Low voltage question

[-robw-]

My brain remains confused by this:

A 24v (low voltage) battery switch won't work with a 48v (low voltage) battery bank, Huh? Switch purports to support 300+ amps so how can it be that it would even care between 24v or 48v (heavy contacts, right?) I mean, in either case - 24 or 48 - we're talking very low voltage. Is there a paper or voice that would explain this?

[SunEagle]

My brain remains confused by this:

A 24v (low voltage) battery switch won't work with a 48v (low voltage) battery bank, Huh? Switch purports to support 300+ amps so how can it be that it would even care between 24v or 48v (heavy contacts, right?) I mean, in either case - 24 or 48 - we're talking very low voltage. Is there a paper or voice that would explain this?

It depends on what the voltage rating is for that switch. If it is not rated for 48V or more then it could fail. Also remember that most "battery" switches may be only good for 12V systems if they were designed for vehicles.

[-robw-]

Sure, but in either case - 24 or 48 - we're talking very low voltage. I'd like to understand why a 24v switch won't work with a 48v system. There must be a paper to explain why, because on its face it's illogical.

[SunEagle]

Sure, but in either case - 24 or 48 - we're talking very low voltage. I'd like to understand why a 24v switch won't work with a 48v system. There must be a paper to explain why, because on its face it's illogical.

I can only say if you put 48v on a 24v rated device it will heat up and eventually melt. It all has to do with the material voltage rating. If you want some type of paper then go read the National Electric Code.

[-robw-]

Voltage doesn't "melt" connectivity, amperage does, It's beyond me why two 1/4" contracts will support 300+ amps but not 48 volts. Jesus, I could drop 48v in my bathtub and hang out for 2 days

Sorry for that but I'm just trying to understand.

[-robw-]

Seems to me a simple answer. I think we all understand amperage, and also the difference between higher voltage wiring. I can't find anything online that would explain how a 24 volt difference is meaningful, which it obviously can be.

[sdold]

The voltage rating of a switch usually has to do with arc suppression, a switch used above its voltage rating might suffer arcing and burned contacts.

[SunEagle]

Seems to me a simple answer. I think we all understand amperage, and also the difference between higher voltage wiring. I can't find anything online that would explain how a 24 volt difference is meaningful, which it obviously can be.

You obviously have made up your mind to use whatever switch you have on a 48V system. I say you can do what you want but please be careful.

Hopefully that switch has a 60 volt rating so there shouldn't be any issue. But if it is only rated for 12volts then anything might happen when it is being opened under load.

[neweclipse]

Ask the Underwriters Laboratory, they have no problems seeing the difference between 24vdc and 48vdc...

Voltage is "pressure"...would you put 100psi thru a 1 GPM nozzle on garden hose all day?
Current is "flow"...you could put 100 GPM at 5 psi through a 2" i.d. 4mil thin wall plastic sleeve all day, but best not try that with 100psi.

Put another way, you could lay a wet bare hand on a 1000 amp @ 1 volt bare conductor..but NEVER try that on 1000 volts @ even a tiny fraction of an amp...Volts = Pressure

The "good news" is that you can use a 48vdc switch on 24vdc.

[PNPmacnab]

There must be a paper to explain why, because on its face it's illogical.

My go to book is Gaseous Conductors by James Dillon Cobine. This is the bible on things that go arc in the night. As a general rule, once you get over 30V serious arcing can occur. It is based on switch materials, open gap and mechanical speed of the switch. There are other considerations outside of common use. One thing that surprises many is that the central arc is not the hottest part. It is the transition from metal to the gaseous conductor. Welding and EDM are based on this.

[littleharbor]

[QUOTE=neweclipse;n405834]

The "good news" is that you can use a 48vdc switch on 24vdc. [/QUOTE


Post #9 is the first place I see DC being mentioned. Direct Current, as opposed to Alternating Current is the tricky thing to be switching. Ac, being that it is switching directions 60 times a second, (here on the USA), and going to zero volts midway between direction changes,will extinguish the arc when switched off right away. Dc, otoh being continuous flow of current needs special treatment to extinguish its arc before it burns up the contacts of the switch. Something like that. I'm sure the pros here can explain this a bit more elegantly.

[Salts]

Post #9 is the first place I see DC being mentioned. Direct Current, as opposed to Alternating Current is the tricky thing to be switching. Ac, being that it is switching directions 60 times a second, (here on the USA), and going to zero volts midway between direction changes,will extinguish the arc when switched off right away. Dc, otoh being continuous flow of current needs special treatment to extinguish its arc before it burns up the contacts of the switch. Something like that. I'm sure the pros here can explain this a bit more elegantly.

Nope, that's pretty much it.

[-robw-]

Not true. Marinco has a 48v switch and I've been using it for 2 weeks w/o issue. Aside from a few minor complaints I posted elsewhere, everything is working wonderfully.

I'm just trying to understand something about voltage that seems illogical. Like I said, "I could drop 48v into my bath and hang out for 2 days". So why is it that heavy enough contacts handling 300+ amps can handle 24 but not 48 volts?

You obviously have made up your mind to use whatever switch you have on a 48V system. I say you can do what you want but please be careful

[-robw-]

My go to book is Gaseous Conductors by James Dillon Cobine. This is the bible on things that go arc in the night. As a general rule, once you get over 30V serious arcing can occur. It is based on switch materials, open gap and mechanical speed of the switch. There are other considerations outside of common use. One thing that surprises many is that the central arc is not the hottest part. It is the transition from metal to the gaseous conductor. Welding and EDM are based on this.

Interesting. Since you read it would you elaborate as pertains to my question?

[-robw-]

Nope, that's pretty much it.

Not to be rude but 48v could not burn up butter.