SPDT switch size question

[Newman39Fan]

I am going to put in a SPDT toggle switch for changing back and forth from the battery supply and the converter. My question is what size do I need for this. The wiring from the battery and converter will be 8g wire. Do I need a 40a switch due to the wire size or will a smaller one - 25a - work?

[eamarquardt]

If your converter is a converter/charger why install a switch at all? Keeping the battery in the circuit will "do no harm" and might help smooth out the voltage when a sudden load might drop the voltage before the converter has a chance to react. Plus, keeping the battery connected to the converter/charger will ensure that it is always charged.

Hope this helps.

Cheers,

Gus

[Newman39Fan]

It is not a converter/charger, just converter

[Dale M.]

I am going to put in a SPDT toggle switch for changing back and forth from the battery supply and the converter. My question is what size do I need for this. The wiring from the battery and converter will be 8g wire. Do I need a 40a switch due to the wire size or will a smaller one - 25a - work?

Technically a converter is a "charger"....

Doubt seriously you will find a 40 amp "toggle switch"...

Probably what you want is more like a "battery disconnect switch"....



Or maybe a relay....



Dale

[eamarquardt]

I am going to put in a SPDT toggle switch for changing back and forth from the battery supply and the converter. My question is what size do I need for this. The wiring from the battery and converter will be 8g wire. Do I need a 40a switch due to the wire size or will a smaller one - 25a - work?

25 amps will drain even a moderately sized battery in a couple of hours. I doubt that your load will be that high for very long. Look at what you intend to run and calculate your load. I'm pretty sure it will be under 25 amps. 8 gauge wire is good for about 70 amps

http://www.wiktel.com/standards/ampacit.htm

So, unless the is a huge price difference, size difference (making it difficult to install a larger switch) I'd just go for the 40 amp switch and understand it is "overkill" but my approach is usually "overkill in moderation".

Hope this helps,

Cheers,

Gus

[mikeschn]

You'll probably want to use a DPDT switch.

And yes, calculate your loads. If you are only using it for lights, fan, TV, etc, a 15 or 20 amp switch is more than plenty.

Mike...

[eamarquardt]

You'll probably want to use a DPDT switch.

And yes, calculate your loads. If you are only using it for lights, fan, TV, etc, a 15 or 20 amp switch is more than plenty.

Mike...

I see no need for a DPDT switch as a SPDT is all that is needed to switch the positive (for sake of convention only as switching the negative side would work just as well) side of the circuits. Even with the negative sides of the two supplies being connected there would be no complete circuit and the net effect is the same as if you used a DPDT switch.

Cheers,

Gus

[mikeschn]

I had two isolated circuits feeding into the switch.

Now, be gentle, I'm no electrician!!

but I had the red and black leads from the battery feeding into one side of the switch, and the red and black leads from the power supply feeding into the other side of the switch...

When the DPDT switch was down, the power supply would feed the bus boards.

When the DPDT switch was up, the battery would feed the bus boards.

Now you're probably going to tell me that I could tie the black line from the battery to the black line from the power supply. But since I'm not an electrician, I don't know that kind of stuff.

Mike...

[Engineer Guy]

Good looking Products here:

Bluesea Marine

[eamarquardt]

I had two isolated circuits feeding into the switch.

Now, be gentle, I'm no electrician!!

but I had the red and black leads from the battery feeding into one side of the switch, and the red and black leads from the power supply feeding into the other side of the switch...

When the DPDT switch was down, the power supply would feed the bus boards.

When the DPDT switch was up, the battery would feed the bus boards.

Now you're probably going to tell me that I could tie the black line from the battery to the black line from the power supply. But since I'm not an electrician, I don't know that kind of stuff.

Mike...

That's exactly what I'm saying. Now you do know, ha! I thought I was "gentle". One thing that hasn't come up is that if you do use a DPDT switch, with say a ten amp capacity, you can "upgrade" the capacity of the switch to 20 amps by using both poles for just the positive side of the circuits.

Cheers,

Gus