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Old 05-22-2020, 11:21 AM
lasers lasers is offline
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Default DC to DC converters instead of charge controllers for solar power.



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Lately I have been playing around with homemade wind turbines and waterwheels to produce power to charge a battery bank. In doing so I am able to build them and the generator part of of scrap and have no money into it. The problem is to get that power into a battery I need to run it through an MPPT charge controller to step the power up or down as needed to get it to charging voltage. And a cheap MPPT controller is $80, that gets expensive when you want to experiment with half a dozen of them.

I am wondering if an adjustable boost/buck converter with input and output protection would do more or less the same idea. Through ebay I can buy a 5 amp one for $2.50 on up to a 20 amp one for $9.50(shipping included) The smaller ones even have input and out put volt and amp meters.

My thought is at that price I could run two in parallel to safely get the 25 amps I need for my big panels or one small one for my small wind turbine.

The thing is, I don't know how they work exactly.

Most of them go into fault mode when the input is below .7 volts. Do they automatically come out of fault mode when the power goes back up or do you have to manually reset them to get them out of fault mode?

Can they put out a constant set voltage(13.9 volts) with a variable input ? Or do they need a constant input to get a constant output? Since most of them have some type of micro controller and mosfet transistor so I assume they can handle large, constantly variable input but still keep a pretty stable output? Anyone with first hand experience on how these things work?



As long as I am getting into a bit more technical questions I am also wondering about full bridge rectifiers. Is it possible to get a on size fits all or do I need different sizes. A couple generators I have put out up to 120 volt @8 amps and some put out 19 volts at 4 amps. Would a large rectifier work on the smaller generators?

And will a rectifier work on 3 phase ac?
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Old 05-22-2020, 01:39 PM
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Originally Posted by lasers View Post
As long as I am getting into a bit more technical questions I am also wondering about full bridge rectifiers. Is it possible to get a on size fits all or do I need different sizes. A couple generators I have put out up to 120 volt @8 amps and some put out 19 volts at 4 amps. Would a large rectifier work on the smaller generators?

And will a rectifier work on 3 phase ac?
A full wave bridge rectifier works very well on three phase AC. The unit must be sized to handle the current load and may require a heat sink and/or active cooling for high current. A large unit could be used with low current for a one-size-fits-all, but these are more expensive. Higher voltage is more efficient due to the voltage drop across the diodes which is about 1.6 volts (for example, 1.6v is a larger chunk of 12v vs. 24v - so, 24v would be more efficient all else equal). Note also the DC voltage will be approximately 1.3 times the root mean square of the incoming three phase AC voltage. So, select the alternator and desired speed carefully to match the desired DC voltage.

Traditionally, wind and hydro are controlled with a diversion load connected to the system via a relay powered by a relatively simple battery charge controller using an adjustable voltage sensing relay. These can be had for about $10-15. The controller switch closes on high voltage when the battery state of charge is high to energize and close the diversion load relay and dump excess current to protect the battery from excess charge. The load is deenergized after the voltage drops to a lower setpoint that often can be programmed.
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Old 05-22-2020, 03:58 PM
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With rectifier diodes you have to be aware of the reverse breakdown voltage. A bridge designed for 19 VAC may have diodes with a smaller reverse breakdown voltage than 115 VAC.

I am sure you can use a higher voltage one for low voltage low current applications but not the opposite. When it comes down to cost for a mass produced item you must choose exactly or you are paying for specs you don't need like high current at high voltage.

For non critical projects you can play around as long as the current and breakdown voltages are not exceeded.

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Old 05-22-2020, 06:18 PM
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With rectifier diodes you have to be aware of the reverse breakdown voltage. A bridge designed for 19 VAC may have diodes with a smaller reverse breakdown voltage than 115 VAC.

I am sure you can use a higher voltage one for low voltage low current applications but not the opposite. When it comes down to cost for a mass produced item you must choose exactly or you are paying for specs you don't need like high current at high voltage.

For non critical projects you can play around as long as the current and breakdown voltages are not exceeded.

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When it comes to bridge rectifiers, just this morning I went and got about a dozen of them from a scrap metal dealer I help out a bit. They are all probably way larger than I need(not even sure they are all rectifiers) and I want to make sure if I use on larger than necessary I am not causing it not to work or wasting a lot of power.
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Old 05-23-2020, 02:21 AM
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When it comes to bridge rectifiers, just this morning I went and got about a dozen of them from a scrap metal dealer I help out a bit. They are all probably way larger than I need(not even sure they are all rectifiers) and I want to make sure if I use on larger than necessary I am not causing it not to work or wasting a lot of power.
Look up the part numbers and check the specs. The peak inverse voltage will dictate how high a voltage you can rectify. A bit if math required.

