Single-Ph PMA Cap and Current Gain

[ghurd]

The basic idea is derived from a single phase PMA making voltage and current pulses.

The larger the current pulse, the greater the line's voltage drop.  The PMA is operating at a slightly higher voltage than the battery, but only during the pulse when the current is flowing well or peaking.

If these voltage peaks could be saved for times when the current is lower, then it would average out to more amps.

Meaning place the rectifiers on top of the tower, and a cap on the DC side.

My problem in proving the idea was "parts".  I never seem to have what I need, when I need it.

Today was different.

I am working on a mini GE ECM.

"Arktic 59", 3-ph, 6 coils, 8 poles (?), 3.3" dia, 1/15th HP.

The tests are with one of the 3 phases.

The readings are with a true RMS meter.

The line supplying the loss is 40 feet of #24 speaker wire, stretched out.  80 feet round trip.  Plus about 8' of #16, and meter leads.

Each phase has 14.3 ohms coil resistance.

The cap is an electrolytic 63V 1500uF.

The battery was maintained at 12.7V.

All numbers were repeated in a second test, in the same order.

The Results.

First: 650RPMs.

No cap, open V, 8.8V (bouncing between 8.6 and 8.9).

With cap, open V, 12.3V rock solid (no surprise).

No cap, 0.1ma into the battery.

With cap, 0.3ma into the battery.

Remember, the battery was at 12.7V.  When the PMA stopped, so did the current.

Last: 800RPM.

No cap, open V, 16.6V.

With cap, open V, 20.2V.

No cap, 131ma into the battery.

With cap, 140ma into the battery.

I have no desire to disassemble this windmill more than I already did.

Meaning I won't be testing this idea, on this particular motor/PMA, at more RPM levels.

The wind is howling for the first time since I made this one, and instead of testing it in good wind, it lies intermingled with piles of test wires and meter leads on the dining room floor.  My wife will not be pleased, in exactly 40 minutes from the time this was typed.

OK.  Sure.

I completely understand people thinking "A whole 9ma.  So what?"

I believe this is relative to scale.

If one spring holds 100kg at 25cm, there is no reason to believe 10 identical springs will not hold up 1000kg at the same 25cm.

Let's look a bit deeper...

That extra 9ma does not sound like much.  It is 7%.

The voltage loss in the 80' of #24 at 135ma is only 0.277V.  Power lost in the wire is 1/50th of a watt.

Power gained into the battery is 1/8th of a watt.

That is very considerable (~57 times?).

Larger current flow, or more voltage loss in the wire, would have a greater effect.

I am completely lost on this part.

The battery is at 12.7V.  The RPM is 650.

Open V without a cap is about 8.8V and the charging current was 0.1ma.

Open V with a cap is 12.3V and the charging current is 0.3ma.

The test was repeated several times.  The meters did not seem to be confused.

I could understand a short spike of current if the cap was not involved, but the results with the cap have me scratching my head.

The 12.3V open cap supplying any current (even 0.3ma) into a 12.7V battery, that's just plain weird.

Let's talk about it.

G-

These ideas will Not be relative to brushed PM motors being used as generators.  (ie: Ameteks do not count)

[tanner0441]

Hi

So what your saying is?  If I put 3 1000 Uf caps in series with the feed from my Chinese copy 12V unit instead of sitting just below the voltage it starts to charge at I am going to have current flowing on the battery side of my charge controller.  As I have said many times I am in a poor wind site and as the load goes onto the generator it does not always have enough wind to push it just over the top.  In 3 weeks I have had just over 2.3 KWH recorded on my KWH meter

9mA is not much but if it is gain not loss then when you have nothing it is a start.

I will watch this posting with interest..

Brian

[ghurd]

So what your saying is?   "If I put 3 1000 Uf caps in series "...

No.  

I did not intend to say that.  At all.  This is "another new idea".

Nothing is in series.

The cap is in parallel with the rectifier's DC side, the rectifier and cap are near the PMA, and the battery is far away.

The concept revolves around "peak voltage loss" in the line between the battery and the rectifier.  

The "peak voltage loss" happens more pronouncedly with single phase PMAs.

I expect the concept would only help 3-ph machines at slightly over cut-in voltage.

The gain would decreace as RPMs increase.

Conversely, I expect the gain would increase as amps increaed.

Confusing stuff. (wife is now here)

I tend to work solid numbers with AC motor conversions.  An ECM is the same as a 3-ph conversion in my mind.

