Any motor/generator guys on here? - Project Complete - Thank You - Page 1
Forum section: electronics / projects

author: JayArr
author_rank: Contributor
timestamp: May 03, 2021, 07:46:31 pm
content: Hi AllMy latest project is a generator. I bought it used on Craigslist and it worked perfectly - no problems at all. It is listed as 4000W but that's peak and it is 3600W running.It came wound as two 120VAC 15A circuits in series and also provided a 240VAC 15A socket.What I need for my travel trailer is 120VAC at 30A. I figured it would be easy to swap the stator windings from series to parallel to get my 30A.The universe, however, decided to complicate things....When I pulled the end off I found five pigtails (I expected three). It seems there are four sets of windings, each 120V leg has two sets of windings and the center tap of those windings is what is connected to the AVR for voltage detect.On top of that the windings aren't in the configuration I've seen schematics of or that I expect.Take a look at my schematic and tell me if you understand what they did here.

author: wizard69
author_rank: Super Contributor
timestamp: May 03, 2021, 09:59:22 pm
content: I know a little bit about AC motors but this generator has me puzzled.Quote from: JayArr on May 03, 2021, 07:46:31 pmSo 3 sockets? Also if I understand your description correctly you already have 30 amps of 120VAC power, it is just split across two "Phases". It isn't clear as to how the 120 outlets are wired up.I suppose you could run the 240 AC into a transformer as another way to get to 30 amps.Quote30 Amps is a lot for a travel trailer, are you sure that it needs that much power to be functional? If there is a big load, say an air conditioner, I'd seriously consider simply putting it on a separate circuit.The reason I ask is that 30 amp outlets are fairly common at RV parks, it doesn't actually imply what a trailer will actually burden the connection with. Another thing worth considering if the trailer is old would be to migrate to more efficient electrical appliances.QuoteI'm not sure what is up. It could be a case of a gen set that is designed to support a wide array of markets. You might want to search for a technical manual if you can find the actual manufacture of the generator.You may also want to watch out for other potential issues such as a controller that only understands the current connection method and the possibility that the engine might not be able to drive the generator properly if the load changes dramatically. This leads me back to being inclined to leave the gen set alone and solve the power problems in another manner. If the gen set has to be replaced in the future you may find yourself going through another modification event. For me it is better to see the gen set as a module that is easily swapped with another power source as needed.

author: JayArr
author_rank: Contributor
timestamp: May 03, 2021, 10:50:08 pm
content: Thanks for the reply WizardYes, correct, two out of phase 120VAC windings that have been joined in series to make 240VAC available.My Xantrex battery charger pulls 22Amps at full throttle so a 30A source is required.I've thought of a transformer but a decent (non-Chinese) 5000W transformer is 89 pounds and $1000. That's not a solution I can afford.I've already bought and paid for this genset, I've also bought a new carb, a propane conversion kit, new rubber mounts and a K&N air filter so it would be really hard to walk away from.It's just wiring, I'm sure it can be done I just have to keep asking until I find someone who knows how.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: May 03, 2021, 11:12:48 pm
content: There are different configurations of generators, depending on brand, output, etc. You did not mention the brand of your genset.This YT guy repairs generators and seems to know how to repair them very well, maybe he has a video that fits your needs. I am subscribed to his channel and watch his videos frequently.https://www.youtube.com/channel/UCr_GXW2Y56hOpGchXYNqZOQ

author: james_s
author_rank: Super Contributor
timestamp: May 03, 2021, 11:24:18 pm
content: Usually the problem is going the other direction, most inverter generators have the 30A 120V socket but can't do 240V which is ideal for powering a house. You could always sell that generator now that you've got it in good working order and put the money toward an inverter generator which will be much nicer to your fellow campers, unless you're off in the middle of nowhere with nobody else around. Those 3600 RPM generators are obnoxiously loud, having gone to an inverter generator I'd never go back. The windings must be 180 degrees out of phase though in order to get 240V so it should be possible to wire them in parallel.Can your charger accept 240V? That might be another option, run that on 240 at which point the current is half. Whether that is feasible depends on what other 120V loads are in the camper and how they're wired.

