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Low amperage output
By modernmarvelinspired, Section Newbies Posted on Sat May 17th, 2008 at 09:16:38 PM MST
question on conversion rewind

Hello, I currently have a problem with what I consider low amperage. My battery bank is 24v.
At 10mph I see around 24 watts, which is fine but around 25mph I only see about 100watts. This is a 1/2 hp single phase conversion. It hits charging around 200rpm.
The start winding has a resistance of 5 ohms, and the run windings have a resistance of 5 ohms as well. The start winding is rectified, then in series with the run winding. The run winding also has its own rectifier. I'm using a 5 ft prop which seems to accomidate the genny quite well, no stalling.
My question is I have some 16awg wire laying around and have really been thinking of taking the old stock windings out and putting this 16awg in. I'm aware that this would probably turn this into a 12vdc genny. Currently the machine hits 42 vac at around 370 rpm, 220vac around 2000 rpm. I fear i just have too much resistance. I feel like if a garbogen can make 500+ watts in a 30 mph wind, mine should be atleast doing better than what it is at 25 mph.
When I saw the amp meter hit about 5 amps during a strong gust of wind, the battery voltage never rose above 24.5 vdc. I was using a fluke volt meter for this measurement of voltage.
Any help please and thankyou.

Low amperage output | 11 comments (11 topical, 0 editorial)

Re: Low amperage output (3.00 / 0) (#1)
by ghurd on Sat May 17th, 2008 at 03:48:26 PM MST
(User Info)

The start and run are in series?
And they both have their own rectifier?
I don't follow the reasoning for that.
It would do better if they were rectified seperately, then the outputs paralleled.
G-

Re: Low amperage output (3.00 / 0) (#5)
by modernmarvelinspired on Sun May 18th, 2008 at 07:47:47 AM MST
(User Info)

I thought about what you said ghurd. I see why you don't understand why I put the start winding in series with the mains. For some reason I'm not getting the same voltage out of the start winding as i am from the mains. The start winding voltage is actually quite a bit lower than the main winding voltage.

Lets say the genny is spinning at 220 rpm, the main winding reads 23vac. But the start winding only reads 10vac. I dont understand this beacuse the more I thought about it doesn't make sense. The start winding and the main windings have the same resistance. I wonder why the voltages are so different.

Ya I would guess that if it was reaching 24vdc the same time that the mains were then I could parallel them. This is why I put them in series after rectification.

Any help thankyou

[ Parent ]

Re: Low amperage output (3.00 / 0) (#2)
by modernmarvelinspired on Sat May 17th, 2008 at 07:31:39 PM MST
(User Info)

Yes ghurd, they are in series, but I tried both, and in the same winds that day i experienced 2 more amps when they where in series. It seemed that paralled with each other there was not any difference.

In some very strong wind gusts, i'd say around 35mph the paralled configuration it did not make any differece, but as more gusts came, being series together i saw more amperage. I watched for about 30 min both ways just to make sure.

Re: Low amperage output (3.00 / 0) (#3)
by Flux on Sun May 18th, 2008 at 01:21:32 AM MST
(User Info)

You are not doing too badly. At best you could probably hope for double at 25mph.

You have a lot of resistance and also the windings are 90 deg out of phase so you are seeing the vector of the individual voltages.

Rectifying separately and feeding 12v should give you more amps, but don't forget you need twice as many amps for the same power at 12v so you may be as well off as you are.

If your trial with windings rectified separately feeding the battery was at 24v, try it again at 12v and see if you can get more WATTS. If not you are not going to improve things by rewinding.

If the parallel connected thing does produce more watts then you can wind with more turns to get the same thing at 24v.

Don't forget you change other factors when you connect in parallel. You are never going to stall as it is at 24v but you may do so with it parallel connected at 12v.

Ultimately you may do slightly better by rewinding it for 3 phase but generally there is very little difference between the 2 phase case ( which you have in parallel) and 3 phase. You will likely be able to find a compromise that gives nearly double the power at 25mph if you are prepared to trade the performance at 10 mph. No details of your prop so I can't offer much other help.

Flux

[ Parent ]

Re: Low amperage output (3.00 / 0) (#4)
by modernmarvelinspired on Sun May 18th, 2008 at 07:20:08 AM MST
(User Info)

Hello Flux, thankyou for your reply , i was hoping to hear from ya.
My blades probably havea tsr of about 5 or 6, there are three of them total making a diameter of 5 ft.

If I were to go to 12v, I would have to go to a larger prop because it hits 12v at pretty low rpms. My main concern with the 12v aspect was wether or not the windings could handle the current. Since there would be more amps running at 12v than at 24v.

