replace old nimh 8-pack
02-09-2016, 03:32 PM
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replace old nimh 8-pack
For the engine/servo battery on an older rc plane, currently have a "9.6v 650mah NIMH" which is basically an 8-pack of rechargeable AAAs. The battery is not working well now. As a replacement, I suppose I could just buy some higher-discharge NIMH AAAs (like camera cells) and make the same configuration, but I'm wondering if I could substitute some other sort of lighter lithium battery that might last longer too. I don't want to spend a lot of money though, and I'm not sure what discharge rates I should be looking for. The current battery doesn't have discharge rate listed, but it should be same as typical nimh used for rc engines, I suppose. Thanks for any suggestions.
02-09-2016, 03:42 PM
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02-09-2016, 04:17 PM
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What is this battery actually powering? Is this in an electric(motor) plane ?
If so I assume the receiver is getting its power from the ESC ?
Can you post some pics of the plane and its set-up?
You could use a lithium pack but only if you have or purchase a charger that can charge and balance a lithium pack.
If so I assume the receiver is getting its power from the ESC ?
Can you post some pics of the plane and its set-up?
You could use a lithium pack but only if you have or purchase a charger that can charge and balance a lithium pack.
02-09-2016, 08:05 PM
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You can use LiFe batteries for exceptional power to weight, Here is one source but you can buy individual 3.2 volt cells and make your own also,
http://www.batteryspace.com/96lifepo4batterypacks.aspx
http://www.batteryspace.com/96lifepo4batterypacks.aspx
02-09-2016, 10:51 PM
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Hi Jimmy--thanks for link, but that's a pack of AA batteries (much heavier than what I've got now). I'm looking instead to perhaps dramatically decrease weight by using for example lithium, but want to know the discharge rate I would need--there are so many options. I just need to know the minimum rate I should look for in a lithium rechargeable that would be at least as much as the rate of a 9.6v pack of quick-discharge nimh AAAs.
02-09-2016, 11:05 PM
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To Flyinwalenda--
Yes, it's a conventional electric plane. The 9.6v 650mah nimh battery pack (basically 8 AAAs in a bundle) powers everything on board.
Here's a simple youtube vid of same model in use: https://www.youtube.com/watch?v=H8BfxTAw2Mg
I'd just like to know what discharge rate I should look for in, say, a lithium battery with similar voltage.
Actually, the nimh setup achieves about 11.5 volts at complete charge, but this stabilizes quickly to around 9.6, so I assume using a lithium setup of anything from say 9.5 thru 11 volts would work great, assuming the discharge rate was at least as high as the current nimh.
Yes, it's a conventional electric plane. The 9.6v 650mah nimh battery pack (basically 8 AAAs in a bundle) powers everything on board.
Here's a simple youtube vid of same model in use: https://www.youtube.com/watch?v=H8BfxTAw2Mg
I'd just like to know what discharge rate I should look for in, say, a lithium battery with similar voltage.
Actually, the nimh setup achieves about 11.5 volts at complete charge, but this stabilizes quickly to around 9.6, so I assume using a lithium setup of anything from say 9.5 thru 11 volts would work great, assuming the discharge rate was at least as high as the current nimh.
02-09-2016, 11:11 PM
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Hi Topspin--nice link. It seems very close to what I'm looking for. Any ideas on the discharge rate I should be looking for? It would have to be at least as much as that of the original 9.6 nimh (8xAAA) pack that came with the set. Any tips on buying chargers for such LiFe batteries?
Thanks much.
Thanks much.
02-10-2016, 05:08 AM
#8
That looks and sounds like a simple brushed motor/ducted fan set-up.
A 3-cell LiPo pack will be around 12v fully charged and around 10v discharged.
A 3-cell LiFe pack will be around 11v fully charged and around 9v discharged.
Your set-up may not handle a LiPo pack due to the higher voltage. It may eventually burn-out the esc or motors. A LiFe pack may be better suited.
An issue you will have is that the speed control (esc), more than likely does not have the capability of changing its low voltage cut-off. Therefore running a Lixx pack will be risky unless you add on a battery alarm that plugs into the balance port of the pack and will sound when the battery gets too low.
If you use a LiFe pack then this is not as much of a concern as these packs can be discharged down below cut-off and will bounce back........LiPo's will not. A LiFe pack has a rather flat discharge curve compared to a LiPo (or the current NiMh pack). You will not notice a dramatic decrease in power as the battery discharges but when it reaches the end it is like falling off of a cliff. Best bet for the Lixx packs is to use a timer for flights,set a baseline, and come in before the pack reaches critical levels.
