Electricity Generator Brushless Alternator Testing – Generator with a capacitor.

Electricity Generator Brushless Alternator Testing – Generator with a capacitor.

Hi I am Styles from Generator Guru, and today I am going to show you how to test your capacitor and Alternator On a brushless alternator Electricity Generator. What happens sometimes is you go out, into your shed, get your generator out, it was running fine last time, you start her up and the engine is running fine, but you have no electricity coming out. Now we need to find out what could have gone wrong with the generator. To do this, we need to find the capacitor. On this type of generator, this one is a Stephill, they are all a very similar layout, the capacitor will be in the end part here, or in the housing where the plugs come off. In this case, it is underneath the housing. What I am going to do is remove the housing, I will remove the end as well, just to show you what is going on there. Ok there it is, this is the capacitor here Just to make it easier I am going to remove this so you can see. This is obviously the housing for it. Now in this case, and in most cases the capacitor is round. We know it is a capacitor, not an AVR, because it has 2 connections, or 4 maximum. I am going to take this out You will see there is 2 tab connections on the top. Sometime there are 4, in case someone want to run them in series or in parallel. Now, in this case, it is an 18 micro-farad, or an 18 followed by what looks like a “uf” symbol. Now what we need to do is see what the state of the alternator is. With a brushless alternator there is only actually one test. Without the capacitor attached, pick up these 2 wires. Don’t worry which one is which. What we want to do is get our multi-meter and set it to the “V” with a little squiggly. That means Volts AC. Now what we normally would do, is run the generator up, because we want to see what voltage we can get out of the alternator. I won’t actually do that as it will deafen you. Once we have run her up, what we want to do… actually, when you got the tab connectors you can connect them before you run it up. which is alway quite nice as these go around at 3000 to 3600 rpm so you got to be really careful. Into the tabs like this. Start up the generator. Get the engine going and what we want to know is what the reading it. It shows here. It should be about 5 volts. Give or take 2 volts. If that is the case, you have a nice healthy alternator, then all you need to do is replace the capacitor. If you are not getting that reading then please contact us and we can advise you from there, because we need to find out what is happening in your alternator. In the case of the capacitors you need to be sure you get a GENERATOR capacitor To transcript All it does [the capacitor] is releases a charge into the windings to get them excited so they produce electricity. To transcript They are not too expensive. You want a long life one as well. to transcript So, just to recap. If you are getting about 5 volts AC on your alternator on the 2 tabs you took off the capacitor make sure it is a generator capacitor you are getting about 5 volts then your alternator is in great condition. Obviously, while you got it open try to give it a little clean. Do not use oil, WD40, or anything like that. Do not use water. Just use your fingers, brush off what you can. Don’t get any water into it at all. As electricity and water do not mix. When it comes to capacitors, make sure you get a good brand and one that is self-extinguishing. These will blow for 2 reasons. 1) You have asked to much of the generator so it is blowing it and could save the alternator. 2) If there is a surge in the alternator, which can happen from a little bit of dust. This will blow to protect everything beyond the alternator. Now I know you have circuit breakers.. but this is much more sensitive So, you want one that is self-extinguishing. Because as you can imagine if you get a fire in here with this gas tank on top, it is not a good combination. I have these on my website, which as you can see is GeneratorGuru.com. If you need any advice, pop to the website and drop us an email. We are always happy to help! I’m Styles, from Generator Guru, signing off. See you next time!

88 thoughts on “Electricity Generator Brushless Alternator Testing – Generator with a capacitor.

  1. Helpful information, thank you. I replaced a defective 16 uF cap. with a 20 uF. I had someone tell me the higher rating will effect the output voltage, and the frequency will be incorrect if I adjust my engine speed to compensate. That doesn't makes sense to me though, as the cap has nothing to do with the output itself. Correct?

  2. Thanks for the feedback 🙂

    The capacitor excites the windings, so it will affect the output. There is a 5% +/- so you can vary it between 15uf and 17uf.

