diy solar

diy solar

Few questions to those that made DIY batteries.

Luk88 said:
I'm trying to find out how far to discharge to avoid any swelling. Of course the chance of it happening now that the cells are new is a lot less than after 2 years of cycling for example.
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I think 50-60% shoiuld work for new cells. My cells were two to three years old and as I mentioned, only three of them were swollen and they were all part of the same three cells in parallel. The other 45 were fine.
 
Ampster said:
I think 50-60% shoiuld work for new cells. My cells were two to three years old and as I mentioned, only three of them were swollen and they were all part of the same three cells in parallel. The other 45 were fine.
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Yes, that makes sense for my cells now.

But I wonder. Let's say one has cells in the middle of their cycle, and calendar life. Let's say ~2k cycles a 5 years old (cycled daily).

Can we discharge sufficiently down, to avoid any swelling at all during couple of hours with fixture removed? Sadly, this is one of these "more research needed" problems...

Coming back to BMS battery disconnect. I've been looking at manuals for all my devices and I can't find it mentioned anywhere as a "don't disconnect the battery while charging" rule. I only saw it online.

My inverters have a sticker that says "Don't connect the battery while AC is on." but that's a different thing.

Furthermore, the manual says to install a dc disconnect between the battery and inverter, but doesn't mention any rules in connection with its use (not even the one on the sticker placed in the device).

So, I'd like to ask, is there anyone here that had a charger/AIO damaged by a battery disconnect event?

I'm struggling to understand how the charging circuit in such situation is in any way different than let's say a constant current power supply with max voltage. If you disconnect it, the voltage goes to max setting and stays there.

What would be the mechanism of such damage and is it just speculation, or did it happen for someone?
 
Rednecktek said:
Never had an issue, just used a precharge resistor before I turned back on.
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I think inverters should have a sort of "slow start" circuit. Whenever I was connecting cables physically I used 0.5ohm charge resistor, but once I hooked it all up with a bms. I left it off for the next day. Then when I switched on the BMS (via blootooth) the "anti short" protection kicked in and disconnected it. I thought, surely it has charged, right? Wrong, I enabled it again, and it tripped again. I had to disconnect the wire. Precharge with a resistor. Then reconnect and switch on.
 
Rednecktek said:
Never had an issue, just used a precharge resistor before I turned back on.
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Two questions, Is this precharge resistor something that can be used temporarily, while commissioning or does it typically stay in the circuit? I'm picturing pre connecting with alligator clips and removing it once tph battery connection is made.
Second, Can you post a link to where I may purchase one?
TIA
 
littleharbor2 said:
Two questions, Is this precharge resistor something that can be used temporarily, while commissioning or does it typically stay in the circuit? I'm picturing pre connecting with alligator clips and removing it once tph battery connection is made.
Second, Can you post a link to where I may purchase one?
TIA
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It is used just when making an initial connection.

We can't leave it in the circuit unless some elaborate switching scheme is used (automatic or manual).

I use a resistor very similar to this:

 
littleharbor2 said:
Photo? I'd like to make on but I/m having difficulty picturing what it looks like.
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I bought the 2-pole momentary switch online, - just a rocker switch with a spring inside so it is only "on" while I am pushing on the button.
Wire the pos and neg from main bus to the inverter input DC buses around your main disconnect for the ESS, and put a resistor on the Pos lead.

Here is a pic of a similar set up on my mobile DIY 8s pack. The main 2P Pack breaker in the photo is "ON". To precharge this breaker will be "OFF", then press and hold the precharge to charge up the inverter capacitors, then switch the breaker to "ON" with your other hand, and then let go of the pre-charge switch.

Electrically, the Line side neg is wired to the Main battery Neg, and the Load side Neg is wired to the pack terminal Neg. the Line side Pos is wired to the BMS output Pos, and the Load side Pos is connected to a small resistor (ebay/amazon/aliexpress) then to the pack terminal Pos.

{ As an added bit of protection I put an online automotive 10A fuse wired between the resistor and the pack terminal Pos - just to protect the small wire since otherwise the only protection is the BMS which on this pack is 150A which is too high for the small pre-charge wire ga.}
IMG_5126 (1).jpg
 
OffGridForGood said:
I bought the 2-pole momentary switch online, - just a rocker switch with a spring inside so it is only "on" while I am pushing on the button.
Wire the pos and neg from main bus to the inverter input DC buses around your main disconnect for the ESS, and put a resistor on the Pos lead.

