adding capacitor on output of inverter

System · October 2006

Recently installed a Xantrex 4000 watt, 48 volt, Sine Wave Plus Inverter/Charger. My ceiling fans are now noisy. Xantrex tech support says to install a 50 mfd 370V motor run capacitor on the AC outputs. I also run refrigerator, TV, lights, stereo, on the circuits powered by this.
I have purchased a capacitor, but am unsure how to install. Have 6 gauge wire out of the inverter. Do I just leave those running to the AC breaker, and add a line from one side of the capacitor connected at the AC Out Hot, and another from the other side of the capacitor to the AC Out Neutral? What size wire do I need to use -- 6 gauge? Or can I use smaller gauge wire? Don't see any markings on the capacitor connections -- are both sides the same?
Thanks for any help/explanation of how to install this capacitor, or any other feedback.
I plan to ask Xantrex these sames questions, but would like to hear independent opinions.
TIA

System2 · October 2006

Re: adding capacitor on output of inverter

To me, 50 MFD seems like a lot to add and I expect will result in extra "idle" draw from the batteries, however the Xantrex people are the experts. The way they explain it, you just connect one lead from the capacitor to one side of the AC output from the inverter and the second lead from the cap, to the other AC output terminal of the inverter. This is an AC capacitor, designed to be continuously across an AC supply so it won't matter which lead goes to which AC output terminal of the inverter. 16 guage wire is plenty heavy for this job, as long as you locate the capacitor right at the inverter, which you should anyway.
I would check the idle draw from the batteries before and after installation of the capacitor and depending on how much difference the cap makes, you may want to live with a buzzing fan, especially during those long dark winter days.
The inverter supplies "Pure Sine" in a number of steps, rather than a pure, smooth sine wave like you get from your local utility Co. The capacitor will "filter" the sharp edges of those steps, resulting in a smother sine wave. It's those "steps" that are making your fan buzz. But to filter it out with a capacitor, but I expect you will see the inverter using more power.
Let us know how it works out.
Cheers
Wayne

BB. · October 2006

Re: adding capacitor on output of inverter

It sounds like they are worried about the number of motors, which are inductive, affecting the power factor (phase between voltage and current). With inductive AC circuits, the current will lag the voltage. Placing a capacitor across the lines, will help bring the current back in phase with the voltage (current leads voltage with capacitive AC circuits).

Even utilities will tie a bank of capacitors into their distribution lines during the summer (AC and water pumping in the CA Central Valley).

If this does fix your problem (noise motors), you can probably wire the cap(s) in the switched leg of the motor and it will probably help reduce current draw from your battries when most of the loads are turned off.

-Bill

niel · October 2006

Re: adding capacitor on output of inverter

you know bb that's an excellent idea putting the capacitor with the fans so when the fans are turned off the capacitor is switched out of circuit too. i think a much smaller value cap on each fan would be perfect. you would leave a small one inline at all times for the frig as it's a bit more difficult to wire it in unless you tear into the frig. 5-10mf of that same minimum voltage rating for each cap and nonpolarized as polarized would be electrolytic and would become explosive exposed to ac.

System2 · October 2006

Re: adding capacitor on output of inverter

Wayne,
What MFD would you have suggested? The first tech person I talked said 5 MFD, I thought. Called back for more specifics (hadn't told me 370V), this techie told me 50 MFD. Could the first one have meant if installing at one ceiling fan only?
Is there any disadvantage using 12 gauge wire v. 16 gauge ? (I already purchased connectors which take 12-10 gauge , and have some 12 gauge wire)
So, the capacitor use some power. But will some of this be made up in motor efficiency? Without asking for a course in electronics, can you tell me why it would draw power when idle?
Thank you very much for your previous reply.

System2 · October 2006

Re: adding capacitor on output of inverter

BB, niel,
So, you suggest perhaps a 5 mfd (370V?) cap at the noisy fan, and something less than 50 mfd at the inverter? What mfd would you suggest? Unfortunately I went ahead and ordered the 50 mfd 370V cap and have received it -- to return, if they would accept a return, would still cost me shipping both ways.
niel,
Please explain your last line: "5-10mf of that same minimum voltage rating for each cap and nonpolarized as polarized would be electrolytic and would become explosive exposed to ac." It is over my head.
Thanks

James · October 2006

Re: adding capacitor on output of inverter

i believe he is refferring to electrolytic capacitor which are usually marked_____DC VOLTS and
with a + and - mark (polarity)

System2 · October 2006

Re: adding capacitor on output of inverter

scrubman wrote:

Wayne,
What MFD would you have suggested? The first tech person I talked said 5 MFD, I thought. Called back for more specifics (hadn't told me 370V), this techie told me 50 MFD. Could the first one have meant if installing at one ceiling fan only?
Is there any disadvantage using 12 gauge wire v. 16 gauge ? (I already purchased connectors which take 12-10 gauge , and have some 12 gauge wire)
So, the capacitor use some power. But will some of this be made up in motor efficiency? Without asking for a course in electronics, can you tell me why it would draw power when idle?
Thank you very much for your previous reply.

First I would like to say that the idea of locating the capacitor on the motor side of the switch is a great idea. As to size, I would probably have tried a 5 MFD first, to see if that cut the motor buzz and go higher if required, but since you already have the 50, give it a try and see what happens. Every situation will be different. 12 Guage, or heavier wire is no problem, just more expensive and harder to work with than necessary. You already have 12 guage - go ahead and use it. Yes, it takes energy to charge up the capacitor in one direction, only to immediately discharge it again and re charge it in the opposite direction and to continue to do that 120 times a second, for as long as it is in the live, 60 Hz circut.
Also, you make it sound like the capacitor is expensive. It shouldn't cost you over $20 and even that would give the seller a huge markup. Are you being ripped off?
Re the exploding capacitor: An AC motor run capacitor can stand up to the work involved with the constant, rapid charge/discharge, however, electrolitic capacitors designed for DC work, are not capable of being reverse charged and will leak current heavly, if any reverse coltage is applied, building up gasses and heat within itself, until it actually blows out it's safty vent (if it has one) , or failing that, rupture, spraying out a cloud of stinky, hot electrolyte and probably a blast of metal foil and paper like insulaton all over the place. Fun, if you have someone else to clean up behind you.

mike95490 · October 2006

Re: adding capacitor on output of inverter

scrubman wrote:

Recently installed a Xantrex 4000 watt, 48 volt, Sine Wave Plus Inverter/Charger. My ceiling fans are now noisy. Xantrex tech support says to install a 50 mfd 370V motor run capacitor on the AC outputs.

What did they say, 50 milli Farad or 50 micro Farad?
Either way, the 370V seems low to me, as you will likely have 240V across it, the inverter has 2 leads going to 2 different circuit breakers, either lead to Gnd is 120V, if that follows household wireing standards.

BB. · October 2006

Re: adding capacitor on output of inverter

The motor caps are typically oil filled. The US line voltage of 120 VAX x sqrt (2) = 170 volts peak. So, 370 VAC working voltage should be more than fine for 120 VAC motors.

Technically, a capacitor across the AC line voltage (or an inductor) does not use any power (current and voltage wave forms are 90 degrees out of phase--sort of like pressing on a spring with your hand then relaxing with the spring pushing back). However, you do have I^2 * R losses (heating of the wire by passing current through it). So, there are losses in the wire and in the inverter for having to generate and move the current--eventhough there is "no work" being done.

The motor caps should be 50 micro-Farad, not milli-Farad (yea--really had to pay attention in engineering to make sure which "M" Farad was on the test)... Generally, in my field, the M=m=u (micro) Farad, and I never ran across anything in milli-Farads--instead you would always see 1,000 uF (,000 micro Farad) instead of 1 mF...

To be clear, for this application you will want a 370 VAC RUN Capacitor, and, as an example, a fractional horse power fan motor (1/15 HP), recommended 3 Mfd for light loads, 4 Mfd for medium, and 5 Mfd for heavy loads... If your motor(s) are larger, I would try going up by motor size... if 1/15 hp = 4 Mfd, then 1/2 horse would be ~ 30 Mfd.

From one catalog I looked at, 2Mfd was the smallest, and 50-80Mfd were the largest values.

Also, there are Electrolytic START Capacitors too... Those are only for starting and will probably overheat if left connected to the circuit. The voltage ratings are typically much lower than 370 VAC, and they are much larger too (typically 50-1,000 Mfd in rating).

Given that you have a true sine wave inverter (<5% harmonic distortion), I would kind of worry about the motor buzzing. If the small caps can fix it, and don't cost you much in energy (i.e., you can switch them with the load in most cases), and it fixes the problem--you can't argue with success.

A quick test might be to disconnect all loads and see one fan motor is noisy... If not, then I would leave it on and try switching in some other loads too... It could be that you may have some older devices (older electronics) that use power supplies with very poor power factors--the "earlier supplies" (usually more than ~10-15 old) used a diode rectifier to charge a high voltage cap on the input--basically, there would be zero current flow except for a large peak right near the crest of the AC voltage peak. It is possible that a large stereo, older computer, or other such power hungry device is placing these very narrow current peaks on your inverter and causing various other devices to "ring". It is a long shot, but if you have problems finding a culprit, I would try this experiment.

