lipo mini cut-out at 1,5C

[cwah]

Hello there,

Today I was cycling with my 20s8AH 30C zippy (4 x 5s8AH) and it suddently become saggy at only 1000W peak. That's around 1,5C for my pack.

I was bulk charging to 81,5V (4,1V/cell) without balancing them, but it shouldn't be a problem as my pack was quite uniform.

I plugged my lipo alarm and all my cells were around 3,9V (after few km), but one of my pack has a balance cable cut out, so I couldn't read the cell voltage.

How come I have sag at such a low C rate, could a pack makes the whole lot of 4 lipo saggy? And if it's only the balance cable that is cutted of, it should still be ok isn't it?

[cwah]

..

[neptronix]

You need to define what saggy is.

How many volts are you dropping from resting voltage when you apply the load?

How many amps are you seeing that sag at?

[cwah]

Voltage drop from 80V to 79V. I put 9amps on it. That's really low and I shouldn't have any sag.

But I keep having start and stop. Very bad cycling experience.

[neptronix]

Voltage drop from 80V to 79V. I put 9amps on it. That's really low and I shouldn't have any sag.

But I keep having start and stop. Very bad cycling experience.

Completely normal.
You've got 20 cells, each cell is sagging by only 0.05v when you apply a 9 amp load. That is exceptional.

If you were to look at that on a graph, it would barely register.

I think you must have not seen how other batteries perform under a similar condition...
If you double your amp hours, you will cut your voltage sag in half, BTW.

As it is now, you are losing a whopping 1-1.5% of your power to sag, thus your batteries are 98.5-99% efficient at that voltage. This is drastically better than >95% of commercialized battery designs.

[cwah]

But is it normal to have a lot of "mini stop" while I'm ridding. It's really unpleasant, it's like I stop using the throttle from time to time.

What was strange is that from 77V and lower I didn't have any sag. Not sure to understand what happened.

Was the sag was a result of the high voltage (the sag was at 80V but disapeared at 77V) or was it because I used my lipo immediately after charge? I did a break of 1 hour, maybe the cells were able to rest and no more sag

[neptronix]

What do you mean by mini stops? is your power cutting out?

You do have sag below 77v, it's just not as notable when you are at the nominal charged voltage of RC Lipos ( 3.85v/cell ). All batteries have an internal resistance curve, and right in the middle of the charge tends to be where they perform at their best.

Your battery sag is normal and nothing to worry about, all RC lipos sag to some degree, from 1C, all the way to their maximum C rating, where they will sag like crazy.

Go play with some SLA or lifepo4 ( non-a123 lifepo4 ) and you will be very grateful for what you have!

But is it normal to have a lot of "mini stop" while I'm ridding. It's really unpleasant, it's like I stop using the throttle from time to time.

What was strange is that from 77V and lower I didn't have any sag. Not sure to understand what happened.

Was the sag was a result of the high voltage (the sag was at 80V but disapeared at 77V) or was it because I used my lipo immediately after charge? I did a break of 1 hour, maybe the cells were able to rest and no more sag

[cwah]

my 36V10AH Limn2o4 battery from conhismotor never had sag! But I only had 2/3 of the advertised capacity

What is happening is my bike is moving like I was stopping the throttle from time to time. That's what is sag for me: mini-stop where the bike doesn't run anymore for half a second then continue working.


Too bad to have sag with 30C lipo. I was thinking about getting the 15C zippy for their price, would that be worse?

[neptronix]

my 36V10AH Limn2o4 battery from conhismotor never had sag! But I only had 2/3 of the advertised capacity

What is happening is my bike is moving like I was stopping the throttle from time to time. That's what is sag for me: mini-stop where the bike doesn't run anymore for half a second then continue working.

Too bad to have sag with 30C lipo. I was thinking about getting the 15C zippy for their price, would that be worse?

Yes, it had sag, absolutely. You have obviously not measured it. That battery puts out a fraction of power that your new RC Lipos can.

All batteries sag to some degree, unless maybe you are applying a 0.5C load on a 90C nanotech.. you probably need a 5 digit multimeter to measure the voltage drop...

Yes, the zippy 15C would have double or triple to triple the voltage drop per equivalent load and amp hours.

When the power suddenly cuts out, that is not sag. sag is when voltage drops, the battery makes heat, and you lose watt hours. It doesn't make your power cut out intermittently.

Are you running a cycle analyst with amp or speed limiting? what kind of motor and controller are you running?
9A seems like an awfully low amp rating...

[cwah]

oh ok, that's not sag then. It's mini cut out at 80V.

I use the cycle analyst to limit the amps to 9 to have enough range. I still have start around 1000W as the current limitation is not instant. I use conhismotor mini direct drive motor (250W 24V ) with Lyen racing controller (max 150V ). Crazy set up actually lol

Any idea what would be the reason for that?


ps: going to change the title

[neptronix]

oh ok, that's not sag then. It's mini cut out at 80V.

Any idea what would be the reason for that?

ps: going to change the title

Glad you recognized the difference. I was about to fly off the handle

Like i said, do you have a cycle analyst.. and why are you running only 9A?

Is your wiring screwy?
Have you tried things at 10S ( 38v? )

[cwah]

Yes, I use the cycle analyst (direct plug) to limit the curent. I only run at 9A to be able to go back home

At 9A I'm at 700W continuous. I usually do something like 10-20km distance when I'm out. If I get higher amps, I won't have enough power to go back home.


I used 10S16AH from time to time but I stopped using that. This problem only happened today, I was wondering if the voltage was too high.

What is screwy wiring?
BTW, that's my wiring setup:


I use a 24 pin ATX connector to be able to remove the controller when I have to

[neptronix]

Well, you may have a pin loose.

Also, why don't you use your controller to limit current? the higher the voltage, the slower winding the hub, the harder time that the cycle analyst has limiting the current, especially if the controller is set for a very high current.

[cwah]

But if I have a loose pin, shouldn't I have problem from 80V to 75V? My mini cut off stops from 77V onward.

I also use the controller to limit to 15A. But that's 1200W at 80V and too much power usage if I want to travel a bit longer

[dogman]

It's either the controller, or the CA limiting that's doing the cutouts.

I had a well worn, run hard controller start doing that on me. I never found out what exactly was happening, but the controller would turn off for little blips, always when under max throttle. It wasn't battery related, or low voltage from battery related. Something in the controller was popping and resetting. Or the controller, which was sensorless, was losing synch or something.

I suggest you up your amp limit on the CA and see if anything changes.

[cwah]

Ok, going to try without the CA amp limiter and see the result today

[cwah]

I've set the max amp to 30A on the CA. Still have this problem.

And it get even worse, the throttle completely stopped working from time to time. It was raining today, so maybe the connectors were wet, will see if I still have this problem when it's not raining.