Generator questions..any Tech guy's around.?

[ninefinger]

Look at the system and break it down to deal with each part in its own right then combine the pieces together to get your steam-drive-electric-generating-battery-charging goal.

Using a (BLDC) is probably the most robust and one of the easiest to set up as a generator.

The electric generating is easily accomplished with a Brushless DC motor (BLDC) driven by something - in your case a steam engine. As mentioned these motors are rated by KV and as your steam engine is likely to be low rpm you want to find ther lowest KV motor you can get.

The output of the BLDC when driven by something is an 3-phase alternating current. Your application calls for DC to charge a battery. Simple - a bridge rectifier will change the 3 phase - make it yourself from some diodes

For a source of inexpensive (relatively speaking) BLDC motors look at on-line far east hobby stores - here is an example http://www.hobbyking.com/hobbyking/store/__4652__KD_63_24L_Brushless_Outrunner_193Kv.html $55 isn't very bad at all (plus shipping). So using that one as an example you'll probably need to spin it at ~ 2500rpm to get your desired voltage output.

2500 rpm too fast for your steam engine? No problem - just use gearing or a belt drive to step up the rpm from the engine to the generator. A 2.5:1 step up would let your steam engine run at a more comfortable 1000rpm.

After all of that then you can look at adding voltage regulators and such to keep the output voltage constant so you don't cook your battery.

My 2 cents..

 

[tomrux]

sorry to burst ya bubble here but there is no such thing as a "brushless" DC motor.

they are sychrnous ac motors driven by an inverter able to convert a dc input voltage into a rotating ac voltgage. normaly three phase.

a sychronous motor, when driven by a mechanical source, will output a basially stable ac voltage level that changes frequency with speed.

a brushed motor when driven will output a DC voltage that changes level with speed.

losses through rectifiers and regulators are going to more than double you input power requirments.
Keep it simple

pick a few brushed motors and try running them at different speeds till ya get what you need

Tom R

 

[jpeter]

I'll add my 2 cents. It was suggested to use an automobile regulator with a permanent magnet motor. Well, auto generators and alternators use a field coil for creating the field. The current through the field coil, thus the strength of the field, is controlled by the regulator so the output of the alternator is controlled by controlling the strength of the field magnitism. A perminent magnet field provides no way to control the output. Permanent magnet generators were sometimes used but controlling the output was problemmatic. One solution was to build the generator with extra brushes on the commutator which then could be selected by relays in the regulator. The cutout relay would today be replaced by a diode. Back in the day there was no good diode to be had.

 

[Don1966]

I guess I need to put my 2C in to. I haven't seen any calculations on power. It takes 746 watts for one HP of mechanic motion. The rule of thumb is to size your engine 1.5 x larger then generator. Of coarse you are using it as a demo and can get by with 1.2 x the generator. This is not an exact figure but I am just keeping it simple here. So if you use an alternator of 12volts and 30 amps you have 360 watts, which is equal to about .5 hp of electrical power multiply that times 1.2 equals to about .6 HP of mechanical power. Just keep it simple. If you use gears to drive it then figure the ratio for HP.

Don

 

[gus]

sorry to burst ya bubble here but there is no such thing as a "brushless" DC motor.

they are sychrnous ac motors driven by an inverter able to convert a dc input voltage into a rotating ac voltgage. normaly three phase.

a sychronous motor, when driven by a mechanical source, will output a basially stable ac voltage level that changes frequency with speed.

a brushed motor when driven will output a DC voltage that changes level with speed.

losses through rectifiers and regulators are going to more than double you input power requirments.
Keep it simple

pick a few brushed motors and try running them at different speeds till ya get what you need

Tom R

Hi Tom ,

Thanks for the enlightment. Was into aeromodelling.Been using DC motors to power model planes.Then came along the "Brushless DC motors". This came with red yelloe blue.I got suspicious. The controls and drive that came along
had three wire connections to motor.Then it dawned on me.Its got to be a three phase motor with inverters.

Gus from faraway Singapore.

 

[tomol409]

All you need can be found on an old car (before alternator era) which would have a proper 12v dynamo with the correct output and an AVC unit with cut-out to control things. This would give the sort of output you need . The voltage would be regulated - that is high when battery voltage is low and cutting down to low as battery voltage rises. Try some car breakers yards.

 

[gus]

All you need can be found on an old car (before alternator era) which would have a proper 12v dynamo with the correct output and an AVC unit with cut-out to control things. This would give the sort of output you need . The voltage would be regulated - that is high when battery voltage is low and cutting down to low as battery voltage rises. Try some car breakers yards.