G-

[Madscientist267]

I like the idea, theory sounds solid.

As for:

For this, it sounds like there may be some transients that aren't immediately apparent. Not sure, as like you say 12.3 OTV cap (theoretically pure DC) dumping current into a 12.7V battery (known to be pure DC) does defy a few things.

O-Scope?

Steve

[Ungrounded Lightning Rod]

Your high-resistance wire was after the cap and the cap was close to the genny, right?

The genny could put a charge on the cap through the low resistance from the genny to the cap and the cap deliver it over a longer period through the wiring resistance.  Meanwhile the cap would be held at battery voltage until the next current spike came along.

Put the cap next to the battery on the other end of the wire and I bet you don't see a significant change.

= = =

Note that for measuring charging current you want an average-reading meter, not a true RMS.  A true RMS meter will overstate the charging for non-level waveforms because it overcounts the peaks and undercounts the valleys.

[Nothing40]

A year or two ago,I did a small experiment with some caps.

Now-I don't have a windmill,just a small ~10W PV panel,and some 'grid assistance' from a small power supply,for those overcast days.

I've got alot of capacitance on the 'LOAD' side of my setup [breaks out the calculator] -about 195,000uf on the output.

I got curious and added a bunch of caps to the 'CHARGE' side of things,and noticed that the charge current went up a bit(~10ma),and the voltage went up a bit (~.25V)

I was thinking that maybe the caps were filtering out some of the ripple/peaks from the PSU,thus the slightly higher voltage and current.

I dunno. Just an observation I made.

I am a big fan of caps,not for any 'magical extra charge' reasons,but for helping to hold a steady voltage when a heavy load switches on,they can supply that extra 'surge' current for the heavy load.

Adding a couple of small film caps in parallel wouldn't hurt either-They would help to clean up any high-frequency noise,etc.

Since I play with (HAM)radio and stuff,I went kinda overboard with my HF/RF noise filtering on my system,I've got bypass caps and ferrite cores all over the place to keep any of my RF signals from leaking into my 12V system,that might disturb my DSL modem,router,or other items running from the 12V bank.

/end rambling  

[ghurd]

"The genny could put a charge on the cap through the low resistance from the genny to the cap and the cap deliver it over a longer period through the wiring resistance.  Meanwhile the cap would be held at battery voltage until the next current spike came along."

Yes.  That is the entire concept.

Power going into the PMA end of the wire is always less than power coming out on the battery end.

I^2R.

Reduce the large spikes of I, and spreading the I out over more time, results in less wire loss.

Not sure if I would call the 0.08 ohm wire high-resistance in the big picture, considering the DC coil resistance is 1800 times greater.

The reading difference between true RMS, the $3 HFs, and a few other meters were closer than most people would believe.

Quick look at the charts.  Solid RPMs from 760 to 2180, Star, Jerry, and 1 of 3 phases.

Greatest 'error' I see at the moment is less than 2.75% and that is for open voltage of a single phase at 760RPM.  Might be something higher deeper in the stack of papers.

[domwild]

Ghurd,

Very interesting!

1. There is an article out by a Dr Chalko for a hydro/Fisher&Paykel system, which benefits from caps. However, his system is a high RPM, high frequency system. I believe the caps were on the wild AC side.
   
2. Came across a student project by "Engineers without borders" for Gujarat, India, where caps are used on the DC side but from memory it is not discussed why they are there.
   
3. Gizmo's website (thebackshed.com.au) has 17 webpages on the topic of the benefits of caps, but caps on the AC side of a mill.
   
4. A precis of a Brazilian Master thesis uses inductors and caps (AC side) and a SEPIC DC-DC buck/boost converter to buck/boost the mill's voltage and also to fix up the power factor problem at the same time.
   
   

Can dig up the links if interested.  

Regards,

[tecker]

The gains in voltage and current is because your cut in .

[ruddycrazy]

Hiya Ghurd,

           Mate over here in Oz a mate reckoned he got got great gains by putting caps in parrallel with a 3 phase F&P genny for great results. Well me being a lazy bugger I simply put 2 400 volt 470uf caps back to back, put them in SERIES with each phase from a 100S F&P wired in delta. When a mate saw what I did and replicated it well... read here for the results

http://www.fieldlines.com/story/2008/9/23/8477/59397

Cheers Bryan

[Flux]

Single phase is strange so testing one phase will cause confusion.

