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DC motor as generator, overheating.

DC motor as generator, overheating.

DC motor as generator, overheating.

(OP)
Hi - 1st post - be gentle smile

I have an old water mill, with a large 8 tonne iron water wheel on the side.

This drives a chain / belt / gearbox setup that drives a generator.

Due to the fun of waterwheels, I have decided to go down the route of DC->Inverter->grid setup - but thats not the problem.

I have approx 2kw worth of water flow (variable) - and the generator is producing 800 odd watts (output) - but the casing is at 90+ degrees centigrade. This is half a ton of 50Hp reliance / Baldor motor....

Motor spec on the plate:-
50Hp, 1100 RPM, 300vDC Field, 500V armature.
Running at:-
1Hp output(yes, one), 1100rpm, 280VDC field, 410VDC arm

Field is created by taking 240V AC, rectifying, and smoothing with some random big capacitors I have kicking about (6, motor start jobbies - 30uF each)

why oh why oh why is it making more heat than electricity?

RE: DC motor as generator, overheating.

Is the field in the right direction?

RE: DC motor as generator, overheating.

(OP)
yes - its bi-directional, and so works the same both ways...

RE: DC motor as generator, overheating.

The power used for excitation is not to be ignored. Some motors used to have up to 5 % excitation power compared to rated power. That may not be the case here, but is a possibility.

Even with 2 % excitation power, you will have the same nominal excitation power as the useful output from the generator.

Friction losses and windage losses can be rather large in old machines. Bearing conditions may have a part in the low efficiency. If you run 50 HP, the losses will not be large in comparison. But at 1 Hp, that's quite another story.

Also, if there is a compound (series) winding, make sure it is correctly connected.
 

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC motor as generator, overheating.

(OP)
The field is 60 to 100 watts (as measured with a plugin type meter)....

Bearings arnt good - Ill accept that - its a little noisy, and a lot less when I greased it..

heres a similar motor to what I have:-
http://www.reliance.com/cgi-bin/dcexplode.pl?D5150R-BV its not 'old' particuarly.

Its STABSHUNT not series... but you would be right smile

RE: DC motor as generator, overheating.

According to the spec sheet in the link you gave, the field dissipates 933 watts when hot. More when cold.
You may not need the filter capacitors. The inductance of the field is a pretty good filter.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: DC motor as generator, overheating.

Is the motor's fan going in the correct direction?

 

Mike Halloran
Pembroke Pines, FL, USA

RE: DC motor as generator, overheating.

Regardless of the generator load, the shunt field is fully energized and will be dissipating heat continously. What is the field current you are seeing at 285 V DC ?

I would remove the series field (STABSHUNT is a series field winding) from the circuit for the generator operation.

RE: DC motor as generator, overheating.

"field is 60 to 100 watts"

How do you mean? Does it change that much? It ought to be rather stable. And about ten times as much as that. Around 1000 W, I would think.

Are you sure that your data are right?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC motor as generator, overheating.

Is it possible that the capacitors and the inductance of the field are creating a tuned circuit and the resulting higher frequency AC is heating the field poles with eddy currents? Remember the field poles may be solid rather than laminated and so be susceptible to AC induced eddy currents.

Quote:

The field is 60 to 100 watts (as measured with a plugin type meter)....
Based on the information that you have provided, this does not make sense. It should be 600 W to 1000 W.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: DC motor as generator, overheating.

No Bill. That doesn't happen. But the capacitors could/should be removed. Peak rectification adds abt 40 % to voltage.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC motor as generator, overheating.

(OP)
sorry - this is a little closer to what I have. The actual version isn't listed, as its a special order item.

http://www.reliance.com/cgi-bin/dcexplode.pl?D5050R

I have connections for:-
field (F1 and F2)
Armature (A1 and A2)
And series? stab? field (S1 and S2)

I believe that S1 and S2 are large cable - a similar size to the armature cables - and thus a bit irrelevant for me as they are the stabilising field - I don't need a precise speed control, which is what I believe this is for.....

