Switches Anyone ?

[jerrysimon]

Been looking at putting a switch on my E Brompton.

I was going to just put this on the +ve, would this work ?

DPDT Toggle : Toggle Switches : Maplin

Says 6amps 125V so 15amps 36v ?

Any pointers would be good

Regards

Jerry

 

[jerrysimon]

This one is water proof

Rocker Switch White Waterproof Boat 125V 250V On Off on eBay (end time 09-Jan-10 16:16:00 GMT)

Jerry

 

[z0mb13e]

You should work out the power rating for the switch - which is

Power (P) = Current (I) x Voltage (V)

(Just to confuse things P= Watts (W) I= Amps (A))

P = 6A x 125v
P = 750w

Therefore if we assume you are using a 36v battery...

I = P/V

I = 750w / 36v
I = 20A

So the switch should be good for 20A at 36v

I just got a flash back to an Electronics class I did a long time ago

Edit: If the rating is for VAC then the 20A at DC is a different prospect... use these calcs as a rule of thumb

 

[z0mb13e]

Actually its starting to ring little alarm bells from long past electronics classes - I think the DC rating is considerably lower than the AC rating - I just can't remember why or how to work it out.

Look for the manufacturers DC rating on the switch and go with that rather than the AC rating...

 

[z0mb13e]

A quick google later and the general concencus is derate the AC current rating by a factor of 5.

However - the switch rating is for the power that the switch is able to handle whilst the switch is being operated. In the ebike scenario the current is going to be pretty low as long as the motor is off, so you will only be actively switching a small current. You would then need to consider if the switch is capable of carrying the full load without overheating - this is where the DC rating is important.

 

[z0mb13e]

I've been trawling electronics catalogues looking for high current DC switches and short of the usual Master Switches (the ones with the big red key switch) there don't seem to be many that are rated to match.

The highest rated I found was 10A @ 28VDC

Makes me wonder how the switch in the Wisper battery works - perhaps it is just supplying a small current to the BMS which in turn is doing the high power current switching in silicon.

Anyone ever taken one apart to have a look?

For those interested Digikey is pretty handy for switches

http://dkc3.digikey.com/PDF/UK091/SectI.pdf

And here are a selection of high current DC switches

Robot Master DC Power Switches

 

[shemozzle999]

Been looking at putting a switch on my E Brompton.

I was going to just put this on the +ve, would this work ?

DPDT Toggle : Toggle Switches : Maplin

Says 6amps 125V so 15amps 36v ?

Any pointers would be good

Regards

Jerry

Just saw this, not 36v but sure it could do the job. Also consider mechcanically operated relays.

Battery Isolator Key Cut Off Switch Car / Boat NEW on eBay (end time 28-Jan-10 15:30:41 GMT)

 

[jerrysimon]

Thanks guys, lots of detail and ideas.

The 36v Tongxin I have in my E-Brompton I don't think will draw much more than 10amps when loaded and I have a 15amp blade fuse in the circuit anyway. I may actually reduce that to 13amp if I can find one.

In the end I am trying the 10 amp Maplin Toggle Switch with a water proof cover. This is being fitted on the Brompton bag so I can just switch everything off/on.

It unlikely that the bike will even be moving when I switch it off/on and with the fuse/switch I think its belt and braces anyway.

Regards

Jerry

 

[Blew it]

I've been trawling electronics catalogues looking for high current DC switches and short of the usual Master Switches (the ones with the big red key switch) there don't seem to be many that are rated to match.

The highest rated I found was 10A @ 28VDC

Makes me wonder how the switch in the Wisper battery works - perhaps it is just supplying a small current to the BMS which in turn is doing the high power current switching in silicon.

Anyone ever taken one apart to have a look?

For those interested Digikey is pretty handy for switches

http://dkc3.digikey.com/PDF/UK091/SectI.pdf

And here are a selection of high current DC switches

Robot Master DC Power Switches

Over the years I've had experience of several different battery types on E-bikes, without exception, the keyswitch has always carried the full amps demand allowed by the controller. In the case of the Wisper 905, the keyswitch carries the full 17-18 amps.

 

[Haku]

I had to replace the switch on my original Urban Mover battery as it was failing, the wires to the switch are much thinner than the wires to the bike connector on the bottom, which I take to mean the switch merely activates the BMS.

 

[winterdog]

Thanks guys, lots of detail and ideas.

The 36v Tongxin I have in my E-Brompton I don't think will draw much more than 10amps when loaded and I have a 15amp blade fuse in the circuit anyway. I may actually reduce that to 13amp if I can find one.

In the end I am trying the 10 amp Maplin Toggle Switch with a water proof cover. This is being fitted on the Brompton bag so I can just switch everything off/on.

It unlikely that the bike will even be moving when I switch it off/on and with the fuse/switch I think its belt and braces anyway.

Regards

Jerry

what will you be hosting the switch in ?(box or cut in to the bike)

 

[jerrysimon]

what will you be hosting the switch in ?(box or cut in to the bike)

Not on the bike but in the Brompton front bag using a woodern back plate on the inside of the bag, to mount it on

See this thread.

Regards

Jerry

 

[jkirkebo]

The Ezee keyswitch carries the full battery amperage. And you can buy it separately, if it'll fit the project:

Keyed on-off switch with keys

 

[monster]

if you want to switch ebike currents then the best switch i have found is DPDT 16A Rocker GU54J 16A Rocker Switches : Rocker Switches : Maplin it has two switches that work in parallel, connect them both and you should be good for 20-30 amp DC.

 

[jerrysimon]

Yep I saw those and for most ebike applications that would be a good switch. In the end went for the 10amp one with a waterproof cover.

As I said I am convinced that my Tonxin/Brompton setup will not pull more than 10 amps.

I have also put a 10amp fuse on it and to date it has not blown.

Regards

Jerry

 

[john]

When operating a switch from the battery, the current can be much higher than the current limit of the controller, even without the motor running. This is because the controller has large capacitors which are charged when the power is switched on.

The actual maximum current depends on the battery and controller and is difficult to calculate. However, the higher the current capacity of switch, the longer it is likely to last.

 

[jerrysimon]

As I said I am convinced that my Tonxin/Brompton setup will not pull more than 10 amps.

Eats humble pie

I now have the 15amp fuse back in. When I get my Tunigy meter I can can test actual figures.

Jerry