For the discharge rate, ducted fan set-ups typically demand more power than conventional set-ups so you should get a pack with the highest discharge rate or "C" rate that you can. A higher "C" rate means a slightly larger and heavier pack . Measure and weigh the current pack and check specs on Lixx packs and get the largest capacity & largest "C" rate you can that comes close to matching the dimensions and weight of the factory pack.
Here is a very good lower priced multi-chemistry charger :
http://www.horizonhobby.com/kx80-80w...ger-p-kxsc1002
A 3-cell LiPo pack will be around 12v fully charged and around 10v discharged.
A 3-cell LiFe pack will be around 11v fully charged and around 9v discharged.
Your set-up may not handle a LiPo pack due to the higher voltage. It may eventually burn-out the esc or motors. A LiFe pack may be better suited.
An issue you will have is that the speed control (esc), more than likely does not have the capability of changing its low voltage cut-off. Therefore running a Lixx pack will be risky unless you add on a battery alarm that plugs into the balance port of the pack and will sound when the battery gets too low.
If you use a LiFe pack then this is not as much of a concern as these packs can be discharged down below cut-off and will bounce back........LiPo's will not. A LiFe pack has a rather flat discharge curve compared to a LiPo (or the current NiMh pack). You will not notice a dramatic decrease in power as the battery discharges but when it reaches the end it is like falling off of a cliff. Best bet for the Lixx packs is to use a timer for flights,set a baseline, and come in before the pack reaches critical levels.
For the discharge rate, ducted fan set-ups typically demand more power than conventional set-ups so you should get a pack with the highest discharge rate or "C" rate that you can. A higher "C" rate means a slightly larger and heavier pack . Measure and weigh the current pack and check specs on Lixx packs and get the largest capacity & largest "C" rate you can that comes close to matching the dimensions and weight of the factory pack.
Here is a very good lower priced multi-chemistry charger :
http://www.horizonhobby.com/kx80-80w...ger-p-kxsc1002
02-10-2016, 09:26 AM
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Here's a possible choice for a 3S LiFe substitute.
http://www.valuehobby.com/power-syst...h-3s-life.html
Don't sweat the 5C rating, AAA Nimh cells have very poor ability to deliver any amount of current. The listed pack can deliver a sustained 9A draw, I doubt that any AAA Nimh pack could come anywhere close and I doubt that your plane draws anywhere near that if it was sold with a AAA 650mAh Nimh. Needless to say, you'll have to splice your connector from the old battery to discharge wires on the new battery. It would probably be a good idea to parallel both of the discharge leads after removing the plugs and plice both to the connector that your plane uses.
Good luck,
Pete
http://www.valuehobby.com/power-syst...h-3s-life.html
Don't sweat the 5C rating, AAA Nimh cells have very poor ability to deliver any amount of current. The listed pack can deliver a sustained 9A draw, I doubt that any AAA Nimh pack could come anywhere close and I doubt that your plane draws anywhere near that if it was sold with a AAA 650mAh Nimh. Needless to say, you'll have to splice your connector from the old battery to discharge wires on the new battery. It would probably be a good idea to parallel both of the discharge leads after removing the plugs and plice both to the connector that your plane uses.
Good luck,
Pete
02-10-2016, 12:12 PM
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Hi Flyinwalenda and Pilotpete2--great info both of you, thanks. I'm learning!
The 9.9/9.6 (3s) LiFe's sounded like the way to go, but checked into their weights--all heavier than the 107g of my current nimh pack.
I'm kind of afraid it would weaken the ride too much, so just wondered if there are any 3s LiFe's out there with perhaps lower mah but lighter weight--can't find them myself.
Also, I notice some 3s LiFe's are designated "transmitter" batteries: do you think their discharge rate would be enough for the motors on this plane? Some such batteries are also for airsoft.
The 9.9/9.6 (3s) LiFe's sounded like the way to go, but checked into their weights--all heavier than the 107g of my current nimh pack.
I'm kind of afraid it would weaken the ride too much, so just wondered if there are any 3s LiFe's out there with perhaps lower mah but lighter weight--can't find them myself.
Also, I notice some 3s LiFe's are designated "transmitter" batteries: do you think their discharge rate would be enough for the motors on this plane? Some such batteries are also for airsoft.