The field cables are tiny, and powered by my dodgy rectified mains setup. The 60 to 100 watts range is dependant upon speed, temp, and output current / voltage - I have not examined the relationship. At any given moment, the power consumption is steady.

Please bear with me - I'm working from home, on a limited budget, on a 100+ year old waterwheel that takes 45 minutes to stop, and half an hour to start again....

I cannot see a way of removing the series coil, if indeed I have one. Ill check again (the casing is boiling hot, so its not easy...)

Thanks again people.

RE: DC motor as generator, overheating.

(OP)
<scurries off and opens case to look at connection diagram>

OK - its connection version 406770-1 found here
http://www.reliance.com/pdf/pdf/dccd/406770-1.pdf

I do NOT have the optional AX1 connection to remove the 'inter-coil'

I have NOT connected A2 to S1 for series field - S1 and S2 are open circuit.

I have turned off the water - and am waiting for it to slow enough so I can turn off the field winding power (it speeds up dangerously when I do this)

Guy

RE: DC motor as generator, overheating.

(OP)
Sorry to double post - cant see the edit button...

Right - have now disconnected the capacitors, and the field power meter is now reading 500 watts - I guess it has a very poor power factor correction system..

RE: DC motor as generator, overheating.

You should not remove the interpole coil AX2-A2. Do not connect A2 to either of the series field (S1-S2 or S3-S4), Both the series fields should not be in circuit.

Give Shunt field supply to F1 & F2. Take the generator voltage from  A1 & A2.

If the output is connected to a dc battery system, you have to isolate the generator from the battery system and then only switch off the field power. If you remove the field power before you isolate the generator from the dc battery system, the machine will work as a motor with no field current and will race to destruction.
 

RE: DC motor as generator, overheating.

guydewdney; You just HAVE TO provide us with a picture or 5 at some point. I am dying to see this.

Water works running a generator.  Like a little bit of heaven.

Keith Cress
kcress - http://www.flaminsystems.com

RE: DC motor as generator, overheating.

"have now disconnected the capacitors, and the field power meter is now reading 500 watts"

Good! That is more likely. Your 60 - 100 W were probably due to a misplaced decimal point. And, remember, this is DC. No power factor involved.

Another thing that seems very peculiar: You say that "it speeds up dangerously" when you remove field winding power. Again, I do not understand. Is it a motor or a generator? A motor speeds up if you remove the shunt field and have series field connected. You have a generator and the series field is not connected. Have you really experienced that "speeding up dangerously"?

(For all that want to tell me about it: Yes, I know that DC motors and DC generators are the same thing smile  )

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC motor as generator, overheating.


"Bearings arnt good - Ill accept that - its a little noisy, and a lot less when I greased it.."

surprise

Hold up here! Bearings should not be noisy at all, Look here first.

Regards

RE: DC motor as generator, overheating.

I hope that you have a diode between the generator and the battery bank. If you are connected to the battery bank without a diode and the generated voltage is low the batteries will try to run the generator as a motor and it will get hot.
Further to Gunnar's comment re Motors and generators being the same, I consider the difference between a DC motor and DC generator to be only a few volts or a few RPM. If a DC motor is driven over speed by the load, a small percentage increase in the speed will cause it to generate and push power back into the supply. Likewise, if a DC machine is driven at a constant speed, the voltage (which may be controlled by the field strength) only has to change a few volts to go from generating to motoring.
With a proper diode in the circuit the output current will be zero until the generated voltage exceeds the battery voltage and the machine will not waste power by trying to motor.
BTW, field voltage at 280 V rather than 300V will but the speed at which the machine changes from a motor into a generator about 300/280 or   7% higher. That would push your minimum speed up to 1100 RPM x 300/280 or 1179 RPM.
 

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: DC motor as generator, overheating.

