It would be nice if...

[Angus Digital]

Maybe I'm asking too much but, it would be nice if the manufacturers of cell holders be it for 18650, 21700 or 26650 cells etc, would at least provide a diagram of how one would typically configure some cells into their products. Because of the shape of many bicycle frames it's not always easy to just install a square or rectangular battery pack which makes for a simple X,Y matrix layout I know that there are a few combinations possible for a given cell holder but it can't be that taxing to just at least have an online link with a page of battery cell combination graphics say for 36v, 48v or 52v batteries, (for e-bikes) I think those voltages are the most common although I know there are others. I have put just one set together here on my computer with a picture of the cell holder in question but it took me absolutely ages. Hopefully I haven't made any errors. Correct me if the pictures are wrong.

 

[Woosh]

Maybe I'm asking too much but, it would be nice if the manufacturers of cell holders be it for 18650, 21700 or 26650 cells etc, would at least provide a diagram of how one would typically configure some cells into their products.

You can ask your supplier for wiring diagrams.
most of the time, your best cell grouping is pretty intuitive and at last resort, you have google images and this forum.
e-bike batteries usually prioritize gravimetric density, the batteries get smaller and smaller over time so there is little demand for odd shapes. Your case is pretty rare on this forum, you choose the cheap cells first then try to figure out what to do with them. If I need range (bikes for deliveroos), I would choose the cells first, I would use the 5000mAH cells (Samsung 21700 50E, good price/quality) in this case, then work out the other parameters (capacity and case) next. You'd get a much lighter and smaller battery for the same capacity.

 

[Sturmey]

I worked with batteries for years so I always recommend caution. I am looking at your layout. The batteries on top are on the positive pole and are directly over and adjacent to the other end of the string (negative )pole. So you have full battery voltage between adjacent cells.
So I think you could put in extra packing/insulation in this case or string out differently.
Batteries get a lot of knocking about and are suppose to be mechanically robust. Indeed, EN15195 mentions a 'drop and hammer test' standard.

4.2.3.7 Mechanical strength
EPAC shall have adequate mechanical strength and be constructed to withstand such rough handling that
may be expected in normal use. Compliance is checked by:
 applying impacts to the battery pack mounted on the EPAC by means of the spring hammer as specified
in IEC 60068-2-75. The battery pack is rigidly supported and three impacts are applied to every point of
the enclosure that is likely to be weak with an impact energy of (0,7 ± 0,05) J. After the test the battery
pack shall show no damage that could impair compliance with this European Standard;
 detachable battery packs are submitted to free fall at a height of 0,90 meter in three different positions.
After the test the battery pack shall show no damage that could lead to emission of dangerous substances
(gas or liquid) ignition, fire or overheating.

 

[Angus Digital]

I worked with batteries for years so I always recommend caution. I am looking at your layout. The batteries on top are on the positive pole and are directly over and adjacent to the other end of the string (negative )pole. So you have full battery voltage between adjacent cells.
So I think you could put in extra packing/insulation in this case or string out differently.
Batteries get a lot of knocking about and are suppose to be mechanically robust. Indeed, EN15195 mentions a 'drop and hammer test' standard.

Yes I take your point about the positive and negative connections being close together, but the beauty of doing drawings first and then posting them on forums like this is that I can get feedback. I'm pretty certain I can re-design the layout so that the terminals aren't so close together or even at opposite ends of the battery... I'm on it.

 

[Angus Digital]

You can ask your supplier for wiring diagrams.
most of the time, your best cell grouping is pretty intuitive and at last resort, you have google images and this forum.
e-bike batteries usually prioritize gravimetric density, the batteries get smaller and smaller over time so there is little demand for odd shapes. Your case is pretty rare on this forum, you choose the cheap cells first then try to figure out what to do with them. If I need range (bikes for deliveroos), I would choose the cells first, I would use the 5000mAH cells (Samsung 21700 50E, good price/quality) in this case, then work out the other parameters (capacity and case) next. You'd get a much lighter and smaller battery for the same capacity.

