There seems to be a lot of discussion lately about using the ST head for charging at various voltages.
This fellow seems to have solved the problem.
http://www.navitron.org.uk/forum/index.php?topic=952.0 (http://www.navitron.org.uk/forum/index.php?topic=952.0)
Is this a valid solution.? Seems fairly simple. (KISS in other words)
veggie
yes in theory it should work, but
you are limited to the nameplate amperage whether you are at 12volts or 120volts
and you may be thermally limited due to decreased airflow from the fan, which might be very significant
cutting the rpm in half dramatically reduces the airflow, it is not a linear function
i would not be surprised that the ampacity of the st head would be cut by at least 50% at lower rpm.
if you can live with that, then it is a simple method that has merit and application.
bob g
Instead of 12 vdc, how about going with 48 volts an then adding a step down transformer for higher amperage and charge rates. From there to a solar charge controller to take gentle care of the batteries?
Having a system that can charge at low speed and then, with the flick of a switch and an engine speed change, give full 230 VAC for emergency power is very compelling. Or is this being a bit too optimistic ?
veggie
don't let me rain on our parade, believe me there are countless ways to skin the cat.
until we explore all the various methods, do the testing, and document the results
its hard to say for sure what method works best and for what reasons.
so many variables, voltage, amperage needed, run times, to name a few
we need more out of the box thinking, which will lead to more options
options are always welcome in my opinion
bob g
Thanks for posting the link. I had been curious about the relationship between excitation voltage and output voltage.
I had thought of this but never considered the reduced airflow. Good catch.
the reduced airflow at lower rpm could be remedied with a ducted electric fan
to increase airflow.
another thing i am unsure of is the st heads ability to produce power in a linear fashion
over a wide rpm range, it might be well less than half power at half rpm.
also care in making sure the field current is not exceeded is going to be a concern i would have
i am not sure how much over the field can take without burnout, so
the use of some sort of regulator or current limit scheme would seem prudent?
the last thing i want is any part of a suggestion that might damage an otherwise good st head,
damage is all to easy when one starts to experiment in operating parameters well outside of the oem
design.
so it would seem to me, in order to run at reduced speed and charge at a lower voltage, we need
to assure the following
1. adequate airflow, and probably some sort of temp sensor to monitor stator temps
2. some dynamic control over excitation current, by dynamic i mean some sort of regulator and overcurrent
protection
3. then do enough testing under real world conditions, with the head operating in a thermally stable temperature range
in an ambient temperature that is as high as it will ever be asked to run in, so that we are sure it is stable.
4. some method of output amperage control, that would keep the stator from an over current condition should the batteries be
lower than anticipated or batteries low and a load comes online.
just some things to consider fwiw, and there are likely other concerns as well?
bob g
Bob's raised most of the important issues, but I'll add one more.
Most battery manufacturers warn against chargers with high ripple current. This is the AC component of rectified DC. AKA "Lumpy DC".
In the article above the guy is running at half speed, with only 25Hz output. The money saved by avoiding a transformer will be spent several times over trying to filter the output, since filter size and cost grows exponentially with lower frequency. (This is also why modern switching supplies with 100KHz and above speeds are so small and cheap, and some small DC-DC converters now switch at 1MHz.)
So while controlling the excitation to regulate the ST output voltage is a good idea, and reducing the Lister(oid) speed at reduced power loads is a good idea, reducing the single phase ST generator head speed is not such a good idea.
If you were starting with a 3 phase head, which is much better for generating DC and would require little or no filtering, then reducing speed could be considered, assuming you address the issues of cooling and loading that Bob has mentioned.
BruceM
Pardon my ignorance, but could you do what the guy in the link did, but run at full speed? If the excitation voltage is dialed down, does the output Vrms go down accordingly? Would that eliminate the need for a step down transformer? Still need filtering of course.
Marcus
Sure, you can just reduce the excitation to get any output AC voltage you want. But your output current will be limited to the rated max voltage current. Only a transformer can convert watts in (volts x amps) to watts out while converting voltage.
Wait, wait, wait! I'm getting excited here! Here's another way to skin a cat. My ST head is a 7.5 kw. A listeroid 6/1 can only sustain 3000 watts anyway. So, let's say I put a dimmer switch into the excitation coil circuit, dial the dimmer down until the output from the ST head is the appropriate voltage (for rectification and filtration into your desired charge controller). Then measure the resistence across the dimmer, and insert appropriate resister instead. No? Add a switch to short the resister when normal ST output desired. True, the ST 7.5 is now approximately an ST 5, but what does that matter.
Marcus- If you are considering this for a 48V battery bank, then OK, though forget the dimmer. A variac would be better. The harmonic winding puts out 4 sharp spikes per revolution, two positive and two negative going. The dimmer's triac control isn't set up to handle the very short duration, or the higher voltage peak. A small variac will not complain, however, and could be used permanently.
I'm assuming you're still going to feed a PWM solar charge controller to do the battery charge regulation, right? Otherwise, you'd need a special AVR design.
Yes, for 48 V battery bank charging.
No, I have a Outback MX80 which is MPPT not PWM.
Remember, I was going to use the toroidal transformers to step down, then big transformer windings as a inductive filter. Thanks for the tip on the variac.
BTW, about those toroidal transformers I bought on e-bay: the seller never sent them. That was 1 month ago. He won't reply. I'm going to have to file a claim and complaint. Arggh.
Marcus
The MPPT controller also does PWM of sorts (they use a buck/boost converter).
