Battery disconnect for nominal 48v systems?

RobertGreen

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@RobertGreen

Go read that chart once again.....QOU is rated for DC, same specs as QO

Also Schneider’s Multi-9 din rail breaker is rated 60 volts DC in single pole and 120 volts DC tandem. These are what I find in German and Austrian electrical equipment in use here. These are listed in the Square D catalog but are manufactured in Germany.

Schneider Electric (Germany) bought Square D and incorporated them into the entire product line.

In my commercial work, I do stock only Square D, Schneider, and Siemens
Good catch! I had noticed the "120/240 V~" marking on QO breakers before, and it hadn't occurred to me to dig deeper to find the DC rating.
 

Tecnodave

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Im surprised, Is that in your Sunny boy inverters. They use QO plug on buss breakers? I don't really touch grid tie solar, Living out on the edges it does not make any sense to me to grid tie. Most of my commercial electrical work is Agriculture or Industrial, with a smattering of remodels thrown in.

For very high reliability installations I use Siemens all copper buss farm panels, I prefer them over Square D, but I have to look for them, no locals stock them but nearby is Salinas, California, a “can do“ city

Around here the Strawberry farmers are king, we are the Strawberry Capitol of the world. Farmers that pop a water pump on a 4 day weekend will lose a million bucks in lost production before they see most electricians. Im available to select clients 24/7/365...that comes with a price. I do not need to mess with residential. I did a 2 am to noon 100 h.p. motor swapout and took home a months wages. And yes you can call 24/7/365 and get a loaner pump motor delivered within a few hours. Complete rebuild on a 1930’s vertical shaft 100 h.p. motor delivered to farm including loaner motor pickup and delivery...$2500, what a deal.....Shop will not even look at a motor smaller than 10-15 h.p Ag pump motor shop in Salinas....
 

Hedges

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Im surprised, Is that in your Sunny boy inverters. They use QO plug on buss breakers? I don't really touch grid tie solar, Living out on the edges it does not make any sense to me to grid tie. Most of my commercial electrical work is Agriculture or Industrial, with a smattering of remodels thrown in.

The Sunny Boy and Sunny Island don't have any AC OCP built in. Some Sunny Boy have a combiner with touch-safe fuse holders. Sunny Island has DC circuit breaker for battery (I don't know the exact rating.)

Various Sunny Boy require breaker/fuse of different ratings for grid connection.
Sunny Island requires breaker/fuse for both AC input and output. It can pass up to 56A through. Max 70A fuse on input (which gives 25% headroom). It says to use max 56A protection on the output (but that wouldn't work unless it was rated for 100% of breaker value; for thermal/magnetic we need 25% headroom.)

For paralleling feed-through from grid, it says to match wire length. I have about 40' on input and 20' on output (6 awg) and expected that to balance well, but the QO breaker dominated resistance and caused imbalance.

I've shipped out little motors for rebuild, like 2 HP pool pump. I got a 2-speed, but found 1800 RPM wasn't fast enough with DE filter at all plugged up. A pressure-side pool sweep came with the place, but kept blowing hoses. I got a suction-side, an to adjust the input bleed to where pump was cavitating to get it to work. Pool stayed clean of debris, but I burned up a couple pumps. One would run on low, but on high there seemed to be greater force, loading armature until it dragged (bearings going?) I now use a 3-phase with Hitachi VFD, set it where it pumps without making cavitation sounds. No automatic sweep, push the vacuum once a week. That's been working about 15 years of intermittent use.
 

Tecnodave

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I have dealt with a few Sunny boy installations and knew that the small ones do not have AC OCP but I have never seen a bank of 4 of them. Im surprised that the internal impedance of the QO breakers would affect the balancing of the units. Im still not quite clear as to how you replaced the QO with din rail. I have used bolt on adapters that allow a unfused feed to be bolted onto a QO bus, Is that what you are doing?
 

Hedges

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Not bolt-on adapters on the bus fingers, rather at the main lug ends. Then the DIN rails breakers in another box feeding it. This was for the 225A QO breaker panel on output of Sunny Island fed by the battery inverters.

(On input side, I already had a 100A visible blade switch which previously fed the main lugs when this was grid-tie only. For OCP on input when installing the battery inverters, I mounted a DIN rail inside the switch box and put two dual breakers there. With house now powered through Sunny Island, I also added an interlocked "generator switch" breaker panel so Sunny Island could be bypassed to put house directly on grid.)

I was surprised too. I expected 60' of 6 awg to dominate resistance.
You would expect excess resistance to result in heating and tripping at low current. Those QO breakers work fine individually although I haven't tested their trip threshold. I do have a 100A breaker that started tripping well below 70A, and wouldn't reset until some days later. I wonder if it slowly cooked and changed its characteristics, perhaps due to poor connection with wire (no burned insulation, though.) Home Depo wouldn't exchange, so I plan to contact Schneider to take advantage of their lifetime warranty.

Sunny Boy or Sunny Island?

Sunny Boy wouldn't involve multiple parallel paths from same source to same load. Each is independent, with its own PV array, feeding common AC grid. No problem there; each just drives its power into whatever AC voltage is present.

Sunny Island can have 1 to 4 in parallel for 120V system (220V for European model.) It can have 2 wired for 120/240V split-phase, or 4 which puts 2 in parallel on each phase. Each monitors current to/from grid which is not to exceed 56 Arms. When internal relays are connected to grid, load draws current through two in parallel, or AC coupled PV Sunny Boys backfeed current in parallel. Master SI reports total power to/from grid, and the other three Slave SI each report the power passing through them.