    Hope this helps 🙂

  3. Hi, Thanks for your helpfull video, I have followed your instructions on my 4kw Italian alternator and got a reading of 4.2v at the capacitor terminals.I also have 5 volts at the plug not 220v. I have a few capoacitors around so I tried them and the condition didnt change. I noticed that their is only 1 diode on the rotor and the oposit side appeared as tho the diode might be missing? is that posible? should I buy the right capacitor or look into the diode?

  4. Thanks for the tips, I have got a used and the fellow I got in from took it apart to wire it for 240/120 & mess up the wiring order. So now I have to figure it out. So here I am on youtube looking for answers.

  5. I ordered a new chicago electric 10 kw belt generator 120/240.And it has a 45uf capacitor 450v and thing is i have to wind engine out to get to do any thing.So what size of a capacitor should have.

  6. I have a 3000 watt generator check voltages at L1 to L2 and R1 to R2 have 5 votes from L1 to R1 0 votes
    Brushes have 8 to 10 votes
    I did change out the AVR did not help
    But the output for 120 vac I’m getting 29 votes for 240 vac the reading is 58 votes
    What would be the my next step thanks

  7. You need to watch my other video about Brushed AVR Generators. But it sounds like the diodes in the rotor have blown and need replacing.

  8. Test the winding for continuity. Should only show 1 way. If not replace your diodes.

    Hope this helps!

  9. this is good video … I was wondering … If I don't know where I connect the capacitor … I mean which terminals …. should I measure the resistance of the exciter and the main winding … and how much should be the resistance of the exciter and main winding … I mean the resistance of the exciter winding should be more than the main winding or less … please let me know if would like to help me …. best regards

  10. Thanks for all the excellent info.
    I have a Dewalt DG6000 brushless generator that produces no power through the protected 120V outlets and 2.3V at the 120V and 240V unprotected twist lock outlets. The capacitors are 20uf and both test at 22uf. The leads from the alternator to the caps. Produces 4.3V. The circuit breakers test good and I have no power. I'm confused. I don’t want to start throwing parts at it until I know what to buy.

  11. hey guru
    thank for the video. I am getting only 2 volts when throttled up and wondering if a bad diode could cause this issue. Capacitor is leaking and bad it is rated 22uf. Will replace but not sure if it will make a difference
    Any thoughts or ideas about the 2 volts would be great

  12. You can only connect it one way and it work. If it isn't producing power shut down the machine and change them around. It will not harm the capacitor if you have put them on the wrong way at first.

    Hope this helps 🙂

  13. Yes it was a very windy day. I plan on re-recording asap. In the meantime if you have any questions please post them here.

  14. It sounds like the capacitor is blown. Just to double check do a continuity test through those wire both ways. It should only work 1 way if set on lowest voltage.

    Hope this helps.

  15. For some reason we are not able to reply via YouTube to questions at this time. If you have questions please contact us via our website. GeneratorGuru.com

  16. I have an old Powermate model#PM52-2000, That was given to me. Motor runs great but no power. Its brushless from what i can tell so ill try this. I hope its the capacitor and not the stator/rotor since those are discontinued.

  17. Hi my name is john i am a small engine tech i have a yamaha gen mod yg6600d i have a problum i was looking at your video i have a wireing dig on the gen it is brushless the ave has 2 wires comming frome the alt assy black/ white plug the gen runes like it is under a load with nothing on it when i dic the plug the load goes away the avr has a cap that goes 2it and a nother 3pin plug that goes frome the ave to the gen i think the avr is shorted it has a new cap can u give me some help thank u

  18. Hello, I have a Coleman Powermate, model #PM0542000.01. Prior to performing this test I measured ~2 Volts at my receptacle. I performed this test and measured 4.3V AC. Based on your video, my alternator functions properly. I replaced my 12.0 microfarad, 350V capacitor with a 12.5 microfarad, 370V. I am still measuring ~2 Volts at my receptacle. Please help!

  19. the capacitor I got to replace the blown one has two wires coming out instead of the hard metal terminals, will that work?

  20. I got the same genny as you have in the video and witout the cap installed I get around 24 – 30VAC across the two wires. It also doesn't charge the brand new cap I bought (18uf / 425V). Any ideas?

  21. Hi ,in my generator working only 110 socket ,there is no voltage in 220 socket.what this could be?Tried circuit breaker and they are fine.Capacitor is new one.

