What ah should I expect to get running a 48v 10.5ah battery

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mcristiani   10 W

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What ah should I expect to get running a 48v 10.5ah battery

Post by mcristiani » Jan 02 2018 9:02pm

Hello,

If I purchased a well-built 13s pack, charged it fully - 54.6v, set the controller to max at 14a and rode it until it died on a normal temp day how many ah should I expect to see on a cycle analyst?

Not 10.5ah, I am thinking.

Follow on question... If there is 'dead space' that can't be accessed in any battery, would I get more cumulative ah out of a single 20ah battery instead of running two 10ah one after the other.

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amberwolf   100 GW

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Re: What ah should I expect to get running a 48v 10.5ah battery

Post by amberwolf » Jan 03 2018 1:33am

it depends

due to the peukert effect, you'll always get more out of paralleling two small batteries than using one till it's empty then starting on the other.

as to whether a different battery will give you more or not, that depends on whether it's got the same, better, or worse cells in it, and how it's bms, if any, is setup for lvc and hvc, compared to the first battery.

if everything is exactly the same between a 20ah battery and a 10ah battery except the number of parallel cells, then the 20ah battery would last longer than two 10ah used one after the other rather than in parallel. but it would last exactly the same as both the 10ah used in parallel.

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dogman dan   100 GW

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Re: What ah should I expect to get running a 48v 10.5ah battery

Post by dogman dan » Jan 03 2018 10:45am

Lets assume its a pretty darn high quality battery, and it does put out 10.5 ah when tested at the factory.

Chances are, that test was not a 14 amps test, but 5 or so. Because of Peukerts effect, you will not get the full 10.5 amps riding at 14 amps. ( this should be a 20-25 mph cruise) However, its entirely plausible that you would get very close to 10 ah, when its new, and perfectly balanced fully charged.

Ride slower, and you might even see the full 10.5 ah.

But,, we don't ride in labs, or get perfect charges every ride, or ride in good weather every ride. And the battery is only new for a few months. Cold costs you, but wind does too, increasing the amps you have to pull from the battery, increasing pukerts. Long term, if you can wring 9 ah from it any ride for a few years, you did good.

Cheap ass battery, you might be doing good to ever get 9 ah out of it, brand new.

And then you also want to leave some reserve in there anyway, so my old rule of thumb of one ah per mile for 36v, and .75 ah per mile for 48v, when traveling at 20-25 mph, is still valid. Hell yes you can get more when you want to, but an ah per mile is what you should count on, going fast as you can on either voltage.

And two miles per ah, if you ride slow and pedal more.

But if you bump up to 20 ah, and still pull only 14 amps continous, you will be back close to the factory test amps, and should see very close to the full amount from a good battery. Or, slow to 8 amps, to get the same thing out of the 10 ah. It also helps if the seller builds an 11 ah pack, but calls it 10 ah. Many of the better batteries will be doing this, not claiming the theoretical capacity, but the actual practical capacity you could expect in the real world.

Its all about lowering the discharge rate per cell. The lower you get it, the happier the cell is. It makes no heat discharging, which is where that ah went when you hauled ass on the small battery.

For my long rides, I loved to run 30 ah or more, and still keep the amps very low. No voltage sag under load means maximum capacity and distance. I could wring 80 miles from 30 ah of 48v that way.

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Re: What ah should I expect to get running a 48v 10.5ah battery

Post by mcristiani » Jan 03 2018 12:09pm

Info above is great. thanks.

I want to add some additional info:

Just confirming we are all talking in terms of li-ion batteries here. Not trained as an engineer, I believe Peukert while originally identified for la batteries, it also applies to li-ion - to some degree?

i always pedal hard. 14ah is really only off the line or on a hill. Cap is 14. I expect I usually run 6-9a draw.

Thanks again.

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Re: What ah should I expect to get running a 48v 10.5ah battery

Post by rote » Jan 03 2018 11:54pm

Good info amberwolf and dogman dan, thanks. mcristiani, I recently had a similar question for myself.

