How do i figure range from collected e-meter 2 data?

[Jammied]

Today I hooked up my E-meter 2 just to check max watts and mah used during a 2.5 mile trip one way. I recorded on the 2.5 miles home also. I am currently using 36v 18ah SLA. It is a Dillenger 350w geared front hub on a Kent monterey Trike with a 7spd rear free wheel.

So the 2.5 mile trip on the way to town with a tail wind and a steady speed of 10mph I used 616ma
The ride home into the wind and a steady speed of 5mph I used 855mah

Starting voltage was 40.42v and when I returned home it was 39.17v and is showing a low voltage sag when under power of 36.92v. It also had a peak watts of 566w and a peak of 15.2a and I believe the controller is set to a max of 15a or so?

So how do I calculate the the distance I can travel on a charge with these numbers?? Sorry I'm a noob and didn't find the info when I searched here on the sphere

 

[Rassy]

I always get a kick how rc guys always like to talk in mah instead of amp hours. But that is beside the point. You should be looking at Watt Hours instead of Amp Hours when trying to figure your potential range. I'm also not sure if you are really interested in your range using the SLA since other posts indicate you are looking at other batteries.

So in a perfect world you went 5 miles and used about 1.5 AH from your 18 AH battery so under the same conditions you would expect to go 60 miles on a fully charged 18 AH battery. But, on your test runs both the speeds and the conditions were very different on each leg of your trip. Plus there is the variable pedal power you may have contributed. Plus SLA will seldom deliver their rated AH.. Plus, the actual Watts you use is dependent on the voltage, and due to both voltage sag and the voltage discharge curve of the battery your voltage at any moment may have been anywhere between 37 volts and 40 volts and maybe even more or less. So to help remove these variables the Watt Hours used makes a better basis for determining the range you can expect from a certain size battery. Also keep in mind that batteries don't usually like to be run to much over 80% DOD.

I am aware I didn't answer your question, but I don't think your question has a simple answer. Many here like to run their battery down until it quits in order to determine it's true capacity (Watt Hours, not actual miles covered in the test). I don't like to "torture" my battery that way, so I like to keep my usage below the 80% DOD rated for the battery. However, it does happen, and last month I went on a 40 mile ride using a 500 Watt Hour battery (2 year old 48 Volt 10 AH LiFeP04). Ran out of juice at about 475 Watt Hours just 50 feet short of the finish.

 

[markz]

Yup you gotta look at it in terms of Volts times Amp-Hours = Watt-Hours.
I figure roughly 40Wh/Kilometer which is equal to 25Wh/Mile, that seems to be the average.

 

[Jammied]

OK then 1000mah=1ah so to convert one would simply take 616mah/1000= .616ah That should help the e-bike crowd figure ah from mah. HAHA just having fun. Not trying to hurt any feel goods

But yeah the variable would be the voltage to be able to figure wh/mile I should have data logged and then a average voltage for this trip would show in e-meter suite on the pc.

I am looking at different batteries but even with a different chemistry of battery the watts an hour should be very similar. Trying to figure what ah size and chemistry for a replacement now that other battery chemistries have come down in price. but I'm still not sure that a more expensive battery chemistry type will out last the SLA to make up the difference in cost?

 

[Rassy]

I understand the decision making. Over a decade ago my favorite ride was a delta recumbent trike with a front hub motor plus two more hub motors on a diy trailer, all 36V running from one throttle and up to 100 pounds of SLA in the trailer as needed for range, so that I could get up the final 20% grade to my house. Forget pedaling that without motor assistance. All the SLA was changed out for 48V LiFeP04 8 or 9 years ago.

Now my favorite ride is a tadpole trike with a crank drive and a 10 pound battery. I no longer live up that steep hill, but the tadpole has been up it with no problem. What's really nice is I can pedal along with no motor assistance when I feel like it, at least on the flat to moderate hills, so no more range anxiety since my route home in Eugene is basically flat.

 

[MadRhino]

The only precise measure of capacity is w/h. A/h being a variable capacity because it is dependant of voltage variations over the course of your ride. Since the voltage is getting lower with the distance that you ride, the A/h used in the first mile is not an indication of how much you will use in the 10th mile. You will use more A/h per mile, for every more mile that you ride. Using the w/h as a measure, you will have a reliable indication of your power usage per mile.

 

[amberwolf]

I am currently using 36v 18ah SLA.

Based on my experience, you can basically call that a 9Ah battery pack; it's not likely you'll get more than about half of it's rated capacity at the power levels even basic ebikes use.

Since range can be more precise with Wh vs Ah, we'll convert everything to that. Since you don't have the voltage tracked for teh whole trip you can just use 36v for the average on everything. If your power meter records Wh, then you should note that down as well as Ah, but use the Wh in the calculations.

