ST head modification for 48 volt battery charging

[mobile_bob]

probably just a can of spray laquer, but you didn't hear it from me!



do you have a body shop around you? or a paint supplier for automotive paints?
if so check with them about some laquer, maybe you can get a pint can for very little cost.

failing that, there should be some shellac in pints cans at the hardware store in the furniture
refinish dept,

either would work better than nothing, and probably as good as is needed for this application.

what i don't know is how hot these heads really get in the stator core, and specifically the windings
i know my st7.5 running at 7500watts doesn't even get warm to the touch on its case, but i never
took the time to take reading of the windings.

i can't imagine that they get hot enough to melt laquer or shellac, unlike an automotive alternator that
gets hot enough to fry a steak on, those i would suggest doing glyptal

good luck

bob g

[mobile_bob]

i see that there has been a companion thread started by Marcus, which is a very good thing
in that it will likely develop into another very good alternative for useing the st head for battery charging

after reading his comments about retaining the ability of the st head to produce 120/240, i wanted to take
this opportunity to restate that the modification of the stator as outlined her on this thread does not preclude
its use as a 120/240 head.

it can with the aid for a couple of contactors, be switched from charger back to 120/240 operation
and it is possible that it might be able to both charge and provide one leg of 120, but that needs to be
determined via testing.

just didn't want folks to lose sight of this capability of the modification of the head.

bob g

[mbryner]

Yes, Bob G and I had not lost sight of that.   Either solution will still require rectification, filtering, and a charge control circuit.    Many different components would fit into each, depending on specific requirements.    The DC charging leg and providing AC leg at the same time is the most intriguing, especially if the coils can be placed at 180 deg instead of 90 and the ST is not unbalanced, but then if you need 240 you have to up-transform.   OK, I'll stop rambling because I'm not the expert......   

[BruceM]

The other possible plus (a big one) for the 60V mod is that by reconfiguring the windings to 180 degrees, the growling of mismatched 120V loads on a 240V configured head might be eliminated. That would make the ST heads a lot more useful for many folks.

[bschwartz]

Maybe the first mod I try after getting things tied and laquered, is to try the 180 degree arangement of standard 120/240 AC and work from there.  I can check on the unbalanced load growling, then break out the 60v legs.  Then try two 60v legs 180 degrees, paralleled for the DC and keep two legs set as 120 ac for normal loads.  Easiest to most complicated seems to make sense.  Its also easier to try the various 120v ac combinations as they don't need rectification or filtering.

[Apogee]

Brett,

Not that you asked or anything, but imho I think you are making a BIG mistake not just ordering some Glyptal online and doing the job right.  You could have already had it by now.

Yes, you might find some alternative that is cheaper, but they make the correct stuff for a reason.  If the cheap alternatives worked just as well, don't you think the motor shops would be using them?

I'm concerned that you are going to put something else in there and have problems down the road.  Then you'll have a mess because you'll have the wrong stuff in there and will be trying to clean it out before you either use the correct stuff or have the head re-dipped by a motor shop...

The time taking a gen head back apart, then troubleshooting to try to figure out where a winding fatigued and failed, is certainly worth far more than $40 imho.

http://www.caswellplating.com/aids/glyptal.html

Yes, you and Bob are right about the fact that early on motor winders likely used some lacquer or shellac derivative.  However, they also stopped using it for a reason.

Food for thought.

Steve

[BruceM]

Brett, I'll bet the swap to 180 degrees will cure the ST load imbalance growl.

Think about the imbalance in bearing and housing loads with the 90 degree (stock) setup.  All those years, all that grief, because of an idiotic winding design choice.  Egads.  

Now thanks to Brett and Bob, we'll have a fix.

[flywheel]

Brett,

Not that you asked or anything, but imho I think you are making a BIG mistake not just ordering some Glyptal online and doing the job right.  You could have already had it by now.

Yes, you might find some alternative that is cheaper, but they make the correct stuff for a reason.  If the cheap alternatives worked just as well, don't you think the motor shops would be using them?

I'm concerned that you are going to put something else in there and have problems down the road.  Then you'll have a mess because you'll have the wrong stuff in there and will be trying to clean it out before you either use the correct stuff or have the head re-dipped by a motor shop...

The time taking a gen head back apart, then troubleshooting to try to figure out where a winding fatigued and failed, is certainly worth far more than $40 imho.

http://www.caswellplating.com/aids/glyptal.html

Yes, you and Bob are right about the fact that early on motor winders likely used some lacquer or shellac derivative.  However, they also stopped using it for a reason.

Food for thought.

Steve 

Check on ebay, there are usually sellers of the small spray-on cans of glyptal.
                                                                                                        flywheel

[bschwartz]

Steve, you are ABSOLUTELY correct that glyptal would be the best choice as it is designed for this use.  If this were my main source of power for my home, I'd use glyptal.  If I didn't have another generator head that I'm happily using, I'd use glyptal.  But for me this is experimentation.  I enjoy seeing what I can use for projects that was 'designed' for something else.  I am doing all of this mostly as a hobby.  If I use something not designed for an application and it goes "POOF!"  Oh well.  I'm still having fun.  My vehicles weren't 'designed' to run on waste vegetable oil, but I'm using it just the same.  Apparently the ST head wasn't designed to use poles 180 degrees apart.  Does this mean I shouldn't be rewiring it? 

           "The time taking a gen head back apart, then troubleshooting to try to figure out where a winding fatigued
             and failed, is certainly worth far more than $40 imho."

