Hard wiring with no batterry

[Timolgra]

On my off road bikes which have no battery I have for a couple of years taken a live feed from the lights or horn to power my GPS.
I leave batteries in the unit (taped up etc) for when the engine is not running.

To date I have had no real problems with this.

Then I find a rectifier 'thingy' on the market to supply 15v especially for this situation. It may also be used to charge a small battery. Does this 'thingy' give a smoother power supply?

The reason I ask is that when I tried to plug my heated jacket in which draws less power than a head lamp, the light on the temp control flickers or pulses at all engine speeds but doesn't heat the jacket at all.

Do I need a 'thingy' for either or both purposes, if so what is it and where can I get one or have one made?

Thanks Tim

 

[Howard Millichap]

The generators on off road/enduro bikes are useless. 100w if you're lucky. Just enough to power lights, horn and ignition. Your jacket might ONLY need 50w but when the bike is already using 95w of the 100w supplied.......well, you work it out.

500w generators as fitted to the GS weighs too much to put on a racing bike. That's why gp bikes run with a battery only and use a total loss system.

 

[Timolgra]

My jacket requires 38W maximum, but doesn't work when I have no lights running at all, so should theoretically be well within the generator output.

When I raced grass track bikes we used a total loss system, (battery only) not necessarily to just save weight which of course it does but also to reduce drag/load on the engine, ie not to waste power.

Tim

 

[Rob Farmer]

Tim,

It could be that the rectifier you are using is a "half wave" device, similar to those used on the smaller Honda trail bikes, these only provide a charge on the positive half cycle from the alternator and were only intended to provide a crude charging system for the battery. this would explain the pulsing on your jacket control unit. Some of the older trail bikes used AC straight from the alternator to power the lights and horn I wouldn't want that anywhere near my GPS.

You need a "full wave" rectifier that will produce a constant positive voltage. Maplin Electronics http://www.maplin.co.uk do a rectifier that will handle upto 10Amps for £1.99 (part number KBPC1002). Your jacket will draw 3.16Amps (Ohms law - 38/12).

I would be careful about connecting a GPS straight onto a rectifier. Maplin also do a voltage regulator that will convert a DC voltage of between 14V and 30V into a smooth 12V output (part number L78M12CV @ 49 Pence each).

Hope this helps.

 

[Greg Masters]

I think that I'm with Howard on this. The generator on Thunderbird 6 is only rated at about 25w max - 15w for the headlamp, 3w for for the taillamp and the remainer to trickle charge the battery from which is drawn the intermitent stuff like winkers, horn and brakelight.

If I added an electric jacket, the generator would be the only thing going into meltdown!

The rules of electricity state that an unregulated generator will try to meet the demand placed upon it (limited only by the input energy ie engine speed). If it generates more than its rated capacity, it will overload and burn out.

Tim - I dunno about your bike, but I wouldn't hook all that gear up to mine!

Greg

 

[Rob Farmer]

Greg,

I'm showing my ignorance on small trail bikes here, and probably putting up misleading info to boot; if thats all the alternator is rated at then theres no way you want to be putting a heated vest, or any other large load, onto the system.

I'd also disregard what I said about the regulator - if the lights pull the voltage down below 14V you will not get a steady 12V from it.

That will teach me to read the question properly :flush

 

[Timolgra]

I have spoken to Mike Lambeth who prepares 'overland' and rally bikes, he suggests:

Finding the first place of DC power after the rectifier.
make up a battery pack of 10 or 11 1.2V AA rechargeables.
The batteries are wired in series to make 12V plus this pack is wired in parallel.

The idea is that you then have a smooth and constant power supply that has the added advantage of not trying to turn the GPS off when the engine stops and tries to then run off it's own power, also the lights or side light could be used without the engine running.

Of course a small gell battery could be used instead but this would be heavier and perhaps more difficult to find a suitable mounting place, whereas a home made battery pack could be mounted in a variety of ways.
I will give a go when I get time and inspiration then post the results.
Tim

 

[Howard Millichap]

Of course a small gell battery could be used instead
Tim

Take a look at some of the 12v batteries use in household intruder alarms. Some are quite small and not too heavy. Would probably fit behind the h/lamp cowling.

 

[Timolgra]

Take a look at some of the 12v batteries use in household intruder alarms. Some are quite small and not too heavy. Would probably fit behind the h/lamp cowling.

I'll have a look. I had also thought that there is a bit of space there, some bikes fit them in the air box if there's enough room without causing a restriction or perhaps behind the LH side panel but it's in the mud etc. then.
Tim