  22. So I checked my brushless generator (porter-cable bs525) and I'm only getting 0.5 to 0.6 v AC.  I guess my alternator is dead.  What and how much am I looking at to repair this? 

  23. I test the alternator and I'm not getting any votes are used to different multimeters sure. What do I do next

  24. Thank you Styles!  Very helpful video – new capacitor ordered from your site (exact part match from manual).  

  25. Need advice? We have Generator Engineers who can help!
    You can contact us through your local Generator Guru website to contact the Guru who specializes in your Generator Model.

  26. Need advice on how to fix your Generator? We have Generator Engineers on Chat on our website, ready to guide you through the repair.
    You can contact us through your local Generator Guru website:
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  27. Hi There, Did this test and am getting 13 to 14vac,.Resistance across the 2 capacitor wires are 7.8ohms I feel sure the alternator windings are at fault. The capacitor in there was a 15uf and had blown causing some power tool bty chargers that were pluged in to burn out.

    Kind Regards Geoff

  28. hi my name is john and I have master MGH 10000 portable generator and I am reading 70 to 80 volts out of the outlet Ben 10 volts across the whining any ideas

  29. i have a blue max 8000e  no output to the plugs  on either 110 or 220 v setting . the capacitor ears was broke off . i am getting 9.6v  from the exciter circuit i am waiting on an exact  replacement . if after replacing this it still has no output what do i do next

  30. We have a new generator that suddenly started not giving power it is a power generator 7500 series. it will run for a couple of hours giving power fine and then suddenly stop and when we start it again it won't give power. I am shocked because it is brand new straight out of the box.

  31. Hi i need so help i have done a test as shown in the vid and i am getting a reading of 16.80 from the to wires does that mean the alternator is at fault

  32. Thanks. Question. You mention 5 Volts. is this universal? I have a Dewalt DG6000 with a 40 microfarad running capacitor.
    Also, I am unfamiliar with the difference of a generator capacitor and general capacitor. I have purchased Edilson 40mdf running capacitors. They last about 3 weeks and fail.

  33. hi I have a scorpion 3000 , 240v not putting out any power only about 5v ac it has been sitting for a while and may have lost its magnetism?
    it has a 12 v DC outlet also and was wondering what is the best way to flash the fields?

  34. Hi, thanks for the video.
    My name is Jose Monica from Portugal, and I have a very old Honda EX650 generator 220Volt. The condenser is damaged, and I can't find the capacitance of it. Can you help me?

  35. You guys have been a big help with me and my generator issues. I ordered some parts and installed them into my generator and am now just waiting on the rest of the 2nd round of parts I ordered so I can complete the repair and put the rest of my generator back together.

  36. I've got a Northstar 13000 brushless generator set that's putting out only 111 volts at 61.5 Hz. Since there's no AVR on a brushless, what might be done to increase the voltage output to 120V per leg so that my refrigeration compressors don't struggle? If this capacitor is out of tolerance, how does it affect the voltage? Larger capacitance makes lower or higher voltage?

  37. Good day, I have a LAUNTOP 5000 Diesel generator that is running but oil is spitting out through the fuel vent. Anyone have any idea what the problem maybe and how to fix it??? We don't have a manual and having problems finding one online.

  38. THANK YOU SO MUCH! You've been really helpful, and I appreciate it! I have a DeVILBISS PowerBack GT5000 and I didn't knew that has a capacitor inside the alternator cover. I did exactly what you said and… BINGO! 4 to 5 volts! I check with SEARS and they have it. Part# GS-0592. Hope this will help others! …GOD Bless!


  40. Hi, I have Honda G300 Generator which is not producing an electric, what and how I can check the alternator whether it produce any voltage please?