In decades gone past, when PC's became popular there was a credit card processor with a sea of PC's that kept overheating the distribution wiring--voltage and current were OK, until the actually looked at the current wave form and found these huge peaks causing I^2 * R heating losses... Newer PC and devices are "power factor corrected" and should not cause these problems.

-Bill

System2 · October 2006

Re: adding capacitor on output of inverter

Wayne,
Guess I got ripped off -- $35 + shipping was the best I could find for 50mfg/370V (on the web) -- none available locally. Can you name a good source here, as I may try a 5mfd cap at one of the ceiling fans?
Mike,
I am sure they said "microfarad". The inverter puts out 120V. Although I have an autotransformer I plan to attach later, when I have more PV panels, to step up to 220/240V for my well pump.
BB,
I will try this when I get a chance.

Thanks all

mike95490 · October 2006

Re: adding capacitor on output of inverter

scrubman wrote:

- some snippage -

Wayne,
Guess I got ripped off -- $35 + shipping was the best I could find for 50mfg/370V (on the web) -- none available locally. Can you name a good source here, as I may try a 5mfd cap at one of the ceiling fans?

Mike,
I am sure they said "microfarad". The inverter puts out 120V.

Microfarad is the standard name. 370V for 120 circuits would be OK You want a RUN capacitor, and use 5uF at each noisy motor, not at the panel.
Try a local electric supply warehouse, the kind that has light ballasts and such. Homeowner Warehouse stores will not likely have them.
I did not catch what city you are in/near

McMaster-Carr http://www.mcmaster.com/ http://tinyurl.com/qlgwx
has them, search for capacitors 5uF for less than 5 dollars. Fast shipping. EVERYTHING I can't get at home depot, I order from them, good prices, and exactly what you order, and real stuff, not cheap stamped threads a nut won't fit on.
http://www.grainger.com/ has them too, not as wide as choices. search for capacitors

Good luck

(Odd, if it's a true sine wave inverter, why would the motors need caps?)

niel · October 2006

Re: adding capacitor on output of inverter

sorry for not getting back in here sooner. i was just warning you not to make the mistake of getting an electrolytic capacitor because they can be explosive when reverse voltages are applied and they won't work for this application.
the voltage ratings on the capacitors can be higher so if the sales guy says he only has them in 450v you can use them and yes it is micro farads and is listed as mfd, ufd, and possibly mf. joke there someplace. :roll:
i only suggested the range of 5 to 10mfd to be used at each fan and made the suggestion of one at the inverter only because of difficulties in wiring one into the refrigerator as this is an automated appliance that isn't using a switch.
now you do have the 50mfd cap so try it and see if your problem goes away for if it doesn't do not just go out and buy the smaller valued caps as they wouldn't work either at this point. that would warrant another call to xantrex to tell them it didn't work. they may suggest something else with your input of failure when you followed their suggestion.
btw, if it works you can just keep the 50mfd cap inline or go with the smaller ones at each fan as an option so as to facilitate the switching of them out of the circuit when not in use.

System2 · October 2006

Re: adding capacitor on output of inverter

Niel,
Yes, I believe I have the right type of capacitor, although I paid almost 3 times what the McMaster website Mike mentioned has them listed at.
Even though it may use a (very) slight amount of current, and perhaps some "idle" draw as noted by Wayne (though I don't understand why), assuming this solves my noisy fan problem, will I also be getting some benefit to other motors of having even cleaner power than before?
Of course Mike nailed it -- if it's a true sine wave inverter why would I have to be doing this at all.
Will report back here after trying it.

Windsun · October 2006

Re: adding capacitor on output of inverter

Not sure where you looked for the capacitor, but Google shows dozens of sites with them for sale for $10 or less.

niel · October 2006

Re: adding capacitor on output of inverter

scrubman,
"Of course Mike nailed it -- if it's a true sine wave inverter why would I have to be doing this at all." quoted by you.

what we term as pure sinewave is not technically pure, but is within a certain tolerance, that being less than or equal to 5% thd. that means a mod sinewave inverter is over 5%. this figure didn't pop out of a hat either as electric utilities use that as their standard for ac quality. now i believe there is 56 steps to xantrex inverters rather than a smooth line connecting the dots. don't hold me to that number of steps without confirmation from somebody else or if i search it. the more the number of steps the better the performance as it won't deviate as far from the true sinewave as less would. sometimes under heavy load the inverters will degrade in there step performance as well as power factors coming into play. there are inverters out there that do outperform xantrex with outback and exeltech as 2 examples with outback having the highest number of steps that i am aware of with 256. in any case try the cap you have and see if it cures your problem.

adding capacitor on output of inverter

Comments

Categories