New Generator running

[winni]

I have recently built a generator as per the typical volvo disk brake type. I have used 20 neo magnets which are about 1inch diameter and about 3/4 inch thick. i have 20 coils each with about 100 turns using 0.75mm wire. My output seems to be good. Turning by hand i get about 20 volts when wired in parallel. When i hook it up to a 12volt spotlight it lights it up no problem. When i put my multimeter on and put it on the 10ampDC setting, it goes way off the scale as soon as it starts turning. The only other meter i have is a AC amp meter that goes up to 100amp. If i hook this up, it measures about 70 amps. Could this be right, or do i need to get hold of a DC amp meter that measures alot higher than 10 amps?

[LEXX]

Is the output rectified?  If you are taking the electricity directly off of the coils then the AC reading is correct, if you have rectified then the reading off of the DC meter is correct.  I must say tho, 70 amps sounds pretty high especially turning it by hand, how do you have it set up??  How many watts is the bulb in your 12V light?  Also, check the volts that it is producing, you might not be making that many volts but lots of amps, is the bulb at what you would call full brightness?

LEXX

[iFred]

Something does not sound right here. Something is off. There is no way that you are generating that kind of power with what your using! Check your measurments again, I think your in error. Your wire which is .075 is #18 gauge I believe. Check your meters and what they are set for.

-------------------------------------------------------------------------------------

OHMS LAWS!! Read them, memorize them, Print them - USE THEM!

1826, George Simon Ohm found that for a given circuit at a given temperature, a definite ratio existed between the potential difference (voltage) and the current. If the voltage were doubled without changing the temperature, the current would also be doubled. This ratio of voltage to current is called the resistance, R, of the circuit. Thus,

V / I = R = a constant

If V is measured in volts, and I is measured in amperes (amps), then R is in ohms. Hence, the ohm is one volt per ampere.

The relation between V, I and R is called Ohm's Law, in honor of good ol' George. The law should be familiar in all three of its possible forms:

R = V / I

I = V / R

V = I x R

By extension, we can also calculate the power, P, dissipated by a resistive element:

P = V x I

By simple substitution, we arrive at the other two common expressions for power:

P = V² / R

P = I² x R

These expressions for power apply to Direct Current (DC) circuits. AC alternating current is even more complex.

-------------------------------------------------------------------------------------

[winni]

i dont know what the wattage is for the spotlight, but it definitly lights up very bright and you can feel the heat comming off it. I am confident that i am achieving 20 volts and in excess of 10 amps, but am unsure of what reading i am getting from the AC meter. I have a rectifier that it is going through. When i turn by hand i can get about 180rpm to measure volts, but when i hook up the light to measure amps, it gets alot harder to turn so probably only get about 100rpm (very rough estimate).

The setup is 20 magnets with 20 coils on a disk of about 12 inch diameter with steel laminates behind the coils.

I guess my real question is can i somehow use the AC amp meter to test the DC load somhow - like can i hook it up before the rectifier to measure the amps or is there a table i can convert the reading i am getting when i hook it up after the rectifier?

[Flux]

You seem to be trying to measure the short circuit current, which is rather meaningless.

You seem to have single phase so any ac measurements should be before the rectifier. Using the meter on ac after the rectifier will depend entirely on the meter what it actually measures.

From the voltage (dc ) and the lamp test, things are looking good.

Forget all about measuring the short circuit current and measure the dc current with the rectifier feeding a battery, with your ammeter in the line between the rectifier + and battery +.  You will have to work pretty hard to get 10A out of it but if you can it looks good.

If you go over 10A and want to measure higher do the same test into the battery but put your ammeter on AC and put it in series with one of the ac ( input ) connections of the rectifier. There will be errors due to wave form depending on the type of meter but the result will usually be within 10%.

Flux

[LEXX]

Yes, you can hook your ammeter in line before the rectifier, but what you are saying is that you are getting over 200 watts at 100 RPM....hmmm  Flux is right, use a battery instead of a light, it will give you a more stable reading.  With the battery hooked up you can be sure what your Voltage is, it's the same as the battery, then just multiply by the Amps and voile.. Watts!  Oh course there will be a slight error due to rectification as per Flux but it will be as close as you can get withthe equipment you are using.

