How to connect a DC to DC converter?

[cwah]

Where did you obtain that switch from?

My bike has the exact one as that. The switch section snapped off from the handlebar clip but I glued it. The other thing is the indicator switch isn't waterproof at all. Last week I was on the way home and the indicator beeper wouldn't cancel at all until I got home and sprayed WD40 in it.

I had it from Lyen.

So far I can't tell if it's working well or not because I'm only using the horn button as regen. All the other cables are not connected.

If you know any better switch I'm interested

 

[cwah]

cwah, ground is ground, 0v, you don't have 2 different ones...the converter 'ground' is the same as the controller 'ground' (ground is the wrong terminology but hey it it helps you understand) You need to switch the positive side of the lights separately from your three speed switch, so if the green button is a latch type and not used for anything else then wire to that...put it in series with the 12v feed from the converter to your lights...

Thanks for the explaination.

I tried this:

So it's using the ground from the controller and the power from the DC converter.

But there is no power at all. I tested on the wattmeter and there is 0 V.

I suppose I missed something, but I don't know what

 

[NRG]

You tested what on the Watt Meter? Use your multimeter (MM) on the lowest resistance setting, connect the black lead of the MM to the battery negative wire and connect the red lead of the MM to one side of the switch.

With the switch set to off, one side of the switch should read 0 Ohms IE a short, the other side of the switch should read infinite Ohms IE: an open circuit

If its an open circuit reading then this is the switch contact you use to connect to the black wire on the converter, the purple one in your diagram. If you connect to the other switch contact your lights should be on all the time. If none of this works then you cant have a 0v or ground connection on that switch.

 

[rog_london]

Yeah, I know. I don't have much knowledge in electronic but I'm learning. That's quite satisfactory to be able to achieve thing by myself

I now want to connect the light to my 3 speed switch:

The problem is that my actual 3 speed switch is already connected with my controller:

The ground and another cable are used in order to activate the regen on my bike.

Is there a way to use the same multi-speed switch for both the controller and the light? I suppose I'd need 2 different ground wire because it's different voltage?

Ah, well, they do say 'the devil looks after his own'. Full marks for having a go - I just hope Sod's Law doesn't sneak up on you and bite your bum. It's probably waiting for the most opportune moment, when you're 20 miles from home, it's pitch dark, and chucking it down with rain.

I suppose I should look on the bright side and take comfort from the fact that under such circumstances getting on line and asking for help might not be practical....

And of course I am joking! It's just that the more you know about 'electrics' the more respect for it you develop.

One possibly useful thing - I know your lights are 12 volt, but if your main switch is controlling your 70-odd volt feed to the bike's controller, of course you can switch the converter off by breaking the circuit on the 70 volt side - this will turn your lights on and off just as easily as switching the converter's 12 volt output. Put a slightly different way, consider your lights and converter as a single entity - in other words, you have 70 volt lighting, not 12 volt lighting. Then you won't have mixed supply voltages to worry about.

One other thing - as Frank has hinted, put a fuse in the converter's input side. About 5 amps should be about right. That will be a much higher value than the normal current draw, but will blow in an orderly manner if you have a problem. A 30 amp fuse is only good for the feed to your controller. If by accident you short out the 12 volt output of the converter, what happens next depends on how good an internal design it has - if it's a decent one it will simply shut down and not suffer any damage or cause any other problem - but if not it might self-destruct on a shorted output.

Rog.

 

[cwah]

Thanks a lot guys.

I finally made it work. I have my switch turn on multiple lights at the same time.

I used the multi-meter to check for continuity between the cables as you said NRJ. And I found that the light and the 3 speed switch cables all have their own "ground". So I plugged everything in serie et voila!!

Thaaanks


Next step: Get the light activate when I use the brake. Not sure yet where I'm going to install the sensor.


ps: I don't have a 5 amps fuse. Do you know where I could buy that? Either on ebay or in london?

 

[neptune]

You can buy a fuse from any shop that sells car accessories and/or in-car entertainment . Ask for an inline fuse and holder, and buy a couple of spare fuses at the same time. Halfords is a possibility.

 

[NRG]

Well done cwah, Halfords, as neptune says, sell in-line fuses...check the bubble pack rack in the electrical section...

 

[cwah]

I wouldn't be able to do that without you guys.

Thanks and I'm going to pop in halford this weekend

 

[rog_london]

I wouldn't be able to do that without you guys.

Thanks and I'm going to pop in halford this weekend

Thanks for that! We've just put our rates up to £51 per hour, but I'll let you off the travelling time.....

The fuse value is not critical - if your lights draw around half an amp (that's according to the website) you'd need a 1 amp or (slightly) greater value of fuse in the 12 volt side of your converter (to protect the converter), and ideally a second one-amp fuse in the 70 volt supply side to the converter - to protect the bike's wiring if you're really unlucky and manage to launch the converter.

I picked 5 amp in my original notes because I didn't at that point have the full story of what you're up to. Your converter may be good for 10 amps but if you're only drawing half an amp or slightly less - fuse accordingly.

The idea of a fuse is to pick a value significantly higher than your estimated load - to avoid 'nuisance' blows due to switch-on surges and such - but not too high, so that if there's much more current flowing than you expect, it will pop quickly. Get a few spare fuses - if you never need them, they're cheap enough to sit in a drawer. You should not need anti-surge fuses which are a bit more expensive (not much) but not appropriate here. The ones you want will probably be labelled 'T1A' or something similar.

Maplins will flog you in-line 20mm fuseholders and of course the fuses to go with them. There are different fuse sizes - not just values - 20mm is the sort you need, and very common.

Then if one of those does blow, don't fall into the trap of trying a bigger fuse - it may sound silly to say that now, but you'd be surprised.....

