Manuell switch, rated 48v used with 96v battery ok?

[odi]

Hi all.
I've found a manual switch rated for the amps i wanna draw. Its a 12-48v marine switch rated to about 400amps.
My question: my battery is 300amps, but its 96volt.

As long as i dont draw more then 300amps will the 48v rating really matters or will it be okay with 96volt?

I will have a resistor across switch, both for avoiding spark, but also for loading up the controller.

 

[harrisonpatm]

Not likely. I've used this type of switch and it will arc across an open connection at 90-120v. Maybe you'd be able to get away with it, but I wouldn't count on it, and I certainly wouldn't expect it to last very long at 96v; the contacts will build up carbon from the arcing, and lead to increased resistance

 

[nicobie]

The contacts will weld shut without a precharge circuit.

 

[odi]

The contacts will weld shut without a precharge circuit.

So with a resistor across for precharge it will be ok?

 

[harrisonpatm]

So with a resistor across for precharge it will be ok?

Not necessarily, because as I mentioned, the gap it creates by opening the contacts is not necessarily enough to prevent arcing at higher than its rated voltage. Depending on specific variables, current may attempt to flow across open contacts, even if there already is a precharge resistor in place.

 

[nicobie]

So with a resistor across for precharge it will be ok?

Yes. Charging The controller up with a 100 Ohm resistor in the precharge circuit will keep the contacts from welding together. This has worked fine on my 96V bike. You just have to remember to use the precharge circuit before switching on the controller. Can't leave the precharge circuit on when riding the bike or the resistor will burn up.

 

[odi]

Yes. Charging The controller up with a 100 Ohm resistor in the precharge circuit will keep the contacts from welding together. This has worked fine on my 96V bike. You just have to remember to use the precharge circuit before switching on the controller. Can't leave the precharge circuit on when riding the bike or the resistor will burn up.

How have you solved this? Do you have a small switch for the resistor to?

 

[nicobie]

Yes. I use a momentary on push button switch before switching the controller on.

 

[Comrade]

as I mentioned, the gap it creates by opening the contacts is not necessarily enough to prevent arcing at higher than its rated voltage

You need less than 1mm to prevent 100V DC from arching. There is absolutely no chance no way not under any condition less than 1mm gap inside that switch when it's off.

 

[harrisonpatm]

You need less than 1mm to prevent 100V DC from arching. There is absolutely no chance no way not under any condition less than 1mm gap inside that switch when it's off.

Ok. Maybe I used the wrong word; sparking? Disconnecting while under load and creating a spark that quickly ruins the contacts? Because that's what happened to mine. Application was 90-110v/100A solar disconnect, and two different switches had audible sparking/arcing/fizzing that persisted when the switch was moved to the off position, for up to 10 seconds. Current was still flowing to the charge controllers, even though the switch was "off." This happened to two different solar strings. I had the same switches on other solar strings, at lower voltage of around 60-70v, and those would always disconnect fine. I replaced them with DC-rated circuit breakers, and disassembled one of the switches to find carbon/scorching on the contacts. I don't have pics, this was months ago. Newly purchased switch, only a few dozen cycles.

What caused this to happen with my switches, if not arcing? I'm not an electrical expert. And if this switch was only used to disconnect when not under load, then maybe itd be fine, I don't know. OP mentioned he was planning to use it for 300 amps. I was just reporting my similar experience.

 

[Comrade]

if this switch was only used to disconnect when not under load

That's my assumption if we are talking e-bike battery.