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LiPo Discharger

Old 06-12-2022, 10:26 AM
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Flysfloats
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Default LiPo Discharger

It seems that I have been abusing my batteries for a long time. I have always charged them after flying and many batteries will go long periods of time between using again. I now have some planes with 6S batteries and I am concerned about damaging them due to the higher cost of larger batteries. Doing some research it appears that the best recommendation is to discharge batteries if they are not going to be used within a day or two. I am not organized enough to use light bulbs, etc to discharge so I am considering buying a "Discharger". Hobby King has this unit for $79=
ISDT FD-200 200W 25A Wireless APP Control Discharger for 2-8S Lipo Battery

I would appreciate your comments on this charger in particular, recommendations on other units, and other advice that will help me out.

Last question is do you use a volt meter to verify the "storage voltage" of the batteries? And if so, what voltage is good for 2S, 3S, 4S, 5S, & 6S batteries?

Thanks all for the help. Side note, STILL have not flown my Regal Eagle EDF because of weather and not trusting my current flying skills, sigh.


Old 06-13-2022, 09:24 AM
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ticedoff8
 
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Depending on the make of your existing charger, it may support discharging as well. If it has a "discharge" option, use it.

But, more importantly, when you get home after flying, charge your packs to the "storage charge" voltage (about 50% to 60%) instead of 100%. The storage charge voltage will allow you to store the batteries indefinitely, and then you charge them to 100% the night before you plan to fly.
In general, you don't want to store LiPo packs at 100% for more than a couple of weeks before discharging them (like flying).
If you find yourself back home after a day to the field with 1 or 2 packs that are still at 100%, then use the plane as your discharger. Strap the plane to the ground and run the motor for 2 or 3 minutes. Then recharge to the storage voltage.

Keep in mind that it is not the voltage of the pack that would be your "truth". "Truth" comes from the voltage of the individual cells.
A fully discharged LiPo cell is around 3.2v and a fully charged LiPo cell is 4.2v.
You could take that fully charged value of 4.2v and simply multiply it by 6 (for a 6S pack) and say "Well, its 25.2v. So, in this case, all the cells must be at 4.2v and it is 100% charged". You may be wrong about that. If you didn't do a "balance charge" mode, then 1 or 2 cells could be a 4.3v or 4.4v and the others could be a 4.0 or 3.9. That pack is out of balance and on its way to the recycling bin.

The "storage voltage" for a LiPo cell is between 3.6v & 3.8v.
But, unless you check the pack's individual cells with a LiPo battery checker connected to the pack's balancer lead, you are guessing.

Now that you are more in-touch with the condition of your expensive packs, you'll find there are a couple of meters that will (literally) save you hundreds of dollars in the long run on batteries.
- One is a Watt Meter. This will tell you how much power the EDF is pulling out of the pack. If the Watt meter shows that at 100% power, the motor is pulling 50A out of the pack, you now know how much it is stressing the pack. In this example, you would need to buy packs that would deliver at least 50A to 55A. Another way to look at this is that if your EDF is using a 3300mAh pack, it would need a "true" C-rating of 15C (3.3A x 15C = 50A). Notice that there is nothing in this calculation related to the pack's voltage or cell count. It's all about Watts and current.
- The other is the ESR/IR Mark II meter. Among all of details it provides about the pack, it will tell you the "true" C-rating for discharge. This one parameter is the difference between a battery lasting 5 or 10 flights or hundreds. Especially on EDF.
- The last would be a good LiPo Battery Checker that connects to the pack's balancer lead. The ESR/IR Mark II is also a LiPo battery checker, but there are others that are cheaper and you can keep it in your field box to check the pack after each flight (to make sure you are not over discharging the packs) - but the cheaper LiPo Battery Checkers do not replace the ESR/IR Mark II meter.

Fundamentally, you have to understand that the LiPo battery distributors lie about the "true" C-rating of their packs. And spending the most money on a "brand" is no indication of the quality of the pack. They never test this stuff. They just print labels and ship them.
But, if the ESR/IR meter tells you the pack's "true" C-Rating is 30A, and the Watt meter tells you the at 100% power the motor pulls 50A, this pack will have a very short life span in your EDF.
Use that pack on something that only pulls 25A and you'll get a long life.

Never over discharge a pack. That is a death sentence.
If your EDF's ESC is set to "Low Voltage Cutoff", you may as well start an investment fund at a brokerage firm so that you have money to buy replacement packs, because you are going to need a lot of replacement packs. By the time the ESC indicates the pack's voltage is too low, it's too late.

Always use the balancer mode when charging a multi-cell pack. Never use a charge mode that does not balance the cells in the pack as the pack is being charged.
By not using the balancer mode in the charger when charging a multi-cell pack you will shorten its life, and potentially cause one of the cells to burst while charging (due to over-charging that one cell) and start the entire pack on fire. This would be catastrophic.

Last edited by ticedoff8; 06-13-2022 at 11:49 AM.
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Old 06-14-2022, 06:19 AM
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Flysfloats
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Wow, awesome reply, thank you. This new, to me, procedure will be challenging. I have never charged a battery to a "storage" voltage but will try in the future, especially with the more expensive 5 &6 S batteries. Upon viewing my charger, it does have a discharge feature. I don't know if it has a feature to set the discharge to a particular voltage and then cutoff automatically. SO, I will have to monitor the discharge if I use the charger.

With my calculations it appears that a "storage" voltage for 5 S batts is 19.0 volts and for a 6 S batt, 22.8 volts. Again, don't know how to set these voltages to auto shut off. The charger does shut off when 100% is reached. My charger is a Thunder AC 6 Dual Power. I now will not buy a dedicated discharger, but will use your methods to achieve this.

The other challenge is trying to decide when I should charge the batteries to 100% for flying since I usually make up my mind to fly in the morning depending on weather and projects.

Things can be complicated, sigh.
Old 06-14-2022, 08:33 AM
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The Hota Thunder AC6 is really old tech. This was a cheap, knock-off charger when it was new 10 years ago.
And, at 50 Watts maximum charge rate, it is a slow charger. It might charge a 6S pack at a maximum of 2A. And forget about parallel charging multiple packs.

While I can't find the manual, I'd bet it doesn't have a automatic charge setting for "Storage" either.
Normally, you'd monitor the charger and battery when you are charging in case something goes wrong. And with an automatic balancer charge-mode and 100% cutoff, that means sticking your head out the door once in a while to see if the garage is on fire.
But having to manually halt the charger when all the cells in a pack reach 3.7v is a pain and not something you are likely to do on a regular basis.

I'd add a "new charger" to the list of things you may need to buy.

In the mean time, make sure you use the balance charge mode.

Last edited by ticedoff8; 06-14-2022 at 08:48 AM.
Old 06-19-2022, 11:49 AM
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Tticeoff8 off nailed it. Good info.


Last edited by Dumbthumbs67; 06-19-2022 at 11:51 AM. Reason: Misspelling

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