28vdc motor

[Rob Kroeker]

Hi,
I'm not all that familiar with electrical generation, but I have a 28vdc motor, a car battery, and a 400 watt inverter. I was thinking of making some type of windmill on the roof of my house and connecting this dc motor to it in order to generate electricity.
The motor is originally used in a juice machine application. The computer control board on the juice machine determines what voltage dc is sent to the motor, and the motor spins at that set speed (in this case, slow or fast).
When I put my multi-meter on the leads and turn the dc motor by hand, it generates DC voltage...anywhere from 0-28 or more vdc?! What happens if I have this connected to a 12 vold battery? If my generator is spinning at a rate that produces 20volts, will that screw up my battery? What happens to my invertor connected to the battery? How do I go about generating DC voltage with this thing?
thanks

ps - the actual motor can be found at the following link:
http://store.3wire.com/webstore/Parts/PartDetail.aspx?PartNo=1010881&uom=EA

pps - Would there be any advantage in looking at a Li-ion battery as opposed to a conventional car battery?

[Joe Blake]

Hi Rob,

Welcome to the board. When you say you connected your multi-meter to the motor, did you have a load on? eg a battery? Spinning the motor by hand is not likely to damage the battery, so try connecting a 12 volt battery to the output, with the v-meter in place and see the results. No doubt you will need some sort of regulator/cut out in place eventually, ie when start producing more serious amounts of power, but at the low power you're supplying (by hand) I'm guessing the voltage output will drop down to the battery's requirements. Certainly that's my experience with solar photovoltaic panels, that they put out a specific amount of power (ie watts) and as long as the voltage is greater than the battery's need, it will come down and the amperage will go up, but the total power is the same. (This is important to know this because a PV panel may have a nominal output of (say) 12 volts but under load it will drop down to 8 or 7 volts, which can drain your battery, so I've found if you want to charge a 12 volt battery, whack 2x12 volt (nominal) PV panels in series and they will work.)

(This is just a "quick and dirty" experiment so don't carry it too far.)

Have fun experimenting. ;)

Remember that an inverter (ie from 12 dc to 240 (or 110)) volt AC will incur losses in the inversion. (The efficiency can vary from 90 to 95%, depending on the inverter). So if you're considering doing the "self sufficiency" thing, keep in mind that sometimes it's better to buy the 12 (or 24) volt appliance that run will directly off the battery, rather than an inverter. These days it's possible to buy 12/24 v fridge/freezers and even a 12 volt computer and screen, even microwaves and DVD players.

Re the question of Li-ion batteries, it's probably a matter of $$$. I'd do some experiments with the lead-acid first and get a feel for what I might need, and perhaps when your L/A is knackered, get something else. Battery technology is improving almost weekly, so I'd hang off getting something "new" straight away, give the cost a chance to come down. I've been using L/A for about 5 years now and they do an excellent job in a stationary application. I even use them on my electric tricycle, but I'm sure Li-ions would be lighter and more powerful.

Regards
Joe

[Rob Kroeker]

Awesome! thanks for the start - Ya, I didn't take the whole "load" thing into account. The motor though is designed for 28vdc - does that mean that somehow I'll have to bring it down to 12vdc (or put two batteries in series and bring it down to 24)? And how exactly would one do that?
Yes, good point about the inverter. I'm not sure exactly what I'd run off of it, but I was thinking about wiring it into one of the circuits for my house for emergency back up when the Grid goes down (like say, on the furnace fan motor etc.)
Thanks again!

[Joe Blake]

To keep things absolutely simple, a suggestion. Get 4x12 volt batteries, put them into series of two, ie positive of one connected to negative of the other, (ONE set of terminals only - don't join both sets of terminals, otherwise you get a dead-short circuit and it's bye-bye batteries - http://www.freesunpower.com/battery_diagrams.php )

that way you'll have 24 volts, you can have one pair on charge (the 28 volts is only 4 volts more than the nominal voltage), and you then have two more to play with, either run them in parallel as 12 volts (ie negative joined with negative and positive joined with positive) or 24 volts or even two separate power sources for two separate 12 volt applications.

The link will be helpful to you.

A good search term on Google is "caravan". Many products for caravans are designed to run off 12 volts.

Regards,

Joe

PS re wiring in your inverter to your house circuit, that will probably be a big no-no in many countries. Only trained/licensed people should fool about with main voltage. Even 12 volts can be dangerous under certain circumstances.

[Rob Beckers]

Awesome! thanks for the start - Ya, I didn't take the whole "load" thing into account. The motor though is designed for 28vdc - does that mean that somehow I'll have to bring it down to 12vdc (or put two batteries in series and bring it down to 24)? And how exactly would one do that?
Yes, good point about the inverter. I'm not sure exactly what I'd run off of it, but I was thinking about wiring it into one of the circuits for my house for emergency back up when the Grid goes down (like say, on the furnace fan motor etc.)
Thanks again!

When used as an alternator the motor voltage should be more or less proportional to its RPM. It was probably designed to run at a very high RPM @ 28V, maybe too high to use as a windmill alternator. So, hook it up to a 12V battery and take a look at its RPM, if it's more in line with what you need. Using it to charge a 12V battery may be a more doable project in that case.

For use as a windmill generator I'd hook up a diode in series so you're not driving the motor from the battery when there's not enough wind. Even though the motor is made for a higher voltage you can still use it to charge a lower voltage battery. What will happen is that once the motor reaches battery voltage, the battery will 'clamp' the voltage at that level. The motor will can still run a faster than that set voltage, it'll produce more current and cause more heat in the stator windings (to the point where it'll eventually burn up, if needed you can add a series resistor to avoid this).

-RoB-

[Mark Parsons]

ps - the actual motor can be found at the following link:
http://store.3wire.com/webstore/Parts/PartDetail.aspx?PartNo=1010881&uom=EA



Greetings Rob,

The link you quoted shows the motor rated 28VDC 300RPM. If it is for a household juicer, I assume it is rated at least 1/2hp. If so, it sounds like an almost ideal motor for a wind turbine generator and 12V or 24V battery charging. I bet it is a PM Brushed DC motor so some brush maintenance for longevity would be required. However, price looks good at $86. The motor photo wouldn't come up in my browser.

If you can verify the 300RPM and find out the HP and maximum amps ratings we can provide some guidance for turbine swept area size to use with this generator.

Regards,
Mark