Bummer about the transformers. I've had very few deadbeat sellers, but sometimes it happens.
Hey, I have to retract what I said about the toroid transformers. One came in the mail today and the seller wrote that he has had a delay in shipping.
Using a dimmer, I would put it in the circuit in place of the resistor, btwn F2R and R1 on the schematic in the ST manual ( http://utterpower.com/ST_manual.pdf ). If I were to use a variac, would it be placed in the circuit in the same place?
Yes, the dimmer (a dual SCR or Triac part-wave switching control device) would go in place of the dropping resistor, but a dimmer will likely fail on the first surge load, which boosts the harmonic spike over 400 volts, the dimmer is designed for 180V peak. The dimmer is also not designed to switch a wave with only a millisecond or two time duration.
The Variac would be connected to the harmonic winding on the input side, and it's output side fed to the bridge diodes. One problem- you may have to turn it all the way up to get the generator started.
A Variac can also use the AC output as the input. Same situation- you have to turn it up very briefly to get it started. Bill Rogers helped me with this years ago- it's amazing how NOT using the harmonic cleans up the AC waveform of the ST heads. For a steady load, the Variac connected to the AC ouput of the ST will let you dial in any output voltage you want. Connected to the harmonic, it should give you fair regulation despite changes in load.
Is there any reason you wouldn't just want to use a variable DC power supply instead of the harmonic windings? It would bypass the bridge diodes and provide a nice smooth input. On second thought, where would you get the 120v ac (or what ever your power supply needs)..... nevermind.
Marcus, do you mean rheostat or dial type variable resistor? Like this http://cgi.ebay.com/Ohmite-6-300W-Rheostat-Type-N-25-Ohm-3-46-Amps-Used_W0QQitemZ370329832500QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item563960cc34. A heavy duty one like this one would not have to be temporary and I'm considering installing one myself for on the fly fine adjustment of AC voltage and might do what you have in mind.
Hi
It is interesting that the required field winding voltage is lower than the desired output voltage from the main ST generator windings. Using a standard B type heavy duty external voltage regulator for a car alternator should work great. Most of the automotive solid state voltage regulators have current limit on the field driver and over voltage protection on the alternator output, There is less chance for the ST head to burn up. I could be wrong, all comments welcome. You couls use an A type alternator regulator, The B version is what I have on hand.
What to do:
1) Rectify the output of the ST generator with a 10O amp or more full wave bridge rectifier. These devices have a large metal plate that needs to be attached something that stays cool like a heat sink or the air cooled stator housing. The current rating was figured by taking the power rating of the ST head and dividing by 120Vrms and multiplying by a safety factor of 1.5, picking the next higher available current rating. Don't forget the fuse or circuit breaker rated for voltage and current you plan to run. If you have a 12KWatt ST generator, 12KW/120Vrms equals 100Amps available current to charge with. Since it is desired for the fuse to blow before head, Pick 60 amp fuse or circuit breaker
2) Clean up the rectified DC with Electrolytic capacitors with a voltage rating of atleast 1.5 times your intended output voltage and as much capacitance as possible to get rid of the pulsating current. If you plan to switch between 28 volt DC and 120 or 240 VAC using a switch, Make sure to disconnect the rectifier and capacitor bank if the capacitor voltage rating is less than 200volts. ( this would be fun to watch, similar to your car bursting into flames and then having to replace it)
3) Using the B type regulator, Connect one side of the ST field winding to the negative side of the rectified DC output. Connect the positive side of the rectified DC to the alternator output terminal and ignition switch terminals of the voltage regulator. Connect the the unused ST field winding to the field terminal of the voltage regulator. Use of a fuse in series with the filed lead is a good measure of saftery.
4) The harmonic windings is not used and secured appropriately
5) Connecting a battery bank to the rectified output of the ST Generator paying attention to polarity.
Placing a switch in series with the ignition terminal can be used to disable the generator output( more or less) and reduce current draw when engine is not running.
What did I miss or should be concerned with? I would suggest running the ST head at rated speed to ensure cooling of both the head and rectifier module.
Which do you think would last longer, an ST head or a high output heavy duty alternator?
Sara
Sara:
thanks for the off the shelf and somewhat out of the box thinking
to start with
#1, #2 seem reasonable, keeping in mind though most folks want to use an st5 which is limited in current capacity.
#3 will limit the output voltage to that of the regulator, so if it is a 12volt regulator, even an st12 at 100amps is going to do well
to produce 1200-1400watts, twice that if you have a 24volt regulator to work with, but there are many looking for a 48volt solution
and i am unaware of any mass marketed off the shelf 48volt regulator suitable for charging a battery bank.
#4 seems like a good thing too.
now my other concerns, and i present them because i don't know
my st7.5 needs 62volts at 2.7amps @full loading. i suspect the field would have to be driven hard
at 14volts to get the machine to produce useful power at 12volts nominal, and many oem regulators can
drive 5amps of more into a field. i don't know if the field can handle that , or whether one can even get the
field to take 5amps with only 12volts presented? probably not.
as for which would last longer? for 12volts or 24volts, all things being equal, my money would be on the high output alternator.
for 48volts? might be a tossup
bob g
http://books.google.com/books?id=uQMKAAAAIAAJ&pg=PA128&dq=alternator&lr=&rview=1&cd=3#v=onepage&q=alternator&f=true (http://books.google.com/books?id=uQMKAAAAIAAJ&pg=PA128&dq=alternator&lr=&rview=1&cd=3#v=onepage&q=alternator&f=true)
Vintage Electrics