(OP)
Theres no battery bank - it runs, as in the first post - to a grid tie inverter. It cannot 'motor' and as such, there are no diodes.

Yes - it speeds up when the field power is disconnected - I have seen over 1500 rpm (rated is 1100). This is due to it unloading the driver (water wheel) and allowing it to free spin.

I have found http://www.reliance.com/pdf/instruction_manuals/dc/C3088.pdf this document, which relates to DC motors in this range. It suggests connecting A1 to S2 and using A2 and S1 as the power connections. I am trying this next, along with a self exciting field winding, as I appear to be generating minus 400 watts (taking more to run the field winding than it generates.... doh...)

Im not going to replace the slightly rumbly bearings until I have proven the principle - this thing is in my house, down steps, and is incredibly heavy. If I can get some sensible power from it, then I will replace the bearings. If I can't, then I have saved myself a few hundred quid on some massive bearings and hours of time.

60-100 watts is measured using an AC plug-in houshold energy meter, the sort of thing sold by 'eco' companies. It is a cheapo version, and thats why the PF was so far out. With no caps in the circuit, it may be behaving itself, and reading roughly correct.

This isn't precision engineering - and theres no manuals for water wheels or Victorian layshaft bearing losses - so theres a lot of guesswork.....

Guy

 

RE: DC motor as generator, overheating.

If the generator speeds up that much when the load is removed (by de-energizing the field) then it is probably generating much more than your instruments indicate.
Does the generator speed up when you disconnect the inverter?
You may have internal faults in the generator which are loading the water wheel down and heating the generator internally. If the generator speeds up when you disconnect the field but doesn't speed up when you disconnect the inverter with the field still energized you probably have internal problems.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: DC motor as generator, overheating.

It is good that this is off-hours. Site rules do not allow us to discuss non-professional issues. But on week-ends, I think it is OK.

As Waross says. If it speeds up when unloaded, it is probably producing a lot more power than you think. The problem may be in your measuring equipment. Get yourself a decent DC clamp-on and a voltmeter. I am not at all sure that the 'eco' meter is good at DC.

And, please, do not mention power factor when discussing DC. It simply does not sxist, has no meaning at all, and makes the yhread look "dangerously unprofessional" to site administrators.  

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC motor as generator, overheating.

I think my typing reveals how upset I was. Read "exist" and "thread".

Your place sounds quite interesting, Guydewdeny. I would love to see it. I can bring all the instrumentation you need. All I ask is a cool beer. Where in the world is it?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC motor as generator, overheating.

(OP)
Skogsgurra - power factor does exist with AC systems. The field (was) powered by the AC 240v 50Hz UK mains. This went through a rectifier (bridge). The eco meter (something similar here http://cgi.ebay.co.uk/Ecosaver-Electricity-Plug-In-Energy-Monitor-Meter-NEW_W0QQitemZ110404072962QQcmdZViewItemQQptZUK_Gadgets?hash=item19b4987602&_trksid=p3286.c0.m14&amp;_trkparms=65%3A12|66%3A2|39%3A1|72%3A1683|240%3A1308|301%3A1|293%3A1|294%3A50 )is plugged into the AC mains - not DC.

Anyway - powering the field from the armature appears to have worked - it uses the residual magnetism to generate a small voltage, which excites the field, which creates a larger armature voltage, and over a few minutes (I was surprised at how long it took...) it reaches a steady state of 180-odd volts DC, freewheeling.

Loading the generator using the PC configurable grid tie inverter, which naturally slows the genny, I now have 260 odd watts from somthing like 20 litres per second, over 4.5 metre head (theoretical 9.81*4.5*20 = 880 watts, so a total efficiency of 30% water to exported electricity)

Better than nothing. I now have V belt slippage to fight with! (the torque is incredible - somthing like 38,000ftLbs when all the buckets are full.)

