I want to use a Square D circuit panel for the individual fusing of up to 15 LTO batteries. I am desiring attaching each battery individually to a 2 pole 20amp circuit breaker in the panel. This will turn the panel into a common bus bar with a 300amp fuse on the 4-0 positive lead going to my inverter. Because I am running the circuit breakers in the reverse direction of normal electrical flow they are intended, do I have to reverse the polarity of the wires attached to the circuit breaker in order to make them trip
Using electric panel & circuit breakers for solar battery bank fuses
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Gotta watch that short circuit rating - plenty of batteries out there can put out mad short circuit current. you'll need some proper fusing.
for example a tesla pack is able to put out over 1500 amps for 3 seconds (0-60 time is 2.4ish) at rated voltage. wonder what it puts out if you short it? I don't want to be near that test.
also thought i'd drop this here:
for example a tesla pack is able to put out over 1500 amps for 3 seconds (0-60 time is 2.4ish) at rated voltage. wonder what it puts out if you short it? I don't want to be near that test.
also thought i'd drop this here:
The Square D panel is a QO142L 225D which is rated for DC. My batteries are 22.5ah each which the 20amp breakers are more than sufficient for. My question was regarding the breaker wiring, not the setup I am implementing. I don't know if they require a different connection to make them trip as, essentially I am using the panel and breakers in reverse of normal setup
Thanks, I posted the Square D panel model I am using which is made to handle DC current as are the 2-pole, single switch 20amp breakers. My question is the wiring of the breaker's positive and negative terminals to insure that they will trip correctly.
I'd check their literature they likely specify if it matters. with some breakers polarity does matter.
Yeah, as soon as you said Square D I knew you were someone who had done the research (unlike the peanut gallery) and picked QO, or possibly a cheap noob grabbing HOMeline on price. My bet was the first one.
QO breakers don't specify a polarity. Because Square D assumes you'll be using the neutral bar for common; but they can't know if your system is negative or positive common/GND (not to be confused with safety ground). The way you're doing it, given their interleaved bus stab design, polarity on a 2-pole breaker is decided by position. Move it up 1 space, you reverse polarity. Be VERY careful with that!
"Mad" eh? You know every consumer grade breaker is rated to interrupt either 10,000 amps or 25,000 amps. Even the lowly QO220.
Cute, but that's not amps. That's volts. As I often say, DC power turns from Dr. Jekyll to Mr. Hyde somewhere around 60 volts (note the DC rating of QO is 48V, down in the "still well behaved" range). Once DC power turns evil, it cannot be bargained with. It cannot be reasoned with. It does not know pity, or remorse, or fear, and cannot be stopped until the component it's arcing across is dead.
What you're seeing in those videos is a paltry 10 amps (or 40 amps in one case) at 200-400 volts. The unbelievable arcing you see there is just mid-voltage DC being its Schwarzeneggerian self.
Here's another, turn your sound way down, and wait for it
600 V DC: "I can do this all day!"
OP will be fine at 12-24V. DC is docile at those voltages, and the Square D breaker certainly has the amp interrupt rating.
By the way, notice the one scene where they had a 3-pole breaker and they "snaked" the power through phase 1, looped back through phase 2 and forward through phase 3 (so all 3 interrupts were in series). This is a common tactic, because mid voltage DC is such feisty stuff, it's hard to find (sanely priced) breakers for it. *Proper* DC contactors have either magnetic or pneumatic blowouts, with big arc chutes.
Thanks for the realization I have done a lot of homework on my new solar system and battery bank. I just couldn't find the information I needed regarding whether the breakers had the capability of connecting either feeding direction to allow them to trip in my configuration. I assumed they did but, because I have more knowledge of AC than DC, I don't want to take the risk of testing without information giving me some assurance I am doing this process correctly. I appreciate your comments and emphatically concur with your remarks. Thanks again for your reply.
The LTO batteries I am using are 60V maximum however I will be topping the charge parameters at 57V maximum and 47V minimum running all batteries individually in parallel through the Square D breaker box with a 300amp fuse on the positive output..Know I probably mentioned this previously but, just in case you missed it, I want to reinterate how I am using it for clarity.
