I am newbe to this Forum and to ebike enthousiasm. Sorry, my english is minimal.

I need to add front and back lights to my new E6100 Series Shimano STEPS driven ebike. I opted for lighting directly hardwired to 36v --400Wh-- main battery instead of using daily rechargeable (removable) smaller batteries. Because some users seem to get ebike computer issues, I chose not using motor drive 6v --max. 1Amp.-- terminals. My lights are : watts and lumens are unknown except lux data ... Front: https://www.aliexpress.com/item/33031604906.html?spm=a2g0s.9042311.0.0.c3ba4c4df0oU3g Back: https://www.aliexpress.com/item/32958304799.html?spm=a2g0s.9042311.0.0.c3ba4c4df0oU3g

A 12 volts,1.5 amp Horn will complete those accessories , wired via a 42v to 12v apprpriate buck adapter.
For that new circuit, I plan to install wires, switches, main fuse and connectors etc outside the battery .

My questions are: 1- Is a tap -- in parallel-- inside main battery on exiting conductors is the right place and best way to do? 2- Could that add any problem some way with central ebike system drive controller? 3- Is it a recommandable practice?

Hope my asking to be clear.

I thank you for answering my interrogations and/or giving me some appropriate advice.

  • 3
    \$\begingroup\$ Your question is unclear. Are you looking to re-arrange the wiring for existing lights or add new lights to the bike? If you are simply changing the existing wiring and not adding new lights what is the reason for this? What are "6v-52v front and back lights" is this a typo or do the proposed lights accept voltage in the range 6-52 Volts? \$\endgroup\$
    – mhaselup
    Dec 20, 2020 at 4:26
  • \$\begingroup\$ @ mhaselup: I clear that question a bit: I would add new lights on a NO LIGHTS new ebike. You are right, proposed lights accept voltage in the range 6-52 Volts. \$\endgroup\$
    – SM1234
    Dec 20, 2020 at 16:01
  • \$\begingroup\$ We will need a lot more specific detail to be in a position to give an opinion. What is the capacity of the battery (Ah) and power rating of the lights and bicycle motor. Links, specs, etc? \$\endgroup\$
    – mhaselup
    Dec 20, 2020 at 23:51
  • \$\begingroup\$ @ mhaselup: I thank you for your remarks. I have improved some way my initial post. \$\endgroup\$
    – SM1234
    Dec 21, 2020 at 17:30
  • \$\begingroup\$ this will likely come down to how much leeway there is in the battery capacity to support additional demand. \$\endgroup\$
    – mhaselup
    Dec 22, 2020 at 1:12

2 Answers 2


Use a motor-generator.

In other words, a simple and safe solution might be to put an old classic dynamo and the matching light on E-bike. This would allow unmodified usage of typical components, does not require to connect anything to E-bike electronics, unlikely to cause problems for controller and may even reduce the battery consumption as both you and say riding downhill could contribute some power for the light. Finally, the light will stay operational after draining the battery, if you still need to ride at night.

  • \$\begingroup\$ Dynamo is a good solution to avoid touching to existing electronic components and save on battery capacity. My reserve could be about dynamo 'continuous' noise side . Thank you for your fast answer and good suggestions. \$\endgroup\$
    – SM1234
    Dec 22, 2020 at 17:29

There are too many unknowns to provide a definitive answer. You are going to have to try an empirical approach and see what works. I would only introduce a single change at any one time and see if it works over a couple of days before introducing the next modification.

As you suggest connecting the light(s) in parallel with the battery is the best approach. You should be able to do this without interfering with the existing bike wiring and you can make measurements e.g. of the current being drawn by the light to get a better understanding of how things are working. I would anticipate the likely issue you would have is insufficient capacity in the battery to power both the bike and the lights. This could manifest itself as reduced "powered cycling" time or in the worst case the battery voltage sagging and preventing the drive controller from functioning correctly. I don't imagine that this will cause any permanent harm, you'll just have to give up on the lights. Get the lighting working properly before you add the additional complexity of a dc-dc convertor for the horn.

The approach above seems reasonable but only the manufacturer could state that this is recommendable practice-good luck with that. I would make a provision for switching the lights off during daylight as this will save power and you can also experiment with the impact of the lights.

  • \$\begingroup\$ My research did not permit to get precise data about these lights. So I can't find conversion of 80 lux to lumens to get watts approximation, assuming 80 lux is reliable...For sure I will have provision for possible switching the lights off during daylight . \$\endgroup\$
    – SM1234
    Dec 22, 2020 at 17:50
  • \$\begingroup\$ I am confident about direct derivation from 'main battery' because manufacturer electronic system is intact. I agree with you about manufacturer recommandation for that derivation. My last question would be: why are there so few posts IMHO about that derivation subject? I thank you for your help. \$\endgroup\$
    – SM1234
    Dec 22, 2020 at 18:12

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