Any motor/generator guys on here? - Project Complete - Thank You

[JayArr]

My plan is to supply the field slip rings with a variable DC supply, I have a 120V 3A source that I hope will be OK.

I'll slowly increase the field current while monitoring the output voltage until I have 120VAC

At this point I'll measure the exciter voltage and the voltage reference voltage.

I'll then hook up the exciter winding to the AVR with a 120/18V transformer from the output to the voltage detect wires of the AVR. I'll put a 60W lamp on the brush wires. I should be able to vary my field current such that when I increase the field current so that the output voltage exceeds 120V the 60W lamp goes out and when I decrease the field current so the output goes below 120VAC the 60W lamp should turn on.

If this works I'll disconnect my variable supply from the rings and hook the AVR up to them. It should now work and regulate to 120VAC

If this works I'll think about digging into the AVR to change the small signal bias network resistors so it runs on 9V instead of 18V.

[james_s]

IIRC the field voltage is normally around 12-24VDC in most of these.

[JayArr]

Thanks James, I wasn't aware that the field voltage was that low. I'll keep that in mind.

[wizard69]

To be more accurate I wouldn't mess with it without a manual.   There seems to be some extra windings and frankly I'm not sure what they are for.    Also you have to worry about having enough engine power to actually drive the generator if you change how much energy it can produce.

To your point about a lower current charging solution, some of the best places to camp don't have sites with an excess of power so it isn't a bad idea to come up with a lower charging current solution.   Often you run into a situation where you might have a 15 amp or 20 amp outlet to tap into and not much more.   So yeah it is a good idea to be able to leverage the capacity of a standard outlet to recharge.

So yeah in a nut shell I wouldn't mess with it without more information.   Maybe somebody here will have it, or maybe a good generator repair shop.    A stated before I suspect the the actual generator head is designed to support many markets and finding the right wiring arrangement may be possible.   

Dave

The generator's AVR feed is from a low-side tap on both phases, so it can compensate for the total load.  As-is, if you apply an unbalanced 120V load, regulation will be significantly degraded. 

 If you simply paralleled the windings, the voltage to the AVR would be halved, assuming you reconnected it between the tap and Neutral, and even if you could sort that out, the windings may not be well enough matched to prevent large circulating currents.  Therefore, I agree with  Wizard69: its impractical to rewire this generator for single 120V 30A output without a full rewind.

If the Xantrax charger doesn't have an easy to use option to limit its input current, and can't easily be reconfigured for 240V input, you'd probably be best off getting a 120V-240V universal or switchable input auxiliary charger (or a pair of 120V chargers) with a significantly lower maximum input current that you can connect when required.  It would also be useful when on low current 120V site feeds.

As you have realised, an autotransformer to convert from 240V 15A to 120V 30A, (which requires two 120V 15A windings in series), would be large, heavy and expensive, and may well have a high enough inrush current to trip the generator's breaker, so I'd be reluctant to go down that road even if I could get a really good deal, unless I could 'try before buy'.

[james_s]

Changing the amount of current it can produce  coupled with a corresponding change in voltage doesn't change how much energy it can produce, or how much engine torque is required to turn the generator. Going from 240V to 120V doubles the current but halves the voltage, the power is still the same.

[JayArr]

James is correct, I'm not changing the power of the unit, it's still 3600W it's just configured different. The motor doesn't care whether it's 120VAC at 30A or 240VAC at 15A

When we camp at a place that has power the batteries don't get depleted because we use the shore power so there is no great demand to recharge them. Same in the driveway, it's plugged in and the batteries are on float charge all the time which doesn't take much at all. The only time the charger would need 22Amps AC is if the batteries were very discharged and it needed to pump all 100ADC into them.

I've found a couple of repair manuals for Kubota and Wacker Neuson generators that use the same SawaFuji head and I've copied their configurations and rewired it. I'll have to do some tests but I should have it running this weekend.

[JayArr]

Here's a question regarding the feedback voltage problem.

When I put the stator windings in parallel my feedback voltage gets cut in half, from 18V to 9V. My first instinct was to modify the AVR by changing the resistor ratios.

The suggestion of using a transformer percolated in the back of mind and today it occurred to me that maybe I can use any small voltage transformer with a center tap.

If I take the 9V I'll now be getting for feedback voltage and apply it to the center tap and one side of a low voltage transformer won't I get 18V out of the other leg? Will it work as an auto-transformer if I just ignore the primary and use the secondary winding only? If this is the case then it doesn't even matter what the secondary voltage of the transformer is, as long as the center tap is 'centered'. I can grab something out of the junk box and use it as a voltage doubler and that way I don't have to modify the AVR.

Have I missed anything?

[james_s]

Yes that should work, as long as the voltage across what is now the primary is not much higher than the original secondary voltage of the transformer, otherwise the core will saturate.