LEXX

[PHinker]

200 watts turning by hand is amazing.  That's more than 1/4 horsepower.  I took an old exercise bike and set it up on its end.  I replaced the magnetic resistence (aluminum disc spinning in close proximity to some ceramic magnets) with a 1 hp dc motor and the best I've been able to generate 'pedalling' by hand is about 80 watts (and not for very long either!). Granted, there are some losses in my setup since I'm not direct driving the motor.

[picmacmillan]

hello flux...i am about to convey my ignorance in to respect to running a volt meter...i just tried what was suggested in your post....i have had my first experience with the mysterious blue smoke what is the difference between an ammeter and a volt meter.....i just fried my volt meter trying to check the amps?...i did as was said and put a meter between the rectifiers and the battery..with the genny outputs + and -, i then seen that my volts was 13.? volts..good enough...i turned the genny and got my volts up to 14.?volts at an estimated 180 rpm...then the damage came...i turned my volt meter to amps and all hell broke loose...smoke came billowing out?..what in the world did i do wrong?...sorry for stepping on the original post but if he does what i did in not understanding? then he is going to be buying a volt meter just like me.....i think there is a lot of folks out here that don't understand this part of the genny building business...we can't know everything about everything......pickster...p.s....do i get a badge for being in the blue smoke club? :)pickster

[jimjjnn]

I suggest going to your local auto parts store and getting a cheepo induction amp meter. Accuracy may not be the best but I have used them for years and saved a lot of blue smoke .Most have two grooves in the back for hi current and low current. I think I bought 4 of them for about $17 US a year ago. Accurate enough for me. Never more than .02-.05 amps off. Only smoked one meter in my life and learned from that one time. Scope-meter. Boss was P..... off.

[winni]

I tried a new multimeter last night and got completley different results (i think the old multimeter is cactus). Amps measured 2 into the spotlight and volts were at 40. This is obviously alot more realistic, but i will try measureing amps into a battery as suggested and see what i get. I am pretty happy with the result any way.

Thanks for the comments and help.

Winni.

[jimjjnn]

Dang !! Old age getting to me.

Forgot to mention after stepdown transformer, install your bridge rectifiers for d.c. output. Sorry 'bout the lapse in memory.

Also, 'nother thought. Using transformers, the losses will be less than the hi-price cable will have

[Flux]

Hi pixter

Sorry about the smoke.  A voltmeter has a very high resistance and is connected across whatever you want to measure, because of its resistance it takes little current.

An ammeter has virtually no resistance and is intended to go in SERIES with the load.

It has little resistance so that it does not reduce the load current.

I can only think that somehow you had your meter connected from the rectifier pos to battery neg. That would explain why you were measuring battery volts. To measure current, you should nave broken the lead from the rectifier to the battery left the pos lead on the rectifier pos and connected the meter neg lead to the battery pos so that the ammeter was replacing that lead you broke.

Because the ammeter has low resistance and you shorted the battery you got the smoke.

Flux

[ghurd]

I tell people to put the Amp meter (ammeter) in where and how a fuse would go in.

Or think about it like a piece of wire.  You replace a piece of wire in your circuit with the amp meter.  You wouldn't put a piece of wire from battey plus to minus would you?

That said, I go through LOTS of meter fuses when I get rushed.  I have more melted meter leads than meters.  And I often take 4-5 meters for service calls, just in case.

It happens.

G-

[Flux]

Ghurd

That's a good way for beginners to think about it, the clip on induction ammeter that someone mentioned here is also a good idea. The modern multimeter with extra holes for current and silly ranges is far from ideal. Shunts are better but try explaining that.

I think a lot of this confusion about ammeters comes from this idea of connecting ammeters directly across alternators that people seem intent on doing, in the belief that this gives something useful.  It really doesn't work with a 1Mva alternator and even in the case where it does no harm it also gives useless and confusing information.

Flux

[picmacmillan]

thanks for the explanation, i will save this post and read it oer until i get it....need more coffee so far..pickster

[wooferhound]

to measure VOLTAGE with a meter it should go in PARALLEL with the voltage source

to measure CURRENT with a meter it should go in SERIES with the voltage source

When you meter is set to read AMPS, there will be a short circuit between the probes

When you meter is set to read VOLTS, there will be 10000's of ohms between the probes

[Jerry]

Hi iFred

Your right about (this sounds like to much power). As far as the 18 ga. wire keep in mind there are 20 of these 18 ga. coils in perelell.

What gage is 18 ga. X 20 = ?  This is simular what I've just done with 9 coils of 24 ga. wires. So the actul resistance will be much lower then just one coil.

                         JK TAS Jerry