Celcapz - no spot weld battery kits

[Cisco-man]

Hi.

what’s the expert opinion on these kits for assembling a battery pack with no spot welding required? Certainly not a cheap solution.

Pardon our interruption...

 

[AGS]

I looked at them last year but decided against using them. They are probably ok for building a static battery, but not for an Ebike. They have a history of cracking and make the overall size of the pack quite a lot bigger.

They aren’t that expensive if you are building a 1 off pack if you balance the cost of a decent welder and the nickel strips together with all of the other gubbins to finish the pack off. But they are an expensive way to build if you are building packs frequently.

 

[Cisco-man]

Yes, I agree - too bulky to begin with.

No laughing, but I have this concept in my mind, or keeping all my 18650 cells as naked, untouched cells. Then build a battery charger that charges a given quantity of these (maybe 40) up to the 4.2v safely when I wanted to use them.
To use them, I would simply load these in to a twenty cell pack (10s 2p) with no BMS required - a simple plastic case. If going on a long ride then just load up forty into two packs, and so on.
(I said, no laughing) The beauty of this, is that each individual cell can be nurtured and monitored, and replaced when they get tired, etc. and you only build the pack you need.

 

[Cisco-man]

And storing 40 or so non-linked cells would be far safer too.

 

[saneagle]

Yes, I agree - too bulky to begin with.

No laughing, but I have this concept in my mind, or keeping all my 18650 cells as naked, untouched cells. Then build a battery charger that charges a given quantity of these (maybe 40) up to the 4.2v safely when I wanted to use them.
To use them, I would simply load these in to a twenty cell pack (10s 2p) with no BMS required - a simple plastic case. If going on a long ride then just load up forty into two packs, and so on.
(I said, no laughing) The beauty of this, is that each individual cell can be nurtured and monitored, and replaced when they get tired, etc. and you only build the pack you need.

The problem is the contact resistance. It's fine for one amp, but when you get up to the 5 to 10 amps that you'd need from each cell, there's a real danger that something's going to get hot.

 

[Cisco-man]

The problem is the contact resistance. It's fine for one amp, but when you get up to the 5 to 10 amps that you'd need from each cell, there's a real danger that something's going to get hot.

I guess that’s why the Celcapz system suffers from cracking plastic - as AGS says. Not to say that an improved battery contact clamp couldn’t be thought up though.

 

[Sturmey]

...... I would simply load these in to a twenty cell pack (10s 2p) with no BMS required .........

Here is one problem. Lets say one cell fail to connect. Then during discharge, the remaining cell in the same parallel group will have to carry all the current and will discharge fully where as the other groups with 2 cells will be only half discharged. At this stage, there is even a risk of reverse charging that single cell as the other 9 cell groups at say 3.7 volts = 33 V could continue to try to push current through the discharged cell.
Normally, the BMS would protect the cell so its now more important than ever to fit a BMS as there may be some doubt about the reliability of the connections.
I have bought cells from NKON with solder tabs in the past (as an alternative) but they charge 20 euro extra for this now (20 cells).
When you add the costs together (e.g. cells, cell holders, BMS, charger, case, insulation rings, tabs or nickle strips), I dont see any real saving in making my own battery at the moment as I see the equivalent ready built batteries can be got at nearly the same price. But compare the prices yourself as I live in Euro Zone.

Samsung INR21700-50E 4900mAh - 9.8A

Capacity: 4900mAh Rated Voltage 3.6V - 3.7V Charging cycle termination voltage 4.20V ± 0.05V max discharge current: 9.8A Do not discharge deeper than 2.5V Plus pool: Flat top Chemistry: Li-ion Protection circuit: Without Diameter: 21.1mm Height: 70.6mm Weight: 69g

eu.nkon.nl

 

[Ghost1951]

The problem is the contact resistance. It's fine for one amp, but when you get up to the 5 to 10 amps that you'd need from each cell, there's a real danger that something's going to get hot.

I am fantasising about how to make a battery out of 24 of these LiFePo4 batteries with threaded studs at each end. It should not be too hard to make a decent connection with these and it would give the owner access to individual cells for repair if needed during the life of the pack. I expect the battery would need to fit into a triangle bag under the crossbar of the bike.

Just half baked thinking , but 24 of these in a 12s2p configuration would pack about 460 watt hours at a working pack voltage of about 38 volts.

Why LiFePo4? Cycle life (>2500 cycles) and safe. These are also priced at £5.60 each if you buy 24, so £135 the lot. Pack would weigh something like 3.5kg.

End of charge voltage of the pack would be 43.8 volts in 12 s configuration at 3.65v per cell, so might be able to use my ordinary lithium 36 volt charger which would never completely fill the batteries.

