How can I modify alternator voltage

[veggie]

Thanks for all that useful info Bob.
I will continue to research this stuff as well.
Let me (us) know as you learn more about that $39 unit. Looks like a great low priced solution.

Veggie

[BruceM]

Very impressive, BobG!  Feeding the alternator + output to 3 - 12v batteries in series and using the lower voltage battery as feedback for the standard 12v regulator is a brilliantly simple solution.  Only finding a 12v regulator with a separate battery voltage sense, not hardwired to the positive output remains to be solved.  Wow! 

[mobile_bob]

Bruce

this was the basis of the white paper i published here back in '09 or so

at that time the only isolated sense regulator i could find was one of the balmar units or rebadged units sold by xantrex

at that time i found various units that were similar in operation to the balmar, most all of which i bought and tried out, all of which worked just fine for using the 12v nominal alternator for 24 and 48 vdc operation as described in this topic and the white paper.

it is my belief that this scheme could be used for any voltage (DC) that one might want up to maybe 120vdc or so, the limit becomes what the bridge rectifier will handle (PIV rating) and the insulation quality of the stator, along with obvious safety issues relating to exposed studs for the output current.   the only reason i could see going to anything over 48vdc nom would be the use of surplus ups inverters which sometimes come in all sorts of higher dc front end voltages, i have seen 60, 72, 96 and higher voltages... again that might be something to work with if one had a source of surplus ups inverters in higher dc voltage battery banks?

while i am not particularly scared of 440 3 phase i am however really scared of 240vdc battery banks, of which i had one 15kva inverter from an exide ups system.... that sort of battery bank (240vdc) has a horrendous amount of instantaneous power as evidenced by a hole that looked like a "ma duece" had her way with the steel cabinet!  i made up my mind that working with that inverter was something i really had no real need for.

of course i digress , something i am getting better at in my older age.

anyway, alternators such as the ones Veggie has have some really excellently insulated stators, so i think a new stator could certainly handle some pretty high voltages without burnout in that regard.

lastly the other requisite that the leece alternator that Veggie has to choose from has an isolated ground post, so that the output of the rectifier bridge is fully isolated from the case ground... this is something that is a must for what is proposed.

having the battery bank isolated from the grounding of the engine/alternator and the regulator save for where it must be connected saves those pesky unforeseen back feeding on the ground side that cost me one 400 dollar balmar.

i tried to sample from the #2 battery in a string of 4 batteries, which of course required tapping a ground off the #2 to get the needed 12volt sense, but also provided a 24volt path that proved to let the magic smoke out of the regulator because of another ground path. 

so i am a big proponent of a good schematic, and only sensing off of the #1 battery and making darn sure there is no way there is any backfeeding of anything other than 12v nominal getting back to the regulator.

the use of a 40 dollar regulator sure takes the stress out in prototyping, loosing a 40 dollar regulator due to a mistake sure is no where near as painful as 400 dollars!   i still can't bring myself to throw out that regulator!   

bob g

[BruceM]

I also remember one of the marvelous research papers on  claw pole alternator designs which you posted, BobG.  Very interesting and educational.  Claw pole is a lot more efficient than I realized, and is underutilized outside of automotive alternators.

I agree on the sometimes very expensive lessons for DIY R&D.  I've had some expensive education myself. Like my brilliant 1500 watt switched capacitor variable output linear 120VDC battery bank charger. It had such bad PF as capacitors were dynamically switched in before the filter choke boosting voltage and current that it made my custom ST-3 AVR regulate so low that the 240AC power relays chattered and fried.  After redesigning the AVR to do RMS voltage regulation I then found that while the charger worked, my shop heat lamps were then unbearable re: flicker.  In disgust I then abandoned the brilliant capacitor switching design the custom PCBs to the trophy shelf and motorized a old variac instead.  The technically primative Variac design, of course, has worked flawlessly since it's first test run and the 9 years of service since.  I've tried to avoid brilliant designs since.

[veggie]

As it turns out, my 36 volt battery does consist of 3 small AGM units, so sensing from battery #1 (12 volts) as Bob suggests is not a problem.
While Bob looks further into the $40 regulator, I have a question regarding regulation of the field power.

REGULATOR IDEA:
A small Arduino microprocessor board has several pins capable of outputting a pulse width modulated signal in 5 vdc and the PWM frequency can be software controlled.
Other pins on the board can read the voltage of the 36 volt battery bank (by means of a voltage divider converting 36 volts to the board's 0-5vdc input)
Does this make for a simple and inexpensive regulator platform?

Begin loop
-Read Battery Voltage (Input pin)
-Compare to desired target voltage
-Increase/decrease field winding PMW signal accordingly (PWM output pin)
Loop

Granted there may be some other electronic components needed. But the overall package would be fairly inexpensive (since I already have this stuff).
One thing I don't know how to do is take the 5vdv PWM signal from the Arduino and step it up to the voltage necessary for the Field Coil (12vdc???) while still retaining the pulsed output.
Another thing needed would be a simple algorithm to determine how much to change the PWM frequency each time a change is needed. The simplest way would be a series of if/then statements based on the offset between the desired and target battery voltages.
If one wants to get fancy, a fuzzy logic or PID routine could make the decision.

Any thoughts on this ?

Veggie

[veggie]

 ... AND !
After digging around on the web I came across this fellow who seems to be doing just that.
An Arduino configured as a voltage regulator.
Perhaps this might work.?

https://www.youtube.com/watch?v=zfGm0gZhgCc

I defer to our resident electronics expert "BruceM" for input ?
Can the 20mA,  5v PWM signal from the Arduino be stepped up in amperage to satisfy the requirements of a field coil (Perhaps up to 4 amps)
Maybe a transistor or a FET in the circuit?