As for professional / non professional discussion - wheres the grey line? I have an honours degree in Mechanical Engineering... but I was useless at the motors bit smile And people have asked me to help 'fix' their waterwheels for money - which makes me a professional water wheel electricity generation installer... smile

Guy

RE: DC motor as generator, overheating.

Where's the grey line?? It's quite wide and it moves around from time to time.
I suspect that a lot of your lost energy (poor efficiency) may be in the drive train.
I would love to see your site also, but at the moment I can't afford to visit anyplace that fit's the description "The field (was) powered by the AC 240v 50Hz UK mains."
Can you post some pictures?
And I agree with Gunnar, even disregarding AC/DC/power factor issues, look for better instrumentation.
You may be able to use the interpole winding as a current shunt.
Even though there is not a lead from the interpole internal connection, the interpole winding will be connected to one set of brushes. If you are able to accurately measure the resistance of the interpole, you may determine the current by measuring the voltage drop across the interpole. Voltage/Resistance will give you current. The accuracy is temperature dependent so check the resistance of the interpole winding when the machine is at operating temperature. You can probably do this with a medium quality digital multi-meter.
If Gunnar pays a visit we want even more pictures.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: DC motor as generator, overheating.

UK! That's a lot closer than USA. And, if you are in the Lake District, I will probably be there to visit a paper mill soon. Pud and Scotty live there, too. Plan to see them as well. You may have to buy more than one beer...

About professional vs non-professional. I thought I should mention that issue. The site is rather enormous and there is a problem keeping it useful. So, "homework" (both student's and dabbling in fields of non-expertise) are usually red flagged. Anyhow, this thread has brought us an interesting insight in hydroelectric plants. And a new friend. So, I think it is safe.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC motor as generator, overheating.

(OP)
I'm afraid I am at the other end of England - sunny Somerset.

I am interested in this statement

You may be able to use the interpole winding as a current shunt.
Even though there is not a lead from the interpole internal connection, the interpole winding will be connected to one set of brushes. If you are able to accurately measure the resistance of the interpole, you may determine the current by measuring the voltage drop across the interpole.

I see no reference to an interpole winding - is this another name for the 'intercoil' referred to in the documentation?

Thanks

guy

RE: DC motor as generator, overheating.

Skogs,

I'm not in the Lake District but you'll pass not far from me on your way there. Harry is a bit further north in the civilised bit of the country - I guess you will be using the ferry to Newcastle? Would love to meet up for a beer, I think you can find my contact details elsewhere.
 

 

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: DC motor as generator, overheating.

Yes I was referring to the intercoil winding.  The resistance of the armature circuit is less than 0.5 Ohms, the intercoil winding will be just a part of this. The voltage will be quite low, possibly less than one volt at light loading. Even if you can not determine the resistance with adequate precision you will be able to get a voltage proportional to the current or loading by measuring across this coil. This may be useful.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: DC motor as generator, overheating.

Hi,
 If this is a motor now being driven as a generator as stated, your interpoles will be the wrong polarity in relation to the direction of rotation and the field polarity. You will have to reverse the interpole polarity in relation to the armature polarity (this can usually be done on the brush holder connections). I don't know if this is the source of your heat problem but it should be corrected.

Thanks

RE: DC motor as generator, overheating.

starkopete

you might want to rethink that.

RE: DC motor as generator, overheating.

I agree with edison123.
The series poles are not in use. We are discussing the commutating poles.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: DC motor as generator, overheating.

Yes, changing polarity of the interpoles will produce heavy sparking and shorten brush and commutator life. Leave them as is.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC motor as generator, overheating.

(OP)
Well - that was fun. It was a friends birthday last night, so we all went to the pub. Much Cider was consumed.

At 3AM the wheel starts 'making strange noises' according to my painfully sober wife.

Still not really safe to operate heavy machinery, I attempted to investigate, but failed.

This morning reveals worn out brushes, and a slight hangover.

