Cooling

[Knownot]

So I see lots of battery strings packed tightly together. Why? Do these batteries not need cooling air to flow all around them? Do these batteries not experience temperature fluctuations that would be better handled if the weren't packed together in a box with zero air flow? Wouldn't it be better if every cell had an inch or so of air all the way around it?

This just seems intuitive to me, but I don't know.

 

[newbostonconst]

Most people want to clamp them together for space/design and for houses with large banks the discharge rate is so low that the heat has time to dissipate.

 

[Knownot]

Most people want to clamp them together for space/design and for houses with large banks the discharge rate is so low that the heat has time to dissipate.

Makes sense, just that from an engineering standpoint looking at lifespan, heat is my enemy, and if I can space them out a little, I would expect them to live longer. But as you say, with low demand over time, it may not be the issue I think it is.

Thanks for the reply

 

[newbostonconst]

Makes sense, just that from an engineering standpoint looking at lifespan, heat is my enemy, and if I can space them out a little, I would expect them to live longer. But as you say, with low demand over time, it may not be the issue I think it is.

Thanks for the reply

The other hard part is going to be able to find buss bars that allow you to do what you are wanting without having to make your own. Most people buy there bus bars from the place they buy there cells.

 

[Knownot]

The other hard part is going to be able to find buss bars that allow you to do what you are wanting without having to make your own. Most people buy there bus bars from the place they buy there cells.

That's understandable too. I can make my own, so I'm thinking of spacing the batteries about a half inch when I assemble. Can't hurt can it?

 

[newbostonconst]

I made my own for a 108 cell pack of 55ah cells and it was a lot of work....if you make them out of aluminum it is easy and on the cheap side but copper is hard and expensive. I also bought 48 copper ones off Amazon that I had to drill out, that wasn't to bad.

 

[jtvt]

I haven't noticed any temperature change with charge/discharge. Charge maxes out at under 200a in my setup which is across 4 48v banks. So under 50a per bank for charging. But that never is for very long since my daily DoD is low. Typical discharge rate is much lower than that. Any high discharge rates (water pump, etc) are too short lived to be a problem. My cells are not in a box, but on a shelf. They are compressed.

I think your question may evolve into a "compress or not to compress" question.

 

[OffGridInTheCity]

I'm 18650 cells but there are similarities. In the beginning I worried about heat as well. However, after 3.5years of operation I notice that my cells do not have ANY HEAT AT ALL that I can detect. On average my powerwall operates at <0.1C / cell charge/discharge. The max is 0.2C for short periods of extreme load.

As mentioned above, the level of charge/discharge greatly affects this issue. At really low C, for 18650 cells. there's no detectable heat.

 

[Knownot]

I made my own for a 108 cell pack of 55ah cells and it was a lot of work....if you make them out of aluminum it is easy and on the cheap side but copper is hard and expensive. I also bought 48 copper ones off Amazon that I had to drill out, that wasn't to bad.

I have a 10'x1'x1/8" sheet of aluminum in the shop that's a leftover from decking my workbench. I have a bandsaw and a drill press too, so making busswork shouldn't be too difficult for me.

 

[Ampster]

So I see lots of battery strings packed tightly together. Why?

Compression is recommended by some cell manufacturers. I did not see a reference to cell type in your posts.

 

[Knownot]

Compression is recommended by some cell manufacturers. I did not see a reference to cell type in your posts.

I have yet to purchase a set. I'm trying to gather as much information from those with experience as possible before starting the project

 

[Ampster]

I have yet to purchase a set. I'm trying to gather as much information from those with experience as possible before starting the project

Good plan. Don't form any conclusions about cooling then. Size your pack for your needs and as others have said cooling will not be an issue at the typical low discharge rates in a stationary storage application. In my situation I discovered that some heat conduction takes place through the terminal tops so using heavy bus bars allows compression and no compromise on cooling.

 

[Knownot]

Good plan. Don't form any conclusions about cooling then. Size your pack for your needs and as others have said cooling will not be an issue at the typical low discharge rates in a stationary storage application. In my situation I discovered that some heat conduction takes place through the terminal tops so using heavy bus bars allows compression and no compromise on cooling.

Thanks. This forum has been a wealth of info so far. I've just been reading threads and trying to get an idea of what it's gonna take to replace my lead acid ~1700ah battery with a LiFoPo4. I need over 440ah minimum with my equipment, but my ultimate goal is to have ~2500ah of usable depth.

 

[newbostonconst]

I have yet to purchase a set. I'm trying to gather as much information from those with experience as possible before starting the project

Be aware that the terminals on the cells aren't centered to each side....So if you put the cells end to end the bus bar will be one length and if you put the cells side by side the buss bars will be another length....this is a pain if you don't know this or change your battery layout later only to find out your cells are spaced nice or the bars are too short to do what you want.