[T3sl4co1l]

Interestingly, the coupling will probably be much better than from the primary.  A typical split-bobbin transformer has the primary and secondary wound bifilar, so the coupling within pairs should be quite good.  For any other type, it'll be about the same as normal.  Note that the VA capacity is about half, because you're only using half the wire on the thing.  Same ampacity, and same maximum voltage as above, or more precisely, same voltage per frequency.

Tim

[wizard69]

James is correct, I'm not changing the power of the unit, it's still 3600W it's just configured different. The motor doesn't care whether it's 120VAC at 30A or 240VAC at 15A

Yes that is correct you don't change the power if you have corresponding changes in current and voltage to keep power constant.   I'm more concerned about what might happen is your assemblage of windings allow for more current or impacts efficiency.   Maybe I will have to go back to your sketch but I was under the impression that there are several unused windings with this generator head.

When we camp at a place that has power the batteries don't get depleted because we use the shore power so there is no great demand to recharge them. Same in the driveway, it's plugged in and the batteries are on float charge all the time which doesn't take much at all. The only time the charger would need 22Amps AC is if the batteries were very discharged and it needed to pump all 100ADC into them.

I've found a couple of repair manuals for Kubota and Wacker Neuson generators that use the same SawaFuji head and I've copied their configurations and rewired it. I'll have to do some tests but I should have it running this weekend.

Great news as I'm certain that many of us will want to know.   Personally I'm looking into the RV market and was actually leaning towards solar as the power source.   For backup an engine powered welder / generator was also being considered.   More for the welder than a power source.   My thought is that solar would mean far less intervention on my part to keep the RV powered up.   Of course then you have to avoid trees.   

If you don't mind what size RV is this?   This is a retirement thing for me, most of my camping over the years has been in tents, so I don't have a good feel for RV's.   

[JayArr]

Hi Wizard

This is a 20 foot trailer we tow with our 6 cyl Envoy. It's a good size for my wife and I and a dog or two. We're getting close to retirement as well. It's an older one but it has a queen size bed and a bathroom with a shower so my criteria were met. It came with two deep cycle 12V batteries that will run everything but the air conditioning and the microwave. We have two big bottles of propane on the tongue that run a hot water heater for showers/kitchen, the stove/oven, the furnace and the fridge. We can camp for three days before the batteries need a charge. I've purchased this American made Briggs and Stratton engine generator because it has an electric start that I can wire to the batteries, I want my wife to be able to start it and there was no way she was going to be able to pull start a generator and the cheapest Honda with electric start was $2500. I found that I could easily convert a B&S engine to propane. I bought a kit and will just plumb it into the existing propane network of the trailer, then I don't need to haul or worry about gasoline. The trailer electrical "plugs in" by way of a special RV plug (TT-30P) that looks like a dryer plug but is only 120VAC and 30Amps. The plan is to simply put a receptacle on the generator that is TT-30R and when there is no shore power I'll plug the trailer into it's generator and charge the batteries for an hour or so every couple of days.

Solar is expensive to set up, there are a bunch of electronic modules, once it's all installed and paid for it's carefree as long as the sun shines. A generator is more of a sure thing but you pay for fuel and you have to actually run it every two or three days. I don't mind the chore, there is lots of free time in the day at a campsite so running the genny is just something I'll have to start, then go have a coffee and then go shut it off. not too onerous for me. YMMV.

We camped in tents for most of our life, believe me you're going to enjoy this a whole lot more!

[james_s]

Some of my favorite childhood memories were of camping, occasionally in tents, but we often rented a 24' trailer at a campground and my grandparents had a cool 1960s 26' motorhome, it was bright turquoise and white and stuck out like a sore thumb, cool blue shag carpet inside.

Anyway as far as generators go, once I used an inverter generator I'd never want to go back, even the Harbor Freight ones are decent. My friend has a Champion inverter gen with electric start, I don't recall what he paid for it but it was duel fuel gasoline/propane right out of the box. You can have a conversation in a normal talking voice standing right next to one, the old fashioned 3600 RPM screamers make such a racket you can barely yell over them and the din is inescapable.

[JayArr]

I received a box of new AVRs this week and tonight I got around to testing them. First I put a light on the output wires that go to the brushes. Then I input 12V to the yellow wires to pwer the AVR and the light turns on. Next I hook a variable supply to the blue sense wires and vary it, when it hits 18V the light shuts off.

So far so good except that my rewiring will cause me to only have 9V on my sense winding.

I tried my idea of the center tapped transformer. I just found a small one in the scrap box, cut off the primary leads because I don't need them and I fed one winding and the center tap with my variable supply. I connected the two outer winding wires to the AVR sense contacts.

It works! The light now turns off when my variable supply hits 9V instead of 18V.

I know there was little reason to believe it wouldn't but it was nice to see just the same.

Next tests will be on the generator!