The series field winding IS now in circuit - the C3088.pdf file linked to above shows to wire it differently according to shaft rotation direction, and wether it is a generator or motor. It is rotating CCW when looked at from commutator end, and is wired A1 to S1, A2 is +ve and S2 is -Ve

As for pics - we have a general website - www.gotopia.co.uk

heres a pic of the wheel spinning for the first time is 40 odd years
http://files.engineering.com/getfile.aspx?folder=cdd38dc6-8eb3-4bdc-a14d-7e36a43ebccc&amp;file=spinning1.JPG

RE: DC motor as generator, overheating.

Hey! That looks like a lot more than 1 HP! No wonder your machine is running hot.

If you make this properly, I guess that you can make good money out of it.

Keep us posted once your hangover is over.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC motor as generator, overheating.

Here is a check that may be made with just a voltmeter.
With your machine disconnected, apply 120 VAC to the shunt field. Measure the AC voltage at the brushes. It should be zero volts. If it is not zero volts, rotate the brush holders until you do read zero volts across the brushes.
This is your initial brush position.
Now rotate the machine slowly while watching the voltage across the brushes. It should remain at zero. If the voltage at the brushes varies when the armature is rotated, you have a strong indication of possible shorted or grounded turns in the armature.
Now remove the 120 VAC from the field. If you have sparking at one edge of the brushes when running normally, shift the brushes slightly to cover the sparks.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: DC motor as generator, overheating.

(OP)
Thank you waruss

I take it 240 VAC will be just as suitable? The brushholder carrier ring (plastic) is held by 4 bolts, and is easy to swing round for brush replacement (so you can get to the bottom ones etc) - I take it this is what you refer to?

There are marks on the edge of it - much like timing marks on a car / bike crankshaft - but nothing to align it to! I had to move the carrier to access the brushes, and put it back in the same place, but I shall do your test at the next opportunity, subject to confirmation that what I think you mean is correct.


On another note - I have now put in series a 500 watt halogen security light to reduce the field voltage, which is about the best I can cobble together at home with all the shops shut... smile

Guy

RE: DC motor as generator, overheating.

Because of the inductive reactance of the field it will draw much less current with AC than with DC. 240 VAC should be OK on a field rated for 300 VDC.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: DC motor as generator, overheating.

guydewdney, I believe that your idea of why the water wheel/generator speeds up when the field is disconnected is correct. Specifically, the power produced by the generator necessarily reduces the speed of the wheel. You are taking power from the wheel. Once the field is removed, you stop taking power from the wheel and it speeds up.

For a shunt wound generator (which you have), the power output of the generator would be reduced to almost nothing once the field is turned off. The residual magnetism of the field poles will produce a voltage that is proportional to speed, but that voltage should be small and, without excitation (field), should decay to nothing if an actual load is present. In other words, when you turn off the field, the load presented to the water wheel should turn of as well.  

With respect to the temperature of the DC generator (or a DC motor), the fields will generate heat continually regardless of load. The temperature rating that your motor/generator can sustain continuously without damage is on the data sheet you provided and is Class F = 155C. The outside temperature will often be 20C or more than the inside temperature (which the rating is based on), so take this into consideration.   

Next, the power output from your generator is obviously in question. I do not know how your inverter operates. Most commercial inverters are designed to convert AC to DC and may include circuitry to restict power flow in the other direction. Assuming that your inverter is designed for regeneration (DC to AC), then the amount of power that you pass to the line will be proportional to the difference between the rectified voltage and the line voltage. Higher rectified voltage means higher power output to the line.

Finally, I am curious to know; are your power output readings based on the net power produced at the utility meter, meaning total generator power output minus your internal consumption, or is the total output 800W gross? If your readings are net power to the utility minus your consumtion, then your actual generator output is obviously higher than you think.     

Sorry for the long post but I got carried away. I hope this helps you.  

RE: DC motor as generator, overheating.

