altenator design question

[brutus1955]

i figured i would try here, thinking perhaps there are those in the design of alternators on the forum

i have a project that i am working on, i will first lay out the parameters of what it is i have to work with, and what i am trying to do,, followed by a question.

i am working with a prestolite 110-555jho alternator, it is a large frame j180 mount alternator that is typical of those used on heavy duty trucks.

it is rated at 160amp at room temp and around 140 hot rated
at around 5k rpm. it is a 12 pole wound rotating field claw pole lundell design. 12volt nominal

i am going to rewind it from its original delta connected stator to a wye configuration for 120 volt ac line to line.
at around 3800rpm.

this unit will not be used on a truck, but will be used to feed a transformer bank ~400hz

the goal is to get the maximum efficiency at this level.

now then rewinding the stator i can basically do whatever i want at this point, so now the question.

i would like to rewind it in a bifilar manner, that being
counter wound dual coils on each pole. having 6 lines coming out,, two groups of three phase 180 degree's apart

my thinking is with counter wound coils i can reduce or eliminate the air gap leakage reactance, because the current flowing through the two counter coils to the output
negates the counter mmf of the iron of the pole.

in a standard single coil pole, the current in the coil sets up an opposing magnetic force to that of the rotor pole
which shifts the flux across the airgap. if counter wound dual coil there would be no mmf in the pole caused by the current in the coils,, therefore a reduction in shift of the flux across the airgap.

is this possible? if so are there examples of such a machine?

denso makes a bifilar wound alternator, of which i got a core to open up and investigate,, but each coil is wound the same direction so basically it is a two in hand winding and not a true bifilar winding.

also my second question

is there a book or text on alternator design available that was written in more current times,, i have several from the early 1900's but nothing newer than about 1920 or so.
while alternator theory probably has not changed in the last 100 years i figure there has to be something more up to date?

like i stated i am going to rewing the stator anyway, just thought i would check and see if going the true bifilar direction has any merit before i invest my time doing so.

any help would be appreciated

bob g

 

[waross]

How critical is your frequency? I would reconnect it in wye as it is, belt it up to about 6000 or 7000 rpm or more and force the field. However, eliminating the back emf is an interesting idea. This approach may shorten your circuit considerably. Let us know how it works.


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

 

[brutus1955]

the frequency is not critical it is just a byproduct of the drive ratio of the setup i am working with, one which i would like to stay with if possible.
i can go lower in rpm/frequency, but not faster at least without an increase in cost that i am trying to avoid.

but then again, there is a cost benefit analysis i suppose.

what did you have in mind?

i am open to any and all input

thanks
bob g

ps. for the record this is not a project for any class, just a project that i am working on for my own use and amusement.

 

[brutus1955]

not sure how to edit my last post,

i did try the wye connection of the original stator
the result was 85 volts no load line to line, with full field, which is short of where i need to be.

i am thinking i would like to get to around 160 volts line to line open circuit no load at full field, to have some head space under about a 30amp load at full field.

just thought i would add that or consideration

thanks
bob g

 

[itsmoked]

If the original system could only put out 2.25kW why do you expect to change the wiring and get 4.8kW out of it.

I would expect the magnetic circuit to handle only so much flux. The amount to provide ~2kW.

Or am I missing something?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Missing the speed Keith. As the speed goes up with the same available torque, the voltage and available kW output increase with no increase in current.
There is an excellent FAQ on frequency conversion that covers the increase in available horsepower when the frequency supplied to a motor is increased from 50 Hz to 60 Hz. LOL
brutus1955
If you can increase the speed about 50% or 60% the voltage should get above 120 volts. You may first try increasing the field voltage. If increased field voltage has little affect on the output voltage you are below saturation. Once you reach saturation, there is no point in further increases in field voltage.

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

 

[brutus1955]

Waross:

i believe i am below saturation, because in the first test we went from 12 volt excitation to 24 volt and picked up about a 10% increase in voltage at full speed 6krpm.
24 volts is too high for the rotor, because it makes significant heat at that level.

exciting to 6volts results in about 15% undervoltage from that of 12 volt excitation.

Itsmoked:
the machine losses in the original design are dominated by the leakage inductance under high current, providing a serious voltage drop, which in turn protects the machine from burnout to a certain extent.
the voltage drop can be as much as 40-50 volts at 140amps or so, which is a significant amount of power.

because the alternator is designed to operate in a hostile environment, underhood temps being very high, and because it is designed to operate over a very large rpm range there are a series of comprimises in play.

in my appication, i can keep it cool, the rpm will be fixed
and because the current is but a fraction of the oem unit design, i don't need the designed protection afforded by the high leakage inductance.

at least that is the theory

some of the leading researchers are getting ~4kwatt output from a 1.5kwatt alternator with various methods, controlled rectifier bridges being one and the use of transformers to step down the voltage and raising the current being another.

so it is being done, i just am looking to gain a bit more in efficiency if possible with the bifilar counter wound poles.

bob g

 

[itsmoked]

I fully understand that waross,(very funny), but I understood that brutus was actually limiting the rotational speed to below the original application speed which would exacerbate the issue.

brutus; I await your results!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

The alternator is generating AC currents and voltages. This means that the inductive reactance of the windings is a factor in the voltage drop. The loses will be the DC resistance of the windings times the current. The inductive reactance increases with the speed or frequency. Most of your voltage drop a higher speeds willbe reactive and will not cause losses.

Sorry Keith, I couldn't resist. The output of an alternator is limited by the current that it may carry safely, times 13.8 volts. If we remove the 13.8 volt battery charging limit, as brutus1955 wishes to do, the voltage and the kW output may be raised by raising the field strength to saturation, or increasing the speed, or both.

brutus1955;
I am sorry to be a little brusk. I am working 12 hr. shifts in a hostile environment.
If you want to reduce leakage flux, reduce the air gap.
When a 240/480 volt genset is connected in double delta for use as a single phase set at 120/240 volts, The connection looks like what you are looking for. BUT, the windings are connected in the same direction. If you reverse one set of windings, the machinewill generally self destruct quicker than you can evaluate the effect on the leakage flux. It's called a short circuit.
Do you need three phase? A wye connection will give a voltage advantage of 173%. A zigzag connection will give 200% of coil voltage but it is only applicable to single phase.
Have you considered using transformers with a lower primary voltage?

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

 

[brutus1955]

Waross:

yes i am using three transformers to step down the voltage
and regain the high current output

i plan on being Y connected on the stator for the 1.73 increase in voltage and to eliminate the circulating currents within the stator.

the transformer output will go directly into a bridge rectifier, and from their to the battery bank, a sense line will come from the battery back to the regulator, and regulator to control the field.

the regulator is programmable so i can set it for voltage and current into the batteries, which will limit the output of the alternator and keep it within safe operating parameters.

at least that is the plan.

thank you for your further comment

i appreciate it very much

bob g