Posts: 26
Joined: 1/8/2003 From: wichita,
KS, USA Status: offline
I like my triton charger. It does all that. But I just noticed the settings for Ah only go to 2.5 and I just got a KOK2000-15c-3s2p 11.1V 4000ma Lipoly and wonder if I set the Triton at 2.5 and 11.1 w/ thermal probe will it charge this monster? Anyone know? Rick
Posts: 32
Joined: 5/19/2004 From: Asheville,
NC, USA Status: offline
Question from a LiPo newbie. I'm just finishing up a conversion of an old Oly II sailplane to electric assist. Power system is an MP Jet 28/20-7 brushless outrunner motor, CC Phoenix 35 ESC, Graupner 14-9.5 folder and 3-cell Kokam 2000 15C pack. According to my Whatt Meter, at full throttle I'm drawing 36 amps from a fully charged pack with this setup. Expecting about a 20-second full throttle motor run for launch. My question is... will this draw of 36 amps damage the LiPo pack which has a max output of 30 amps? Thanks for your help on this.
Posts: 180
Joined: 8/5/2003 From: Frederick, MD, USA Status: offline
quote:
ORIGINAL: cub driver
Question from a LiPo newbie. I'm just finishing up a conversion of an old Oly II sailplane to electric assist. Power system is an MP Jet 28/20-7 brushless outrunner motor, CC Phoenix 35 ESC, Graupner 14-9.5 folder and 3-cell Kokam 2000 15C pack. According to my Whatt Meter, at full throttle I'm drawing 36 amps from a fully charged pack with this setup. Expecting about a 20-second full throttle motor run for launch. My question is... will this draw of 36 amps damage the LiPo pack which has a max output of 30 amps? Thanks for your help on this.
Bob
Bob
Assuming that your current profile is continuous for the duration of each run and for the fulkl capacity of the battery; Yes, you will harm the pack or at least have short life. If you keep the burst to about six seconds, the pack will be OK. The KOK 2000 will do the best job of any un-paralleled pack in the 2000 to 2100 mAh class. The ideal pack for you would be the KOK 3200 which would not be fazed by the load you need. However, since you have made the investment in the KOK 2000/15C, the least expensive alternative is a second 3S1P pack of KOK 2000 plus a parallel interconnect module. The material below was just drafted to go in our web site soon, so you might as well review it and give me your questions and comments at fred@fmadirect.com
A SHORT GUIDE TO USE OF FMA LI PO BATTRIES
This is designed to be a short guide. Back up information in much greater volume is available in the FMA Direct Li Po Compendium at www.fmadireect.com. An example or two will help you to see how this works.
Operating Li Po batteries. Motors, and ESCs is not unlike operating a model engine. The engine overheats due to overload or lack of proper lubrication and is ruined. The uninitiated may put too large a propeller on the engine to over load it and, again, cause it to overheat, seize and be ruined.
SEE ATTACHED DISCHARGE CURVES FOR THE KOK 2000/15C
Think of the curve above as you would the instruments for an aircraft engine. In full - scale aviation, engine gauges have zones for proper operation marked on them. In particular, rpm and temperature have arcs of yellow where operation for specified short terms such as take - off are marked in yellow. Normal cruise settings are marked with a narrow white arc. The absolute maximum that must never be exceeded has a red line. Thus, most are familiar with the popular term about something being “red lined”.
A few simple rules to follow
FIRST AND FOREMOST: Avoid selecting your pack so that it has to operate at the maximum allowable discharge rate. 1. Find out how much voltage and current your system will require before you pick a pack. The maximum is set by the spec for the motor and ESC you choose. Let us assume that you are going to use a brushless motor and ESC that can deliver a maximum of 30 amps at 16.8V. That will require a 4S pack to deliver 16.8V. If the motor/ESC can handle a maximum of 500 watts, then maximum current drain would be 30 amps (16.8 X 30 = 504 watts) 2. In general, it is best to use the highest voltage your motor and ESC specify. That means that current is lowered and flight time will be the longest you can get. 3. Use LIPOCALC II to help you find the pack that fits the need best. Input the maximum voltage and current you expect to use and record the results. Now reduce the “throttle setting” to 70% and record the results. 4. Select the pack you need based on the maximum current (100% throttle) that will be demanded. 5. Study the discharge curves for the cell that is used in the pack identified by LIPOCALC II. Let’s say it is a 4S1P pack of the KOK 2000 used for the chart above. 6. LII Po Calc II computes that a 4S1P pack will deliver the needed wattage at full throttle. The 30 amps draw = 15C for the KOK 2000, i.e. right on the “redline” in the chart ABOVE. That is OK for a second or two at a time. If one ran at 100% throttle for the full flight, the pack would reach a temperature of 158 Deg F and that is too warm. 7. By reducing throttle to 70% to place a 10C load on the pack, flight time is extended to five minutes, 42 seconds. More importantly, pack temperature is reduced to 113 Deg F. THAT IS SIGNIFICANT! 8. If you choose to fly longer, Li Po Calc II shows you the options as you let it calculate. Selecting a 2P pack of the KOK 2000 increases flight time to about 11 minutes. This also means the pack will be operating at 30/4AH = 7.5C maximum even at full throttle and temperature would be 97 Deg F. Thus, throttle setting is no longer critical. 9. Set the cut-off above 2.5V, or nearer 3V in most situations.
Secondly: Stay out of the “zone of temptation.”
