Totally confused by watts and amps

[Johnyy]

I have a Bafang BBS01B 36V 250W Mid Drive and a bullet battery on the downtube of 5.5 Ah and 187.2Wh. It's range is only about 10 miles, but to date that has been ok. Now I need a rear rack for panniers and want to significantly improve my range. I have seen threads here talking of 90 mile range (yes I have searched for answers). Quality batterys by Samsung or Panasonic would be good I do know. But I am completely confused about which measures I should be looking at to judge range - amps watts or what?. Seems I am dyslexic with electricity

For example here are 2 ebay items and I have a feeling one is better than the other, but I have no clue

36V 15Ah (with rear rack max 750W) -

48V 15Ah 500W 750W 1000W Rear Rack Lithium Ebike Battery Electric Bike Battery | eBay

36V 15Ah with 25A BMS Lithium Ebike Battery. 48V 15Ah with 30A BMS Lithium Ebike Battery. Battery Capacity: 15Ah. Fit Motors: 48V 500W / 750W / 1000W. Fit Motors: 36V 200W 250W 350W 500W 750W. 1× Lithium Battery with mounting plate.

www.ebay.co.uk

36V22.5Ah with rear rack -

https://www.ebay.co.uk/itm/393937497492?hash=item5bb8812d94:g:IJIAAOSwHytjFw-5&amdata=enc:AQAIAAAA4JvYcLvyZOvlzYBIdfsejv7gVecYn/7RdOfLErvDc+GcL0nPyxpvj9TFE2aIiGM91sqrGy9Wxgien0fmDsy8bJNkAS5L12RpN3p8CPgu2tfIapEayshjrrX0hqnSV88xxqcjkPKUrlM3o9t4rauYFVZ3Bm/pYUB9chCsj0Qk8ymnhqiCtZzDxlhKQq29DM+MumAVaNK3HqnxTC9bysXHeFfrmSAkQ5ccA6QBlmPffROvFs9NpPydvstGk9ANrclKHScvyrUWQ/rvfhGj0VeG5JIOdiohQJqjIDCMBVAZ3wT4|tkp:Bk9SR8bGgOH3YQ

Any help deciphering all this would be appreciated

 

[soundwave]

more ah means more range and bigger capacity

 

[matthewslack]

It is not watts or amps. For capacity it is watt-hours, Wh, and amp-hours, Ah. Watt-hours is equal to amp-hours times nominal voltage, so 22.5Ah at 36 volts is 810Wh.

Watts and amps are relevant when considering maximum power capability, irrelevant when looking at capacity.

Use the right units, it might look like a convenient shortcut to say watts instead of watt-hours but it just gets confusing.

810Wh means the battery can supply 810 watts for an hour, or fewer watts for more hours, say 200 for about 4 hours.

 

[StuartsProjects]

I have a Bafang BBS01B 36V 250W Mid Drive and a bullet battery on the downtube of 5.5 Ah and 187.2Wh. It's range is only about 10 miles,

OK, so you have a benchmark.

Talk of distance that others get is going to depend on terain, the bike and the amount of effort the cyclist puts it. You could talk about what distance is normal for weeks.

However, if your 5.5Ahr battery is working OK and it does 10 miles, then a battery of 11Ahr (twice the Ahr) at the same voltage would be expected to do twice the distance, so 20 miles.

Convert to Watt hours if you want, but if the battery voltages are the same, you dont have to.

 

[saneagle]

There are three important characteristics when choosing a battery in order of importance:
1. Power or current rating. The battery needs to be able to provide the current that the motor's controller allows. In your case that's 18 amps, but you need a safety margin, so choose a 25A battery. If they don't tell you the current rating, you can work it out from the power rating 500w divided by 36v = 13.8A, but the problem is that they might mean that it's for a bike with a 500w controller, which is typically 22A at 36v. If you're lucky, they will show a specification in the listing. You can look down that and normally see max current = xxxA or max burst current = xxA.
2. Capacity is more straight forward. The more you have, the further you can go. As said above, it's expessed in AH or WH. You can convert from AH to WH by multiplying by the battery voltage and WH to AH by dividing.
3. Weight. The heavier the battery, the heavier you bike. Even 1kg makes a difference, so you should always make sure that you get enough capacity for your ride, but don't make your bike too heavy to be a pain when you ride to the shop to get a newspaper. Different cells of the same weight can have different capacities. It's possible to have a 2kg 36v 15AH battery or a 4kg one, so always check the battery's weight.