What matters for charging batteries is mean current, using a true rms meter will confuse the issue if it does measure rms on the dc ranges. I don't know what these multimeters measure on dc current, I always assumed that the true rms was limited to ac ranges but you certainly don't want a rms reading for battery current.

For single phase the battery virtually acts as a capacitor but you are clouding the issue by adding line resistance between the capacitor and battery so the rms current will be the component that causes loss in the cable.

It seems reasonable that in this single phase case your capacitor will reduce line ripple current and reduce line loss. If you do it 3 phase the capacitor will do nothing so unless you intend to run it single phase you are just adding confusion.

Sorry I haven't had time to plough through all this properly so I may have not quite got the point of it and others may have found the solution. I will try to find time to read it properly if I get caught up with other issues.

Flux

[Flux]

Having had more of a look at this there may be another issue that comes into play.

I agree that your line resistance is on the low side for the extra line loss due to ripple to account for all of this.

Batteries are complex electrochemical things and the models often used to represent them are pretty crude. I said that a battery looks like a capacitor to a single phase rectified supply and that is true. We also for many purposes can consider the internal resistance to be very small ( milliohms) and that lets us explain a lot. There is also a complicated issue of it being an electrolytic cell with polarisation and gas potential and all sort of issues. It is generally accepted that as the thing charges the charge efficiency falls and the voltage rise from the surface charge bit doesn't tie up with the basic low internal resistance. The thing acts as a much higher resistance in this region ( in the ohm range) and if it wasn't for this pwm charging without inductors would be in trouble.

I have a feeling that removing the voltage peaks associated with the current peaks probably improves the charge efficiency during pulses and the smoothed capacitor current charges it better than pulse peaks that mainly cause gas during the peak.

If this is true then placing the capacitors near the battery will have a similar effect.It should be possible to separate the line loss bit by trying it at both ends.

Flux

[ghurd]

I am on a quest for something.  Not sure what it is until I find it. But it will be more simple than the F&P stuff!

I did read through the posts on Gizmo's site several times, and honestly I have a hard time following long posts in that format (Go Scoop!).  Some of the numbers seem out of whack to me.  College was a long time ago.

A link to #2 would be nice.

G-

[ghurd]

The battery?  I did not expect that answer.  It makes sense the way you explain it.

Battery is a 34AH SLA. 12.7V was handy.  Low amps to avoid problems related to the battery, too much wire voltage loss, or a capacitor too small.

I wanted a litlle bit of line loss, but not too much.  Something replicating a larger system.

I will try it again with a cap on both ends.  

No suitable caps here at home.  1500uF is the largest.  Next is maybe 100.

When repeating the same test, any ideas about the caps would help.

Larger on the bridge end and smaller on the battery end?

How big is big enough?  How long is a piece of string?

I believe this one will run at 0.4A most often, and peak out at 2A with all 3 phases.

It will be using all 3 phases when flying.

Thanks Flux,

G-

[domwild]

Ghurd,

Here is the link, hope, hope!~

http://floatingsun.net/udai/files/project3_design_review.pdf

Good luck!

Regards,

[ghurd]

Thanks Dom!

It is what I asked for.

Do not take this personally.  This is an attack on the pdf, as I understand it.

Too much unusable time on my hands.  So here starts the rant...

I do recall that pdf!

Not for the DC side cap...

For $59 in parts and $21,004 in labor.  It seems I don't charge enough for my kits!

Correct.  They do not say why the cap is included that I see.

I can not see a reason for it in a 3-ph machine.

Looks like his cap is related to the 'fancy circuit' that shows up as jibberish here.

The 12V Stecca solar controller over the 48V windmill looks like smoke signals waiting to appear.

Looks like 8 x 12V batteries, mixed up in 12, 24, and 48V systems?  Wow.

All those 48V, 24V, and 12V items mixed up together give me a headache worth $21,004.

The efficiency in one area can be doubled with 2 off the shelf $25 parts.

And I will tell them how... for $8,888.82... if my ratios are on.

The system looks like a 48V heating element with very serious 12V secondary uses.

Quick math.  In rated wind, all batteries will be over voltage in about 3~5 minutes, probably closer to 1 minute.  Fuses are blowing, 12V5AH boil dry, C40 is confused, inverter shuts down from overvoltage, etc.

The 4AH battery paralled with a 288AH battery looks like some automatic FEMM fix on a goofy circuit.  If the circuit needs 292AH to function properly, then in a few weeks or months, it won't work anyway.

Best for last.

Why use 12V inverters for a 48V input?

Like I said, much of it shows up as jibberish.

end rant

G-