author: jmelson
author_rank: Super Contributor
timestamp: May 03, 2021, 11:38:58 pm
content: Quote from: JayArr on May 03, 2021, 10:50:08 pmPoke aroound scrapyards, especially those that take in a lot of industrial equipment. Those often have "step down" transformers, that are used to run 240 V units from 480 V mains, and have some series/parallel straps to select what it will do. You would set the HV and LV straps both for the low-voltage selection. That would be with 1-2 and 3-4 strapped on both ends. Feed the transformer 240, and you get twice the amps on the 120 side. As for the weight, there's not much you can do about that. But, you would pay scrap metal price for the transformer, a LOT less than a grand!Jon

author: Ian.M
author_rank: Super Contributor
timestamp: May 03, 2021, 11:44:36 pm
content: 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'.

author: bdunham7
author_rank: Super Contributor
timestamp: May 04, 2021, 12:10:20 am
content: If you rewired it with the winding at the bottom in parallel with the one at the top and then used point D as your neutral, wouldn't the AVR work pretty much the same way as the original, except with just a percent or so higher output voltage? If not, or if you think the AVR windings can't take the 30A, you need to make your own voltage regulator.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 04, 2021, 12:19:35 am
content: Quote from: bdunham7 on May 04, 2021, 12:10:20 amHmm, could you move the neutral one tap up (one side of AVR) and parallel the two higher voltage windings? This way, load (or fault, for that matter) current doesn't flow through AVR windings (which presumably are only rated 15A like everything else?), AVR still gets the same voltage, and who cares about shifting the neutral..? If the AVR has an implicit neutral connection elsewhere and cares about this center tap, maybe it doesn't work so well, I don't know.Tim

author: moffy
author_rank: Super Contributor
timestamp: May 04, 2021, 12:22:03 am
content: I agree with Ian.M, if you were to wire the two 120v AC windings in parallel you would first have to test for circulating currents. Just short them together with a suitable current shunt and watch the current, maybe a 15A breaker as well. Watch the current to see you are not getting too much. Then do the same again with a load to see that they still match(the load would be split into two equal parts with each half applied to one 120v AC winding).In all of the above ensure that the regulator is connected correctly and working.

author: bdunham7
author_rank: Super Contributor
timestamp: May 04, 2021, 12:26:13 am
content: Quote from: T3sl4co1l on May 04, 2021, 12:19:35 amThere's the problem, I think that it won't. The open-circuit voltage is probably a lot higher than when loaded, this is how the AVR would compensate for load. It's hard to say whether the windings could handle it without looking at the wires or doing some measuring--the AVR windings are only two while the others are three, so they don't seem to be the same. Anyhow, a safer solution would be to parallel everything and then use either a small 1:2 transformer to the AVR or else redesign the AVR.

author: JayArr
author_rank: Contributor
timestamp: May 04, 2021, 05:28:35 am
content: So I did a little digging and I've found that my generator portion was made by SawaFuji, they apparently made a lot of generator heads for Homelite, Kubota Wacker Neuson and even Honda. I've found some manuals for Kubota and Wacker Neuson that shed some light.I also did an experiment with the AVR. I fed it 12V into the yellow wires and hooked a light bulb across the field wires that go to the brushes. The light bulb lights but as I raised the voltage on the sense wires (blue and brown) the light goes out at 18VAC. That's quite low and explains why my gen has the extra windings. A lot of AVRs sense directly off the 120VAC output but that means they are using high value resistors to divide down the sense voltage to a manageable level and high value resistors are more prone to drifting and going open.I've pulled the wiring apart to separate the lower two windings then I inverted each and joined them in parallel with the uppers. See picture. This will double my current and make it a 120VAC only generator.Here's a question I have. B and C are connected and fed to the AVR, Their corresponding point on the second winding is H and E. Do I tie all four together (BCHE) or leave them separate?The problem with this configuration is that the voltage to the AVR is now half of what it used to be so I'll either have to modify the existing AVR or build a new one that cuts off the field current at 9VAC (instead of 18). It shouldn't bee too difficult, I build regulators for alternators all the time, I'll make it adjustable while I'm in there. The hardest part will be digging the potting/epoxy out of the box to get to the board.

author: bdunham7
author_rank: Super Contributor
timestamp: May 04, 2021, 05:40:50 am
content: https://www.eevblog.com/forum/beginners/removing-potting-epoxy/Be careful, some of the chemicals mentioned are pretty bad, if you can even find them. I'd try 24 hours in a sealed container covered with relatively harmless acetone (some nail polish removers are 100% acteton) before I moved on to the horrible stuff.

author: JayArr
author_rank: Contributor
timestamp: May 04, 2021, 05:53:01 am
content: I've done this hundreds of times, I just use the hot air nozzle from my solder station. Every epoxy or potting compound I've encountered becomes soft and crumbles when it's hot. I just heat it up to about 350C and dig a little out with a small screwdriver or dental pick. As it cools down it gets hard again so you have to keep heating and digging. It makes a hell of a mess of your workbench but you just sweep it up later. It's still not a fun job but beats the heck out of trying to dissolve it with chemicals. I'll take some before/during/after pics when I do it.

author: Ian.M
author_rank: Super Contributor
timestamp: May 04, 2021, 06:05:07 am
content: Can the AVR even drive enough current through the field coils for full output at only 9V?I'd start by measuring the AVR supply voltage and current at full AC output load with the generator in its original configuration, then figure out how to get it that voltage when the windings are paralleled for 120V, e.g. with a 120V:18V transformer, stripping secondary turns one at a time till the output voltage is high enough.

author: JayArr
author_rank: Contributor
timestamp: May 04, 2021, 06:28:07 am
content: I think you misunderstand Ian, 9V is the trigger point on the voltage sense lines that turns the field current off.The field is driven with around 80VDC from the exciter winding but controlled by the voltage sense lines. The stator windings are tapped such that 9V on the tap point occurs when the output is 120VAC.

author: Ian.M
author_rank: Super Contributor
timestamp: May 04, 2021, 07:08:20 am
content: If the field is powered from the AVR feedback taps on the windings, modifying the AVR for a lower cutoff voltage will reduce the max. field current (because at half the cutoff voltage diode drops in the AVR will be far more significant and with less than half the voltage available to the field coils they'd need to be much lower resistance) and thus reduce the max AC output current. Its not much use paralleling the windings if as a result the AC output voltage 'falls off a cliff' when you try to draw over lets say 20A!The only way that's *CERTAIN* to avoid that without rewinding the field coils is to supply the same voltage to the AVR in the 120V configuration, as it gets in the 240V configuration, hence my and Bdunham7's suggestion to use a transformer to feed the AVR. It also has the benefit that you won't need to de-pot the AVR.

author: richard.cs
author_rank: Super Contributor
timestamp: May 04, 2021, 09:21:46 am
content: Quote from: JayArr on May 04, 2021, 05:28:35 amHow about feeding the AVR from the full 120 V output using a 120 to 18 V transformer? It'd only need to be a very small, low-power one (could also use a 240 V to 36 V transformer to keep the core flux low and the transformer linear - small transformers are notoriously crap).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 04, 2021, 01:33:15 pm
content: Another note, use toroidal or at worst shell type transformer -- split bobbin kind have lots of leakage and will make a poor potential transformer.Tim

author: Robert Smith Eco Warrior
author_rank: Regular Contributor
timestamp: May 04, 2021, 02:04:22 pm
content: I run a 110v diesel generator that has two 55v windings in series. I have wired them in parrallel to give me 55v. I can vary this a little by adjusting the engine govenor speed a bit. I made a big bridge rectifier and this gives me about 54v DC. I then directly charge my off grid batteries from this. I have to run this for a few hours occasssionally on really gloomy periods over the winter. Now that the sun is shining again the solar panels are providing everything we need.There may be an issue with wiring the windings in parrallel that there may be eddy current flows producing big currents within the joined up windings. I am thinking I shall make two bridge rectifiers and then join them on the dc side to try to avoid that problem.

author: JayArr
author_rank: Contributor
timestamp: May 04, 2021, 02:16:26 pm
content: QuoteThe field is not powered from the AVR feedback taps, it's powered from the exciter coil that runs to a separate bridge within the AVR. The exciter coil produces lots of power and it is sent to the field coil through the carbon brushes and slip rings by way of a darlington transistor. The darlinton transistor is turned on and off by the feedback voltage.

