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Old Jan 26, 2015, 06:30 PM
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"C" rating on Life Source battery packs.

Hello friends,

I have been researching battery packs for a while and feel like i have a good grasp on things but I have a couple questions that I can't seem to find the answers to. I'm definitely going with a LiFe pack. This will be for a Goldberg 40 size cub, spektrum 4 channel receiver and 4 Spektrum A6110 HV standard servos. I chose the HV servos because the rating on the standard and digital tops out at 6v and the life batteries are 6.6v (maybe the standard servos would handle it anyway?)

1) Life source packs have a "C" rating. For instance the 1300 mAh pack comes in a 1C or 10C. The way I'm understanding it is the 1C will put out 1.3 amps continuously and the 10C will put out 13 amps continuously. How do i know which is needed? I imagine 13 amps would fry something meant for 1.3. Spektrums LiFe battery packs do not have this C rating on them.

2) Is there a way, other than experience, to know how big of a battery you need? I was planning on the 1300 mAh, or 1450 mAh (depending on what brand i go with) and imagine it will be plenty of power. Is the only difference between those and a 2200 mAh going to be flight time (and weight of course)?

Finally, I wouldn't mind hearing your brand preferences and reasons for said preferences.

Thanks in advance!
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Old Jan 26, 2015, 07:20 PM
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Originally Posted by Username14 View Post
Hello friends,

I have been researching battery packs for a while and feel like i have a good grasp on things but I have a couple questions that I can't seem to find the answers to. I'm definitely going with a LiFe pack. This will be for a Goldberg 40 size cub, spektrum 4 channel receiver and 4 Spektrum A6110 HV standard servos. I chose the HV servos because the rating on the standard and digital tops out at 6v and the life batteries are 6.6v (maybe the standard servos would handle it anyway?)

1) Life source packs have a "C" rating. For instance the 1300 mAh pack comes in a 1C or 10C. The way I'm understanding it is the 1C will put out 1.3 amps continuously and the 10C will put out 13 amps continuously. How do i know which is needed? I imagine 13 amps would fry something meant for 1.3. Spektrums LiFe battery packs do not have this C rating on them.

2) Is there a way, other than experience, to know how big of a battery you need? I was planning on the 1300 mAh, or 1450 mAh (depending on what brand i go with) and imagine it will be plenty of power. Is the only difference between those and a 2200 mAh going to be flight time (and weight of course)?

Finally, I wouldn't mind hearing your brand preferences and reasons for said preferences.

Thanks in advance!
A large number of my club members have gone to those LiFe or their higher powered A123 version. These LiFe two cell battery packs have far greater high current, short duration capability than those five cell Nickel "AA" sized battery packs.

As for peak current requirements, I've got two giant scale models with seven Hitec 645MG servos installed. The peak current pulled by those servos while just spinning the transmitter sticks round and round hit 14 Amps, as measured by my $$$$ Fluke 87V digital multimeter, using its one millisecond response peak min-max function.

Pulling a momentary peak current of 14 Amps out of a LiFe pack is pretty much a non-issue. Pulling 14 Amps out of a five cell Nih AA size pack is an issue.

What is an issue is the Milliampere Hour capacity of your LiFe battery pack. Depending on the size of your model, and the type of flying you do with it, a reasonable value is pulling around 200 MilliAmpere Hours out of your battery pack for each flight. That would be on a 65 inch wingspan model with around 1500 Watts up front, equivalent to a 72 sized 4 stroke glow engine.

So, with a 1200 Mah battery pack, you'd get six flights before your battery went flat. Using my personal rule of never using more than 50% of the battery capacity during any days flying, that brings it down to three flights.

Nice thing about LiFe and A123 batteries, they are very efficient in their charging process. And, you can top them off in 15 or 30 minutes or so at the field. If your charger shows 1150 Mah after your battery is charged, your model used 1150 Mah X 95% charge efficiency, or 1092 Mah.

Based on these results, most of my club members are using the 2200 Mah LiFe battery packs for their models, going up to 30 cc gassers. (FYI, when flying these types of models, because of the value of the model, these same club members are using dual LiFe battery packs for redundancy of the battery pack, its switch, and other associated parts.)

So, put perhaps two flights on your model, top it off at the field, and see how many Mah YOUR receiver LiFe took. Then go from there on how many safe flights you can get.

FYI, the voltage discharge curve on these type cells is pretty flat, so just measuring its voltage to determine how much capacity is left doesn't work.

The first JPG shows a two cell 3200 Mah LiFe versus a 5 cell Nih battery while pulling 12 Amps. That Nih battery dropped off so fast, my Western Mountain battery analyzer barely showed what happened.

The second shows the A123 versus the 5 cell Nih battery with a two amp discharge. Their voltages are nearly identical, showing that a two cell LiFe or A123 battery is a direct drop in replacement for a 5 cell Nih pack.

As far as brand names, Tower Hobbies has a variety of LiFe battery packs. Just go to www.towerhobbies.com and search for "LiFe"
http://www3.towerhobbies.com/cgi-bin...ries&search=Go

Hope that helps.
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Old Jan 26, 2015, 09:41 PM
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Originally Posted by Username14 View Post
Hello friends,

I have been researching battery packs for a while and feel like i have a good grasp on things but I have a couple questions that I can't seem to find the answers to. I'm definitely going with a LiFe pack. This will be for a Goldberg 40 size cub, spektrum 4 channel receiver and 4 Spektrum A6110 HV standard servos. I chose the HV servos because the rating on the standard and digital tops out at 6v and the life batteries are 6.6v (maybe the standard servos would handle it anyway?)

