Sla vs lifepo4 distance guess-timation question

[e-beach]

Hi all, another dumb question from “yours-truly”.

My bike has been running on 3- 12v- 12Ah (144 wh each) SLA’s in a 36v configuration.
I am now about to upgrade to LiFePo4’s but I am still confused as to how far I might be able to go on the batteries I am considering.

My existing SLA pack can get me about 12 miles maximum before the controller starts cutting out at 20v under load.

I am about to go to a 36v 15Ah LiFePo4 pack with these, per-cell specifications.

Normal capacity 15000mAh (15Ah)
Normal voltage 3.2V
Inter impedance <8mΩ
Maximum Charge Current 2C(30A)
Maximum Charge Voltage 3.65±0.05V
Maximum Continuous Discharge Current 10C(150A)
Discharge stop voltage 2.0V

Given the above data, about how far should my new pack take me?

Any help would be greatly appreciated!

[MadRhino]

In theory, adding 3 Ah would give you 20% more range.
Yet, your Lifepo4 are good quality and shouldn't sag as much as the lead, giving you another 10% at least
Add the fact that saving the weight of lead will make your bike more efficient, for another 10% maybe.

My guess is that your new Lifepo4 battery will extend your range by 40%
That is if you continue to feed the same power and ride the same speed of course.

[dumbass]

I converted 2 bikes from SLA to lifepo4 packs. The first was from twin 24v 18ah SLA to a single 24v 20ah 2c lifepo4. I don't believe in riding to cut off. But I can say I got at least as much range with the single life pack as I got from the twin SLA packs. And the SLA packs were still in very good condition so it was a fair comparison. The second was from a 24v 10ah SLA to the same 24v 20ah 2c life pack. At least 3 to 4 times the range.

One thing you need to remember when your comparing is compare apples to apples. Your SLA pack has heavy sag therefore, you are likely going slower then you will when you use Lifepo4. That added speed will consume more power. So if you want a true comparison you need to ride the same as you did with the SLA pack.

Bob

[Ykick]

What I know is that 12Ah SLA is really only legit 7Ah, maybe 8Ah on a good day for eBike application. 15Ah Lifepo4 will actually deliver closer to rating - probably an honest 12-13Ah legit eBike capacity? You'll probably use a few more Wh/mi due to less sag, as dumbass mentioned.

If you're getting 12 miles now with your SLA, 20 miles would be a very realistic estimate using 15Ah (rated) Lifepo4 battery from this century.

[dogman]

At what speed?

My rule of thumb for range for a 36v lithium battery at 20-25 mph is 1 ah per mile. This rule is intended for calulating a battery size for a certain distance commute, and includes a reserve that will get you home on the day you have a headwind, and avoids 100% discharges on most days.

So that's the minimum you can expect, 15 miles at full throttle. If you try, you should be able to make 30 miles for sure by riding 15-16 mph.

[Ykick]

He didn't give a speed DM and I completely agree but he says he's getting 12 miles from his current SLA (12Ah). If accurate, he must be running a fairly efficient setup and/or non-rocket. Ain't no way 12Ah SLA delivers much more than 7-8Ah legit capacity. That's why I stretched this estimate more than I normally would for WOT 36V/22A.

[e-beach]

At what speed?

At what is speed is correct.

I have been doing nothing but city riding with lots of stops and starts. Street riding at 20-25 with peddle assist when I can, but sidewalks when safer or faster. Around here afternoon traffic can be so slow that 7-10 mph on the sidewalks is faster then the city buses. A CA is in the future, but for now, I can only guess-timate around 10-11 mph average cause it takes 20-25 minutes to go the 3.5 miles from my place to the beach.

So, 15 miles seems a little short, but I would surly love the 30 miles!

[e-beach]

a fairly efficient setup and/or non-rocket.

Pretty much a non-rocket. I think my rocketing-rooster days are mostly behind me.

[Pure]

If you keep your speed at or under 20 MPH you can, with pretty good certainty, get about 1.5 miles per usable Ah. But you never want to use all 15Ah in a 15Ah pack. That's with no head wind, no pedaling, and no hills.

DM's estimation of 1 mile per Ah, leaves you with room to account for such things that we almost always encounter.

[dogman]

At average speeds under 15 mph, you'll see the 30 miles. My personal best range was at about 14 mph, and I went 39 miles on a 36v 20 ah. Even at 18 mph average, you'll see 25 miles for sure with no problems.

Don't hesitate to discharge a lifepo4 with bms till the bms clicks when you need to. BTW, a 36v 20 ah pingbattery will fit in the same physical space as your current slas, an weigh half as much. So if you really want range, go for the 20 ah.

You should see almost triple the range you get from your sla's, but your range on sla's is exceptional. Chances are, with less range anxiety you'll ride a bit faster and get 2.5x your current range.

[e-beach]

At average speeds under 15 mph, you'll see the 30 miles.

Thanks for that! A little less stress is always good. Definitely looking forward to a good ride to Dodger Stadium and a Clay Kershaw no-hitter!

[Pure]

Yeah speed (ie increased wind and rolling resistance) is a killer of Ah. The faster you go the more you use, and that amount is largely increased at anything over 20 mph. As I understand it, that's the speed that wind resistance/aerodynamics becomes a major factor.

[Ykick]

Wind/air resistance increases exponentially with speed. Something to the effect of doubling wind speed requires 8x multiplication of power. Example - if 200W pushes you through air @ 15MPH the same system would require 1600W to overcome wind resistance @ 30MPH.

[e-beach]

Example - if 200W pushes you through air @ 15MPH the same system would require 1600W to overcome wind resistance @ 30MPH.

mmmmmmm.....

Makes me wonder just what kind of fairing might be helpful in cutting through the wind for an upright bicycle........

Maybe not this one....




Or this one...


Time to give the concept a good think...

[n3glv]

Yeah speed (ie increased wind and rolling resistance) is a killer of Ah. The faster you go the more you use, and that amount is largely increased at anything over 20 mph. As I understand it, that's the speed that wind resistance/aerodynamics becomes a major factor.

Direct observations of my ezip 24v PM motor bike, 12mph 6.5Amps 14mph 13Amps!
Waiting for FedEx atm for my 40AH LiFEpo4!!!!!!
Will post range results, but I did 19mi with twin 10Ah SLA in parallel. (5.8 on single)
Double the capacity of sla, half the weight (18.8 vs 35lbs) and if the controller does
not cut me off, nearly 12v of working voltage span vs less than half that on SLA..
60mi? (dare I dream?)
Anyone know the cut-off for a stock currie '35A' pwm box? (min-max)

[dogman]

My personal best with the same size (about 700- 800wh) in watt hours was 39 miles. I was riding about 13-15 mph, and pedaling about 70watts.

Same pack took me 35 miles many times, at 18 mph. 60 is quite possible of course, by riding 20 miles with the motor off.

[e-beach]

My final outcome to my question was:

12ah SLA's got me 10-12 miles with little peddling.
15ah Headway LIFEPO4's 20-22 miles with little peddling.

Or about 60% further with LIFEPO4's