Quote (Postrhatcher):

The outside temperature will often be 20C or more than the inside temperature

The other way round..

Keith Cress
kcress - http://www.flaminsystems.com

RE: DC motor as generator, overheating.

Bear in mind that even if there is no external fan there is usually an internal one to cool the rotor and move air through the stator. If you were to apply the field continuously to a stationary machine then the windings might well overheat without the internal air movement to help cool them.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: DC motor as generator, overheating.

itsmoked is right, my post should have read: The outside temperature will often be 20C or more less than the inside temperature (which the rating is based on), so take this into consideration.   

Thanks for the correction itsmoked. BTW, I like the name.
 

RE: DC motor as generator, overheating.

(OP)
My power readings are from the Grid Tie Inverter (GTI).

It has power in, power out, voltage in / out etc etc readings. Its made by Power-one / Magnatek, and is called a PVI-3600-UK (its based on a photovoltaic product, 3.6kw, and configured for the UK - obv an engineer came up with the name ;) )

As the genny is now self excited, the power reading is total out.

I have discovered a document detailing the current / efficiency curve of the motor, and it suggests that at the 5amp level that I am at (and cannot go any higher - the GTI has 6A fuses...) the efficiency is somthing like 30% :( I think its just toooo big for the application. If I could get the armature amps up to somthing like 30A, then efficiency is suddenly 80+% -its almost a vertical line at the low end, then horizontal from 30A to max.

Anyone got a 15Hp / 10Kw 500V DC motor kicking about? :)

Next thing Im going to try - feeding the F1F2 field with rectified and adjustable mains via a Variac (ah - the joys of eBay..). I had a long chat with the engineers at Cummins, and they seemed to think that an AC generator would be a Bad Idea (TM) as the 'load' is highly capacitive due to the smoothing caps in the inverter. So Im going to try approx 120V from the Variac and slowly increase it until somthing interesting happens :)

We shall see.....

RE: DC motor as generator, overheating.

(OP)
Waross - I have performed the check you suggested - I read 0.2VAc on the brushes - I assume this is within tolerance (or I might well be missing the point, and its the last 0.001V that matters ;)

Varistors arrived today to protect the end user(s) from large back emf's due to grid shutdown / fuse blowing...

RE: DC motor as generator, overheating.

You should be able to get zero volts by moving the brushes slightly. This is the initial position for the brushes. If the brushes spark slightly in service they are then moved slightly so as to "cover" the sparks.
The second part of the test is to rotate the armature.The voltage should remain constant at zero or a low value. Slight voltage variation as commutator segments pass the brushes may occur, but voltage swings once or twice a revolution indicate armature problems.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: DC motor as generator, overheating.

(OP)
OK - I have re-done the first part - I was surprised at how much I had to move the brush holder - approx 1/2" anti-clockwise from 'upright' to achieve zero volts on the brushes.

I have a slight sparking on the trailing edge of one brush I can see - I cannot confirm the same from other brushes until I remove covers. I have just had to replace a link in the main drive chain (1 1/2" pitch chain - similar to an ANSI chain - but 100 years old) and that has knackered me out - plus it takes over an hour to do a re-start - so I'll leave that for another day (I don't have a 1000V insulated crowbar to move the brush holder....)

RE: DC motor as generator, overheating.

(OP)
Silly question - if half the brushes were in use, then the current in each of the armature coils would be doubled (assuming constant total output current) thereby increasing the overall efficiency....

or is this madness? ISTR that the 12 o clock pole (N) is directly connected to the 9 o clock (W) pole, and thus the 3 and 6 are the 'same'

RE: DC motor as generator, overheating.

(OP)
Update - I have been informed of a new possible method of creating my power:- inverter drive running in full regen mode.

Mods - would you permit me to start another thread asking some really really dumb questions about this setup, or are you sick of thickos like me?

RE: DC motor as generator, overheating.

Are you saying replace your DC motor/generator with something else?

