The "Meg" Build

[Lt.Dan]

Batteries showed up today! Well 6 of the 7 boxes. I ordered 20 cells and 2 BMSs and only 17 showed up with no BMSs.

I hate FedEx. In the last 5 years I have never had 1 good transaction/experience.

 

[Lt.Dan]

Charging the batteries now. Since I don't have a BMS yet I can't wire them in series and charge, so I am using a bench top power supply (the one Will recommends on his website), set to 32v and max amps, and then using a 30 amp buck converter to step 32v down to 3.6v at 30amps. So its charging at roughly 100-105 watts now instead of 35 watts! But DANG that buck converter is getting warm at 30 amps. 20 minutes in and its steadily at 150* F. The little fan on the bottom is kicking ass and the heatsink seems to be doing well for it. All wiring connections are at 69* F or less.

I'm also charging inside of my Marco toolbox's Hutch. This way if something happens (like hardware malfunction) there's nothing to catch fire lol

 

[K8MEJ]

I hate FedEx. In the last 5 years I have never had 1 good transaction/experience.

For Fedex Ground, amen! My buddy at Fedex says it costs about $500,000 to buy a good route. The route owner then hires the cheapest possible drivers and can easily make $1,000,000 in revenue per year. He said the route owners make money hand-over-fist and only care that the packages eventually get to their destination in whatever condition. While he makes his money selling Fedex Express to his corporate accounts, he spends more than 50% of his day trying to "fix" issues with Fedex Ground. He calls ground services "the bane of his existence".

When I'm given a choice I always choose UPS for regional domestic packages, USPS Priority for stuff coming from the West coast (I live in Ohio), and DHL or UPS for international parcels. I wouldn't pick Fedex Ground to move dog food even if I had a month lead time.

 

[Gazoo]

So its charging at roughly 100-105 watts now instead of 35 watts! But DANG that buck converter is getting warm at 30 amps. 20 minutes in and its steadily at 150* F. The little fan on the bottom is kicking ass and the heatsink seems to be doing well for it. All wiring connections are at 69* F or less.

That's a lot of voltage applied to the buck convertor. What if you turn the voltage of the power supply down to 5 volts or so. Will the buck converter still put 100 watts into the cells? It would run a heck of a lot cooler.

 

[Lt.Dan]

That's a lot of voltage applied to the buck convertor. What if you turn the voltage of the power supply down to 5 volts or so. Will the buck converter still put 100 watts into the cells? It would run a heck of a lot cooler.

The buck converter is rated from 20v-70v input, so its well within its capacity, its just very inefficient going from 32v to 3.6v. If I try and turn down the voltage on the power supply, the amps coming out of the buck converter drop though, I tried several different times.

I'm only using the buck converter with me there to nurse it and constantly check temps (like every minute lol). Whenever I am away, the power supply is set to 3.6v and 8 amps and then connected directly to the batteries.

I've already made an oopsie when I was trying to rearrange them, I accidentally shorted out 2 batteries and blew the stud off of one of them. That wasn't fun. Gotta learn somehow.

Any ideas to fix this one? Maybe mill the terminal flat and drill/tap a new hole? The battery still measures 3.31v.

Or is it junk now?

 

[Bud Martin]

Charging the batteries now. Since I don't have a BMS yet I can't wire them in series and charge, so I am using a bench top power supply (the one Will recommends on his website), set to 32v and max amps, and then using a 30 amp buck converter to step 32v down to 3.6v at 30amps. So its charging at roughly 100-105 watts now instead of 35 watts! But DANG that buck converter is getting warm at 30 amps. 20 minutes in and its steadily at 150* F. The little fan on the bottom is kicking ass and the heatsink seems to be doing well for it. All wiring connections are at 69* F or less.

I'm also charging inside of my Marco toolbox's Hutch. This way if something happens (like hardware malfunction) there's nothing to catch fire lol

View attachment 44689

I would not try to pull 30A from that Buck converter, I usually do 80% max, also keep close eye it since when Buck converter MOSFET failed shorted it will dump 32V to the output.

 

[Lt.Dan]

Good to know, ill try and dial it back to 25a or so.

I would not try to pull 30A from that Buck converter, I usually do 80% max, also keep close eye it since when Buck converter MOSFET failed shorted it will dump 32V to the output.

 

[Gazoo]

Any ideas to fix this one? Maybe mill the terminal flat and drill/tap a new hole? The battery still measures 3.31v.

Wow! I have never seen a stud blown off clean like that. That would have scared the crap out of me. Hope you are wearing eye protection.

It could not hurt to try to mill and tap and use a helicoil. You do not want to go more than 6mm deep from the top of the terminal. I know 6 or 7 is common with EVE cells. Of course you will want to capacity test that cell after you have tapped it. My guess is there is nothing wrong with it so hopefully it can be saved.

Of course the terminal height will not be the same as your other cells. You could use a short cable for an interconnect. Personally I am a fan of braided busbars.

 

[Lt.Dan]

Wow! I have never seen a stud blown off clean like that. That would have scared the crap out of me. Hope you are wearing eye protection.

It could not hurt to try to mill and tap and use a helicoil. You do not want to go more than 6mm deep from the top of the terminal. I know 6 or 7 is common with EVE cells. Of course you will want to capacity test that cell after you have tapped it. My guess is there is nothing wrong with it so hopefully it can be saved.

Of course the terminal height will not be the same as your other cells. You could use a short cable for an interconnect. Personally I am a fan of braided busbars.

It was really quick, and since it blew the stud off, the cable I was attaching disconnected fairly quickly, so no other damage was done.

I always wear proper PPE, and try to always use the proper tools. I even broke out the rubber handled ratchet.