A true statement if your goal is only to solve the electrical issues.  If I save $30 by using another product that will work, and I do that 10 times, I have saved enough money to purchase another generator head.  If it doesn't work, well I have new information to share with the group 

Thank you for your concerns, and again, I agree with your suggestion for an off gridder

[BruceM]

Brett, one very important thing to look out for:

When you bring the coil leads out,  you need to make sure you get the "polarity" right.   If you connect one wire each from a pair of coils together,  then spin the field coil and check the voltage across other two ends, you will see if they are canceling each other (very low voltage) or coming up with 120V.
If the former, tag common connected wires +, the other end -.   For 60 volts, they'd be connected together in parallel, just as your test.  If you measure 120V on testing, then switch the leads on the unit being tested before tagging + and -. 

For the third and fourth coils, hookup and compare to the first coil you've already tagged.

If you applied 12V to each coil and checked the magnetic field of each stator coil at the outside of the houseing with a DC gaussmeter, that would also do the trick, but I expect you don't have the gaussmeter.  A compass might do it, since you only need to know the coil polarity. 

For a 240V hookup,  each 180 degree, 60V coil pair would have a plus and minus connected (series).
The opposite pair, will also have a plus and minus connected, temporarily, for yet another polarity test.  One end of each 120V pair in series should be connected together, this will be the neutral.  Then measure while spinning, the voltage between the other two ends.  If it's 240V, Bob's your uncle.  If it's very low voltage, switch one of the series pairs end-to neutral. 

DON"T HOOK UP THE LEADS TO A LOAD without doing this first, you can smoke your field coils.

Maybe Bob could help come up with a diagram that shows this better.

Note to Marcus:
This issue also comes up when hooking transformers in parallel; the transformers may look alike on the outside, but the winder may put one or more coils in a different direction internally.  So you have to energize to check or at least have a fuse on each primary so that smoke doesn't happen.  If fuses blow, then you have to hunt for the reversed winding, and switch it's leads.

BruceM

[mobile_bob]

Bruce as usual has brought up yet another valid concern, and this is how i would address it

yes we could put together a sketch, but we would have to make some assumptions on how the winder placed the leads
and from experience i am not sure i wanna be responsible for that, so

you can bring out all 4 wires for each pair of coils that you want to start with and, either

rectify each coil and then parallel connect the product of each coil connecting positive to positive, negative to negative
to get you ~60vdc, or

if you decide to parallel first and then rectify the product of two coils, i would connect start to start of each coil, and then
connect finish to finish of each coil with a fuse inline with one lead, so that it will blow when you make the connection if they
are out of polarity with one another, or

you can make the connections in parallel, energize the coil with 12vdc, and then try and spin the rotor by hand, if the coil polarity
it wrong they will work or fight to cancel each other and severe cogging will result, if on the other hand they are in  polarity with each other
there will be almost no cogging (dramatically reduced from that of the coils connected out of polarity with each other)

i will draw up a sketch of connections that we can check against, but i would rather folks try the above methods first just to make sure
of their connections, it is just too easy to miss read a sketch and end up with smoke in my opinion.

thanks Bruce for bringing this concern to light, something i had let slip because yet again i made an assumption based on what i would
do, and quite frankly i do this with enough regularity that it is an automatic function for me to just grab a fuse holder to make preliminary
hookups.  don't do it often with generator pole groups but i do it with some regularity with transformer primary and secondaries in control system panels changing from 440 to 220 and secondary windings to get the needed 24volt control voltage at full rated kva.  even though there is usually
a schematic on the transformer i still use the fuse method, because i have been bit with incorrectly labeled parts, or someone has changed the leads around for whatever reason before i got there.

bob g

[mobile_bob]

here are two sketches to compare results against, please no one use these sketches and something carved in stone
until we verify the outcome.

one is for connection for 60volt output, the second is for changing the coil displacement from 90 degree's to 180 degree's
the idea being a change in placement might make a difference in the groan/whine made by these heads when loaded on
on leg.

comments welcome, and if i made an error please let me know so that i can correct it.

bob g

[BruceM]

Nice diagrams, Bob, thanks.  It popped into my head that neither of us has mentioned this to Brett when I was not sleeping in the early hours this morning.  Just testing each pair makes it easier, as you suggest. My explanation sucked.

I was wondering, what is the magnetic orientation of the ST, 4 pole rotor?  It must be N-N and S-S on each axis, right? 

[mobile_bob]

Bruce:

good question about rotor pole orientation, but if i had to wager
it would be NSNS standard configuration

otherwise the magnetic circuit in the iron gets really lousy and inefficient

if however it turns out that it is NNSS, maybe that would be a reason to explore another modification
that being to the rotor to space them back to NSNS which would make a much better and efficient use
of the iron and nice short magnetic circuits

i can't imagine this would be the case, i understand the reasoning for the 90 degree coil displacement
on the stator, because the stator was originally designed to be a 230-240 only single phase head
and simply cutting in between coil 2 and 3 was an easy mod to get 120vac for use in our part of the world.

i can't even think how NNSS would work even in a straight 230-240 vac single phase head?

but who knows?

maybe while Brett has his apart he can put 12volts on the rotor and use a compass to determine if the poles
on the rotor are oriented as i suspect NSNS or possibly in the NNSS configuration

that probably should be the next step, because i drew the sketch assuming a NSNS rotor configuration
and if it turns out to be something different, the sketch would then be wrong.

good questions,

one thing for sure we are going to know more about the st head after this exercise than we did going in!

i know i will



bob g

[BruceM]

I was assuming something like this: