Help me find a suitable power switch please

[Fordulike]

Can anyone point me to a shop, where I can buy the following DC power switch please.

Use: Inline switch from battery to controller.
Must be able to handle 48v DC with a current flow of 30A.

Would prefer a rocker switch, but can be toggle or twisty knob, and with a fairly small footprint
i.e. doesn't look like it's been swiped from Frankenstein's laboratory

If I were to use a 12v DC switch in this set-up, would it mean that It would have to have a 120A rating?

 

[flecc]

If I were to use a 12v DC switch in this set-up, would it mean that It would have to have a 120A rating?

Yes, the equation keeps the same balance, summing to 1440 watts. Maybe a battery isolator switch would be ok for the job.

 

[Fordulike]

Yes, the equation keeps the same balance, summing to 1440 watts. Maybe a battery isolator switch would be ok for the job.

Thanks for the link.
I like the idea that one of them has a removable key.

 

[flecc]

If you enter "battery isolator switch" in Google, there are a number of outlets including ebay sellers.

 

[Fordulike]

If you enter "battery isolator switch" in Google, there are a number of outlets including ebay sellers.

I did see the marine isolator switch on eBay, but figured it looked a bit bulky.
After seeing the same product in your link, it states that it can be recess mounted, so that might be the one to go for.
I plan to mount the controller and switch on the underside of a seat post rack.
Recessing the switch would make the set-up a lot neater

 

[jerrysimon]

I was recently looking for a isolator switch for my light bike setup. I chose a mini rocker rated at 6A/250Vac My setup is 36v and the controller is rated at 12amps max ?

Is that rated too low ? What is the calculation ?

Regards

Jerry

 

[flecc]

That's definitely comfortable Jerry. I'm not sure if Vac mains switch ratings are RMS based like the mains supply, but even if based on peak to peak value, your demand is still safely within the switch capability.

 

[jerrysimon]

Thanks Tony. I think is means Volts AC as apposed to Volts DC ?

Regards

Jerry

 

[flecc]

Thanks Tony. I think is means Volts AC as apposed to Volts DC ?

Regards

Jerry

Yes it does, but the question mark is on how that's expressed. Our 220 volt mains is expressed as the RMS figure (root mean square) meaning the average over time is equivalent to 220 volts DC.

However, the peaks of the waveform are about 370 volts, so a rating of 250 volts ac could be either the RMS value or the peak value is 250 volts. If the latter, it's DC equivalent would be only about 167 volts.

Your 36 volts x the 12 amps is 432 watts of power for a switch to cope with. In the two ways above, the 250 volts 6 amp switch would cope with either 250 x 6 = 1500 watts, or 167 x 6 = 1002 watts, both very comfortably in excess of need.

 

[jerrysimon]

Thanks for the clarification Tony.

Regards

Jerry

 

[NRG]

Jerry do you need 30amp?

These Schurter combined rocker switch and thermal breakers are rated for 60vDC and 20amp...you could double up on the poles to lower the current through each but it would still trip at 20amp....I run one of these on my Peugeot and ran 22amps through it for a short while...

TA35-CBTWF200C0 - SCHURTER - CIRCUIT BREAKER, 2P, 20A | Farnell United Kingdom

 

[Scimitar]

I was recently looking for a isolator switch for my light bike setup. I chose a mini rocker rated at 6A/250Vac My setup is 36v and the controller is rated at 12amps max ?

Is that rated too low ? What is the calculation ?

Regards

Jerry

A switch must be de-rated for DC use. Your 250V 6A AC switch might weld its contacts together when handling DC, and unless you know for sure the gap between the contacts is big enough to break a DC arc, you can't trust it.
CPC/Farnell, RS Components and others will happily sell you a switch that's rated for AC and DC use.

 

[oigoi]

Personally I would use a switch that is rated for the required amperage, regardless of the voltage rating. The switch contacts have to be able to conduct a certain amount of current, regardless of the voltage

 

[jhruk]

It should be noted that switches are never rated in watts, but always separately for amps and volts, and ac or dc. There is a reason for this. The design will be affected by these factors separately and you cannot trade one for another.

Ideally you should choose a switch whose specification, dc for e-bikes, exceeds your usage for both amps and volts. Determining this is not always straightforward. For example a controller may have a maximum current rating of 15amps but when it is initially powered up the current drawn to charge the capacitors may be considerably more. For this reason special circuits are sometimes used around the switch to minimise the damaging effects of these surges on the switch contacts.

Having said that the situation of switching an e-bike controller is not critical and I often use a switch which is roughly the right, with the emphasis on dc current rating. If it fails it’s not catastrophic and I can change it easily. Car parts suppliers are often handy for cheap ones. I wouldn’t do that for a critical aircraft system though.

 

[banbury frank]

Hi When we used lead acid battery's we used MCB s as a main protection and on off switch

A 20A should be fine from B&Q 6.50p

MK Sentry MCB Type B Any Size From 6amp to 50amp New | eBay


Frank

 

[Scimitar]

Hi When we used lead acid battery's we used MCB s as a main protection and on off switch

A 20A should be fine from B&Q 6.50p

MK Sentry MCB Type B Any Size From 6amp to 50amp New | eBay


Frank

That's exactly what my main switch is - a 32A MCB which is rated for DC current as well as mains. Of course, each battery pack has its own inline fuse as supplied by Bosch

 

[flecc]

As Scimitar, oigoi and jhruk posts indicate above, I suspected that it's best to convert to peak-to-peak voltage on switch ratings to access ability, rather than think of the stated voltage as rms. At a guess I think the power and current handling then would cover most situations.

 

[NRG]

If you're going to use an MCB for DC operation then use the correct device IE:

Miniature Circuit Breakers: DC MCBs - EP100/104UC, MCBs for photovoltaic applications

AC breakers are not designed for DC use as they utilise the air gap and AC current to extinguish any arc, using such a breaker for DC will kill the contacts rapidly and may fuse them closed.

 

[Fordulike]

If you're going to use an MCB for DC operation then use the correct device IE:

Miniature Circuit Breakers: DC MCBs - EP100/104UC, MCBs for photovoltaic applications

AC breakers are not designed for DC use as they utilise the air gap and AC current to extinguish any arc, using such a breaker for DC will kill the contacts rapidly and may fuse them closed.

Great link, thanks

 

[Fordulike]

If you're going to use an MCB for DC operation then use the correct device IE:

Miniature Circuit Breakers: DC MCBs - EP100/104UC, MCBs for photovoltaic applications

AC breakers are not designed for DC use as they utilise the air gap and AC current to extinguish any arc, using such a breaker for DC will kill the contacts rapidly and may fuse them closed.

It is my understanding that circuit breakers don't trip as soon as the rated amps are hit, but require a prolonged period of time over the rated amperage.
If I were to use one of these, would I match it to the rating of the controller?
Would it be likely to trip if the controller peaked momentarily above it's rating?
Does this make sense?