Life Battery Question
 

So this may seem like a dumb question, but I am going to ask anyways. right now I am running Lipo batteries with my brushless sct's. But I am considering switching to LiFe batteries My charger already will charge them and they dont have all the hazards of LiPo. But lower voltage. what I m wondering is since both my brushless systems in my sct's are rated to handle up to 8.4v NIMH how much of a strain would it be to run a 3s LiFe rated at 9.9v? Could I just get an ESC fan and run just fine? or would this fry my esc?

Good question because a 8.4 NIMH pack is actually close to and maybe over 10v when it's fully chargerd, BUT it doesn't stay there very long under load. So honestly I don't know....Duster and a few others should be able to tell you.

7 cell nimh packs will show over 10V sometimes at full charge, but rest assured the slightest load will bring that down real fast.

Some ESC/motors can handle the extra without real problems, but others may cook right away. In my experience Novak controllers will fry with any increase past the rated limit. Castle controllers are typically underrated a bit and will hold up. But, if you are not comfortable with possibly smoking something then you should not do it. Pick up a lower Kv motor to go with your Sidewinder and you can run up to 11.1V if you like within the rated limits.

+2 Don’t make the rather common mistake of thinking nimh charge Voltage is the same as discharge Voltage. Due to internal resistance they will be considerably different. As they age and the charge Voltage goes up the discharge Voltage goes down even.

Back to the life, aren’t they 10.8 Volts fully charged for a 3s, and come close to holding that for a while? Much higher than 7 nimh under load , seems kinda risky for a 7 cell nimh rated controller. But if it’s rated for 3s lipo no problem.

I'd only try a 3S Life if your electronics are 3S rated. 3S life will be 10.8v when charged (3.6v/cell) as pointed out. Its usually not just a matter of extra cooling, usually there's a weak link like the BEC in the esc that won't tolerate the extra voltage.

LiFes are also heavier than lipos, about 25% more so you're trading down in voltage and increasing weight as opposed to lipo.

The 'danger' of lipo is much overhyped imho.

Hmm good to know I thought they were 9.9v just because that's what the website I was looking at stated. If its higher than that not going to do it. I just keep having issues with lipos I balance them everytime and have all my esc's set for lipo cut off but some how have managed to fry 2 in as many months. :( thanks for the input guys

My suggestion and experience is that if you can handle 8.4 you can handle 9.9 provided that you don't lock up the drive train and hammer the throttle. I've seen speedo's rated for 4s fry on 2s when someone tries to bring a broken car into the pits and keeps hammering the throttle and smokes the speedo.

So ... on to the specifics, could you post what brnad and model your speedo is. That will help us figure out how many amps/volts your speedo can handle which would make it easier to give you a definitive answer.

LiFe is 3.3v/cell 'nominal' where lipo is 3.7v/cell 'nominal'. Fully charged LiFe is 3.6v/cell where lipo is 4.2v/cell fully charged. The nominal voltage is supposed to approximate the voltage under discharge conditions, but its of little real use other than to help confuse the issue.


The 9.9v for LiFe is no diff than saying a 3S lipo is 11.1v (which when charged its 12.6v).

Associated SC10 W/Havoc 8.5, Traxxas E-Revo W/HV Pro 7.5, Losi Strike W/Sidewinder 5700KV

so really it would be running at 7.2v? for a 2s Life?

Thats correct, 7.2v, 2S LiFe, fully charged.