[JayArr]

OK, quick questions since I'll be working on this project this weekend.

How much is too much "circulating current" or "eddy current" between the two parallel windings?

Each winding is 120VAC and 15A, I'm putting them in parallel to get 120VAC 30A.

If I test it with a shunt between the two output windings what would you consider an acceptable eddy current?


I'm going to assume that any eddy current is simply the difference in output between the two windings due to how they were wound. For example - if one winding got an extra turn it will produce slightly more and that will run back to the winding with less. Is that correct?

So would 1% be acceptable? 5%?

I'm also guessing that if I put a 0.01 ohm shunt between the two windings and then connect them both to a load I can measure the voltage difference across the shunt and the current through a 0.01 ohm will be close enough to what will occur with no shunt. Or should I leave the shunt permanently in place for operation?

JayArr

[T3sl4co1l]

Yes, more or less.  Also, if they're not mechanically symmetrical, there might be a phase shift, which would be at an angle to the terminal voltage so adds up slightly different (however, it would have to be quite some angle for this to actually matter).  Or harmonics due to differently shaped slots, perhaps.

How much is acceptable, is how much lost capacity you can accept.  Probably 5 or 10% would be on the annoying side, both in terms of wasted efficiency as well as reduced capacity.

The shunt won't show anything different under load, given the division of currents across its resistance.  (i.e. ideally you'd load both either side of the shunt equally, but if you're loading just one, obviously you'll see a bit more current through it.)

It can be removed for operation.

Tim

[JayArr]

Thanks Tim

Just to be clear...

When we talk about 5% to 10% are we talking current? 5% of the rated output current of 15A as a circulating current = 0.75A? Or are we talking 5% difference in output voltage between windings. 5% of 120VAC - 6VAC differential.

I'm thinking I should measure the voltage differential first with no load and a large shunt (10 ohms?). Then put a smaller shunt in and see what the current is like, again with no load.

These generators are retail grade, Home Depot, Lowes, Harbour Freight kind of units. Often the windings are terminated on a strip that allows the winding configuration to be swapped from series to parallel with the jumper bars and some spade terminal switching. On some models there is even a switch on the control panel to switch from 240VAC/15A to 120VAC/30A.

My firm hope is that the two windings are nearly identical and that my "re-wiring" is correct so they are now both in phase.

[T3sl4co1l]

Current, yes.  The OCV difference should be smaller than that.

Tim

[JayArr]

OK - it works.

To summarize:

It is important to keep the phase of the windings correct when switching from series to parallel. I had 240VAC from A to H with D as neutral as it was originally wound and it may look easy to just connect A and H but they are 180 degrees out of phase so you need to "flip" one set of windings so they come into phase with the first and "add".

I used a small transformer I found in my scrap box to double the feedback voltage. I took the feedback voltage from B/C and D and fed it to one leg and the center tap of the small transformer secondary. The center tap and the other leg of the small transformer then output was double since the secondary now acted like an autotransformer.

I am getting my feedback from only one of the two windings but that does not seem to matter since they are in parallel.

Before I hooked the two windings together (A and G) I ran the generator and measure between them. There was only 0.25V so the circulating current is negligible.

Thanks to all who gave me advice and suggestions. If anyone has further questions just ask or send me a PM.

[Doctorandus_P]

TLDR;

I had a short look at those Xantrex chargers:
https://www.xantrex.com/power-products/battery-chargers/overview.aspx

And saw currents of 20A, 40A and 60A, but that's for a 12V output, which would be a lot less on the mains voltage input.

Those chargers also have a variable input voltage, and it's range is even as wide as:
> Auto-ranging AC input voltage capability (90-265 volts AC)

So your charger may just work on 240Vac.

[JayArr]

Thanks Doc but I'm installing a Xantrex Freedom 458 inverter/charger. I already own it, a customer abandoned it because he had to leave town before I could finish the repairs. I've rebuilt it for my own use.

Charger:

Input - 120VAC,  22A

Output - 13.5VDC, 100A

Automatic three stage charging


Inverter:

Input - 12VDC, 200A

Output - 120VAC, 2200W continuous


The genny should run the charger without any problem (3600W genny on a 2640W charger load) and the charger will charge the two 12V deep cycle batteries to 90%++ in less than 2 hours. (12V*100A*2H = 2400WH, batteries are 12V*90A*2batteriesinparallel = 2160W)

These are rather crude calculations but close enough to paint a picture.

Battery recharging will be required every two to three days depending on microwave usage.

I can also always start the genny for dinnertime cooking or anytime we want to run the air conditioning.

The pictures show the generator on a stand I welded up that matches the tongue of our trailer, it will sit right on the tongue over the batteries between the propane tanks and the front wall. There will be a box over it lined with sound deadener and it gets plumbed into the propane lines of the trailer so there is no gasoline.