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› What capacity/discharge rate for HBK2
07-14-2008 05:20 AM  9 years agoPost 1
quaid

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London, UK

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Hi guys,

I am moderately new to electrics and have just got an HBK2 for myself. Changed to the 3900 motor and Esky ESC (and a GY240). I want to get some Li-Pos but haven't been able to figure out the discharge rate/capacity to get - searched for it but couldn't find the info.

Would help if someone could let me know the highest usable capacity and discharge rate.

Best.

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07-14-2008 05:57 AM  9 years agoPost 2
TJinGuy

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Socorro, NM - USA

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edit: First an explanation of how to really determine what you need. The ESky BL ESC is a 25A. That means it can handle 25A continuous, so you need a battery that can meet that need. Batteries use a C rating like 20C that is nothing more than capacity of the pack and some number used as a multiplier. For example a 20C 2100mAh pack can continuously output 42A of current (20 * 2.100A = 42A). Batteries come in lots of rating from 8C to 30C but most of the batteries you will find are between 15C and 25C. So you need one that can handle 25A. Lets say you decide to go with a 1500mAh pack, then you need a 16C or greater pack to supply enough current. If you choose a 2100mAh pack, then you will only need a 12C pack.

I would recommend some 2100mAh packs. As for discharge ratings, aim for 15C or 18C packs for a King2 unless you plan to use them on a bigger heli. These will be the smallest and lightest packs. You can also run 1500 and 1800 packs but they are just less common and will give you less runtime. The FMA Revolectix 2100 red label packs are probably one of the best choices for the King. They are one of the smallest/lightest 2100 packs you will find, fit in the stock canopy and level out the CG almost perfectly. Plus at $50 each, they are a good deal and only $10 more than a cheap pack like a Mega Power.

- Chris

Team New Mexico
TJinTech

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07-14-2008 05:59 AM  9 years agoPost 3
Gregor99

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Western Wa

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My HBK2 with the Esky 3800 averages about 9amps with a 10t pinion. With the 3900 you'll be running slightly less. Here are my current batteries and how they run.

FMA 1350 15c - Tend to run a little warm. Shorter run times, (70% to 75% usage) is required to keep the temps down. No chance of running this pack with an 11t. Run time is about 5 minutes. I could run it longer but like to keep the temps down to make the packs last.

FMA 1300 25c - Also tend to run warm, but can be run down to 80%. Runtime is up to 6.5 minutes.

Outrage 2200 25c - Yes, perhaps a large battery. It runs 10 to 11 minutes and comes off cool.

Note that even though I'm averaging 9amps that means I have peaks much higher. If you run a pack at close to its max rating for any length of time, it won't last. Look at the C rating like the redline in your car. Sure you can run up to redline once in a while. But if you run at redline all the time, the motor won't last.

Revolectrix Beta Team

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07-14-2008 05:36 PM  9 years agoPost 4
quaid

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London, UK

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Hi again.. Chris - thanks for the explanation. I am banking towards a 2200mah/20C-25C setup.(To get hi- flying time and oomph). Will that be too much for the ESC?

Best.

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07-14-2008 10:45 PM  9 years agoPost 5
TJinGuy

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Socorro, NM - USA

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I can't find a good way to explain this but the capacity of a battery doesn't matter to something like an esc. The voltage does and that is all the esc cares about. Now you need to be able to supply enough current to the esc or you will have voltage problems and that leads to esc issues.

Anyhow not to try and confuse you but the only thing you need to worry about with the esc regarding batteries is

1) voltage of the pack. In your case that will be a 3s pack or 11.1V.
2) that the batter can provide enough current for flight. In your case that would mean 25A. Anything more is just extra and won't directly help you.

So if you are looking for a battery for a King2, you need 3 things answered.

1) what size in mAh.

I have already recommended 2100 packs. These are a good size and will give nice long run times.

2) what C rating so that you have enough current available.

I have already written out how to figure that out but lets assume that you at least a 15C pack.

3) what physical size/weight is the pack so that it will fit in your King2.

Now this is something that is probably more important than the 2 previous questions. You need a fairly specific pack size. It can be no wider than 33mm, no thicker than 25mm and no longer than 100mm if you want it to fit easily into the stock canopy. On weight I found that a 150g pack weighted out my heli about perfect, so I would aim for that. Any heavier and the heli has a hard time lifting it and any lighter and you have to adjust the pack for a correct CG. Here is the pack I would actually recommend
http://www.fmadirect.com/detail.htm...2210§ion=69

- Chris

Team New Mexico
TJinTech

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07-15-2008 05:54 AM  9 years agoPost 6
waylander

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Edmonton, Alberta -​Canada

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Just to get into this in a bit more detail, you've gotten some good information and I just want to add to it.

The battery you choose is related to the ESC, you want the continuous and peak (max) discharge rates to exceed what the ESC can pull. The Esky 25amp esc can pull 25amps continous and max of 50amps. So you want a battery that can meet those values.

As a side note, the esc is chosen based on what the motor can demand so in reality the motor determines the esc, and the esc determines the battery.
If you choose a 2200mah battery then you want a C rating of at least 12C (12 x 2.2 = 26.4amps) and a burst (max) of 25C.

Another side note, the C rating is a rating which determines how quickly a battery can discharge it's capacity. Even batteries manufactured at the same plant to the same specifications can have different discharge rates (even if they have the same capacity) and the "C" rating system allows the user an easy way to determine the discharge rate based on the capacity of the battery.

A higher C rating will keep the battery cool as you aren't pulling the max out of the battery all the time.

Remember that the amount of amps the battery can discharge is = C rating x capacity (in mah) / 1000 = amps.

Please see the following from the Air Thunder website http://www.airthunder.com/lipoabc.aspx

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07-16-2008 12:48 PM  9 years agoPost 7
quaid

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London, UK

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Hello again.

Thanks for the explanations everyone. Very helpful. I was just concerned that if I use a hi discharge rate either the ESC or Motor will burn out.

It seems an equally bigger concern is the size of the battery - will be careful.

Thanks again.

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07-16-2008 03:20 PM  9 years agoPost 8
TJinGuy

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Socorro, NM - USA

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High discharge rate only gives you the ability of high discharges. It does not mean you will only get high discharges. Think of it like this, your cell phone only takes .5A to charge but you can use a car battery as a power source and that can handle like 300A discharges.

- Chris

Team New Mexico
TJinTech

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07-18-2008 03:46 AM  9 years agoPost 9
quaid

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London, UK

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Thanks guys.

@TJinGuy - sent you a PM for another issue

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