Thankyou again

[ Parent ]

Re: Low amperage output (3.00 / 0) (#6)
by Flux on Sun May 18th, 2008 at 08:05:59 AM MST
(User Info)

It would help to know the actual cut in speed at 24v with the windings paralleled. From your ac figures you are possibly to slow for even 24v. It may be that with a single winding feeding 24v you are already stalled so adding a second would stall harder.

I assumed that you used the series connection to get reasonable cut in at 24v but it may be more a case of the fairly ineffective nature of the series winding bringing you out of stall easier.

If it cuts in at 10 mph with single winding on 24v you are slow enough. You could try adding series line resistance to the paralleled windings at 24v or even temporarily try it at 36v.

I am inclined to agree with you about 12v if it is that slow. I think I would try it at 36v to see what happens, that way you can see where you are going.

Flux

[ Parent ]

Re: Low amperage output (3.00 / 0) (#8)
by modernmarvelinspired on Sun May 18th, 2008 at 09:00:46 AM MST
(User Info)

My genny hits charging at around 210-220 rpm. This is just using the main windings.
But the start winding at 220 rpm is measuring only around 10vac, while the main is around 19vac or 20 vac. So in a 10mph wind its making around 15 to 20 watts, but doing any thing with the start winding doesn't make any difference till the wind really picks up.

Hope this helps.

[ Parent ]

Re: Low amperage output (3.00 / 0) (#9)
by Flux on Sun May 18th, 2008 at 12:51:33 PM MST
(User Info)

Yes this does help. Some single phase motors have identical start and run windings and are usually used for reversing capacitor run work.

As you had identical resistance on the start and run windings I assumed that most likely this was what you had. It seems just chance that your resistances are equal in this case and you have a start winding with few turns and wound with very thin wire, possibly capacitor start but just as likely resistance split phase start.

In reality the start winding is virtually useless to you and will contribute very little, the thing is never going to even approximate to a 2 phase machine. Single phase things don't do very well anyway but even so I think you are stalling with the main winding. By adding the start winding in series you are doing little more than adding 5 ohms as a form of line resistance and it is bringing you a bit more out of stall.

Without rewinding to a true 2 phase or 3 phase you will not get any great improvement but I still think it will go better at 36v.

Flux

[ Parent ]

Re: Low amperage output (3.00 / 0) (#10)
by modernmarvelinspired on Sun May 18th, 2008 at 04:58:55 PM MST
(User Info)

Hey Flux, I never did truly seperate the 4 coils that make up the main winding. Today I went ahead and took it down, dug inside of it and seperatated all the leads that the 4 coils have. The best configuration I've come up with so far is two coils paralled, two coils in series. Then took the two coils in series and put them in series with the two that are paralled.

This brings the cut in speed down to about 190 rpms. At 370 rpm now I get 60vac, instead of 42vac. I'm sure this will limit my amperage a little, but it truly seems like I made this better.

By the way the coils were poorly sodered, so I re-sodered them, which i'm sure will help more amps to come through. I think I read somewhere that some cheaper induction motors the splices from the leads to the coils is sometimes not that great.

I'm going to make a set of 8 foot blades, according to hugh's plans and see how it does. I'll definately try to let you guys know. I think his plans for 8 foot rotor is around 7 or 8, which they should do just fine

I dont think i'm gonna use the start winding at all, it doesn't really seem to do well by itself. Like you said.

Thankyou for your time
MMinspired

[ Parent ]

Re: Low amperage output (3.00 / 0) (#11)
by Flux on Mon May 19th, 2008 at 01:01:56 AM MST
(User Info)

A few things don't tie up. You should cut in at 24v with single phase when the peak ac equals the dc. Conduction will be small at the start and increase with speed. You should start to see output at 20v ac. If you get 60v ac at 370 rpm this implies a cut in of 370/3 which is nearer 123 than 190 rpm.

This is incredibly slow for a 5ft prop. I am not sure why you are getting best results with such a low cut in speed unless your prop is much lower tsr than you think. Certainly you are more in the speed range of the 8ft prop and whatever happens the large prop will have far more power. I am not sure that such a tiny alternator is going to hold down an 8ft prop so you will need to make every attempt to make it furl as early as possible. In low winds you will be way ahead but you will need to watch it in high winds.

Flux

[ Parent ]

Re: Low amperage output (3.00 / 0) (#7)
by finnsawyer on Sun May 18th, 2008 at 08:55:49 AM MST
(User Info)

After reading through the comments I'd just like to say this looks like a good case to get a dual trace oscilloscope, as you seem to have different amplitudes and phase angles with the two windings. It's hard to do serious work without knowing what the waveforms are doing.
GeoM

Low amperage output | 11 comments (11 topical, 0 editorial)

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