Blue Sea battery disconnect question.

[GlennWest]

Mine is marked input and output. It is only a two lug switch. Does it matter? It is backwards for the way I need it. 

[Kirk W]

If it is a switch it would not matter at all. The contacts are either open of closed and current for a battery goes one direction when discharging and the other when being charged. 

[GlennWest]

Thank you. Is what I was thinking. They went thru the trouble of marking them was concerning me. Now they do make 3 and 4 lug switches also. May be why. Mine just two. 

[GlennWest]

While researching Blue Sea switches I was looking for a single switch to feed both inverters. All the 3 post units were 32v. Only the 2 post units were 48v. So I want with two switches.

[GlennWest]

I may have messed up. I see now it states max 48v. My system is 57v. But I am positive David Dixion uses same switch on his Volt battery bank.

[Darryl&Rita]

33 minutes ago, Kirk W said:

If it is a switch it would not matter at all. The contacts are either open of closed and current for a battery goes one direction when discharging and the other when being charged. 

High current switching, especially DC, is very definetely dirrectional. The internal arc chutes are built for a specific electron flow direction. Whether these switches are built with that high current in mind is the question.

[Kirk W]

15 minutes ago, Darryl&Rita said:

High current switching, especially DC, is very definetely dirrectional.

Absolutely true, but the direction of the high current would depend on whether the battery was being charged or discharged. With minimal current it doesn't matter.

[oldjohnt]

5 hours ago, Darryl&Rita said:

High current switching, especially DC, is very definetely dirrectional

Hi Darryl, Its been a while (long retired EE) but best I recall and observed some DC relay contacts/materials use different coatings BASED ON POLARITY/CURRENT FLOW... As we know current flow WHEN SWITCHING is what's most critical versus just through closed contacts. NOT having any data or specs, it's my best engineer's judgment if such a switch or relay were to be installed MY ADVICE WOUILD BE WIRE IT AS LABELED even if it may work just fine otherwise, and I would avoid as much as possible any switching under load especially high current.

 John T

[Kirk W]

3 hours ago, oldjohnt said:

t's my best engineer's judgment if such a switch or relay were to be installed MY ADVICE WOUILD BE WIRE IT AS LABELED

Sine the lables are input and output, does that mean when the battery is discharging, or when it is being charged?  

I don't disagree with you in most situations, but if you don't open or close it under significant load, why does it matter and which way matters? 

Edited November 15, 2022 by Kirk W

[GlennWest]

Since I am using as a simple disconnect if it breaks circuit and they just two legs it can't matter. I will when weather permits, raining, check with my meter. Actually just had toe operated on today. Nothing serious but can't wear shoes for a few days

Edited November 15, 2022 by GlennWest

[oldjohnt]

14 hours ago, Kirk W said:

but if you don't open or close it under significant load, why does it matter and which way matters?

Like I said 

18 hours ago, oldjohnt said:

As we know current flow WHEN SWITCHING is what's most critical versus just through closed contacts.

  Looks like we basically agree in theory in that if there's no significant load, it matters little. 

  As far as WHY, I don't have any specs or data whatsoever, but I do recall relay contacts in some situations use different coatings based on polarity, have to ask relay manufacturing engineers that's above my pay grade lol. 

  NOTE I do agree with Daryl who posted: High current switching, especially DC, is very definetely dirrectional. The internal arc chutes are built for a specific electron flow direction. 

 REGARDLESSD not having any specs or data my advice remains as I posted above but believe its a persons choice to wire as labeled ORRRRRRRRRR just the opposite.  Its just because even though I lack the data or expertise to explain WHY it matters, when its so easy to wire it one way or the other, WHY NOT GO AHEAD AND WIRE IT AS LABELED ??????????????   Thats what I would do...

18 hours ago, oldjohnt said:

MY ADVICE WOUILD BE WIRE IT AS LABELED even if it may work just fine otherwise, and I would avoid as much as possible any switching under load especially high current.

 THANKS for the good questions and fun sparky chat, I hope this helps even if we bored the non sparkies 

 John T  Live in the RV from Hot Springs Natl Park

 

 

Edited November 15, 2022 by oldjohnt

[GlennWest]

Well I could just mount it upside down. Then posts on correct side

[Randyretired]

Disconnecting high powered DC circuits is complicated.  In a temporary solar array with 1800 watts I used a cheap DC rated breaker, rated for 63amps at 1000v. The wire was large enough it didn't need protection.The first time I switched it off under load (120v around 10 amps)  it made a sound similar to a welder.  That was the end of it.

Edited November 15, 2022 by Randyretired

[GlennWest]

2 minutes ago, Randyretired said:

Disconnecting high powered DC circuits is complicated.  In a temporary solar array with 1800 watts I used a cheap DC rated breaker, rated for 63amps at 1000v. The wire was large enough it didn't need protection.The first time I switched it off under load (120v around 10 amps)  it made a sound similar to a welder.  That was the end of it.

Mine might. I didn't want to hook up to inverters with 260v going to it. Be only 42 amps though. Put solar on 63 amp DC breakers. Will see.

[Kirk W]

But which way is right, discharging or changing? Old John is avoiding that part of the question. 

Edited November 15, 2022 by Kirk W

[GlennWest]

I was referring to comment on solar breaker not my original question. Not the battery disconnect. Mount battery disconnects upside down will put it right. Just didn't want to do that. 

Edited November 15, 2022 by GlennWest

[Jaydrvr]

3 hours ago, Kirk W said:

But which way is right, discharging or changing? Old John is avoiding that part of the question. 