author: Ian.M
author_rank: Super Contributor
timestamp: May 04, 2021, 02:53:28 pm
content: Ok, then your plan to modify the AVR should be viable. However the two feedback inputs are antiphase, and you are going to have to do a significant amount of reverse engineering to figure out how to modify it to get a single input with double the sensitivity.I suggest bodging it for now with one of the transformer suggestions so you can check for circulating currents in the paralleled windings, then if it passes that test, it *MAY* be worth depotting the AVR, though I'd be inclined to spend some time looking for an off-the-shelf or DIYable substitute before attempting depotting.

author: JayArr
author_rank: Contributor
timestamp: May 04, 2021, 03:08:17 pm
content: That's a good idea, I have a large variac I could use to not only bodge it but maybe I could use it to find a sweet spot for the AVR, in case it's not exactly half of what it used to be.

author: james_s
author_rank: Super Contributor
timestamp: May 04, 2021, 05:45:55 pm
content: Quote from: T3sl4co1l on May 04, 2021, 01:33:15 pmShouldn't really matter for this sort of application, these inexpensive consumer generators are not precision devices, even a cheap transformer should work just fine over the narrow range of voltage it needs to handle.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 04, 2021, 05:49:18 pm
content: I mean, it's got a regulator, it must be better than, what, 20%? Split bobbin transformers are usually worse than that, just out of the box. So... YMMV, I guess.Tim

author: JayArr
author_rank: Contributor
timestamp: May 04, 2021, 06:01:22 pm
content: 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 120VACAt 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 120VACIf 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.

author: james_s
author_rank: Super Contributor
timestamp: May 04, 2021, 06:29:23 pm
content: IIRC the field voltage is normally around 12-24VDC in most of these.

author: JayArr
author_rank: Contributor
timestamp: May 04, 2021, 09:01:27 pm
content: Thanks James, I wasn't aware that the field voltage was that low. I'll keep that in mind.

author: wizard69
author_rank: Super Contributor
timestamp: May 04, 2021, 11:11:04 pm
content: 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.DaveQuote from: Ian.M on May 03, 2021, 11:44:36 pm

author: james_s
author_rank: Super Contributor
timestamp: May 05, 2021, 01:02:06 am
content: 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.

author: JayArr
author_rank: Contributor
timestamp: May 05, 2021, 03:45:10 am
content: 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 15AWhen 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.

author: JayArr
author_rank: Contributor
timestamp: May 07, 2021, 05:55:54 pm
content: 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?

author: james_s
author_rank: Super Contributor
timestamp: May 07, 2021, 06:01:33 pm
content: 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.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 07, 2021, 07:09:09 pm
content: 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

author: wizard69
author_rank: Super Contributor
timestamp: May 08, 2021, 12:35:44 am
content: Quote from: JayArr on May 05, 2021, 03:45:10 amYes 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.QuoteGreat 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.

author: JayArr
author_rank: Contributor
timestamp: May 08, 2021, 02:16:57 am
content: Hi WizardThis 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!

author: james_s
author_rank: Super Contributor
timestamp: May 10, 2021, 04:51:32 am
content: 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.

author: JayArr
author_rank: Contributor
timestamp: May 20, 2021, 04:09:57 am
content: 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!

author: JayArr
author_rank: Contributor
timestamp: June 11, 2021, 03:28:16 pm
content: 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

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 11, 2021, 04:36:46 pm
content: 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

author: JayArr
author_rank: Contributor
timestamp: June 11, 2021, 05:07:41 pm
content: Thanks TimJust 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.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 11, 2021, 06:10:58 pm
content: Current, yes. The OCV difference should be smaller than that.Tim

author: JayArr
author_rank: Contributor
timestamp: July 04, 2021, 02:27:32 pm
content: 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.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 04, 2021, 03:33:43 pm
content: TLDR;I had a short look at those Xantrex chargers:https://www.xantrex.com/power-products/battery-chargers/overview.aspxAnd 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.

author: JayArr
author_rank: Contributor
timestamp: July 04, 2021, 05:23:44 pm
content: 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, 22AOutput - 13.5VDC, 100AAutomatic three stage chargingInverter:Input - 12VDC, 200AOutput - 120VAC, 2200W continuousThe 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.