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where to buy a 42V DC 30A on-off switch

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steven charles

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hi. i'm wondering if anyone can point me to a place to buy an on-off switch for my ebike. i struggling to find a source of one that meets my battery and motor requirements, and ideally i'd like to buy it from a UK supplier.

so the motor is rated to 30A maximum continuous discharge and i have a 42V battery (10S li-ion 18650's)

it would also need to be waterproof and protrude less that 11mm so toggle switch might be too tall

RC components don't seem to go above 10/15A and car stuff is 12V so don't seem to find what i need. any advice of the industry to look in would be great thanks.
 
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D8ve

D8ve

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Cpc components (farnel) is where I would look.
12 volts or 42 wouldn't worry me greatly. The insulation for low voltage should do both fine.
 
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steven charles

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ok i'll have a look. that wasn't my understanding as to how much voltage a switch could take. i thought if it was too high then could damage the switch as well, hence the ratings they had. i will check again
 
Alan Quay

Alan Quay

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Suitable switches can be found, but the biggest problem is the inrush current when switched on.

That said, I have fitted 16a switches that have lasted years, and been used every day. Basically, the bigger the better but you will struggle to find anything rated more than 12v.

I don't bother these days. If leaving bike for weeks, disconnect battery. If just a few days switch off with display.





Sent from my HTC One_M8 using Tapatalk
 
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D

Deleted member 4366

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You already have switches. Why not use them? One is called a BMS, and the other is called a controller. They both have MOSFETs in them that completely block the battery. Can you explain why you think you need a separate switch?
 
Alan Quay

Alan Quay

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d8veh said:
You already have switches. Why not use them? One is called a BMS, and the other is called a controller. They both have MOSFETs in them that completely block the battery. Can you explain why you think you need a separate switch?
Click to expand...
The problem is that a controller will consume a standby current. I just put a watt meter on mine, it's consuming about 0.5 wh/h (I'll confirm a more accurate figure later).

Not much, but on my battery that's nearly 10% every day.


Edit: just checked after 6 hours it's consumed just over 6wh, so 1wh/h.
 
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D

Deleted member 4366

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There's no standby current if you put the switch on the wire that provides it!
 
D

Deleted member 4366

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The wire that provides the standby current isn't the main battery line. It's the switch wire in the controller. OP seems to have lost interest now anyway.
 
Alan Quay

Alan Quay

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d8veh said:
The wire that provides the standby current isn't the main battery line. It's the switch wire in the controller. OP seems to have lost interest now anyway.
Click to expand...
Does the on/off button on the display not do this?

The current I measured was with the controller switched off from the display.

Sent from my HTC One_M8 using Tapatalk
 
D

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Alan Quay said:
Does the on/off button on the display not do this?

The current I measured was with the controller switched off from the display.

Sent from my HTC One_M8 using Tapatalk
Click to expand...
When the LCD is switched off, the drain is in the order of micro-amps. It would take 23 years to drain a 10aH battery at 50 micro-amps. The battery's internal self-draining would be a lot higher than that.

Alan Quay said:
Edit: just checked after 6 hours it's consumed just over 6wh, so 1wh/h.
Click to expand...
How much does your wattmeter consume?
 
Alan Quay

Alan Quay

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d8veh said:
When the LCD is switched off, the drain is in the order of micro-amps. It would take 23 years to drain a 10aH battery at 50 micro-amps. The battery's internal self-draining would be a lot higher than that.
Click to expand...
I measured it today, on a brand new S06P controller with 890 (LED) display. It's possible that the 6wh consumed was down to the watt meter itself.

Perhaps I should stick my DMM on there and see if I get a different result.

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Alan Quay

Alan Quay

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Alan Quay said:
I measured it today, on a brand new S06P controller with 890 (LED) display. It's possible that the 6wh consumed was down to the watt meter itself.

Perhaps I should stick my DMM on there and see if I get a different result.

Sent from my HTC One_M8 using Tapatalk
Click to expand...
OK, so I put my meter in instead, and the previous result must have been down to the watt meter (either it's out of cal. or it consumes a lot of power, probably a bit of both)

The current draw in standby was not really in the measurable range of my meter, less than 1 uA. When switched on but idle, I it draws about 70 mA.


