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rapidly serviceable battery settup
#11
(10-03-2019, 08:37 AM)Scottietheyoung Wrote: anyway here is the basic concept of the sprung connectors with mechanical attachment to nickel strip. 

Have you done a resistance test on those springs? They look like the standard steel springs with nickel plating. You may find you loose a lot of power to heat while under medium to full load of the packs.
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#12
(10-03-2019, 12:21 PM)Korishan Wrote:
(10-03-2019, 08:37 AM)Scottietheyoung Wrote: anyway here is the basic concept of the sprung connectors with mechanical attachment to nickel strip. 

Have you done a resistance test on those springs? They look like the standard steel springs with nickel plating. You may find you loose a lot of power to heat while under medium to full load of the packs.

Yes nickel plated steel springs. I am hoping that with 6 banks of 14 modules load will be extremely minimal for each cell/pack. though to begin with I intend running two banks of 14. That should limit draw to less than .02 of an amp for each cell under full house hold load. Do you see this being an issue?
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#13
A problem with "steel" springs not only the higher resistance, but they become brittle over time from being compressed.

Let's say under 200mA load the steel spring wastes 10mA. Over an hour of that load is 100mAh, 10 hours is 1Ah. Now multiply that by how many cells you have in parallel. Even though the waste is small, it still can add up over time. Even if the waste is 5mA, it still adds up.
That's why I asked if you measured the resistance because it will tell you how much will be wasted.

Obviously, the more cells in parallel, the lower the waste as each cell will be less current flowing through. So, there is a kind of wasted energy curve getting closer to 0mA as the parallel count gets larger and the current per cell gets lower.
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#14
(10-03-2019, 11:51 PM)Korishan Wrote: A problem with "steel" springs not only the higher resistance, but they become brittle over time from being compressed.

Let's say under 200mA load the steel spring wastes 10mA. Over an hour of that load is 100mAh, 10 hours is 1Ah. Now multiply that by how many cells you have in parallel. Even though the waste is small, it still can add up over time. Even if the waste is 5mA, it still adds up.
That's why I asked if you measured the resistance because it will tell you how much will be wasted.

Obviously, the more cells in parallel, the lower the waste as each cell will be less current flowing through. So, there is a kind of wasted energy curve getting closer to 0mA as the parallel count gets larger and the current per cell gets lower.

I understand the resistance side of things but the only reason they become brittle is through heat cycling. So if current is low there is no reason to believe it will get hot and become brittle. I worked with all kinds of metals and spring steels as a fabricator for 10 years.

(10-04-2019, 03:38 AM)Scottietheyoung Wrote: [quote="Korishan" pid='55374' dateline='1570146675']
Let's say under 200mA load the steel spring wastes 10mA. Over an hour of that load is 100mAh, 10 hours is 1Ah. Now multiply that by how many cells you have in parallel. Even though the waste is small, it still can add up over time. Even if the waste is 5mA, it still adds up.
That's why I asked if you measured the resistance because it will tell you how much will be wasted.

Thanks for this thought angle, my thinking was that even with just two banks running of 120P 14S the maximum load a cell would see is .018 of an amp. Do you think the losses would be worth worrying about at that kind of draw? I had assumed the current being so low would negate the need for genuine concern here?
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#15
(10-04-2019, 03:38 AM)Scottietheyoung Wrote: I understand the resistance side of things but the only reason they become brittle is through heat cycling. So if current is low there is no reason to believe it will get hot and become brittle. I worked with all kinds of metals and spring steels as a fabricator for 10 years.

Kewls. You're way ahead of the game, then Smile

(10-04-2019, 03:38 AM)Scottietheyoung Wrote: Thanks for this thought angle, my thinking was that even with just two banks running of 120P 14S the maximum load a cell would see is .018 of an amp. Do you think the losses would be worth worrying about at that kind of draw? I had assumed the current being so low would negate the need for genuine concern here?

That's where knowing the resistance of the springs/connectors will help out. If the resistance is really low, then it's probably no big deal. Also, measuring the resistance (especially if you do everyone one), you could find which ones might need a little extra solder if it's higher than the others. Altho, from the strip you showed, I think you got that part licked pretty good, too Wink
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