(the reason Ah vs mAh is used is that Ah and V converts directly to Wh)

So to see how many Wh the battery pack has to start with, call that 36v * 9Ah = 324Wh. Call it 300Wh for a nice round number.

So the 2.5 mile trip on the way to town with a tail wind and a steady speed of 10mph I used 616ma
The ride home into the wind and a steady speed of 5mph I used 855mah

So teh trip out took .616Ah * 36v = 22.176Wh. Call it 22Wh.

The trip back took .855Ah * 36v = 30.78Wh. Call it 31Wh.

So it took about 53Wh to go 5 miles under those specific conditions at those specific speeds. 53Wh / 5 miles = 10.6Wh/mile. So call the efficiency of your ride about 11Wh/mile.

That means that if conditions are the same and you ride the same speeds, then 300Wh at 11Wh/mile will get you 300 / 11 = 27.27~ miles. Call it 27 miles range.


That's under just those specific conditions. If there's less headwind, all else the same, you'd get more range. IF there's more headwind, all else the same, you'd get less range. If you ride faster, you'll get less range. If you have hills, or more stops/starts, you'll get less range. Etc.


BTW, the Cycle Analyst will monitor all of this stuff directly, including speed, Wh/mile, etc, and although it can't tell you your range directly, it makes it easier to figure out.




Another BTW: while doing this isn't completely accurate, it's reasonably close: If you like to have a "gas gauge", you can run the battery down to empty, reset the meter to zero, then recharge it. As long as your meter can read negative Ah / Wh, this will then show you how much is "in" the battery. Take your first trip, and it'll "count down" toward zero. Get home, and recharge without resetting the meter; it should come relatively close to the number it did before.

(the exception is that with SLA, the Peukert effect can make charging inefficient too (it's what makes that 18Ah really only about 9Ah), and so the count would get progressively further off.)

 

[Jammied]

Thank you.
That is how I thought it should be figured but I used 39v and got like 24.04wh for the trip in and 33.345wh for the trip home. I thought I was using the correct equation but wanted to be sure. I was taking it fairly easy as another rider was with me on my Schwinn Meridan but the battery is bad so it was all leg work for her and I was pulling the baby buggy with my 2 yo in it.

Now the Schwnn has a 850watt DD front hub and uses 3x the wh the kent does but it is more like a electric moped then electric bike

But thanks now to decide whether it is worth the cost to swap to a different battery chemistry

 

[d8veh]

It's much better to only look at the Wh used because amp-hours change in size as the battery runs down, but watt-hours are constant.

You can't go by your battery's rating of 9Ah. the ratings can be wildly out. It's much better to run your battery down once to see how many watt-hours it gives, then all you have to do is compare your watt-hours used with the total that the battery gives to see how much further you go. each time you ride, your Wh/mile will be different, but after a while, you'll be able to see what affects it, so you can estimate what you'll use on any ride. You will also know what you need to do to reduce it.

 

[Jammied]

Exactly. So the variable would be the voltage. I used .616ah on the one way and .855ah on the way home. So I do know how many ah's I used but one could use the generic 36v as the voltage? That would be 36*1.471=31.396wh's so 31.396/5=6.72wh/m correct? But if the average voltage was higher or lower that will all change I do understand that because v*a=w and the voltage is changing constantly. So if I were to data log a full battery and maximum distance until depleted it would tell more of a true story other than the capacity will decline as the pack gets more charge/discharge cycles.

I just used the e-meter 2 because I already have it and was curious but with its data log feature I think maybe we could figure a more accurate proximity of total travel distance. Never used a CA so not sure what all of the functions it has available

 

[docw009]

Because of of energy lost in chemistry, I expect that watt-hrs shown when charging the battery will be more than watt-hours shown when running the motor. Last time I checked though, it seemed like I put in 20-25% more than I took out. Seem right?

 

[Jammied]

Seems correct.
Although I have been charging each SLA battery individually with a 4 port I-max charger. The weaker/older batteries always take more ah to recharge and is also how I know that I currently have a battery about to give up.

Might just be me and the way I recharge but it seems SLA batteries are very hard to almost impossible to find the capacity when recharging. Where as the lithium varieties seem to be easier to figure capacity from charging and discharging.

But I seen on ebay a seller selling 36v 4.4ah packs for the same price as one 12v 18ah SLA. But doesn't state what the bms is set up for? But 5 of these would be 22ah 792wh they are lg cells

 

[amberwolf]

Might just be me and the way I recharge but it seems SLA batteries are very hard to almost impossible to find the capacity when recharging. Where as the lithium varieties seem to be easier to figure capacity from charging and discharging.

That's the Peukert effect I posted above.

