Electrical question.

[swanman]

I want to set up a test bench for a 12 volt motorcylce wiring harness. Instead of using the battery as the power source, I want to use house current and step it down to 12 volts. There is a 10 amp fuse on the battery so I guess I need output at no more than 10 amps.

Is this sensible, safe, feasible?? Cheap??

I have seen some transformers on TM for garden lighting that are cheap. 230v to 12 volts output a coupla amps. Only $9.

Anyone want to give advice before I blow up the house and/ or kill myself with a huge electric shock.

[Ixion]

Easy enough and safe enough. But you'll need to rectify it to DC, and if you have electonic thingies in there you'll need to smooth it. Why not just buy a liddle battery charger ? Give you 12v DC , though not very clean. I'm sure some of the electronical boffins here can add more useful info

[bugjuice]

why not just plug it direct to a bike battery? Doesn't have to be part of the loom etc, just straight at the battery.. unless it's something you're wanting as a permanent feature of the house..??

[2much]

The maximum current of the circuit is dependant on how much the accessories "load" draw, not what the power supply is capable of. Get a good power supply capable of atleast 10 amps.

You're pretty safe to do this, just be careful not to short anything.

Oh, and don't try to use the starter motor on this setup.

[far queue]

You can build your own 12v 12amp power supply from an old PC power supply. I built one about 6 months ago. Have a look here for how to do it ... http://web2.murraystate.edu/andy.bat...owersupply.htm

[jonbuoy]

Your ancillary stuff (lights,ignition etc) is probably 10 amps total but the starter motor, if you have one, will take way more than that probably more like 30amps for a couple of seconds. Depends on what you want to test on the loom I guess. The PC power supply is not a bad idea - still won't let you crack the starter though. A 30amp 12v psu will be pretty pricey.

[swanman]

why not just plug it direct to a bike battery? Doesn't have to be part of the loom etc, just straight at the battery.. unless it's something you're wanting as a permanent feature of the house..??

It is a battery off a street magic, and hasn't got much oommpf. Also on the side of the battery it states not to "boost charge" and a charge rate of .3 amps, which is a lot less than my battery charger.

I have actualy taken the complete wiring loom off with all the lights etc and laid it out on the bench top. I am using this as a learning exercise so need to have a constant power source that doesn't go flat.

[swanman]

The maximum current of the circuit is dependant on how much the accessories "load" draw, not what the power supply is capable of. Get a good power supply capable of at least 10 amps.

You're pretty safe to do this, just be careful not to short anything.

Oh, and don't try to use the starter motor on this setup.

Good advice. Cheers

Why can't I use the starter motor on this set up? It is only a little street magic so maybe it draws less than a regular bike.

[Motu]

I have a little power supply I plug into the mains,about 5 amps I think.I use it to test small circuits and actuators,better than using a car battery that can weld small components together.Enough oomph to run a car cassete deck out of the vehicle.But a small battery charger can work just as well.

[FlyingDutchMan]

If you're the engine running off a supply, disconnect the alternator (as close to it as possible). It has huge potential to screw things up pretty badly, as it really a current source rather than a voltage source - it will try and pump current back into your power supply - needless to say this can cause all sort of things to go POP.

[Sparkz]

What could work too is use a bike/ car battery and leave a trickle charger permanently connected to keep it topped up.

It could supply as much current as you need, even a starter motor, while the mains only supplies a small charging current.

[swanman]

http://www.trademe.co.nz/Browse/List...px?id=48132751

I saw this on TM. Could this do the job?

[jonbuoy]

Nah mate, I think thats a 220 - 12v AC transformer. You want a DC one, I think most of the outside lights are AC. I think Jaycar/Dick smith do something.

This ones in Jaycar CAT. NO. GH1379 $35

12v 5 amps.

Won't be enough to crack the starter but will drive indicators and ignition I think.

[aff-man]

Baaa If it out put ac then just wack in a cheap rectifier (about $4) and she'll be right...

If you want to you could even chuck a couple of capacitors across the load and put a regulator in..

Depends on what you want to run...

If it's just lights indicators etc etc then "dirty" DC shouldn't be a problem... IF you trying it out on something with fuel injectors then you gonna have to clean it up quite a bit.

..... I think what 2much is going on about is that the starter will draw a lot of current... might make things go bang.

[2much]

Good advice. Cheers

Why can't I use the starter motor on this set up? It is only a little street magic so maybe it draws less than a regular bike.

..... I think what 2much is going on about is that the starter will draw a lot of current... might make things go bang.

Yep, exactly.

To be honest I'm not sure how much a streetmagic starter motor would draw, I'm guessing probably about 20-30A (Car starter motors can draw upwards of 100A). Even though it's only a small motor it still requires alot of power to turn it over fast enough to fire, compare it to pull starting your lawn mower.

All it will do is pop the fuse in your Power Supply.