I really fancy those Samsung 50E 21700's

 

[Sturmey]

If I may say something, its an ambitious project you are undertaking in terms of fully building out the battery. I presume you have a lot of experience. It would be a lot easier if this is your first build to do a 4P rather than 5P as there would be surplus room and more choice with layout. Indeed, many commercial prebuilt batteries I have come across are not full built out and have spare room. Also if you make a serious mistake like puncture a battery with a spot welder when battery is nearly built, you have a little bit of room to play with.. (Some people recommend that you practice on old cells before you start). I am not an expert here and others may give better advice. The last battery I built, I used lego type holders I bought from ebay as NKON had run out. They were poor quality, I had to put tape on end of some cells as some were loose/easily turning in holders and the whole block started to come loose during assembly, so I had to use superglue in joins to hold together.
It probably would have been easier to buy a ready built battery. The main reason I built is because of the availability of very cheap surplus powerwall cells (Samsung 33j 21700) that are designed for long life and tested to last well over 2000 cycles at 4.1 volts with minimum deterioration (although they work out less energy dense and need to be either laser welded or bought laser tabed and then soldered as I did, as they have thin aluminium cases). I do very high milage.

 

[Nealh]

With your diy homebuilt spot welder have you tested the weld to see how far the spot penetration is or if bluing burn marks appear on the opposite side/face of the object.
The Boss spot welder thread explains more about testing for burn thru and weld strength , typically craft knife snap blades are recognised as being not to different to battery cell cans and nickel , with the likes of the malectric or kweld one can adjust the weld strength to prevent any excessive burn through and heat to the inside of the can.

Some good technical type topics on ES, and many contributions from world members of the community with their experiences.
Of particular interest some may overlook is the use of the slotted nickel or copper buss strips.

BOSS LEVEL CUSTOM SPOT WELDER - Page 2 - Endless Sphere (endless-sphere.com)

"Copper/nickel sandwich" buses for series connections - Endless Sphere (endless-sphere.com)

 

[Angus Digital]

With your diy homebuilt spot welder have you tested the weld to see how far the spot penetration is or if bluing burn marks appear on the opposite side/face of the object.
The Boss spot welder thread explains more about testing for burn thru and weld strenght, typically craft knife snap blades are recognised as being not to different to battery cell cans, with the likes of the malectric or kweld one can adjust the weld strength to prevent any excessive burn through and heat to the inside of the can.

Some good technical type topics on ES, and many contributions from world members of the community with their experiences.
Of particular interest some may overlook is the use of the slotted nickel or copper buss strips.

BOSS LEVEL CUSTOM SPOT WELDER - Page 2 - Endless Sphere (endless-sphere.com)

"Copper/nickel sandwich" buses for series connections - Endless Sphere (endless-sphere.com)

I really appreciate your knowledge and advice as I'm relatively inexperienced when it comes to cells, batteries, welders etc. I will check out the links...

 

[Nealh]

Another very good thread worth a read, just 14 pages of good night time reading.
Common pack design mistakes, how to avoid? - Endless Sphere (endless-sphere.com)

In particular the current share between cells and the two off takes of +/- are of consideration.

 

[guerney]

Another very good thread worth a read, just 14 pages of good night time reading.
Common pack design mistakes, how to avoid? - Endless Sphere (endless-sphere.com)

Thanks for posting that very informative link - I've saved it all as a 243 page PDF for the eReader.

 

[Nealh]

What one needs to know is the max current expected to be drawn, this is down to the motor controller. Once this is known one can then calulate the minimum Buss mm2 Ampacity required to transfer the max rated current for the series conections.
Calculating Buss mm2 is easy, simply multiply the Buss width ( and not the length) X the thickness .

Parallel Buss is unimportant as current flow is very minimal at most it generally only needs to be a few amps.

 

[Nealh]

More reading , all offering good advice and tips to save on mistakes.
18650 spot welding -how to- ULTIMATE REPOSITORY - Endless Sphere (endless-sphere.com)

 

[Angus Digital]

I really appreciate your knowledge and advice as I'm relatively inexperienced when it comes to cells, batteries, welders etc. I will check out the links...

Strangely enough I did actually use some stanley knife blades to practice on before I went onto welding cells for real.

 

[soundwave]

12v 70a crap connection and it will kill

 

[guerney]

More reading , all offering good advice and tips to save on mistakes.
18650 spot welding -how to- ULTIMATE REPOSITORY - Endless Sphere (endless-sphere.com)

Wow, that one's converted as a 443 page PDF. Cheers for the interesting info. I'd better read them in daylight - looks like perfect nod-off bedtime material.

 

[guerney]

12v 70a crap connection and it will kill

The new AMDs look good, not as fast or flamey.

 

[Nealh]

There's tons of stuff on ES and some really good reference stuff , but one has to sort the wheat from the chaff and do his /her own research as well.