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kalel
11-03-2005, 11:17 PM
I have read the stickys, and still have a question that maybe someone can help with.

apex 1300mah 2s 10C

I have the above battery and a cheap apex charger (AC for $12). I know that it charges slowly, and should be fine. I am worried about the discharge from my bl motor.

Does the fact that it is 1300mah and 10C mean that it can safely discharge at under 13 amps? I am a little confused about this. If motocalc says that it pulls 15 amps, I need to either change prop or gearing, or get a 15C battery--is this correct?

Rugar
11-03-2005, 11:48 PM
I have read the stickys, and still have a question that maybe someone can help with.

apex 1300mah 2s 10C

I have the above battery and a cheap apex charger (AC for $12). I know that it charges slowly, and should be fine. I am worried about the discharge from my bl motor.

Does the fact that it is 1300mah and 10C mean that it can safely discharge at under 13 amps? I am a little confused about this. If motocalc says that it pulls 15 amps, I need to either change prop or gearing, or get a 15C battery--is this correct?

I would keep keep it under 11amps or so with that battery and even then just for short bursts with lots of cooling. Motocalc is just a estimate and should be used for just that, a estimate. One of the best investments you can get for electric flight is a Watt Meter. It will save you money and your equipment in the long run by telling you what you are really putting out.

Steve
11-04-2005, 12:02 AM
Yes, you pretty much understand that correctly. Most manufacturers over rate the ability of their batteries, so it's safer to not expect to push them to their stated limit. In your case, a 10C rated battery should be able to deliver 13A continuous discharge, but as the other poster recommended, it would probably be better to expect 8-10 as a more realistic target.

So....you're prop should be sized to keep you in the 8-10A range at WOT.

No way to tell what's up without a watt meter.

kalel
11-04-2005, 01:18 AM
Yes, you pretty much understand that correctly. Most manufacturers over rate the ability of their batteries, so it's safer to not expect to push them to their stated limit. In your case, a 10C rated battery should be able to deliver 13A continuous discharge, but as the other poster recommended, it would probably be better to expect 8-10 as a more realistic target.

So....you're prop should be sized to keep you in the 8-10A range at WOT.

No way to tell what's up without a watt meter.

I have seen watt meters for sale, but which one do you guys prefer?

Barfing Pumpkin
11-04-2005, 01:27 AM
I have seen watt meters for sale, but which one do you guys prefer?

Astro makes one, so duz Medussa........

10C = 13amp on a 1300 pack, but as the othr guys have said, don't push it that hard. maybe 8-10 max. you get bettr bat life that way. Dont recharge at 10C, big mistake. Charge at 1 amp for better slow charge.
Get a charger for lipo's, its worth it as lipos arent cheap.

Jack

Matt Kirsch
11-04-2005, 02:33 PM
kalel, you've pretty well got it, but you might have "C" and "A" confused a little bit where you said "I should get a 15C pack, right?" or something to that effect.

There are two ways to get more Amps:
1. Get a pack with a higher C rating.
1300 * 10C = 13 Amps --> 1300 * 12C = 15.6 Amps --> 1300 * 15C = 19.5 Amps
2. Get a pack with higher capacity.
1300 * 10C = 13 Amps --> 1500 * 10C = 15 Amps --> 2600 * 10C = 26 Amps

hoppy
11-04-2005, 05:11 PM
Yes, you pretty much understand that correctly. Most manufacturers over rate the ability of their batteries, so it's safer to not expect to push them to their stated limit. In your case, a 10C rated battery should be able to deliver 13A continuous discharge, but as the other poster recommended, it would probably be better to expect 8-10 as a more realistic target.


or MUCH less...

I wouldn't plan on getting (or using) over 75% continuous of the C rating on the battery.

hoppy
11-04-2005, 05:15 PM
I have seen watt meters for sale, but which one do you guys prefer?

I have both a WattMeter and a Sears Clamp-on.... I use the Sears 99% of the time to measure current draw.
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=03482062000&tab=spe#tab

Steve
11-04-2005, 11:04 PM
Hoppy,

If you had to choose again, would you still get a Wattmeter and a clamp on ammeter, or just the ammeter?

I have both a WattMeter and a Sears Clamp-on.... I use the Sears 99% of the time to measure current draw.
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=03482062000&tab=spe#tab

hoppy
11-04-2005, 11:44 PM
Just the Ampmeter - Reason? I use the ampmeter to determine the current draw of the motor at full throttle. I'll change props until the amperage is at the top of the recommended high efficiency range. The battery pack is selected ahead of time to provide the max current needed. For instance, if the motor had a high efficiency range of 6-10A, I'd use a battery pack with a 13+C rating and than change props till the current draw was 10A at full throttle. Of course the maximum watt capability of the motor would also be taking into consideration. Now, why the clamp on? Because it can be used with the plane in it's flying condition. No need to break connections, just put the clamp around either battery lead. This can be done anywhere with a minimum of fuss and can be done regardless of the connectors used on the plane. Now it doesn't provide all the data the Whatmeter does but it fills my needs.

GeraldRosebery
11-04-2005, 11:59 PM
I have read the stickys, and still have a question that maybe someone can help with.

apex 1300mah 2s 10C

I have the above battery and a cheap apex charger (AC for $12). I know that it charges slowly, and should be fine. I am worried about the discharge from my bl motor.

Does the fact that it is 1300mah and 10C mean that it can safely discharge at under 13 amps? I am a little confused about this. If motocalc says that it pulls 15 amps, I need to either change prop or gearing, or get a 15C battery--is this correct?

DO NOT rely on calculations for current draw. Buy a watt meter and measure it. In the long long a watt meter is a better investment than replacment battery packs!

GeraldRosebery
11-05-2005, 12:00 AM
I have both a WattMeter and a Sears Clamp-on.... I use the Sears 99% of the time to measure current draw.
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=03482062000&tab=spe#tab

I have both and while the clamp-on is often more convenient it does not tell the whole story like the watt meter!

hoppy
11-05-2005, 03:27 AM
I have both and while the clamp-on is often more convenient it does not tell the whole story like the watt meter!

True, you have to muliply the amps shown on the Clamp-on by the pack voltage to get watts. For a 3s pack I assume 10.5V, for a 2s, 7V. Not exact, but close enough to keep the motor/battery within spec limits. SInce I got a charger with a mah display and discharge capability, the Whatmeter has gathered dust. What applications do you use your whatmeter for?