Originally Posted by ronj100
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.