You could possibly run a gridless inverter from from your DC source.

Are contemplating something else than your existing monster motor?

In a completely gridless situation like yours you might consider just using a rack of automotive alternators running in their normal mode charging a battery bank.  Then you have a large number of options to get from 12VDC to your standard house power.  Also a dead alternator becomes something you can carry in two hands instead of a logistical nightmare. And, any failure of a single alternator would be a graceful degradation rather than 'lights out'.

Keith Cress
kcress - http://www.flaminsystems.com

RE: DC motor as generator, overheating.

(OP)
Sort of - more along the lines of runnign a 5.5kw 3 phase induction motor, using a inverter as a 'brake'.

total cost, new, 1600 pounds.

How 'efficient' is the brake?

RE: DC motor as generator, overheating.

Guy,

You NEED to visit this site:  www.fieldlines.com

I contribute regularly there, as I'm running an off-grid wind system among out-buildings around my acreage.  I have converted a 7.5 HP motor into a DC generator using permanent magnets.  On bench tests get about 2 kW out of it at 500 RPM.  My current windmill generator(s) were created from 3 HP motors, and they produce 6-700W at 700 RPM.

Since your hydro energy source is limited to about 2kW, I think you could equip yourself with a more manageable generator.

Anyone got a 15Hp / 10Kw 500V DC motor kicking about? :)

uh... how about a 25HP... wink
 

Steven Fahey, CET

RE: DC motor as generator, overheating.

Very efficient.  However you would have several other issues to deal with moving the entire thing back towards Weird Ville.

1) Before those drives will "regen" they generally need to see a fixed frequency steady bus to feed onto.  They don't want to feed onto an dead bus.

2) You need to "excite" the induction motor to have it generate anything in the first place.  How would this occur without a live bus to power the VFD in the first place so it can then excite the motor.

See?  Two tickets to a freak show.

With, say, auto alternators, they would have their fields excited by the batteries in the first place.

 

Keith Cress
kcress - http://www.flaminsystems.com

RE: DC motor as generator, overheating.

(OP)
Please forget anything to do with auto alternators - speed is nowhere near right.

The system will regen back to the house 3 phase supply. It is supplying the inverter, which supplies the motor.

there are NO BATTERIES involved.

RE: DC motor as generator, overheating.

That's fine.

I thought you were off grid. If that's the case why would you have power from the house in the first place?

Or is that a wrong assumption on my part..

Keith Cress
kcress - http://www.flaminsystems.com

RE: DC motor as generator, overheating.

(OP)
Sorry - maybe I should be clearer:-

I am ON grid. I currently have no method of being off grid. The DC motor currently feeds a Grid Tied inverter which requires the grid (single phase) to work.

The suggested inverter drive system will require the presence of a good 3 phase supply. In the UK, we have to comply with certain regulations that prevent connection to the grid by generators unless certain conditions are met (mostly relating to quality of supply, and a 'settling in' period). I have three phase.

To this end, I have a certified 'box-o-tricks' which prevents me from connecting unless these conditions are met. The conditions are laid out in a document called G83/1 - which is not freely available to the public (yet its a 'public', rather than industrial, set of guidelines or rules).

Once I have finally sorted out my 99.99% of the time on-grid and exporting electricity, I shall look at the off grid problem for when the power goes down. To this end, I have an old 1950's Lister CS diesel engine which runs on just about anything - but thats not the problem here.

My question to the Gods of Motors that reside here is this:-
When using an inverter drive in regen mode, driving a (say) 5.5kw 6 pole or 8 pole motor at (say) 500 rpm, with a 1kw 'brake' effect - how efficient is it? Will the motor overheat with no external cooling (assuming normal operating conditions)? This would be the worst case - the opposite mode would be running the motor at say 900 rpm and 'braking' at 5kw - which I understand would be quite efficient, as everything is running at its rated loads, its just the motor is leading not lagging

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