And MobileBob ! do you know the voltage range that the 12 volt Leese Field Coils typically require?
Although the battery voltage is 12, I wounder if the typical field voltage provided by the regulator is much less (like 0 to 6 or something)?

Veggie

[veggie]

BruceM,

How fast can a Solid State Relay (SSR) change state ?
Can it handle the frequency ?   Hmmmm....
The output of the SSR to the field could also be 12 volt instead of 36v if needed by using just one of the three batteries for power.
The big question is whether the SSR can switch fast enough.

The two heavy connections on the alternator sketch are it's output. The two spade connectors represent the field.
See picture.

Veggie

[veggie]

Maybe an SSR can in fact switch fast enough to control the field winding.
I found these as examples of high frequency SSR switching....

MOTOR
https://www.youtube.com/watch?v=LL2Sryi57xA

MOTOR
https://www.youtube.com/watch?v=NQ08OztPkb8

SPARK PLUG
//https://www.youtube.com/watch?v=AZWdRX2MGNg

[mobile_bob]

i think a mosfet could be used as the link between the arduino and the field coil

iirc the leece neville under the following parameters used 10vdc at around 3.5amps

that was for 100amps output, at 28,8vdc running at 4800rpm

of course the voltage and current will change if any of the parameters change, the voltage and current are tied together
to a large extent and both go down as the rpm rises, or go up as the rpm is lowered. and of each will change as the demand for output current is reduced.

because i could not easily change or increase the rpm on the trigen as the belt drive was fixed and the rpm set on the engine at 1800rpm the voltage and current were significantly higher running at 57.6vdc at 50-60amps for 48vdc charging... i don't recall exactly, but if memory serves me the voltage was around 12volts and closer to 5amps to the field.

bob g

[mobile_bob]

fwiw

the delco alternators from pre computer days used pwm scheme to control the field current and ran at around 400hz
so switching speed is not high by most standards, at least electronically, too fast for a relay, but certainly something any power transistor can handle.

as a matter of fact the delco regulator from the late 60's and up into the 80's used on the alternator style like your delco used as a regulator a circuit board with one power transistor (DO-3?) and a couple of small transistor, some resistors and a pot to adjust the output.  those schematics are widely available and might be a good place to start for making a 36v regulator. 

the use of a microcontroller, in my opinion, unless you are planning on other functions seems to be overkill for what is needed.  but heck roll with what you feel comfortable with.

bob g

[veggie]

Thanks very much Bob, that gives me a starting place for field voltage levels.

Reasons for using the Arduino are....
1- Dirt cheap $18
2- Programming allows me to alter frequencies and charge mapping in minutes
3- Stuff like this is available....Mosfets with the accompanying resistors
http://www.ebay.ca/itm/3V-5V-Low-Control-High-Voltage-12V-24V-36V-E-switch-Mosfet-Module-For-Arduino-D-/112073228788?hash=item1a1815c1f4:g:zfcAAOSwqfNXmM-M
A mosfet board that connects directly to the Arduino may work very well.

Oh...yes...and the biggest reason of all, I know very little about sizing electronic components and building circuits myself so using "building blocks" like Arduino and Arduino "add-on's" makes projects go a little smoother. I am also a programmer, so making the Arduino do various things is not that hard for me.

Onward,
Veggie

[mike90045]

Beware of the field sucking power from 1 battery, that it gets undercharged.

[Tom Reed]

Good point Mike or over charging the other 2. I was up your way last night fighting the Oil Hill fire.

[mobile_bob]

that is why you don't provide power to the regulator from the string, but rather from the starting battery
the regulator only takes off the sting at the 12volt level as a sense, and doesn't take but something on the order of a few
milliamps.

if we were to take the regulator power and by extension the field power from that first battery in the string, then yes in a very short while there will be an imbalance in the string, and that is about the last thing you want happening.

an imbalance in the sting is very hard to get back right again.

the white paper goes into detail on this if i recall correctly.

the bottom line is this, never under any but dire emergencies should anyone tap into a series string of batteries and take off power.  tapping for a sense line is another thing all together and not really a problem.

all series strings over time will have some imbalance issues, that is one of the purposes of equalization.  also not that the number one battery in the string could be swapped out for a weaker sister so that the sense line is attached to that one and aid in getting the weaker one back or nearly back to normal levels of charge.

bob g

[mobile_bob]

more thunkin

if you are going to build a purpose built regulator, there is no reason why you could not take the power from the full string
at 36v nominal and via pwm reduce the effective field voltage down from 36 or whatever to sub 12vdc needed by a 12volt field.  then you could sense the voltage of the total string and avoid all the other stuff.

not really any different than an st head with an electronic regulator, where the output is 120/240 and the field is something much less, like 60vdc.

the field can be anything and limited by what you can get off the shelf in parts,  the output can be anything other provided you have enough rpm and diodes able to handle the higher voltage.

some years ago, i rewound a leece neville JB series for 60 hz output at 600rpm,  it was capable of making 120volts dc at 6amps due to the small wire used to rewind the stator.  the field required 12vdc at 5 amps to do that job.
interestingly at around 2400rpm it would put out 480ac at 240hz with the same 12vdc at 5amps field current. 

and no i never used it for anything other than an exercise in what is possible.  and yes i think i still have it somewhere packed away and if i find it will destroy the thing for fear it might show up in my auction after i am gone.  i sure would not want anyone playing with that thing because it can and will kill quite easily.

point being there is much that can be done with off the shelf parts and a little ingenuity. moreso if you have some background it electronics/microcontrollers and such.

bob g