Deciding to DIY my solar battery was one of my worst mistakes ever

[kolek]

A DIY battery is a lot more doable if you don't stress over the details. Throw on the regular busbars that come with the battery. Grab any BMS. Don't bother to top balance. Don't use a torque wrench. Don't bother with compression. Don't build a case. Don't worry about giant sparks when you connect the battery to the inverter. Don't bother calculating the wire thickness. Maybe almost electrocute yourself a couple times. Even then the project would still suck. It would just suck a lot less.

Unfortunately, I tend to be way too much of a perfectionist, to the point of just being stupid. The net result is I get practically paralyzed trying to figure out simple things like, "what is the exact best material I should use between the cells" and I spend 3 hours researching it. When you go at it from that point of view, it's like a neverending project.

Edit: Note the above is not "advice." It's just what some people do who don't stress the details. Personally, I can't operate like this.

 

[Tulex]

I think if you don't mind spending the money, and you can get what you want in a premade battery, and you aren't doing it for the fun, then certainly buy.

But I'm not made out of money, I didn't have room for standard batteries, and I do like projects. On top of that, I know the quality of the build.

Beyond that, much of the discussion about what has to go into a battery is overdone, at least in my opinion. You don't really need compression, you don't need flexible busbars, they don't even need to be in a container. There are so many examples of what people have done on here that it's just not that hard. Follow their lead, use some common sense, it just works.

All that being said, I know a guy who installed a new door knob assembly. When I stopped in, he asked me why the door wouldn't close. He had installed the latch assembly backward, yet he couldn't see that. So, DIY isn't for everyone.

 

[1201]

A DIY battery is a lot more doable if you don't stress over the details.

Throw on the regular busbars that come with the battery.

. They are solid copper

Grab any BMS.

Does that make it easier to assemble?

Don't bother to top balance.

if you diy and use your savings on more battery, at a low c rate, they will top balance themselves.

Don't use a torque wrench.

Are there people out there who are really using a torque wrench to build their batteries?

Don't bother with compression.

some prebuilt batteries are not compressed

Don't build a case.

. Ive never been able to figure out the sense In buying a $500 case for a $2000 battery. That $500 can buy a lot more battery

Don't worry about giant sparks when you connect the battery to the inverter

Terrible advice

. Don't bother calculating the wire thickness.

More bad advice

Maybe almost electrocute yourself a couple times. Even then the project would still suck. It would just suck a lot less.

 

[SilverbackMP]

I designed and built all of my boxes…bit time consuming but fairly easy with a track saw.

My electrician and I wire the first one together, and I was able to use that as a model to wire the rest. Without him helping, I might have been fked.

On compression, I say it need some, but nothing crazy and I damned sure am not going down the rabbit hole that I’ve seen others go down. Mine consists of three row of strapping tape on a group of eight cells and 1/4 rubber floor material lining a solid box with flexible cutting board material used as shims to get a tight fit.

 

[42OhmsPA]

Mainly research is what's time consuming. Currently I'm trying to figure out the correct torque figure for the battery fixture I created. One person on this forum says:

"300 kgf looks to me to be 660 lbs of clamp load. 25 in/lbs of torque on 5/16-18 threads"

another guy says:

"The spec from EVE was 300 KG force which rounds off to 660lbs. Battery face is approx 6.85"x 7.874" = 53.94 sq inches
660lbs/53.94sqin=12.23 lbs per sq inch
Divide 660 by 4 bolts that's 165 lbs Axial (clamping) force per bolt.
Using 4 course 1/4 in threaded rods that should equate to roughly 8 INCH pounds torque per bolt. Realistically, that's a snug twist of the wrist on a regular nut driver for the average build mechanic."

So 1 person says 25 in/lb, the other says 8 in/lb, I don't know which is right. If anyone in this thread happens to have authoritative information, that would be great. My fixture is using 6 threaded rods.

I can understand and relate to where you're coming from with some of your points. I definitely spent the most time in the research and planning stages for my first build and over-analyzed many things thanks to some excellent discussion on this forum.
Spent hours building my own bus bars that would handle a 2C discharge, back and forth on compression, terminal torque etc.
The second expansion was so much easier using common sense along with what I learned the first time.
I'm currently working out a deal for 48 cells for the third expansion.
I've saved thousands of dollars building my own, yes my time is valuable; however the knowledge gained is invaluable.

My takeaways after putting a few MWh through my packs.
-Compression isn't necessary if cells are used in low C rate applications. Lashing straps to hold them work great for me.

-Torque the cell terminals by hand and use common sense (only do this if you've been wrenching for years and have a feel for it).
I suppose using a torque wrench on the first build gave me a better feel for it as well.
-Insulators between cells are absolutely needed, I like flexible cutting boards.
-JBD BMS's are great and would be awesome with active balancing.
-Sparks should be non existent unless your welding, cutting, grinding... Use a resistor to precharge.
-At least double whatever capacity you think you need.

 

[shadowmaker]

And if I ever have to fix it, I'll be in a much better position than if I had bought finished batteries.