Here is a pic of a similar set up on my mobile DIY 8s pack. The main 2P Pack breaker in the photo is "ON". To precharge this breaker will be "OFF", then press and hold the precharge to charge up the inverter capacitors, then switch the breaker to "ON" with your other hand, and then let go of the pre-charge switch.

Electrically, the Line side neg is wired to the Main battery Neg, and the Load side Neg is wired to the pack terminal Neg. the Line side Pos is wired to the BMS output Pos, and the Load side Pos is connected to a small resistor (ebay/amazon/aliexpress) then to the pack terminal Pos.

{ As an added bit of protection I put an online automotive 10A fuse wired between the resistor and the pack terminal Pos - just to protect the small wire since otherwise the only protection is the BMS which on this pack is 150A which is too high for the small pre-charge wire ga.}
View attachment 209123
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Thank you for this. Way more elaborate than I pictured. I thought it was something like a jumper with alligator clips on each end.
 
I "try" to keep alligator clips for temporary stuff/testing.
The parts are all cheap and it will take you less than an hour to set it up once, and then enjoy the convenience forever.
 
littleharbor2 said:
Two questions, Is this precharge resistor something that can be used temporarily, while commissioning or does it typically stay in the circuit? I'm picturing pre connecting with alligator clips and removing it once tph battery connection is made.
Second, Can you post a link to where I may purchase one?
TIA
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Here's the resistor I use. YiePhiot 2PCS 50W 25 Ohm Resistor Aluminum Case Wirewound Chassis Mounted Compatible with Ring Doorbell, Nest Hello Doorbell, SkyBell Doorbell Etc https://a.co/d/7QaQHu6

I ran a wire lead to one end and jump the breaker for 5-10 seconds before closing it.
 
littleharbor2 said:
Two questions, Is this precharge resistor something that can be used temporarily, while commissioning or does it typically stay in the circuit? I'm picturing pre connecting with alligator clips and removing it once tph battery connection is made.
Second, Can you post a link to where I may purchase one?
TIA
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I built mine with a small project box, a momentary contact button, a LED, and a resistor to go around the main breaker. Since my systems are only used occasionally I tend to shut everything down so the pre charge resistor is Step 1 in my startup instructions. I have a small wire connected to each leg of the main DC breaker so the power goes in from the battery, around the main breaker, and out to the inverter.

Here's a wiring diagram of what I build with example numbers:

Precharge success.jpg
 
Rednecktek said:
I built mine with a small project box, a momentary contact button, a LED, and a resistor to go around the main breaker. Since my systems are only used occasionally I tend to shut everything down so the pre charge resistor is Step 1 in my startup instructions. I have a small wire connected to each leg of the main DC breaker so the power goes in from the battery, around the main breaker, and out to the inverter.

Here's a wiring diagram of what I build with example numbers:

View attachment 209143
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Exactly what I'm thinking of. Thanks.
 
So, for those interested, after an almost full charge at 0.3C my cells did increase the pressure on the fixture quite a bit. How do I know? I can see the 3mm mild steel sheet flexing under load.

It flexed so a gap of about 1mm appeared between the cell wall and the middle of the plate. But the cell has not swelled to fill the gap. This means I'll need to weld on a piece of support onto that sheet steel piece.

Also, I was incorrect that Higee doesn't mention compression in their datasheet. They don't mention it anywhere in the wording. But on the technical drawings of the cell where dimeeare given it says 71.8mm at 300kgf. So clearly they want 300kg of force on the cells too.

Edit: Now the task is to discharge them... Not so easy with 14kWh of energy.

BTW, how do you like my temporary "don't drop a washer" brand bus bars?

20240414_104155.jpg
 
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What’s the clearance of those bus bars, 1/4”? That’s sketchy as shit right there.

Such an odd arrangement.

Also if the plate is bowing that means crazy about of pressure on the corners of the end cells, bad mojo can happen.
 
That arrangement would reduce the stress on bus bars from cell expansion, but that clearance would worry me. One solution would be narrower but thicker bus bars but that creates a challenge of getting them flat on the terminal tops.
 
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