a small and quick question...........lol

[snake]

hi friends,i have an ametek 38vdc and i wanted to test for amps to see how much power it may produce coz some guys told that it produces at about 5amps @ 13.5volts.

so i hooked it in a 12v car battery and connected my multi meter in series with the motor

i was thinking that @ 13.5vdc,it will produce 5 amps as a wind turbine and maybe it will read approx 5amps when hooked to a 12 volts battery

but i could only read 0.22 amps with no load.

can someone please tell me what i didnt do right or understand please?

thanks

[zap]

0.22 amps sounds about right with no load.  'No load' is the key.  Try keeping the shaft from rotating and watch the amp load increase... and the friction burn on your fingers!

[Flux]

I think your friend is trying to tell you that it will survive producing 5A into a 12v battery.

Your no load motoring current seems reasonable. If you stall it you will get a higher current. I don't know what current it will stall out at 12v but it's probably not going to be very high but don't push it above 10A for many seconds.

These things were intended as servo motors and presumably at 38v nominal in this case.

They were never intended as generators but they do work reasonably well as such. You can't expect much more current at 12v than rated current as a motor so don't push them too hard. long term they overheat but heavy short term overload may damage the brushes and commutator.

You will probably have to run it at a speed where it produces well over 24v open circuit for it to charge a 12v battery at 5A. They have a relatively high internal resistance.

The figures 5A at 13.8v really don't have any meaning. If you set it to 13.8v open circuit and connect a battery you are only at cut in with a floating battery so the current will be mA.

Flux

[snake]

does it mean that if the battery takes 0.22amps at 12 when powered by a battery will  give the same output when it is used as a wind generator?

[Flux]

No .

What it does as a motor has no relevance to what it will do as a generator. The only thing common to both is the emf. It will have the same emf at the same speed as a motor or generator. Sadly you can't get at the emf, you can only see terminal volts.

What it does as a generator depends on the energy you feed into it from the wind. You will have to run it faster as a generator than it would run as a motor at the same load current.

As I said previously if it cuts in at 12v at a certain speed you will have to turn it 2 or 3 times as fast as that to get it charging 5A into a battery.

The wind is the only thing that determines what it does as a generator, you have to feed energy into it and what goes into your battery is what you extract from the wind less the losses in the generator. Given enough wind and a suitable prop it will produce more than it can stand and will burn out. You have to furl or do something clever to prevent that.

Typically these small motors are officially rated for a bit over 5A. With the intermittent duty of wind power you can push them a bit but I think 10A is about the limit. Life depends a great deal on how much you overload it.

They were not meant for wind generators, their original use has now gone but many have found a nice market selling them as wind generators. They work and are a good starter project if they come cheap enough. Learn and move on to better things when you have experience.

Flux

[snake]

thanks flux,i thought that it would give the same output as the input.

please tell me how must i connect my multimeter to the motor as a wind geneator to know how much amps it is producing.

[Flux]

You must build the wind generator first, you need a blocking diode in series to prevent it motoring from the battery. It will then charge the battery in a wind if you get things right.

You need the multimeter on Amps range and it needs to be connected in series between the mill and the battery.

Basically the same set up as your motoring experiments but with a blocking diode and the motor being turned by the wind.

There is nothing whatsoever you can predict without the wind bit, that is your source of power and success or failure depends on you having wind and suitable blades.

Flux

[hiker]

a 50watt car headlite draws about 5amps--hook up a drill to your motor and spin it

up--if it hits anywhere around 12-14 volts-thats about 5amps..

try two headlites--see what happens..........