Battery disconnect for nominal 48v systems?

jameshowison

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Setting up a 48v nominal system. Two 48v batteries in parallel, the Jakiper server rack batteries. Each has a circuit breaker disconnect on the battery.

Most schematics also feature a main battery disconnect right at the positive busbar, using the red disconnects from Blue Sea. I would just add one of those in so that I can turn off the battery but they are rated at 48v max, and Blue Sea says they aren't for use with 48v nominal systems that can run up to 58-60v when fully charged.

So what are people doing for a battery disconnect for 48v nominal? Will's 48v workshop system seems to use a surface mount Blue Sea circuit breaker (like a 285 series), but those also seem rated for a max voltage of 48v.

Not something to worry about? Just use the disconnects on the server rack batteries (would need to ensure both are off!).
 

RobertGreen

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I would double check with Blue Sea themselves because I thought someone has said their voltage rating is "nominal" rating so it is 48V nominal battery bank that it could handle.
Victron, Blue Sea, Perko, and others all produce battery disconnect switches rated at "48v" which are commonly used on 48v-nominal systems.
I'd be interested to hear if any of these manufacturers actually forbid this practice, as it seems a bit misleading if they are not actually compatible with a "48 volt" battery.

Albright makes some of them too, rated 48v max, but then they also claim that it is "Suitable for voltages up to 48 Volts DC, commonly used on 12 Volts, 24 Volts and 48 Volts DC electric vehicle systems." according to their datasheet.

Clear as mud? :p
 

jameshowison

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Thanks all. Some good options there. FWIW, I wrote to Blue Sea technical support with:

Disconnect for nominal 48v system (ie 58v max)

Are any of your battery disconnects rated for a nominal 48v system? ie voltages up to 58 or 60v?

I see 48v max on these listings.
And they replied:
Hello James,

The only switch we have that is rated for 48V nominal systems is our 7700 or 7702 ML-Remote Battery Switches. They are rated up to 64V maximum, but they do require a 12V (7700) or 24V (7702) control system to be used remotely.

7700: https://www.bluesea.com/products/7700/ML-RBS_Remote_Battery_Switch_with_Manual_Control_-_12V_DC_500A

7702: https://www.bluesea.com/products/7702/ML-RBS_Remote_Battery_Switch_with_Manual_Control_-_24V_DC_500A

Please ask if you have any additional questions.

Best Regards,
Blue Sea Systems Tech Support
 

Struc

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Depends on how much you want to push the limits. I bought a switch from Aliexpress that is rated for 600A Continuous @ 50v max. It's the same as this one but half the cost if you wait for it from China. Amazon Battery Switch

I plan on never pushing more than 125A though it at 54v or so. For me, it was a reasonable assumption that it can handle that.
It's not entirely built yet, so I'll let you know if it goes up in flames. ;)
 

rhino

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I know Victron shows rotary switches in their 48V system schematics so they must exist. I have a switch from Marinco that also says simply "48V" so I am double checking with them if that is nominal or max.
 

Maintenance guy

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It is rather pathetic that all of them are false advertising to an extent. not one of them are useful for lithium system that range to 58 volt for 48 volt systems. so basically our retail system is flooded with useless junk, ie an accident waiting to happen with no accountability what so ever. they are all really rotten manufacturers.
 

RobertGreen

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I know Victron shows rotary switches in their 48V system schematics so they must exist. I have a switch from Marinco that also says simply "48V" so I am double checking with them if that is nominal or max.
Victron's "Wiring Unlimited" document seems to suggest that NH fuse disconnects are a good option for systems over 24v, at least for disconnects. Indeed, the ratings on a lot of those things are great; some of them up to 1500V DC and with a large (tens of thousands of AIC) interrupt rating.

The only problem is that I haven't found a decent domestic source for them yet in the USA.
 