I'm curious if there is anything else I can do, like press in a stud to get equal amount of torque applied. The studs that are on it are VERY solid, and I'm extremely happy with them. I haven't had a single fear in tightening one down.

 

[Gazoo]

If I understand you correctly, I don't know how much pressure can be applied to the terminal. Pressing a stud might cause the whole terminal to press down. In case you didn't know, the studs are pressed into the pedestal. And then the pedestal is laser welded to the cell terminal.

I like the way those studs are mounted too. How many amps do you plan to draw from the cells once you have them in service? My concern is the surface area of the pedestal. Others are concerned about that as well and as far as I know no one has run a test to see if they can carry large current. It doesn't mean they can't, but no one knows for sure as far as I can recall.

 

[Lt.Dan]

If I understand you correctly, I don't know how much pressure can be applied to the terminal. Pressing a stud might cause the whole terminal to press down. In case you didn't know, the studs are pressed into the pedestal. And then the pedestal is laser welded to the cell terminal.

I like the way those studs are mounted too. How many amps do you plan to draw from the cells once you have them in service? My concern is the surface area of the pedestal. Others are concerned about that as well and as far as I know no one has run a test to see if they can carry large current. It doesn't mean they can't, but no one knows for sure as far as I can recall.

Yeah I thought about that, I don't know the structural integrity inside the battery and if it will just push through, as we will need to use more than likely several thousand PSI to press it in all the way.

I only have a 200 amp Daly BMS, which is more than my inverter will draw. But I'm working on a way to increase surface area as we speak. I will be making custom laser cut 1/8" bus bars though.

I do plan on running test with as big if a draw as I can find. My inverter will only draw 6500watts, or around 135 amps though. Then I'll take my IR gun and see if any build heat.

 

[Lt.Dan]

Success! I drilled more than what people recommend, I went to 7.5mm and used a forming tap instead of a cutting tap, which makes for better and stronger threads. Then followed with a bottoming tap to get 90% of the way down. It feels pretty strong, but this one i will probably just assemble once and leave it.

And no, that's not the bolt I'm using, its just one I found that fits right now.

 

[Lt.Dan]

Batteries are almost done parallel top balancing. They are down to about 4amps right now. I made this cool bus bar that attaches all 16 cells in parallel at once. No more dozens of bus bars to deal with.

I did cut all new 1/8" 110 copper bus bars to accommodate the distance I will have my cells apart. The factory ones do not allow 2 batteries end to end, because they are too short. So here's what I made.

Taken while cutting them:


Laser was having a rough day so I had to file some burr down to make sure they all sit flat.


Anybody know if there is any negative consequences to heating up copper like this? I just hope it's not less conductive lol.

 

[K8MEJ]

I'm proud to be the first person to suggest a group buy of copper bus bars from Lt. Dan!

How about it, Dan? Would the shop allow it?

 

[Lt.Dan]

I'm proud to be the first person to suggest a group buy of copper bus bars from Lt. Dan!

How about it, Dan? Would the shop allow it?

Yeah no problem. I can do bus bars up to 1/4" thick, and I can even offer tin plating.

 

[jwelter99]

Yeah no problem. I can do bus bars up to 1/4" thick, and I can even offer tin plating.

Cool! You willing to do custom lengths - I'm working on a project now where I have a couple 3 cell "fat side to fat side" EVE280's to parallel and a couple 6 cell.

I was going to bug the local marine shop we get bus bars from but they are busy and grumpy with all the spring boat work going on. Seems a ton of lithium retrofits going on.

 

[jwelter99]

I'm running a 48v system. And the only reason I am hesitant to go to a DC to DC converter is because none of them are smart charging. When talking with battleborn, we determined that they would hold the 12v Batteries at too high of a charge voltage for far too long, and cause battery degradation. Hence the suggestion for the 120v victron 10a smart charger, because it is a 3 stage charger and won't hold it at a high state of charge for extended time.

Another thought I have, which I am completely ignorant when it comes to this, but what happens when you try and turn a 12v starter with a 48v battery? Will it burn it up?

I did find out onan recommends 450 cranking amps to start the generator.

The other option would be a MPPT separately setup to charge the 12V house battery bank and the 120VAC charger just when solar production doesn't allow it.

For that big generator you are pretty limited to needing that 12V bank to start it. You can check to see if Onan offers a 48V starter for it which would be the ideal option. Pretty common in marine applications to convert generators to a 48V start when house banks upgraded to 48V.

 

[Lt.Dan]

Cool! You willing to do custom lengths - I'm working on a project now where I have a couple 3 cell "fat side to fat side" EVE280's to parallel and a couple 6 cell.

I was going to bug the local marine shop we get bus bars from but they are busy and grumpy with all the spring boat work going on. Seems a ton of lithium retrofits going on.

Yeah just give me the length from stud to stud that you need, and how wide you want your bus bar.

Just know I can't compete with China when it comes to this stuff ? the 12"x12" piece of 1/8" Copper i bought was $100 alone, but it should make around 28-30 bus bars.

 

[jwelter99]

Yeah just give me the length from stud to stud that you need, and how wide you want your bus bar.

Just know I can't compete with China when it comes to this stuff ? the 12"x12" piece of 1/8" Copper i bought was $100 alone, but it should make around 28-30 bus bars.

Completely understand the price issue and happy to pay "made in America by someone who cares" prices

 

[K8MEJ]

Yeah just give me the length from stud to stud that you need, and how wide you want your bus bar.

Just know I can't compete with China when it comes to this stuff ? the 12"x12" piece of 1/8" Copper i bought was $100 alone, but it should make around 28-30 bus bars.

Lt Dan, if I recall correctly, did you make your bus bars for EVE 280Ah cells?