Hi Tom,

Years back I came across a small slide valve steam engine coupled to a car alternator to generate power at a very remote outback station in Queensland,Australia.Took some fotos.Will post if I can find it.Must be Kakadu??? Crocodile country.

In the workshop, my repairman used an electric motor to drive alternator to charge batteries when our charger packed shop.

 

[skyline1]

Hi Martin,

An old type car dynamo and it's regulator box would probably work for this but a more modern alternator would be an even better solution.

Although they are alternators they usually have all the rectifying diodes and regulating electronics built in and are designed for just this sort of job, battery charging.

there are a couple of disadvantages though, they need to run at quite high speed 3000 to 5000 R.P.M. and they can be quite large and don't exactly look the part.

D.C. permanent magnet motors of about 180 Watts (about the size you require) are very common in industry for variable speed drives. I have used them myself professionally. They are usually high voltage ones though driven through small thyristor drives. Lower voltage and speed ones are available and are often used for wind turbines.

Small P.M. motors can make excellent generators though. I have two of them. These are the types used for tape decks and V.C.Rs and have very powerful rare earth magnets.There is one of them in the second picture (bottom left, didn't realise it was there actually)

They are powered by small steam turbines so I don't have a problem with speed they run at 30,000 R.P.M.+ in fact they need to run fast to produce sufficient torque. Very strange characteristics little steam turbines !

The larger of the two (couple of pics below) Produces 10-12 Volts at about 250mA (about 4 Watts) which is much less than you are proposing but is a usable amount of power from such a small motor.

I have designed a regulator for them which could be scaled up for your application based around LM317 Regulator chips. It is built into the switchboard you can see in the pictures. The switchboard although not quite finished yet is a real working one.

P.M. Me if you would like details about the regulator. as I have all the schematics and P.C.B. layouts and I may be able to make a P.C.B. for anyone interested.

 

[metaltrades01]

Hi There,
I have been away working out west in a remote location and haven't been able to access to the internet, so its time to catch up.

Thanks for all the advise and info, its much appreciated, up to the last reply i made, I came to the conclusion that I had several options, to use a... alternator, an old car generator, brushed DC motor with integral gearbox similar to what is used on bicycles etc (and available on ebay) and i think there a couple of other options mentioned.

Just before I left I spoke to a tech guy involved in renewable power generation, who said that any method that I planned to use to gear up an alternator or generator is inefficient and would soak up a lot of power, and advised me to use a permanent magnet DC motor and direct couple it to the steam engine.

He went on to say "Motors and generators like this are rated at xxx volts per rpm, or xxx rpm per volt, so this motor is rated at around 1800/72 or 25 rpm/volt and 0.04 volt/rpm. This means that at 300rpm it will produce 12 volts open circuit, so it is pretty much in your required rev range. To charge a battery you would need it outputting around 15 volts, which would take 375rpm."

After the conversation I bid and won a brushed dc motor on Ebay from the US.

(As a side note...firstly I direct coupled the DC motor to a 12v 5amp fan, and then secondly to a car ventilation/air conditioning fan (amperage unknown) and to my amazement on both occasions the fans turned as i turned the DC motor by hand- so the motor must have a reasonable output).

So the question is now, how to regulate it...

 

[gus]

Your DC Gen. looks like the real A.C. Genset I worked on.

Wow ! Mini Street Lights too.

 

[Ken I]

A.C. servos used on NC & robotic aplications also make good generators - being permanent magnet rotors with three phase windings for vector driving to position - quite often these motors are scrapped because of encoder failure even though the motor is still good.

Typically 200V = 3000 rpm and whatever Horsepower its rated at it will do as a generator.

These things come in sizes from watts to kilowatts.

Try any local NC or robotic supplier and see if they have any scrap motors.

Ken

 

[skyline1]

Hi Fellas

Gus,

Glad you like It . I've worked on full size ones myself too so I tried to make it look like one of the little private sets of the early 1900s when electrical power was pretty new and there was no grid as such. They were all different some A.C. some D.C. and used all sorts of different Voltages and Frequencies.Typical outputs were in the 25 - 50KW range.

A little imagination is required here, This one has been upgraded to one of those new fangled "turbine" engines but we've kept the old boiler. the "Electric Mechanic" loves it, but the Boilerman hates it says it's too noisy.

This sort of thing was often the case in full size with these things evolving and being upgraded as technology progressed.

Little turbines are ideal for this sort of thing and they make a super sound, real high pitched turbine whistle, at full speed it must actually be ultrasonic 'cos it sometimes makes the local dogs howl.