1) Life source packs have a "C" rating. For instance the 1300 mAh pack comes in a 1C or 10C. The way I'm understanding it is the 1C will put out 1.3 amps continuously and the 10C will put out 13 amps continuously. How do i know which is needed? I imagine 13 amps would fry something meant for 1.3. Spektrums LiFe battery packs do not have this C rating on them.

2) Is there a way, other than experience, to know how big of a battery you need? I was planning on the 1300 mAh, or 1450 mAh (depending on what brand i go with) and imagine it will be plenty of power. Is the only difference between those and a 2200 mAh going to be flight time (and weight of course)?

Finally, I wouldn't mind hearing your brand preferences and reasons for said preferences.

Thanks in advance!
Regarding your #1. Increased current capacity will not "fry" anything. If you have a circuit that pulls 1 amp and you had a battery rated at 1000Ah (1Ah) and you replace it with a 5000mAh rated battery the circuit is still only pulling 1A. All you have done it to replace the original battery with one that will last 5 times a long.

Glen
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Old Jan 27, 2015, 08:37 AM
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I thought the battery would be "pushing" 13 amps into the receiver. So you're saying that, regardless of the discharge rate, the system will only pull what it needs? And that is my system is only pulling 1Ah, the battery will not discharge at the 10c rate?

That's making a lot of sense. I'm guessing that because I'm using a glow engine, so I'll only have 4 servos that need power, I have no reason to get anything stronger than a 1C. (I have no idea how much power my system will pull).

I've found that there is no C rating on the spectrum LiFe batteries because they haven't actually been released yet, scheduled for late February.

Does anyone know if a standard servo, rated for 6v, will handle the 6.6v from the LiFe battery, or do I have to have the HV servos?
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Old Jan 27, 2015, 09:28 AM
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United States, FL, Jacksonville
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Don't get fussed up about the C ratings of receiver batteries unless you're getting into big digital servos on a giant scale its a non-issue.

Also, a "6v servo rating" means its appropriate for use with a 5 cell Nickel pack, just a 4.8v rating means its appropriate for a 4 cell nickel pack, fully charged a 5 cell pack is the same as your A123 or LiFe battery. The only way you'd need HV servos is if you're planning on running a 2S lipo that will be over 8v fully charged.
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Old Jan 27, 2015, 09:30 AM
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Originally Posted by Username14 View Post
I thought the battery would be "pushing" 13 amps into the receiver. So you're saying that, regardless of the discharge rate, the system will only pull what it needs? And that is my system is only pulling 1Ah, the battery will not discharge at the 10c rate?

That is exactly right.

That's making a lot of sense. I'm guessing that because I'm using a glow engine, so I'll only have 4 servos that need power, I have no reason to get anything stronger than a 1C. (I have no idea how much power my system will pull).

You do not size the battery by the C rating. You size if by the voltage and mAh. And you need to know how much current the system requires to make that determination.

I've found that there is no C rating on the spectrum LiFe batteries because they haven't actually been released yet, scheduled for late February.

Does anyone know if a standard servo, rated for 6v, will handle the 6.6v from the LiFe battery, or do I have to have the HV servos?

If they will not you can put a BEC (Battery Elimenator Circuit) between the battery and the receiver. This will regulate the battery voltage to 5V or 6V.
May I suggest you read this: http://www.tjinguytech.com/charging-how-tos

Glen
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Old Jan 27, 2015, 10:19 AM
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Right, I know what ballpark i need to be in for my pack size, but there are still choices and price differences. Let me use a specific example.

Life source by hobbico has an 1800 mAh pack with a 10C rating for $35. They also have a 1900mAh pack with a 3C rating for $40.

So the 1800 mAh pack CAN output more (but won't because my system won't use it) but the 1900 mAh pack stores more energy and will last a little longer.

I guess I don't really have a question there. Hahaha

Does the C rating affect charging time at all?

Thanks everyone for spelling this out for me.
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Old Jan 27, 2015, 12:46 PM
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Originally Posted by Username14 View Post
Right, I know what ballpark i need to be in for my pack size, but there are still choices and price differences. Let me use a specific example.

Life source by hobbico has an 1800 mAh pack with a 10C rating for $35. They also have a 1900mAh pack with a 3C rating for $40.

So the 1800 mAh pack CAN output more (but won't because my system won't use it) but the 1900 mAh pack stores more energy and will last a little longer.

I guess I don't really have a question there. Hahaha

Does the C rating affect charging time at all?

Thanks everyone for spelling this out for me.
I'd go for the 1800 Mah with 10C rating, both because of higher current potential, and it's $5 cheaper.

These LiFe batteries can be topped off at the field with a quality balancing type of charger in a half hour or so.

As far as current capability goes, take a look at your 120 Volt outlet in your home. It's got a 15 or 20 Amp breaker behind it, but you won't be pulling 15 Amps, unless you plug in a toaster or similar. Or an one horsepower electric motor when you stall it out by overloading it.

Same with our receiver batteries.
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Old Jan 27, 2015, 02:03 PM
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The Hobbico LiFe Source packs rated at 3C are intended for use in transmitters. Use the 10C variety for RX/Servo power. You can use the 3C packs, but I prefer the higher C rated packs because they are better able to supply continuous voltage under flight loads.
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