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LIFE Battery Voltage for idiots


SoggyBoots
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SoggyBoots

Hi all just wondering if anyone can tell me if I'm making a mistake here.

I have recently acquired a new 2cell LIFE pack and am charging it up. When the charge is complete and I take it off the charger after about 30-60mins the voltage goes down to 6.6v I know this is nominal voltage but thought straight off the charger the battery would hold its charge at 7.2v or am I mistaken?

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I was doing some tests on a yacht the other day. Newly charged 2s LiFe, reading 6.6v with radio switched on, dropping to 6.4v under load (rudder servo and sail winch running).

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SoggyBoots
1 hour ago, Maria Freeman said:

I think LiFe batteries are 6.6 volts and LiPo’s are 7.2volts 

I thought that they were 3.6v per cell when charged and 3.3v per cell at nominal voltage or after some use

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Same with mine, they charge up to 3.6v per cell, but then drop back to 3.3v per cell very quickly and stay there. I have some 700 mah 2s turnigy packs in some models and they can see the voltage drop to below under 6v quite easily under load. 

Whereas my Lipos charge up to 4.2v per cell and then drop off more slowly.

One of the things with Life cells is that the resting voltage initially drops to 3.3 v per cell and then stays there until they are almost discharged and then drops off, with Lipos there is a steeper discharge curve so it's easier with a Lipo to use resting voltage as a measure of remaining capacity. My battery checker always under estimates how much is left in my Life cells.

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SoggyBoots
2 minutes ago, FrankS said:

Same with mine, they charge up to 3.6v per cell, but then drop back to 3.3v per cell very quickly and stay there. I have some 700 mah 2s turnigy packs in some models and they can see the voltage drop to below under 6v quite easily under load. 

Whereas my Lipos charge up to 4.2v per cell and then drop off more slowly.

One of the things with Life cells is that the resting voltage initially drops to 3.3 v per cell and then stays there until they are almost discharged and then drops off, with Lipos there is a steeper discharge curve so it's easier with a Lipo to use resting voltage as a measure of remaining capacity. My battery checker always under estimates how much is left in my Life cells.

Very good to know. I had my battery warning set for a similar voltage drop to lipo. I'll turn it up a few so that it lets me know as soon as it's starting to drop.

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Best plan is to operate the radio for a while and then note the voltage under load and then set an alarm just below that, set it too high and it will go off every time you try and move some servos. Unlike Lipos you can run down Life cells a bit more and they won't be damaged.

Here's a typical LiFe discharge curve at different rates, while typical the voltage drop under load will depend on the actual battery.

 

2s-6-6v-2000-mah-robitronic-life-battery-capacity.jpg

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SoggyBoots
1 hour ago, FrankS said:

Best plan is to operate the radio for a while and then note the voltage under load and then set an alarm just below that, set it too high and it will go off every time you try and move some servos. Unlike Lipos you can run down Life cells a bit more and they won't be damaged.

Here's a typical LiFe discharge curve at different rates, while typical the voltage drop under load will depend on the actual battery.

 

2s-6-6v-2000-mah-robitronic-life-battery-capacity.jpg

That's the plan can see under load I'm getting 6.4-6.5 so will set to 6.2 as a buffer

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I used to find that vapex lifepo4 packs ran at about 6.5v when in the model.

The voltage on all packs drops off after the charge (lead acid/ NiMH/ nicad/ lipo etc). 

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