Additionally, you could include battery life. You can get LiFePO4 batteries in the same case as normal ones that last four times as long (effectively forever), but LifePO4 is much heavier - double what a normal one would weigh for the same capacity and takes more space, so a typical Dolphin, Silver Fish or Hailong type wouldn't be a high capacity one.

You could also think about cell quality, which is very complicated. If you run the battery well within its rating, cell qulity isn't so important. Some Chinese brand ones can last very well, but that doesn't mean they all do. Probably best to stick with known brands, but nearly all batteries come from China, and they sometimes put fake ones in or lie about what's inside, so best not to take that too seriously. You can get all of the above perfect to your specifications, but the guy who built it did it in a very cheap and/or uncontrolled way, so a weld breaks after a week. How can you plan for that?

Both the batteries that you linked can comfortably provide 20A.

 

[Woosh]

Seems I am dyslexic with electricity

1 Volt * 1 Amp = 1 Watt
1 Volt * 1 Amp * 1 Hour = 1 WH (spell: one watt hour)

5.5 Ah and 187.2Wh

Your bike runs on 36 Volts (average), your battery is rated like this:
36 Volt * 5.5 Amp * Hour = 198 WH (Watt Hours)

A new 36V 15AH battery gives you 540WH, roughly 3 times the range of your old battery.
A new 36V 22.5AH battery gives you 810 WH, about 4 times the range of your old battery.

It's good to know what kind of things those units (Volt, Amp, Watt and Watt Hour) measure but not necessary, what's important in choosing a battery is the insurance, service and guarantee because they are sealed units and not user serviceable except for the fuse which is accessible from the outside. Also, batteries don't last forever, you should think of recycling the old batteries and chargers after 5 years.

 

[Ocsid]

Also, batteries don't last forever, you should think of recycling the old batteries and chargers after 5 years.

Why and how does a charger "age"?
I can see non identical batteries, possibly resulting for changes /advances in technology, could need a different charger/ or routine, but surely if replacing a like for like battery, the original charger will be as suitable today as it was 5 years ago?

 

[Woosh]

it's a relative risk.
Over time, components age and degrade, especially paper capacitors. 5 years is a good compromise.
Batteries are at their most vulnerable to fire risks when 100% full, a situation that is common at the end of the charging process. People tend to forget that they have left the charger plugged in and switched on overnight for example.

 

[Ocsid]

A good reason as in the computer industry, as Samsung did, then the bike charger should have a facility to limit recharging to 80%?
A value that might well suit a high percentage of users and bring both greater safety and longevity gains?
If it's dangerous to leave a charger unattended, and or to push to 100%, why are those basic issues not addressed in the kit design?

 

[Johnyy]

I live on a hillside so all my trip use battery heavily - although going the other way not so much, so I guess it balances out

But my biggest take from above is it's about Ah. Looking at the eBay items above it seems to be that one of them is 22.5Ah and the other 15Ah. The 22.5 appears to be better value but I am suspicious of the difference in price

 

[Bonzo Banana]

I know in theory a 800Wh battery should last 4x as long as a 200Wh battery but I think in reality you will get more than 4x the range because the individual cells will be discharged at a much slower rate which gives bonus capacity plus battery packs typically have a reserve amount of charge in them which is typically proportionately less with a larger battery pack. So I wouldn't be surprised if a larger battery pack had more range than you expected plus kept that capacity for longer too after the same amount of discharges.

Of course as someone will point out there are lots of variables including the type of cells used and how the BMS operates to protect the cells from being fully discharged. Also someone who uses a 4A or 3A charger may not get as much capacity long term as someone who uses a 2A charger.

 

[Woosh]

If it's dangerous to leave a charger unattended, and or to push to 100%, why are those basic issues not addressed in the kit design?

they are, the charger's 42V limit for 36V battery is well proven for decades. However, when the batteries age, that limit must be lowered.
The problem is the output voltage is set in the vast majority of chargers by a potentiometer instead of digitally set. There is no way you can program the chargers to make them adaptable to ageing batteries.