So D8veh's correct, you don't need a switch on modern controllers.

I know it was an issue on some older ones, as I had a battery go down to LVC when left connected for a few weeks.

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D

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The whole purpose of the BMS is to switch off the battery under certain conditions. Many modern BMSs have a switch on them already. If not, it's fairly straight-forward to add one.

Similarly, with controllers, the MOSFETs are very efficient switches. The battery wires go directly to the motor, but are blocked by the MOSFETs. Only the controller's CPU will switch them on, so your main switch only needs to prevent power getting to the CPU, which is what the switch on the LCD/LED panel does, or you can add your own if it doesn't have a control panel.

In either of those situations, you can use any small switch because no power is involved.

You therefore have two options for switching off your battery. The only time you need a separate switch is when using say high voltage Lipos without a BMS and you want to avoid that nasty spark, in which case I'd copy the same arrangement that you have in the BMS: A row of 4 MOSFETs in parallel with a small remote switch to switch them on/off. This is what I used to use for my lipos:



 
Alan Quay

Alan Quay

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Now I think about it, the controller I had that consumed power had no display, and no connection for one. Also, no facility for a switch, so I guess it was always on, and consuming 50-100mA.

Sent from my HTC One_M8 using Tapatalk
 
D

Deleted member 4366

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Nearly all controllers work the same way and have similar components in them. The battery wires go straight to the motor, but are blocked by the MOSFETs. A branch is taken off the positive to power the controller. The voltage on that branch is cut down by a big resistor, then it's regulated to 12v by a 12v regulator. The 12v is then regulated down to 5v by a 5v regulator that provides the power for the CPU and sensors.

The easiest way to put an on'off switch is to cut one leg of the big resistor and join each side of it to wires that go to the switch. All the controllers that already have switch wires or a switch on the LCD, or wherever, use the switch to interrupt that branch between the main battery wire and the big resistor.
 
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Steve Wilked

Steve Wilked

Finding my (electric) wheels
Feb 17, 2016
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Pelsall West Midlands UK
steven charles said:
hi. i'm wondering if anyone can point me to a place to buy an on-off switch for my ebike. i struggling to find a source of one that meets my battery and motor requirements, and ideally i'd like to buy it from a UK supplier.

so the motor is rated to 30A maximum continuous discharge and i have a 42V battery (10S li-ion 18650's)

it would also need to be waterproof and protrude less that 11mm so toggle switch might be too tall

RC components don't seem to go above 10/15A and car stuff is 12V so don't seem to find what i need. any advice of the industry to look in would be great thanks.
Click to expand...
Why do you need 30 amps? At 42 Volts that's 1260 Watts! How many banks of 18360 cells are there in parallel, ...you should not drain any one bank of cells more than 2 x C. Usually C = 2000mA, the better cells can do higher, maybe 2500mA, possibly 3000mA for a short time. So say 5 Amps each bank (10 cells per bank for 34 - 42 Volts). You would need 6 banks to give 30 A. That's 600 of the 18360 cells! Is your battery that big??!!

Sent from my HTC One_M8 using Tapatalk
 
Steve Wilked

Steve Wilked

Finding my (electric) wheels
Feb 17, 2016
9
0
69
Pelsall West Midlands UK
Steve Wilked said:
Why do you need 30 amps? At 42 Volts that's 1260 Watts! How many banks of 18360 cells are there in parallel, ...you should not drain any one bank of cells more than 2 x C. Usually C = 2000mA, the better cells can do higher, maybe 2500mA, possibly 3000mA for a short time. So say 5 Amps each bank (10 cells per bank for 34 - 42 Volts). You would need 6 banks to give 30 A. That's 600 of the 18360 cells! Is your battery that big??!!

Sent from my HTC One_M8 using Tapatalk
Click to expand...
Oops, ...Sorry, ...too many 0's... 10 x 6 = 60 cells!

Sent from my HTC One_M8 using Tapatalk
 
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