Topic: Battery/switch Redundacy

NiMh and NiCd should not be charged in parallel.  Lithium batteries can be charged in parallel.

I assume when you say Lithium you're not meanining LiPo just for clarification.

J

If you do go with diodes, for the few pence extra you could make the diode in each battery feed a paralleled pair, if one fails short its no problem as its feed is then .3v above the feed from the other battery, if one of the pair fails open the other is still there in parallel. I'd use power schottkys for the lower forward drop and lower power dissipation and I'd rate them generously at say 20A each, say four-off something like these: http://uk.rs-online.com/web/p/rectifier/6247570/

Cheers
Phil

I assume when you say Lithium you're not meanining LiPo just for clarification.

J

LiPo or LiFe may be charged in parallel, with care.  Although different capacities can be parallel charged, care is required to ensure a lower capacity pack cannot be charged too fast..  i.e. 400mAhr 2S and 2,000mAhr 2S pack could be charged in parallel, but care is needed to ensure the 400mAhr pack maximum charge current is not exceeded.  Generally the pack balance the charge between the packs automatically, but several factors could upset that.  In practice I would recommend only charging packs of approximately the same capacity, age and state of charge together to be safe, and then only charging at the maximum rate of the smaller pack.  If anyone if unsure of what they are doing with any batteries, the safe answer is don't do it!  LiPo can be damaged by overcharge or over discharge with a fire resulting, particularly when over charging.  Although fires are rare with just two cell packs, LiPo must be treated with great respect.  Fires seem most common when 3S packs are charged at the rate a 4S pack might expect, as then the chargers auto voltage sensing cannot discriminate between a discharged 4 cell pack and a nearly full 3 cell pack.   LiFe are reputedly much safer.

Hmmmm, I don't see any advantage in charging LiPo's in parallel, I can see serious disadvatages and potential danger. My advice would be don't do it.

J

Hmmmm, I don't see any advantage in charging LiPo's in parallel, I can see serious disadvatages and potential danger. My advice would be don't do it.

J

I agree.  In most cases it's simple - don't do it.  However, some packs are designed to be charged that way, i.e. 2S2P packs.  Again, if anyone does not have a full understanding of the dangers DO NOT DO IT.    There is one case when I do it more frequently, that is when charging two packs in one model, both identical LiFe, and both have been used in parallel with two switches as per the main discussion on this thread.  In that instance the model is hanging in the garage roof, and a Y lead is easy to rig, and there is no rush to charge, but I am keen to ensure both packs are balanced.

I was planning on charging the two LiFe packs in sieries in the plane using the deans connectors, and on of these



and one of these



This way I can quickly charge up the batteries at the field. Once home I will charge the separately so that I can monitor their condition. The other option of charging them up separately would tie up both of my chargers at the field .