A123 Low Voltage Protection ?

[marc993turbo]

Hi there!

I am using A123 packs (2p3s) cells with my Brushless Maxx and Savage.

I am looking for a good low voltage protection since the lipo protectors are not usable with the A123 cells because of the different cut-off voltage...

The A123 should habe 2.0-2.1Volt and the common lipo cut off would be around 2,5-3,3 Volt.

Not very compatible...

The only good ESC for the A123s is the Schulze 32.170 i am using since the ESC calculates the cut-off value based on a percent value of the voltage it measures if the pack is connected with the esc.

Are you guys using Low voltage protection for your A123 packs at all?

Help would be nice.

Marc.

[zeropointbug]

I run A123 packs (7s, and 7s2p packs) I run no low voltage cut-off. There is absolutely no reason to use it for these cells.

[MetalMan]

When I run A123s I use Castle Creations controllers, which feature an adjustable cutoff. I set mine for 2v/cell. However, like zeropointbug said, it's not really needed. When these cells are nearing the end of their charge, they DUMP HARD AND FAST. Just make sure you stop running when they do dump.

[tashpop]

i was going to run one, but looks like that'll be one less thing to worry about.

In my experience, the packs dump long before the minimum voltage is reached. The only way that I can see hurting an A123 pack is if you accidentally leave it plugged in and the servo just sucks it completely dry.

[zeropointbug]

That is exactly true AAngel.... a guy over at the RCU forum (IIRC) has A LOT of testing on them and found you need to over discharge them, and HOLD them there for an extended period in order for them to be damaged, and by damaged, I mean loose some capacity, and slightly higher cell resistance.

ALTHOUGH, one thing that could cause problems is if one of your cells is significantly lower than the rest, and you overdischarge and then you reverse the lower cell, and that would probably do alot more damage, maybe even make it unusable.

[marc993turbo]

Originally Posted by AAngel

In my experience, the packs dump long before the minimum voltage is reached. The only way that I can see hurting an A123 pack is if you accidentally leave it plugged in and the servo just sucks it completely dry.

... thanks for your replies!

I think i am a little bit to cautious when it comes to lipos and fepo4 since my experiences with the last generation nimhs were bad enough...

...drain them a few seconds too long and - buff, the next run the cells have 200mAH capacity less.

So i read all the horror storys about those sensible new technology power cells and became to cautious...

But it seems for me that the fepo4s are much less sensible than the last generation nimhs.

Till now the fepo4´s are running very well.

But the best for me is the way i can charge the cells: put them on my schulze isl 8-936 and puff - they will be charged with full 10Ampere current in a few minutes!

Two packs of A123s and i can run as long as i want!

That was the way i wanted to run my rc cars which was not possible with nimh cells...

So i will take your advice, run till they drop their voltage and stop.

thanks!

Marc.

[Xtremespeed]

Don't be afraid to run them with no voltage protection. I run mine until it dumps. You can't miss it. Feels like a Wal-Mart radio control car when it dumps. Have never seen the voltage drop low enough to cause any damage. A123's are tough.

[zeropointbug]

Yes, they dump super quick, when I do speed runs for a whole runtime, speeding back and forth on a dirt road... then I do one speeding down the road 1/4 mile away, then coming back I suddenly have no power.... OOPS! I have to run and get it because it has no energy left.

I am still surprised how quickly they dump, and there is only maybe 10 millivolts difference between almost fresh pack and the instant before it dumps, very flat discharging curve. I am starting to get the feel for seeing the dump before it happens though, it takes time.

BTW, what do most ppl run their lipo's to? I am hearin various numbers like some do 90% DOD, and others do 80%. I would like to know.