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Lithium cell tests
I also dont think these proposols are necessary for A123 M1 cells.
Cell balancing is only necessary if you using a simple (with no individual cell monitoring) charger. If you use a cell monitoring charger (e.g. the standard DeWalt 36V charger), then it will switch off when the first cell peaks - no problem.
However, I envisage that most people will use a simple charger at events - 1) it avoids having to fiddle around connecting all the balance leads and 2) the chargers are cheaper.
IF youre using a simple charger, then you should periodically balance your cells, but A123 cells do not suffer from thermal runaway like LiPos when overcharged, so overcharging is not a safety issue. They presumably will eventually go pop if seriously abused, just like NiCads, but without the fireball of LiPos.
Over-discharging is also not a big issue with A123 cells. Yes, it will damage your cells if you do it, but they will not explode. Again, not a safety issue. I have left a pack discharging on 100 Watt bulbs accidentally. Held completely flat for at least 10 mins. They recovered afterwards and were fine, but some cells in the pack are now showing a reduction in capacity, though not enough to really affect their performance in the robot yet.
I tend to say that you should have a sufficient number of battery packs in your robot so that in a hard fight, you will use no more than around 70% of their charge. This also ensures that the current is kept to sensible levels.
At the moment I think that the only Lithium cells of any type that should be allowed in Heavyweights are the A123 cells. If something better comes along, they can be examined separately.
I dont believe the A123 cells require any special regulations at all. Advice on best practice in caring for them yes, but not regulations.
John
(Message edited by terrorhurtz on November 20, 2007)
I also dont think these proposols are necessary for A123 M1 cells.
Cell balancing is only necessary if you using a simple (with no individual cell monitoring) charger. If you use a cell monitoring charger (e.g. the standard DeWalt 36V charger), then it will switch off when the first cell peaks - no problem.
However, I envisage that most people will use a simple charger at events - 1) it avoids having to fiddle around connecting all the balance leads and 2) the chargers are cheaper.
IF youre using a simple charger, then you should periodically balance your cells, but A123 cells do not suffer from thermal runaway like LiPos when overcharged, so overcharging is not a safety issue. They presumably will eventually go pop if seriously abused, just like NiCads, but without the fireball of LiPos.
Over-discharging is also not a big issue with A123 cells. Yes, it will damage your cells if you do it, but they will not explode. Again, not a safety issue. I have left a pack discharging on 100 Watt bulbs accidentally. Held completely flat for at least 10 mins. They recovered afterwards and were fine, but some cells in the pack are now showing a reduction in capacity, though not enough to really affect their performance in the robot yet.
I tend to say that you should have a sufficient number of battery packs in your robot so that in a hard fight, you will use no more than around 70% of their charge. This also ensures that the current is kept to sensible levels.
At the moment I think that the only Lithium cells of any type that should be allowed in Heavyweights are the A123 cells. If something better comes along, they can be examined separately.
I dont believe the A123 cells require any special regulations at all. Advice on best practice in caring for them yes, but not regulations.
John
(Message edited by terrorhurtz on November 20, 2007)
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