But I seen on ebay a seller selling 36v 4.4ah packs for the same price as one 12v 18ah SLA. But doesn't state what the bms is set up for? But 5 of these would be 22ah 792wh they are lg cells

Depending on how you use the batteries, I'd get one larger pack rather than paralleling smaller ones, because if teh smaller ones arent' capable of high enough discharge rates the BMS's might shutdown, cutting power off as you try to accelerate or go uphill. If the BMS's are rated too high for the cells in them (happens with smaller packs) you can end up being too hard on the cells so their lifespan is lower than it should be.

But if you're not hard on them then having smaller packs can help, as you can carry just the amount you need for the trip, and short trips you'll have a lighter battery, while longer trips you can parallel all of them.


Either way, the cost over time is usually a lot less for Li than lead, as long as you start out with Li packs that can supply the current you need iwthout sagging too much (meaning too high a load on the cells).


BTW, if you find Li packs taht seem to be a lot cheaper than other people's comparable Li packs, you might want to suspect that they are not good packs (often built with counterfeit cells, or re-shrinkwrapped junk/garbage cells like Ultrafire/etc).

Buy from a reputable vendor that isn't across an ocean from you so you can send them back or get them fixed if they do fail or arent' right in the first place. (and it's less likely that you would have to send them back or get them fixed if it is a reputable vendor).

 

[Jammied]

well this is the listing. But doesn't give specs for the BMS http://www.ebay.com/itm/NEW-LG-36V-4-4AH-BATTERY-PACK-18650-EBIKE-VAPE-POWERWALL-BATTERIES-20-CELLS-BMS-/172630688902?hash=item2831974486:g:nKUAAOSwuspY9YNZ

 

[Jammied]

Well as a side note I tested the Schwinn with the 850w DD hub today with the same 36v 18ah pack and the same 2.5 mile one way trip so 5 miles total.

On the way into town I used 1.531 ah so total of 55.16wh for 2.5 miles
on the way home it used 1.482ah so total of 53.35wh for that 2.5 miles
And a total of 108.51wh for the 5 miles so 21.7 wh/m

the range difference is interesting although did get a peak of 947w

 

[markz]

well this is the listing. But doesn't give specs for the BMS http://www.ebay.com/itm/NEW-LG-36V-4-4AH-BATTERY-PACK-18650-EBIKE-VAPE-POWERWALL-BATTERIES-20-CELLS-BMS-/172630688902?hash=item2831974486:g:nKUAAOSwuspY9YNZ

The ad states nothing of what LG cells actually are. I'd be very suspicious. Could be a cell thats rated very low in discharge.

 

[geoff57]

Hi
I tend to use LiPo cells from hobby king if they are good enough for the zero TT race bikes their good enough for me. The biggest cell they do is 5 Ah that's how they sell them as they sell mostly for the R/C market, to get a reasonable size battery pack you need to build them in parallel before building the individual packs bought are tested to match them this produces a good high capacity pack.
When ordering don't go for high discharge its not needed and is just a waist of money, the balance wires from the cells should be joined as long as they are in the right place mark the sub-packs to make sure there are no mistakes.
Go to Aliexpress for a charger and BMS for the charger I get one that puts out 1A per 5Ah so a 10ah battery pack requires a 2A charger. BMS's are sold with a stated max A discharge choose one that is over twice the rated value of the controller used so if the controller is rated at 800w and run at 36v then the formula you use is 1600W/36V=44.5A, you could go for a 40A BMS but I would go for a 50A.
While at hobby king pick up a cell monitor that measures cell voltage on the balance leads, it should have cell voltage and how close to the same voltage the cells are, leave a lead from the battery balance connections outside the battery pack to measure/plug in the meter, this is used only when still to test the pack and make sure the battery is in good condition.
This can help you to design a battery pack protect it and charge it. If you want a quick charge setup say 10A or more chargers can be bought or lower power chargers can be parallel up but if this is done then a HVC circuit must be built at a cell by cell level the BMS may not be quick enough to handle it the HVC is linked to a power cutoff circuit on the mains side of the charger/chargers.
A cheap basic type of BMS can be made using LVC and HVC boards the LVC circuit cuts the power if the voltage gets too low in any one cell, the rule of thumb is that if the LVC circuit kicks into often on a typical journey then charge the pack till the cell voltage reads 3.8v if the cell voltages are very diferent then do a balance charge if the cell voltage are very similar then you need a bigger battery pack or a booster pack in parallel, in an ideal world the LVC circuit should never activate.
That's how I build my battery packs but every one here is right you may buy a pack or make one in Ah's but once you have it the first thing you work out is the Wh's of the pack. For example a 36v 10 Ah battery pack has a capacity of 360Wh with a fair bet that you will be able to draw 300Wh before damaging the battery, once 300 Wh has been drawn measure the voltage of the battery pack a Lithium Ion or Polymer should be 3.3 v or more.
Geoff