I thought the same when I found out my cell #15 was defective in one of my 10kWh rack batteries. Got the replacement cell(s) as warranty and DIY the whole job even they offered I could get it changed professionally for free if wanted. Plug&Play. Really easy to do because those busbars were not laser welded. I was mentally ready to deal with laser welds, so I'm quite sure I could have managed those too if needed. While at it I Installed Neey 4A smart balancer which made top balancing super easy but took some 30 hours. Next time I'll get 8A version or even bigger one to make it not only super easy but fast too.

I know now I could DIY battery if needed but there's no economical sense for me to do so as I can get premade cheap enough.

 

[1201]

-At least double whatever capacity you think you need.

exactly. I remember when I thought a rack of 6 100a ah batteries was enough , lol.

by DIYING I was able to double my capacity to 57kwh for less than one rack and it has many benefits.

• lower charging and discharging c rate
• lower gauge, less expensive wire
• cycling the batteries less
• less stress and less heat on everything

now I'm spoiled. If my batteries even get down to 50% soc I start getting antsy

 

[kolek]

@42OhmsPA or anyone else who might know torque on these bolts...

Thanks for your feedback. Just wanted to clarify, it's the torque on these bolts, the ones that add compression, that I'm asking about, not on the battery terminals. (Note this is not a picture of my battery, it's a picture I found on this forum).

 

[SilverbackMP]

@42OhmsPA or anyone else who might know torque on these bolts...

Thanks for your feedback. Just wanted to clarify, it's the torque on these bolts, the ones that add compression, that I'm asking about, not on the battery terminals. (Note this is not a picture of my battery, it's a picture I found on this forum).

There’s like a 100 page post where folks argue, debate, and rehash that.

 

[42OhmsPA]

@42OhmsPA or anyone else who might know torque on these bolts...

Thanks for your feedback. Just wanted to clarify, it's the torque on these bolts, the ones that add compression, that I'm asking about, not on the battery terminals. (Note this is not a picture of my battery, it's a picture I found on this forum).

Personally I'd go finger tight turn plus a turn but I know others will have differing opinions.

I'd also add a plate or piece of angle from one side to the other to spread the load, wood will change over time. (I know it's not your build).

 

[42OhmsPA]

There’s like a 100 page post where folks argue, debate, and rehash that.

Yup, made my head spin at times.

 

[SilverbackMP]

exactly. I remember when I thought a rack of 6 100a ah batteries was enough , lol.

by DIYING I was able to double my capacity to 57kwh for less than one rack and it has many benefits.

• lower charging and discharging c rate
• lower gauge, less expensive wire
• cycling the batteries less
• less stress and less heat on everything

now I'm spoiled. If my batteries even get down to 50% soc I start getting antsy

Good point, I still have a pack pulled out that I need to replace a cell in. I could probably revive the cell, but it’s going into the 12v pile for a future trolling battery build.

 

[hwy17]

I am posting this for humor and not with the intention to ridicule anyone. It is based on my own experience.

 

[kolek]

Personally I'd go finger tight turn plus a turn but I know others will have differing opinions.

I'd also add a plate or piece of angle from one side to the other to spread the load, wood will change over time. (I know it's not your build).

Oh, don't worry. lol. I'm using a solid 11mm thick sheet of aluminum for the end pieces.

 

[hwy17]

Oh, don't worry. lol. I'm using a solid 11mm thick sheet of aluminum for the end pieces.

Nice. That's what I had planned for mine too, half inch aluminum plates. Until I tried to put them in my toolbox case and found that I measured all wrong. And that's where I instantly converted to the no compression team.

 

[kolek]

I am posting this for humor and not with the intention to ridicule anyone. It is based on my own experience.

Perfect, yep, the "virgin" dude fits my personality to a "T."
Is that your original artwork?

 

[hwy17]

Is that your original artwork?

Yes I did make that for today. Not the template, just the text of course.

 

[kolek]

Nice. That's what I had planned for mine too, half inch aluminum plates. Until I tried to put them in my toolbox case and found that I measured all wrong. And that's where I instantly converted to the no compression team.

Hey, you can't do that! Are you saying you switched from the "virgin" team to the "chad" team just like that?! lol

But in all seriousness, I really question if the "chad" team really ends up with a decent result in the end. Maybe they do, I just don't know.

 

[hwy17]

Hey, you can't do that! Are you saying you switched from the "virgin" team to the "chad" team just like that?!

At multiple points in my build I went chad. Sometimes by choice, sometimes by error and frustration.

I was originally planning to have automatic precharge with automatic offline recovery. Now I have manual precharge with manual recovery. My next one probably won't even have manual precharge, and will rely on the other batteries in the bank for the precharge.

 

[SparkyJJO]

My "workshop" is a mess (garage) and I need to finish the bottom of my box (overengineered and underengineered at the same time, oh well). I did the stupid and am making my own bus bars because the ones that came with the cells are too dinky IMO (another mistake on my end I guess, more DIY).

My biggest issue is while I love DIY, I don't have a lot of the resource called TIME. I have 3 kids 5 and under. When am I going to have time?