Ah usage

Howie

Howie

10 mW
Joined
Mar 8, 2011
Messages
33
Location
Michigan
Hi,

I've been running 20s of the 8000mAh Zippys and love them so far. I've read that it helps extend the life of the battery to not discharge further than 80% and I'm confused here. Let me explain this and hopefully someone can point out what is probably the obvious... :)

8000mAh x 80% = 6400mAh. So I watch the cycle analyst and try not to exhaust more than about 6Ah. The numbers vary but what I'm seeing used, and what I'm putting back in, these don't match up. For instance.... I just went for a ride after installing the 3 way switch and wanted to try the 120% speed setting, and I got 44mph :). According to the CA, I used 7Ah but the first battery I just charged took 3220mah. The other 3 will be about the same according to past performance.

This seems like one of those things that should be obvious but I can't figure this out. If we figure each battery expends 3.2Ah, why is the CA telling me I used 7Ah? The 3220mAh I'm putting back into the 8000mAh batteries is only about 40% of their capacity, so could I actually double my usage before charging?

Basically, how do I determine how many Ah per battery I've used if the CA is giving me a totally different figure?
 
I never pay attention to the ah usage. Go by the voltage, It will be much easier. With 20s lipo, 74V is about right.
 
It is possible that your cycle analyst is not correctly calibrated. If so, it will be giving you exaggerated amp display also, by a factor of two.

Like wes said, go off voltage not and not AH, that will give you the real picture.

24_dischargingmechanics.gif


If you wanted to do a ~90% discharge, you would charge to 4.15v/cell and then stop discharging at around 3.6v/cell ( resting voltage, not including sag from when you are drawing peak amps.. ).
 
Something isn't calibrated.
 
liveforphysics said:
Something isn't calibrated.
Click to expand...

Agreed..

On the bike, what controller do you have ? and what do you register on the CA at low speed and full throttle ( how many watts or amps is the CA reporting when accelerating ? )

The charger is likely right, telling you what you put back in, i suspect the CA on the bike is the one out of wack..
 
Indeed. Place a current clamp on the charge lead and make sure that the current in matches the negative current on the CA. If it doesn't quite match up you might need to adjust the shunt resistance from the 0.25 mOhm by a few hundredths of a mOhm. Rinse repeat and when the two are equivalent you should be better placed to monitor currents.
 
Have you calibrated the CA to your controller? You need to make sure the Rshunt value on your CA matches up with your controller, eg, for my Lyen 12 Fet it is 2.7mohm, and for my 24 Fet controller it is 1. If i just hot swapped my CA between the two controllers without calibrating the Amp readings would be all out of whack.

EDIT: I meant to mention, this is presuming your CA is a DP, not a standalone
 
This is how I calibrated my CA shunt value which should be pretty close.

http://endless-sphere.com/forums/viewtopic.php?f=2&t=28407
 
I hope I don't miss anything here but if I do, just let me know...



TylerDurden said:
Are you charging in series and operating in parallel? Vice-versa?
Click to expand...

I charge each 5s pack individually and run all 4 packs in series so it's 20s1p. I charge to 4.15 and and I haven't logged the cycles, but I they seem to always go on the charger at 3.9 at the highest to 3.65 at the lowest and I'd guess average about 3.8 or so. I balance charged the first two cycles at 1c and all cells are within .02 according to the battery medic so I just do a faster non balance charge now but watch for anything that suggests another balance charge.

Ypedal said:
liveforphysics said:
Something isn't calibrated.
Click to expand...

Agreed..

On the bike, what controller do you have ? and what do you register on the CA at low speed and full throttle ( how many watts or amps is the CA reporting when accelerating ? )

The charger is likely right, telling you what you put back in, i suspect the CA on the bike is the one out of wack..
Click to expand...

I have Lyens 12 fet. I'm sure I've seen 3900W under acceleration and 45-49 amps. I don't have anything to judge against since this is the first and only ebike I've ridden, but it seems like the wattage I see while riding is higher than it should be. That's based solely on what I read and peoples descriptions so there may be something to that. The Amax on the CA right now shows 130. I see 115 or so pretty much always but figured that was the block time thing letting the current spike higher, who knows? If it matters, my wh/mi is pretty rough. I've seen 80wh/mi and 50-60 is pretty normal, not sure if that sounds right. Also, on the profile I have loaded in the controller, the phase current is 88 and the rated current is 35.

