 01234 751095 Email smservicesuk@smservicesuk.co.uk http://smservicesuk.co.uk

Article by John Kent of Bumpy Green Model Aerodrome
May 2004