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Batteries & Chargers Discuss Li-P, Li-Ion, NiMh, Nicad battery technology and the chargers that juice 'em up!

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Old 01-19-2013, 05:40 PM   #1
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Default how to check a lifepo4 at flying field for remaining use

What is methods are there to check a lifepo4 at the flying field to determine how much remaining time you can safely use it?

Lots of stuff on the web, but some of it is conflicting.

There are many different types of voltage checkers that say they are for a123 or life, yet some sources say that checking voltage on these types of batteries is no indicator of remaining useage.

So whats the scoop? Can they be field checked? Or is the only method to use them for a few flights at the field and then recharging them to determine flight usage by amps put back in?

For instance, can a device like this really tell you about remaining usage in a lifepo4?


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Old 01-19-2013, 09:00 PM   #2
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can a device like this really tell you about remaining usage in a lifepo4?


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yes!!! thats the way to go,and not very exspensive.

narrow is the place to land...wide is the space to crash....choose the narrow way!
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Old 01-20-2013, 05:31 PM   #3
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Any US sources for that device?
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Old 01-20-2013, 05:53 PM   #4
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Default sources

HK usually has them, but they are backordered.
Someone has them on r/c universe right now.

Anyway, I placed the same thread on R C Groups and all the feedback I have received so far states that this will not help you determine if you have enough charge left in your reciever pack to fly.
Lifepo4 and A123 can not be evaluated in this fashion.

http://www.rcgroups.com/forums/showthread.php?t=1812657
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Old 01-20-2013, 06:42 PM   #5
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Originally Posted by ronj100 View Post
...all the feedback I have received so far states that this will not help you determine if you have enough charge left in your reciever pack to fly.
Lifepo4 and A123 can not be evaluated in this fashion...
That is what I have always understood.

Too bad PLD has shut down production. Looks like he made some great little devices. Thanks for the response.
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Old 01-20-2013, 07:31 PM   #6
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Default mah logger

Yes, his device would have been useful for the flying field. I have done some brief research online and there are a couple of mah loggers but they are too spendy at this point. If I can find one in the $40 dollar or less range I may purchase one.

I recently ordered all new receiver packs for my planes. A123's for my gassers and Lifepo4 for glo size planes. I'm going to retire all my nimh's. So in the mean time I'm doing research to get up to speed on these battery types.

One idea I read about, and liked, was to add an extension to the balance lead so that you can access the battery during the flying day and recharge without dismantling your plane. From what Ive read you can push gobs of energy back into them in a short period of time without any penalty.
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Old 01-20-2013, 07:46 PM   #7
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Have a look at these threads and others by kyleservicetech. He has written much about this.

http://www.wattflyer.com/forums/showthread.php?p=755946
http://www.wattflyer.com/forums/showthread.php?t=63489
http://www.wattflyer.com/forums/showthread.php?t=58989

And this:

http://www.fly-imaa.org/blog-posts/n...scale-modelers
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Old 01-20-2013, 07:51 PM   #8
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Ron - I hate to say it but for LiFE batteries you can't use a meter to determine how much capacity they have left like you can with NiMh as they have a nearly flat discharge curve.

They are awesome cells - but will drop quickly from fully charge voltage of 3.6v/cell to 3.3v/cell and they will stay at that level until they are almost flat. So at 90% capcacity they will be at 3.3v/cell and at 30% they will be the same. Then they drop rapidly.

So what you have to do is determine just how many flights you can fly before recharging by monitoring the amount you put back in them.

I usually go to about 50% capacity and then recharge. that is ultra safe but works for me.

Mike
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Old 01-20-2013, 10:19 PM   #9
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Originally Posted by ronj100 View Post
What is methods are there to check a lifepo4 at the flying field to determine how much remaining time you can safely use it?

Lots of stuff on the web, but some of it is conflicting.

There are many different types of voltage checkers that say they are for a123 or life, yet some sources say that checking voltage on these types of batteries is no indicator of remaining useage.

So whats the scoop? Can they be field checked? Or is the only method to use them for a few flights at the field and then recharging them to determine flight usage by amps put back in?

For instance, can a device like this really tell you about remaining usage in a lifepo4?

Yeah, I'd be very reluctant to use a simple voltage tester (or voltage/load tester for that matter) to determine if a LiFe or A123 receiver battery has enough amp hours to safely fly another flight.

Their voltage discharge curve is just to flat. I've done a number of tests on both A123 and LiFe batteries. These batteries have about a 1% dip in voltage between 80% and 20% state of charge. Since that 1% is probably measuring accuracy of these meters, their test results may be meaningless on these types of batteries.

Best way to do it is to first top off your battery, then simply fly off two or three flights, and top it off again. These LiFe and A123 cells are very efficient in the charge process, so if you use 1000 Mah on a bunch of flights, it will take about 1050 Mah to recharge it.

My standard rule for receiver batteries is to absolutely NEVER fly more than 50% of the battery under any conditions. That gives you a safety factor incase you decide to go around a few more times, do more acrobatics than usual, and so on. Some of my club members have found that a single 8 minute flight on a gasser takes about 200 Mah out of the battery. So on a 2300 Mah A123 battery, that would be about 1000 Mah for safe use, and with 200 Mah per flight, that's five flights.

If your receiver/servo system can handle a 5 cell Nih battery pack, it can also handle a two cell LiFe or A123 battery without the hassle of a voltage regulator. I've run discharge curves on a 5 cell Nih battery pack, and a two cell A123 battery pack. The voltage at the start and end of the discharge curves are virtually identical.

Your results can and will vary. You absolutely must do the fly some flights, recharge the battery, see how much you put back in routine to see whats safe for each of your models.

With heavy wires, you can recharge these A123 cells from total discharge to full charge in 15 minutes with a high power charger such as the Cellpro PL6 and PL8 line. These chargers also show exactly how many milliamperes was put back into the battery. Many other quality chargers will also do the same. If your battery only has the balance cables, the maximum charge rate through the balance wires is about 2 Amps.

One of my club members flies those $$$$ wet turbine models. On my recommendation he switched over to A123 cells for both the receiver and jet power systems. He since switched everything to the A123 cells. They work, and work well.

Also a number of club members also are going to the LiFe batteries for their gasser models, both for receiver and ignition. Nice thing about these LiFe and A123 batteries, they hold their charge for a long long time, like many months. And they don't really care if you store them at 20%, 60% or 100% charge.

DennyV
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