Calculating the load on the ebike battery.

[calab]

Is this the proper way of doing the math?

Controller is a generic 36v (10s) 35 amps

Battery is 36v 10s 22ah 8p I do not know what they use for 18650's, so I cant find the info for nominal or max discharge. Plastic encases the 5s2p 6ah or 5s3p 9ah. The Ryobi ONE+ sleeves are green, they are the normal ONE+ and not the High Performance Ryobi's (probably more discharge?)

35a/8p = 4.375 amps per parallel grouping of 10s.

4.375 amps divided by 10s = 0.4375 amps per 18650 cylinderical cell. Theoretical discharge amps per cell, taking out resistances of joints, tabs and series connection method (I am using 10awg solid copper house wiring).

 

[amberwolf]

Amps only divide or multiply (or add or subtract) by the number of *parallel* cells, not series.

Volts only divide or multiply (or add or subtract) by the number of *series* cells, not parallel.


Keep Amps=parallel and Volts=series in mind whenever dealing with batteries.

 

[amberwolf]

Controller is a generic 36v (10s) 35 amps

A controller doesn't have an "s" number, only a battery does, because that number designates how many cells of the specific chemistry used in that battery are in series to generate it's voltage. A controller only has a voltage rating and doesn't care how many series cells there are or what chemistry they are. (not counting the rare controller that has a voltage display that has a setting specifically for this to make the meter account for chemistry/etc differences).

Battery is 36v 10s 22ah 8p I do not know what they use for 18650's, so I cant find the info for nominal or max discharge. Plastic encases the 5s2p 6ah or 5s3p 9ah.

If you are using packs that have 2p, you use four of them in parallel to make an 8p pack. If each is 6Ah, then that is 4 x 6Ah = 24Ah.

If you are using packs that have 3p, you can't make an 8p pack. You can make a 6p, or a 9p. A 9p pack would be 3 x 9Ah = 27Ah. A 6p pack would be 2 x 9Ah = 18Ah.

You can combine two 3p packs and a 2p pack to make an 8p pack. It would be 2 x 9Ah = 18Ah plus 1 x 6Ah = 24Ah.

I don't see a way to get a 22Ah 8p pack out of the types you list.

To then get a 10s pack, you would series two identical sets of whatever you paralleled above, so it takes twice as many packs as just the single paralleled set.

35a/8p = 4.375 amps per parallel grouping of 10s.

Theoretical discharge amps per cell, taking out resistances of joints, tabs and series connection method (I am using 10awg solid copper house wiring).

Note that the "discharge amps per cell" you're calculating is not the rating of the cell, but the demand upon it. If you don't know how much each cell can provide, then you can't predict how they will behave when this demand is placed on them.

If the packs as a whole have a continuous discharge rating, then you simply use that as a pack rating, and multiply it by however many packs like that that you have in parallel for one set. (don't add the ones in series with that, they don't count for amps, only volts).

For example, if each pack is rated to provide 10A (a made up number for this example), and you have three in parallel, then together they can only provide 30A. If your controller needs 35A to do what you want the system to do, you will have to use four packs in parallel to do this. (and since you need 10s and the packs are 5s, you have to use eight packs total, two seriesed sets of four paralleled packs).

 

[calab]

Thanks, I will have to redo my calculations to figure out what the load demand is on a single 18650 in 10s8p tool pack battery with no bms.

Divide 35a by 80 total 18650 cells (10sx8p) in pack for 0.4375a?
If its that easy, I missed the boat. and yet I got the same # of 0.4375a. That does make sense for the battery demand the controller seeks on a per 18650 basis. I do need to find out the specs of the 18650 used in the tool pack brick. I have my 5s 3p 9ah Ryobi brick has 2 dead cells encased in it, pcb's taken off the bricks.

I can go up to 45-50a with little increase on each 18650 demand from controller, 0.625a.
Still way under 1a per 18650. My Grintech 52v battery has a 40a bms, but its limited to 35a due to controller.
Most cells are 5-10a+ for a good 18650, these tool pack batteries need to throw a solid strong punch with 1p (1.5ah and 2ah bricks), 2p (4ah, 6ah bricks) or 3p (9ah bricks), a drill on 1p 1.5ah needs 20a, so 2a per 18650 on 10s8p.

Amps only divide or multiply (or add or subtract) by the number of *parallel* cells, not series.

Volts only divide or multiply (or add or subtract) by the number of *series* cells, not parallel.


Keep Amps=parallel and Volts=series in mind whenever dealing with batteries.

 

[amberwolf]

Divide 35a by 80 total 18650 cells (10sx8p) in pack for 0.4375a?

No, you cannot total all the cells that way.

Please reread what I typed, including the examples, and try setting up your math the same way.

I don't know how to explain it any simpler than the "rules" I posted, which you also quoted--nothing in series adds for amps, amp hours, etc. Leave ALL "s" numbers completely out.

 

[calab]

Yes, I am still missing the boat. I reread his posts all the time to try and figure it out. I need to do more research and Google for it to all sink in.

caleb,
A suggestion and you used the same math in another thread which was incorrect, re-read Amberwolf's post. As usual, he is spot on and does a great job explaining things on this forum.

 

[calab]

I will have to come at it with a clearer, calmer mind to get the Battery-Fu some of you have.

This is the battery in question, 21ah 10s 36v thats seriesed 18v, a/s on battery and my nice best yet soldering job for the adapter, heat shrink all the same length with corresponding colors and end caps. I impressed myself, I had the soldering-fu tonight. Out of pure need for the extended range. I did love how much lighter the bike felt without it, but I need wh, not ebike weight savings.

Fresh Gorilla Tap, smells nice.

Did you happen to notice the gap in the connected xt90?
I had saved a used xt90 a/s, but the solder somehow flowed wrong. Too much solder is what it was, too much already pooled or too much added.
Cant win 'em all, not perfect. I want to see Hobbykings solder joints to compare. Mechanical connections of a different connector is my next leap forward.

Never mind the batteries odd shape



















Since I was on a roll I had to switch the chargers female connectors to male, to fit into the xt90 a/s batteries female. One new xt90 and the blackened one is a used xt90, melted the previous used one with to much heat. A can of air is always helpful to cool things down. Yes I need to cover the shielding ground that you see in the pic, probably with some liquid electrical tape.

 

[john61ct]

21ah 10s 36v thats seriesed 18v, a/s on battery

So two 18V sub packs in series? Each 21Ah 5S