Tecnodave

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In the USA, under 50 volts is low voltage so falls under a different set of rules, so a 48 volt system (which will have voltages over 50 volts) legally must be in conduit, batteries must be in a steel box with wiring to the inverters, charge controllers “must be “ in conduit where as a 24 volt system will not be subject to any high voltages anywhere, and the DC wiring does not have to be in conduit.

All qualified certification agencies will test to a much higher voltage than the “approved voltage” , I cant offically tell you this but I know for certain that most Bxxx Sxxx switches are tested to 72 volts but are certified to 48 volts.

Blue Seas switches are really rebranded Buss/Bussman rebranded, Buss does the certification and does push them over 72 volts

This question was posed to Robin Gudgel, president of midnight solar, about his breakers, and he responded with “don't lose any sleep over it, they will be fine”

Square D certifies their QO line to 48 volts DC , but tests to 72 volts, they used to be certified to 72 volts,

Please note, that is the QO line only, not the Homeline which are AC only.

The difference in AC and DC breakers is the “arc chute” which helps extinguish the DC arc, AC breakers do not have an arc chute as at zero crossing the arc will “self extinguish”
 

RobertGreen

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Hedges

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I wouldn't worry at all about a 48V rated switch holding off 60V. I might worry about an AHJ refusing to sign off a permit based on that.
I would not want to open the switch under full load.
As people have pointed out, the only apparent issue is access to > 50VDC by the lay person.

Breakers and fuses, which open under overload, I would have greater concern. Some give varying AIC ratings for different voltages. Those with a single rating probably have a similar curve, but we don't know.
 

Tecnodave

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Interesting. On page 7-2 on this document (https://download.schneider-electric...CT1901_SEC-07.pdf&p_Doc_Ref=0100CT1901_SEC-07) it appears that the QO and QOB are DC rated at 48v and 5K AIC, but not the others like QOU, QOBH etc
Thanks for pointing that out, I missed that. I have used QOU for DC.....ouch, now only use CBI (Midnight Solar) for din rail, I like them much better. Now i'm going to have to do research on my Schneider (Germany) din rail breakers, that are used in some european electrical equiptment, they are totally different than anything that Square D has done.
 

Hedges

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Thanks for pointing that out, I missed that. I have used QOU for DC.....ouch, now only use CBI (Midnight Solar) for din rail, I like them much better. Now i'm going to have to do research on my Schneider (Germany) din rail breakers, that are used in some european electrical equiptment, they are totally different than anything that Square D has done.

For AC, I've found QO270 had large variation in resistance from unit to unit, which caused imbalance in paralleled circuits (grid feed through relays of my inverters.)
The Schneider DIN rail 2-pole 63A breakers solved the problem.
 

Tecnodave

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Interesting. On page 7-2 on this document (https://download.schneider-electric...CT1901_SEC-07.pdf&p_Doc_Ref=0100CT1901_SEC-07) it appears that the QO and QOB are DC rated at 48v and 5K AIC, but not the others like QOU, QOBH etc
@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
 

Tecnodave

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For AC, I've found QO270 had large variation in resistance from unit to unit, which caused imbalance in paralleled circuits (grid feed through relays of my inverters.)
The Schneider DIN rail 2-pole 63A breakers solved the problem.
Are you speaking of QOU and Multi-9 breakers? I think the Multi-9 is a far superior design, I do see them in industry but they are timely to obtain. narrower than any other din rail , they are hard to substitute for. I confess to using Midnight Solar MNEAC breakers in a pinch where there were Multi-9 breakers in use.
 

Hedges

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I think it is QO270 and Multi-9 C60 63A


I already had a pair of the Schneider after visible blade disconnect as OCP for inputs of four inverters.
Outputs landed on two QO270 in the PV combiner box. I observed imbalance in inverter wattage display. I first fixed the imbalance by landing unfused on main lugs (use lugs with 2 holes & set screws each). Then added another pair of the Schneider in line with that.
 
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