SW900 headlight won't turn off

[jimmychill]

Here's another one. The bike I just bought (used) has a headlight, but it's always on. the only way to turn it off is to cut the wire, which is exactly what the previous owner did. In fact, holding the up button on the SW900 to turning it off only makes it brighter! Any suggestions?

 

[vfr400]

The transistor that does the switching is blown because someone put a too powerful light on it. The controller can only switch very weak lights.

It's much better to wire your lights directly to the battery with a normal switch, then you can use some lights that are bright enough to see where you're going. Some controllers provide a pair of red and black (or other colour) wires for lights, which are basically a branch straight off the battery wires so you can connect your lights with a matching connector.

 

[jimmychill]

Thanks again, vfr. That makes sense. The previous owner had some extra lights attached, which could have overloaded the transistor.

 

[Thingamajig]

Sorry to ressurect this old thread (Google bought me here)

But wouldn't it be possible to simply replace the transistor with something more capable of handling a higher amperage?

I ask because i recently got a sw900 display with a similar issue (light is always on unless power source is removed or switched off directly) and i'm looking to try and repair the sw900 as it otherwise works fine.

 

[vfr400]

Yes, you can repair the transistor if you want and if your logic says that it's a good solution.

 

[Thingamajig]

Any ideas where to start with a possible upgrade? I believe this is the datasheet for the transistor in question:

CZT127 datasheet, transistor equivalent, Kexin

CZT127 datasheet, CZT127 transistor equivalent, Kexin, Features and benefits, Stock and price

datasheetspdf.com

But not quite sure where to start with a suitable "upgrade" or, for that matter, where to even obtain one.

 

[vfr400]

Any ideas where to start with a possible upgrade? I believe this is the datasheet for the transistor in question:

CZT127 datasheet, transistor equivalent, Kexin

CZT127 datasheet, CZT127 transistor equivalent, Kexin, Features and benefits, Stock and price

datasheetspdf.com

But not quite sure where to start with a suitable "upgrade" or, for that matter, where to even obtain one.

We were hoping that you'd be able to tell us.

If that's the transistor that failed, it's rated at 5A so something catastrophic caused it to blow. You need to find out what that was otherwise the next one might suffer the same fate.

 

[MontyPAS]

5PCS X CZT127 SOT-223 CENTRAL | eBay

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Be aware if you use a higher rated SMD transistor, make sure that both the tracks on the PCB and the interconnects can handle the increased current. TBH hardly worth the faffing about.
Whats the difference of using a switch directly wired to the battery, and fecking about with the display to turn on/off...... no brainer really

 

[Thingamajig]

5PCS X CZT127 SOT-223 CENTRAL | eBay

Find many great new & used options and get the best deals for 5PCS X CZT127 SOT-223 CENTRAL at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

Be aware if you use a higher rated SMD transistor, make sure that both the tracks on the PCB and the interconnects can handle the increased current. TBH hardly worth the faffing about.
Whats the difference of using a switch directly wired to the battery, and fecking about with the display to turn on/off...... no brainer really

For my circumstance it's cable routing and space - legitimately dont have any space to mount an additional switch. Currently just exploring my options hence posting.

Cheers for the link btw, might buy a few in so i can at least repair the existing unit.

 

[MontyPAS]

For my circumstance it's cable routing and space - legitimately dont have any space to mount an additional switch. Currently just exploring my options hence posting.

Cheers for the link btw, might buy a few in so i can at least repair the existing unit.

The transistors are cheap enough to give it a go.
I use rechargeable lights with integral switch, so no need for any more space.
Been using this around the dark lanes where I live

Planet X PowerbankWide Beam Headlight

www.planetx.co.uk