The idea needs a lot more thinking though at this stage. Back of a fag packet calculations only.

 

[Cisco-man]

View attachment 58703

I am fantasising about how to make a battery out of 24 of these LiFePo4 batteries with threaded studs at each end. It should not be too hard to make a decent connection with these and it would give the owner access to individual cells for repair if needed during the life of the pack. I expect the battery would need to fit into a triangle bag under the crossbar of the bike.

Just half baked thinking , but 24 of these in a 12s2p configuration would pack about 460 watt hours at a working pack voltage of about 38 volts.

Why LiFePo4? Cycle life (>2500 cycles) and safe. These are also priced at £5.60 each if you buy 24, so £135 the lot. Pack would weigh something like 3.5kg.

End of charge voltage of the pack would be 43.8 volts in 12 s configuration at 3.65v per cell, so might be able to use my ordinary lithium 36 volt charger which would never completely fill the batteries.

The idea needs a lot more thinking though at this stage. Back of a fag packet calculations only.

There’s certainly some merit in all this, but as usual it takes someone with drive and money to move it forward to a marketable product. I guess for me it’s always going to be just a mental exercise.

 

[Az.]

Then build a battery charger that charges a given quantity of these (maybe 40) up to the 4.2v safely when I wanted to use them.

How long/big would that be?

 

[Ghost1951]

How long/big would that be?

Cells are 32mm x 70mm and weigh 140 gm each.

For approx 38v nominal in 12s 2p config, you'd need 24, so if two rows of 12 you'd have a rectangle 12x3.2cm approx 39cm by 7cm high and 7 cm wide. Obviously, the packaging of the cells and accommodation of the BMS and connectors and padding is not included and is unknown at this stage of fag packet thinking - so in inches for fossils like me 15 to 16 inches long, about 3 inches wide, and about 3 inches high. Very rough. Worth going over again carefully.

Might be worth making one in 12s 3p and getting 50% extra capacity at 50% extra cost with a cell pack 4.5 inches high (no packaging in that height).
Unknown cells of unknown quality and no doubt there are many reasons to not touch this with an insulated barge pole.

EDIT:
If you made it 12s 3p you would have 21 Ahrs for about £200 (cells only).

 

[Cisco-man]

How long/big would that be?

You could charge them in strings of ten in series using your 42v charger, with BMS type connections across each battery (as per now). The batteries still take up the same area as they always do, just would benefit from a slightly different bms to balance them better.

 

[Ghost1951]

You could charge them in strings of ten in series using your 42v charger, with BMS type connections across each battery (as per now). The batteries still take up the same area as they always do, just would benefit from a slightly different bms to balance them better.

No expert, but i think charging in strings of ten with 42v charger might not be good. That is IF you were using LiFePo4 as suggested here. Ten series Lithium Iron Phos would terminate charge at 36.5v. Not 42v.

Maybe i introduced confusion by suggesting a different battery type. You can buy a suitable bms for this chemistry of course.

 

[saneagle]

You guys are brilliant at thinking up ways to make simple things complicated. What's wrong with buying a battery, installing it, charging it with an ebike charger, and using it?

 

[Ghost1951]

You guys are brilliant at thinking up ways to make simple things complicated. What's wrong with buying a battery, installing it, charging it with an ebike charger, and using it?

It's pi ssing down with rain here. Wanted something to think about.

 

[Az.]

You guys are brilliant at thinking up ways to make simple things complicated. What's wrong with buying a battery, installing it, charging it with an ebike charger, and using it?

It is to simple. As advanced e-bike users we want 6m long charger to charge 40 cells individually. We are happy to remove them from battery case before charging and then patiently put them back again.

 

[Cisco-man]

I knew you’d take the mick eventually! As Ghost1952 says, it’s p ing down with rain, and it’s just thought exercise for me. I DO like these LiFe cells though. Anyway, the “old” ways should always be tested or we’ll never progress things.

Ooooo, I’m now Esteemed!

 

[Ghost1951]

I knew you’d take the mick eventually! As Ghost1952 says, it’s p ing down with rain, and it’s just thought exercise for me. I DO like these LiFe cells though. Anyway, the “old” ways should always be tested or we’ll never progress things.

Ooooo, I’m now Esteemed!

I always held you in high esteeeem my precious..... (said in Gollum voice.

Do you have shiny thingssssss....

 

[Ghost1951]

It is to simple. As advanced e-bike users we want 6m long charger to charge 40 cells individually. We are happy to remove them from battery case before charging and then patiently put them back again.

Nice.

That would fill a rainy afternoon.

 

[saneagle]

It's pi ssing down with rain here. Wanted something to think about.

I thought that's what you would say. I've been through all this myself, until I realised that KISS is the best.