"mad" lol yeah pick an adjective. my tig puts out 200A at 18V and the destruction that can wreak in seconds is impressive.
DC is a different animal than AC. only 5kA rating on 48VDC, which it's quite possible to get out of a Lithium pack on short circuit, in which case you might sacrifice the breaker while the fuse blows in a worst case situation. I'm not sure if the QO breakers have a method to extinguish an arc (beyond opening the contacts) or not. some breakers do.
No, it's very much amps. it's a 400V nominal pack that can put out over 480kW. 480000/400=1200 amps. 16x 24V "packs" inside, in series, so they maintain that ampacity.
i would not want a QO220 breaker to be the only thing protecting my property from that battery.
Good point. OP, you may want to evaluate that. I don't know if QO panels let you fit a hold-down clamp in *every* position.
Yes, it surely is. If you see old houses where the light switches have a definitive SNAP to them, that's an extra mechanism designed to violently throw the contacts quite far apart, for the purpose of snuffing DC arcs. Because those switches were DC-era.
A much more complex and big-throw snap switch is standard equipment for even the most trivial circuit in old streetcars. Go check out a trolley museum sometime and ask to see the switch internals. If they think you'll "get it", they'll cheerfully pull the pole down and open one up for you. It's just a door that opens.
If Square D breakers didn't have a means to snuff a DC arc @ 48V @ 5 KA, they would not be so listed by UL
I don't know what the story is with those "wrong-way" breakers in your videos. How does reverse polarity kill a DC breaker? Are these Alibaba specials?
In that case, it's *both* volts *and* amps. Why does a car need 480kw? BART cars aren't 480 kw.
Well, at what point do you actually trust UL listings and competent hardware from Tier 1 suppliers? You have to draw the line somewhere.
Geez, I have enough trouble getting people to stop trusting Alibaba.
Also, since OP only wants to pull 20A per battery, this seems like an excellent job for a *fusible link*. Put a 12 AWG fusible link in there, the QO will handle anything under about 1000A, and anything over, the fusible link will just vaporize.
my point is the supply (battery) may put out more than that if it's Li-ion.
as far as I know the only issue is they're polarity sensitive
why does anyone need a car that has 600+hp and does 0-60 in under 6 seconds? that's a philosophical inquiry that i'd rather not derail this thread with. the car/batteries are there so don't drop a wrench across the terminals. it might melt.
apparently nearly 600kW (1500 amps @400V):
fusible link/DC fusing sounds good. people always seem to end up wanting to do more than they thought they did when they started.
Y'know, another way to solve that is the old power company trick of make your service wires small enough that 10KA is *impossible*. For instance OP wants to breaker at 20A, so use 12 AWG wires. If the line to your 24V battery is 6' long, that's 19 milliohms round-trip, and that will remove any possibility of current above 1250A.
I saw an interesting study on whether a historic streetcar could be powered by a Tesla battery pack straight out of a Model S. Answer: Easily! It's going 30 mph instead of 80 mph, but the battery doesn't know that!
yeah if the motor is happy it's fine. all the battery cares about is cell voltage and temperature. keep those in check and in the short term there's not much to do that'll damage it.
problem with your 12ga wire is if the breaker fails what stops that wire from turning into a red hot pile of slag? i'd put in a big DC fuse no matter what. if nothing goes wrong they never get replaced. typically the fuse goes right at one of the battery terminals.
problem with your 12ga wire is if the breaker fails what stops that wire from turning into a red hot pile of slag? i'd put in a big DC fuse no matter what. if nothing goes wrong they never get replaced. typically the fuse goes right at one of the battery terminals.
Hey, just a heads up to those of you who responded to my question here over 2 years ago. I am now running two racks of 20 LTO SCIB batteries using 2 Square D QO142L 225D breaker boxes with 20 Square D QO double pole breaker switches in each box connected to a 300AMP T fuse and common buss bar for my battery bank system on my off-grid farm. This provides 44kW of stored power based on 1.1kW per battery. The system has worked extremely excellent and a lightening strike tripped all of the breaker switches without harming the system. I reset them all and everything worked as usual after I replaced the 300AMP fuses.
It's nice to know that something works out the way you have intended it to.
It's nice to know that something works out the way you have intended it to.
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