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Old 05-23-2020, 07:59 AM
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Here is an MPPT controller up to 100 A for $19

https://www.wish.com/product/5c7f46c..._BwE&share=web
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Old 05-23-2020, 08:04 AM
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though I am curious how you are spinning the Permanent Magnet Motor with the a windmill.
A typical one that stands like 20 feet tall or one that I have seen where they took a barrel and shaped it. How is that working our for you
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Old 05-23-2020, 08:47 AM
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I use an inverter making AC 110 from my shop trailer solar/wind/battery bank, to the house 100' away, and to a 12 volt battery charger on a second battery bank at the house.
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Old 05-23-2020, 11:05 AM
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though I am curious how you are spinning the Permanent Magnet Motor with the a windmill.
A typical one that stands like 20 feet tall or one that I have seen where they took a barrel and shaped it. How is that working our for you
I took a fan radiator fan motor from a Chevy venture. Mounted a 10 inch saw blade with a 5/8 arbor hole to it. I cut 3 notches in the blade and bent each notch to 30 degrees and to each bent piece of the blade I mounted a 36" wood blade. From there I used the bearings out of the front post of bicycle to make a furling tail and the tubing from the bike to make a swivel. The tube from the bike fits inside a 20 foot piece of 1 1/4 inch steel pipe that is stuck in the ground and nailed to the eaves of my shed.

I looped an extension cord around the pipe about 10 times from the windmill to the battery bank. The head of the mill can go in a few circles before I have to untangle the cord(I need to come up with a better solution for that). I will probably pull some brushes out of a motor and make a connection that can spin but still make constant contact.

That put out about 16-19 volts at 4-6 amps in a good wind so 64 to 114 watts.

I wasn't overly happy with that so I removed the saw blade and turbine blades and replaced them with the back sprocket of a bike. Then I cut up the frame of a bike and used the bike crank, sprocket bearings and tube it is all mounted in to gear up the speed the motor spins. To do this I cut both peddle cranks off where they bend then on the side opposite the sprocket I ground the stub that was sticking out down to 5/8" and tapped it to 5/8 course thread. Then with a small pile of washers and a nut I put the saw blade and wood blades on that shaft, put a bike chain between the two sprockets and put the assembly back up. Unfortunately after all that work and extra complexity and extra parts that will eventually cause it to fail, I am getting nearly the same output.

One problem I have is I didn't balance the blades and one of the blades appears to be several ounces heaver than the other two so it takes a decent gust to start it spinning, once it is spinning the wind can die way down and it will continue spinning and putting out power, it is the initial starting that is the problem. I also assume that out of balance isn't doing it any good when spinning at high speed.


Edit: Most Chevy's from the mid 90's through the mid 2000's with the vortech engine have two radiator fans that don't match each other. One is smaller, round and has no cogging when spun by hand and the other is bigger, triangular shaped and has obvious cogging when spun. I tested them both and they both had more or less the same output at the same speed and both have 5/8 mounting shafts. I ended up using the smaller one because cutting the hole for mounting it was easier and I didn't really like the vibration caused by the cogging when testing it a high speeds(over 1000 rpm)
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Old 05-23-2020, 08:38 PM
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@lasers, if you have time, a separate thread on the windmill, hopefully with pictures, would be appreciated by me and I expect quite a few other members.
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Old 05-24-2020, 03:42 PM
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@lasers, if you have time, a separate thread on the windmill, hopefully with pictures, would be appreciated by me and I expect quite a few other members.
Here you go. https://www.survivalistboards.com/sh...2#post20331722
it is long and rambling and I don't know if it gives a good idea of how it was build but it is the best I can do and hopefully it is understandable enough to give you and idea of how it is built.
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Old 05-24-2020, 04:08 PM
arleigh arleigh is online now
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I don't think you want your mill spinning at 1000 RPM,
Most only spin at a few hundred and those are well balanced.
If it takes that much speed for the motor to generate you may have to gear or pulley it to transfer more speed to the shaft motor. Gears would be best chain and sprockets ok , but belts and pulleys take energy away from the work. "it takes power to bend the V belt" less power to bend a flat belt. but rubber belts and sunlight are not good friends.
Wood blades are a gamble too. centrifugal force is very powerful thing. You might consider aluminum blades.
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Old 05-24-2020, 04:32 PM
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Originally Posted by arleigh View Post
I don't think you want your mill spinning at 1000 RPM,
Most only spin at a few hundred and those are well balanced.
If it takes that much speed for the motor to generate you may have to gear or pulley it to transfer more speed to the shaft motor. Gears would be best chain and sprockets ok , but belts and pulleys take energy away from the work. "it takes power to bend the V belt" less power to bend a flat belt. but rubber belts and sunlight are not good friends.
Wood blades are a gamble too. centrifugal force is very powerful thing. You might consider aluminum blades.
That 1000 rpm was testing just the motor(attached to another motor). I doubt the turbine blades get above a couple hundred rpm. Then I have a 2/1 gearing to step the speed up.
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