  41. I have 10v coming out of the output and 10v at the capacitor tails with the cap disconnected, the cap is 10uf and I put a 100uf just to see if there was any difference but the output was the same please help

  42. Getting no power from my SIP medusa, the 10uF capacitor is testing as a complete dud. and the voltage from the alternator is 8.9VAC, you video says 5VAC ± 2. Am I too far out the desired range?? TIA

  43. have a echo 5500 brushless generator,,, 2 ,,28uf capacitors wired parallel,, 2.53vac out of alternator,,, and can see wires got hot between alternator and first cap ,,,,low voltage and have cycle fuse to get start showing voltage bout 60vac

  44. Hi i have a 6kva generator with no power.. im geting 1.6v at capacitor connection wires with capacitor disconnected and its 2v with capacitor connected what you think? Thank you

  45. Say GG, new sub here. I have an 1997 (guessing) Northstar PPG 8000 that I got with a blown cap. I replaced both as long as I was at it (Appli Parts Run Cap 12.5 uF, 370vac, 50-60Hz) and still no output. Do I need to flash the field and how do I do that? It's brushless. Great vid, thanks! PS/ In it was a Facon 12.5 uF and a Ducati 16 uF. The latter blew. Greetings from New Jersey btw.

  46. I am having problem with my cheap China petrol generator .the engine runs perfectly and generates 110v on one plug but when I switch to 230v plug it doesn't go above50 v which for UK region is the power you need to run most appliances .this generator inbrushless so no AVR but has an 18uF black rectangular capacitor 300v 50 Hz type .can anyone help diagnose problem .?I suspect capacitor is faulty but can't find this type online

  47. Replacing the capacitor worked for me. Thank you. But still voltage is bit wavey(200-230v) . Any fix for that?

  48. Im getting a reading of 13.1 volts on the test, is this ok? its the exact same model generator as in the video.

  49. I'm on your webpage now and have selected what I THINK is the correct capacitor using the variable capacitors near the top of the page and plugging in what numbers I have. However, I can't confirm this with anyone. Your link at the top of this page sends me into an endless loop that I can't get out of, no matter how many times I ask for help.
    Is there a secret to getting confirmation that I have the correct capacitor? Thanks.

  50. Excellent video Guru, I have a Generac XG8000E. I pulled the cap out and used my MM to measure the gen voltage and I am getting 1.5 volt, does this sound like a faulty cap? Thanks!

  51. Good video. I just picked up a 5250 watt brushless generator. Hope I don’t need to fix it but you never know.

  52. Hola tengo ploblema con mi generador de 950w el estator genera 6v pero no me da desalida nada de corriente 220

  53. Thank you very much thank you very much I learnt a lot I will still keep a close eye on your channel keep it up good work

  54. We did the replaced the capacitor we are running 5 volts at the alternator but still not getting any power

  55. I just bought a yamaha ef6600dh anf the staor was burnt and buddy had sent it too be fix by someone and they started too remove said bunt winding so i have no way of know what the the # of wire pre slot . its brushless pos..i think they change the capacitor with worng udf and back feed and overload.. but anyways i know it was 17 gauge soft enamel wire i do this the big line from 1too 18 was 60 wire in the slot but not sure its a 36 slot 1ph 2 poles EI stator .. REASON why i say brushless pos .is if you didnt buy it new it pos in most case becasue of ppl thinking higher udf the better its not really it isnt …

  56. Thank you for the lesson for the capacitor I Needed to know how it works thank you for explaining it Helped a lot.

  57. Tengo una falla en un generador de 8000watts, tengo que bajar la regulaciĂłn del AVR , para arrancar , y despuĂ©s que arranca tengo que regularlo nuevamente al voltaje que trabaja, en estĂ© caso es a 120voltios… Cuál será la falla ?

  58. What if some have an in between sized capacitor?? My Campbell Hausfeld that produces 2,500 watts peak, 2,100 watts continuous and is powered by a flat head vertical shaft Briggs & Stratton 5 HP engine. It has a Facon brand 12.5uF (+-5%) 450 volt capacitor. The model number of the capacitor is 7G73125L62. The generator was bought new back in 1995. It current has 223 hours on it. It's used to keep the Amana upright fridge (7.2 amps running) going during a power outage.

  59. Hi there, I tested my old etq 5000 generator and it reads 2.5v from those same leads you’re testing. I replaced the cap with a new one same ratings. When I test past those connectors to where the cap would be I get 1.5v any suggestions???

  60. I’m getting 10volts AC. When I connect a drill to and pull the trigger I get 98 volts and after a minute it shuts off on low v

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