electric flight uk - British Electric Flight Association - Jan Bassett's

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Not wanting to write an article on this (I have far too much to do and too little time already), I decided to respond to Peter directly and include the text in the ‘Letters to the Editor’ feature. I appreciate your concerns, but they are unfounded when using a balancing charger or external balancer. There is no need to perform any soldering or change pack connections to achieve balanced charging. Hopefully the following will explain it properly. Firstly, the limiting voltage for a 3S pack should be 12.6V (4.2V/cell) and therefore 13V should never be seen. If a LiPo charger is at 13V when set for 3S there is a serious safety fault with it and it should not be used. I have modified your spreadsheet to show the action of the balancer circuits. Charging at 5A with balancers connected Each balancer is a variable resistance provided by a FET, which dissipates the unwanted current as heat. Typically they start to operate at 4.21V and limit individual cell groups to 4.25V. This is so that they don't interfere with the function of the charger. As the pack nears fully charged, the pack voltage rises to 12.6V and the charger will limit it to that. If one group on a 3S pack is extremely low it could be at 4.1V, with the others at 4.25V. As the voltage on this group increases above 4.1V, the voltages across the other packs will drop, maintaining the 12.6V overall. You will notice on your diagram that cells 4 and 5 are exceeding the 1C charge current of 2.5A. I produced another chart at 4.5A (0.9C), but cell 5 still exceeds the 1C cell rate at a pack rate of 0.8C. Reducing the current further to 4A (0.8C) drops the current to an acceptable level. For this last diagram I had to 16 E.F.-U.K.
Charging at 4.5A with balancers connected increase the resistance of each cell otherwise the voltages were all below 4.2V and the balancer would have been doing nothing. This is one of the reasons why we recommend a maximum rate of 0.75C when charging packs connected in parallel. This reduces current means that the cells should stay in the safe zone even when considerable imbalance is present. In most case the negative of cells 1 & 2 and positive terminals of cells 3 & 4 share a single pin on the balancing connector. Thus a 4-pin balancing connector is all that is required for a 3S pack. Most LiPo balancers have an LED that Charging at 4A with balancers connected E.F.-U.K. 17
Page 1 and 2: ELECTRIC FLIGHT U.K. ISSUE No. 83 W
Page 3 and 4: Electric Flight - U.K. Issue 83 - W
Page 5 and 6: Dear members, Chairman’s Chatter
Page 7 and 8: The following change to the BEFA Co
Page 9 and 10: Letters to the Editor Firstly a let
Page 11 and 12: Next is a series of letters / email
Page 13 and 14: Both these Schulze chargers can cha
Page 15: Now, the parallel pairs will eventu
Page 19 and 20: Method 1 Three FET devices are conn
Page 21 and 22: uy a PC board with assembled FETs,
Page 23 and 24: Cell Balancers Make + Model Cells L
Page 25 and 26: New-2-U A Brief Round-up of New Ite
Page 27 and 28: Another recently introduced item by
Page 29 and 30: Two models from Graupner on this pa
Page 31 and 32: TLC from your TLO By Alan Bedingham
Page 33 and 34: propeller on 3S LiPo and only pull
Page 35 and 36: I was flying the Vermont Belle, try
Page 37 and 38: Readers’ Models Your chance to sh
Page 39 and 40: On Finals, very graceful Gordon's s
Page 41 and 42: E.F.-U.K. 41
Page 43 and 44: Two A4 sheets of instructions cover
Page 45 and 46: The Collet type These exert an enor
Page 47 and 48: Wing & Wheels Model Spectacular is
Page 49 and 50: Last year the meeting was washed ou
Page 51 and 52: Hobby Lobby B-25 Mitchell. 19lbs 2x
Page 53 and 54: Balsacraft fan Edward Brimo brought
Page 55 and 56: Apologies to David ? This 10 year o
Page 57 and 58: Perkins ARTF Tiger Moth by John Tho
Page 59 and 60: Later one of the new 18/15 outrunne
Page 61 and 62: A Smarter Dart by John Stennard I
Page 63 and 64: With the model assembled I soon fou
Page 65 and 66: With some expo and reduced movement
Page 67 and 68:
Intermodellbau 2005 by Dave Chinery
Page 69 and 70:
The colourful Hollein stand had its
Page 71 and 72:
Making an exhibition! This year’s
Page 73 and 74:
22nd Black Lion Indoor Fun Fly. 10a
Page 75 and 76:
FOR SALE / WANTED Member's Sales &
Page 77 and 78:
New to ELECTRIC FLIGHT? START HERE
Page 79:
FANS Morley ‘Jet Elec’ Fan ....
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electric flight uk - British Electric Flight Association - Jan Bassett's

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