Voltage conversion problems

[HydroCamper]

Greetings all,

I built a small portable hydropower system to take with me for camping out of a trolling motor. Most streams are not fast enough to reach 12 volts. The most I have got so far is 5 volts with about 2-3 volts being average.  I am having trouble figuring out what is the best way to convert 2-5 volts to 110 ac. Most inverters cut off at 10 volts, so they won't work. The only solution I can think of so far is to charge 1.2v batteries independently and to recombine them through switches or manually to make 12 volt bank. Is there a better way?

Travis

[Ungrounded Lightning Rod]

In rough order of desirability:

1. Rewind the trolling motor with four times as many turns of wire of about half the diameter of the original wire.
   
2. Change the prop for one with a different pitch - and a bigger swept area while you're at it.
   
3. Switching upconverter
   
4. Four trolling motors wired in series and mounted in parallel.
   
5. Motor-generator to upconvert.
   

[ignesandros]

You could step up the voltage by making your own transformer. Base it on your application... depending on the espected voltage output, you use a factor of windings around an iron cored ring, depending on the voltage. In other words, assuming you require 12V to use an inverter and your average with the hydro system is 3V, you'd use 4x as many wraps of magnawire for the output loops as the input loops. For lower current applications, you probly want to use a smaller iron ring and lighter gauge magnawire and for higher current, more robust components. Look into transformers if you don't quite follow.

-Andrew

[terry5732]

The transformer involves losses, but they are small. Much easier than rewinding motor though. You want to go from 3 volts to 12+, or roughly a 4-1 conversion . So look for a transformer that was for 110v to 30 v in a good amperage rating. Put your unrectified output from trolling motor to transformer and then rectify.

[drdongle]

Better yet get a motor that puts out more voltage. Since you don't describe how your system works I can't be more explisit.

[ghurd]

Most trolling motors will have a DC output, so a transformer will not work without other circuits added.

G-

[wooferhound]

You are not mentioning anything about a battery. You need to be charging a battery or your system will not work. Even if you get your generator to put out 12 volts, as soon as you hook up the inverter with load your generator will stop or slow down considerably. With a battery you can accumulate your small amount of power over time, and then use what you need from the battery when you need it.

[HydroCamper]

Based on all the comments I read this morning, it seems that the transformer idea is the best for the following reasons. If a person rewinds the motor for a higher voltage (Thats great because it miminimizes loses and the current can go straight to the inverter) than that causes problems with using it for different applications. It might work great for a slow moving stream, but as soon as it put into a fast moving stream it could easly put out too much current for the inverter to accept. So using the transformer, or several, a person could use the one that best fits the stream speed allowing the generator to be move around from place to place. Most off the shelf inverter under 1500 watts can accept voltage ranges from 10-14 volts. So step up transformers of 2, 3, 4, 5, and maybe a 6 would meet just about every situation. Probably only the 2, 3, and 4 would every be used, because if the generator is only running at 2 volts the the power generation may be two small to worry about. The loses of the transformer don't seem to be of much concern because the unit appears to be putting out lots of extra power. I was really amazed how well it worked in my testing and how simple it was to use. The motor is completly stock, running in reverse, with a simple cage built around it. I hope to take some pictures of it post them later on.

[kitno455]

does the motor have brushes, or some other internal means of converting ac into dc? if so, you cant just hook a transformer to it.

i would try a bigger prop first. then a re-wind.

oh, and woof said it. you cant just hook an inverter to this thing. it will stop dead under load. need a battery.

allan

[HydroCamper]

Some additional details:

Voltage generated: 2-5 volts

Final out voltage desired: 110VAC

Watts produced: maybe 100 at 2 volts and 100s to maybe over a 1000 at 5 volts.

Watts used: 350 surge, 30-40 normally.

Has anyone seen a scematic for converting 6 volt to 12 volt dc?

Can a person substitute a different transformer? or does the resisters and capacitors also have to change?

Travis

[kitno455]

how are you measuring the watts output? i really doubt that you are getting 50 amps out of that little motor and prop at 2v, and 200 amps at 5 volts is impossible, you would have melted the wires.

allan

[HydroCamper]

Its probably not that high then. If I get a better multi meter or amp gage I will hook it up and see how much power it is really producing.

Cheers,

Travis

[Ungrounded Lightning Rod]

Remember that you need to measure voltage and current at the same time - or at least under the same load.  Loading the motor changes the speed, which changes the voltage.

If you measure unloaded voltage and loaded current, then multiply them, you will get a number much larger than the actual power you can draw.

Better yet, if you're planning to charge 2V cells then reconnect them for 12V discharge, confiure the motor to charge a partially-discharged 2V cell and measure the voltage and current doing that.

[ignesandros]

Yeah, those numbers look wrong for a trolling motor. What kind of motor is it (make/model)? I'd love to see pix when you get them. Sounds like something fun to try. You might even be able to use something similar in just about any stream. Try making the cage more of a funeling scoop to improve voltage, too.

-Andrew

[HydroCamper]

I tried putting together a circuit that would transform 4 VDC to 12 VAC, but nothing seemed to work. I tried modifing an existing 12VDC to 120VAC circuit. (http://www.i4at.org/lib2/inverter.htm) If anyone has a circuit they think would work I would be willing to put it together to give it a try. Looks like its back to rewinding the motor or charger indivdual batteries and putting them together to make 12 volts. It does not look like it is possible to charge a 1.2v battery using 2 volts and still have them all combined to make 12 volt while the 12 volt combination is being used? Does anyone know for sure if this is true?

[kitno455]

or, replace the prop with a higher speed design to get the rpms (and voltage) up.

allan

[joelhacker]

Good point...don't forget OHM's power law.

[HydroCamper]

I have posted some pictures of this project to the hydro section.

Travis