Rog.

 

[cwah]

Hehe, quite expensive hour rate lol.

I think I have to stick with the 5 amps fuse because I plan to add the magicshine MJ-880 light on it:

Magicshine MJ-880 Bike Light Torch LIGHT UNIT 2000 LUMENS!! upgrade from mj-872 | eBay

This light is small but very bright. That's exactly what I'm looking for.

However, it's rated at 8.4V and my converter output 12V.


According to few people online, some managed to run other magicshine on 12V without problem. So I think I'm going to give a try.

 

[rog_london]

Hehe, quite expensive hour rate lol.

I think I have to stick with the 5 amps fuse because I plan to add the magicshine MJ-880 light on it:


This light is small but very bright. That's exactly what I'm looking for.

However, it's rated at 8.4V and my converter output 12V.


According to few people online, some managed to run other magicshine on 12V without problem. So I think I'm going to give a try.

Not really - of course they don't pay ME £51 per hour - I wish! It's getting quite common to charge that for professional services. I design/commission/troubleshoot commercial fire alarm systems.

Do you know what the current drain of your lamp is (or the wattage rating). I'd say you were pushing it a bit with 12 volts, I might have a suggestion when I know its requirements.

Rog.

 

[cwah]

According to the specs, it uses a 8.4V6.6AH battery. At max luminosity, the battery can last about 2.3 hours:
Magicshine MJ-880 NEW 2000 lumen bike light - Magicshine's most powerful light yet. Order from the official Magicshine UK distributor today!

So it uses 6.6AH/2.3hours= 2.8A or around 24W.

That's why I thought a 5amps fuse was ok for that.

 

[rog_london]

I've just looked up the MagicShine, and reading between the lines on the website it takes just under 3 amps on full power.

I assume you plan to dispense with the Li-Ion battery pack which comes with the lamp?

You might like to give it a little 'headroom' by connecting three ordinary diodes in series. I recommend Maplins part number UK61R, which is a 6 amp job. They will drop between 2 and 3 volts almost independently of the forward current, so your £100 light will not see more than 10 volts. Cost one pound each.

You can solder the three in a string in the supply to the lamp protected by a short length of heat-shrink sleeving. They'll get barely warm, dissipating no more than 3 watts each. Do string them out, though, so they are not on top of one another, to maximize cooling.

Oh, band on each diode is towards the lamp, if you're putting the string in the positive power lead.

Rog.

PS - crossed post. Your 2.8 amps is correct.

 

[cwah]

Yes, I plan to use it with my main battery

If I use 3 diodes, I'm going to loose 9W. That's huge compared to the power of the light at 24W. Almost half of the power would be lost in heat.

I've read in endlessphere that the magicshine light can handle up to 18V. So maybe I can give a try without diode? I can just use it at half power

 

[rog_london]

Yes, I plan to use it with my main battery

If I use 3 diodes, I'm going to loose 9W. That's huge compared to the power of the light at 24W. Almost half of the power would be lost in heat.

I've read in endlessphere that the magicshine light can handle up to 18V. So maybe I can give a try without diode? I can just use it at half power

If it's been shown to handle 18V with no problems, just go for it - you definitely won't need the diodes. I'm surprised it will go that high, but it does depend on exactly how the regulator works within the lamp.

I expect, knowing that, that there's a DC to DC converter involved within the lamp, which might well give it that sort of range. In order to waste as little power as possible they would probably do that, along with automatic cutoff if the incoming supply dropped as their battery went flat.

One more thing about YOUR converter - bear in mind that as your bike battery voltage drops, the converter will draw more current to maintain its 12 volt output - so hopefully your bike battery has a cut-off BMS built into it.

Rog.

 

[cwah]

Actually it's only a post from a member saying it can handle 18V. But few members use the light at 12V without problem.

The only issue is that I've read that it has 10V capacitor... but I suppose the capacitor should be able to handle 12V? Anyway few members managed to make it work at 12V.

I'm using lipo batteries, so no bms cut-off. But I'm very cautious with the lipo and unplug them as soon as there is less than 25% of the total capacity remaining.

 

[rog_london]

A capacitor in that application will probably not be all that critical, so I'd expect you to get away with that.

Sounds as though you're about there! Best of luck with it.

Rog.

 

[cwah]

Thanks rog. Hope that everything is going to work.

Will post picture once the light set will be completed

 

[cwah]

Received my Magicshine MJ-880 today and pluged it to my 12V converter:

This light is incredibly small for 2000 lumens and perfect for a small bike such as the Brompton.

Just a problem:
It makes a lot of heat when I turn it on... still a bit afraid to run it at 12V rather than the 8.4V standard... I hope it will keep working for a long long time..

 

[Aushiker]

I appreciate that this is an old thread but my question is on the same topic so thought it might be better asking here and hence keep all the information in the one thread.

I have purchased a Grin DC-DC Converter - 6V(10W)

My intention is to use this in combination with my 36V battery to power a Busch & Muller Lumotec IQ2 Luxos B and a Busch & Muller Toplight Line Brake Plus rear light. The rear light is wired to the front light, so the power from the battery goes to the front light. The wiring at the light end should be straight forward as it has wiring already in place for the dynamo.

The battery which is coming is a EM3EV 36V Samsung frame mounted one.

My question is really about wiring the DC-DC converter into the system and if giving the early comments is it worth putting a fuse in place on the input side and one on the output side? I guess inline fuses would be suitable. If yes, suggested sizes?

With wiring can I simply cut into the battery - motor wiring (the motor is a Bafang BBS01 so the controller is built in)? I guess some sort of suitable connector would be the best option here or do I need to solder it directly into the battery.

Something I have missed?

Thanks
Andrew