We're pleased to introduce the Multi-cell Monitor- up to 7S (MM7) for use with Lithium packs having a connector to access individual cells. MM7 is designed to monitor individual cells during flight and cut the throttle when any cell reaches a preset voltage. MM7 has many features to provide the user with the most versatile protection available:

  • Simple Hookup
    • plug ESC cable into MM7
    • plug MM7 cable into Rx
    • plug MM7 into pack when ready to fly
  • Works with 2S to 7S packs
    • 1.35" x 2.00"
    • 11 grams w/cable
  • Plugs Directly Into Most Connectors
    • ThunderPower
    • PolyQuest
    • DuraLite
    • Hobby Lobby "Twenty"
    • Standard mating connectors available
      • 5-pin for 2S to 4S
      • 8-pin for 2S to 7S
    • MM7 adjusts for different wiring
  • Programmable Cell Type
    • LiPo & eMoli (Milwaukee V28)
    • M1 (DeWalt 36V/A123 Systems)
  • Programmable Cutoff
    • eight user-programmable voltage cutoffs
  • Throttle Compensation
    • Cutoff lowered as function of throttle [current]
  • Filter Algorithm to Avoid Premature Cutoff
  • Cutoff Override
    • high/low/high throttle stick cycle provides 20 seconds of emergency power
    • repeatable at flyer's discretion
  • Four Warning Modes
    • abrupt throttle cutoff
    • off-on-off "blip"
    • gradual power off
    • HELI (very gradual)
  • Optical Isolation
    • isolates battery noise from receiver
    • allows MM7 "chaining" for multiple packs and/or more than 7S
    • works with BEC and opto ESCs

The early LiPo packs allowed no access to individual cells. These packs usually stayed in balance but some did not - with dire consequences. As more manufacturers provided access to individual cells, "balancers" were introduced to the market to monitor and to some extent balance these packs while charging. There is, however, a difference between balanced packs and matched packs. A matched pack is one whose cells all have essentially equal MAH capacity. It is a safe assumption that most LiPo packs are not matched. These packs still can stay balanced, but when discharged, the cell with the lowest capacity will end up with the lowest voltage. This voltage difference can be large with deep discharge. Even though many ESCs can cut off at a prescribed pack voltage, one cell can end up at a significantly lower voltage than the others. Our experience is that this can ruin an expensive cell or cost the loss of a plane. NiCad and NiMH exhibit similar voltage behavior but the harm is usually much less costly.

If the MM7 interests you, please read the instructions. If they seem too complicated, it's probably best not to buy one. Also, note that this circuit is not intended for very small planes and is not ultra-miniaturized. For perspective, the photo below shows MM7 mounted on a Thunderpower 2100 mah pack.

MM7 on TP2100 pack

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