# diode bridge

Discussion in 'General Electronics Discussion' started by donkey, Feb 17, 2012.

1. ### donkey

1,301
56
Feb 26, 2011
this should be easy to answer...
if i take 4 dynamos run them in series and they produce.. lets say 1.5v each.. and then run that through a diode bridge to make the current DC, would i get roughly 6volts?
I think i saw somewhere that said the diode bridge will cause a loss of voltage but the main question isn't regarding that I am trying to figure out how to combine the voltages and maintain the current(roughly) of 4 dynamos.

2. ### jackorocko

1,284
1
Apr 4, 2010
if it is producing AC then when rectified it will be 1.414 times as much DC minus the diode drop.

I think it is gonna be pretty hard to wire AC generators in series. Hmm, good question

Last edited: Feb 17, 2012
3. ### twister

172
7
Feb 12, 2012
You are right. You can't just hook AC generators in series or parallel easily, without BIG sparks. It can be done however, the power companys hook in parallel every day. You can do it too. Just hook one side of the generators together and then hook a 100 watt lite bulb between the other side. The lite will flicker if they are not at the same speed and phase. Increase or decrease the speed of one of the generators till the flicker slows or stops. When the lite bulb goes out they are in phase and can be hooked together.
I have never seen generators hooked in series before.

4. ### jackorocko

1,284
1
Apr 4, 2010
What kind of generator is this anyway? seems odd that a generator will only output 1.5V

5. ### Laplace

1,252
185
Apr 4, 2010
The word 'dynamo' usually refers to a generator employing a commutator to produce DC current. If that is what you have, then a diode bridge should not be necessary for your setup. However, if your dynamos are generating AC then visualize the problem of just connecting two in series: frequency and phase are important. If two dynamos generate the same frequency but the result is 180 degrees out of phase with each other, then the series connection produces nothing at all going into the diode bridge. If each dynamo had its own diode bridge, and the bridge outputs were connected in series (assuming each dynamo has a floating output) then the output is still zero because 1.5 volts is lost in the diode bridge (less if the diodes are power Schottky diodes). So unless you have a method to control the phase of each dynamo, or are able to generate more voltage than would be lost in the diode bridge, or are able to run each dynamo at a different frequency, the suggested series connection will be problematic.

6. ### donkey

1,301
56
Feb 26, 2011
first of all the dynamo giving 1.5v was an example... i was more looking at them hooking up together.
second when I say dynamo i mean those little things that go on bikes to produce power.. the run of your tyre
I had 1 worry about hooking them up in series or parralllel and that was if the circuit was closed would the dynamo turn into a motor? wouldn't the one producng the most power cause the others to turn. If so that is not what i want. I thought about each dynamo having its own bridge but i think that will cause the same issue. oh well this is one i have to test i figure

7. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,505
2,849
Jan 21, 2010
One potential problem is that these dynamos often have the frame of the bike as one of the outputs.

This essentially means that any connection other than parallel is going to require insulating them from the frame.

To place them in parallel, you would be advised to rectify the outputs first.

You will find that their open circuit voltage is quite high. I had one which was capable of about 80V, but fell to around 8 under its rated load.

8. ### twister

172
7
Feb 12, 2012
I believe those generators are DC generators. I don't think there would be any problem hooking them in series or parallel as long as they were putting out approximately the same voltage and turning at the same speed. You could hook them together with a small load to test. Then if everything stays cool increase the load a little at a time.
Many motors can be used as a generator or a generator used as a motor. A DC generator from a car can be used as a motor. Also AC induction motors can be used as a generator.

After reading Steve's post, I must be wrong. They must be ac generators.

Last edited: Feb 18, 2012
9. ### jackorocko

1,284
1
Apr 4, 2010
Maybe they do produce AC and have a rectifier built in? I don't know but that would be the first thing I would figure out if I was donkey.

10. ### donkey

1,301
56
Feb 26, 2011
thanks everyone for the responses so far. but i am still trying to figure out something that has not been truly answered.
if dynamo 1 is outputting more voltage and current then the other dynamos will dynamo 1 bacome the power source and the othe other 3 dynamos become motors? ie will the other dynamos try to consume power rather than produce it? and if so is there any way to rectify this?
the way i see it both in parrallel and series when the circuit is closed if any one of the dynamos produce more than the others it will become a power source and the others will turn consuming the power i am trying to produce

11. ### twister

172
7
Feb 12, 2012
If they are connected in parallel then the one that is producing more power will motor the weaker one. If they are connected to a load, however, the more powerful one will carry most of the load and will therefore slow down till the weaker one take up a smaller portion of the load.
This is the same principle that an induction motor can be used for a generator. If you hook this motor to the power line it will run and can be used as a motor. If you hook a gas engine to that motor and try to turn it faster than it is turning it will stop consuming electricity and instead produce electricity and it will turn the power meter backwards.