My 2 cents:
I have the same battery specs (13s 5P; 48v nominal) but I got a cheap generic Chinese pack off amazon. From info gathered off this site, I calibrated my Cycle Analyst to RShunt 4.5 mOhm. I also run a LCD3 and the wattage is usually a little off from the CA, with the CA showing a little less watts while throttling. With this setting, I generally yield about 6.9-7 Ah (from 54.6V to ~45V) as indicated by the CA. (I usually pedal half the time and/or with PAS on relatively flat roads.) Disappointed, I recently set the RShunt value to 4.0 mOhm - haven't fully tested it out yet. Maybe I'll get 8 Ah. I don't know, we'll see.

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dogman dan   100 GW

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Re: What ah should I expect to get running a 48v 10.5ah battery

Post by dogman dan » Jan 04 2018 9:00am

When you push a lithium battery very hard, it heats up. This is from internal resistance, and costs you capacity. It takes watt hours to heat the battery cells. I'm not sure if this is perkerts effect per se, but there is peukerts effect on all batteries. Just not as much as with lead. Once you see a lot of voltage sag, like 6v under load or more, you will also notice the battery gets at least warm, or even hot.

Might keep an eye on that thing rote. its got some weak cells in there.

My cheap ass battery was similar, a 20 ah pack put out at best 18 ah new, at a 1c discharge rate. So it had at least one poor cell in there. A year later, it did this to my house while charging.

Charge your battery outside, if its performing that bad.
P2110070.JPG

mcristiani   10 W

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Re: What ah should I expect to get running a 48v 10.5ah battery

Post by mcristiani » Jan 04 2018 7:35pm

Holy S#4t. That's your house?

What do you think happened? Battery caught fire charging, but any idea why? And it had a bms?

I built a 13s3p - see thread below - that won't get above 52.7 on charge. When I ride it I was only getting 4ah. I found one block that was crashing and replaced it. I think there might be another block that is also bad, but need to get some more test runs on it. I am using ncrb cells.

https://endless-sphere.com/forums/viewt ... =2&t=89589

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Re: What ah should I expect to get running a 48v 10.5ah battery

Post by mcristiani » Jan 05 2018 3:31pm

I rode battery #3 today into work. I am at <3ah on a Cycle Analyst and already getting down to a lower limit of 42v with full load of 14a. It then stabilizes around 44v while cruising at 8-9a.

Also to re-state, I can't get past 52.7v on a full charge at the moment.

I have lvc on controller at 40v. I was thinking I would ride it home - as far as I can get - to see if I can get the controller based lvc to trigger. If this trips before the bms then I am thinking there isn't a directly flagrant block that is dead i.e. nothing has crashed to 2.5v yet.

In regards to the BMS, I have been able to gather two data points.
#1 - I used a volt meter to find a block that kept crashing. The BMS would trip when the voltage for that block hit 2.5v.
#2 - A friend put the bms on a bench and saw that it cuts off at 33v and then turns back on when voltage goes back up to 40v.

Once I am home, I will open it up and take a look at individual block voltage: at rest, under load, after charging is complete.

Any thoughts/ideas would be appreciated.

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Re: What ah should I expect to get running a 48v 10.5ah battery

Post by rote » Jun 13 2018 3:51pm

Hey guys, to update. For the first year I owned a CA, I was calibrating the RShunt value to match my KT-LCD3 display as I assumed the latter was accurate. After doing so (at the ~4.5 mOhms), I was disappointed in my battery pack's output of ~7Ah as mentioned above.

Well, after getting a pretty accurate watt/amp meter to use for charging, I decided to see how much Wh I was putting back in the battery. The battery meter showed almost a 100 Wh difference from the CA's reading (eg, battery meter shows input of 450 Wh, while the CA would show about 350 Wh burned (and about 7Ah)). I began to realize that it was the LCD3 that was likely inaccurate (volt reading is fine, but I think the chip that calculates or measures? the Amps to display the Watts is not accurate, or soldering the blue and white CA wires to the KT shunt might've also affected the accuracy. Last, as far as I can tell, you can't calibrate the LCD3). So I set the RShunt value to 3.55 mOhms -- now the CA's Wh burned nearly matches the battery meter's Wh inputted. And now I'm getting about 9.5 Ah out of my pack. :)

dogman, wow, I hope no one was hurt.

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