QO breaker panels are available "main lug" or "main breaker". I replaced the single large lug with the following dual lug.


I mounted a 6" x 6" x 2' wiring box above the breaker panel and put contactors in it for load-shed (house load disconnected at low battery so inverter can keep supplying AC to Sunny Boys while waiting for sun to come back up.) I added two dual 63A DIN rail breakers in the box so each SI has OCP.

I had thought SI could accept 56A from grid and add 50A (6kW/120V) for 106A load, but manual says 56A max output. Except surge of course.

Here's a big system, DC coupled with Sunny Island Charger rather than AC coupled with Sunny Boy. But it looks like multiple 3-phase clusters each with their own battery, which would then be connected together on AC bus with Multi-Cluster Box. No wires or relays in parallel.


This one is AC coupled to Sunny Boys.

 

Tecnodave

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Thanks, Hedges

Now I understand what you are doing, had I thought about a bit more. Makes a lot of sense.

Still really surprised that there would be that much variance in QO breakers, more inline impedance than 60 feet of 6ga.
I would have never guessed that.
My solar system is all din rail, or Carlingswitch, much more of an industrial system, but din rail is not at all accepted here in the US as it is elsewhere in the world. Ive seen photos of din rail in homes in Australia.

My local inspector saw my setup and was baffled, he had never seen anything like it.
 

keepsake

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I have a Siemens double pole 100 amp breaker in use for 55v battery bank. In reality at 150 amps I see one side at 100 amps and the other at 50 amps. So very unbalanced, at least with DC. Running hot battery side in parallel on both terminals on breaker, and both side of busbar are tied together to inverter in.
 

Ampster

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I see one side at 100 amps and the other at 50 amps. So very unbalanced, at least with DC.
Are the poles ganged like a 240 volt AC breaker? You are close to the breaker capacity on one leg. What size is the wire that the breaker protects?
 
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keepsake

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The internal resistance of the breaker would be two-fold difference. Not as noticeable mismatch at 240 ac volts usage.

For this test: I ran two #4 wires from battery hot to each breaker screw terminal. Bus side was tied together to inverter. Observed inverter at about 150 amps DC side. Clamp on meter, with hall sensor, observed 50a on one #4 lead, 100a on the other.
Just saying, these matters are not solved cheaply.
 

keepsake

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Yes. Breakers were inherited from 240 vac usage. Double-pole, standard Lowes fare.
 

Hedges

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My system ran fine for 18 months with Schneider 63A multi-9 2-pole breakers, two in parallel. (not immediately parallel, but through 4x Sunny Islands and 60' of 6 awg). I have a pair of these breakers on input to Sunny Island, and another pair on output.

A week ago, power shut off. Logs show 25A +/- going through each leg, then one pair went to zero and the other carried 50A, then tripped off.
I didn't find a reason for 63A breakers to trip, especially the first pair operating < 50% of rated current. Maybe a momentary spike, a rat-gnawed wire shorted??

Clamp AC ammeter didn't seem to show as large an imbalance between circuits. But even the logs were only about 10% spread. Not like the 3:1 I saw with QO270 breakers.

1647720850765.png

These breakers came from a batch of 10 used pieces I picked up. I hooked my circuit breaker test system back up (oil filled radiator heaters for current source, 3:1 current transformer feeding DUT circuit breaker 40V).
Other breakers carried 60A without problem. Some varied in voltage drop.
The problematic breakers, on pair tripped at 60A. The other did not.

I swapped in a healthier pair of same model, running OK for a week so far.

I'm considering getting Midnight 60A magnetic-hydraulic breakers. Or other model from their supplier CBI, to get a different trip curve.
Magnetic-hydraulic breakers supposedly can run at 100% rather than needing to be derated to 80%.
Thermal breakers have a time constant as long as 15 minutes or more, heating from over-current and cooling to ambient. Fast-trip above 5x.
Magnetic-hydraulic have a delay on the order of a second (or fast-trip for large overload.)
 

Tecnodave

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Yes. Breakers were inherited from 240 vac usage. Double-pole, standard Lowes fare.
HELLO.....Do you know that AC rated breakers will burst into arc and fire when exposed to DC electricity.......????

ESPECIALLY.......High current fault....!!!!

GOOD WAY......To burn down whatever that you are doing

DONT LISTEN TO ME...........Go check it out......

GET.......those AC rated breakers out of there before you burn down....

REALLY....,!!


YES..... Im being really blunt
 

Hedges

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Many of the Square-D QO breakers are rated for DC (at reduced voltage) as well as AC.
None over 70A so far as I know. And not the main breakers, only branch circuit breakers.

I don't know if the Siemens are or not. Don't use them that way unless you find DC ratings for them.
As Technodave says - that can lead to fire.
 

Tecnodave

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Siemens breakers are NOT rated for DC use. The only commonly used (American) AC panel breaker that is rated for DC use is the Square D QO line only and only to 48 volts ((UL listing) but are tested to 72 volts DC
 

keepsake

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DONT LISTEN TO ME...........Go check it out......

Can you please cite any links to this concern of fire risk ?
Thanks.
 

keepsake

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Does this DIY forum have the ability to sell stuff ? I need 250 amp breaker and this site is so helpful, they deserve some revenue.
 

Struc

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Hedges

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DONT LISTEN TO ME...........Go check it out......

Can you please cite any links to this concern of fire risk ?
Thanks.

DC breaker wrong polarity


AC breaker used for DC


AC breaker on way too high DC

 
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