Do Lithium batteries REALLY make sense?
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RE: Do Lithium batteries REALLY make sense?
..make all the servos and RXs 7.4V-rated...
Now, the weak point seems to be in those connectors. Gotts to upgrade.
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RE: Do Lithium batteries REALLY make sense?
About internal resistance... every cell is different. Some of GP's newer ultra high capacity Sub-C and AA cells have internal resistance so low they can withstand very high charging current without overheating. This comes from a very good friend of mine, who is a semi-retired Gold Peak (GP) engineering manager. They are able to develop 15min charger for the 2400+mAh AA cells - that's 10+A charge current - while the cells remain cool to the touch. Sanyo may have been the golden standard in years past, but GP (and others) are outdoing them these days.
As for 7.4V-rating and higher current handling... that is my hope too, but I am not holding my breath waiting for it. the RC electronics industry by nature is very slow to respond to changing market dynamics. All the legacy products out there dictate that manufacturers conform to old convention, or risk alienating the majority of the customer base. The RC radio connector and wiring form factors were developed some 30~40 yrs ago and will likely stay the same for some time to come. I hope I'm wrong about this, and the majors will get together to agree on new standards and specs.
LiPo chemistry holds enormous potential (pun intended), it's choking it down to conform to antiquated specs that's the problem. If the day comes that I can plug 2-cell LiPos directly to my RX, I will retire all my NiMH in an instance.
As for 7.4V-rating and higher current handling... that is my hope too, but I am not holding my breath waiting for it. the RC electronics industry by nature is very slow to respond to changing market dynamics. All the legacy products out there dictate that manufacturers conform to old convention, or risk alienating the majority of the customer base. The RC radio connector and wiring form factors were developed some 30~40 yrs ago and will likely stay the same for some time to come. I hope I'm wrong about this, and the majors will get together to agree on new standards and specs.
LiPo chemistry holds enormous potential (pun intended), it's choking it down to conform to antiquated specs that's the problem. If the day comes that I can plug 2-cell LiPos directly to my RX, I will retire all my NiMH in an instance.
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RE: Do Lithium batteries REALLY make sense?
ORIGINAL: ptgarcia
I have a questions for the experts out there. I hear talk about receiver batteries of whatever chemistry (I'm not talking about LiPo's powering electric powered planes) being able to supply 15C to 20C (20 amps +) on discharge. I also hear talk about the connectors to our receivers only being good for 3 amps. So does this mean unless you have 7 connections to the receiver or a special power distribution system of some sort you can't take advantage of that 15C current supply?
I have a questions for the experts out there. I hear talk about receiver batteries of whatever chemistry (I'm not talking about LiPo's powering electric powered planes) being able to supply 15C to 20C (20 amps +) on discharge. I also hear talk about the connectors to our receivers only being good for 3 amps. So does this mean unless you have 7 connections to the receiver or a special power distribution system of some sort you can't take advantage of that 15C current supply?
I build my own wiring harness and bus boards - it's really not that difficult if you are somewhat decent at soldering. Plus my custom harnesses have charge ports are all the same for RX, ign, and TX, which makes field charging very easy.
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RE: Do Lithium batteries REALLY make sense?
If the day comes that I can plug 2-cell LiPos directly to my RX, I will retire all my NiMH in an instance.
The folks at troy built are also experimenting with this setup. Maybe you can contact them to see what their findings were. I talked to them maybe 2 weeks ago and they said that the bench runs have been successful.
Nobody including Hitec supports 7.4 V on their servos. My guess is that they would like for us to do their field testing first.
Just for the record. I am NOT one of those people who have tested unregulated lithiums. So, take my statements for what they are worth.
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RE: Do Lithium batteries REALLY make sense?
I don't see why 7.4v compatability would hurt older equipment. Building receivers and servos so they can handle 7.4v won't make them unable to handle 6.0v or 4.8v. If I'm not mistaken, the receivers are already okay with 7.4v, its the servos that are the question mark.
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RE: Do Lithium batteries REALLY make sense?
Agreed. One of the concerns with 7.4V systems have been the higher current draw but lets face it, the 5955 will unofficially put out over 400oz of torque at 7.4 V. There is no need for 7,8,9 and 10-12 servos in our 33-35-40% planes. A 2,6 composite can be run with only 6 servos. probably drawing less current than the alternative 6V system. JMO.
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RE: Do Lithium batteries REALLY make sense?
That 2200mAh LiPo pack may only yield effectively 1870mAh if the regulator carries an efficiency of 85%. The rest gets dumped out the heat sink.
Using approximations, since the batteries average 7.9V (halfway between full charge and nominal voltage), you lose 4.18 Watt-hours to the heat-sink, and the servos get 13.2 watt-hours (using P=VI). But... 2200mAh should still be delivered at the reduced 6V.
So... the net effect... your system never sees the full energy density of a LiIon pack, but it does see the full current providing capacity.