For aircraft, the “zone of temptation” is usually entered by repeatedly restarting after the first cut-off occurs. As with many rules, there is an exception. Some Kokam HC cells, when operated right up against the maximum allowable discharge are a little above the 3V line. A sudden application of throttle in that situation could cause a motor cut-off. Thus, the cut-off for the KOK 700, 1500 and 2AH should be set for 2.8V. In general, experience is showing that most airplanes have stopped flying before cut-off occurs, so this may be a moot point.
Gas Gauging using the discharge curve data
Please refer to the discharge curves above for the discussion of gas gauging.
1. Most OEM applications of Li Pos such as cell phones use a “gas gauge” to inform the user of the status of the battery. 2. RC applications are so price competitive that the added cost of individual pack gauging is not practical. 3. However, if the user has a digital voltmeter (DVM) a good emulation can be had. 4. The receiver and servos and ESC current without the motor running approximate the 0.2C load at which the cell is rated as shown in the 0.2C curve above. The discharge curve for the pack is nominally 3.7V/cell X # of cells at 0.2C. Recognize that this is a nominal value and will vary with the specific pack, how close the current is to 0.2C and how old the pack is. 5. The Kokam cells are shipped at half - charge and hundreds checked prior to in-house pack assembly measured exactly 3.81 at 50% capacity before charging. It is well to check this voltage before charging in order to ”calibrate” your set - up. 6. For the example curve: if your DVM says 3.5V under the light load, the cell has been depleted to 3.68V = 1625 mAh. That is about 80% of capacity and time to stop flying if you wish to maximize cycle life or minimize risk of a cut – off and a short flight.. 7. Keep track of pack voltage after each flight, track it against the discharge curve, then calibrate when the pack is recharged. Also, keep a record of flight time. Record the capacity it takes to charge the pack. Divide the capacity needed for charge by flight time in minutes to get the average capacity consumed per minute. Now you have it gas - gauged and can use the DVM to see what is left after each flight or use the average consumption per minute to estimate capacity used. 8. Always remember that almost all crashes occur on “that one last flight”! Leave a margin.
Posts: 26
Joined: 1/8/2003 From: wichita,
KS, USA Status: offline
Got an email that I had a reply - no reply. Whats up FMA? I like my triton charger. It does all that. But I just noticed the settings for Ah only go to 2.5 and I just got a KOK2000-15c-3s2p 11.1V 4000ma Lipoly and wonder if I set the Triton at 2.5 and 11.1 w/ thermal probe will it charge this monster? Anyone know? OK I assume it will, but will it get the FULL charge if I babysit long enough? What I'm tryin to find out is if I need a different charger for this big a battery and which one. Thanks Rick
Posts: 26
Joined: 1/8/2003 From: wichita,
KS, USA Status: offline
Got an email that I had a reply - no reply. Whats up FMA? I like my triton charger. It does all that. But I just noticed the settings for Ah only go to 2.5 and I just got a KOK2000-15c-3s2p 11.1V 4000ma Lipoly and wonder if I set the Triton at 2.5 and 11.1 w/ thermal probe will it charge this monster? Anyone know? OK I assume it will, but will it get the FULL charge if I babysit long enough? What I'm tryin to find out is if I need a different charger for this big a battery and which one. Thanks Rick
Posts: 32
Joined: 5/19/2004 From: Asheville,
NC, USA Status: offline
Fred, thanks for all the helpful info. I already have a second 3S1P 2000 pack as well as a parallel interconnect module. I set it all up tonight (fortunately it all fits in the Oly II) and it seems to run fine. Cell temp was just under 90F after a 20 second full throttle run. I have a feeling I won't need full throttle to get satisfactory launches with this setup. We'll see how it does this week. Thanks again for your help.
Posts: 180
Joined: 8/5/2003 From: Frederick, MD, USA Status: offline
quote:
ORIGINAL: rammar
Got an email that I had a reply - no reply. Whats up FMA? I like my triton charger. It does all that. But I just noticed the settings for Ah only go to 2.5 and I just got a KOK2000-15c-3s2p 11.1V 4000ma Lipoly and wonder if I set the Triton at 2.5 and 11.1 w/ thermal probe will it charge this monster? Anyone know? OK I assume it will, but will it get the FULL charge if I babysit long enough? What I'm tryin to find out is if I need a different charger for this big a battery and which one. Thanks Rick
Triton will give a full charge but it will take about 2.5 hours.
Posts: 180
Joined: 8/5/2003 From: Frederick, MD, USA Status: offline
quote:
ORIGINAL: rammar
Thanks Fred, I figured it would take a long time. Do you know of a faster charger? Rick
As soon as we have the Skyvolt 6S charger in stock (now Aug/Sept) you can do the charge in 20 minutes. The Astro 109 and one of our Charge Control Modules can do it in one hour.
Posts: 13
Joined: 9/12/2002 From: Louisville,
KY, USA Status: offline
I have an FMA super nova 250S charger, and had never used until now on Nimh batteries. I just bought two new nimh packs - one is a 4 cell 1700 mah recv pack and one is an 8 cell 1700 mah transmitter pack.
When charging the 4 cell pack with the super nova, it ran for only a few minutes (charge rate 1000 ma) and then shut off. I assumed it had already been charged. Just to be sure, I thought I would cycle it once. At a discharge rate of 800 ma, it showed being fully discharged in just a few minutes.
The same thing happened on the 8 cell pack. Either I have two bad packs or something is up with the charger. So I tried charging 4 cell again. This time I put a volt meter on the leads going to the pack while it was charging.
I noticed that the reading was about 0.5 volts lower than was showing on the chrager LCD. This would explain the premature shut off.
I am now noticing that the same charger is shutting off earlier than it should on Nicad packs too.
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RE: Welcome to the FMA Direct - Kokam LiPo Support Forum - 
