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Old Oct 06, 2012, 12:44 PM
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Horizon MINI Super Cub battery problems

This bird comes with a 7.4V 300mAH LiPo, no C rating on the box.
Charger appears to be (I've since lost mine) a 300mAH charge rate.
The charger works off've a mains adaptor into a 12VDC cigarette lighter socket, which the charger is supplied with in the UK.

I've had a couple of flights out of the battery, now it won't hold charge. Shows 8.4 on a voltmeter, but trying it on a couple of different planes, it doesn't power them for more than a couple of seconds. I've encountered 3-4 different tales of this in my workplace (a model shop) and am wondering if anyone out there knows the cause, and/or the solution?

Also, what would others suggest as a replacement for both battery and charger?

Thanks in advance!
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Old Oct 06, 2012, 03:12 PM
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When you did run this, how far down did you discharge the pack?

I suspect you discharged it too low and damaged the battery.
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Old Oct 07, 2012, 05:12 AM
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Quote:
Originally Posted by ShaKaan View Post
This bird comes with a 7.4V 300mAH LiPo, no C rating on the box.
Charger appears to be (I've since lost mine) a 300mAH charge rate.
The charger works off've a mains adaptor into a 12VDC cigarette lighter socket, which the charger is supplied with in the UK.

I've had a couple of flights out of the battery, now it won't hold charge. Shows 8.4 on a voltmeter, but trying it on a couple of different planes, it doesn't power them for more than a couple of seconds. I've encountered 3-4 different tales of this in my workplace (a model shop) and am wondering if anyone out there knows the cause, and/or the solution?

Also, what would others suggest as a replacement for both battery and charger?

Thanks in advance!
Battery: http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html

Charger: http://www.hobbyking.com/hobbyking/s...cessories.html

Wattmeter: http://www.hobbyking.com/hobbyking/s...dProduct=10080

Read: https://sites.google.com/site/tjingu...arging-how-tos

Glen
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Old Oct 07, 2012, 01:06 PM
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Thanks ggcrandall for your fantasitcally concise reply. Never even bothered to take a meter to the field to test packs after flight. One query, if you'll allow - won't the 45-90C allow the motor to pull too much for current for the ESC? With a 5-10 minute flight, I'm assuming the stock batteries are 10-15C.

TheWoodCrafter - the batteries never had a full flight on the MSC due to my lack of ability - the last flight of the MSC ended in a nose in crash with the electronics completely dead (ie no lights flashing, no response) For the other people I've spoken to, I've no idea.

Having done a little research into this, I'm guessing I cooked the ESC - judging by the threads on the Super Cub. The remaining flight or so has been on a Nine Eagles Extra 300 which has done similar things to its batteries as well, but has an LVC (I thought the MSC did as well...). What the LVC is set to, I've not had chance to find out. I assumed (haha) that it would be sufficient.

Also thought I'd upgrade my batteries for the Extra 300, didn't bother asking advice first and got a 2S 240mAH 25C from my LHS - the Eagle flew my other batteries, then halfway into this one's flight, the throttle cut - which I took to be the LVC cutting in. Now all of my other batteries (including the one for the MSC) will last a few seconds before the throttle cuts out. Given this has a snap-off prop to prevent ESC burnout on crashing - could this be due to the motor pulling too much current from the new battery, as the old one, following the previous logic, had a ~15C rating?
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Old Oct 07, 2012, 01:27 PM
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You can't pull too much current with the motor through the ESC based on a higher "C" rated battery.

The motor will only draw what it was designed to draw.
Just because the battery can provide more current, doesn't mean you will burn out anything because of it.
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Old Oct 07, 2012, 03:33 PM
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So, in a totally hypothetical situation:
the ESC is rated at 10A
the motor naturally draws 20A
battery is 1000mAH 10C

What current would the motor draw? What would happen to the battery? If you change to a 1000mAH 20C what current would the motor draw then?

:-)
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Old Oct 07, 2012, 05:15 PM
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Quote:
Originally Posted by ShaKaan View Post
So, in a totally hypothetical situation:
the ESC is rated at 10A
the motor naturally draws 20A
battery is 1000mAH 10C

What current would the motor draw? What would happen to the battery? If you change to a 1000mAH 20C what current would the motor draw then?

:-)
You don't mention the voltage of the battery. You have to know the voltage to determine the current.

But if the motor draws 20 amp and the ESC is rated at 10 amp the ESC will be destroyed. The ESC must be rated higher than the motor current.

Here are the basics. For a given voltage the motor and prop combination determines how much current (amps) will flow in the circuit.

Increasing the mah of the battery will only increase flight time not current.

Increasing the "C" will not increase current or flight time. "C" is the maximum amount of current the battery can safely provide. If the current in a circuit is 10 amps (for example) and the battery "C" is 10 then increasing the "C" of the battery will not increase the current in the circuit.

A 1000mah 10C battery can safely supply 10 amps (in theory at least). A 1000mah 20C battery can safely supply 20 amps (again in theory). So if the battery is 1000mah 10C and the current in the circuit is 10 amps then replacing the battery with a 1000mah 20C battery the current will still be 10 amps.

Also if you replace the 1000mah 10C battery with a 2000mah 10C battery the current will still be 10 amps.

Changing the value of the mah or the "C" will not change the current.

Glen
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Old Oct 07, 2012, 08:20 PM
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I had the same problem w/the batteries on this plane. The problem went away w/the same battery type when I went to another charger. IMHO the provided charger is faulty.
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Old Oct 08, 2012, 03:31 PM
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Makes sense!

Let's try a slightly different question then - Does 1000mAH 10c mean I can never, under any circumstances, draw more than 10A? Or, say, if I short the battery, will I get 20A(or whatever. More than 10A)? Presumably this won't do the battery any good, but that isn't what I'm worried about here. Basically, is the C rating a hard, unbreakable limit, or is it a guidline for circuit design & safe operation?

Thanks again.
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Old Oct 08, 2012, 04:30 PM
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Most of the time the discharge C rating is a tool for the marketing guys.

Many manufacturers are not truthful about the rating.

So no, It is not a hard and unbrakable limit.
Almost all of these batteries will provide as much as twice the C discharge current for brief periods of time.
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Old Oct 08, 2012, 06:44 PM
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Quote:
Originally Posted by ShaKaan View Post
Makes sense!

Let's try a slightly different question then - Does 1000mAH 10c mean I can never, under any circumstances, draw more than 10A? Or, say, if I short the battery, will I get 20A(or whatever. More than 10A)? Presumably this won't do the battery any good, but that isn't what I'm worried about here. Basically, is the C rating a hard, unbreakable limit, or is it a guidline for circuit design & safe operation?

Thanks again.
1000mah 10C means that 10 amps is the maximum SAFE current the battery can supply. However if you place it in a circuit that asks for 20 amps or even 40 amps or even 100 amps the battery will supply that much current. Although it doesn't take much imagination to realize the battery will quickly, and most likely spectacularly, expire under those circumstances.

In practice you should not pull more than 80% of the rated capacity. i.e. your 1000mah 10C battery should not be asked to supply more than 8 amps.

If not already mentioned you need a wattmeter to verify the current and wattage values in your system.

Glen
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