Table saw motor popped the (capacitor?) while running on my generator.

bentherebenthere Solar Expert Posts: 109 ✭✭
Oops. I let the magic smoke out of my table saw motor. I was working at the homestead today and tried powering my table saw with my Honda EG3500. The 1hp saw motor is listed as 14 amps at 115 volts. I didn't even manage to finish one cut. The (capacitor?) under the external cover is covered in oil and was smoking.

I was able to use my circular saw (listed as 12 amps) without any problem.

So, here's the question. Do you think it was just by chance that I was running on the generator when it happened? I have put my multimeter on the generator and found it at 65hz with no load. I'm not sure if I should find that worrisome or not. Advice?

Is it, in fact, a capacitor that rides piggy back on my motor? Should I order the same one or is there a reason to try something different?

Thanks,

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Table saw motor popped the (capacitor?) while running on my generator.

    Off hand, it sounds more like the saw motor wasn't getting up to speed and the starter cap overheated. This may be a flaw with the saw, or an unexpected low-voltage condition with the generator.

    Your saw rating would be peak draw under operating conditions, not start-up. The start-up current could possibly exceed the generator's "surge" capability. Ever used this combo before?

    The 2 amp difference between the two saws could translate to 10 amps (+/-) on start-up and be enough to go over limit on the gen.

    Sorry to be so non-specific, but "1 HP" motors have a lot of different specs depending on who made them, when, and for what purpose!
  • jacobsjacobs Solar Expert Posts: 72 ✭✭
    Re: Table saw motor popped the (capacitor?) while running on my generator.

    My experience is that it takes at least a 5000 watt generator to start and operate a 1hp capacitor start motor. Your circular saw is a universal motor. Even though nameplate ratings are similar, the capacitor start motor probably has a much higher running amps. The difference between the two is like comparing apples to oranges.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Table saw motor popped the (capacitor?) while running on my generator.

    you are borderline with the specs with one leg of the generator and those of the saw. the genny is rated to 14.6a on each leg. http://www.dynamitetoolco.com/Honda_EG3500_Economy_Generator_p/hon-eg3500.htm
    it would be different if it was all 120vac and at 29.2a, but it's only able to push 120vac at 14.6a due to it being a 240vac generator. one side overloaded(due to surge) and the other void of a load. i'm surprised the cb didn't pop before the cap did. you may be able to solve this by transforming from 240vac to 120vac with a 2:1 stepdown transformer that can handle the wattage. the alternative would be for you to buy a larger genny. replacing the cap with the same specs should be fine imho.
  • bentherebenthere Solar Expert Posts: 109 ✭✭
    Re: Table saw motor popped the (capacitor?) while running on my generator.

    If I were to convert to (not sure if this motor does it, I know some do), or find a 240 volt motor, it would then utilize both legs of the genny, right? If so, wouldn't that also double my available wattage. Would you still expect to have trouble with a 1hp motor like that?

    That question is especially interesting to me as the place has an air-lift well and I was planning to run it occasionally with my currently-wired-240-volts 1hp air compressor.

    Alternatively, I could get my PV system in place so that I have a battery bank capable of running the saw(s) and use the genny to then charge the battery bank as needed. That was my original vision for this generator.

    The problem with that plan is that this place has had problems with vandalism in the past. I was planning to wait for the PV system until we move on site. We'll be fencing next weekend and after that I could deploy a dog to guard the fort. I think he'd get lonely out there and would rather stick with us.

    I played with the genny a bit more and was able to get it to idle at ~ 61-62hz, when I spin up the circular saw, it drops down to ~55hz for just a moment, then comes back to about 59.9hz. I didn't think to watch the voltage.

    Thanks for all the help!
  • bentherebenthere Solar Expert Posts: 109 ✭✭
    Re: Table saw motor popped the (capacitor?) while running on my generator.
    Ever used this combo before?

    No. In fact today was my first real use of the generator.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Table saw motor popped the (capacitor?) while running on my generator.

    that was my thought that it would free up 2x the wattage, but i am not one who runs power tools like that so close to a generator's ability, thinking surges as well. a 2 to 1 stepdown transformer is another large expense for you, but so would another genny or a pv system be making the call yours on what you may wish to try. maybe some of the other guys can share their opinons on this to help you make up your mind.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Table saw motor popped the (capacitor?) while running on my generator.

    I just looked at the specs on that Honda as provided by Niel: it isn't going to start that motor on 120V. It <I>should</I> manage it on 240. I wouldn't recommend the transformer route: it's probably too expensive and there can be other issues with motor/transformer/generator set ups.

    My advice would be to check the saw motor and see if it can't be rewired for 240 - a lot less current, even on start-up the spec plate should contain the info and there's probably a wiring diagram inside the connection box). Also less potential voltage drop through the wires. You should be using a 12 gauge extension cord on this if its any distance; amazing how much voltage loss there is through 50 feet of 16 gauge.

    Of course, first you have to fix the saw!:p
  • EcnerwalEcnerwal Solar Expert Posts: 101 ✭✭✭✭
    Re: Table saw motor popped the (capacitor?) while running on my generator.

    Replace with same-rated capacitor. It is often advised to replace the starting switch when replacing the starting capacitor - up to you. They often fail together. Unless, of course, it's actually a run capacitor - the nameplate on the motor should tell you which it is, and what size it should be.

    If it can be rewired for 240V, do it. Slightly higher frequency is not usually a problem - low frequency can cause overheating; frequency may also drop under load (check it and see).

    The compressor is also going to want to be 240V, and even then may not work - they are beastly to start, and I'm not aware of any small compressors having "unloaders" that will let the compressor spin up under no load (to help get started and up to speed) before actually starting to compress air. Thus, you might be able to start the compressor when the tank is empty, but not be able to restart it when there is air in the tank - the extra resistance of starting up and immediately compressing to the lower limit of the switch is often enough to make the start a *lot* harder. If you are clever with air solenoid valves and control logic, you might solve that one by making your own unloader (when compressor starts, tank is shut off (or just use a check valve - simpler) and compressor to tank line is vented - 10-15 seconds later, vent is closed and tank opened (if not using check valve). When compressor stops, open the vent line and wait for next start. Be sure to have a relief valve in the section between the compressor head and the tank valve, in case the tank valve (or check valve) sticks and fails to open - pressure in that line would go up very fast, and it's not where the usual pressure relief is installed.

    A direct fuel-powered compressor is often more sense than running an electric compressor off a generator. Those, of course, have (usually mechanical or hydro-pneumatic) unloaders (the motor keeps running whether or not it is compressing air.)
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