Martin,

Here's a pic of my LED regulator and I've P.M.ed An Idea for a battery charging circuit to you. Should be fairly simple to build on a piece of Veroboard or a little P.C.B.



Glad to learn about your motor now you know it actually works it's just a question of getting it to charge a battery. This might interest you. more little Permags in action.



This is my little model showman's engine with it's mini dynamo.



And the little Chair - o - Plane ride that it drives just like full size, I've got a video clip of it somewhere doing it, if I can find it I will upload it and put it on the forum

Regards Mark

 

[jpeter]

Here's and ebay link to what you need. http://www.ebay.com/itm/DC4-5-32V-t...754?pt=LH_DefaultDomain_0&hash=item3f1d9240ca

It's a dc to dc converter. You input most any dc voltage and it'll output whatever dc voltage for which you've set it.

 

[jpeter]

Just a little history:
Back in the day cheap charging systems, motorcycles, 3-wheelers, etc, often used permanent magnet alternators. Diodes were used for rectification. Your motor, most likely, uses brushes to rectify the AC. Anyway, these PM units generally had two charging rates, controlled by switching between a full wave or half wave rectifier. Which to use was often determined by whether or not the lights were on. The light switch was often double pole having a seperate set of contacts to do the switching. Sometimes a regulator did the switching.

An interesting tidbit: Motor volts/rpm is commonly referred to as KV.

Automotive generators/alternators use regulators to control the strength of the field magnets. They do this by modulating the current through the field coils. More current means stronger magnets thus higher output. A PM generator, of course, has no field coil to control so controlling the output requires some type of work around. That's why, in an earlier post, I recommended a DC to DC converter. BTW, I've never used one in that service but it seems like it outta work well and ebay has them for pretty reasonable prices.

 

[albertorc19]

You may take a look at www.jameco.com. Those guys have a lot of electronic kits at reasonable prices. Look for Jameco part No. 2161369, it isn't a regulator but may be useful for your project. You can also look for a kit based on the UC3906 which is an integrated circuit (IC) specifically designed to control the charging of acid lead batteries, this IC's data sheet provides schematics for a complete circuit but you need some experience on assembling electronic circuits. Altronics sells a basic kit that seems to be based on the manufacturer's data sheet.

 

[metaltrades01]

Thanks for the info, I'm thinking that i will use a basic regulator to start with and at a later date get a high tech regulator like this one... http://secure.oatleyelectronics.com//product_info.php?cPath=21&products_id=832 ..which the Tech guy I recommended it to me yesterday,

& he goes on to say...
"you could also look at a maximum power point tracking unit, these will take a variable input voltage considerably higher than the battery voltage and step it down to the correct voltage while boosting the current, so if you have 5 amps coming out of the generator at, say 20 volt, you might have 6 amps or more going into the battery." ....something I didn't know existed.

 

[metaltrades01]

In the next few weeks (or more - as the boiler I plan on using is out of commission at atm) I'll couple the generator to a 2 1/4 x 2 3/8" steam engine I have, and give it a test run, the engine is considerably bigger than the 1 1/2 x 1 1/2" engine i plan on driving the generator with, but it will give an indication of output etc.

I presume that it is possible to post short video's here.? ...if so, i'll post a vid of it running

 

[jpeter]

In recommending the dc to dc converter I'd missed the point about battery charging. I thought the goal was to have a constant voltage output from a variable voltage input even if the generator was turned so slow the generated voltage was below the needs of the load. The buck/boost dc to dc converter provides a constant voltage output for lighting lights and such even if the input voltage is too low. With the mppt controller I'm curious what happens when the input voltage drops below the desired output voltage. Is the controller able to boost the voltage to the desired output voltage? Interesting discussion here.

 

[gus]

Thanks for the advise Albertorc19, I don't know a lot about electricity generation. I'll go with the regulator.
I'd be keen to see the results that you get.

Martin

Hi Martin.

Been using AVR with AC gensets.Therefore know nuts about DC Voltage regulator. As a young kid saw my uncles replacement them on their cars in the 1950s when dynamos were used and alternators yet to be born.


Please advise source of DC Regulators.

 

[skyline1]

Hi Jim

I may be wrong here but I think these MPPT regulators are a form of HF Buck/Boost regulator but with added feedback to monitor the battery voltage and current and hence it's charge state. So they probably can boost the voltage to a degree but naturally at the expense of current.

Being High Frequency switchmode units they can be made quite efficient without the need for bulky transformers..

Regards Mark