Motor+Circuit for a water generator - Page 1
Forum section: electronics / beginners

author: JuculianD
author_rank: Contributor
timestamp: October 28, 2018, 09:51:10 pm
content: Hello,you have already helped me a lot since. I just want to say thankyou to everyone again for your kind help - I am slowly getting out of "newbie" but I cannot call myself very experienced.Anyway.I want to build a generator for a sailing yacht that is generating some power. It does not need to be much, should be 12V at 3-5A.I am not sure about the motor. I do not want a regular DC motor because it should not have any wear.I would like a BLDC motor.After looking around for some time, I have found some motors that are suitable from the Kv for my project and would generate around 5V without any transmission.Do you have an idea for a better motor (stepper??)?My other question is about getting the motor to charge the battery. Would a diode pack and a regular step up converter be enoug?Sorry for that solutionCan somebody please help me about that? Do you have any professional ideas maybe with some mosfets and active switching. I really dont know.I would also like to have 2 motors, can I connect them in series to increase the voltage?Sorry for all that questions,you would help me a lot.Dont hesitate to ask for anymore information.Thanks,Julian.

author: t1d
author_rank: Super Contributor
timestamp: October 29, 2018, 11:45:31 am
content: I have looked at lots of DIY designs, for hydro-power generation, land and marine. There are l-o-t-s of these designs, on the net. Boat forums often have a section just for power generation and they might be a better place to find boat-specific information... The marine environment creates lots of unique considerations, that might not be considered as well, by this forum...You say that you want a water powered unit, and they are available, but more rare. These units have a propeller on a flexible shaft that is hung overboard. That creates drag. Mostly, boats use solar and/or wind generators and, being a sailor, that is what I would recommend, to you.The generator portion of the unit is the tricky part. You can use lots of different types of rewound car alternators, various electric motors, etc. But, the problem is designing for efficiency. So, lots of people use commercial generators, that are manufactured for DIY projects, and build out the rest of the system, themselves.Other significant issues are the battery/power storage bank and the distribution system. Additionally,boats have unique grounding systems, that you do not want to cross up.Your amperage desires may prove to be tough to meet, too. Of course, money can cure that.When considering a generator, you need to check to see if it is approved for a salt water environment, if that is where you will use it. Otherwise, the unit may fail, quickly.As I said, there are manufacturers that make generators for DIY projects. Just google for them. Prices vary. You can even get cheap ones, on Ebay, for $60, IIRC. You might use something like that, to build a prototype, but I would not rely on it, for real use.Please give details, about the boat (size, blue water cruiser?, salt water?, engine type, etc.), what you intend to power, if the system you are building is to be the primary system, or just the backup, and your budget.One last thing... this is a big subject, with a steep learning curve... Even to buy a ready-made unit. So, be prepared for that. You say you are still somewhat "newbish," so you will have to be very careful not to miss important considerations.

author: spec
author_rank: Frequent Contributor
timestamp: October 29, 2018, 07:51:48 pm
content: + JuculianDAs t1d says, the marine environment can be very harsh.But, if you want to experiment, the attached schematic shows a general circuit to connect a motor/generator to a lead/acid battery.The diode should be a Schottky type with a forward current rating of at least 20 amps to give a low forward voltage drop. The diode should also have a reverse voltage rating (PIV) of at least 20V. Lastly, the diode needs to have a low reverse current (see link below for a suitable diode).The regulator is a buck/boost switching regulator board available from ebay etc for around 10 Euros. A buck/boost regulator produces a constant output voltage if the input voltage is above, equal to, or below the output voltage. This means that you will not require two motor/generators connected in series to produce sufficient voltage to charge the battery.You would need to set the voltage at the cathode of the diode for the optimum charge voltage for your particular battery (probably around 13.75V). This is done by the output voltage adjuster potentiometer on the regulator.If you set the output current limit of the regulator to about 3A, that would be about right for most lead acid batteries with a capacity of around 50 amp/hours (typical 12V battery capacity of a mid-sized European car).For your application, the battery needs to be a deep-discharge type, rather than a normal car type which would not last very long. But a normal car battery could be used for experimentation.Both the diode and regulator will need to be attached to suitable heatsinks.Links:typical buck/boost regulatorhttps://www.ebay.co.uk/itm/Auto-buck-boost-regulator-Constant-current-voltage-5-32v-3A-UK-Stock/191676953707?hash=item2ca0d6346b:g:RyYAAOSwu4BV4dsw:rk:1:pf:0Diode (dual type- just connect both diodes in parallel)http://www.onsemi.com/pub/Collateral/NTSV20H120CT-D.PDF

author: t1d
author_rank: Super Contributor
timestamp: October 29, 2018, 10:02:15 pm
content: Great circuit, Spec!JuculianD, something to add to the circuit is a switch, to change over from charging the battery to using the battery. In the States, these are called "Perko" switches. There are many types and many features. You will need to research what will meet your needs. Break-before-make, grounding path, etc.https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l2632.R3.TR12.TRC2.A0.H2.Xperko.TRS0&_nkw=perko+battery+switch&_sacat=159136I can not emphasis the grounding issue strongly enough. You must get it right, from the start, period. The issue is setting up electrolysis, through the metal parts of the boat. I have seen lots of metal hulls, metal rigging and outboard engine feet extensively damaged. Even the drive shaft and propeller, on inboard motors.I have heard and seen sad stories of where the owner had new sacrificial zincs and added something minor, to the electrical system, a deep finder, for example... They got the ground wrong, the power immediately used up the zinc and started eating the boat.On bigger vessels, the owner might have added a common household clothes washer and have dire results. Why, because the new washer had the neutral and ground wires tied, inside it, and that established an incorrect grounding path. And, all this damage can be done with just 12 volts. I even know of incorrectly grounded boats, in marinas, causing damage to nearby boats.And, you must be careful when tying to a marinas shore power supply. You can not rely on the owner to have installed the system correctly. You must know how the various parts of your power system(s) work and you must use test equipment to check the marina supply, before you connect to it.Remember you are working with electricity and water. It deserves as much respect as working with gasoline and matches. There are complete text books devoted to boat power. I suggest you do some reading. Start with boating magazines. They regularly have articles, on the subject.We can help, more, when you give us the details on the vessel and what you want to accomplish.

author: JuculianD
author_rank: Contributor
timestamp: October 30, 2018, 03:04:25 pm
content: Wow, that was very much helpful information.Thank you very much for your enthusiasm!To add some information about me:I am experencied in doing those projects and dont worry, I will make it seawaterproof. There will be nice CNC Parts etc.I do also have some experience about electronics and I am also selling my own electronic PCBs in Germany in some time. But I do not know exactly about generator + diodes for rectification.So I appreciate any information about that.I also thought about using a step up converter but I dont know about using those motors. I have found some suitable Brushless Motors with 60Kv.If I turn them with approximately 300 RPM they will make 5V of Voltage. How much current can I draw from them (the voltage will drop as well..)? Is it just limited by the internal resistance of the windig and the force by the propeller?I am also unsure about the rectification. I do have 3 wires on the BLDC motor. I should use 6 diodes for a full bridge rectification, right?How should make a Full Bridge Rectifier for those 3 coils?Thank you very much again for your help.

author: spec
author_rank: Frequent Contributor
timestamp: October 30, 2018, 03:12:06 pm
content: Quote from: t1d on October 29, 2018, 10:02:15 pmThanks t1d, but it is pretty standard stuff.Quote from: t1d on October 29, 2018, 10:02:15 pmI'm intrigued by this change-over switch. Is that a safety requirement in the marine world?I had imagined that, like with the case of a car alternator/battery system, that the generator would be connected permanently.

