No weld: using 10x 4pc packs ?

Batteries, Chargers, and Battery Management Systems.

No weld: using 10x 4pc packs ?

Postby qwerkus » Tue Sep 05, 2017 3:40 pm

Hello,

I'm new to DIY batteries, and am particularly interested in no-weld techniques. The obvious reason would be that I don't have expensive spot welding tools, and that I'm a strong believer in recycling. Now how about using 10-13 of those cheapo 4-cell-holder in series (see attached file)

I guess some of you must have tried it, and there is a reason no one uses them to build ebike battery packs. So I would love to read those reasons. Only real drawback I could think of is stability: the cells probably don't hold very well in those. But perhaps using thin foam between the racks would increase stability to a point where they are safe to use ?
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Re: No weld: using 10x 4pc packs ?

Postby fechter » Tue Sep 05, 2017 4:03 pm

I'm sure there are ways to keep the cells from getting knocked out of position, like zip ties. I think the main drawback is the contacts will tend to develop high resistance over time. With enough pressure on the contacts, you can exclude oxygen and have a reliable long term connection, but the required force is typically more than it takes to dent in the end of the cell. Point contacts don't need as much force, but you are then limited in how much current you can pass.

Current rating might be another reason. With thick enough contact material, this should not be a limitation, but many of the cheaper ones use thin nickel plated steel, which will start heating up before you reach the cell's actual rating.

For low current applications, like a laptop or small electronic gadget, these seem to work out fine. For higher current like a bike, not so good.

Check out this topic:
viewtopic.php?f=31&t=87434
You can get a good idea for the limitations. So far the Vruzend units seem to be working out for most people.
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Re: No weld: using 10x 4pc packs ?

Postby qwerkus » Tue Sep 05, 2017 4:55 pm

fechter wrote:I'm sure there are ways to keep the cells from getting knocked out of position, like zip ties. I think the main drawback is the contacts will tend to develop high resistance over time. With enough pressure on the contacts, you can exclude oxygen and have a reliable long term connection, but the required force is typically more than it takes to dent in the end of the cell. Point contacts don't need as much force, but you are then limited in how much current you can pass.

Current rating might be another reason. With thick enough contact material, this should not be a limitation, but many of the cheaper ones use thin nickel plated steel, which will start heating up before you reach the cell's actual rating.

For low current applications, like a laptop or small electronic gadget, these seem to work out fine. For higher current like a bike, not so good.

Check out this topic:
viewtopic.php?f=31&t=87434
You can get a good idea for the limitations. So far the Vruzend units seem to be working out for most people.


Thank you for your interesting reply. So basically, I would have to:
1 - replace all connectors with nickel plated copper ones
2 - add a spring behind each contact - Vruzend style - to make sure there is enough pressure at the contact zone
3 - foam + zip tie the entire thing to make sure it does not move

Finding and bending nickel plated copper might be doable, especially if I can use tin plated ones. But finding that small springs - quite difficult!
Last edited by qwerkus on Tue Sep 05, 2017 4:56 pm, edited 1 time in total. View post history.
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Re: No weld: using 10x 4pc packs ?

Postby robb » Tue Sep 05, 2017 5:16 pm

I am using a 13s 52 cell battery using these. So far no problems. It is for a xiongda 2 speed motor so draws around 10 to 12 amps. Have only done about 600 miles so far but it all seems good. I have simply used a couple of wraps of insulating tape to keep batteries secure red on positive end and black on other. Then held the 13 blocks together with insulating tape and slid the pack into a plywood box.
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Re: No weld: using 10x 4pc packs ?

Postby qwerkus » Tue Sep 05, 2017 5:23 pm

robb wrote:I am using a 13s 52 cell battery using these. So far no problems. It is for a xiongda 2 speed motor so draws around 10 to 12 amps. Have only done about 600 miles so far but it all seems good. I have simply used a couple of wraps of insulating tape to keep batteries secure red on positive end and black on other. Then held the 13 blocks together with insulating tape and slid the pack into a plywood box.
Rob


Awesome! Do you have pictures of the pack ?
Last edited by qwerkus on Tue Sep 05, 2017 5:28 pm, edited 1 time in total. View post history.
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Re: No weld: using 10x 4pc packs ?

Postby Hillhater » Tue Sep 05, 2017 6:12 pm

This thread is for you..
viewtopic.php?f=14&t=76013
This forum owes its existence to Justin of ebikes.ca
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Re: No weld: using 10x 4pc packs ?

Postby spinningmagnets » Tue Sep 05, 2017 7:56 pm

That style is much better than the similar style that has coil-springs as the conductor and also as the contact-compression provider (IMHO). The "springs" do double duty in the stock configuration. The kind you linked to have a "leaf spring", and I like those much better because you can overlay a strip of 0.20mm thick copper foil to use as the conductor. I suppose this could be done to the coil-spring type also, but...since they are the same size and price, I am certain the leaf-spring will work better.

