Compress or not, flexible busbar or not

[justgary]

I could be very wrong, but I don’t think those pads can withstand/sense 660lbs of force. I think they are for much less compression

That also tend to be very low impedance devices, which require special amplifiers to use. I'm not saying you couldn't use them. I have a small pile of them that I got surplus. I'll check them to see if I could get them to work.

 

[Cheap 4-life]

I said measure the desired force and the torque required to achieve that force.

Read this on another thread, ,, Couldn’t a scale be put between the walls to be used and short pieces of threaded rod and nuts and torque to pounds desired. Then use that same torque on the pack?

 

[fafrd]

Couldn’t a scale be put between the walls to be used and short pieces of threaded rod and nuts and torque to pounds desired. Then use that same torque on the pack?

Yes, that should work (calibrated springs sure sound a heck of alot easier).

 

[Cheap 4-life]

Yes, that should work (calibrated springs sure sound a heck of alot easier).

Yes then you have to order/pay for springs. And in some of your examples leave the spring in which imo could lead to issues having a spring in only one corner..
Was just thinking the scale would have to be able to measure 660lbs which most do not

 

[fafrd]

Yes then you have to order/pay for springs. And in some of your examples leave the spring in which imo could lead to issues having a spring in only one corner..
Was just thinking the scale would have to be able to measure 660lbs which most do not

I never suggested leaving a spring on only one rod - calibrate with o e spring per rod and then either leave them all in place or if you’ve made two holes per rod position, attach the second set of rods without springs and then completely remove the first set of rods with springs…

The springs cost a fraction of what you’ll be spending on threaded rod, let alone any rigid perforated stock you elect to use for cross-braces…

You are really making this much more complicated than it needs to be.

 

[Cheap 4-life]

My mistake, read your comment wrong. There’s many variables and it’s not the most uncomplicated thing. Removing the springs requires extra holes and rods for a rigid fixture. I’m not doing rigid but I’m discussing it for others that might want to.

 

[fafrd]

My mistake, read your comment wrong. There’s many variables and it’s not the most uncomplicated thing. Removing the springs requires extra holes and rods for a rigid fixture. I’m not doing rigid but I’m discussing it for others that might want to.

My read is that if you are doing a one-off, constant 300kgf based on the use of calibrated springs is easier and cheaper than attempting to properly build a rigid fixture.

If you are a battery manufacturer selling thousands of batteries, rigid is probably cheaper because whatever more complicated rig you need to use to assure you’ve got your cells under the correct name reassure will be amortized over many batteries benefiting from that solution…

 

[Skypower]

This is my seventh pack and the first two have been in service about a year and a half in my work truck.

I like your fixture + springs. If you haven’t already, check the torque on the cell terminals.

 

[brum]

Talking about compression and how it is done - the plywood is flexible. Should this be a concern and how much does a 20mm plywood sheet bends when used for the discussed use-case?

 

[justgary]

Talking about compression and how it is done - the plywood is flexible. Should this be a concern and how much does a 20mm plywood sheet bends when used for the discussed use-case?

EVE specifically states either 8mm steel or aluminum. I'm surprised that they use the same thickness for both materials since they have different properties, but that is what they say. If you plan to use plywood or another material, you can look up the properties on an engineering materials site to compare your material to 8mm aluminum.

Like you mention, one thing I don't like about plywood is the fact that it will take a set under force (it will bend and stay bent). This means that you would have to monitor your force applied to the cells over the long term. This is probably something you will want to do anyway. Using a steel backer like unistrut may help distribute the force better. Another thing I don't like about plywood is that it will absorb water if any happens to be present. A thick coat of paint might help.

At some point, it is easier to just use aluminum plate and move on.

 

[brum]

Same concerns. Plywood will likely sag. Thanks for sharing your thoughts on the question.

I found a calculator for shelf sagging. And it states that 12psi is too much for plywood. This is for 180x210mm shelf size - close to that of a 304Ah cell. If the parameters are entered correctly and the load is uniform on the surface the 18mm (3/4") plywood would sag close to 1mm.

So it seems that an 8mm aluminum plate will be used inside my enclosure. And this brings the complication of insulating it properly to avoid the chance of a short circuit.

 

[Cheap 4-life]

Same concerns. Plywood will likely sag. Thanks for sharing your thoughts on the question.

I found a calculator for shelf sagging. And it states that 12psi is too much for plywood. This is for 180x210mm shelf size - close to that of a 304Ah cell. If the parameters are entered correctly and the load is uniform on the surface the 18mm (3/4") plywood would sag close to 1mm.

So it seems that an 8mm aluminum plate will be used inside my enclosure. And this brings the complication of insulating it properly to avoid the chance of a short circuit.

Not really a complication. There is resin glass type of separators. https://diysolarforum.com/threads/lifepo4-cell-separator-material.28023/post-329206
Also they usually send separators with the cells.

 

[fafrd]

Same concerns. Plywood will likely sag. Thanks for sharing your thoughts on the question.

I found a calculator for shelf sagging. And it states that 12psi is too much for plywood. This is for 180x210mm shelf size - close to that of a 304Ah cell. If the parameters are entered correctly and the load is uniform on the surface the 18mm (3/4") plywood would sag close to 1mm.

So it seems that an 8mm aluminum plate will be used inside my enclosure. And this brings the complication of insulating it properly to avoid the chance of a short circuit.

Pressure is pressure is pressure, and thus concern is yet another reason to go with a constant 300kgf fixture rather than attempting to build a truly rigid fixture calibrated to 300kgf @ 30-40% SOC.

I’m using 3/4” pine endcaps in my fixture (behind similar perforated stock cross braces. I have absolutely no concerns about electrical conductivity between my fixture and my cells nor any concerns about clamping pressure going outside the 280-320kgf range I calibrated to (if my pine endcaps ever ‘sag’ my springs will take up the slack).

 

[Cheap 4-life]

Flexible busbars arrived

 

[fafrd]

Flexible busbars arrived

Nice! How much were they?

 

[Cheap 4-life]

Nice! How much were they?

$4.40 each shipped. Arrived in 12 days. They are more flexible than they look as @rhino and @cinergi suggested

 

[brum]

It would be nice if somebody can compare the flexibility of these to the braided wire busbars. The braided ones are cheaper and based on a test performed by Andy from the Off-Grid garage youtube channel - they are as good as the solid busbars in terms of resistance.

 

[Cheap 4-life]

I have read of re torquing issues with the braided do to the way they are constructed. That’s why I chose the laminated. Also Andy did say in a video that the braided are not very flexible at all

 

[brum]

Ordered one piece of both. I'll compare them one to another and I'll share the results.

And some offtopic: This order however brought a totally new experience to me. An hour after I put the order I got a call from a private number. One of the sellers wanted to make sure I want 1 piece only. I have like a 1000 orders from Aliexpress and this is the first time somebody calls me!

 

[noenegdod]

$4.40 each shipped. Arrived in 12 days. They are more flexible than they look as @rhino and @cinergi suggested

From last year. Shows the flexibility: