Homemade LED Rearlamp

[Haku]

Just been doing some rough calculations and I think it's a perception thing about the LEDs draining more power than I thought.

Ok, amps = watts/volts, so assuming my battery is outputting 29v (fully charged) and powering a 200watt motor, the motor is drawing 200/29=6.897amps at maximum so in comparison some LEDs drawing 0.09amps is almost nothing.


I'm curious though, has anyone measured in amps the drain of a 24v 200watt ebike motor at maximum power?

 

[coops]

Hi Haku,

Nice looking lights, I might have a go at this soon .

I'm not sure if it helps, but a motor "rated" at 200W only means (as I understand it) thats the rated continuous total power used by it i.e. it can run at 200W, 24V 6.9A continuously, and thats usually the peak efficiency too. Many ebikes use less than 200W net at 15mph or below when pedalled lightly, though maybe slightly over 200W at 15mph if not pedalled.

The actual maximum/peak power usage depends largely on the motor's capacity & the controller's current limit and varies quite widely: two motors with the same 200W rating could have peak power of around 300W to 600W or more, depending on those factors.

So a 200W rated motor running at its rated speed would use around 7A or less at 26-29V, but could use anywhere between say 10-20A at maximum power. Is that what you meant?

Stuart.

 

[Haku]

The front reflector is a standard Cateye you see on a lot of new bikes, found it almost impossible to find an identical one to buy, the one pictured is cracked down the middle, thankfully I was given another one which I'll be putting probably 15 LEDs in.
The back reflector is one of 6 identical ones I got from an eBay auction, along with some small circular ones and some small ones shaped like hands, no mounting fixtures on them just double sided sticky pads so I'm going to have to glue some bolts into them or something.

The power usage, yeah that's what I meant power usage in regards to motors is somewhat new to me so I was just going by the quoted 200watt for the motor and my own multimeter tests on the battery at full charge. Any help in that area is appreciated.

If as you say motors can use 10-20A at maximum power then 0.09A drain from my existing 11 LED setup is as close to almost nothing as possible. Which is nice

 

[coops]

Yes, I think LEDs make a good choice for ebikes because of their low power drain .

I'm sure there's lots of posts on the forum regarding hub motor power, but essentially your current draw calculation would apply to an "idealised" journey at top motor speed on a flat road with no stops, starts or hills, but maybe a little pedalling as I said .

So say 200W is being used, 15mph speed and your battery is 200Wh (Watt hours) or in other words 24V 8.3Ah, the 200W can be sustained for 1 hour, which at 15mph gets you 15 miles .

Introduce gradients and stops/starts which need increased power usage and your average power use goes up so your range decreases. Thats it, really .

Stuart.

 

[Sector]

Power consumption

Haku,

You could think about it like this.

In a 2 hour ride your lamp would consume .09 x 2 = 0.18 Ah

In another post you said you had an 8 Ah battery.

So your lamp is only taking 2% of the energy in your battery. 2% is so small you wouldn't notice the loss of it.

Enjoy your extra-bright light!

(Remember to turn it off when you get home, although it would take nearly 4 days to discharge a fully-charged battery.)

Pete (Sector)

 

[Haku]

2 hours? with the hills round here I'm lucky if I get an hour!

Have to say that cycling at night is a lot more fun with a decent front 'headlamp', especially down unlit roads and cyclepaths.

The lights get power when the battery (& consequently bike) is switched on so there's zero chance of accidentally leaving the lights draining the battery when I'm not using the bike, however there is a chance I could forget I have the lights switched on and cycle around during the day with them on and not realising - I was thinking about an automatic light switch that works the same way as streetlamps, a simple photoelectric sensor & circuit would do the trick.

 

[coops]

Good lights must be much safer too, I'll bet . I'll probably try to improve mine, especially for my first ebiking winter... it seems very forward thinking at the "height" of "summer" .

A photoelectric sensor sounds a good idea too Haku... so long as its not one more thing to go wrong! Good luck!

Stuart.

 

[Haku]

I prefer night riding because there's less people about, cycling to Tesco at 3am is much more enjoyable than at 3pm

The photoelectric sensor idea might be more difficult than I first thought, your lights might go out if you go under a streetlamp! circuitry to ensure that doesn't happen could get complicated with a sensitivity adjustment and a timing function so that when the sensor sees short lows or highs of light level it doesn't affect the current state of the lights (on or off).

I also wondered about brighter LEDs to get even more light, the LEDs I have are 3v 20mA 12,000mcd brightness and a quick scout on eBay you can get thirty 3.4v 25mA 55,000mcd LEDs for about £6 from Hong Kong. More testing to do I think.

 

[Haku]

I've been idly looking around the web for other people's homemade front bike lights and there's some great stuff out there, especially on the CandlePowerForums site. Almost everyone who's making their own bike light setups are using the luxeon star type of LEDs as they yeild much more light per watt than the normal type of LEDs, but they don't have a built-in magnifying glass to project the beam like normal LEDs so optics are needed (hacking up cheap Hong Kong AAA torches seems to be a good way).

For example, the 12,000mcd (millicandelas) LEDs I'm using right now output approx 1.145 lumens each (3.4v at 20mA), the Cree® XLamp 7090-XRE outputs up to 87.4 lumens (3.75v at 700mA) each (but needs some heatsinking). So to get my normal LEDs as bright as the XLamp I'd need over 70 of them...! and it would use double the amps.

I'm still going to make my 15 front LED light setup as when it's completed it'll be extremely convenient to use and I'm looking forward to seeing just how bright the supposed 55,000mcd LEDs are, but I may look into doing a lighting setup with a Cree® XLamp 7090-XRE in the future because it's only $13 for the LED.

 

[Ian]

I purchased some 80,000 mcd LEDs from a supplier in Hong Kong but to the eye they appear to be no brighter than UK sourced 8000-12000 mcd LEDs, it's not unusual for Chinese suppliers to over specify their products as major toy companies have recently found to their cost.

I considered using Luxeons in my front lamp but the difficulties of efficiently deriving a suitable supply at the relatively high current of 350mA from the bike battery combined with the need for heatsinking and additional optics put me off. I simply added 27 LEDs in 3 series chains of 9, + 3 resistors, to the existing 7 LED headlamp. The result is a powerful lamp that consumes a mere 80mA from the 36V battery in steady mode and the unmodified beam angle of the LEDs is ideal.

 

[Haku]

When I get the 55,000mcd LEDs I'm going to stick 10 along side my 12,000mcd on some breadboard and put each at their maximum voltage to see which really is brighter. When I was toying with the white LEDs I have earlier in the year I put 60 on some breadboard powered off 4 rechargable AAs with a DC-DC converter, it was immensely bright and ate the batteries in about an hour.

The mcd rating of LEDs is drastically affected by the beam angle, using this rough mcd to lumens calculator the 5mm 55,000mcd 20degree output about 5.25 lumens, on eBay you can find 10mm 160,000mcd white LEDs but in reality they're only about the same brightness (approx 5.5 lumens) as the 5mm ones because the 10mm LEDs have a more focused 12degree beam angle.

Those 27 LEDs you've put onto your headlamp are probably using the same (or more) amount of power as a single Luxeon but the requirement for optics, a DC-DC converter for the right voltage and optics is a lot more hassle than simply drilling some 5mm holes and sticking the LEDs (with built-in optics) in.

 

[Ian]

One day most lamps will be LEDs. In addition to bicycle lighting I have a number of LED downlighters in the house, more of the same in my touring caravan where the low power consumption is a real advantage and several ornamental LED lamps in the house and garden.

 

[Haku]

So far the LED lighting 'solutions' I've seen in shops leave a lot to be desired as they're using traditional 5mm LEDs which just can't deliver the kind of light levels that Luxeons and similar do. But it's still early days.

Those 55,000mcd LEDs arrived today, you were right, they're no brighter than the 12,000mcd LEDs I have and they need a little more voltage (I suspect they use more amps but haven't measured that yet), they are slightly bluer though. It sppears if you want really bright lights you use a mass of high brightness 5mm LEDs or some Luxeons or Cree XLamp's.


edit: just tested the two different sets of white 5mm LEDs, the new apparent brighter LEDs use approx 40% more power than the bag of ~70 I had leftover from an earlier project this year, but they aren't 40% brighter. Guess which LEDs I'm going to be using (hint: these)

 

[Haku]

I've been looking more into the various motorbike handlebar switches as most fit 7/8" diameter handlebars which is the same as on my ebike (and presumably most other bicycles), there's quite a lot going cheap on eBay (search for: handle* switch) and I've also been googling for them too.
Some ideal ones I've found are: techquadshop.com - Handlebar ON/OFF switch
/ Switch: Handlebar On/Off Switch (toggle) - 040-HBS-01 (same as first link) / Switch: Handlebar Three Position plus Kill Switch - 040-HBS-02 (which would be ideal for a setup with low/hi beam, ie half the LEDs and all the LEDs in your front light, unfortunately the KILL button won't kill cars )

But the most interesting one is this:

it doesn't normally come with switches installed, leaving you to put whatever switch(s) you want into it, and there's enough space inside for a DimensionEngineering DC-DC converter too. Unfortunately I can't find anywhere that sells it, this place has it listed for $12 but they haven't replied to my query and that page has been there for 8 years.
If anyone can find me that box I'd be eternally greatful.

 

[JohnInStockie]

Reflectors

Do you think somethink like these would be useable?

John

 

[Haku]

Do you think somethink like these would be useable?

Certainly, that's almost exactly what I'll be using for my back light/reflector, which I'll be supergluing a bolt into it to mount on the back of the pannier rack.
The ones I have I can take the clear red plastic away from the black backing by bending it slightly and prised them apart, then superglue the two pieces back together once the bolt is mounted inside & the LED holes drilled.

edit: the red ones in this pack are identical to what I have (and I got some red hands and red circles too)

My bike light setup is a little bit on hold whilst I drum up some money to get cabling, a waterproof fuse holder and a waterproof switch cover.


Haku, who's nursing scrapes after doing a impromptu superman impression on his bike concrete is so unforgiving

 

[Ian]

As Haku says, with a suitable mounting they should be OK. Reflectors seem fairly hard to buy by mail order but most decent bike shops usually have a selection. The last time I looked in Decathlon they had a couple of types on sale, not shown on their website though. It might be worth a look if you're anywhere near their Stockport store.

 

[JohnInStockie]

Mamma mia - ouch!

 

[JohnInStockie]

Thanks for the advice. Just wondering whether deep rear light casing are any better at all (see these). Which would be the better/easier to make for a soldering novice?

 

[Ian]

The thin ones are probably easier for LEDs, but you could use a pair of those marker lamps as they come, just wire them in series to the bike battery. At 5W each they would be much brighter than normal bike lights.