0.20mm-0.25mm thick copper sheet is cheap, readily available, and can be easily cut by scissors.

In this way, the steel leaf spring is doing the job it is best suited for (long-term repeatable compression pressure), and 99% of the current will flow through the path of least resistance...which would then be the copper ribbon that is in-between the cell and steel leaf-spring. It may not look very professional, but inserting a separate copper conductor will suddenly convert this type of cell-holder into a very viable solution for some jobs.
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Re: No weld: using 10x 4pc packs ?

Postby amberwolf » Wed Sep 06, 2017 1:19 am

There were some people that used those plastic 2 and 4 cell holders but ran into problems with them melting / deforming from the heat of the cells / connections / wires.

I coudln't find a specific post about them though; it was several years ago.
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Re: No weld: using 10x 4pc packs ?

Postby qwerkus » Wed Sep 06, 2017 1:46 am

Hillhater wrote:This thread is for you..
viewtopic.php?f=14&t=76013


Love your thread. Very informative, and good tone!
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Re: No weld: using 10x 4pc packs ?

Postby qwerkus » Wed Sep 06, 2017 1:47 am

spinningmagnets wrote:That style is much better than the similar style that has coil-springs as the conductor and also as the contact-compression provider (IMHO). The "springs" do double duty in the stock configuration. The kind you linked to have a "leaf spring", and I like those much better because you can overlay a strip of 0.20mm thick copper foil to use as the conductor. I suppose this could be done to the coil-spring type also, but...since they are the same size and price, I am certain the leaf-spring will work better.

0.20mm-0.25mm thick copper sheet is cheap, readily available, and can be easily cut by scissors.

In this way, the steel leaf spring is doing the job it is best suited for (long-term repeatable compression pressure), and 99% of the current will flow through the path of least resistance...which would then be the copper ribbon that is in-between the cell and steel leaf-spring. It may not look very professional, but inserting a separate copper conductor will suddenly convert this type of cell-holder into a very viable solution for some jobs.


Very smart idea, especially if if can source some adhesive copper. You're right: it ain't gonna be pretty, but it would save me the trouble of re-doing all the springs. Now all I'm missing is some sort of standardized box where one could slide the 4-cell racks next to each other.
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Re: No weld: using 10x 4pc packs ?

Postby spinningmagnets » Wed Sep 06, 2017 2:02 am

I should have mentioned that I searched your posts (you are new, so there were not many to scan). You want a 500W geared hub (36V X 14A)? and at 4P, the pack will draw less than 4A per cell during acceleration. For this application I would recommend one of the high-capacity cells, like the MJ1 and GA cells. Both are factory rated at 3500-mAh per cell.

Either one will run cool at occasional 4A, but...I agree with the poster above, that...anyone reading this thread should know that the plastic used in these cell-holders is made from Chinesium, and does not tolerate much heat before deforming.
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Re: No weld: using 10x 4pc packs ?

Postby qwerkus » Wed Sep 06, 2017 4:12 am

spinningmagnets wrote:I should have mentioned that I searched your posts (you are new, so there were not many to scan). You want a 500W geared hub (36V X 14A)? and at 4P, the pack will draw less than 4A per cell during acceleration. For this application I would recommend one of the high-capacity cells, like the MJ1 and GA cells. Both are factory rated at 3500-mAh per cell.

Either one will run cool at occasional 4A, but...I agree with the poster above, that...anyone reading this thread should know that the plastic used in these cell-holders is made from Chinesium, and does not tolerate much heat before deforming.


Lol: chinesium - the 119th element of the periodic table. Yes, that's the plan, though I would rather stick with 10s3p and 480W max power to save 500g weight, which means 4.4A per cell during acceleration, and only 2.5A during cruising. But honestly, I'm still weighting whether or not it's cheaper to build a pack myself, or just buy some ready made in china. If the vendor guaranties the use of high quality cells, It certainly is difficult to beat chinese prices while building something stable. The only real advantage I see in DIY packs is the possibility to easily replace cells in no-weld packs, either with this setup, or using nbi magnets. But this comes at the cost of lower stability, and a lot of trouble!
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Re: No weld: using 10x 4pc packs ?

Postby Pyrotrons » Wed Sep 13, 2017 3:37 pm

This could get me flamed, but, I've been soldering 18650's for years with no trouble.

Sand off the finish on the ends, use liquid flux, use a powerful iron with a big chisel tip, get the wire-end in position beforehand, and solder it quickly so as to not let the heat soak into the innards.
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Re: No weld: using 10x 4pc packs ?

Postby fechter » Thu Sep 14, 2017 7:23 pm

Pyrotrons wrote:This could get me flamed, but, I've been soldering 18650's for years with no trouble.



We won't flame you for that.
I've soldered plenty of 18650 cells too and have not had any problem that was noticeable. Your technique sounds like what I did. There are a few topics about it somewhere. That said, I now have a spot welder and prefer to use that.
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