 

[Nealh]

I would opt for the down tube battery that uses the 21700 samsung or LG cells , both will be good for a bbs01 .
The rear rack battery uses 2500mah 18650 size cells, there is no info on the cell brand , most likely are medicre china cells.

 

[Johnyy]

Well spotted Nealh and thanks. I had seen the words Panasonic, LG or Samsung at various places but not noticed they were missing from the 36v rear rack. That goes a long way to explaining the price difference with the 15Ah

And yes it's actually the rear rack I need so I can use saddle bags. And the existing 5.5amp fitting is going to remain on the cross frame (in theory it's a reserve I could carry

So I am now tending toward the 15Ah simply because the quality of the battery's are Panasonic 21700's

 

[Nealh]

Pannasonic are ok , I think those are likely the Tesla ones . I suspect they may be early generation 21700's and likely the ones thatTesla have had issues with.

Digging about I see the 18650 2500mah cell as being Luhua , a no name not heard of before.

 

[saneagle]

I just bought a battery from those guys that came on the forum a couple of weeks ago. They have 10% off for easter and another discount that reduced the cost of the 20Ah 48v one to £288 with shipping. I ordered it on 25th at 18:25. They shipped it immediately and I got a message at 23:35 from UPS saying that it would be delivered on 26th. There was some problem at UPS and they didn't deliver it then but it came this morning, so around 40 hrs from when I pressed the button.

It came very nicely presented with a sticker, a little leaflet about recycling, a charger and some 5mm screws to fix it to the bottle fixing position, though I wouldn't use them on a 4.8kg battery. Instead I use three 6mm screws into my own installed rivnuts.

It was 48.8v when it arrived, and so far, it's been charging unattended in my kitchen. I'll fix it to my bike when it stops raining and hopefully try it over the weekend. I'll let you know how it goes. Just as I wrote that, I could hear charger fan stop, so I went out to check. The light is green and the voltage is somewwhere between 54v and 55v. My normal meter has a flat battery, so I had to use my cheapo spare that doesn't show decimals on that scale.

There is something that needs clarification. I ordered the 20AH 21700 cells one, but the one I that came has a label that says 20AH 13S6P. 21700 cells weigh around 70g, which would put the weight at 5.46kg without the case, when mine is 4.8kg including the case, which would be right for 18650 cells. Have I got the cheaper 17Ah one with the wong label? All will be revealed some time soon in the future. What do you guys think?

I bought that battery because I'm hoping to do some long rides when the weather warms up and the rain goes away.

Electric Bike Batteries & Е-Bike Accessories | Greenlance Limited

Power up your ride with Greenlance! Discover premium Electric Bicycle Batteries featuring top-quality Samsung cells and backed by a 2-year warranty. Elevate your E-BIKE experience with reliability and performance.

greenlance.co.uk

 

[Johnyy]

Interesting. Two maybe foreign nationals in UK (welcome) with Eastern European names, and the Ebay add says postage from Poland. Almost sounds a bit like Green Cell, my existing 5.5 Ah battery supplier who are in Poland. None of which matters except my original battery seems ok

 

[Nealh]

The 21700 celled case will come in about 200g lighter then the 18650 celled case.
Only they will know what tboth the batteries actually weigh , maybe they have simply sent the wrong battery .

21700 x 52 cells = approx. 3.56 kg.
18650 x 78 cells = approx. 3.74kg.

Case +bms and wiring being much the same in weight.

 

[saneagle]

Right. It's all sorted now. They sell two different 20ah batteries: One has 18650s and the other 21700s, and I ordered the wrong one. I noticed that as soon as we started chatting, so I felt like a bit of a tw4t. I used their chatline and they immediately offered to swap it for the one I wanted, but I was going to buy another one later anyway if it was OK, so I just ordered another one - the correct one this time. They only had one of the 21700 ones left, so anybody else will have to wait until June.

At least I think we've confirmed that they're not a couple of cowboys.

 

[Johnyy]

So do you think the 21700's are definitely suspect old stock? Or perhaps after all this time they sorted the problem out? Why were they a problem for Tesla please?