Edit: I haven't calibrated the CA(DP) to the controller, I just figured they'd be fine together, I was totally ignorant to that entirely. :oops:
 
As I said in my post Howie, have you set the Rshunt value in the Cycle Analyst? In Advanced setup, go to the Rshunt value, and this should be set at 2.7 for a Lyen 12 Fet. From new, this value in the CA will be 1, which if left at this will give you incorrect readings. Check this first, as I suspect you have left this value at 1 - change it to 2.7.
 
Philistine said:
As I said in my post Howie, have you set the Rshunt value in the Cycle Analyst? In Advanced setup, go to the Rshunt value, and this should be set at 2.7 for a Lyen 12 Fet. From new, this value in the CA will be 1, which if left at this will give you incorrect readings. Check this first, as I suspect you have left this value at 1 - change it to 2.7.
Click to expand...

You called it. I don't remember not going through the advanced setup, but the value was 1. I'll give it a shot tomorrow and see how it goes. I did buy two 900 lumen flashlights for headlights, maybe I'll go tonight. :)

I appreciate the help!
 
on a similar note (not to hijack this thread...)

i am using a 12s setup. my starting voltage was 49.2 (4.1 X 12) and my end voltage was around 44.6 (~3.7 X 12). when i charged up my lipos, i ended up putting in about 10 ah. total capacity is 15ah. my charger said i was down to 23% when i went to charge. i started at 85% so according to my charger, i used up slightly more than 60%?

from this thread, it looks like i should go off volts, not ah. i expected to get a little more range out of my batteries. do these numbers looks correct?

i'm going off CycleAnalyst numbers (which are somewhat accurately calibrated on my bike) and info from my charger.
 
Well, you could discharge down to 3.6v/cell or even 3.5v/cell average.. so at 3.7v/cell you still had some juice left. Maybe 10-15 percent or so.

You can go off amp hours if your amp metering device is very well calibrated.
Remember also that batteries very slowly rise up in voltage after being discharged hard. I've had lipos that had a 9C discharge rate put on them get pretty warm.. and go from 3.3v/cell average to 3.45v/cell average in about 30 mins.

But voltage doesn't lie. Even the worst voltage reading devices aren't usually off by more than 0.01v.
 
Ypedal said:
neptronix said:
Even the worst voltage reading devices aren't usually off by more than 0.01v.
Click to expand...

Wrong. :lol:

The HK battery medics can be off by much more..!
Click to expand...

Really! I suppose i was referring to something more like a low grade multimeter / watt meter / cycle analyst. I've never seen much in the way of different voltage readings from them.

I was thinking of buying 4 battery medics today.. they're really that bad huh?
 
I have two battery medics and I see them pretty consistently off from what my charger says. I have a 1010+b and I trust the charger more than the battery medics.

Trusting the voltage makes sense, but it seems there is a whole lot of meat in the 3.75 to 3.85 range and I'd hate to get caught too far from home and have the voltage start to drop quick. I tried the shunt at 2.7 and the CA said I used 2.68Ah and the charger put back 3.3Ah. The cells were 3.85V per cell going back on the charger. I just charged to 4.15V and rode 11-12 miles, CA said I used 5.239Ah, cells are 3.79V going on the charger. Also, Amax was 69.9 and the current and watts seem to be in a more reasonable range. I'd see 3500-3900W tops under WOT from a dead stop.

Is it fair to just keep checking the Ah reported on the CA vs what the charger is putting back in and adjusting accordingly until I find the setting I like or will the efficiency of the charger skew that? I'd like to leave a little emergency buffer built in with the CA showing I've used more Ah than I really have, just not too much. :)
 
The controller is the 12 x 4110 extreme modder that I've seen a lot of people mention, and if I recall, he mentioned anything over 50A could lead to problems with the phase wires. I don't want to melt the phase wires but I'm ready to upgrade them to 10 or 12ga if it happens, or next Winter.

I just pulled the first pack off the charger and it put in 5.02Ah after the CA said I used 5.24 or so. That little extra in the tank is what I was looking for, and if I used roughly 5Ah on that last 11 mile or so ride, I shouldn't have any problem getting 15 miles out of the 6.4Ah that equals the 80%. Maybe more if I'm not WOT so much, and pedal along too. :)
 
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