If you potentially can expect roughly the same current levels in and out, I don't see where it would make any difference. If your discharge currents are expected to be substantially higher than the charge currents, you MIGHT consider that to be a priority. Jay

[oldjohnt]

4 hours ago, Jaydrvr said:

If you potentially can expect roughly the same current levels in and out, I don't see where it would make any difference. If your discharge currents are expected to be substantially higher than the charge currents, you MIGHT consider that to be a priority. Jay

   Thanks Jay, Therein lies the question, is the switch designed/intended to turn potential Charging or potential Discharging current on and off ????????????????? I still say absent any engineering specs or data I would wire it as labeled AND ONE HAS TO ASK THE MANUFATURER for the answer, there's no way any of us can know that without more information. 

   While I cant answer more, I will take a pure engineering guess that it being a switch to disconnect a battery IE a HUGE stored energy source, the manufacturer may have considered DISCHARGE CURRENT to be the primary concern??  Following from that pure guess, if it's true as Daryl and I agree that polarity makes a difference in switch and relay design (I cant know if the manufacturer considered and designed for that or not) he may have labeled it accordingly IE MY GUESS IS HE DESIGNED TO PRIMARILY SHUT OFF DISCHARGING CURRENT (instead of lower charging current) FROM AN ENERGY SOURCE TO A LOAD !!!  Hey its a battery On Off switch right ??? Its NOT a Charging On Off switch lol

ANOTHER REASON WHY ITS DISCHARGING CURRENT THATS MOST CRITICAL

 If you consider a huge RV coach battery bank has the stored energy capacity to deliver POTENTIALLY THOUSANDS OF DICSHARGE AMPS, while a typical RV Converter/Charger may only be able to deliver 30, 50 100 or more CHARGING AMPS    Its again, my best electrical engineers guess an On Off switch considers and is designed to handle PRIMARILY DISCHARGE CURRENT. Sure if its not being switched or very low current theres little difference, but Im willing to stick my neck out and say the potential thousands of amps of DISCHARGE CURRENT (versus maybe 100 of charging) is the primary concern when designing a battery On Off switch.  

 

8 hours ago, Kirk W said:

But which way is right, discharging or changing? Old John is avoiding that part of the question

   There ya go, I cant answer a question for which I have no specs or data but I can give it my best electrical engineers shot the design was possibly to switch DISCHARGING CURRENT out of the energy source to loads and I agree with Daryl that polarity makes a difference in high current DC switching design. 

     I gave mine, so now which way do you think is right discharging or charging ??????????? and why??????????

 Sorry if this bores the non sparkies here, but I love these techy electrical threads, sorry I dont know how Blue Sea made their design, you have to ask them.  I dont know if direction of current flow mattered to them or to what extent they considered high current switching I DONT KNOW IM NOT SAYING ..You guys have to figure it out this is above my pay grade

PS Kirk I will be in Longview then Livingston Texas at SKP soon, I will wave as I go by, it would be fun to talk shop. 

 John T Retired but still ever curious electrical engineer 

 

Edited November 16, 2022 by oldjohnt

[Darryl&Rita]

Not a lawyer, nor an insurance agent, adjuster, or sales rep, but I'd bet the Pinkie ring I didn't buy that in the event of an "incident" involving any of the wiring being discussed here, an insurance company would do the fastest side-step you ever seen. They take great delight in anouncing their record profits, quarter after quarter, and those don't come from being generous with payouts.

At any rate, minimize the currents being switched, and the problem resolves itself. At lest, until that one time the owner/owner's representative forgets. In this case, hopefully the maufacturer spec'd a large enough safety margin to contain the chaos.

[oldjohnt]

12 hours ago, Darryl&Rita said:

Not a lawyer, nor an insurance agent, adjuster, or sales rep, but I'd bet the Pinkie ring I didn't buy that in the event of an "incident" involving any of the wiring being discussed here, an insurance company would do the fastest side-step you ever seen

X2 Darryl,,,,,,,FWIW As an electrical engineer and a lawyer it's my experience and professional opinion that's certainly possible !!!!!!!!!!! I have no idea how Blu Sea and the engineers based their design, Im NOT saying, only throwing out possible scenarios and pure guesses. Im sure all agree NOT to switch under heavy loads REGARDLESS if charging or especially discharging and wire per the instruction manual EVEN THOUGH I CANT EXPLAIN WHY ABSENT ANY DATA...Ask Blue Sea why if in doubt...

  John T   BSEE,JD 

Edited November 16, 2022 by oldjohnt

[Randyretired]

Disconnecting only when there isn't a load may work for everyday but if something happens and the switch isn't up to it expect welding inside the switch.  Mostly that will just ruin the switch but it could also weld it closed.  For lithium batteries it might also be helpful to have a Bluetooth enabled BMS that can be instructed to disconnect if time allows.  I am also wondering if there are quality switches made for bidirectional loads.

[Darryl&Rita]

11 minutes ago, Randyretired said:

Disconnecting only when there isn't a load may work for everyday but if something happens and the switch isn't up to it expect welding inside the switch.

And there's the rub. That's also why items get a safety margin built in. Chinese reverse engineered items often lack the safety margin.

[GlennWest]

Wow. You guys make me question if I made a good choice. I thought I did good getting Blue Sea switch.

[Jaydrvr]

25 minutes ago, GlennWest said:

Wow. You guys make me question if I made a good choice. I thought I did good getting Blue Sea switch.

Blue Sea products are great, well engineered and well built. You can't go wrong with them. Jay

[Randyretired]

8 minutes ago, Jaydrvr said:

Blue Sea products are great, well engineered and well built. You can't go wrong with them. Jay

I tend agree with Jay but when there is a directional connecting order I wonder what this switch is intended for.   On many solar applications the charging current can be substantial and not easily stopped.   The discharge current may even be larger.  Why would a switch designed for a battery disconnect be directional as this appears to be?  Which way does the manufacturer recommend?