author: spec
author_rank: Frequent Contributor
timestamp: October 30, 2018, 03:29:44 pm
content: Quote from: JuculianD on October 30, 2018, 03:04:25 pmNo problem from me JuculianDRegarding your technical questions about using motors as generators, just search the internet- there is a heap of information on the subject. One very popular motor is from a treadmill.A typical car alternator will give you about 20V at up to 80 amps or so maximum, but car alternators are not very efficient, only about 50%. All the same there is no reason why you could not experiment with a car alternator as they have all the circuity to charge a battery already built in. Car alternators are also rugged and reliable.About rectifying a three line output- yes you are on the right track. A three phase bridge rectifier would be required- just take a look at a car alternator schematic.Another approach, is to use a motorcycle alternator- not the type that is integrated with the crankshaft output, but the type that are a separate unit, like the old DC generators. Once again, with the bike rectifier regulator you would have everything done for you. The advantage of a motorcycle alternator is that it is smaller and lighter than a car alternator.You question about the output characteristics of a motor used as a generator has many aspects, that depend on the type of motor, motor rotational speed, and current loading. But, to a very rough approximation the out put voltage is proportional to rotational speed and inversely proportional to current load. To give an example, a motorcycle alternator for a 12V system will produce around 80v RMS off load.

author: JuculianD
author_rank: Contributor
timestamp: October 30, 2018, 05:39:43 pm
content: I definetely do want to use a brushless motor with 40mm width - 60Kv.I will now do a PCB design with the diodes and also a charging controller if possible.I am now going to take a look in the internet.Thank you very much.

author: t1d
author_rank: Super Contributor
timestamp: October 31, 2018, 01:24:45 am
content: Quote from: spec on October 30, 2018, 03:12:06 pmWell, my responses have been wide, in scope, because we still have not been informed about the boat, etc. As for being a requirement, it depends on the boat... But, it is always a safety concern. It may also be required by the boat insurance underwriter; it usually is, in the fine print...Depending on the parts of the system (engine type, battery type, charger type, etc.,) the switch may be an operational requirement. For example, having the charging system tied to the starterof some typesof outboards engines, at the moment you start the engine, can fry the outboard engine electrical components. We still need information about the boat, the engine, the intended sailing region, etc.Have we been told, exactly, what the generator powering method will be? Wind, or hydro?JuculianDA major consideration, in choosing the generator, is the amount of torque that is needed, to turn the generator, throughout all the expected RPM ranges, of use, because, the torque needed changes. For example, I looked at building a floating generator, to ride in a small stream. It was going to be difficult, to turn the generator (of the size needed for the target voltage/amperage) with the water current that was available.Take any spare motor, of the same type, as you intend to use, and try spinning it, by hand. It will be much more difficult, than you would think. If it is making any significant usable power, it is not going to freewheel.Then, chuck the shaft, of the motor, into a drill motor. Secure the motor's body. Attach your multimeter leads. Spin the motor, varying the RPM. Observe the power, that you get. You will gain much insight, by this simple experiment.You may not want to buy anything, until you have a complete design, for the entire system. I think that you have a long way to go... learning the factors... designing what will work, for you... I don't mean to dampen your enthusiasm, just somethings to think about.Check YouTube and Instructables for project ideas.

author: JuculianD
author_rank: Contributor
timestamp: October 31, 2018, 09:15:11 pm
content: I have taken a look in the internet and found many useful ideas. I have a full concept now and do know which components to use. I do also know that the mechanical system will work. Obviously I will have to engineer as soon as I am have the parts to make it marine-proof. But that I will do that with my father.Now, I am doing my electronics. I have found an open source project on github for a MPPT circuit with 32bit processor that is suitable for my project. I am now trying to get used to KiCad.It is a great software but I am used to easyeda. I can not get my components imported as I can with LCSC + EasyEDA. Any ideas on that? Just take a diode with a similar footprint and change the name to the one I am using?As soon as I have made progress I will let you take a look