Andrewg
07-22-2004, 06:33 AM
For LSH and offshore we have LiPo technology which can perform as well or better than GP3300's.
I belive this begs the question of whether new rules regarding lithium should mandate cells in series only.
PERFORMANCE
It is possible now to run LSH and offshore classes on a single string of Apogee 4.1ah cells. And the pack weight is 1/2 a set of 3300's. So boat acceleration will be improved and runtime extend toward 6 minutes.
Steve Neu just published figures on smaller Apogees and found they were rated at 10.5 c but could be discharged at 15c and on 10C gave 90% of capacity. 4.1's are rated for 40amps continuous - more than the NAVIGA guys can pull from a pack of 3300's for a 6 mono or 5 minute hydro race, and they are not slow.
In short they are an excellent option for 5+ minute racing. (who wanted 10 minute enduro''s?)
Second several manufacturers already have LiPo cells ranging up to 40AH. however most of the capacities over 4ah are limited to 5C discharge rates. They only have to push those cells to 10 or 12 C which seems to be very doable given that Apogee has done it and a 5ah pack is a 60A constant draw.
At current rates of improvement those cells could be here in another 12 months.
COST
LiPos remain expensive to purchase relative 3300's but everyone is saying that in racing 3300's pack it in after 25 runs. Whereas from the flight boards no one is sure about 500 cycles but seem confident enough to suggest a 100 cycles at full performance is valid - Apogee are conducting long term tests on their cells now.
Using the Apogee4.1's and GP 3300
At $42 a Lipo cell = GP3300's for 100 cycles 4200/100 = 42c per cycle.
At $4.70 for a stock GP3300 - 25 cycles = 3*4.70/25 = 56.4c per cycle
Heres the crunch (if racer reports of 3300's loosing the edge at 25 cycles are correct) for racers.
At 40A a 4.1AH LiPo's give 5.5 mins runtime or in 100 cycles 553 min of runtime
At 40A 3300/s give 4.52 mins runtime in 25 cycles that 112.5 min of runtime
That means LiPos cost 12.5cents/min of runtime. Lipo's cost 7.6cents/min. and Lipos are getting cheaper at a much faster rate than the mature NiMH and Nicad technologies.
OK SO WHY SERIES
Paralleling erodes any cost advantage and paralleling provides a performance gain of 26% max if the second pack is used to the maximum current capability.
The 700BB and offshore classes with more laps and timed races are perfect in terms of current draw for existing LiPo technology. And as the most popular classes possibly the best arena to try it in. Alternatively as you have twice the enrgy density maybe LiPo could be declared a Pro class for a year or two until setups and cell tolerances in marine use are established?
On the other hand a series only (4*$42=$168 for P-Class pack) and a parallel only ie 1S2P class would provide for hi amp setups (at $336 a P-class pack) with current technology.
Even in aircraft where current draws are lower, particualrly in hi performance aircraft it is not unusual for the paralleled cell packs to cost as much as a model itself.
Are LiPo dangerous?
As with many new technologies the problems seem to relate mainly to people not changing their behaviour to suit the new technology. Perhaps they forget how we abandoned burp charging and high delta peak voltages when NiMH became more popular
From the flight boards it is also clear the fragility of these cells relates to impact. In the one verified case of fire in a pack in a car the pack had been damaged and shorted. Other problems have been related to the wrong charger type or charge cycle being used. Anyone here ever shorted Nicad or NiMH cells?
And before any one asks have I used LiPo...... yes and I wrecked them using the wrong charge cycle on a charger! BTW I have made the same error with NiMH too. Luckily i got both while they were just smoking lol Error is just the button press or two I didnt make. I tend not to make those errors now.
I belive this begs the question of whether new rules regarding lithium should mandate cells in series only.
PERFORMANCE
It is possible now to run LSH and offshore classes on a single string of Apogee 4.1ah cells. And the pack weight is 1/2 a set of 3300's. So boat acceleration will be improved and runtime extend toward 6 minutes.
Steve Neu just published figures on smaller Apogees and found they were rated at 10.5 c but could be discharged at 15c and on 10C gave 90% of capacity. 4.1's are rated for 40amps continuous - more than the NAVIGA guys can pull from a pack of 3300's for a 6 mono or 5 minute hydro race, and they are not slow.
In short they are an excellent option for 5+ minute racing. (who wanted 10 minute enduro''s?)
Second several manufacturers already have LiPo cells ranging up to 40AH. however most of the capacities over 4ah are limited to 5C discharge rates. They only have to push those cells to 10 or 12 C which seems to be very doable given that Apogee has done it and a 5ah pack is a 60A constant draw.
At current rates of improvement those cells could be here in another 12 months.
COST
LiPos remain expensive to purchase relative 3300's but everyone is saying that in racing 3300's pack it in after 25 runs. Whereas from the flight boards no one is sure about 500 cycles but seem confident enough to suggest a 100 cycles at full performance is valid - Apogee are conducting long term tests on their cells now.
Using the Apogee4.1's and GP 3300
At $42 a Lipo cell = GP3300's for 100 cycles 4200/100 = 42c per cycle.
At $4.70 for a stock GP3300 - 25 cycles = 3*4.70/25 = 56.4c per cycle
Heres the crunch (if racer reports of 3300's loosing the edge at 25 cycles are correct) for racers.
At 40A a 4.1AH LiPo's give 5.5 mins runtime or in 100 cycles 553 min of runtime
At 40A 3300/s give 4.52 mins runtime in 25 cycles that 112.5 min of runtime
That means LiPos cost 12.5cents/min of runtime. Lipo's cost 7.6cents/min. and Lipos are getting cheaper at a much faster rate than the mature NiMH and Nicad technologies.
OK SO WHY SERIES
Paralleling erodes any cost advantage and paralleling provides a performance gain of 26% max if the second pack is used to the maximum current capability.
The 700BB and offshore classes with more laps and timed races are perfect in terms of current draw for existing LiPo technology. And as the most popular classes possibly the best arena to try it in. Alternatively as you have twice the enrgy density maybe LiPo could be declared a Pro class for a year or two until setups and cell tolerances in marine use are established?
On the other hand a series only (4*$42=$168 for P-Class pack) and a parallel only ie 1S2P class would provide for hi amp setups (at $336 a P-class pack) with current technology.
Even in aircraft where current draws are lower, particualrly in hi performance aircraft it is not unusual for the paralleled cell packs to cost as much as a model itself.
Are LiPo dangerous?
As with many new technologies the problems seem to relate mainly to people not changing their behaviour to suit the new technology. Perhaps they forget how we abandoned burp charging and high delta peak voltages when NiMH became more popular
From the flight boards it is also clear the fragility of these cells relates to impact. In the one verified case of fire in a pack in a car the pack had been damaged and shorted. Other problems have been related to the wrong charger type or charge cycle being used. Anyone here ever shorted Nicad or NiMH cells?
And before any one asks have I used LiPo...... yes and I wrecked them using the wrong charge cycle on a charger! BTW I have made the same error with NiMH too. Luckily i got both while they were just smoking lol Error is just the button press or two I didnt make. I tend not to make those errors now.