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Posted: 11 Dec 2018, 11:25am
My Cargo bike is finished and I'm in touch with Woosh to sort out a 48V rear hub kit which hopefully I'll have soon!
I would like to fit permanent lights to the bike - like dynamo lights, and run them off the main battery, as this seems like the most logical thing to do (It seems pointless building a dynamo wheel when I have a ready power supply).
Has anyone done this and if so using what approach? I could use the 48V supply with a DC/DC converter, but I imagine that the voltage to the PAS, the speed sensor, the brake switches etc is much lower. Does anyone know what voltages these run at? I would use LED lights so current draw would be low.
Hoping someone can shed some light - no pun intended!
Posted: 11 Dec 2018, 12:14pm
Although you could tap off on the system voltage, even though the lighting power is low compared with the motor, might be prudent to use a separate convertor (modern dc-dc convertors are super efficient) so if the main driver system fails or even a fuse blows then you can still see where you are going!
I say tap off but you would need some knowledge of what is pure stable voltage dc and what might be a modified modulated dc signal?
Posted: 11 Dec 2018, 1:33pm
Grab a multimeter when you have the devices - work out which outputs stay live even if you haven't requested any assistance for a while.
A dynamo still isn't a bad option - it will carry on working, even if you drain the main battery, and it isn't reliant on the power saving electronics of the battery behaving itself.
Posted: 11 Dec 2018, 5:38pm
There's no reason why the voltages to the various devices is low, plus most of them are simply switches, even if they could power your light it'd go off whenever the switch closed.
Then there's the potential issue of you loading the devices too much so the bike gets confused about what's happening.
Even with 'just' 3w that's a fairly hefty load for something that's not designed for it.
If there is a low voltage supply it's likely to be that provided to the display but what it's power is rated at is anyone's guess. Some displays provide a USB charger - can you get one with yours? If so might provide an alternative supply.
IMO though its far safer to either use a dynamo (I do) or use a buck converter to get you a supply from the battery.
Posted: 11 Dec 2018, 7:03pm
Thank you the replies - some good points made. I hadn't thought about the PAS cutting power to the motor, which would of course render that supply useless. The 48V woosh kit doesn't use a separate speed sensor, as it's built into the hub. If the battery pack/controller still has a supply for speed sensor this might be usable depending on voltage and wire size. I'll wait and see.
Posted: 11 Dec 2018, 7:59pm
Just take heed on advise drawing power from the motor controller.
Prudent maybe as said to have a dynamo as back up for a failed light feed to the battery, if it goes flat.
Posted: 12 Dec 2018, 9:02am
B+M luxos IQ-X ebike front light. Takes 6-60v. No on off switch but wonderfully shaped beam and brightness.
Posted: 12 Dec 2018, 9:25am
My rack mounted battery has an integral rear light. I have wondered how the lights would remain on when you braked or even changed gear if they were fed from the motor.
Posted: 12 Dec 2018, 11:48am
You are correct, if the lights were powered from the motor supply they would go out when not pedalling, braking or exceeding 25Kph.